"Wally" wrote in message
k...
Jim Lesurf wrote:

The way I see it, the only thing measurements will tell me is whether
sound I like has an even response, or a bumpy one. :-)

It can also provide you with information which can be studied and
used to indicate which further steps might (or might not) lead to
further improvements, perhaps more marked than so far obtained.

It can also provide a basis for you and others to assess if some other
methods might yeald similar results with less fuss or expense, etc.

Hence appropriate measurements, correctly interpreted, can tell you
more than you assume. :-)

Okay. See thread on driver resonances in isobaric pairings. :-)

I'm not averse to measuring, as such. I'm just not terribly sure how to go
about it, and not hugely keen to spend piles of cash on it. For example, I
found a sound level meter in Maplin, but it's 70 quid - and only goes down
to 300Hz.

CPC does some that have a bigger range and at a good price.

http://cpc.farnell.com

Peter Scott

"Jim Lesurf" wrote

If we ignore all the above complications and assume two speakers, each
radiating *in phase* at the same level then the result at a listening
location equidistant from both is a *6dB* rise. Not 3dB.

I thought that was only if they were reproducing the same signal.

"In phase" may imply that - how can they be in phase if they are reproducing
different signals - but I think some people take "in phase" to simply mean
wired correctly.

Tim

A couple of things regarding crossovers...

1. Manufacturers and customers often confuse polarity and phase.
Phase is frequency dependent; polarity can be changed with a switch or
leads reversal.

2. The best way to set up your triamplified system with electronic
crossover would be to beg or borrow two items:

An electronic test setup, whether it be MLSSA, TEF, Smaart, et al.
This will allow you to watch the adjustment of your parameters in near
real time, visually see the true capabilities and limitations of the
enclosure/loudspeaker system and adjust your crossover accordingly.

Prior to testing, procure one of the Thiele Small loudspeaker enclosure
design packages that include the speaker parameters of the components
you own. This will quickly get you in "the right ballpark".

Good luck.

wrote in message
ups.com...
A couple of things regarding crossovers...

1. Manufacturers and customers often confuse polarity and phase.
Phase is frequency dependent; polarity can be changed with a switch or
leads reversal.

2. The best way to set up your triamplified system with electronic
crossover would be to beg or borrow two items:

An electronic test setup, whether it be MLSSA, TEF, Smaart, et al.
This will allow you to watch the adjustment of your parameters in near
real time, visually see the true capabilities and limitations of the
enclosure/loudspeaker system and adjust your crossover accordingly.

Prior to testing, procure one of the Thiele Small loudspeaker enclosure
design packages that include the speaker parameters of the components
you own. This will quickly get you in "the right ballpark".

Good luck.

Very useful advice. Thanks. My experience so far with
tri-amping is all good. I now have a system that is a lot
closer to what I want. Its just that the lights dim when I
switch it on! This is with using a car sub and some not
particularly high-spec tweeters. It is strange to hear the
effect of increasing, for example, the high treble. The
whole band moves up rather than an increase in slope
as you used to get with simple tone controls.

Now I've got to do the difficult bit and decide on the sub.

Peter Scott

In article , Tim Martin
wrote:

"Jim Lesurf" wrote

If we ignore all the above complications and assume two speakers, each
radiating *in phase* at the same level then the result at a listening
location equidistant from both is a *6dB* rise. Not 3dB.

I thought that was only if they were reproducing the same signal.

The context of the discussion from which the above quote is snipped was
that the two speakers were being driven from the same source (signal)
albiet with a crossover that may affect the amplitude/phase relationship.
The "ignore all the above" indicated that the crossover, etc, didn't change
the phase relationship so the two units were being driven with the same
signal in time alignment.

Slainte,

Jim

--
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Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

wrote in message
ups.com...
A couple of things regarding crossovers...

1. Manufacturers and customers often confuse polarity and phase.
Phase is frequency dependent; polarity can be changed with a switch or
leads reversal.

