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Thoughts on the use of large speaker arrays

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Thoughts on the use of large speaker arrays

Postby josq » Tue Dec 19, 2017 10:13 am

As some of you might know, occasionally I have been debating the use of large speaker arrays in Hauptwerk systems. In the most extreme cases more than 100 speakers are used, but 10-20 is more common.

There are some situations in which the use of large speaker arrays is perfectly valid. Some people are using Hauptwerk sample sets as sample libraries to build custom organs that can be optimized to their acoustic environments, e.g. church installations. In such cases, a large number of speakers is often a necessity.

However, many people use Hauptwerk to aim for a faithful reproduction of famous pipe organs in their home environment. I consider myself one of them. In this case, I have some serious doubts about large speaker arrays.

I assume most people here have a limited budget for audio of (maybe) 5000 euro's/dollars/pounds at most, probably less. Apart from a good sound card and a subwoofer, should one spend this money on a large number of not too expensive but reasonable speakers, or should one rather invest it in a single pair (or two pairs for surround) of very expensive high-quality monitors?

Buying all the equipment to make A-B comparisons is very expensive, so I think many people jump into the deep. I am attempting to assess the matter based on solid arguments before making significant investments somewhere in the future. Subjective experience might be impossible to translate from one situation to another, so therefore I am looking for objective observations. This is not an easy matter, therefory I remain open for new arguments. I do not feel qualified to give a final verdict.

My main argument against large speaker arrays is based on the observation that speaker positioning has a very, very large influence on frequency and phase response. Keep in mind that phase and especially frequency response should be as linear as possible for faithul reproduction.

Ideally, a stereo pair of near-field monitors should be placed at ear height, at about 1m distance, forming approximately an equal sided triangle with the listening position. Preferably, no objects should be placed in between, and tweeters should be directly pointed at the ears (for now, I exclude omnidirectional speakers from my analysis). If you compromise on speaker positioning, the influence of room acoustics (reflections from your walls and furniture) rapidly becomes dominant, destroying the frequency response of the speaker. Individual frequencies easily can be boosted or muted by 10db or more! The phase behaviour also quickly deteriorates. Often, excellent speakers give very poor results because people pay too little attention to positioning, or compromise because of visual esthetics.

Apart from positioning, room correction software and (if possible) hardware is very strongly recommended to get better frequency response.

When you keep adding more speakers, it will increasingly become harder to place them at or near the optimal positions (and to perform software-based room correction). At some point, every additional speaker pair will behave worse due to increasingly suboptimal positioning. You run the risk of decreasing the realism and quality of reproduction, rather than increasing it!

So why would someone use large speaker arrays? Some people have referred to an article written by Colin Pykett, http://www.pykett.org.uk/EndOfPipeOrgan.htm#Distortion. This article is worth to be carefully read and provides some powerful arguments for using large speaker arrays in electronic organs. I find this article truly enlightening, yet I think it deserves a critical approach.

The author focuses on two main causes for a lack of realism in electronic organs: intermodular distortion and electronic signal mixing. Here is my first criticism: as mentioned, I think suboptimal speaker positioning combined with the influence of room acoustics is actually the most important reason for lack of realism in many situations.

Intermodular distortion is well explained by mr Pykett. If multiple signals with different frequencies are sent through a single speaker, spurious signals with non-harmonic frequencies will be added due to non-linearities of the amplifier and speaker components. These spurious frequencies are sums and differences of (multiples of) the original frequencies. For example, a 4kHz and 5kHz signal might result in unwanted signals at (5-4)=1kHz, (5+4)=9kHz, (2*4-5)=3kHz, (2*5-4)=6kHz), etc.

Especially in organ music, we sent not just two, but many many more frequencies at the same time through the same speaker. So there will be many spurious frequencies all over the spectrum, forming a disturbing background noise that becomes worse as we play larger chords and use larger registrations.

How significant is this intermodular distortion (IMD) problem? According to mr Pykett, the situation is very bad. IMD specs are often not provided, but he thinks 1% distortion is typical for a reasonable speaker, and in appendix 2 he provides a calculation to show that the total power of unwanted IMD signals easily reaches a level of just 22 dB below the level of the original signal, if just two notes of a trumpet rank are played. This would certainly be audible.

