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

Jim Lesurf wrote:

How do measurements of the frequency response now compare with before
you made the changes?

Unfortunately, I didn't have the meter before the changes started - I got it
after I split the bass from the rest and added the EQ. When I did get it, I
only concentrated on the bass, and found that my initial (and probably
somewhat rushed) by-ear bass EQ settings were rather lumpy. After some
further tweaking using the meter, I think the bass sound is much improved.
There's still room for improvement (according to the meter) in the 25-35Hz
range, but I think need to alter the centre frequencies of the parametric
bands to suit. An initial run through the full range using the Maplin test
CD would suggest that everythng is pretty even from about 100Hz upwards -
this did lead me to raise the bass/mid crossover point to around 350-400Hz.


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

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

Bob Latham wrote:

So I'm very interested in what you are doing, can your active Xover do
400Htz and 2500 Htz for xover frequencies?

Yes. The crossover points are sweepable through the following ranges...

bass/mid: 44 - 930Hz and switchable to 440Hz - 9.3KHz
mid/top: 440Hz - 9.3KHz

It's a Behringer Super-X Pro CX3400, and cost 84 quid. XLR connecters only,
so a pile of XLR to phono adapters were needed as well.


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

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

Stewart Pinkerton wrote:

OK, in that case you have a genuine option going for you. Most of the
best box speakers I've heard have been active designs. Proper ones,
that is, not the Linn/Naim skamkrap.

I'm currently looking at a mid/top cabinet in 18mm birch ply (because I
happen to have some). The sides slope inwards at the top, the back panel
slopes forwards, and the top panel slopes down towards the back. Volume is
about 7 litres. Would you say that this is on the right track?

What are your thoughts on this driver time alignment malarkey? Depending on
how critical this is, the mid/top cabs would either be on their own stands
(for easy moving around), or mounted onto the bass cabs (which I'd prefer to
have out of the way).


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

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

On Wed, 11 May 2005 19:44:45 GMT, "Wally" wrote:

Stewart Pinkerton wrote:

OK, in that case you have a genuine option going for you. Most of the
best box speakers I've heard have been active designs. Proper ones,
that is, not the Linn/Naim skamkrap.

I'm currently looking at a mid/top cabinet in 18mm birch ply (because I
happen to have some). The sides slope inwards at the top, the back panel
slopes forwards, and the top panel slopes down towards the back. Volume is
about 7 litres. Would you say that this is on the right track?

No, the right track is to buy a commercial speaker. There is
absolutely no way that the home-builder can match KEF, Mission, B&W
etc. for matching of drivers to cabinets, and final voicing of the
crossover. This has been proven in several blind trials, where £2-500
commercial speakers totally blew away much more expensive homebuilds
in 'all comers' challenges.

The only area where the homebuilder has a genuine advantage is in
subwoofers.

What are your thoughts on this driver time alignment malarkey? Depending on
how critical this is, the mid/top cabs would either be on their own stands
(for easy moving around), or mounted onto the bass cabs (which I'd prefer to
have out of the way).

Theoretically, it's a good idea, and there was a big fashion for them
in the early '80s, but that seems to have died away, so it seems not
to be a critical factor for most listeners.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

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

"Wally" wrote in message
m...


Most noticable improvements in instrument/music terms are that drums are
more solid - tighter and more punchy; acoustic guitars are much better -
much clearer; and classical music seems to have acquired a dynamic range I
was unaware of beforehand.

I haven't really cranked it up much - I did it once and got a couple of
pops
from the bass drivers, which got me out of my seat and diving for the
volume
control pretty damn quick. At the moment, it goes about as loud as I dared
go when it was just the Cyrus 2 and the 3-way passive crossovers, except
that it's now much, much cleaner - night and day, in fact.

Methinks there's definitely something in this amplifier headroom lark.


I've been experimenting for a while now and have talked about it other
threads. Time to report findings.

Set up is:
Cyrus Pre pre-amp without additional PSU
Behringer 3400
InterM R500 amp feeding Mordaunt Short 55Ti s (20 yrs old) as mids
InterM R500 feeding twin-coil car subwoofer
NAD 3020 feeding two silk tweeters
Crossovers at 90Hz and 3500 Hz
Room about 7.5 x 5 x 2.5 m

As you see from the spec sub is definitely an interim. I will build
one when I know exactly what I want. Tweeters ain't great- cost
about 15 ukp each. I will possibly change these to ribbons, or
maybe not (see below).

