Tri-amping, driver time alignment, and carbon fibre cones
 

In article , Stewart Pinkerton
wrote:
On Mon, 16 May 2005 19:58:04 GMT, "Tim Martin"
wrote:


"Stewart Pinkerton" wrote in message
.. .

That's true, but unless you have access to good SPL measuring gear,
you may have some difficulty knowing where 'flat' is unless
everything is matched.

You don't need to be able to measure the SPL, just the signal generated
by a microphone.

Only if you know that the mic response is flat!

The reason I was recommending measurements in this thread was to give
'before' and 'after' comparisions. Hence I was not concerned with an
accurate measurement of the actual in-room acoustic results, but in any
changes. For that the only real requirements is that the mic response
should be stable and give enough output for a clear measurement. Any
departures from flat mic response would be removable as 'common mode'
variations for before/after comparisons.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
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Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Tri-amping, driver time alignment, and carbon fibre cones
 

In article , Tim Martin
wrote:

"Stewart Pinkerton" wrote in message
...

You seem to be missing a critical point here. Three drivers in a box
will not in themselves have flat responses across their working
frequency bands, so the fact that you are supplying a flat signal in
three parts will have very little to do with the FR of the final
speaker.

Sure, but that has nothing to do with whether identical or different
amplifiers are used for each frequency band.

But may have some relevance if there is a change in the slopes of the
crossovers, their turnover points, or the in-band network alterations of
frequency response.

In general passive 'crossovers' in speakers do not just divide the power by
frequency and distribute it to the drivers. They can also alter the
response to cater to some extent for the in-band variations of the drivers.
If you remove this then the reponse will change - even if you maintain the
same crossover points and slopes for the frequency bands.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
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Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Tri-amping, driver time alignment, and carbon fibre cones
 

In article , Wally
wrote:
Stewart Pinkerton wrote:

You seem to be missing a critical point here. Three drivers in a box
will not in themselves have flat responses across their working
frequency bands,

Are there any that do? Flat to within what spec?

I think the point Stewart is referring to is that the passive networks
which the original speaker engineers employed may have included
arrangements to help flatten/alter the response. This is in addition to the
networks acting as 'crossovers'. If you remove these arrangements the
results will change accordingly.

... so the fact that you are supplying a flat signal in three parts
will have very little to do with the FR of the final speaker.

Check out the crossovers in real high-quality active speakers such as
Meridian or ATC, and you'll find that they are far from flat in their
electrical output.

If this becomes an issue, I have the option of moving the digital EQ to
before the crossover and using it to apply corrections to the full band.
(Or, indeed, adding additional EQ units.)

The snag here is that you don't have 'before' measurements and hence may
not know what changes you have made to the response. As has been
mentioned, trying to assess this by acousics measurements in a domestic
listening room is a nightmare. ;-

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
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Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
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Tri-amping, driver time alignment, and carbon fibre cones
 

"Stewart Pinkerton" wrote in message
...

True, but are you saying that you don't care what happens in the pass
band? You're not going to do any equalisation? You think that passive
crossovers *only* perform frequency division?

I said or suggested nothing like that.

The question we are discussing is whether, in a tri-amped speaker, all the
amplifiers should be the same.

You said they should be, and IIRC said it was otherwise difficult to get a
flat response. I've pointed out that whether or not the amplifiers are the
same makes no difference; with an uncalibrated microphone and test signals
within the frequency range of the LF and mid-range speakers, one can easily
adjust the gain so that the test signal is generating the same sound level
from the bass and mid-range; and one can use the same process to do the
same with mid-range and HF drivers.

Equalisation is a separate issue. It has nothing to do with the issue of
whether the amplifiers need to be the same ... that is, in a tri-amped
system, the process of equalisation will not be affected by whether the
amplifiers are the same. And in the context of equalisation, your comments
about the SPL-measuring equipment needed apply equally regardless of whether
all the amplifiers are the same.

Tim

Tri-amping, driver time alignment, and carbon fibre cones
 

"Bob Latham" wrote in message
...

As far as I understand it there is only one frequency at which two drive
units will radiate the same acoustic energy and this is at the exact cross
over frequency. Above or below this, one or the other driver should be
significantly louder.

That's with the crossover operating. When you're setting up the amplifiers
to match driver outputs, you don't have the crossover operating.

Tim

Tri-amping, driver time alignment, and carbon fibre cones
 

"Bob Latham" wrote in message
...

Oh, I see. Yes, you could do that. It would only be useful though if the
Xover was perfectly flat in each pass band and the same for the drive
units. In the reality drive units are not flat response objects and
consequently xovers have to compensate for this and so they don't have
flat outputs either.

No, the purpose of this particular exercise isn't to obtain flat frequency
response from the speaker - that's a different activity. The purpose of
this activity is simply to turn the volume knob on one of the two different
amplifiers, so that both amplifier/driver combinations will deliver the same
sound level from a given single-frequency test signal within the operating
range of both drivers.

An example is the KEF B110. Great driver but not flat over its working
range. Xovers should feed it around 6db more at 300Hz than at 2000Hz if
you don't do this, the acoustic output will be all over the place. Even
that depends on the box its mounted in.

Sure, but that's nothing to do with whether the same amplifier is used for a
different driver used with the KEF B110.. You have exactly the same problem
obtaining a flat response from the driver, regardless of whether you bi-amp
it, and whether you use the same or different amplifiers when bi-amping.

And of course you can use exactly the same passive EQ technique with the
driver, regardless of whether it's being bi-amped.

Tim

Tri-amping, driver time alignment, and carbon fibre cones
 

"Bob Latham" wrote in message
...

"Yes, that can be done but it gets you nowhere. Stick to Kef units, say you
set the B110 and B139 to radiate the same volume at 300Hz. Move the
frequency up to 400Hz with no crossover and they would be different again
so what is the point?"

The point is simply to adjust the gain when using non-identical amplifiers.
It's very simple to do. You still need to do whatever it was you were going
to do for EQ if you were using two identical amplifiers.

Tim

Tri-amping, driver time alignment, and carbon fibre cones
 

In article , Bob Latham
wrote:
In article , Tim Martin
wrote:

[Snip]

I've pointed out that whether or not the amplifiers are the same makes
no difference; with an uncalibrated microphone and test signals
within the frequency range of the LF and mid-range speakers, one can
easily adjust the gain so that the test signal is generating the same
sound level from the bass and mid-range; and one can use the same
process to do the same with mid-range and HF drivers.

As far as I understand it there is only one frequency at which two drive
units will radiate the same acoustic energy and this is at the exact
cross over frequency. Above or below this, one or the other driver
should be significantly louder.

Tim has already pointed out on of the potential flaws in the above, so I'll
comment on the other one. :-)

There is a problem with your "significantly louder" as it seems to imply
that any combined effect only occurs at one frequency, or in a very narrow
range. This often is not the case.

