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

Jim Lesurf wrote:

The point to bear in mind that the overall frequency response may be
different now for a combination of reasons:

1) Removal/bypass of the original networks. These may not just have
acted as crossovers. They may have alttered the in-band levels and
shapes of response.

I've been doing some browsing, and it would seem that the KEF B110 has a
one-octave-wide lift at about 1.5KHz. I don't know how big a lift it is.
When I do my baseline measurement, I'll be paying close attention.


2) The power amps may have different gains.

They have, but, as I said to Stewart, they each have volume controls, none
is turned up full, and the crossover provides +/-6dB on each band.


3) Your 'crossover' points and slopes may be different to before.

The points are dialled in to match those used by KEF, although I dare say
the active xover has steeper slopes. A steeper slope is generally a good
thing, isn't it?


4) The effective gains for the active crossover may now be different
in the various bands.

As I say above, they're settable - even if there are discrepancies between
bands when the gains are set to zero, there's scope to compensate in any
case.


Hence it remains plausible that you might have obtained much the same
effect by using the active crossover simply as a 'tone control' whilst
using the speakers with fewer amps and leaving the passive networks in
place.

Maybe so, but part of the aim of this is to double up the bass drivers by
making isobaric subs. The main reason for doing this is to get substantially
smaller cabinets - the existing boxes are way too big, and moving them
around simply isn't practical. I also wanted better bass than the lumpy
response I had (the cabinets are 'wrong' for the drivers), and better power
handling. Since I already had two B139s in the speakers, and two spares,
this would seem a reasonable way to go.



Indeed, of the passive networks included arrangements to deal
with some detailed aspects of the speakers, the results *might* have
been better in some way. Problem is that we can't tell without a
suitable comparison test.

As I said, the tri-amped set up is the baseline. The way I see it, it's
easier for me to make changes and assess their effects. For example, if
there are shortcomings in the midrange drivers, I'm not averse to trying
something more modern that has a flatter 'natural' response (and,
intuitively, this seems to be a better approach than taking a driver with a
lumpy response and trying to flatten it with reactive components). FWIW,
I've never been overly happy with the midrange - comments here a few months
ago, about bextrene cones, rang true with my experience of them.


How are you defining "available power" here? It may not be as simple
as just adding together the ratings for the individual amps.

I don't know what I'm talking about, so I'm being simplistic. :-)


That is fair enough from your point of view. You have spent your
money, put in the effort, and obtained a result which you prefer.
That seems an excellent result to me, and clearly justifies the
effort.

No doubt about that - the tonal character is much the same, but the overall
change is, to me, a step-change improvement.


However I am simply trying to point out for consideration by
yourself and others that there may well be a cheaper and easier way
to get similar 'improvements'. This may save others some cost and
effort.

I appreciate your point, but I freely admit that the tri-amp thing is as
much about curiosity as anything. If I discount the digital EQ for the bass,
the actual spend has been about 200 quid for the active crossover and a
second Cyrus. IOW, I would have added the EQ regardless of what system
configuration I was using - the bass was a mess, and I think the room will
always conspire to keep it that way whatever speakers I have. All-in, the
spend, including connectors and cable, has been around 300-odd quid, spread
around bits that are relatively cheap, and easy to sell on if I want to
change the overall approach.


[1] In this context it does not matter much if the sound meter is a
cheap/poor one, or if the room has an odd acoustic. The aim is to do a
'before/after' comparison and have the info as a reference.

Yup. I'll be doing a full range frequency response test sometime fairly
soon.


--
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:


2) The power amps may have different gains.

They have, but, as I said to Stewart, they each have volume controls,
none is turned up full, and the crossover provides +/-6dB on each band.

But do you now have the same relative effective gains in the bands as
before? If not, then some of the differences can be due to 'tone control'
effects...


3) Your 'crossover' points and slopes may be different to before.

The points are dialled in to match those used by KEF, although I dare
say the active xover has steeper slopes. A steeper slope is generally a
good thing, isn't it?

Not necessarily. :-) The point is that as you go through the crossover
region of the spectrum changing the slopes will alter the resulting
response. For example, using steeper slopes may produce a 'dip'.
Alternatively steeper slopes also means that the phases change in a
different way, so you may get other changes for that reason.


4) The effective gains for the active crossover may now be different
in the various bands.

As I say above, they're settable - even if there are discrepancies
between bands when the gains are set to zero, there's scope to
compensate in any case.

Yes. But if you are doing this 'by ear' to get the result you like, the
result may be that you settle on a different response to before. This then
means that you are using the xover as a tone control and getting
'improvements' from that. Hence having multiple amps may not be giving you
the changes you assume.

[snip]

Indeed, of the passive networks included arrangements to deal with
some detailed aspects of the speakers, the results *might* have been
better in some way. Problem is that we can't tell without a suitable
comparison test.

As I said, the tri-amped set up is the baseline. The way I see it, it's
easier for me to make changes and assess their effects.

That is fair enough. However as I have indicated, people who have *not* yet
spent the money on more power amps, etc, might find it useful to be
cautious and assess what I am saying. There may be a cheaper and easier
route for them. Difficult to say without suitable experiments, etc, in each
individual case.

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
 

"Stewart Pinkerton" wrote in message

"Wally" wrote in message
om...

