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Old 27th May 2017, 12:11 AM   #11
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Originally Posted by ICG View Post
The driver got a very low spl (82dB), a very high Mms (230g), a huge Xmax (15mm), low EBP (57,4). For a front loaded horn it got ideally a high spl, low mms, medium xmax, high EBP; that's a car-subwoofer for very small BR or sealed enclosure. There are a lot of problems, the horn does not nearly get you as much spl as a direct radiating (non-horn) driver would give you, you can't get back 15-23dB spl advantage with power. And the power is the next thing, this driver depends on the excursion for cooling - but in a horn it does not do that, the horn greatly reduces the excursion. That means, you can't neither use the maximum power nor the excursion at all because the ends of the voice coil are burning up with a lot lower power than the drivers are rated.

An Eminence DELTA PRO 10MR-8 or a B&C AMX 250 (or others at the same price range) would perform a lot better in a front loaded horn.
Click the image to open in full size.

Actually the blue line in this image is the frequency and phase response of an Alpine SWS-10D2 in a front loaded horn. I had it in my car for about a year, and now it's the subwoofer in my office. (Too much is never enough!)

The Alpine utterly obliterates the B&C and the Eminence in output because it has so much displacement. Eminence or B&C would be a good choice if you have a small amplifier, but if you're bringing a big amp you're going to want a lot of xmax, and the Alpine has more displacement than SIX of those B&C woofers!

In engineering, there's no free lunch, and the efficiency of the Eminence and B&C woofers both come with a penalty : very very low xmax. (The Eminence xmax is 1.4mm!)

If anyone wants to know about Alpine and their unbelievably cheap woofers, read this : http://www.diymobileaudio.com/forum/...5-post105.html

Last edited by Patrick Bateman; 27th May 2017 at 12:15 AM.
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Old 27th May 2017, 10:04 AM   #12
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This guy - Horst Möller - uses 2 separate driver/horn arrangements in some of his designs, which are folded into one enclosure.

In the measurements of his "Kornett" (look at the electrical impedance curves especially) it is shown, that the horns of different lengths impose a varying mechanical impedance on the moving diaphragms of their respective drivers, which leads to

- differently (rippling) VC velocity over frequency and thus to
- differently (rippling) electrical impedance

kornettmess


However Horst Möller tries to have these ripples in the two horns (opening quarterwave pipes) to be "complementary" to each other in some ways, to get somewhat closer to a more resistive behaviour "of the whole arrangement" when ciruiting both drivers in parallel ... by doing so, the driver (of one of the two horns/pipes) seing higher mechanical impedance (and lower excursion) at a certain frequency will tend to draw more current from the amplifier (because of lower back EMF and lower eletrical impedance at that certain frequency range ...).

"True" resistive behaviour (at the acoustic/mechanical side of the transducer using horns and the like) can otherwise only be achieved by a "true horn" having sufficient mouth area. But of course that "stagger tuning" trick (Host uses) does not substitute/compensate (fully) for the efficiency (by impedance transformation) of a "true horn" having sufficient mouth area to be called "a horn" ...

Nevertheless it can be seen clearly, that varying/rippling acoustic/mechanic impedance of such "pseudo horns" (having small mouth area and resembling quarterwave pipes in fact) is a reality, and such are resulting issues (ripple) in frequency response of the sound pressure and phase.

Horst has IMO built a kind of "demonstrator" - if we like - to these effects and his measurements are not the typical "smoothed" ones, that we are used to see at some commercial manufacturers ...

Of course we know, that even quarterwave desings can be made smoother in impedance, e.g. by circumventing some of the lower order resonances by placing the driver with offdet to the closed end and/or heavily stuffing the enclosure ...
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Last edited by LineArray; 27th May 2017 at 10:34 AM.
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Old 27th May 2017, 10:58 AM   #13
ICG is offline ICG  Germany
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Originally Posted by Patrick Bateman View Post
Click the image to open in full size.

Actually the blue line in this image is the frequency and phase response of an Alpine SWS-10D2 in a front loaded horn. I had it in my car for about a year, and now it's the subwoofer in my office. (Too much is never enough!)
That's a horrible response, even that smoothed-to-death. One-note-sub in horn minor. The horn doesn't even load below 55Hz, all there comes is from the driver alone.

