Organ chamber

Hi All,
I am considering a radical change to the speaker system at Zion and I would like to have comments from the forum.

As it sits now the speakers speak directly into the worship space and are either mounted on the wall in the form of Conn 'Pipe Speakers' and a pair of Behringer studio monitors.:

or mounted on baffle boards in this room which I will call the 'Organ Chamber'

The primary reason for this arrangement is the implementaion of the "infinite baffle" concept, whereby the 18 inch full range woofers for the lowest Pedal ranks have approx. 1400 cubic feet of "baffle" and are easily reaching a 20Hz low frequency cut off.
However, because the acoustics in the worship space are relatively dry - due to ample carpeting and pourous ship-lap cedar siding - and the desirable samples used are also dry, the sound is relatively dry - especially in the choir loft.

So, my idea is to open up the baffle and place the majority of the speaker sets into cabinets or enclosures; and place them in the Organ chamber, on their backs - speaking upward. In theory, this would be treating the speakers just as real pipes, letting the sounds mingle and mix and reverberate in the chamber a bit before the sound escapes into the worship space through through the grilll work.

I can't help but wonder if the architects prepared this room for a modest pipe organ that never was to be. A little info upon which to form this theory:

The room is about 7-1/2 feet by 15 feet with a ceiling that slants upward towards the worship space.
The ceiling is 8 feet at the rear and 12 feet at the front.
The opening (grill work) is about 3-1/2 feet high by 12 feet wide.
The walls and ceiling are HARD plaster more than 1 inch thick.

The disadvantage of this arrangement is that I would loose the semi-sealed nature of the room and thereby lose the "infinite baffle" concept which is currently giving me such great low bass response.

An alternative would be to build some sort of subwoofers. Bear in mind the worship space is 85 feet by 45 feet with a 36 foot ceiling. I estimate the total space to be about 800,000 cubic feet. And I need the subwoofers to put out up to 80dB for a single pipe sample - measured from within the worship space.

I have been studying the Tapped Horn subwoofer design made famous by Danley Sound Labs http://www.danleysoundlabs.com/tapped_h ... L=DTS%2020 and I am thinking of implementing four of these, although at $3000 a piece I would probably build my own for much less money based on designs by William Cowen see: http://www.cowanaudio.com/th.html

The largest he has built is relatively flat from 18 to 100Hz


The first question: is the opening of the organ chamber (4X15 ft) large enough to support filling a 80,000 cubic ft space with sound?

Any other comments would be welcome.

Could this be the same speaker box I built in 1964 from an article in Popular Electronics? The woofer at floor level and a folded pipe of equal cross section to the speaker cone that discharges in front of the speaker. Length of tube is 1/4 wavelength. (1145/4*f feet)Tube packed with padding to block higher frequencies.

Said enclosure was touted as only design to dampen the cone resonance peak and create peaks to the response curve both above and below the cone free resonance. Direct and 180 degree inverted sound mixed in front of the speaker.

Also remember the proximity effect - that is, two bass speakers closely placed enhance bass output 2-4 times the sound level when spaced apart.

FYI, I'm also running two 18" woofs mounted as infinite baffle in my ceiing with Fres = 16 Hz. If you can get a solid bass sound in the room, why take that away. Just add some localized woofers.

Sounds like a transmission line, Jon. I built several of these a number of years ago for my stereo. They really do offer very low and clean bass.

Seeing the huge dimensions of the Zion church and very little reverberation, I think is the saddest part of the situation. With such a large area there could be many seconds of reverb! But unfortunately the wall to wall carpet syndrome is in control in most modern churches.

Seeing the huge dimensions of the Zion church and very little reverberation, I think is the saddest part of the situation.

So true, and the biggest challenge. I think a lot of it is the unsealed cedar siding. It seems to suck up more sound than it reflects.

As for the speaker, yes it is a folded pipe or horn. There is a white paper available here: http://www.danleysoundlabs.com/pdf/danley_tapped.pdf
There's nothing new to the concept, although Danley has applied for a patent pertaining to the specific way he folds the horn and places the driver I suppose.

