usually it does. IM distortion occurs below that level also of course. I have to build a test box for these woofers before I do anything else on this. The good news is that this midbass woofer only needs 1 cu ft to function well.
Jay did post response curves, then took them down when he realised most didn't understand and mis-read them. As I recall, there's a big loss. Basically, the "donut" makes the speaker sound on axis like it normally does about 30 degrees off axis. If it didn't, then it wouldn't be reducing the "icepicky beam". Hence the complaints from some about treble loss and the frequent advice in that thread to turn the treble up.
Remember, guitar speakers are not flat above 1K (except for EVM12Ls). With hifi drivers, you'll need to compensate for the donut's roll-off to enjoy the wider dispersion.
OK, thanks. Does the 12PE32 response which I posted above look like a guitar driver response curve to you? I don't really know myself.
Yeah, in order to crossover at 800-1200 Hz I'd need a different horn and driver, probably a 2" one at that ($$$). not sure what to do right now. thanks!
Yes, actually it does, but I din't 'spress mysef too well there. 😉 I should have said "Guitar speakers are used in their un-flat state above 1K." Which, now that I think about it....
Suddenly I'm not so sure the range above where a driver beams is that usable for reproduction. I don't think the foam will stop the comb filtering. Of course, I don't know why a Lowther wouldn't have the same problem....
You should drop Jay an email.
For deaf musician stage monitors crossing at 500 Hz, a 2" may be needed..
A one inch exit 1.75" diaphragm driver on a proper horn has no problem keeping up with a 12" or even a 15" driver crossed at 800-1200 Hz.
Hundreds of commercial designs for over 80 years have proved it works.
Looking at the response of your drivers looks like a 2000 Hz crossover may work out OK, you may want to experiment with the foam donut hole to match dispersion patterns between the woofer and tweeter.
Even with an active crossover, some out of band EQ or a Zoeble will probably be needed to tame the 2-4K mid woofer peak.
Keriwena wrote:
"As I recall, there's a big loss. Basically, the "donut" makes the speaker sound on axis like it normally does about 30 degrees off axis."
If his recollection is correct, the foam may help tame the 2-4K mid peak as well as widen dispersion.
If the crossover range still proves objectionable, you could add a small mid cone driver and passively cross between it and the tweeter.
Art
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So, I think I'm going to punt on these woofers. They are just too much of a pain to make work with what I have, or can easily get. I do have a pair of Dynaudio D54 drivers that are supposed to be really nice midranges, so I think I'm going to build something around them instead. I found a matching tweeter already, and I think the B&C 15BG100 is a good woofer. For the living room hifi, I don't really want a subwoofer in there.
(sorry I keep jacking your thread) I checked my email and nO email present
My email is: daveezlist@gmail.com
My email is: daveezlist@gmail.com
How do you calculate the dispersion of a LF cone driver? I can't find it in the Loudspeaker Cookbook.
I keep flip flopping on this project... the goal is to have a full range speaker (no subwoofer required), which for me is about 35Hz as the lower end. Two ideas are battling for attention in my mind:
the first:
1Khz horn (DE250+ME45) + 12PE32 + 12" subwoofer (in the same box)
crossovers: 1kHz & 80Hz.
the second:
good tweeter + Dynaudio D54 + good woofer (in the same box)
crossovers: 5 or 6 kHz & 900Hz.
I'm having trouble finding a good woofer that goes from 35Hz to 1kHz @ decent sensitivity (the D54 is 96dB). The first system is about 100dB sensitive and the second would be about 96dB. None of the subwoofers I've found that go down to 35Hz go up to 1kHz in a reasonably flat response. I like the simplicity of the first system.
OK, I found the rough approximation for dispersion. A woofer will have a 90 degree dispersion at the wavelength equal to the effective diameter of the cone, assuming it's still a rigid cone at that frequency. So, a 12" woofer is good up to at about 1200Hz for matching a 90 degree horn that's good down to that frequency, for example.