2. The best way to set up your triamplified system with electronic
crossover would be to beg or borrow two items:

An electronic test setup, whether it be MLSSA, TEF, Smaart, et al.
This will allow you to watch the adjustment of your parameters in near
real time, visually see the true capabilities and limitations of the
enclosure/loudspeaker system and adjust your crossover accordingly.

Prior to testing, procure one of the Thiele Small loudspeaker enclosure
design packages that include the speaker parameters of the components
you own. This will quickly get you in "the right ballpark".

Good luck.

Please excuse if this is a repeat. I cannot see the message I
posted but everyone else could. This has happened before.

Very useful advice. Thanks. My experience so far with
tri-amping is all good. I now have a system that is a lot
closer to what I want. Its just that the lights dim when I
switch it on! This is with using a car sub and some not
particularly high-spec tweeters. It is strange to hear the
effect of increasing, for example, the high treble. The
whole band moves up rather than an increase in slope
as you used to get with simple tone controls.

Now I've got to do the difficult bit and decide on the sub.

Peter Scott

In polarity with a DC signal with the speaker occupying the same space,
the 6 dB differential is absolutely correct. With a complex phase
signal, which many commerically available loudspeakers being
non-coherent at best and which differ slightly between even sequential
serial numbers, the issue thus becomes significantly more complex.

This can be demonstrated with two stacked identical loudspeakers fed
identical, but with a relative polarity reversed, signal. This was one
of Don Davis's favorite tricks in his Syn-Aud-Con training sessions.

One of the easiest ways a non-technical person can evaluate a speaker
for obvious phase anomalies is to playback a full bandwidth swept
sinewave at a relatively low level. These are available on dozens of
commercial test CDs. If you hear "birdies", you have a phase problem
at that particular reproduction frequency. A birdie is immediately
obvious, sounding something akin to a Looney Tunes cartoon sound
effect. BEE-OOO-WOOP.

To the best of my experience (I've tested many), only some of the
planar electrostatic and plasma speakers have truly decent full
bandwidth phase responses over the majority of their bandwidth while
not exhibiting compensatory frequency anomalies. A few (a handful)
dynamic speakers from truly capable designers are also on the market.

This is where digital filtering (once it is fully understood) will
eventually take over the commercial signal processing market- the
theory being eventually we will be able to alter frequency without
requisite phase anomalies as happens in the analog world.

To listen to a high quality reproduction system with excellent phase
response is a truly great experience. It does transport you to a
different world, not unlike viewing a real painting masterpiece. A
picture in the book can only bring back memories of the original at
best.

That being said, the major thrust in the commercial market today is not
reproduction (including phase) accuracy- note how many commentators
marvel at higher bandwidth iPod iterations while exclaiming the virtues
of its near perfect performance. One wonders just how many Stax
headphones are actually connected to iPods in this world.

I'm sure we'll have to wait this trend out. Ten years ago 44.1 kHz
sampling on a CD was not good enough and we eventually ended up with
competing DVD Audio and SACD audio products. How an iPod sampling
(generally sourced a 44.1 CD and then heavily compressed) at 128kbps or
even 320k reaches perfection pushes the world of the illogic back to
flogiston theory. Mind you the DVD Audio bit rate is 9.6 MEGAbits per
second.

One of these days I hope I'll read a review of an iPod's technical
performance using high end test equipment. It would be great to see
bandwidth, polarity, phase, THD+Noise, S/N ratio, etc.

Yet I digress...

Arny Krueger wrote:

We seem to have mo-better alternatives in low-cost SPL meters in the
states.
...
Here's almost exactly what I use, UK sourced:

http://www.cornwallelectronics.co.uk/? ...

Thanks for the links, Arny. Just found a local supplier of the digital
version of this one (the peak hold feature looks useful), so I'll be off out
soon to get it.


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

Peter Scott wrote:

CPC does some that have a bigger range and at a good price.

http://cpc.farnell.com

See reply to Arny - the Tandy/RadioShack ones seems to get a lot of good
opinion for measuring SPL on a budget, so I'll be getting one of the 40 quid
digital display jobbies.


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