The results are a revelation. The overall sound is more solid and
sweet, and there is no evidence of tension or strain anywhere. At
last I can feel that an improvement has achieved something. I have
listened to a wide range of music now at some length. including:
Jazz (Davis, Zawinul, Pine)
Gamelan, including big bass drum and sharp percussion
Violin (Brahms op 78)
Rap like Dre
Voice (various)
Woodwind (inc Brahms)
Floyd (especially Fletcher Memorial Home and Tigers)
and so on.

So I am *happy*. My wife who, though non-technical, is a
down-to-earth, critical listener (and critical of my spending
sometimes!) agrees that we have a major improvement. I have
more tweaking to do, including levels and cross-overs but
the above is an interim optimum.

Conclusions a
Incremental improvement
Behringer is a clean flexible tool
Tri-amping gives headroom and clarity
Perhaps I won't need a new sub

Peter Scott

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

In article , Wally
wrote:
Jim Lesurf wrote:

How do measurements of the frequency response now compare with before
you made the changes?

Unfortunately, I didn't have the meter before the changes started - I
got it after I split the bass from the rest and added the EQ.

In that case the following experiment would be of interest.

1) Make a note of the settings at present and the measured (acoustic)
frequency response.

2) Alter the arrangement by using a set of series resisors to sum together
the outputs from the xover, then run the combined result through just one
power amp. Then run the output of the power amp to the speakers in
parallel.

3) See if this sounds much the same as at present. (You may need, first, to
tweak the gains of the xover sections to correct for any differences in
gains of the amps and get much the same acoustic frequency response as
before.)

This would help establish if the differences you hear are due to the system
simply acting as a 'tone control' and have little or nothing to do with
using more than one power amp. I'd be interested to know what you
discovered...

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:

Unfortunately, I didn't have the meter before the changes started - I
got it after I split the bass from the rest and added the EQ.

In that case the following experiment would be of interest.

1) Make a note of the settings at present and the measured (acoustic)
frequency response.

2) Alter the arrangement by using a set of series resisors to sum
together the outputs from the xover, then run the combined result
through just one power amp. Then run the output of the power amp to
the speakers in parallel.

If this involves running the o/p through the passive xovers, then that would
be a pain - I did a bunch of soldering to sort out the connections, and I'm
not keen on pulling it all apart again. (See closing comments below.)


This would help establish if the differences you hear are due to the
system simply acting as a 'tone control' and have little or nothing
to do with using more than one power amp. I'd be interested to know
what you discovered...

The most significant changes are better bass, cleaner volume, and better
dynamics. The EQ is only on the bass channel, so, aside from removing the
passive crossovers, I don't see how there can be much 'tone control' effect
on the mid or top (unless the active crossover isn't as flat as it's
purported to be). I have to assume that the amps are as flat as one can
reasonably expect.

Adding the bass EQ made a huge difference over the interim bi-amped set up
(where the bass was on one amp, and the mid/top was on the other with the
passive xovers still in place). The EQ on the bass hasn't brought a subtle
change - it's order of magnitude stuff.

Less gross is the change in dynamics and volume, but I'm satisfied that this
has definitely improved - when I first replaced the 20W valve amp with the
Cyrus 2, there was a clear increase in volume and, to a lesser extent,
dynamics. However, I was a little disappointed that the quality still
dropped markedly when I played it up loud. I wasn't sure if this was the amp
running out of puff, or the speakers starting to distort (50Wpc was the most
power I'd used with these speakers). Adding the second Cyrus and bringing
the valve amp back into the set up has given me available power of something
like 120Wpc, with no indication of the straining that I was previously
hearing at higher volumes - aside from that previously-mentioned tendency
for the mid to be a bit shouty at times.

So, with regard to an overall 'tone control' effect, the only real changes I
can think of are adding the active crossover and removing the passive ones.
My feeling is that the nett change due to this is likely to be rather more
subtle than obvious. Certainly, for now, my awareness/attention is focussed
on the much improved bass response, the cleaner sound at volume, and the
better dynamics. I feel that I'll have to live with these changes for quite
a while before I can get into the more subtle stuff.

