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Beyond Stereo to multiple Speakers

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Beyond Stereo to multiple Speakers

Postby kwbmusic » Sun Sep 26, 2010 5:41 am

I currently have an audio setup consisting of two Behringer Truth B2031's and a Behringer B2092A sub-woofer.
I wish to explore increasing the number of speakers, which however would also require me to change my sound card. This raises an issue for me as the Behringer sub-woofer receives the main computer output and internally seperates the signal, low to itself, high back to the monitors. No problems for normal stereo.
Does this mean I can not use Hauptwerk to seperately direct the signals to my Behringer sub-woofer, because if I did I couldn't get the appropriate signal to the monitors? Which leads to my larger question, if I wish to have multiple speakers, controlled as directed within Hauptwerk, are the Behringers I have, not suitable?

Or am I being too complex and the simple solution is to disengage the monitors from the sub-woofer and drive them individually from the sound card?

Keith
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Re: Beyond Stereo to multiple Speakers

Postby David Pinnegar » Sun Sep 26, 2010 8:43 am

Hi!

I'm really wondering about the sanity of multiple speakers especially for small domestic practice room installations. The perceived need for multiple speakers flies in the face of audiophile practice and results obtained. One of the founding members of the EOCS, the late Percy Vickery, said that if he could get adequate enjoyment from recordings of the Albert Hall organ out of a pair of stereo speakers, then that was good enough for his home organ. On a small scale, where the instrument is required to reproduce rather than perform, I'm beginning to agree with him.

On my concert organ, wishing to add a Seize Pieds chorus to the pedals, I added an extra unit on an experimental basis by using a channel allocated to a stereo pair of another section of the organ. That section is now in mono rather than c-c# stereo. Blindfolded I don't think that anyone could tell the difference.

There's talk of intermodulation distortion through one speaker rather than two notes coming from two different speakers, but having experimented, the beat note of two notes is the same whether through a single speaker or the two notes from different speakers.

So perhaps the answer is to look at audiophile speakers and, for surround sound, to use one or two at the rear connected between the positive terminals of the front stereo pair, an old trick giving false space, on the basis that room reverberation tends to be out of phase. Furthermore, if one uses two speakers, connecting positives to the amp positives and connecting the negatives of the speakers together but not returning to the amp, the back pair will provide mono out of phase, and thus with an indeterminate spacial effect.

If you're building something on the scale of Clinton Knight's, however, as a performance instrument, that really is another matter.

If your desire for multi channel is simply a matter of disengaging the subwoofer, then using conventional speakers, running your normal speakers through 150-180uF capacitors as a high pass filter will seperate them off happily from the low frequencies and either the sub will have its own filter or you can run beefy speakers in parallel with your standard speakers through passive sub filters generally available on Ebay and quite sufficient.

Best wishes

David P
http://www.organmatters.co.uk
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Re: Beyond Stereo to multiple Speakers

Postby polikimre » Sun Sep 26, 2010 9:35 am

Back to the original question:

you can always route some higher pitched ranks (ones not requiring a sub) to a new pair of speakers, and send the lower ranks to you Behringers through the sub. Alternatively, you can plit the sub off the speakers and set up a channel for it, and send the bottom octaves of the lower ranks directly to it. In either case you'll have to do some voicing to match the sound of the different ranks in amplitude and brightness.
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Re: Beyond Stereo to multiple Speakers

Postby gingercat » Sun Sep 26, 2010 10:28 am

polikimre wrote:split the sub off the speakers and set up a channel for it, and send the bottom octaves of the lower ranks directly to it.

I wouldn't advise sending the bottom octaves solely to a sub as you will lose a whole load of higher frequencies that are still present in even the lowest notes.
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Re: Beyond Stereo to multiple Speakers

Postby David Pinnegar » Sun Sep 26, 2010 11:11 am

gingercat wrote:I wouldn't advise sending the bottom octaves solely to a sub as you will lose a whole load of higher frequencies that are still present in even the lowest notes.


Hi!