Consider a frequency were we have moved away (in frequency) from the
equal-output frequency by enough that one speaker unit is producing 10dB
less than the other. Depending on the relative phases of the two units in
question this can alter the combined result over a range of about +2 dB to
-3 dB. Thus the region where one unit is not "significantly" louder than
the other may be rather wider than you may assume. :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Tri-amping, driver time alignment, and carbon fibre cones
 

In article , Bob Latham
wrote:
In article , Tim Martin
wrote:

"Bob Latham" wrote in message
...

As far as I understand it there is only one frequency at which two
drive units will radiate the same acoustic energy and this is at the
exact cross over frequency. Above or below this, one or the other
driver should be significantly louder.

That's with the crossover operating. When you're setting up the
amplifiers to match driver outputs, you don't have the crossover
operating.

Oh, I see. Yes, you could do that. It would only be useful though if the
Xover was perfectly flat in each pass band and the same for the drive
units. In the reality drive units are not flat response objects and
consequently xovers have to compensate for this and so they don't have
flat outputs either.

Also bear in mind that the passive 'crossovers' also connect to the speaker
units which tend to have frequency dependent impedances. This means the
interaction between the speaker impedance and that of the network is part
of the 'filtering'. By connecting the speaker unit directly to an amp you
change this interaction as well as the 'obvious' effects of the filter as
seen on a crossover circuit diagram.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
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Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Tri-amping, driver time alignment, and carbon fibre cones
 

Jim Lesurf wrote:

I think the point Stewart is referring to is that the passive networks
which the original speaker engineers employed may have included
arrangements to help flatten/alter the response. This is in addition
to the networks acting as 'crossovers'. If you remove these
arrangements the results will change accordingly.

I realise this.


If this becomes an issue, I have the option of moving the digital EQ
to before the crossover and using it to apply corrections to the
full band. (Or, indeed, adding additional EQ units.)

The snag here is that you don't have 'before' measurements

Why are the 'before' measurements so important? If my previous speakers were
crappy little 2" computer jobbies, and I suddenly scored the pile of kit I
have now, unheard and with no history, would it suddenly become impossible
to 'sort' the sound?


and hence
may not know what changes you have made to the response.

I recently acquired an SPL meter, which I mentioned in here a few weeks ago.
The idea is to measure the response as it is now, and then compensate as
required.


As has been
mentioned, trying to assess this by acousics measurements in a
domestic listening room is a nightmare. ;-

But the domestic listening room is where they'll be listened to - isn't
accounting for that part of the whole deal anyway?


--
Wally
www.artbywally.com/FiatPandaRally/index.htm
www.wally.myby.co.uk

Tri-amping, driver time alignment, and carbon fibre cones
 

On Thu, 19 May 2005 18:39:34 GMT, "Wally" wrote:

Jim Lesurf wrote:

As has been
mentioned, trying to assess this by acousics measurements in a
domestic listening room is a nightmare. ;-

But the domestic listening room is where they'll be listened to - isn't
accounting for that part of the whole deal anyway?

Yes, but when you've taken some measurements, you'll see that moving
the meter a couple of inches can make 10dB difference in the SPL at
any given frequency - which is why pros use anechoic measuring
systems. Even top-class room-correction systems such as TACT make
depend on very careful microphone posisioning if they're to give
decent results.

Further, the *power* response is regerded by many as more important
than the axial response, so you'll have to take dispersion into
account when you're considering cabinet design. It's a very complex
business, which is one reason why speakers remain the greatest
weakness in hi-fi gear - along with the room.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

Tri-amping, driver time alignment, and carbon fibre cones
 

In article , Wally
wrote:
Jim Lesurf wrote:
[snip]

If this becomes an issue, I have the option of moving the digital EQ
to before the crossover and using it to apply corrections to the full
band. (Or, indeed, adding additional EQ units.)

The snag here is that you don't have 'before' measurements

Why are the 'before' measurements so important? If my previous speakers
were crappy little 2" computer jobbies, and I suddenly scored the pile
of kit I have now, unheard and with no history, would it suddenly become
impossible to 'sort' the sound?

You are combining differ issues and situations.

The purpose of 'before' measurements before you make a change is to help
assess the *reasons* for any perceived changes. This, in turn, can aid
further changes, and also help assess if alternative (perhaps quicker or
cheaper or easier) methods might have given the same - or better - 'after'
results.

In the specific case we are discussing the purpose would be to assess the
extent to which changes you hear are due to changes in frequency response
which would not require multiple power amps. This would be relevant for
various reasons eg:

1) If you decided to save space, etc, by reverting to one amp, and as a
result of the measurements perhaps get further improvements as well.

2) For others who could perhaps save the expense, etc, of multiple amps if
this turned out not to be the real reason for percieved improvements.

There is nothing 'wrong' in what you have done. The snag is that we can't
tell if using multiple amps is a significant factor, or if it is mainly a
change in tonal response which could easily and cheaply be obtained without
multi-amping. The absence of 'before' measurements makes it difficult to
resolve this.

If you changed one entire system for another then you could use 'before'
measurements to assess if frequency response was a factor or not. But the
changes you have made are potentially more 'controllable' than this, so the
advantages in terms of assessment and understanding would perhaps have
been more useful.


and hence may not know what changes you have made to the response.

I recently acquired an SPL meter, which I mentioned in here a few weeks
ago. The idea is to measure the response as it is now, and then
compensate as required.


As has been mentioned, trying to assess this by acousics measurements
in a domestic listening room is a nightmare. ;-

But the domestic listening room is where they'll be listened to - isn't
accounting for that part of the whole deal anyway?

Yes. But it is not what you have been changing. :-) The point of the
measurements is to help assess what you have *changed*. This is the purpose
of 'before' and 'after' comparisons - as distinct from 'absolute'
measurements with carefully calibrated equipment.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Tri-amping, driver time alignment, and carbon fibre cones
 

In article , Bob Latham
wrote:
In article , Jim Lesurf
wrote:
In article , Bob Latham
wrote:

[Snip]

As far as I understand it there is only one frequency at which two
drive units will radiate the same acoustic energy and this is at the
exact cross over frequency. Above or below this, one or the other
driver should be significantly louder.

Tim has already pointed out on of the potential flaws in the above, so
I'll comment on the other one. :-)

What other flaw is that then? Are you referring to not using the
crossover at all in this exercise?

Afraid that I can't now find the posting which (I think) Tim said this.
However the other 'flaw' I was referring to is that the acoustic responses
may be such that there is more than one frequency were the outputs from the
two units will be equal.

There is a problem with your "significantly louder" as it seems to
imply that any combined effect only occurs at one frequency, or in a
very narrow range. This often is not the case.

I'm sorry. I must admit that I do tend to think of speakers in general
being like mine where the acoustic out from a drive unit falls off at an
increasing rate up to 24db/octave as you move out of band from the
crossover frequency.