What would be the solution? IMD does not occur if separate sources are used for each signal, and is therefore absent in real pipe organs. So what if we can route each sample to a different speaker? We would need many speakers, but the IMD problem would be eliminated. Mr Pykett suggests to use one speaker for each of the notes in a octave, so 12 speakers in total, or preferably 12 speakers per division. Because in Hauptwerk we aim to reproduce stereo samples, we would actually need 12 speaker pairs, or 24 speakers in total for a stereo sample set.

The 1% distortion figure was mr Pyketts estimation for a "reasonable" speaker. What if we use one pair of expensive, excellent speakers instead of an array of 24 "reasonable" speakers? On this forum, the Mackie HR824 (price around EUR 900 for a single unit) has been recommended for Hauptwerk. Specifications: http://mackie.com/sites/default/files/P ... MK2_SS.pdf. These specs give a figure of <0.035% for distortion, including (but not exclusively!) IMD. That's almost 30x better than Mr Pyketts 1%. According to the formula used by mr Pykett, the power of the distorted signal is a function of the square of the distortion percentage. So the Mackies will have almost 1000x (30 squared) lower IMD power (or much less!) than mr Pyketts "reasonable" speakers! This decreases the IMD level by a further 30 dB. In total, the IMD would be at least 50dB lower than the original signal for small chords. I don't think that would be very audible. For large chords, the situation could be somewhat worse, but still quite acceptable.

My preliminary conclusion is that it could be well worth to invest in expensive but excellent speakers to solve the IMD problem, instead of building a speaker array. Moreover, other aspects of speaker quality also would be improved.

What about my own set-up? I have M-Audio's DSM3 as front speakers, and BX8a as rears. I did some analyses using a measurement mic and the free software REW. I was able to detect several IMD frequencies. The individual IMD peaks were 50-60 dB lower than the original signal. I am therefore not worried about IMD in my audio set-up. I did however discover quite a number of other spurious frequencies (no harmonics or sum or difference frequencies). Although I am not sure, I think those result from wind noise in the individual organ pipes/samples. If I am right, undesirable IMD would be far less significant than desirable sampled wind noise in my set-up.

This leaves me to consider mr Pyketts second argument concerning the problems of electronic signal mixing. I don't think these problems are significant for us because per-pipe stereo sampling is used for Hauptwerk samples, but maybe I should try to analyze this issue in more detail later.

Meanwhile, I hope people find this analysis useful. Again, this long story is not meant as some final verdict, but hopefully it will be the start of a discussion which will generate deeper insights.
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Re: Thoughts on the use large speaker arrays

Postby mdyde » Tue Dec 19, 2017 10:53 am

Hello Josq,

Thanks for the excellent article. To add very briefly:

josq wrote:This leaves me to consider mr Pyketts second argument concerning the problems of electronic signal mixing. I don't think these problems are significant for us because per-pipe stereo sampling is used for Hauptwerk samples, but maybe I should try to analyze this issue in more detail later.


Dr. Pyckett's 'signal mixing' effect is essentially that sound sources routed through separate speakers (different points in the listening room) are each affected by the listening room's acoustics differently (due to the differences in speaker positions). By using multiple speakers effectively one is aiming to utilise the effects of the listening room's acoustics. For a dry sample set that's definitely a good thing (and Dr. Pyckett's article was written in the context of digital organs, all of which use dry samples), but for a wet sample set (which already has the real organ's room acoustics recorded into its samples, separately for each real pipe's point in space) interaction with the listening room acoustic will make the end result less true to the real organ and its acoustics. However, some people prefer it anyway, usually mainly because their listening environments aren't dry, and/or because their primary aims are immersive sound in general around their listening room, rather than strictly-accurate reproduction of the real organ in its real environment. High quality headphones, or a properly set-up pair of high-quality near-field monitors (as you described) in a dry/nearly-dry listening room, will give the most faithful reproduction of a real organ for wet samples (that were recorded without microphones having been moved).

There have been some fairly lengthy discussions of that over it all over the years, e.g. in these topics:

viewtopic.php?f=17&t=6498
viewtopic.php?f=17&t=7379
viewtopic.php?f=17&t=6927
Best regards,
Martin.

