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Old 11th April 2015, 01:54 PM   #1
Bach On is offline Bach On  United States
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Default 16 hz for church organ

New to the forum. I've been lurking and reading. But I haven't found a post that matches and directly addresses my questions.

Have built a fairly large sealed box (13 cu. ft.) for a single 15 inch speaker. The cabinet is 3/4 inch thick MDF reenforced with lots of interior and exterior supports. All joints are sealed with caulk. Plenty of glue and screws were used. There is no rattle or noise from the box. The speaker cutoff is currently set at the amp for 177 hz. The amp is a Crown XLS1500 set for Lowpass- all sounds above the adjustable crossover are rejected from the signal (they are routed through another amp to another speaker box).

Here is a link to the speaker.
Dayton Audio ST385-8 15" Series II Woofer

In initial testing, the speaker can produce sounds down to 20 hz. I used a series of sweeps and test tones from a CD to get a sense of what the box can do. Since my ears can't really hear these "sounds", I depended on eye and touch of the cabinet and speaker cone as my primary measurements. I can feel it in the air if I stand right at the cabinet. That's not very scientific- of course.

Some organ pipes can produce pitches down to 16 hz. for the lowest pitch. These pipes aren't used all the time. But they are often used when the organ is already being played loudly. I would not need these sounds every week, but I might need them six or seven times a year. (BTW, there is even an organ pipe that can play down to 8 hz. We have no interest in going that low.)

Obvious question: Must the organ be able to play the sounds down to 16 hz.? No, but it would be good if it could. But cost is a consideration.

An organ speaker will produce the sounds above the crossover frequency. But I'm focused on the homemade speaker at this point. And for background - there will be a total of eight speaker cabinets reproducing the digital sounds. Sounds of certain types will go only to certain speakers. These speakers will be placed in a chamber adjacent to working organ pipes. The digital sounds and the pipe sounds will work together.

The recommendations for the Dayton speaker calls for a smaller box. I'm aware of that. Some had advised that rolloff of lower sounds might not be as steep with a cabinet this size.

I've participated in an organ discussion forum. Some suggested I ask my questions here where people might have more experience.

I'm considering adding two of the following passive radiators to this box.
Dayton Audio SD315-PR 12" Passive Radiator

My thinking is that they might improve the lowest pitch reproduction while allowing me to control speaker cone movement.

Some have suggested just adding an identical speaker to the box.

I was hoping someone would be able to guide me here to do what is best.

Thanks in advance for anyone willing to help.

Bach On
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Old 11th April 2015, 02:36 PM   #2
DrDyna is offline DrDyna  United States
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You'll need a lot more than 13 cuft for 16 hz in a sealed cabinet, unless you EQ. Passive radiators might help, but those have to be calculated and tuned. Your best bet if you want to get down that low would probably be some type of Linkwitz Transform EQ, or designing a bass reflex cabinet for the driver that's tuned where you want it.
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Old 11th April 2015, 03:25 PM   #3
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Quote:
Originally Posted by Bach On View Post
New to the forum. I've been lurking and reading. But I haven't found a post that matches and directly addresses my questions.
Welcome Bach On!

Quote:
Obvious question: Must the organ be able to play the sounds down to 16 hz.? No, but it would be good if it could. But cost is a consideration.
If the organ composition called for 16Hz note, then yes, the organ needs it, or else it cannot play that piece. Can people hear that low, yes, but not with their ears. They can feel it in their lungs and with skin if it is loud enough. Low frequency is thrilling to hear, it causes an adrenaline response which people to experience an emotional response which lasts through the church teaching. People are still feeling frightened and awe from the organ while the threat of eternal damnation is being uttered from the pulpit. We know people love LF sound, thunder, military airshows, car races and harley loud motorcycle rumble, not to mention rock and roll. The bass player for U2, Adam something, he has an organ bass pedal on the floor which allows him to double his bass notes an octave lower on the big chorus themes. People still enjoy LF entertainment, as they did when only God could make LF, in a thunderstorm or in church. They can feel the rumble even if they can't hear it.