Quote:
Originally Posted by Patrick Bateman View Post
The Alpine utterly obliterates the B&C and the Eminence in output because it has so much displacement. Eminence or B&C would be a good choice if you have a small amplifier, but if you're bringing a big amp you're going to want a lot of xmax, and the Alpine has more displacement than SIX of those B&C woofers!
In your example you've chosen 85Hz. These PA drivers reach 118dB there at ~100W (no horn). With the Alpine you need 2kW to reach the same spl. But the Alpine's only rated for 500W, which makes it only 109dB. And then the power compression eats up ~2,5dB of that. And we've not even talked about distortion there. So no, that's not happening here, you can't compensate that with power. That ofcourse changes if you go down to ~30Hz but you'll have problems with cardioid radiating pattern there anyway. If that's not just a hypothetically setup.

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Originally Posted by Patrick Bateman View Post
In engineering, there's no free lunch, and the efficiency of the Eminence and B&C woofers both come with a penalty : very very low xmax. (The Eminence xmax is 1.4mm!)
That's right, you don't get anything for free. If you want a high spl, you have to use more efficient drivers except for in-car or other very small rooms that have the compression chamber effect. But that's not where you can use cardioid anyway. Besides that, I suggested these for a comparable horn, but there are still other drivers which got a lot better spl and similar excursion which still make 15-18dB more (at one W).

But let's set that aside for a bit. I probably misunderstood what your intention is. What exactly are you trying to achieve? Theoretical or real setup? What's the location? Room, venue, open field? What sound levels are needed?
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Old 27th May 2017, 11:13 AM   #14
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If you want to establish e.g. a cardioid radiation pattern by using two pressure sources at a distance, there has to be a constant group delay between that two sources, which has to match the effective acoustical pathlength between that sources.

It is not possible to achieve such a constant (over frequency) GD using undamped (and thus resonating) pipe structures (unless maybe electronically compensating for that in the input of the two sources).

As we learn e.g. from John Kreskovsky, even an undamped U-Frame will not exhibit such a desired cardioid radiation pattern due to her group delay being non constant and also (in part of the frequency range) turning negative. The outcome is a radiation pattern looking more like a dipole, because that undamped structure simply fails to provide that group delay needed in a sufficient and constant manner.

To achieve that, the U-Frame has to be damped, and we end up with a design similar to the well known "resistance box", that can provide such a rear sound source having fairly constant (and pathlength matched) group delay (*).

U-Frame description by John Kreskovsky:

DIY-dipole-1



_____________

(*) The alternative approach to cardioid is to use a rear driver, which is electronically delayed and low pass filtered.
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Last edited by LineArray; 27th May 2017 at 11:16 AM.
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Old 27th May 2017, 11:18 AM   #15
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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. Click the image to open in full size.

I'm not clear in what you are trying to accomplish. Certainly not wide band constant directivity.
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Old 27th May 2017, 11:19 AM   #16
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Patrick had a good idea on the very beginning but this thread as always got derailed into useless examples. You will do your best making two sealed boxes and applying all-pass filter into rear driver and cardioid pattern "pops out" from nowhere. Unfortunately it will be only in your "sims" and in your imagination becouse clever DSP work and enclosure craftmanship further is needed in order to precisely match rear and front drivers response at the specified distance at the back of loudspeaker in order to reach at least 10dB of rear attenuation. What is more, cardioid ends where the distance between drivers is greater than half length of sound wave of design frequency. Divide it by three and you will meet the other side of your real-world cardioid problems where efficiency of this arrangement goes so low that you need to pump another 10dB of gain to this system which results in distortion and power loading rise. When you do common enclosure you deffinitely will avoid much of counter-pressure of air compliance inside but another DSP gymmnick will be necessary in order to compensate crosstalk between drivers reproducing different phase signal in same air inside.

Yes but it is doable with small boxes and sufficient linear volume displacement available.

Last edited by Windforce85; 27th May 2017 at 11:23 AM.
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Old 27th May 2017, 11:47 AM   #17
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Yes but it is doable with small boxes and sufficient linear volume displacement available.
To have compact dimensions is helpful here - as you described - to keep the pathlength short enough for the desired radiation pattern, if the goal is to extend that pattern into upper bass (or even lower midrange) without lobing.

