Allen Renaissance audio board question

[mlaird]

I'm interested in building my own speakers for my Allen organ in order to get the same sound out of a smaller package. In order to do that, I expect that I will have to sacrifice some bass response in order to keep the speakers small. To compensate for that, I would turn up the bass gain on my R-230's audio board. In order to do this in the best way possible, it would be ideal to know exactly where Allen's bass tone control starts and how many dB per octave it can boost the bass before hitting the limits.

Does anyone here know at what frequency Allen's bass control kicks in on a Renaissance organ? How many dB of gain do I have to play with?

[mlaird]

If no one knows this information already, does anyone have some suggestions on how I could do some tests and determine the cutoff frequencies and slope of the filters?

[Admin]

Sorry, I don't know the answer, but I would think that in this generation, balancing would be done on a stop by stop basis through the voicing controls. Earlier Allens, i.e. MOS models, had tone controls on the DAC board, but these were the only form of voicing available.

[mlaird]

Sorry, I don't know the answer, but I would think that in this generation, balancing would be done on a stop by stop basis through the voicing controls. Earlier Allens, i.e. MOS models, had tone controls on the DAC board, but these were the only form of voicing available.

You're certainly right that note-by-note and stop-by-stop voicing is available on my R-230, but there are also broader treble and bass controls on a per-channel basis. I'm thinking that I can use the bass control to compensate for the bass rolloff common in smaller bookshelf-sized speakers. But to make this work well, it will help to know at what frequency the bass boost kicks in, and how much range it has at various frequencies.

[John Vanderlee]

You say 'the same sound in a smaller package'. This goes beyond tone controls. Remember a speaker is basically an air pump. Bass requires large volumes of air to be moved. Unless you can be happy with the boomy thumps that pass for bass in some modern music these days you're not going to find it in bookshelf speakers. One solution might be to channel your pedal notes through a powered subwoofer which can be hidden out of sight.

[mlaird]

You say 'the same sound in a smaller package'. This goes beyond tone controls. Remember a speaker is basically an air pump. Bass requires large volumes of air to be moved. Unless you can be happy with the boomy thumps that pass for bass in some modern music these days you're not going to find it in bookshelf speakers. One solution might be to channel your pedal notes through a powered subwoofer which can be hidden out of sight.

Allen speakers have to be designed to fill a large church with sound, but my living room is somewhat less demanding :-). I am confident that for 16' stops and higher, I can get enough low bass out of smaller cabinets, as long as I boost the bass electronically before running it through the amps and speakers. I can sacrifice efficiency for reduced speaker size. For 32' stops, I will certainly need larger cabinets, but I'm sure I can find a way to do the job with something smaller than an Allen B-20.

Rest assured that I have no interest in boomy one-note "bass" as found in pop music!

[Admin]

I'm thinking that I can use the bass control to compensate for the bass rolloff common in smaller bookshelf-sized speakers. But to make this work well, it will help to know at what frequency the bass boost kicks in, and how much range it has at various frequencies.

I'm thinking that the fallacy in your plan is that the tone controls were intended to compensate for the variations in room acoustics using the full range Allen speakers-- not to compensate for lack of low end inherent in smaller speakers.

[John Vanderlee]

It's a matter of physics.... and not just the speakers, bass has along wavelengths that need room to develop. If it's a small room you may never hear it.

[mlaird]

I'm thinking that the fallacy in your plan is that the tone controls were intended to compensate for the variations in room acoustics using the full range Allen speakers-- not to compensate for lack of low end inherent in smaller speakers.

I'm sure the tone controls were created for that purpose, but a low-pass audio filter doesn't care why I want to use it :-). It only matters what frequencies it affects and by how many dB per octave the control affects the output.

[Admin]

Well, yes, that's my point. Because the Allen speakers are full range, the tone controls may not be suitable in terms of their cutoff frequencies and slope for your purpose of compensating for a bookshelf. As I suggested in my initial response, using the voicing controls is the most flexible and precise way of attempting to accomplish your goal. More work is involved, but the results will be better.

[mlaird]

It's a matter of physics.... and not just the speakers, bass has along wavelengths that need room to develop. If it's a small room you may never hear it.

I had heard that truism for years, but after thinking through the physics and analyzing it, it really isn't true. For a proof by reductio ad absurdum, consider listening to music with earbuds. The "room" between your eardrum and the speaker is only about an inch long. If sound waves are limited by the size of the room they're in, then the sound waves in your ear canal would have to be limited to 1" in wavelength, which would limit you to something around 13 KHz and higher. Obviously, that's not true, so sound waves can "develop" and sound normal even in small spaces. If you again reduce the problem to something really small for the sake of example, you will just need to pressurize and depressurize the room at whatever frequency you want if the wavelength is significantly longer than the size of the room. Flipping the problem around, low C on a 32' stop is 16 Hz, with a wavelength of just over 64 feet. Almost no one has a living room that size, yet many people can have 32' tone in their homes. I'm confident that I can play 32' stops in my living room. I just need a speaker that can produce enough SPL at that frequency, and an amp that can drive it with sufficient power to produce the SPL I want.

