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Reproducing 32' bottom C

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Reproducing 32' bottom C

Postby ajt » Mon Aug 30, 2010 3:51 pm

Reading this article - http://news.bbc.co.uk/1/hi/sci/tech/3087674.stm lead me to consider how effective a 32' through speakers is going to be in a church setting. Knowing almost nothing about loud speakers, I went off googling for 15"/18" drivers that would get down to the 11Hz required for 32' bottom C. Not many of them seem to exist.

Does this mean, therefore, that those bottom few notes are unachievable? I find that hard to believe... Is this something that can be achieved by a tuned enclosure for drivers that don't seem capable of getting down to 11Hz? Or is it a case of live with the lack of oomph at the bottom end, or shell out a lot of money on drivers that go that low?

Presumably, the bigger the driver, the more air it moves, so the more the congregation/audience "feel" the 32' ?
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Re: Reproducing 32' bottom C

Postby telemanr » Mon Aug 30, 2010 4:09 pm

Why are you concerned about reproducing 11Hz? 16.4Hz is the fundamental for a 32' pipe. Or are you just being conservative so the output at 16Hz will be better (louder)?
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Re: Reproducing 32' bottom C

Postby Jim Reid » Mon Aug 30, 2010 4:22 pm

This speaker system will reproduce a 32' Bourdon, Open or Diapason just fine:

http://www.definitivetech.com/Products/ ... %20Trinity

also,

http://hometheaterreview.com/definitive ... -reviewed/

Costly, but wonderful bass.
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Re: Reproducing 32' bottom C

Postby ajt » Mon Aug 30, 2010 4:23 pm

Nope, just being wrong; I thought it was 11hz, but a quick google shows you are correct. Doh!

So, to rephrase my earlier stupid question, does a decent sub at 16Hz move enough air to make a congregation feel the 32'? I'm looking at a fairly small church, seats around 200-250, typical English country church construction; stone everything, wooden pews.
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Re: Reproducing 32' bottom C

Postby bcollins » Mon Aug 30, 2010 5:45 pm

I assume you're on a budget - like my project at Zion - and cannot entertain $3000 Definitive Trinity or Danley Sound Labs - and the like...

What a driver is rated at/for isn't necessarily what it will do in the right enclosure. For example I have a pair of 18" woofers - rated down to 20Hz - but in an infinite baffle I can push them down to 10Hz. Unfortunately, there is little to no energy being projected out the front side of the baffle and into the listening space (the nave). However, it does a great job of rattling all the light fixtures and HVAC vents down in the fellowship hall - as well as the glass between the narthex and the nave.

Point is, the enclosure design is probably more critical. I would venture a guess that most successful 15-16Hz sub-woofer designs have common 20Hz (ish) drivers.

The popular DIY Tuba HT design recommends this speaker - Dayton RSS390HF-4 15" Reference HF Subwoofer * Power handling: 500 watts RMS/800 watts max * VCdia: 2-1/2" * Le: 1.00 mH * Impedance: 4 ohms * Re: 3.3 ohms * Frequency range: 18 - 800 Hz * Fs: 18 Hz * Magnet weight: 150 oz. * SPL: 90 dB 2.83 V/1m, 87 dB 1W/1m * Vas: 9.95 cu. ft. * Qms: 3.10 * Qes: .49 * Qts: .42 * Xmax: 14mm * Dimensions: Overall diameter 15-5/16", Cutout diameter 14-1/8", Depth 6-1/8".
- But is said to have a "Useful output down to 12Hz"
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Re: Reproducing 32' bottom C

Postby engrssc » Mon Aug 30, 2010 5:52 pm

This is a possibility even tho sometimes "it" is criticized. "It" can sound very good and at a reasonable cost. Here is the "it" http://www.decware.com/newsite/hwk15.htm :)

Rgds,
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Re: Reproducing 32' bottom C

Postby ajt » Tue Aug 31, 2010 5:02 am

Thanks all - I think you've answered my naive question; driver specified frequency can be lowered by using the right enclosure. So I could build a sub-woofer using one of the many designs on the web, e.g. the Home Wrecker, and put drivers in that only go to, say, 18Hz, and get the extra couple of Hz required for full reproduction.
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Re: Reproducing 32' bottom C

Postby IanPounder » Tue Aug 31, 2010 5:21 am

Two thoughts:
Is this for the church with the Copeman-Hart, and, if so, have you tried the old sub? C-H subs do usually reproduce 32' tone pretty well.