I don't know what speakers do or do not approach that rate, but I would be
happy to accept it was common. However the problem is that this tends to be
the 'asymptotic' rate, and the roll-off near the nominal turn-over points
tends to be somewhat gentler. This then combines which what I say below in
terms of its effect.

Consider a frequency were we have moved away (in frequency) from the
equal-output frequency by enough that one speaker unit is producing
10dB less than the other. Depending on the relative phases of the two
units in question this can alter the combined result over a range of
about +2 dB to -3 dB.

I don't have any problem or issue with that statement at all.

OK. I was concerned that the term 'significant' can be misinterpreted in
this context.

Thus the region where one unit is not "significantly" louder than the
other may be rather wider than you may assume. :-)

This I do not understand. You've just said "one speaker unit is
producing 10dB less than the other" How is 10db not significant? I have
no problem with the out of band drive unit still having a significant
effect on the *total* output for some distance away from xover.

My point is that 10dB *is* 'significant' in this context, but this was not
clear from what had been written. Thus the risk that people might
misunderstand.

The problem is that the band over which one unit may produce a level which
is more than, say, -20dB down on the other may cover a couple of octaves or
more. Hence changing the crossover details may have effects over quite a
large fraction of the audible range even if the crossover has an asymptotic
rate of the order of 24dB/octave. In a domestic listening situation it can
be vary hard to predict the results of such changes as they affect the
directional properties as well as the anechoic on-axis response.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
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Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Tri-amping, driver time alignment, and carbon fibre cones
 

Jim Lesurf wrote:

The snag here is that you don't have 'before' measurements

Why are the 'before' measurements so important? If my previous
speakers were crappy little 2" computer jobbies, and I suddenly
scored the pile of kit I have now, unheard and with no history,
would it suddenly become impossible to 'sort' the sound?

You are combining differ issues and situations.

I disagree. My point is that one has to start somewhere - it doesn't matter
if I've had a million different systems before the present one, the
*present* one is the *starting point*. The fact that it's largely based on
the previous system is irrelevant. The given start is *what I've got now* -
just like, if I had taken measurements of the previous system, then that
would have been the - entirely arbitrary - start point.

Did KEF compensate for driver anomalies in the passive crossover? I don't
know, I don't care, and it doesn't matter. What matters is whether there is
anything about the system that bugs me, or that I feel can be improved such
that my use of it is more enjoyable.


The purpose of 'before' measurements before you make a change is to
help assess the *reasons* for any perceived changes. This, in turn,
can aid further changes, and also help assess if alternative (perhaps
quicker or cheaper or easier) methods might have given the same - or
better - 'after' results.

I know what the purpose of before and after measurements is. I also know
that only one thing at a time should be changed between measurements so that
there's a decent chance of properly analysing the effect of that one change.
When I take the measurements of the present system, then *those* will be the
'before' measurements.


In the specific case we are discussing the purpose would be to assess
the extent to which changes you hear are due to changes in frequency
response which would not require multiple power amps.

Would it?


This would be relevant for various reasons eg:

1) If you decided to save space, etc, by reverting to one amp, and as
a result of the measurements perhaps get further improvements as well.

I have stated several times, for at least a year, that my main interest with
regard to saving space is to reduce the size of the speakers.


2) For others who could perhaps save the expense, etc, of multiple
amps if this turned out not to be the real reason for percieved
improvements.

When I cranked up the single Cyrus 2 set up, the sound was crap. Solution?
Use a more powerful amplifier. How much amplifier power would be required to
produce a clean sound at the volumes where the 50Wpc Cyrus 2 was straining?
100Wpc? How much would such an amplifier cost, and which one should I get?

I elected to buy an 84 quid crossover and another Cyrus (120 quid), and
added in a valve amp I already had. I trusted the recommendation of another
that the Behringer xover was clean and flat, and bought a second Cyrus amp
that is as close as dammit to the one I already have. This was *easier* than
researching possible alternative amplifiers with more power, finding such
amps for sale, and buying one. I'm doubtful that a more powerful amp of the
same quality of the Cyrus 2 can be found for less than 200 quid. If it turns
out that I'm wrong, I'm sure the Behringer xover can be flogged on eBay for
50 quid or so, and the second Cyrus will happily sell for what I paid for
it.


The bass response was crap - rapid drop from 70Hz, feeble attempt to redeem
itself at 25Hz. Boxes are too big (135L) for the port tuning, backs of the
cabs are full of slots. I want *small* boxes and have two spare drivers, so
I elect to resolve this by building isobaric cabinets. In the meantime, I
use a multi-band digital parametric to sort it until I can get round to
building the new cabs. To be clear: the EQ may or may not be needed when the
isobarc cabs are built - until then, it's a stop-gap to improve the bass
response from the existing boxes.

What is the easiest, cheapest way to fix crap bass response that comes out
of speakers that are too heavy to conveniently move around, and too big to
move into the room by more than an inch or three? (IOW, too damn big to
experiment with speaker positioning.) I can't think of anything other than a
60-quid 12-band digital parametric that is far better quality than it has
any right to be at the price. Of the rush of changes that I went through,
this has been the best individual spend of the lot in terms of making the
system more enjoyable. But! Considering that the single Cyrus was straining
before it had a load of extra bass to dish out, how much of an improvement
would it have been without extra amplifier power? I would have had more
bass, but lower volume before the sound became messy.

So, I'll have my stop-gap parametric to improve the bass until I can be
bothered making bass cabs. Once I've made my bass cabs - my *four ohm*
isobaric bass cabs - how do I amplify these and the 8-ohm mid/top speakers
with one amplifier? Can it be done? How much power will this set up require
over and above what would have been required with single bass drivers?


There is nothing 'wrong' in what you have done. The snag is that we
can't tell if using multiple amps is a significant factor, or if it
is mainly a change in tonal response which could easily and cheaply
be obtained without multi-amping. The absence of 'before'
measurements makes it difficult to resolve this.

For the umpteenth time: The plan is to convert the bass end to isobarics
while keeping the mid and top as single drivers. All drivers are 8 ohm. How
do I acheive this without at least bi-amping? I know next to nothing about
designing passive crossovers, so, even if it were possible, designing some
crossover that will cater for doubled-up bass drivers and single mid and
top, is out of the question. I don't have the know-how or the inclination.


But the domestic listening room is where they'll be listened to -
isn't accounting for that part of the whole deal anyway?

Yes. But it is not what you have been changing. :-) The point of the
measurements is to help assess what you have *changed*. This is the
purpose of 'before' and 'after' comparisons - as distinct from
'absolute' measurements with carefully calibrated equipment.

I changed the shape of the bass response. There is no reason to suppose that
the previous bass response was entirely a function of the speakers. The
*objective* is to get better bass response *in this room*. The purpose of
getting the meter was firstly to help with calibrating the EQ to even out
the lumpy bass response, however much that is a combined fuction of the
speakers and room - to establish a first approximation of something
approaching a flat response on the meter to use as a basis for tuning to my
preference. And secondly to establish a set of baseline measurements such
that subsequent changes can be analysed effectively.

