Woofer with longer excursion, bigger power handling and higher efficiency always is a better solution.
With the second 15" driver you get 6 dB more SPL - an easy no-brainer.
Another no-brainer - if the box is oversized for one 15" driver, than put two 15" drivers in that box! And yes, subtract the volume of the port from the box to get the real volume value.
Two 15" drivers in one overzised (two times) box equals two optimal, single 15" boxes.
No, the tuning frequency (16 Hz) is determined only by the box volume and the port dimensions.
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A near to impossible time of it, actually, since horns tend to unreasonably large unless you have an open corner to put them in . . . they get all wonkey if the mouth is too small for the wavelength. The amount of sound you get from a boxed cone driver (or drivers) is entirely a function of swept area . . . and there's a sim that will calculate it for you at Piston Excursion calculator .
The way we get around that is with a tuned (ported) resonator coupled to the driver . . . the motion of air in the port causes sound radiation at the port mouth, and that's what gives the increased output. We usually "tune" that to the bottom of the desired passband, but you can put the resonance higher, at any frequency you want to boost. Done on purpose that might give your electric guitar a particular desired sound . . . done wrong it produces the classic bass reflex "boom box" (and the ported enclosure's initial bad reputation).
Resonant augmentation is not without its own problems . . . fortunately for organ builders none apply (to any appreciable extent) in that particular case. "Group delay" and ringing don't matter (it takes time for a pipe to sound and decay anyway), wind noise in the port doesn't matter (wind organs have wind noise anyway), and even a port resonance that changed upper harmonics wouldn't matter if you were sounding only one pipe, since that would simply change the timbre (harmonic structure) of that pipe. If that same driver/box combination is going to sound pipes over a two or three octave frequency range (one whole rank) then the pipe resonance can matter if it changes the timbre at some frequencies but not others (the whole rank should have the same "sound").
You don't have to do that if the port is external to the box (which it easily can be if appearance doesn't matter).
From Linkwitz site Frequently Asked Questions , question 21:
Q21 - Why does SPL increase 6 dB for two drivers in parallel, when the electrical power consumed only increases by 3 dB?
"In summary, when two identical drivers are connected in parallel and driven with constant voltage, then twice the electrical power is consumed (+3 dB), the radiated acoustic power is increased by a factor of four (+6 dB), and the free space sound pressure level is doubled (+6 dB) at a given distance."
Nodding along to pretty much all of this.
I think the point that doesn't get hammered enough though, is once a proper low pass filter is in place, resonances become a non issue (down from a nearly non issue to begin with).
If this cabinet is meant to hit 16 hz cleanly, I would really recommend not using it past around 60 or 70 hz, after which it should be rolled off quite quickly.
If this one box is meant to cover anything higher than around 60, I'd add another section to it with another driver that's fed the higher signals, in a completely separate enclosure attached to the top of it.
For the moment though, let's be ill-concerned with what's happening higher, and instead fixate (until conquered) on the issue of getting down low, which I addressed in post 2, and most recently in post 360 (interesting, full circle...)😀
Here's a link to the 18 inch driver suggested by JAG. It is available in dual 2 ohm or dual 4 ohm versions. Our amp will have twin connections putting out the same signal below the crossover frequency. I'm guessing each of those channels could be connected to each of the voice coils.
HT18 18″ Subwoofer | Stereo Integrity
$174 plus shipping. It would seem to me that a 4 ohm version would be a better match with the Crown XLS1500 amp that would power it. I'm anticipating setting the (adjustable) crossover on the amp to 64 hz. This would take it off line for anything above 64 hertz. Thus, it would only be producing sounds for the bottom two octaves of our organ.
My thinking is to FIRST experiment with using the one box. BUT I think I may have the budget and capability to include another box - since so many feel it is needed.
I'm open for confirmation, agreement or contrary opinions.
I'll resize the hole in the existing box to hold this larger woofer. I'll also carve out the six inch hole for the port. I'll look for a 6 inch Sonotube product (or generic) at Lowe's or Home Depot. I'm already going there today.
Since many have advised that even this improved box won't be enough, my questions are what is the minimum sized ported enclosure that would work for this driver? And what size port would work well for that size box?