Back to my original question, I'm really interested in the small speakers for the manual stops, which only go down to around 32 Hz. That's still pretty low as speakers are concerned, but as many speaker designers have noted, the "iron triangle" is low bass, efficiency, and cabinet size ("Hoffman's law"). I want low bass and small cabinet size, so I know that I will have to sacrifice efficiency. Since my living room is quite small compared to a typical Allen organ venue, I'm confident this will not be an insurmountable problem. With their efficient speakers, Allen's amps will probably be idling even at deafening volumes in my living room.

[John Vanderlee]

" For a proof by reductio ad absurdum, consider listening to music with earbuds. The "room" between your eardrum and the speaker is only about an inch long. If sound waves are limited by the size of the room they're in, then the sound waves in your ear canal would have to be limited to 1" in wavelength"
.... And the difference here is that bud seals the air chamber between it and the eardrum so it's almost like being physically coupled to the earbud diaphragm which can certain move at 16 Hz driving the eardrum with it. Quite different from listening in a open space. As a matter of fact, when I play organ recordings on my sound system in the living room, I don't hear/feel the lows until I am elsewhere in the house like 25 or so feet away. Likewise in our auditorium where we have an LL324 the nodes are noticeable in their intensity variations, depending on where you stand.

[jbird604]

The R-230 has the 16' stops all in the same channel, so your best bet would be to use a powered sub on that channel along with a smaller primary speaker. Renaissance technology needs basically "flat" speaker response, the same as fine audiophile speakers, so they are less dependent on the specific characteristics of Allen cabinets, as was the case with ADC and MDS models. I certainly can't tell you what the characteristics are of the tone controls, and such info is probably not even available from Allen in published literature. You could only determine that by trial and error. But just turning over the bass to a dedicated powered sub of good quality would certainly allow you to use much smaller primary speakers. The other channel in the R-230 probably carries little or no bass, since the console system for that channel has only an ordinary 8" speaker and a tweeter. It's only the channel that carries the 16 footers that you have to be concerned about.

[John Vanderlee]

What I said....

[mlaird]

The R-230 has the 16' stops all in the same channel, so your best bet would be to use a powered sub on that channel along with a smaller primary speaker.

My R-230 is actually running with two HR-100s plus a non-Allen subwoofer to fill in the 16' bottom end that the HR-100s can't handle. I'm trying to think ahead to the "someday" when I get a larger instrument, preferably an Allen, which has much more than just one channel containing 16' stops. If I find something like the R-350 at my church, I'd need 8 speakers, and even HR-100s would seem large at that point. I also wouldn't want to need multiple subs for each of the channels with 16' stops. I really only want one sub for the 32' stops.

[mlaird]

I did some experiments, and found that Allen's bass controls on the audio board affect much higher bass frequencies than I was expecting. It's really tricky to tell for sure exactly where the cutoffs are, since I can only play back pipe sounds that have multiple frequencies in them, not pure sine waves. But the best I can estimate, it looks like the bass controls apply in earnest around 250 Hz and below, and seem to level off somewhere around 60 Hz. It seems like they may be using a bass shelf filter, and if you're down in the bottom octave of a 16' stop, it looks like it's about 1 dB per unit change in the bass setting.

This is going to complicate my homebuilt speaker ideas, since the sloped part of the filter extends up so high. If I crank up the bass gain, I'll be boosting the mid-bass between 60-250 Hz, the region where bookshelf speakers can probably play just fine, and I won't be able to boost just the frequencies below 60-80 Hz where I expect small speakers to start rolling off. Also, the rolloff in the speaker response is probably going to be much faster per octave than Allen's bass boost filter can compensate for. I'm going to have to do some more research to see if I can build speakers that will do the job themselves and be mostly flat down to 32 Hz, or if I can do some sort of EQ to make them that way. Alternatively, if I can make a speaker that slowly rolls off starting up high around 200 Hz, then Allen's bass control could be used to compensate for that rolloff, as long as it's slow enough.

[jbird604]

Or invest in several multi-band graphical EQ units and put one in each audio line AFTER they come out of the cage. If EQ-ing a small organ like the R-230, you only need a single stereo EQ unit, which might be found for $100. Larger organs will of course require more units, but still might be a cheaper route than buying or building exotic speaker systems.