To be honest, I'm not particularly interested in trying to establish how
much difference there is between the system as it stands now, and how it was
with all-passive xover and the single Cyrus amp - it was better than the
valve amp on its own, but was still ultimately less satisfying than it
could/should have been.

Looking back into the mists of time, this all started with the idea of
building isobaric subs out of the collection of KEF B139 drivers that I have
kicking around - since this would change the nominal impedance of the bass
end to 4 instead of 8 ohms, I felt that bi-amping was the way to go. (Some
people suggested tri-amping at the time, but active crossovers were too
expensive for me then - I had planned to bi-amp and build some sort of
active crossover since I had a scope and other kit available.) I'm now less
skint, the Behringer crossover is much cheaper than other kit was back then,
and I'm now interested in seeing what can be done with tri-amping for no
real reason other than the hell of it. First indications are positive.

To my mind, the system as it stands is the baseline - for the foreseeable
future, I'm essentially committed to a tri-amped set up, and the idea is to
try and make it better without spending a fortune. While I was initially
less than conducive to using measurements, I would say that I'm more willing
to sing from that particular hymn sheet after seeing driver free air
resonance graphically displayed on the scope, and having heard the
improvement to the bass that came about from using the SPL meter (compared
to my MkI lug-'ole attempts). With this in mind, I'll be taking a set of
measurements of the overall frequency response, such that the effect of
subsequent changes can be analysed objectively.


--
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:

Unfortunately, I didn't have the meter before the changes started - I
got it after I split the bass from the rest and added the EQ.

In that case the following experiment would be of interest.

1) Make a note of the settings at present and the measured (acoustic)
frequency response.

2) Alter the arrangement by using a set of series resisors to sum
together the outputs from the xover, then run the combined result
through just one power amp. Then run the output of the power amp to
the speakers in parallel.

If this involves running the o/p through the passive xovers, then that
would be a pain - I did a bunch of soldering to sort out the
connections, and I'm not keen on pulling it all apart again. (See
closing comments below.)

OK. Fair enough. It may be worth noting here that you have bypassed the
original passive networks for reasons I mention below...


This would help establish if the differences you hear are due to the
system simply acting as a 'tone control' and have little or nothing to
do with using more than one power amp. I'd be interested to know what
you discovered...

The most significant changes are better bass, cleaner volume, and better
dynamics. The EQ is only on the bass channel, so, aside from removing
the passive crossovers, I don't see how there can be much 'tone control'
effect on the mid or top (unless the active crossover isn't as flat as
it's purported to be). I have to assume that the amps are as flat as one
can reasonably expect.

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.

2) The power amps may have different gains.

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

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

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. 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.

Adding the bass EQ made a huge difference over the interim bi-amped set
up (where the bass was on one amp, and the mid/top was on the other with
the passive xovers still in place). The EQ on the bass hasn't brought a
subtle change - it's order of magnitude stuff.

Less gross is the change in dynamics and volume, but I'm satisfied that
this has definitely improved - when I first replaced the 20W valve amp
with the Cyrus 2, there was a clear increase in volume and, to a lesser
extent, dynamics. However, I was a little disappointed that the quality
still dropped markedly when I played it up loud. I wasn't sure if this
was the amp running out of puff, or the speakers starting to distort
(50Wpc was the most power I'd used with these speakers). Adding the
second Cyrus and bringing the valve amp back into the set up has given
me available power of something like 120Wpc, with no indication of the
straining that I was previously hearing at higher volumes - aside from
that previously-mentioned tendency for the mid to be a bit shouty at
times.

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

So, with regard to an overall 'tone control' effect, the only real
changes I can think of are adding the active crossover and removing the
passive ones.

See above. :-)


My feeling is that the nett change due to this is likely to be rather
more subtle than obvious. Certainly, for now, my awareness/attention is
focussed on the much improved bass response, the cleaner sound at
volume, and the better dynamics. I feel that I'll have to live with
these changes for quite a while before I can get into the more subtle
stuff.

To be honest, I'm not particularly interested in trying to establish how
much difference there is between the system as it stands now, and how it
was with all-passive xover and the single Cyrus amp - it was better than
the valve amp on its own, but was still ultimately less satisfying than
it could/should have been.

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. 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.

