subwoofers inside pipe chamber

[dave3]

Does anyone have experience with the performance of subwoofers placed inside pipe chambers? Our new Allen sounds great except I don't hear much benefit from the subs.

Our Great chamber is good size, on the order of 18' x 12' or more with a concrete floor and walls, and shutters still in place positioned all the way open. In the Great we have (4) Allen main cabs and (2) SR-5 subs, with the subs wired to the bass audio channel. Pipes are removed and the speakers are all sitting on the chests more or less centered in the chamber. Running a signal generator into the console's EAC audio in, I get good response down to 50 Hz, then going down it falls off until I hear absolutely nothing at 31.5 Hz. The subs are moving, but the air apparently isn't. Playing the organ gives similar results. The bottom half octave of the 16' Bourdon is less than I expected, though it sounds good with a nice pair of headphones.

There's a lot more troubleshooting that can be done, like moving the subs to a back corner of the chamber, or moving them outside the chamber (not sure where...), but I was wondering if anyone else has experience with this issue.

[David Anderson]

All I can add is that I know of a church with a pipe organ that added synthesized pedal tones, and it took a good deal of tweaking to get them to sound right--with the aid of a professional audio consultant. In particular, if you have two subs, you have to be very careful about whether or not they are interfering with one another. Even if they are electronically in-phase, their spacing from one another can make them behave as if they are out-of-phase in certain situations.

[prm]

Dave3, p.m. me, I can help with this. The SR-5's should be able to "shake the house down!"

[arie v]

Hi,

The SR-5 Allen woofer should be able to get you down to 30 Hz no problem. My guess is that the cross-over level and or the volume at the amp. is set too low. Placement of speaker can be a problem as well. Putting them in a corner, or against a back wall would help. Has the organ been properly voiced?

Sounds like a solvable problem.

AV

[Guest]

The SR-5's should be able to "shake the house down!"

...not in the pipe chamber though. The pipe chamber rather decreases SW potential acting as Helmholz resonator, think motorcycle exhaust.

[dave3]

That's what I was afraid of...that a subwoofer inside a pipe chamber might not work well. The organ has had an initial voicing, but I wanted to hold off on the next round until any speaker placement issues were resolved. I have absolutely no doubt that the SR-5 can perform well, just wanted to first confirm whether anyone has had good success with a subwoofer inside a pipe chamber. Everything I have been able to find on this subject only references placement in corners of the room and such, which is not really the same as a chamber with a finite size opening.

[crapwonk]

If the sound could get out of the chamber when produced by pipes, it can get out when produced by a speaker. I vote for a combination of proper voicing and placing the sub-woofer(s) against a wall for maximum reinforcement. Also, phase cancellation only happens when the frequencies are just right for the actual placement of the speakers and the listener and will not knock out all of the bass.

[jdoc]

Does anyone have experience with the performance of subwoofers placed inside pipe chambers? Our new Allen sounds great except I don't hear much benefit from the subs.

Our Great chamber is good size, on the order of 18' x 12' or more with a concrete floor and walls, and shutters still in place positioned all the way open. In the Great we have (4) Allen main cabs and (2) SR-5 subs, with the subs wired to the bass audio channel. Pipes are removed and the speakers are all sitting on the chests more or less centered in the chamber. Running a signal generator into the console's EAC audio in, I get good response down to 50 Hz, then going down it falls off until I hear absolutely nothing at 31.5 Hz. The subs are moving, but the air apparently isn't. Playing the organ gives similar results. The bottom half octave of the 16' Bourdon is less than I expected, though it sounds good with a nice pair of headphones.

There's a lot more troubleshooting that can be done, like moving the subs to a back corner of the chamber, or moving them outside the chamber (not sure where...), but I was wondering if anyone else has experience with this issue.

or the front of the chamber.........? It is like a Leslie in a living room, a few inches can make all the difference, phase cancellation and standing waves etc.