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Re: Thoughts on the use of large speaker arrays

Postby Romanos » Tue Dec 19, 2017 1:37 pm

FWIW, here's my setup:
https://www.amazon.com/clouddrive/share/bjFtSbkAVPncMlORQ7P5IwdT3MnUbWhmBbyt9P4povC/ta2RD69QQ9eLwkOEVh7GzQ?_encoding=UTF8&mgh=1&ref_=cd_ph_share_link_copy&v=grid

I've been of the persuasion lately that if I could have a do-over, I would get def-techs for a more spacious sound. I find, even triangulated out in my room which definitely helps, that studio monitors are very directional. This is a point of frustration for me personally. I've been toying with the idea of selling my monitors and going down to one good pair of bipolar speakers + sub (in front) for a while just to see how it goes.
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Re: Thoughts on the use of large speaker arrays

Postby 1961TC4ME » Tue Dec 19, 2017 1:57 pm

Romanos wrote:FWIW, here's my setup:
https://www.amazon.com/clouddrive/share/bjFtSbkAVPncMlORQ7P5IwdT3MnUbWhmBbyt9P4povC/ta2RD69QQ9eLwkOEVh7GzQ?_encoding=UTF8&mgh=1&ref_=cd_ph_share_link_copy&v=grid

I've been of the persuasion lately that if I could have a do-over, I would get def-techs for a more spacious sound. I find, even triangulated out in my room which definitely helps, that studio monitors are very directional. This is a point of frustration for me personally. I've been toying with the idea of selling my monitors and going down to one good pair of bipolar speakers + sub (in front) for a while just to see how it goes.


Romanos, you are set up very similar to me. I see in your picture that you too are a bit limited with space much like myself. Your front speakers being stacked and spaced like you have them is good, I'd try get them up off the floor even higher. The lowest driver in my left / right front stack arrangement is actually a bit above my head and the speakers go up from there, this will relieve some of the overly direct sound you are experiencing and likely add some additional space and realism to the sound. As Josq points out, placement and even a minor change in positioning can be everything, even going from the speakers laying on their side (as you have done) to standing them straight up can really change things. My speaker stacks are 3 per side, a pair of larger towers mainly for pedal with a pair each on each side of smaller bookshelf speakers (so 6 front channels total), stacked, they nearly reach the ceiling which is about 9' high. I don't know what your lower speakers with the yellow drivers are set up to do, but I would not have any speakers up front that low on the sides of the console, I'd also move the sub to somewhere else in the room if possible, preferably to a back corner, and of course you want some rear speakers if possible.

Next thing is tinker, tinker, tinker with rank routing. I've had much success and have made very dramatic differences with my like sounding rank routing scheme I've posted about in the past. The difference can literally be night and day taking a so so sounding instrument to and unbelievably good sounding instrument with some rank routing tweaks.

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Re: Thoughts on the use of large speaker arrays

Postby Romanos » Tue Dec 19, 2017 2:52 pm

Oh yes... I have tinkered. This is not my original setup (much improved and in second home). I am actually considering using my Christmas break to completely re-do everything. I'm going to move the sub to the right corner, place the towers next to the console and point the speakers out at the L/R walls and see how that sounds. That way I'll get a wider wall of sound coming back at me. The yellow speakers were the upper harmonics of my pedal division, however one of the two tweeters went out so they are currently silent with another smaller pair doing their job.
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Re: Thoughts on the use of large speaker arrays

Postby Romanos » Tue Dec 19, 2017 2:58 pm

Also Marc,
I'm sure I've read your posts once upon a time, but I can't remember the details now. As I'm about to set up the Rosales I'd be more than happy to re-read your discoveries if you can point me to the right thread.
Thanks! and Merry Christmas!
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Re: Thoughts on the use of large speaker arrays

Postby 1961TC4ME » Tue Dec 19, 2017 3:39 pm

I find (and agree) that IMD can be a result of multiple signals with different frequencies being sent through a single speaker, however I feel it is worsened and is even more so the culprit of IMD when sending multiple signals of different timbres through a single speaker. The pipe organ is a very unique animal of many different timbres, keeping these timbres separate from each other in the signal (i.e., not going through the same speaker) has been one of the big keys to sound improvement in my experimenting, speaker positioning being right there next in line.

