I reall don't understand what you are trying to accomplish here. You have an array of 4 drivers, each separated by a distance, d, and each with successively increasing delay. d/c, 2d/c, and 3d/c. The claim is to control directivity. But the polar response vs frequency doesn't show much in the way of controlled directivity. Below F = c/8d the response is basically monopole. As the frequency approaches F=c/8d it becomes cardioid. As the frequency increases further and wavelength becomes shorter then the array length it degenerates into multi-lobed patterns with the number of lobes increasing with frequency. From one end the axial response is flat, as the delays compensate for the offsets, but from the other it shows as series of nulls and peaks in a pattern the repeats. Maybe I am missing the point here. Certainly you can construct an array that will have a cardioid response at F = c/8d, and monopole below, but the useful upper frequency would be F=c/8d as well because above that directivity is all over the place. The attached figure shows a simulation of such an array assuming omnidirectional sources.
I'm not clear in what you are trying to accomplish. Certainly not wide band constant directivity.
Hi John, thanks for chiming in. I've had good luck with your u-frames in the past, but I no longer have a copy of mathcad to model them. (Does anyone know if hornresp can sim u-frames properly?)
I am interested in controlling directivity in the two octaves between 125hz and 500Hz. What do you think is the best option?
Answering my own question, it looks to me that John K's uframe would be a promising option, but I'd have to scale it down to make it work from 125Hz to 500hz.
Here's a pic of John's uframe subwoofer. I don't know the exact dimensions but I'd estimate 14" x 14" x 18"
Here's some measurements of a similar design from John's page (NaO U-frame). I'm seeing about two octaves of bandwidth (30hz-120hz.) So I'm thinking I could create something with a bandwidth of 125hz-500hz by using a box that's approximately 24% in size. So that would be a depth of 4.32" instead of a depth of 18"
I checked in hornresp, and though it can simulate the effect of stuffing on a u-frame, I do not see any way to simulate directivity of a damped u-frame.
AFAIK, John's mathcad worksheet is the only way to sim them.
An externally hosted image should be here but it was not working when we last tested it.
Here's a pic of John's uframe subwoofer. I don't know the exact dimensions but I'd estimate 14" x 14" x 18"
An externally hosted image should be here but it was not working when we last tested it.
Here's some measurements of a similar design from John's page (NaO U-frame). I'm seeing about two octaves of bandwidth (30hz-120hz.) So I'm thinking I could create something with a bandwidth of 125hz-500hz by using a box that's approximately 24% in size. So that would be a depth of 4.32" instead of a depth of 18"
I checked in hornresp, and though it can simulate the effect of stuffing on a u-frame, I do not see any way to simulate directivity of a damped u-frame.
AFAIK, John's mathcad worksheet is the only way to sim them.
FYI: the paper on cardioids linked on John's page appears to be dead. It's from the team that does Akabak?
You can get it from the wayback machine here : https://web.archive.org/web/20050307233549/http://www.randteam.de/papers_lf/ioa_rs19_2003-lf.pdf
You can get it from the wayback machine here : https://web.archive.org/web/20050307233549/http://www.randteam.de/papers_lf/ioa_rs19_2003-lf.pdf
This one is also interesting IMO, because of the comparisons made between monopole, dipole and cardioid in different settings:
"MODAL COUPLING OF DIRECTIONAL SUBWOOFERS IN RECTANGULAR ROOMS"
A Thesis in Acoustics by Philip Feurtado
Pennsilvania State University, 2013
https://etda.libraries.psu.edu/files/final_submissions/8634
It is purely "simulation based" (as i remember it), but there are a some unique settings/solutions described with respect to "woofer-/room interaction".
E.g. Chapter 4.2. (Fig. 4.12) is interesting IMO due to possible (also practical) solutions or variants based on that "velocity source vs. pressure receiver" compensating effect, when using a dipole for the "lowest end" ... exiting a room (with respect to a preferred listening area) e.g. fairly below Schroeder Frequency ...
"MODAL COUPLING OF DIRECTIONAL SUBWOOFERS IN RECTANGULAR ROOMS"
A Thesis in Acoustics by Philip Feurtado
Pennsilvania State University, 2013
https://etda.libraries.psu.edu/files/final_submissions/8634
It is purely "simulation based" (as i remember it), but there are a some unique settings/solutions described with respect to "woofer-/room interaction".