I thought it's advisable to use exactly the same poweramps (for gain) for
all the amps?

Yes indeed...

Why?

Tim

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

"Stewart Pinkerton" wrote in message
...

You'll get different levels on bass, mid and treble, which you'll have
to adjust via the active crossover.

But you'll have to adjust the levels anyway, unless the sensitivities of the
drivers are exactly equal.

Tim

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

On Mon, 16 May 2005 15:42:21 GMT, "Tim Martin"
wrote:

"Stewart Pinkerton" wrote in message
.. .

You'll get different levels on bass, mid and treble, which you'll have
to adjust via the active crossover.

But you'll have to adjust the levels anyway, unless the sensitivities of the
drivers are exactly equal.

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.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

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

Jim Lesurf wrote:

2) The power amps may have different gains.

They have, but, as I said to Stewart, they each have volume controls,
none is turned up full, and the crossover provides +/-6dB on each
band.

But do you now have the same relative effective gains in the bands as
before? If not, then some of the differences can be due to 'tone
control' effects...

I don't wish to labour the point, but 'before' is history. I don't have the
'before' numbers, so any attempt to draw comparisons is academic.


Not necessarily. :-) The point is that as you go through the
crossover region of the spectrum changing the slopes will alter the
resulting response. For example, using steeper slopes may produce a
'dip'.

Surely the crossover will have been designed to not have a dip?



Alternatively steeper slopes also means that the phases change
in a different way, so you may get other changes for that reason.

I thought this active crossover thing was supposed to be all
phase-compensated or something...


4) The effective gains for the active crossover may now be different
in the various bands.

As I say above, they're settable - even if there are discrepancies
between bands when the gains are set to zero, there's scope to
compensate in any case.

Yes. But if you are doing this 'by ear' to get the result you like,
the result may be that you settle on a different response to before.

'Before' is history. I'm not interested in 'before', I'm interested in
taking what i've got and seeing what can be done to make it more enjoyable.


This then means that you are using the xover as a tone control and
getting 'improvements' from that.

Fine by me. I don't care what happens within the system, so long as I like
what comes out.


Hence having multiple amps may not
be giving you the changes you assume.

They've added power, clarity and dynamics.



As I said, the tri-amped set up is the baseline. The way I see it,
it's easier for me to make changes and assess their effects.

That is fair enough. However as I have indicated, people who have
*not* yet spent the money on more power amps, etc, might find it
useful to be cautious and assess what I am saying. There may be a
cheaper and easier route for them. Difficult to say without suitable
experiments, etc, in each individual case.

I'm doing what I'm doing for myself. What other people choose to do is
entirely up to them.


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

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

"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. Take some frequency within the range of the bass and mid-range
speaker, feed a signal to the bass speaker, and measure the microphone
output. Now feed the frequency to the mid-range, and adjust its level until
the microphone is generating the same ouput.

Repeat for the mid-range and HF speakers.

You don't even need a calibrated microphone.

Tim

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

"Wally" wrote in message
...

I thought this active crossover thing was supposed to be all
phase-compensated or something...

The Behringer crossover slope is fixed at 24dB/octave, and the output is
summed to flat.

These things simply work. I should think that, as one accumulates a
collection of amplifiers, it becomes cheaper to use an active crossover with
"free" amplifiers than to build a high-slope passive crossover.

Tim

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

Tim Martin wrote:

I thought this active crossover thing was supposed to be all
phase-compensated or something...

The Behringer crossover slope is fixed at 24dB/octave, and the output
is summed to flat.

Yeah, that sounds about right.


These things simply work.

That's the impression I'm getting so far.


I should think that, as one accumulates a
collection of amplifiers, it becomes cheaper to use an active
crossover with "free" amplifiers than to build a high-slope passive
crossover.

I was originally considering bi-amping, and building 2-way passive
crossovers out of 'quality' caps and air-cored inductors. The active
crossover cost about the same as the fancy passive ones would have - and I
would still have needed a 2-way active crossover to bi-amp (about 60-odd
quid for the 2-way Behringer).

One of the nice things is that I can change an amp at relatively low cost -
I'm looking out for a Cyrus 1 to replace the valve amp that's driving the
tweeters. If it doesn't work out, I can just track down one of the 50W
Cyruses and punt the Cyrus 1. By the same token, if a 50W Cyrus isn't up to
driving the eventual bass set up, it's less painful to change out just that
amp for something more powerful - and I can do so without wondering if the
sound of the rest of the system will change.


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

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

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!

Take some frequency within the range of the bass and mid-range
speaker, feed a signal to the bass speaker, and measure the microphone
output. Now feed the frequency to the mid-range, and adjust its level until
the microphone is generating the same ouput.

Repeat for the mid-range and HF speakers.

You don't even need a calibrated microphone.

You do, if you want a flat response from your speakers. Also, note
that you need to be *very* careful, if you're measurements are not to
be swamped by room effects. You might even need to move into the
garden for this, with the mic suspended above the speaker, itself
several feet in the air and pointing upwards. And then you've got to
set up your angles and positioning properly to get your full family of
responses to calculate when you have a flat *power* response, rather
than just a flat axial response, or do you want a slightly falling
power response, and if so at what slope, etc etc.

Measuring speakers properly ain't rocket science, but it's
close...................
--

Stewart Pinkerton | Music is Art - Audio is Engineering