It would be great to have a speaker for each rank or even each pipe, but as Josq points out, that's not possible for most if not the vast majority of us, hence in my honest opinion there's a need to do the best you can to separate these timbres from each other and put them together in their own groups. How many channels do you need in order to do this? I'm currently sitting at a total of 10 channels, out of those depending on my grouping and if it's a surround set or not, I'm using either 6 or 8 channels that I can physically route ranks to. Ideally I think somewhere in the neighborhood of 10 to 12 channel you can physically route ranks to would work out nice. These 10 to 12 channels are also all going to need to be arranged in a left / right tower arrangement on each side of the console, that's kind of asking for a lot, but I suppose can be done with the right sized speakers. I've envisioned single left / right front speaker cabinets containing up to 6 speakers per cabinet, speakers all on separate L / R channels.

What I look at is how many different families of sounding timbres do we have in a given organ? The size of the instrument will also play a factor in how many. We have different families of sound, flutes, reeds, mixtures and so on. I try very hard to keep these 'families' separate from each other and sounding on their own separate speakers. When you do it this way, yes, you're going to end up with some speakers that have more ranks routed to them and they wind up doing more work than other speakers, some speakers don't end up with much sent to them at all, but the key is the families are separate and for me along with speaker positioning has greatly reduced IMD and added considerable realism.

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Re: Thoughts on the use of large speaker arrays

Postby 1961TC4ME » Tue Dec 19, 2017 3:40 pm

Romanos wrote:Also Marc,
I'm sure I've read your posts once upon a time, but I can't remember the details now. As I'm about to set up the Rosales I'd be more than happy to re-read your discoveries if you can point me to the right thread.
Thanks! and Merry Christmas!


ahhhh...... let me do some digging! :lol:

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Re: Thoughts on the use of large speaker arrays

Postby 1961TC4ME » Tue Dec 19, 2017 3:57 pm

1961TC4ME wrote:
Romanos wrote:Also Marc,
I'm sure I've read your posts once upon a time, but I can't remember the details now. As I'm about to set up the Rosales I'd be more than happy to re-read your discoveries if you can point me to the right thread.
Thanks! and Merry Christmas!


ahhhh...... let me do some digging! :lol:

Marc


Here you go >>> viewtopic.php?f=17&t=14769

This thread is from quite some time back, Iv'e tinkered some from there but those that tried this had good results as did I, and I've stuck with the basic recipe ever since. Keep those speakers you're routing to stacked L / R on each side of the console.

I don't want (or mean) to take away anything or hi-jack this thread, but feel this info is relevant. Just keep in mind, try keep families of different timbre away from each other, but there are a few exceptions I've found that work ok. I've sent trompettes as an example to the same audio group as lower pitched flutes and get away with it. If your speakers are identical you could go 16', 8' to one pair, 4' and 2' to another pair, reeds to a pair, mixtures, 1', quints and so on to another pair. I find nazards are actually kind of flute sounding so will put them in with the flute ranks and so on. I send a mix-down of all to my subs. Listen to each rank separately to best determine which family you think they best fit in with, make a list of where you want to send them, go to the rank table and load em' up!

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Re: Thoughts on the use of large speaker arrays

Postby josq » Tue Dec 19, 2017 4:15 pm

Martin, many thanks for providing the interesting links (and saving me the effort to analyze dr. Pyketts second argument)!

Romanos, in addition to the comments you already received
* What about placing the monitors even closer to your listening position? I estimate that they are now at a distance of almost 2m, while 1m seems to be recommended (more direct unaltered sound, less undesired reflections, relatively)
* What about moving the monitors away from the corners of your room anyway?
* Are you using any kind of software/hardware room correction?

Marc... ;)
I find (and agree) that IMD can be a result of multiple signals with different frequencies being sent through a single speaker, however I feel it is worsened and is even more so the culprit of IMD when sending multiple signals of different timbres through a single speaker.

There are many effects going on in audio setups and they can't all be attributed to one or two phenomena. I would not expect IMD directly as a result from sending multiple timbres to the same speaker. For example, if you combine many stops, but play a single note only, I would expect very little or no IMD because nearly all the frequencies would belong to one harmonic series, and any distortion product would add to the harmonics already present. So for a single note played you may expect some harmonic distortion, which is not that much disturbing, but in principle no IMD. This is why dr. Pykett recommends to send every note of an octave to a different speaker. So all C's of all ranks would go to speaker 1, all C#s of all ranks to speaker 2, etc. This would be sufficient to eliminate a very significant part of IMD.