I think I've said it before, but I'll say it again. I have appreciated the input I have received. I have learned a lot. I haven't followed the suggestions of everyone. But I'm trying to sift through them and come up with compromises we can afford that will work for our situation.
Bach On
BTW, look at this one.
http://stereointegrity.com/product/hs24-24-subwoofer/
And all donations to our church organ fund are tax deductible. ;-)
http://stereointegrity.com/product/hs24-24-subwoofer/
HT18 18″ Subwoofer | Stereo Integrity
$174 plus shipping. It would seem to me that a 4 ohm version would be a better match with the Crown XLS1500 amp that would power it. I'm anticipating setting the (adjustable) crossover on the amp to 64 hz. This would take it off line for anything above 64 hertz. Thus, it would only be producing sounds for the bottom two octaves of our organ.
My thinking is to FIRST experiment with using the one box. BUT I think I may have the budget and capability to include another box - since so many feel it is needed.
I'm open for confirmation, agreement or contrary opinions.
I'll resize the hole in the existing box to hold this larger woofer. I'll also carve out the six inch hole for the port. I'll look for a 6 inch Sonotube product (or generic) at Lowe's or Home Depot. I'm already going there today.
Since many have advised that even this improved box won't be enough, my questions are what is the minimum sized ported enclosure that would work for this driver? And what size port would work well for that size box?
I think I've said it before, but I'll say it again. I have appreciated the input I have received. I have learned a lot. I haven't followed the suggestions of everyone. But I'm trying to sift through them and come up with compromises we can afford that will work for our situation.
Bach On
BTW, look at this one.
http://stereointegrity.com/product/hs24-24-subwoofer/
And all donations to our church organ fund are tax deductible. ;-)
http://stereointegrity.com/product/hs24-24-subwoofer/
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Yep, yep yep to all of that. You've got the crossover covered, the amp covered, and all the basic points well understood at this point. I think we're golden.
Also, if the 24" is in the budget, absolutely. More displacement is ALWAYS going to be better, and between everyone here, we can help you come up with enclosure(s) that would work well.
Bear in mind though, that driver has quite a bit more power handling, and as such, would benefit greatly from a larger amplifier. Maybe a Crown 6002? We'd have to do a bit of research if you decide you want the 24"s.
Also, if the 24" is in the budget, absolutely. More displacement is ALWAYS going to be better, and between everyone here, we can help you come up with enclosure(s) that would work well.
Bear in mind though, that driver has quite a bit more power handling, and as such, would benefit greatly from a larger amplifier. Maybe a Crown 6002? We'd have to do a bit of research if you decide you want the 24"s.
Hi Bach On,
Post #357: "...a different driver (or more drivers) will create a need for a different length in the port."
For your box using the ST385 the port will work w/ one or w/ two drivers. No port dimension changes necessary. For a square port (eq. to 6"I.D.rnd.) try 5-5/16" to 5-3/8" square x 17-3/4" long; or, maybe you have a few pieces of 2x6 and some leftover particle board?
Before getting a different woofer I would suggest experimenting w/ what you have on hand. You can cut a second driver hole, and try two drivers sealed, single driver ported (w/ the port mounted to a small baffle to plug the second driver hole). Maybe, that would be a good starting point (see Post #5). See what you like (at least we have sofar agreed that different boxes sound differently), and then move the port for dual driver ported. Don't know if your installation allows to put the 2nd driver on the back opposing the front driver (opposing forces and all that), not necessary, but would not hurt.
I see no problems w/ the SI HT18 or w/ the UM18-22 Dayton Audio UM18-22 18" Ultimax DVC Subwoofer 2 ohms Per Coil
Regards,
Post #357: "...a different driver (or more drivers) will create a need for a different length in the port."
For your box using the ST385 the port will work w/ one or w/ two drivers. No port dimension changes necessary. For a square port (eq. to 6"I.D.rnd.) try 5-5/16" to 5-3/8" square x 17-3/4" long; or, maybe you have a few pieces of 2x6 and some leftover particle board?
Before getting a different woofer I would suggest experimenting w/ what you have on hand. You can cut a second driver hole, and try two drivers sealed, single driver ported (w/ the port mounted to a small baffle to plug the second driver hole). Maybe, that would be a good starting point (see Post #5). See what you like (at least we have sofar agreed that different boxes sound differently), and then move the port for dual driver ported. Don't know if your installation allows to put the 2nd driver on the back opposing the front driver (opposing forces and all that), not necessary, but would not hurt.