The only difference between what I'm doing and what you're saying is that
I'm taking the already-altered system as the starting point. I say again: it
doesn't matter what I start with, so long as I have a set of numbers that
describe that start point in some meaningful way.


--
Wally
www.artbywally.com/FiatPandaRally/index.htm
www.wally.myby.co.uk

Tri-amping, driver time alignment, and carbon fibre cones
 

Stewart Pinkerton wrote:

Yes, but when you've taken some measurements, you'll see that moving
the meter a couple of inches can make 10dB difference in the SPL at
any given frequency -

And if I move my lug-'ole a couple of inches, what will happen?


... which is why pros use anechoic measuring
systems. Even top-class room-correction systems such as TACT make
depend on very careful microphone posisioning if they're to give
decent results.

Further, the *power* response is regerded by many as more important
than the axial response, so you'll have to take dispersion into
account when you're considering cabinet design. It's a very complex
business, which is one reason why speakers remain the greatest
weakness in hi-fi gear - along with the room.

I'm willing to be pragmatic and follow cabinet design principles that are
doable, like non-parallel cabinet faces, building something with a cabinet
volume recommended by the driver manufacturer, small baffle area, faired
edges, whatever. I'm after something that sounds decent in my room,
something that isn't a howler. I reckon that it's a reasonable approach to
build a sensible box and trust that it's general character will be fine,
such that the unevenness of the driver is the main thing that needs
addressing.

If using an SPL meter in a domestic room to calibrate the midrange is a dead
loss, then I'll use my ears. Over a period of weeks. In many different
positions. To acheive an EQ compromise that is satisfactory. Heck, I could
even look at the response curve for the driver and have a go at dialling in
the compensation from that.

Would you say that this is attempting the impossible?


--
Wally
www.artbywally.com/FiatPandaRally/index.htm
www.wally.myby.co.uk

Tri-amping, driver time alignment, and carbon fibre cones
 

In article , Wally
wrote:
Jim Lesurf wrote:

The snag here is that you don't have 'before' measurements

Why are the 'before' measurements so important? If my previous
speakers were crappy little 2" computer jobbies, and I suddenly
scored the pile of kit I have now, unheard and with no history, would
it suddenly become impossible to 'sort' the sound?

You are combining differ issues and situations.

I disagree.

Situation 1) : Replace existing speaker arrangements with single amp for
active crossovers and multiple power amps. Then make deductions about how
much of the perceived changes is due to using multiple amps.

Situation 2) : Replace one set of speakers with a different set. Make
deductions about the differences between the speakers.

In (1) you have to take great care about deducing that the use of multiple
amplifiers produced the changes you hear. This picks out one aspect from a
complex set of changes, so you would need specific evidence to deal with
this.

In (2) the deductions may be reasonable as they are applied to the overall
changes.

Thus the difference lies in any attempt to deduce *reasons* for any change
in sound.

My point is that one has to start somewhere - it doesn't matter if I've
had a million different systems before the present one, the *present*
one is the *starting point*.

Not if you are then saying "it sounds different/better to what I had
before".

The fact that it's largely based on the previous system is irrelevant.
The given start is *what I've got now* - just like, if I had taken
measurements of the previous system, then that would have been the -
entirely arbitrary - start point.

See above. It depends on was 'reasons' you decide caused any changes from
what you had before, and if what you have done gives you reliable grounds
for such a conclusion.

Did KEF compensate for driver anomalies in the passive crossover? I
don't know, I don't care, and it doesn't matter. What matters is whether
there is anything about the system that bugs me, or that I feel can be
improved such that my use of it is more enjoyable.

I appreciate that you "don't care". However I think it does matter. If you
are going to recount your experiences here then it may matter since not
being clear on some of these points may mislead others. They may then feel
that they need to buy more amplifiers and build more complex systems, when
in practice simpler and cheaper changes might provide the results they
would prefer. Hence it may not matter to you, but may matter to others who
read what you write. Thus I think it is to their advantage to bring this up
and have them at least consider it before proceeding.

The above isn't meant to imply that multiple amps or active crossovers are
a "bad idea". Indeed, I think they can be excellent. Just that this is much
more complicated than it may seem, and it is very easy for people to get
misleading impressions unless we proceed with care.

The purpose of 'before' measurements before you make a change is to
help assess the *reasons* for any perceived changes. This, in turn,
can aid further changes, and also help assess if alternative (perhaps
quicker or cheaper or easier) methods might have given the same - or
better - 'after' results.

I know what the purpose of before and after measurements is. I also know
that only one thing at a time should be changed between measurements so
that there's a decent chance of properly analysing the effect of that
one change. When I take the measurements of the present system, then
*those* will be the 'before' measurements.

That is fine provided you are not attempting to make an deductions or draw
conclusions about the reasons the multi-amped and active system sounds
different to a previous passive single-amp arrangement.

In the specific case we are discussing the purpose would be to assess
the extent to which changes you hear are due to changes in frequency
response which would not require multiple power amps.

Would it?

It would if you were passing comments as to the reasons for what you have
now sounding different to before.

[snip]

When I cranked up the single Cyrus 2 set up, the sound was crap.
Solution? Use a more powerful amplifier. How much amplifier power would
be required to produce a clean sound at the volumes where the 50Wpc
Cyrus 2 was straining? 100Wpc? How much would such an amplifier cost,
and which one should I get?

Can't say because the comment "sound was crap" does not really give any
clues as to the actual nature of the problem. :-)

A 100 W amp will onlygo slightly louder than a 50 W one if the 50 W one
wasn't current limiting or unstable, or showed some other problem that has
nothing to do with power capability. Hence if what you heard was simply
serious voltage clipping I would not expect 100 W to help much.

[snip comments that seem fine to me]

What is the easiest, cheapest way to fix crap bass response that comes
out of speakers that are too heavy to conveniently move around, and too
big to move into the room by more than an inch or three? (IOW, too damn
big to experiment with speaker positioning.) I can't think of anything
other than a 60-quid 12-band digital parametric that is far better
quality than it has any right to be at the price. Of the rush of changes
that I went through, this has been the best individual spend of the lot
in terms of making the system more enjoyable. But! Considering that the
single Cyrus was straining before it had a load of extra bass to dish
out, how much of an improvement would it have been without extra
amplifier power? I would have had more bass, but lower volume before the
sound became messy.

So, I'll have my stop-gap parametric to improve the bass until I can be
bothered making bass cabs. Once I've made my bass cabs - my *four ohm*
isobaric bass cabs - how do I amplify these and the 8-ohm mid/top
speakers with one amplifier? Can it be done? How much power will this
set up require over and above what would have been required with single
bass drivers?

Can't really say as we don't have enough information. You might find a 50 W
amp is fine, but you might need 500 W. Depends on the actual speaker, the
room, and how loud you want to play what sort of music.