Quote:
I'm considering adding two of the following passive radiators to this box.
Dayton Audio SD315-PR 12" Passive Radiator

My thinking is that they might improve the lowest pitch reproduction while allowing me to control speaker cone movement.
A reflex ported speaker would be the best solution. It has almost no motion of the active driver when the port is playing at it's designed resonant frequency. With a box of 13cu ft, you can use a big port and play very low. You may need more drivers tho. A single 15" may not move enough air to take advantage of the box volume and large port.

Your box is probably too big to use passive radiators with one active because the air pressure changes will be too low, so the connection between active and passive drivers is not efficienct enough.

Quote:
Some have suggested just adding an identical speaker to the box.
This has some advantages. Wiring them in parallel makes them draw more current and play louder for a given voltage signal. Having two instead of one makes them louder. Combined together you get a doubling of acoustic power with two actives, and you get good transient response, and no resonance to taint the tone. But the tone of organ is sine wave, and group delay is not as much of a concern with organ music as with other instruments that have more high freq content.

I would add more active drivers to the box and add appropriate tuned reflex ports to take advantage of the box size. Designing and building ported speakers is more exacting than sealed box, but it is not difficult if you are going for maximum power and SPL at port resonance. Use a box design simulator like WinISD to determine the box design. Add drivers until the boxvolume matches 13cft. The Fs of the driver will affect the reflex port tuning so you need a driver with low Fs. Yours is adequate.

One last thing, the larger the driver area the better for playing low. 15" is large, but compared to the wavelength of 20Hz it is tiny. This is called acoustic impedance. It is why tweeters can be so small and still play their pass band so loud and clear. They have a good grip on the air at those freqs because of their relative large size compared to the wavelengths they play. Woofers have it harder because they can't practically be 10feet wide. So we invent crutches to help them achieve higher acoustic impedance. The ultimate of this is the horn which focuses air on the driver cone, like a lens focuses light on a spot. A "tapped horn" design would be a good application for your organ system, but you'd have to build a different box from scratch.

You may be able to use your existing box efficiently with reflex ports and adding more drivers. Use a simulator to help you find the right combination of drivers and ports to work with your box volume. Build it strong, there is a lot of pressure and vibration from that oscillating air in the port.
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Old 11th April 2015, 04:28 PM   #4
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Since I don't know where to begin, I'll just list points.

1. I doubt if there is any feasible/economic way for you to generate the sound you allude to in a church-sized space. And your woofer may cut off being able to make sensible sound well above that.

2. A person can hear distinct notes down to 25 Hz and maybe lower. And if you can't (whatever the cone seems to be doing to your fingers), your woofer isn't up to the task (and that's a nice woofer you bought and sensibly housed in a sealed box... but I'd add a leak and fill the box with pillow stuffing).

3. The ear fills-in fundamentals even when the speaker can't. Listen to organ recordings which you have good reason to think go way low.

4. Easy to destroy (and long-since to cause distortion) in drivers unless you include circuitry to prevent low notes getting to the driver - and also depends on choice of enclosure.

I get to hear a lot of pipe organ music:

"Phantoms of the Organ" Halloween bash

(a picture of me and the Dayton-Wrights appears in the last post)

Ben
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Last edited by bentoronto; 11th April 2015 at 04:38 PM.
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Old 11th April 2015, 04:57 PM   #5
tb46 is offline tb46  United States
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High Bach On,

As you already have the amplifier, box and one driver I'd recommend getting a second driver, and running both in parallel in your current sealed box.

The alternative is a single driver vented version of your box, e.g.; using 2ea. 6"I.D. x 35" long ducts to tune the box low enough to get to your 16Hz goal. This should work too. There will be a strong group delay peak around the vented tuning frequency, and there will be strong pipe resonances from the tuning ducts.