E.g. Chapter 4.2. (Fig. 4.12) is interesting IMO due to possible (also practical) solutions or variants based on that "velocity source vs. pressure receiver" compensating effect, when using a dipole for the "lowest end" ... exiting a room (with respect to a preferred listening area) e.g. fairly below Schroeder Frequency ...
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Uhm, that does not work. At 500Hz you've got a wavelength of 0,69m, 1/4 Lambda is 0,1725m, that means you will get interferences at the upper end if you place the drivers directly in a row (one right next beside the next). Except you're going for quite small, much smaller drivers, but these will have a problem doing much at 125Hz.
Another thing is, I don't see this setup getting any smaller than a narrow beaming single horn.
I see no problem at all in realizing a "cardioid like" arrangement within Patrick's demands, having a bandwith of 2 octaves (125Hz to 500Hz).
Suitable "pathlengths" may be between 20 ... 30 cm IMO, depending on the size of the driver(s) chosen and the front baffle's size ...
In fact the inherent DI of those (drivers and baffle as to be chosen) will have to be regarded, when properly filtering the rear source.
There are also "enough" drivers on the market available having sufficient volume displacement (possibly used in a multitude) to be used in such a project, without driving them into breakup modes at the "upper end" (because of too large cone area at given diaphragm structure).
The question is to me : Where is the lower XO frequency (and steepness) ?
Is it around 125Hz (12db/octave) ?
Then the system will have to perform even below, which changes matters a bit and might call for slightly larger pathlengths ...
Suitable "pathlengths" may be between 20 ... 30 cm IMO, depending on the size of the driver(s) chosen and the front baffle's size ...
In fact the inherent DI of those (drivers and baffle as to be chosen) will have to be regarded, when properly filtering the rear source.
There are also "enough" drivers on the market available having sufficient volume displacement (possibly used in a multitude) to be used in such a project, without driving them into breakup modes at the "upper end" (because of too large cone area at given diaphragm structure).
The question is to me : Where is the lower XO frequency (and steepness) ?
Is it around 125Hz (12db/octave) ?
Then the system will have to perform even below, which changes matters a bit and might call for slightly larger pathlengths ...
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Pathlength/Lambda min = 0.33 may be seen as "hard upper limit" for pathlength (at the upper end), when making up a dipole from inherently nondirectional sources:
http://www.musicanddesign.com/Dipoles_and_open_baffles.html
http://www.musicanddesign.com/images/DPOB3a.gif
In a practical cardioid that limit can even be "exploited" just a bit IMO, depending on the DI of the front driver and baffle. Of course the rear source's low pass characteristics has to be adapted accordingly.
http://www.musicanddesign.com/Dipoles_and_open_baffles.html
http://www.musicanddesign.com/images/DPOB3a.gif
In a practical cardioid that limit can even be "exploited" just a bit IMO, depending on the DI of the front driver and baffle. Of course the rear source's low pass characteristics has to be adapted accordingly.
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Just one driver example (availability in the US is unknown to me):
W46-1316SM - 4x6" Paper Subwoofer - TB SPEAKER CO., LTD.
This is a long stroke design with very sturdy/damped diaphragm and small size ...
500Hz and above should be no problem due to breakup modes IMO.
If higher levels are needed: Use 2 or more.
And "if needed" even this one can be equalized to operate up to the midrange ...
https://www.parts-express.com/pedocs/specs/264-837-tang-band-w69-1042j-specifications-45667.pdf
(yes it can ...)
W46-1316SM - 4x6" Paper Subwoofer - TB SPEAKER CO., LTD.
This is a long stroke design with very sturdy/damped diaphragm and small size ...
500Hz and above should be no problem due to breakup modes IMO.
If higher levels are needed: Use 2 or more.
And "if needed" even this one can be equalized to operate up to the midrange ...
https://www.parts-express.com/pedocs/specs/264-837-tang-band-w69-1042j-specifications-45667.pdf
(yes it can ...)
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Er, no. The link you've posted is about a two driver dipole setup. But he wants a cardioid setup. For a cardioid setup you need at least 3 drivers. His intended drivers are so far 10", you're already over the critical distance. You need a LOT smaller drivers for that, probably 13cm or 10 (5"/4"). But that means even less horizontal dispersion control. It's pretty useless to have strict vertical radiation control but none horizontally.