There is nothing 'wrong' in what you have done. The snag is that we
can't tell if using multiple amps is a significant factor, or if it is
mainly a change in tonal response which could easily and cheaply be
obtained without multi-amping. The absence of 'before' measurements
makes it difficult to resolve this.

For the umpteenth time: The plan is to convert the bass end to isobarics
while keeping the mid and top as single drivers. All drivers are 8 ohm.
How do I acheive this without at least bi-amping?

This is a different question. The point here is that you could choose (or
at this point, "have chosen") to use the original speaker with its passive
networks, and bi-amped via an active crossover to split the 'low bass' from
the rest of the signals. This is a more common approach and has the
advantage that you don't have to re-engineer the main speakers as well as
add in a low bass section. It is also easier to 'undo' and compare with the
original arrangement to help assess any changes.

To make clear again something I have tried before to indicate: I have not
been saying that multiple amps or active crossovers are 'wrong' in any way.
What I am doing is pointing out how to reduce the risk of coming to
misleading concusions, and to aid getting better results more easily and
cheaply.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Tri-amping, driver time alignment, and carbon fibre cones
 

On Sun, 22 May 2005 02:54:58 GMT, "Wally" wrote:

Stewart Pinkerton wrote:

Yes, but when you've taken some measurements, you'll see that moving
the meter a couple of inches can make 10dB difference in the SPL at
any given frequency -

And if I move my lug-'ole a couple of inches, what will happen?

Exactly the same, which is why, if you want the *speaker* to have a
flat response, you need to take a fair number of measurements at
different mic posistins, and integrate them. Alternatively, move the
whole kit into the middle of the garden, stick the speaker on a
kitchen stool facing up, and suspend the mic above it. That's as close
as you'll get to an anechoic chamber in most properties.

... which is why pros use anechoic measuring
systems. Even top-class room-correction systems such as TACT make
depend on very careful microphone posisioning if they're to give
decent results.

Further, the *power* response is regerded by many as more important
than the axial response, so you'll have to take dispersion into
account when you're considering cabinet design. It's a very complex
business, which is one reason why speakers remain the greatest
weakness in hi-fi gear - along with the room.

I'm willing to be pragmatic and follow cabinet design principles that are
doable, like non-parallel cabinet faces, building something with a cabinet
volume recommended by the driver manufacturer, small baffle area, faired
edges, whatever. I'm after something that sounds decent in my room,
something that isn't a howler. I reckon that it's a reasonable approach to
build a sensible box and trust that it's general character will be fine,
such that the unevenness of the driver is the main thing that needs
addressing.

If using an SPL meter in a domestic room to calibrate the midrange is a dead
loss, then I'll use my ears. Over a period of weeks. In many different
positions. To acheive an EQ compromise that is satisfactory. Heck, I could
even look at the response curve for the driver and have a go at dialling in
the compensation from that.

Would you say that this is attempting the impossible?

Why not just buy a pair of KEF Q1s and a decent sub? It's odds-on that
this will sound better than anything you can build yourself, if it's
good sound you're after, rather than just the fun of home-building.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Tri-amping, driver time alignment, and carbon fibre cones
 

"Wally" wrote in message
. ..
The bass response was crap - rapid drop from 70Hz, feeble attempt to
redeem
itself at 25Hz. Boxes are too big (135L) for the port tuning, backs of the
cabs are full of slots. I want *small* boxes and have two spare drivers,
so
I elect to resolve this by building isobaric cabinets. In the meantime, I
use a multi-band digital parametric to sort it until I can get round to
building the new cabs. To be clear: the EQ may or may not be needed when
the
isobarc cabs are built - until then, it's a stop-gap to improve the bass
response from the existing boxes.

What is the easiest, cheapest way to fix crap bass response that comes out
of speakers that are too heavy to conveniently move around, and too big to
move into the room by more than an inch or three? (IOW, too damn big to
experiment with speaker positioning.) I can't think of anything other than
a
60-quid 12-band digital parametric that is far better quality than it has
any right to be at the price. Of the rush of changes that I went through,
this has been the best individual spend of the lot in terms of making the
system more enjoyable. But! Considering that the single Cyrus was
straining
before it had a load of extra bass to dish out, how much of an improvement
would it have been without extra amplifier power? I would have had more

Wally.

I have a message at the end of this thread that summarises my progress so
far. As you see it is all experiment with what I have and have bought so
far.
I have just bought a sig gen and SPL meter on ebay and am about to see
what the response curve looks like. This is of course in my room. I know
that the science of acoustics requires anechoic conditions but I want a
good sound in my room so that's where I experiment. What I want is to
see a reasonable steady SPL reading as I swing through the audible range.
I like the sound already but perhaps this will help to improve it?

Compromise. There's a dangerous word. When I first got my Revox I teased
an audiophile friend who had just paid zillions for a Nakamichi cassette
deck. He said he had Dolby and I asked how he adjusted the level for
different tape types. You can't on a N? Oh dear- compromise then?
Glare from friend.

Anyway. Why not borrow a car sub? (Please read this quietly!) I am
astonished at just how good it sounds. Its a 12" in a small trapezoidal
box, and not a high-spec one at that. Cost about £150. Don't try to
go down to 32 Hz. My son did with one of his super-bass test CDs.
When the entire output of my 500 watt InterM was going into it he
noted that it was warming quite rapidly! And it wasn't making a clear
note either. Yes pumping power into a tightly damped speaker can
make very low notes, I am sure, but not 32.

Peter Scott

Tri-amping, driver time alignment, and carbon fibre cones
 

In article , Peter Scott
wrote:


I have a message at the end of this thread that summarises my progress
so far. As you see it is all experiment with what I have and have bought
so far. I have just bought a sig gen and SPL meter on ebay and am about
to see what the response curve looks like. This is of course in my room.
I know that the science of acoustics requires anechoic conditions but I
want a good sound in my room so that's where I experiment. What I want
is to see a reasonable steady SPL reading as I swing through the audible
range.

I have my doubts that you will get your wish here. :-) My experience is
that in domestic listening rooms the level often tends to zip up and down
by 10 dB or more if you use a sinewave and sweep the frequency slowly, even
with speakers which - in an 'anechoic' situation - have a fairly flat
response. Fortunately, human hearing tends to 'tune out' a lot of this, so
you often get a better guide by using something like part-octave noise or
otherwise averaging over modest frequency bands. This also makes it easier
to get 'repeatable' results without clamping everything in the room so it
is always in the same location.


[snip]

Anyway. Why not borrow a car sub? (Please read this quietly!) I am
astonished at just how good it sounds. Its a 12" in a small trapezoidal
box, and not a high-spec one at that. Cost about £150. Don't try to go
down to 32 Hz. My son did with one of his super-bass test CDs. When the
entire output of my 500 watt InterM was going into it he noted that it
was warming quite rapidly! And it wasn't making a clear note either. Yes
pumping power into a tightly damped speaker can make very low notes, I
am sure, but not 32.