Both versions will need a high pass to protect the driver from over-excursion; e.g.: for the vented box 4th order @ 16Hz.

Getting down below 25 or 30Hz w/ authority is just difficult. Ideally, you'd be looking for a driver(s) w/ much higher Xmax and power capacity.

Regards,

P.S.: One graph @ 2.83V the other ~ Xmax.
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Last edited by tb46; 11th April 2015 at 04:59 PM.
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Old 11th April 2015, 06:13 PM   #6
wg_ski is offline wg_ski  United States
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Quote:
Originally Posted by bentoronto View Post
1. I doubt if there is any feasible/economic way for you to generate the sound you allude to in a church-sized space. And your woofer may cut off being able to make sensible sound well above that.
The limiting factor is space. I would START with 8 boxes - and that would only produce moderate SPL. Awe-inspiring SPL would require a 'wall of woofers' or a full sized horn.
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Old 11th April 2015, 06:53 PM   #7
sine143 is offline sine143  United States
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Josh ricci gjallerhorn. 1 box, awe inspiring 16hz. .

However. Afaik, an organ does not produce sine waves. Even the the 16hz fundamental will not be present, there should be plenty of gas at 32hz.
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Old 11th April 2015, 07:07 PM   #8
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Quote:
Originally Posted by Richidoo View Post
... no resonance to taint the tone.
Quote:
Originally Posted by bentoronto View Post
... sensibly housed in a sealed box...
If you look at what a PIPE organ is, it's long PIPES that produce output based solely on PIPE RESONANCE.

If you want to do this well for under a million dollars you need a resonant system, ported or some type of horn. And since you are trying to produce a PIPE RESONANCE, I don't see any problem with using a resonant enclosure. (Not that there's ever a problem with a resonant enclosure, but since some people think there is, at least in this case even those people shouldn't have a problem with using resonance to produce the sound of a pipe resonance.)

You need a lot of drivers and a lot of really big boxes with large ports (or horns) to fill up a big church with 16 hz tones at pipe organ spl.
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Old 11th April 2015, 07:50 PM   #9
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Originally Posted by just a guy View Post
If you want to do this well for under a million dollars you need a resonant system, ported or some type of horn. And since you are trying to produce a PIPE RESONANCE, I don't see any problem with using a resonant enclosure. (Not that there's ever a problem with a resonant enclosure, but since some people think there is, at least in this case even those people shouldn't have a problem with using resonance to produce the sound of a pipe resonance.)

You need a lot of drivers and a lot of really big boxes with large ports (or horns) to fill up a big church with 16 hz tones at pipe organ spl.
Bingo! This was exactly what I was thinking when I read through this thread. You will need to reproduce 16Hz at VERY HIGH SPL to even perceive it away from the transducer. Resonance is your friend, and one conventional system that might work well for high SPL 16Hz sound is a bandbass enclosure. Bandpass design trades off bandwith and SPL - if you want to reproduce a wide range of frequencies with it, the passband SPL can't be high. Conversely, if you want one-note-bass, you can get pretty high SPLs in a narrow band. So, I suggest that you look into a 4th order bandpass and do some modeling to maximize SPL in a narrow passband around 16Hz. Unibox is one free program that is useful for modeling such a system because you can also model the port self-resonance to see how band they will be (I strongly suggest you do that). You can download Unibox here:
UniBox - Unified Box Model for Loudspeaker Design - Kristian Ougaard

Although you could just connect this in parallel with your main woofer/subwoofer system it would be much better to have a dedicated amp and a bandpass filter centered on 16Hz to reduce out-of-band noise and excursion below tuning.
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Old 11th April 2015, 08:30 PM   #10
sine143 is offline sine143  United States
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eq "taints the tone" as much as Helmholtz resonance anyways (if you were to apply PEQ to replicate similar response charactaristics to an ideal ported enclosure that is). . remember, EQ alters phase. and 10 db of boost down low is gonna f it up good lol.
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