Back to the foam, I wonder if the hole should be set at less than the wavelength for the highest frequency desired to be reproduced? In other words, if we wanted the 12" woofer to extend to 2kHz, then the hole in the center of the foam should be at most 6.75" in diameter.
Back to the foam, I wonder if the hole should be set at less than the wavelength for the highest frequency desired to be reproduced? In other words, if we wanted the 12" woofer to extend to 2kHz, then the hole in the center of the foam should be at most 6.75" in diameter.
The foam works by attenuation of upper frequencies, which is not a hard cut off at a specific frequency.
You will have to experiment with foam depth, porosity and hole size to arrive at a similar dispersion as your HF horn at your chosen crossover point.
By using a 3" hole for a 12" woofer, Jay is suggesting that 1/4 wavelength would be about right. So for 2K you'd want a hole about 1 2/3". The size of the hole will determine the beginning of the dispersion; the type, density, and thickness of the foam will control the amount of the HF rolloff.
I actually tried that some time ago with a Visaton B200 and got the best results with a 5cm hole. 0°-40°, no foam (upper curves) vs. 5cm Basotect (lower curves):
An externally hosted image should be here but it was not working when we last tested it.
That's interesting Markus, thanks.
I wonder if, or how much, this foam insert reduces diffraction? For most guitar speakers that are mounted on the rear side of the baffle, there must be at least some diffraction going on as sound bounces off that hard circular edge, and I think that the diffraction effect would become apparent at the wavelength of the diameter of the hole, which is in this case of a 12" driver, about 1kHz. You gotta figure that the foam is absorbing not only the sound coming straight from the cone of the woofer, but also from what ever is bouncing around the hole in the baffle. I'm no expert on diffraction, but this is just an idea that came to me that I'm spitting out here so please don't jump all over me if I'm completely misunderstanding diffraction. This foam thing seems so much like the Geddes foam plug for his wave guide that I can't help but think that there's a similarity there.
I do know that for tweeters, covering the baffle surface around it with a sound absorbing material reduces the effects of diffraction, so maybe something similar is going on here?
Oh, I have 4 12"x12" sheets of the magic foam coming from Mcmaster-Carr that I don't think I'm going to need if anyone is interested.
I wonder if, or how much, this foam insert reduces diffraction? For most guitar speakers that are mounted on the rear side of the baffle, there must be at least some diffraction going on as sound bounces off that hard circular edge, and I think that the diffraction effect would become apparent at the wavelength of the diameter of the hole, which is in this case of a 12" driver, about 1kHz. You gotta figure that the foam is absorbing not only the sound coming straight from the cone of the woofer, but also from what ever is bouncing around the hole in the baffle. I'm no expert on diffraction, but this is just an idea that came to me that I'm spitting out here so please don't jump all over me if I'm completely misunderstanding diffraction. This foam thing seems so much like the Geddes foam plug for his wave guide that I can't help but think that there's a similarity there.
I do know that for tweeters, covering the baffle surface around it with a sound absorbing material reduces the effects of diffraction, so maybe something similar is going on here?
Oh, I have 4 12"x12" sheets of the magic foam coming from Mcmaster-Carr that I don't think I'm going to need if anyone is interested.
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I don't think it's similar to Earl's foam. Basotect is much denser (more like fiberglass) and Earls foam is only 30PPI.
Here's one explanation how the foam with a hole might work: Speaker Directivity - The Gear Page
Here's one explanation how the foam with a hole might work: Speaker Directivity - The Gear Page
The recommended foam from that thread is a Mcmaster-Carr open cell poly foam that is very soft. That thread is what inspired me to start this one. But what I meant was it was a similar principle to the Geddes application. His foam plug controls dispersion inside of a waveguide, as I understand it, whereas this foam donut may do something similar for the hole in the baffle of the guitar speaker box.
That's a significant improvement. Better dispersion at 20 degrees and a little smoother for all curves.
Reminds me bit of the BBC dispersion baffles over an 8".
David S.
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