However the DI of the front source (driver and front baffle) also increases with frequency in itself, which has to be accounted for in the low pass filter for the rear source.

On the other hand an (effective acoustical) pathlength being too short will lower the efficiency (of radiation) at the lower (frequency) end, thus calling for increased displaced volume of the sources.

Planning a practical cardioid woofer indeed needs a detailed specification and a "well balanced" and consequent design due to that details.

This thread shows an approach to a cardioid (like) woofer system designed primarily for the frequency range of 60Hz to about 500Hz. The "pattern control" is implemented here without DSP by purely acoustic/mechanical means, nevertheless an equalization of the woofer (as a whole) is needed (and applied) in practical operation.

http://www.hififorum.at/showthread.php?t=8016

It is based on the classical "resistance box" principle described by Kalusche 1950, but with some refinements, as there are e.g. internal "compensation chambers" decoupling from the main chamber in order to have the effective compliance of the enclosure slightly rising toward upper bass and midrange ... to give the rear sound source (madeup by a flow resistor) the desired low pass characteristics, which tends to be too steep otherwise in upper bass with the "overall" dimensons of the system chosen.
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Last edited by LineArray; 27th May 2017 at 12:16 PM.
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Old 27th May 2017, 12:23 PM   #18
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Yes, directivity match between cardioid phase-forced pattern and natural pattern resulting from driver and enclosure itself is critical part of design chain and the place where all DIY works fail at the attempt. Proper driver and enclosure dimensions are related strictly to reproduced frequency range as well as distances and radiation angles between them. Diffraction-controlled enclosure shape is also important becouse you want your wavefront to travel smoothly from driver to driver. Kii Three is for now one and only example of how it should be properly done (Beo90 too but there are powerful FIR arrangements involved and it is like killing the flea with hammer).

All bass drivers in Kii work in common air compliance and every filter slope is just 24dB/oct acoustical LR4. All filters are minimum phase what is remakable. After phase linearization with non-casual inversed all pass true wavefront coherency at the front is recreated. This is relatively easy to understand and even to simulate, but nowhere as easy to build. I have been working on this subject for over two years without any bigger success.

Below you can see directivity magic with only LR4 and all-pass IIR filters used... The direction is good but results aren't perfect still and driver/ways complication is higher than in Kii. And remember, these are only "sims"...

Click the image to open in full size.
Click the image to open in full size.

Last edited by Windforce85; 27th May 2017 at 12:36 PM.
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Old 27th May 2017, 12:27 PM   #19
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Originally Posted by LineArray View Post
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It is based on the classical "resistance box" principle described by Kalusche 1950, but with some refinements, as there are e.g. internal "compensation chambers" decoupling from the main chamber in order to have the effective compliance of the enclosure slightly rising toward upper bass and midrange ... to give the rear sound source (madeup by a flow resistor) the desired low pass characteristics, which tends to be too steep otherwise in upper bass with the "overall" dimensons of the system chosen.

Correction (sorry):

The compliance (provided by the cabinet) is gradually lowering ("stiffness" is increasing ...) here with frequency rising.
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Last edited by LineArray; 27th May 2017 at 12:49 PM.
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Old 27th May 2017, 12:41 PM   #20
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Projekt: Kardioid Haupt-LS - HiFi Forum

It is based on the classical "resistance box" principle described by Kalusche 1950, but with some refinements, as there are e.g. internal "compensation chambers" decoupling from the main chamber in order to have the effective compliance of the enclosure slightly rising toward upper bass and midrange ... to give the rear sound source (madeup by a flow resistor) the desired low pass characteristics, which tends to be too steep otherwise in upper bass with the "overall" dimensons of the system chosen.
Great link and also Dutch&Dutch uses same principle but using internal reflection from the enclosure - reflected wavefront travels back to the driver membrane effectively pumping up the compliance at the higher band. This trick boosts rear atenuation up to 20dB broadband (at least 3 octaves) by only passive mean! Resistive box and giant horns are two only ways to achieve cardioid w/o DSP. Every other attempt will fail.

Last edited by Windforce85; 27th May 2017 at 12:43 PM.
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