There's a lot of sense in that - it depends how seamlessly ones speakers are integrated spacially and as to whether the low frequencies can give the illusion of coming from the same source

Best wishes

David P
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Re: Beyond Stereo to multiple Speakers

Postby polikimre » Sun Sep 26, 2010 11:56 am

Sorry, that's what I meant, I probably wasn't too clear. So either send en entire rank to sub+speakers (preferably a 16ft rank), or just send the bottom portion of a rank.
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Re: Beyond Stereo to multiple Speakers

Postby toplayer2 » Sun Sep 26, 2010 4:02 pm

For wet sampled organs recorded with microphones in a fixed location a case can be made for using two high quality speakers as the result will be essentially the same as listening to a recording of the original organ through those speakers. This does nothing to mitigate IM distortion, but this will be masked to some extent by the music signal. IM distortion is not manifested as beats which are instead caused by tuning effects between two or more intervals. IM is the spurious generation of completely inharmonic signals which are very offensive to the ear. This is often most noticeable with minor and major thirds, but often other intervals as well. Dividing notes among multiple audio channels is effective for combatting IM distortions.

Dry sampled organs will exhibit "signal mixing" effect as described by Pykett. By routing signals with similar spectral distributions to mutliple audio channels one can effectively mitigate this effect. To the ear, signal mixing will cause the ensemble sound to become progressively harsher as more and more stops are layered.

A lot of low quality speakers will not produce a high quality sound. One pair of very accurate speakers may well out-perform a half dozen moderately accurate speakers.

When using Hauptwerk's routing algorithms it helps to use identical speaker models to avoid noticeable timbre shifts as notes move among the members of a group.

When routing bass pipes to dedicated channels, full range speakers must be used with the subwoofer(s) to reproduce the upper harmonics of the bass pipes. An advantage of segregating the bass notes in this fashion is that they are excluded from the other speakers which will mitigate yet another type of distortion first described by Paul Klipsch, "Doppler distortion".

The technique of connecting the positive poles from the two front channels to feed a rear speaker was first described by David Hafler (Dynaco) and became known as the "Hafler Effect". Use of this technique is rare due to its limited value and the advent of true surround sound.

Bottom line, IMO multi-channel audio (assuming consistently high quality) is indisputably superior for virual organ applications.

Joe Hardy
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Re: Beyond Stereo to multiple Speakers

Postby kwbmusic » Sun Sep 26, 2010 7:19 pm

Thank you all, what wonderful "meaty" responses to my query. I take on board David P's caution that for a small home user there may not be much apparent gain. I certainly have enough information though to continue to study and understand this topic as applicable to my circumstances, small room, home use only.
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Re: Beyond Stereo to multiple Speakers

Postby David Pinnegar » Sun Sep 26, 2010 8:55 pm

toplayer2 wrote:This does nothing to mitigate IM distortion, but this will be masked to some extent by the music signal. IM distortion is not manifested as beats which are instead caused by tuning effects between two or more intervals. IM is the spurious generation of completely inharmonic signals which are very offensive to the ear. This is often most noticeable with minor and major thirds,


Hi!

I'm not at all sure about this . . . the sounds that one hears on thirds are IM and are the beat frequencies between the two notes. The problem is that Equal Temperament :-) is so horrible :-) (I have written elsewhere about why musicians tuning to anything other than Meantone with 8 perfect thirds would have been burned at the stake . . . and perhaps IM might be the reason why many might agree :-) ) that the beat frequencies are so far removed from the proper root (fundamental) note of the harmonic chord to which they relate that they sound inharmonic.

The fact that I'm unable to tell the difference between thirds with the two notes through the speakers together or separately possibly says something about the speakers I favour and use . . . The other distortion, relating to bass notes, is as you say, Doppler distortion and this causes great muddiness in sound.

Audiophile speakers which overcome such problems need not be expensive but they need proper appreciation of the physics behind sound reproduction, from which many manufacturers have departed. One has to remember that modern manufacturers are appealing to technically uneducated people who are persuaded that oxygen free copper is preferable to a nice juicy thick run of mains cable, to the great profit of the techno-touts, as well as those making systems upon which one could run electric fires on the output of their amplifiers for a generation who, when bored, plug their speakers into the mains as electric fire hammer drills . . . :-)

Best wishes

David P

PS Dear Keith

I have just tried to PM you with some tips but your PM facility on this site appears to be disabled. If you contact me privately I will happily advise, as I have done Clinton Knight whose organ sounds, from what I read, rather exciting having followed in part the sort of philosophies I recommend. I read of his project and wrote to him as I could see the great effort to which he was going, and wanted to see him rewarded by a result which was outstanding rather than merely mediocre.