The problem here is that what will suffice tends to vary a lot from one set
of circumstances to another. Hence it is hard to predict what will prove
satisfactory for someone. That said, I found that a reasonably cheap and
small (commercial) sub made a distinct improvement. A different one might
be better, but as yet I have not experimented. In my case, though, the
walls are fairly firm, the room is reasonably small, and I only listen at
modest levels, mainly to 'classical' music. If I liked reggae or organ
music or heavy metal, and had a large room with flimsy walls I might need
something rather more substantial in the way of a sub. :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Tri-amping, driver time alignment, and carbon fibre cones
 

"Peter Scott" wrote in message
...
I know
that the science of acoustics requires anechoic conditions ...

No, it requires taking the room into account.

Eliminating the room from measurements elimianetes much of what you are
trying to measure. It's necessary, if you happen to be designing or selling
a general-purpose product which may be used in many different rooms whose
characteristics are unknown. In order to describe the properties of your
product rather than the room it was measured in, you can use an anechoic
room.

However, what you *shouldn't* do is suggest that the measurements obtained
in the anechoic room show what the speaker will sound like when the customer
buys it and installs it. Unfortunately, the hi-fi business being what it
is, there is no end of people suggesting that the listener can fix room
problems by buying "better" speakers.

Anyway. Why not borrow a car sub?

Good idea; I was going to suggest that the spare drivers be put to use
building a pair of subs instead of a pair of isobaric speakers ... then the
existing drivers could be built into smaller IB cabinets. I didn't put the
suggestion forward, because it requires another amplifier for the subs .
Borrowing a car sub avoids that problem.

Tim

Tri-amping, driver time alignment, and carbon fibre cones
 

Jim Lesurf wrote:

My point is that one has to start somewhere - it doesn't matter if
I've had a million different systems before the present one, the
*present* one is the *starting point*.

Not if you are then saying "it sounds different/better to what I had
before".

See comments at end.


I appreciate that you "don't care". However I think it does matter.

Only to the extent that, if they did apply some sort of compensation, then
that implies that there is unevenness in the response that I have to account
for. However, knowing what KEF did isn't the only way to determine whether I
have to apply compensation - I said in my original post that I sometimes
find the mid a bit shouty, which suggests to me that there is indeed
something which needs to be addressed. IOW, I was already aware of this
before you brought up the matter of the passive xovers having response
compensation built in - you mooted what is probably the most plausible
reason for what I'm hearing.


If you are going to recount your experiences here then it may matter
since not being clear on some of these points may mislead others.

Buyer beware - I'm not providing an audio consultancy service.


They may then feel that they need to buy more amplifiers and build
more complex systems, when in practice simpler and cheaper changes
might provide the results they would prefer. Hence it may not matter
to you, but may matter to others who read what you write. Thus I
think it is to their advantage to bring this up and have them at
least consider it before proceeding.

Reading my usenet slaverings about tri-amping on the cheap is hardly a
comprehensive basis for going out and spending loads of money, or expending
loads of effort on what may turn out to be a lost cause.


That is fine provided you are not attempting to make an deductions or
draw conclusions about the reasons the multi-amped and active system
sounds different to a previous passive single-amp arrangement.

I don't think I've 'made deductions'.


It would if you were passing comments as to the reasons for what you
have now sounding different to before.

If I have done that, it has only been in the loosest sense. What I've
essentially been saying is that I did a bunch of changes (all at once), and
now it sounds like X rather than Y. In essence, my comments on the reasons
for the perceived changes have been as follows...

I've associated the cleaner sound at high volume, and better dynamics, with
the addition of more amps (to my mind, the midrange is no longer riding on
top of high amplitude bass frequencies, so there's more headroom for the mid
than there was before). I don't think that's a particularly unreasonable
inference to draw.

I've associated the improved bass response to the addition of EQ to the bass
amp. I think this inference is very well-founded - the EQ has a bypass
switch and the difference is clear.

I have reported that the midrange is a bit shouty at times, but have offered
no reason for why this might be so.


Since reading your comments on the passive crossovers likely having
compensation for irregularities in the drivers, and having subsequently read
elsewhere that the B110 has a lift in the midrange, I could accept that some
of the perceived improvement in clarity and detail could be spurious, due to
this lift. However, I find it hard to attribute all of the improved clarity
at higher volume to this effect - I could accept that it's a combination of
the now-uncompensated mid and the improved amplifier headroom. At some
point, I'll put a meter or a scope on the amp outputs and try and work out
how much power is going into the drivers.



When I cranked up the single Cyrus 2 set up, the sound was crap.
Solution? Use a more powerful amplifier. How much amplifier power
would be required to produce a clean sound at the volumes where the
50Wpc Cyrus 2 was straining? 100Wpc? How much would such an
amplifier cost, and which one should I get?

Can't say because the comment "sound was crap" does not really give
any clues as to the actual nature of the problem. :-)

A distinct loss of clarity in the midrange, maybe more harsh sounding than
when it was being used at lower volumes. Not dissimilar to the valve amp
when it was being pushed, albeit at lower volume. Definitely unpleasant -
the sort of sound that would rapidly induce listener fatigue.


So, I'll have my stop-gap parametric to improve the bass until I can
be bothered making bass cabs. Once I've made my bass cabs - my *four
ohm* isobaric bass cabs - how do I amplify these and the 8-ohm
mid/top speakers with one amplifier? Can it be done? How much power
will this set up require over and above what would have been
required with single bass drivers?

Can't really say as we don't have enough information. You might find
a 50 W amp is fine, but you might need 500 W. Depends on the actual
speaker, the room, and how loud you want to play what sort of music.

In terms of in-room volume, 50W seems to be fairly close to the mark. I
realise that it may sound 'louder than it really is' due to something (the
amp?) being overloaded, but the overall volume level sounds about as loud as
I'd want to go if I want to stay on speaking terms with the neighbours. What
I'm looking for, then, is a similar volume level, but with a cleaner sound.
At present, I seem to have gotten closer to that (for whatever reason!). The
main limiting factor in volume just now is the loose damping of the bass
drivers, coupled with the increase in low bass due to the EQ - it's almost
loud enough, but I'm concerned that there might be damage to the bass
drivers (some music is okay, some isn't).


This is a different question. The point here is that you could choose
(or at this point, "have chosen") to use the original speaker with
its passive networks, and bi-amped via an active crossover to split
the 'low bass' from the rest of the signals. This is a more common
approach and has the advantage that you don't have to re-engineer the
main speakers as well as add in a low bass section. It is also easier
to 'undo' and compare with the original arrangement to help assess
any changes.

The approach I was originally going to take was to bi-amp - isobaric bass
cabs, and new passive crossovers for the mid/top (direct copies of the
standard KEF crossover for a B110/T27 pairing, rather than the 3-way
passives I have at present). This approach is still entirely possible - the
existing active crossover can be used as a 2-way, and I have two 50W Cyrus
amps to use.