[michaelhoddy]

I'm sure the others are covering it well, if the subwoofers are spaced, they are canceling at some frequencies and coupling at others, and this actually will have a profound effect if both are reproducing the same signal, and the spacing is less than the wavelength of the lowest fundamental. It would be better to cluster the subs right next to each other so they at least present as a single point source without cancellation, but with the benefits of the doubled cone and port surface area. This is one of the most misunderstood concepts in electronic organ tone production when it comes to speaker placement.

And the dimensions of the chamber have an incredible impact on what frequencies are being reinforced and cancelled, as any room dimension whose measurement is the same as a fundamental wavelength within the audible range and its harmonics interact significantly with acoustical response. Multiples of a dimension or its corresponding harmonic fractions compound this effect

Your chamber dimensions of 12' and 18' are definitely causing issues in that bottom octave of the 16' register.

When I was designing recording studio control rooms briefly, I used this handy little tool to at least get a sense of how the room dimensions were impacting response. It would be useful for you in determining the effects of the chamber.

http://realtraps.com/modecalc.htm

[davidecasteel]

Using the formula provided in that link, a room 12 x 18 x 8 feet will have first resonances of 47, 32, and 70 Hz. That, of course supposes that the space is fully enclosed. An organ chamber would typically have one end open and that would affect at least one of the resonances. Would putting sound absorbent material on the shorter dimensions allow the 32 Hz resonance to dominate?

flashguy

[Guest]

Iirc 30hz is about 38 feet wave lenght. It will badly interfere with other cabs freq. in the chamber and standing waves will persist. I would instead give the subs a most distant, lowest floor level in the hall, grouped and with enough power.

Boyan

[geoelectro]

I don't service pipe organs normally but I was servicing a combination pipe/electronic Rodgers organ that had a P-1 pedal cabinet in the pipe room. This cabinet has the 30" EV woofer. Normally, that speaker would be set on its side and aimed against the back wall or similar. In this case, the installers put legs on it so it could be aimed straight down. It was about a foot off the concrete. What was funny/interesting was they had to put two fifty pound sacks of concrete on top of the cabinet to keep it from walking around the chamber when playing pedals. :)

Geo

[prm]

We put SR-5's in organ chambers all the time and they work incredibly well if they're placed correctly. Aim them toward a corner and have them as close together as possible or one on top of the other. We've had better results with placing the next to each other. If there's a phase cancellation, your voicer will find it right away and it's an easy fix.

[indianajo]

I'd measure the voltage on the speaker at maximum volume with an analog VOM on AC scale, or a scope. You could have a connection problem at these high currents, or with used Allen gear (since you are working on it yourself, the dealer is not doing it) the amp could be weak. I fooled with an Allen 255 two weeks ago that had obvious amp volume issues, which I left alone because it has been sold off.
If the amp and wiring is putting out rated wattage (P=(V^2)/R where R is speaker impedance) then you can worry about placement.

[jbird604]

I'll add my vote for putting the SR-5's in the floor and in a rear corner of the chamber, side by side or stacked. No hard and fast rule about which way the driven cone faces, though facing it into the corner might work best. (Give it a little breathing room though.)

If the organ chamber is also in a corner of the room and near the intersection of wall and ceiling (as opposed to being halfway up a wall or hanging from the ceiling somewhere), there should be no difference in response from the speaker whether it's inside the chamber or outside the chamber in the sanctuary floor. As a last resort though, you might have to bring them down to the floor, though it's often hard to find a good place to set a sub where it won't look bad or be in danger of getting damaged.

The current placement you describe -- sitting up on the old pipe chests -- is definitely a problem. With no room boundaries to reinforce the bass, there's no way these speakers can create believable bass. Even the heftiest woofer can't make bass down in the 32' pedal range without some help from the room boundaries. Get them down off the chests and put them up next to some kind of solid wall and you will be amazed at the difference that will make.

Also, be sure the voicer does NOT just keep bumping up the levels of individual notes ad infinitum, trying to compensate. I remember very well a situation where the voicer kept trying to get just a little more oomph out of the lowest pedal notes, and we eventually discovered that his efforts actually DECREASED the output level on those notes by overdriving the amp. When I hooked up the computer and started LOWERING the generated levels of the notes, the output level increased dramatically!