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David P
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Re: Beyond Stereo to multiple Speakers

Postby toplayer2 » Sun Sep 26, 2010 11:24 pm

David,

I believe that you are confusing beat frequencies with Intermodulation Distortion. The two are quite distinct phenomena. See:

http://en.m.wikipedia.org/wiki/Beat_(acoustics)

http://en.m.wikipedia.org/wiki/Intermodulation

Joe
Last edited by toplayer2 on Mon Sep 27, 2010 8:17 am, edited 1 time in total.
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Re: Beyond Stereo to multiple Speakers

Postby mdyde » Mon Sep 27, 2010 5:58 am

Hello Keith,

Like Joe, and for the same reasons (mainly significant differences in the way pipes' frequency components add and interact with the listening environment, a.k.a. Dr. Pyckett's 'signal mixing effect'), I too would strongly recommend multi-channel audio with the pipework distributed amongst as many (good quality, accurate, full-range) speakers as possible when using dry sample sets.

Intermodulation distortion should be very small with good-quality speakers (the speaker specifications should quantify it), but the 'signal mixing effect' is very significant indeed for dry sample sets.
Best regards,
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Re: Beyond Stereo to multiple Speakers

Postby David Pinnegar » Mon Sep 27, 2010 10:30 am



Dear Joe

Yes - I had confused the two and thanks for pointing this out. However, as is pointed out by the wiki article, IM is caused by non-linearities.

The reason why I don't hear a difference between the two tones together through the same speaker or separately through individual speakers is that it is possible to design non-linearities out of the reproductive system and my speakers avoid non-linearities.

Martin: if you don't believe it, come and hear them!

This is why I recommend Keith and others in a domestic environment to look at fundamental audiophile physics in choosing loudspeakers, whether for hifi systems or organs and I'm emailing him privately with some tips.

Best wishes

David P
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Re: Beyond Stereo to multiple Speakers

Postby mdyde » Mon Sep 27, 2010 11:22 am

Hello David,

Yes - I had confused the two and thanks for pointing this out. However, as is pointed out by the wiki article, IM is caused by non-linearities.


To clarify: IM isn't caused by non-linearities in the sound being played; it's the result of non-linearities in the reproduction system (speakers/amps).

The reason why I don't hear a difference between the two tones together through the same speaker or separately through individual speakers is that it is possible to design non-linearities out of the reproductive system and my speakers avoid non-linearities.


If your reproduction system is sufficiently linear that IM distortion is not audible then that's as it should be.

However, the primary reason for using multi-channel audio with dry sample sets, is not to reduce IM distortion (which should be small/inaudible with good speakers anyway), but to mitigate the very important, and very significant so-called 'signal mixing effect' :

http://www.pykett.org.uk/EndOfPipeOrgan.htm#Mixing

... along with allowing room reflections to make the pipework sound distributed through space, rather than all emanating from a single point source, since dry samples contain no spatial information.

The 'beats' effect is closely related (also being phase addition/cancellation).

There are lots of topics discussing it in the 'amplification' section of the forum (and multi-channel audio in general), these being a couple of the more lengthy recent ones:

http://forum.hauptwerk.com/viewtopic.php?f=17&t=6927
http://forum.hauptwerk.com/viewtopic.php?f=17&t=6498

Martin: if you don't believe it, come and hear them!


Thanks very much for the offer. Perhaps one day I'll take you up on that, but I work extremely long hours on Hauptwerk (and have done for most of the past nine years), so I'm afraid I'm not sure quite when it would be.

I've no reason to doubt that your speakers are great, if you say so. I just wanted to emphasize again why I believe multi-channel audio, as well as the use of accurate, full-range speakers are both highly desirable for realism when using dry sample sets.

Sorry I don't really have time to get drawn into another lengthy discussion on it (we need to have Hauptwerk v4 finished one day!), but it is important to me that Hauptwerk users get what I'd consider to be good advice. Hence I wanted to stress the main reasons for multi-channel audio.