One has to bear in mind that this is a hobby - I have no professional or
academic interest in the subject, just a layman's techie interest with the
aim of getting a better sound. Something I've been curious about is finding
out what happens when the passive crossovers are removed from the equation:
Just how good are the drivers on their own? How much does all that phase and
reactive load stuff influence what I hear? What will happen if I replace
those networks with an active crossover which is supposed to be summed flat
with no phase anomalies? Will the amplifier(s) then have an easier load to
drive - will I get more for my amplifier buck by driving the drivers
directly? I don't know, because I don't have the theoretical knowledge to
predict, so it doesn't seem like a bad thing to give it a try and find out.


To make clear again something I have tried before to indicate: I have
not been saying that multiple amps or active crossovers are 'wrong'
in any way. What I am doing is pointing out how to reduce the risk of
coming to misleading concusions, and to aid getting better results
more easily and cheaply.

And a point I made a while ago is that I am experimenting with tri-amping,
mainly for the hell of it, and because it will let me play around with the
isobaric idea in a relatively painless way (no passive xovers to deal with,
bass is isolated from the rest of the system).

I'm not advising anyone else to follow the same approach. I reported the
perceived changes after a rash of unmeasured changes for interest's sake
only - it was in no way an attempt to offer something scientific or
technically astute. Any allusions I've made as to the possible causes of the
perceived changes are just my opinion - I'm reasonably technically literate,
but, as I've said before, I don't really know what I'm doing with audio.


--
Wally
www.artbywally.com/FiatPandaRally/index.htm
www.wally.myby.co.uk

Tri-amping, driver time alignment, and carbon fibre cones
 

Stewart Pinkerton wrote:

And if I move my lug-'ole a couple of inches, what will happen?

Exactly the same, which is why, if you want the *speaker* to have a
flat response, you need to take a fair number of measurements at
different mic posistins, and integrate them.

Understood.


Alternatively, move the
whole kit into the middle of the garden, stick the speaker on a
kitchen stool facing up, and suspend the mic above it. That's as close
as you'll get to an anechoic chamber in most properties.

Maybe that isn't such a bad idea...


Why not just buy a pair of KEF Q1s and a decent sub?

Because I don't have 500 quid lying around for speakers. :-) What's the
deal with Q1s at the low end? I see they're reflex boxes - which aren't
generally well regarded.


It's odds-on that
this will sound better than anything you can build yourself, if it's
good sound you're after, rather than just the fun of home-building.

I'm not averse to doing a bit of box building.


--
Wally
www.artbywally.com/FiatPandaRally/index.htm
www.wally.myby.co.uk

Tri-amping, driver time alignment, and carbon fibre cones
 

Peter Scott wrote:

Compromise. There's a dangerous word. When I first got my Revox I
teased an audiophile friend who had just paid zillions for a
Nakamichi cassette deck. He said he had Dolby and I asked how he
adjusted the level for different tape types. You can't on a N? Oh
dear- compromise then? Glare from friend.

So far as I can see, it's all about compromise. Perfection is unattainable.
It's a question of where one makes the compromises, and to what extent.


Anyway. Why not borrow a car sub? (Please read this quietly!) I am
astonished at just how good it sounds. Its a 12" in a small
trapezoidal box, and not a high-spec one at that. Cost about £150.
Don't try to go down to 32 Hz.

I rather think I'd like to go lower than that.


My son did with one of his super-bass test CDs.
When the entire output of my 500 watt InterM was going into it he
noted that it was warming quite rapidly! And it wasn't making a clear
note either.

Er, isn't this a reason to *not* use a car sub? :-)


Yes pumping power into a tightly damped speaker can
make very low notes, I am sure, but not 32.

Damping and power is something that I have to learn more about. My current
plan is the isobaric subs using KEF B139s. They have a free air resonance of
25Hz, and KEF recommend an infinite baffle enclosure, for one driver, of
30-40 litres. I gather that, to get the same response from an isobaric
pairing, one reduces the cabinet volume by half (small bass cabs is what I'm
after). However, I don't know what sort of response KEF's recommended cab
volume will yield - if I have to apply EQ to get it flat, I find myself
wondering how much power will actually be going into the drivers, and
whether the acoustic damping will limit the cooling.


--
Wally
www.artbywally.com/FiatPandaRally/index.htm
www.wally.myby.co.uk

Tri-amping, driver time alignment, and carbon fibre cones
 

On Mon, 23 May 2005 12:38:50 GMT, "Wally" wrote:

Stewart Pinkerton wrote:

And if I move my lug-'ole a couple of inches, what will happen?

Exactly the same, which is why, if you want the *speaker* to have a
flat response, you need to take a fair number of measurements at
different mic positions, and integrate them.

Understood.

Alternatively, move the
whole kit into the middle of the garden, stick the speaker on a
kitchen stool facing up, and suspend the mic above it. That's as close
as you'll get to an anechoic chamber in most properties.

Maybe that isn't such a bad idea...

Just be sure to first check the weather forecast! :-)

Why not just buy a pair of KEF Q1s and a decent sub?

Because I don't have 500 quid lying around for speakers. :-)

Ah well, that's a reasonable answer! :-)

What's the
deal with Q1s at the low end? I see they're reflex boxes - which aren't
generally well regarded.

Don't believe everything you read about ported speakers - it mostly
refers to 30 year-old pre-CD boomboxes. Consider that the B&W N800
series are all reflex designs, as are all the bigger ATC speakers, and
you'll see that there are no simple answers in this game.

Plus of course if you have a sub, you can stuff the ports and get a
tighter but less extended bass response from the small speakers.

It's odds-on that
this will sound better than anything you can build yourself, if it's
good sound you're after, rather than just the fun of home-building.

I'm not averse to doing a bit of box building.

Fair enough - just don't expect your efforts to result in something
superior to a speaker backed by several million quid's worth of R&D by
top designers.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Tri-amping, driver time alignment, and carbon fibre cones
 

On Mon, 23 May 2005 13:04:15 GMT, "Wally" wrote:

Peter Scott wrote:

Compromise. There's a dangerous word. When I first got my Revox I
teased an audiophile friend who had just paid zillions for a
Nakamichi cassette deck. He said he had Dolby and I asked how he
adjusted the level for different tape types. You can't on a N? Oh
dear- compromise then? Glare from friend.

So far as I can see, it's all about compromise. Perfection is unattainable.
It's a question of where one makes the compromises, and to what extent.


Anyway. Why not borrow a car sub? (Please read this quietly!) I am
astonished at just how good it sounds. Its a 12" in a small
trapezoidal box, and not a high-spec one at that. Cost about £150.
Don't try to go down to 32 Hz.

I rather think I'd like to go lower than that.


My son did with one of his super-bass test CDs.
When the entire output of my 500 watt InterM was going into it he
noted that it was warming quite rapidly! And it wasn't making a clear
note either.

Er, isn't this a reason to *not* use a car sub? :-)


Yes pumping power into a tightly damped speaker can
make very low notes, I am sure, but not 32.

