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
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
 

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