If you experience improvements by sending stops with different timbres to different speakers, something else may be going on. I speculate that perhaps the directionality of the sound is an important factor in your setup. Higher frequencies are more directional. So by combining the higher frequencies on one speaker pair, you would not mess up the directionality of the sound. Less critical would be how you assign the lower frequencies (i.e. the less bright stops). Could that be an explanation of the observations that you are making?
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Re: Thoughts on the use of large speaker arrays

Postby Eric Sagmuller » Tue Dec 19, 2017 9:31 pm

Hi Josq,

Just a few comments.

The Mackie HR824 distortion spec, you mention is just for the amplifiers. The drivers themselves produce much more distortion. I have yet to see a manufacturer list distortion of their speakers that were measured at the drivers. So Dr. Pykett's IM distortion spec. is probably not far off.

As far as signal mixing goes, I agree with Martin that it's a much greater concern with dry samples. But it goes far beyond the effect of the room. Just listen to Dr. Pykett's example of two similar diapasons, first mixed electronically and sent to both speakers, then have them sent to separate speakers. The electronic signal mixing effect is drastically detrimental, and the room has little effect on what we hear with this example. I think with wet samples this is mitigated to a great extent, but let me just say I believe there is still an effect.

I guess you could say I'm for large arrays. But how to implement them cost and space effectively, is another matter.

Eric
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Re: Thoughts on the use of large speaker arrays

Postby josq » Wed Dec 20, 2017 4:22 am

Eric Sagmuller wrote:Hi Josq,

Just a few comments.

The Mackie HR824 distortion spec, you mention is just for the amplifiers. The drivers themselves produce much more distortion. I have yet to see a manufacturer list distortion of their speakers that were measured at the drivers. So Dr. Pykett's IM distortion spec. is probably not far off.

Thanks! You seem to be right that not any distortion spec is given for the drivers, just for the amplifiers specifically... Yet, the very preliminary measurements that I performed at my own system seem to indicate that the problem is not very bad.

The electronic signal mixing effect is drastically detrimental, and the room has little effect on what we hear with this example. I think with wet samples this is mitigated to a great extent, but let me just say I believe there is still an effect.


Yes, I think there is still a very specific effect: the sweet spot. For all that I know, you either can optimize to get an almost exact reproduction of the original acoustics, but confined to a single location in the room; or to get convincing sound throughout your room, but not a reproduction of the original acoustics. The rest is compromise.
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Re: Thoughts on the use of large speaker arrays

Postby PhantomoftheOrgan » Wed Dec 20, 2017 9:43 am

Hello,

Your statement is one of the best I have seen on this forum:

"I think there is still a very specific effect: the sweet spot. For all that I know, you either can optimize to get an almost exact reproduction of the original acoustics, but confined to a single location in the room; or to get convincing sound throughout your room, but not a reproduction of the original acoustics. The rest is compromise."

This has been my struggle from almost the beginning of my virtual organ experience. If I move or rotate my head just a little while playing the stereo image collapses. Then I grab my head phones to solve that problem and the image is "inside my head" for lack of a better description. Also, when I have guests play the organ there is no way to get everyone inside the sweet spot.

There is also the problem that if all the reverberation comes from the front, realism suffers greatly. When I load a surround set, I hear some direct sound in the rear speakers, making is seem like an antiphonal division is playing.

There much research and development needed to enhance realism.

All that said, I am very thankful we have Hauptwerk available to get us to this close and I eagerly anticipate the future.
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Re: Thoughts on the use of large speaker arrays

Postby scottherbert » Wed Dec 20, 2017 3:48 pm

I've had in my head the idea of a line array. A vertical alignment of speaker drivers in a single case. What if each of those was driven separately?

~S
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Re: Thoughts on the use of large speaker arrays

Postby 1961TC4ME » Wed Dec 20, 2017 5:51 pm

scottherbert wrote:I've had in my head the idea of a line array. A vertical alignment of speaker drivers in a single case. What if each of those was driven separately?

~S


Exactly what I've been thinking!

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