To me just one single driver would be sufficient to make up a cardioid ... (if this is intended).
You may also have missed/skipped my "driver proposals", although that "driver question" does not seem to be the most important here:
http://www.diyaudio.com/forums/mult...ity-without-waveguides-dsp-3.html#post5091654
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That's not possible. In the bass range it might work with an aysmmetrical dipol-ish enclosure. But in the low mids that does not work, he wants up to 500Hz! The sound waves do not 'bend around' objects anymore at that frequency like they do in the bass. And that's why the two-spaced-towards-the-listener-setup does not work either, the 2nd driver is in the way of the first. That means, you have to put them up vertically. But that way you can't create a cardioid, soooo you'd have to take a 3rd driver.
Yes, I've missed that, sorry. The geometry and oval form seems to be close to ideal for such a setup, great find! The usable spl is poor though, only 80dB, at the rated 30W you can only get 94dB max. Or with the 3 speaker cardioid setup 99dB (the 3rd/inverted only provides 1,5dB, not 3). For around 150 bucks per side that's not very impressive. Don't get me wrong, the driver is very interesting, thanks for showing me, but for this application it's not exactly stellar.
Well, I'm surprised. But why aren't there any angle measurements except 0° and 90°? The simulations I've seen predict several side lobes. What driver size did he use?
Patrick, If you want some directivity up to 500Hz, I would use a dipole created with a 12" or 15" driver in a 15-20" wide open baffle, mounting the driver close to the top edge. All of the "frames" (U-frame, etc.) have resonances that prevent them from being used as higher in frequency (above their line resonance). That's why they are a "subwoofer" and not a "woofer". Of course an OB will not be able to cover the lowest octaves, e.g. down to 30Hz, at any reasonable SPL and without a huge power boost but you can't have it all...
Resistive cardioid seems like it would work fine?
I'd use waveguides above 500Hz, and I don't think dipoles are a good match for waveguides because the waveguide sends virtually no energy backwards.
My main use for such a setup, besides hi-fidelity, is the ability to watch a movie at night without waking up the family. I figure a 6dB reduction in energy to the sides and the back should allow me to listen at a louder level than I would normally be able to get away with.
You might want to re-read post #32 regarding the cardoid...
One word for you: headphones. Really, they will not wake up anyone.
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I think I f I were going to try to build a home speaker system that had midrange cardioid response from 125 to 500 I would start with a basic 2-way design with 8" (22 cm) woofer. Once I had the 2-way designed I would measure it from the rear to see what the rear response was and what needed to be canceled. Then I would add a pair of side firing drivers, inverted polarity, probably 5", to create a more or less omni directional source and delay and LP filter the side drivers as necessary to cancel the rear response. Baffle size and where the side drivers were positioned would be critical because above 500 Hz I would want to depend on the baffle/front driver to control the directivity so I could roll off the side drivers so their output would not be significant above the theoretical cardioid first peak (at f = c/4d). Thus the side drivers would not contribute to the axial response above the 1st peak and would not introduce the nulls, or at least significant dips in the axial response. There might be some smaller dips that could be compensated for by applying eq to the front driver. Since a 8" driver alone will start to be directional about 500-600 Hz I would like to get the theoretical first axial peak at around 1k Hz with the side drivers starting to roll off at about 500 as well. The LP filtering of the side drivers might be sufficient to introduce the required delay as well. And of course, the cardioid roll off would have the be equalized flat. To fill out the system a woofer of what ever design was desired could be added.
Just some thoughts. No ideal how it would actually work out.
Just some thoughts. No ideal how it would actually work out.
@ John K. btw. ,
when i klick on your username to the left of your current/last posting #39 and then select
<View Public Profile>, then i am linked to the "user's-profile" of a user called
"krikor111", which seems wrong to me.
@DiyAudio: Is there something "messed up" in the datatase ?
when i klick on your username to the left of your current/last posting #39 and then select
<View Public Profile>, then i am linked to the "user's-profile" of a user called
"krikor111", which seems wrong to me.
@DiyAudio: Is there something "messed up" in the datatase ?
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