Also, have a look at http://www.bkelec.com/HiFi/Sub_Woofers.htm. There might be something there you could use.
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Re: Reproducing 32' bottom C

Postby ten87 » Tue Aug 31, 2010 5:38 am

ajt wrote:Presumably, the bigger the driver, the more air it moves, so the more the congregation/audience "feel" the 32' ?


Not necessarily. Often times, pro 15" and 18" drivers can't do much below 60 hz, as they are not designed to do so. Bigger is not always lower.

Bob mentioned the Tuba HT. I built two of those for my church, and they would take the plaster off the walls in the chambers if I pushed them too hard. 16 hz is no problem whatsoever. I have doors rattling all over the room! Some quick measurements tell me they're taking no more than 60 watts to fill the church. The drivers can take 500 watts! :shock: Info on the Tuba HT can be found here: http://www.billfitzmaurice.com/THT.html

The Decware Housewrecker is an easier build, but I doubt you would get as much output from it at 16 hz. That may not be an issue though. I was going to build one of those before I found the Tuba HT.

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Re: Reproducing 32' bottom C

Postby engrssc » Tue Aug 31, 2010 7:44 am

ten87 wrote:The Decware Housewrecker is an easier build, but I doubt you would get as much output from it at 16 hz. That may not be an issue though. I was going to build one of those before I found the Tuba HT.


I will attest to the Housewrecker being an easy build. Took me an evening. Would have had it playing that same night except I needed the stain and final finishes to dry, etc. So that finishing part actually took longer than the build itself.

I auditioned all kinds of subs (even commercial subs) and as has been discussed, bigger is definitely better. But big wouldn't pass my wife's "plans". So the Housewrecker was a compromise. The total price "ain't bad" either. After building it and a little tweaking, it runs circles around anything I could buy "reasonably" readi-built. It fits nicely in a corner of the music room and there is no question that it is "around". BTW, "in the corner" makes a big difference in what you hear. Something like 10 or 12 db difference. If you go this route, don't fudge too much on the driver (speaker) you use. All 15's or 18's aren't the same. You "gotta" move air with a sub.

I also took it to church and, here too, there needs to be some compromises due to space limitations. Also, it wouldn't even be correct to say it compared to the Rodgers sub, not even close. Even the Rodgers sounded hugely better on the low end with the Housewrecker connected. It really is a very efficient system. I'm running a much larger amp (500 W) than would be necessary but only because I had that amp. Then too, I've always been taught that it's better to run an amp on the linear portion of the curve.

So given all of the above, the Housewrecker still will make an impact, a big one. Owen Jones put me on to this sub and I have no regrets. :)

Rgds,
Ed
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Re: Reproducing 32' bottom C

Postby David Pinnegar » Wed Sep 01, 2010 6:46 pm

Hi!

I think the real secret is to vent the drive units into some void that shakes the floor. If the pews sit on wooden platforms, then venting them under the pew platforms will make the vibrations felt impressively. If your pews are on a stone floor, you're stuck and simply have to rely on whatever your soundwaves will succeed in shaking.

Having been to a wedding at the weekend where the noise that some thought passed for music involved low frequencies which shook the tablecloths and indeed one's trousers, the answer lies in simple raw power.