[snip]

To my mind, the system as it stands is the baseline - for the
foreseeable future, I'm essentially committed to a tri-amped set up, and
the idea is to try and make it better without spending a fortune. While
I was initially less than conducive to using measurements, I would say
that I'm more willing to sing from that particular hymn sheet after
seeing driver free air resonance graphically displayed on the scope, and
having heard the improvement to the bass that came about from using the
SPL meter (compared to my MkI lug-'ole attempts). With this in mind,
I'll be taking a set of measurements of the overall frequency response,
such that the effect of subsequent changes can be analysed objectively.

One of the things I would recommend people do is to make some 'baseline'
measurements of the in-room response before they start any changes. [1]
This helps to assess any perceived effects and decide what may be the real
reasons for improvements. This in turn aids making decisions, allows the
user to focus on what is worthwhile, and to avoid waste of time or cash!
:-)

[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.

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:
In article , Wally
wrote:

Jim Lesurf wrote:




[snip] to the crescendo


To my mind, the system as it stands is the baseline - for the
foreseeable future, I'm essentially committed to a tri-amped set up, and
the idea is to try and make it better without spending a fortune. While
I was initially less than conducive to using measurements, I would say
that I'm more willing to sing from that particular hymn sheet after
seeing driver free air resonance graphically displayed on the scope, and
having heard the improvement to the bass that came about from using the
SPL meter (compared to my MkI lug-'ole attempts). With this in mind,
I'll be taking a set of measurements of the overall frequency response,
such that the effect of subsequent changes can be analysed objectively.


One of the things I would recommend people do is to make some 'baseline'
measurements of the in-room response before they start any changes. [1]
This helps to assess any perceived effects and decide what may be the real
reasons for improvements. This in turn aids making decisions, allows the
user to focus on what is worthwhile, and to avoid waste of time or cash!
:-)

[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.

Slainte,

Jim


Jim - or anyone. I did try this and got quite bizarre results - huge*
dips at certain frequencies I would not have expected, in fact the only
flat region was between 2kHz and 4 Kkz. That was using various frequency
steps (60) between 100Hz and 6KHz. For a quicker cruel test - say 10
steps - what would you regard as the key frequencies at which levels
should be equal?

Thanks

Rob

* well, the peak signal was 60dB (flat 1.7-3.9kHz) at the listening
place; min 20dB at 500Hz, 100Hz; and 35dB 5.4kHz and 4.5kHz

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

In article , Rob
wrote:
Jim Lesurf wrote:



One of the things I would recommend people do is to make some
'baseline' measurements of the in-room response before they start any
changes.

[snip]

Jim - or anyone. I did try this and got quite bizarre results - huge*
dips at certain frequencies I would not have expected, in fact the only
flat region was between 2kHz and 4 Kkz. That was using various frequency
steps (60) between 100Hz and 6KHz.

TBH the results you got are probably 'typical' rather than 'bizarre'. :-)

The problem is that the acoustics of most normal domestic rooms will
produce large variations in response as you change the frequency of
sustained tones. You will also find that moving the speakers, or listening
location, or other furniture, will alter the details!

This was why I was saying that any such tests are really for 'comparison'
purposes - a 'before' to compare with 'after'. Ideally keeping everything
*except* the changes of interest (e.g. use of active arrangement, etc) the
same. This means the room effects are the same 'before' and 'after' so you
can assess what you are interested in.

For a quicker cruel test - say 10 steps - what would you regard as the
key frequencies at which levels should be equal?

If you want to keep down the number of measurements then the best bet would
be something like 1/3rd octave bandlimited noise. This tends to average
over some of the room 'peaks and dips' and will give a broad-brush
impression for comparisons. This means you can cover 20Hz to 20kHz with
around 10 bands. If using sinewaves, I'd tend to recommend more than 10
frequencies unless you just want to focus on one range - e.g. just the bass
region.

FWIW I have an 'Alan Parsons' test CD which does have banded noise for
tests like these. IIRC they are 1/10th octave, but I can't find the CD at
the moment to check!

In most rooms the best thing is just to experiment a few times to see how
consistent you can get the results before moving on, and then use a set of
test signals that seem to give the most consistent results

Thanks

Rob

* well, the peak signal was 60dB (flat 1.7-3.9kHz) at the listening
place; min 20dB at 500Hz, 100Hz; and 35dB 5.4kHz and 4.5kHz

You have discovered one of the reasons we can take the responses in
magazines with some caution. :-)

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