The horn can be folded once or twice, but the the total length of the transmission line for our purposes would need to be about 18ft. So a single fold tapped horn would stand over 9 ft tall and be about 15" sq.

I would match these with my existing (4) full-range 15" Cletron woofers (which are flat up to about 4000 Hz) in separate cabinets and set an active XO at as close to 64Hz as I could. It would require two 2-channel amps @ 600watts / channel / 4 ohms - and two 2-channel amps @ 230watts / channel / 4 ohms. But would only eat up 4 total channels of available HW channels.

All that would be sent to this speaker set would be Pedal 32' and 16' ranks, and the first octave of manual division 16' ranks. That works out to 7 or so ranks into 4 channels, which is under my 2-ranks-per-channel-maximum rule. Taking into account Pedal is often only single notes played at a time this should be very good and I should experience little to none intermodulation distortion.

Here is a great photo of the interior of a DIY single fold tapped horn:


And here is the more complex multi-fold, multi-chamber design by Tom Danley - per his patent papers:

At least there might be a chance of sealing the cedar, but to take away the carpeting would be a whole nother matter.

Yes a horn type speaker would probably be the way to go. A transmission line speaker is a completely different beast as the line stays the same cross section the whole distance. The output of the line only enhances the output as Jon mentioned. While a horn actually aids greatly in coupling the speaker to the air making it much more efficient.

Nice pictures Bob. The complex horn would be a challenge to build. But I love building speakers so think it would be fun.

When I worked as an Allen rep, they always recommended reflected sound when possible, They often suggested speakers facing the back of a chamber and reflecting back out into the church. So I think your idea of moving everything into the chamber is probably good.
John

Well, now I'm confused seeing the tapered waveguide. Anyway, an efficient horn has an expotential shape and a sharp frequency cutoff. This looks like controlling the air mixing for resonance damping.

FYI - for guys building speakers, there's a terrific store/warehouse about 50 miles from here. Try www.parts-express.com I went in one day to buy two crossovers, they said thay had 458 in stock. I made a 5" diameter dust cap out of balsa, then found out they sold dust caps - in stock. I picked up eight of 8" woofers for half of my 16 channels. Pyle Pro PPA8 with 40oz magnets. Highly recommended mail order source.

Hi!

I don't think I'd want my sound shut up there in that box-room - better to use that as the infinite baffle for some beefy 18inch units for the bass or a battery of en chamade sounds.

Those Conn pipes are really useful for hiding what you might put behind and diffusing the sound as in a real pipe organ. I'd simply bring them out on shelves by a couple of feet to put things behind.

Those sub-woofer horns look AMAZING! But I really don't understand the need for phase cancellation that the arrangement provides with the mixing of the sound from the front of the horn like that with the front of the speaker, especially as the mouth of the horn has about the same area as the speaker. The tip with those speakers is to put them into a corner.

Best wishes

David P

Thanks David,

That really is the crux of the question here:

Regardless of type of subwoofer used... is this opening - which is approx 15 feet by 4 ft - big enough?

Assume that at least 4 of the Pipe Speaker cabinets (the large ones), handling 8' pitch flue work, will remain on the wall. The other ones would go on the floor in the chamber with their tops removed. So up to 20 out of 24 channels of speakers would be in the chamber.

BTW - part of the total plan is to replace all the drivers in all the Pipe Speaker cabinets with Infinity 9623i reference drivers (4ohm) wired in series/parallel. That means each cabinet will be capable of 400 watts RMS at 4 ohms. Right now I'm having to pair up cabinets so as not to overdrive them and the fragile 45 year old single cone drivers.

Just a brief reminder if the organ is more reverbent then the congregation singing, they will get lost easily. So be carefull if you add any type of reverb to the organ and use it during hymn singing. I have worshipped many times in a lutheran church with a brand new allen organ, and the room is accoustically dead, similar design to your space. Well to make the organ sound good they cranked the reverb up, and the organ sounds glorious. However singing with it is a compete disaster, since you hear the reverberation of the organ, but can't here the congregations voice as a whole.

Chris