This is why I recommend Keith and others in a domestic environment to look at fundamental audiophile physics in choosing loudspeakers, whether for hifi systems or organs


Absolutely - good quality, accurate, linear, full-range speakers are very important indeed too.
Best regards,
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Re: Beyond Stereo to multiple Speakers

Postby toplayer2 » Mon Sep 27, 2010 12:08 pm

David,

While higher quality speakers and electronics tend to exhibit less distortion, there is no such thing as a perfectly linear system. Non-linearities can be expressed in the frequency or time domains. All distortions are a byproduct of system non-linearities. IMD occurs in low and high level analog circuits (amplifiers) as well as electro-mechanical transducers (microphones, headphones, speakers). It is precipitated by the interactions of two or more frequencies sharing the same audio path. Some intervals may generate truly egregious distortion while others may produce so little as to escape notice. I invite you to read Pykett's discussion of IMD as it pertains to electronic organs:

http://www.pykett.org.uk/EndOfPipeOrgan.htm#Intermodulation

The key is to segregate the frequencies into totally separate audio paths so that there is no opportunity to interfere with one another. In other words, ceteris paribus, more speakers will reduce IMD leading to a more pure sound that is closer to the sound of pipes. The intervals that often are the worst offenders are the minor third, major third, fourth, diminished fifth, fifth, and to a lesser extent the remaining intervals up to a major seventh. An effective routing strategy is to divide the octave among four audio channels. This will isolate all of these intervals from one another.

IMD and other distortions exist in even "audiophile" grade components. We tend to "get used to it". Organs seem to be particularly unforgiving. Empirically, if one hears a very high quality multi-channel VPO in comparison with the same organ played through two channels, the improvement in clarity and freedom from listener's fatigue is striking.
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Re: Beyond Stereo to multiple Speakers

Postby David Pinnegar » Mon Sep 27, 2010 3:29 pm

toplayer2 wrote: IMD occurs in low and high level analog circuits (amplifiers) as well as electro-mechanical transducers (microphones, headphones, speakers). It is precipitated by the interactions of two or more frequencies sharing the same audio path. Some intervals may generate truly egregious distortion while others may produce so little as to escape notice. I invite you to read Pykett's discussion of IMD as it pertains to electronic organs:

http://www.pykett.org.uk/EndOfPipeOrgan.htm#Intermodulation


Hi!

I'm very aware of Dr Pykett's work and there is truth to it to more than an academic extent for "performance" instruments working at magnified volume where all subltle effects are magnified. The point of what I'm saying is that for domestic use, using high quality transducers which satisfy hi-fi low-cost freaks is quite good enough.

The reality is that at in the domestic environment the non linearities that lead to IMD are negligible and thus merely academic.

The real extraneous frequencies that _are_ audible on thirds in particular are not IMD introduced frequencies but the inharmonic beat frequency between the two notes. Equal temperament is the bane of musical life: a major third should be the 4th and the 5th harmonic. This means that one note will be 4 times a fundamental frequency and another note will be 5 times the frequency, the difference being the fundamental frequency itself.

But in equal temperament, the thirds are wider, sharp, further apart, so the difference between the frequencies, the beat frequency, is higher. It's audible when you're tuning a piano with your head close to the strings, and it's heard when you're near to organ pipes and speakers alike. It happens to be two octaves below the lower note of the third but because the interval isn't pure and the beat frequency is higher, the note is a quarter tone sharp. Foul. It's why certain organ voicers of whom I'm aware consider that anyone who wants a tuning system which does not include 8 perfect thirds in the scale should be burnt at the stake.

The relevance to Hauptwerk in the domestic environment is that many people want to play and practice the organ on a budget at home. Of course whilst multi-channel systems will produce very very good results, there are ways of using a simple stereo setup to achieve very high fidelity in a domestic environment at low cost. The proof of the pudding will be when one of the members of this list picks up from me a modified pair of vintage commercial units picked up off eBay at low cost and modified at similarly low cost. When we tried the modified sample unit next to some very exotic audiophile units my original reaction was to wonder why I was bothering personally with the exotic units - but the reality was simply of scale - the exotic units filled a large space as desired whilst the low cost units were top rate in a smaller environment.

If enjoyment of Hauptwerk is possible on a lower hardware budget, which I believe it to be, then personal funds are more available to go armchair organ travelling expanding one's repertoire of sample sets and associated repertoire.

Computer hardware necessary may well be tax deductable for those in the computer and software businesses, but many users of Hauptwerk and prospective users are students at one end and retired people on down-to-earth budgets at the other, for whom finding ways of experiencing maximum enjoyment at lowest cost are important. For such people in their living rooms, multi channel is not necessary and top rate results are available in other ways.

My modification of the units should be done by the weekend, so if he can pick them up in the meantime, in a week or two, there will be a forum member with direct experience in the next week or so.

Best wishes

David P
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