Damping and power is something that I have to learn more about. My current
plan is the isobaric subs using KEF B139s. They have a free air resonance of
25Hz, and KEF recommend an infinite baffle enclosure, for one driver, of
30-40 litres. I gather that, to get the same response from an isobaric
pairing, one reduces the cabinet volume by half (small bass cabs is what I'm
after). However, I don't know what sort of response KEF's recommended cab
volume will yield - if I have to apply EQ to get it flat, I find myself
wondering how much power will actually be going into the drivers, and
whether the acoustic damping will limit the cooling.

To get maximum acoustic output from those B139s, don't use an isobaric
arrangement. Put them on opposite faces of a box of any size you like
(to balance the forces and reduce cabinet vibration), and use a hefty
amplifier with EQ to flatten the response.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Tri-amping, driver time alignment, and carbon fibre cones
 

Stewart Pinkerton wrote:

Don't believe everything you read about ported speakers - it mostly
refers to 30 year-old pre-CD boomboxes. Consider that the B&W N800
series are all reflex designs, as are all the bigger ATC speakers, and
you'll see that there are no simple answers in this game.

Plus of course if you have a sub, you can stuff the ports and get a
tighter but less extended bass response from the small speakers.

Doesn't that take me straight back to the problems I might face in starting
from scratch? IOW, stuffing the ports changes the characteristics of the
box, thus releasing possible demons that were compensated for in the ported
version?


I'm not averse to doing a bit of box building.

Fair enough - just don't expect your efforts to result in something
superior to a speaker backed by several million quid's worth of R&D by
top designers.

I don't, but I do feel that some 'good practice' in the box building
department should yield something decent, in the sense that, if I avoid the
bad practice (eg, a cube made of thin cardboard), I'm half-way there.


--
Wally
www.artbywally.com/FiatPandaRally/index.htm
www.wally.myby.co.uk

Tri-amping, driver time alignment, and carbon fibre cones
 

Stewart Pinkerton wrote:

To get maximum acoustic output from those B139s, don't use an isobaric
arrangement. Put them on opposite faces of a box of any size you like
(to balance the forces and reduce cabinet vibration), and use a hefty
amplifier with EQ to flatten the response.

What effect would that have on cabinet volume requirements? Double what KEF
say for a single driver?


--
Wally
www.artbywally.com/FiatPandaRally/index.htm
www.wally.myby.co.uk

Tri-amping, driver time alignment, and carbon fibre cones
 

"Wally" wrote in message
m...
Peter Scott wrote:

Compromise. There's a dangerous word. When I first got my Revox I
teased an audiophile friend who had just paid zillions for a
Nakamichi cassette deck. He said he had Dolby and I asked how he
adjusted the level for different tape types. You can't on a N? Oh
dear- compromise then? Glare from friend.

So far as I can see, it's all about compromise. Perfection is
unattainable.
It's a question of where one makes the compromises, and to what extent.

Totally agree, but it was fun. He also damped room resonance using piles
of old Hifi News (Jim please note!)

Don't try to go down to 32 Hz.

I rather think I'd like to go lower than that.

Unlss you've got a 32 foot organ pipe I'm not sure you can! All the
speaker software predicts problems getting much output below about
40 Hz even with a wardrobe.

When the entire output of my 500 watt InterM was going into it he
noted that it was warming quite rapidly! And it wasn't making a clear
note either.

Er, isn't this a reason to *not* use a car sub? :-)
No. Its a very good reason not to pump half a kilowatt into a few turns of
copper that cannot pump them efficiently out into the air.

Damping and power is something that I have to learn more about.
Think of it like a kid's swing. Push it at the right time at its frequency
and you can make it swing high with little effort. If you want to
make it go much more slowly than it wants, you have to hold it and
physically drag it backwards and forwards. It'll work but it takes a
lot of energy.

Peter Scott

Tri-amping, driver time alignment, and carbon fibre cones
 

In article , says...
Unlss you've got a 32 foot organ pipe I'm not sure you can! All the
speaker software predicts problems getting much output below about
40 Hz even with a wardrobe.

Cue Nath..


T.
--
Please Tony, NO!! You'd look dreadful in a basque and fishnets..

Tri-amping, driver time alignment, and carbon fibre cones
 

On Mon, 23 May 2005 16:57:09 GMT, "Wally" wrote:

Stewart Pinkerton wrote:

To get maximum acoustic output from those B139s, don't use an isobaric
arrangement. Put them on opposite faces of a box of any size you like
(to balance the forces and reduce cabinet vibration), and use a hefty
amplifier with EQ to flatten the response.

What effect would that have on cabinet volume requirements? Double what KEF
say for a single driver?

You can make the cabinet as small as you like, you'll be using EQ to
flatten the response below the natural F3 point, as the sub makers do.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

Tri-amping, driver time alignment, and carbon fibre cones
 

On Mon, 23 May 2005 16:55:26 GMT, "Wally" wrote:

Stewart Pinkerton wrote:

Don't believe everything you read about ported speakers - it mostly
refers to 30 year-old pre-CD boomboxes. Consider that the B&W N800
series are all reflex designs, as are all the bigger ATC speakers, and
you'll see that there are no simple answers in this game.

Plus of course if you have a sub, you can stuff the ports and get a
tighter but less extended bass response from the small speakers.

Doesn't that take me straight back to the problems I might face in starting
from scratch? IOW, stuffing the ports changes the characteristics of the
box, thus releasing possible demons that were compensated for in the ported
version?

What 'demons'? Stuffing the port will lower system Qts, raise F3, and
reduce any internal noises that might have been escaping through the
port. The only disadvantage is the raising of F3, and that's not an
issue if you have a sub.

I'm not averse to doing a bit of box building.

Fair enough - just don't expect your efforts to result in something
superior to a speaker backed by several million quid's worth of R&D by
top designers.

I don't, but I do feel that some 'good practice' in the box building
department should yield something decent, in the sense that, if I avoid the
bad practice (eg, a cube made of thin cardboard), I'm half-way there.

Make that about 10%....................
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Tri-amping, driver time alignment, and carbon fibre cones
 

By the way, here's one person's method.

http://www.duffroomcorrection.com

He uses tri-amping, with digital signal processing on a PC to provide
digital filtering and EQ.

He also positioned his subwoofers under the floor; those whose listening
room is on the ground floor of a house with floorboards might be
interested. It's one way to provide a large subwoofer enclosure without
taking up room space!

Tim

Tri-amping, driver time alignment, and carbon fibre cones
 

"Tony Gartshore" wrote in message
...
In article ,
says...
Unlss you've got a 32 foot organ pipe I'm not sure you can! All the
speaker software predicts problems getting much output below about
40 Hz even with a wardrobe.

Cue Nath..


T.
--
Please Tony, NO!! You'd look dreadful in a basque and fishnets..

Making comments like that really hertz

Peter Scott