Best wishes

David P
http://www.organmatters.co.uk
David Pinnegar, B.Sc., A.R.C.S.
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Re: Reproducing 32' bottom C

Postby schantzplayer » Wed Sep 01, 2010 10:03 pm

Just because a driver is not rated to 16 Hz does not mean it won't work at 16 Hz. The frequency response specification usually refers to a certain peak to valley or flatness spec, Say +/- 3db. If the driver is rated at 20Hz to say 500Hz, it should work at 16 Hz but may deliver its sound 4 or more db below the specified range. Easy to accommodate with the ability to voice pipe by pipe. Hardly noticeable as the room itself at those frequencies have peaks and nulls. You would have to voice each pipe anyway.
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Re: Reproducing 32' bottom C

Postby toplayer2 » Wed Sep 01, 2010 11:00 pm

IMO, achieving a respectable presentation of a 32' low C is extremely challenging. Over the years I have built a number of subs including transmission lines, Thiele/Small vented designs, and others. Unfortunately, getting that last octave comes at a price. The Thigpen Rotary is the champ but at $30K it is way out of my league. I did invest in a DefTec Trinity and am extremely happy with it.

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Re: Reproducing 32' bottom C

Postby Gedakt » Thu Sep 02, 2010 12:22 pm

The secret of achieving adequate output at 16Hz - and for the whole of the 32' bottom octave - is equalization. 15" or 18" drivers are best and must be mounted in suitably designed enclosures. But it is no use feeding them with a “flat response”. A true sub-woofer must have an associated equalizer with a curve rising very steeply from about 30Hz down to 16Hz, then cutting-off sharply to avoid thumps from switching transients, etc. The equalizer, which will probably be “active”, is placed at the input to the amplifier. The steepness of bass lift provided by an ordinary "tone control" - i.e. 3db per octave - is quite useless for this application. A slope of 6, 9 or even 12db/octave (dependent upon the driver, enclosure and room size) is required to effectively simulate a pipe organ 32’ stop.

The associated amplifier must be able to handle the additional low frequency level sent to it from the equalizer and be capable of the extra power that will develop. And of course the speaker(s) must also be able to handle this level of power delivered by the amplifier. The limiting factor, assuming the amplifier has the necessary grunt, is the cone excursion of the sub-woofer driver. At 16Hz on full organ this will approach the maximum permissible and is one reason why multiple drivers may be necessary in a large auditorium such as a church.

A well-designed “active” sub-woofer should take care of the above factors. However, if it is planned to place 15” or 18” drivers in an enclosure(s) for the purpose of providing adequate output in the bottom octave, a properly designed equalizer is essential. Simply connecting such a speaker to an amplifier without suitable equalization will fail miserably.

Max
Last edited by Gedakt on Thu Sep 02, 2010 5:48 pm, edited 1 time in total.
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Re: Reproducing 32' bottom C

Postby Eric Sagmuller » Thu Sep 02, 2010 2:23 pm

Gedakt wrote:The secret of achieving adequate output at 16Hz - and for the whole of the 32' bottom octave - is equalization. 15" or 18" drivers are best and must be mounted in suitably designed enclosures. But it is no use feeding them with a “flat response”. A true sub-woofer must have an associated equalizer with a curve rising very steeply from about 30Hz down to 16Hz, then cutting-off sharply to avoid thumps from switching transients, etc. The equalizer, which will probably be “active”, is placed at the input to the amplifier. The steepness of bass lift provided by an ordinary "tone control" - i.e. 6db per octave - is quite useless for this application. A slope of 12, 18 or even 24db/octave (dependent upon the driver, enclosure and room size) is required to effectively simulate a pipe organ 32’ stop. Max


I'm sorry but I disagree on this. A subwoofer that is truly able to reproduce the lowest frequencies will not need much if any EQ unless the room has a rapidly falling response. In fact if placed in a corner will generally add gain near the low end. Some designs can tolerate some added gain but it really depends on the design. And if it needs that kind of EQ then it's a poor design for the job at hand and the effect is very limited, as the woofer will easily be pushed beyond its Xmax (excursion limits).
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