I see no problems w/ the SI HT18 or w/ the UM18-22 Dayton Audio UM18-22 18" Ultimax DVC Subwoofer 2 ohms Per Coil
Regards,
This is wrong. I'm not even going to try responding in a technical manner since it's not getting anywhere with you, but I'll refer you to DSL's website. Every single horn subwoofer they offer, is massively undersized acoustically and none of them have "wonky" response. They have a wide selection of front loaded horns and tapped horns.
It's beyond simple to design a good undersized horn.
The 4 ohm version of the lSI HT18 driver won't be available until May. So an experiment with the existing 15" driver with a port is probably a sound plan. 😀
Bach On
I hate to say it, but now that you've teased the idea of the 24"...if it's in the budget, DOOO EEEET.
The port velocity in the designs that have been provided for you is already pretty high. If you add another driver to the box OR change to a much larger driver with a lot more linear volume displacement the velocity is going to go through the roof and port compression (losses) and chuffing will be a significant problem.
Deward says chuffing isn't a problem, that's wrong. Chuffing is the onset of severe port compression, which is losses. Losses are obviously not a good thing. The port is there to provide gains and port compression, if it's severe enough, can completely negate the benefit of the port.
I'm not going to do any more design work here, I'm not happy with the way the post that started it all, a 300 word personal insult was left intact but my rebuttal with NO personal insults was removed making it seem like I'm the one that broke the rules - all I did was post a very relevant link to counter the resume equals infallibility nonsense but the post that started it all, talking about me messing my diapers and crying for mommy is still there despite having NO technical relevance to anything in this thread. That part alone I don't mind, insult me all you want, but my rebuttal was not a personal insult, it was very on topic and relevant and IT was removed instead of the instigating post. It is what it is, it's done, and I'm not going to complain about it anymore, but I'm not happy about it. I'll stick around for a very limited time to point out the obvious errors that keep flooding into this thread, but other than that I'm not going to provide any more constructive input. I do have to say this thread is probably the oddest forum experience I've ever encountered in my years on the internet.
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In my earlier life as a High School Assistant Principal, students who were caught fighting were brought to my office for processing. Invariably, all participants felt the other had wronged them.
One question I would typically ask the participants was, "Do you believe any of this is really going to matter in your life a year or two from now?"
Bach On
One question I would typically ask the participants was, "Do you believe any of this is really going to matter in your life a year or two from now?"
Bach On
Careful there, unless you're routing the frequencies above that to another nearby box, lest you lose the harmonics (timbre and voicing) of the upper pipes. IMO you're better off sending the entire output of the 32 ft register to that one bass driver and letting it handle the harmonics as well as the fundamental for all pipes in the rank . . . it will sound more "real" that way, both by itself and when coupled (as it always will be anyway) to a 16 and/or some 8s sounding from other speakers . . .
Hi Bach On,
Another thing you could try: I don't know how may of your HC12 woofers you have on the shelf, but you could stuff four of them into the big box for another sealed experiment. I have no idea what T/S they may have, but, they were designed for a sealed box, and this would just be an experiment. I'll attach some simulation windows for single sealed v. quad sealed ST385 (both Xmax @ 20Hz).
It's time to cut some wood, and to have some fun. 🙂
Regards,
Another thing you could try: I don't know how may of your HC12 woofers you have on the shelf, but you could stuff four of them into the big box for another sealed experiment. I have no idea what T/S they may have, but, they were designed for a sealed box, and this would just be an experiment. I'll attach some simulation windows for single sealed v. quad sealed ST385 (both Xmax @ 20Hz).
It's time to cut some wood, and to have some fun. 🙂
Regards,
Attachments
This is a common misconception, but the reality is that if the vent is excited enough, then its open pipe harmonics will be audible, comb filtering with whatever speaker is reproducing that BW higher up regardless of where the sub's low pass is, so the only way to quell them is to either damp the pipe and/or tune it below the lowest frequency it will 'feel' the need to reproduce at high power and/or use a high pass filter to limit its high power capability to 'sing'.
GM
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Drive any pipe hard enough and it will audibly compress; first with just reduced output, then by making chuffing noises due to high frictional losses.
GM
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