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Multi-Way Conventional loudspeakers with crossovers

Cardioid Bass
Cardioid Bass
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Old 27th April 2008, 12:36 AM   #81
Elias is offline Elias  Finland
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Default 90 degree phase shift

Quote:
Originally posted by gedlee


How do you get 90 of phase shift? This is not easy to do. Unless your amps have that "phase" control, which I was never sure did what it said it does. To get a constant phase shift at ALL frequencies is not a simple thing and likely not doable with analog.

Hello,

Relative 90 degrees phase shift between two channels is easy to do in analog domain using couple of all-pass filters set up properly. It can achieve band width of more than a decade with phase error of only couple of degrees. Analog phase shifters like this used to be popular in the 70's with Ambisonics systems.
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Old 27th April 2008, 02:59 AM   #82
gedlee is offline gedlee  United States
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But I doubt that this complexity is in a plate amp! You are talking about a FIXED 90, not a controled phase using only a pot.
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Old 27th April 2008, 07:36 AM   #83
ScottG is offline ScottG  United States
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Quote:
Originally posted by john k...

You introduce new information in new posts.
Yes.

It gets tiresome.

..Apparent Format:

1. An objection is raised.
2. See my work on (..which often requires an expenditure).
3. That response isn't worth anything.. *OR*
4. (..if the response does seem to meet an academic standard and at least initially deemed worthy), change the subject (..often with another objection).

"rinse and repeat."

(..sometimes adding in the occasional defensive posturing.)

I found it was annoying enough to warrant the "inclusion" of the forum's IGNORE LIST. Ultimately the format above is essentially doing just that - ignoring the respondent (..though in a "strung-out" manner).

BTW,

(..trying to get the topic on-track )

What about the "velocity" operation that some cardioids and dipoles provide?

What about cross-correlation ("reduction") with wavelengths that ordinarily sum? and in keeping with this..

What about side-wall ("reduction") summation.

IMO the best "contrast" to all 3 questions is with an in-wall true infinite baffle. It tends to highlight whats right and whats wrong between your standard monopole and most implementations of cardioids and dipoles.
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Old 27th April 2008, 08:25 AM   #84
FrankWW is offline FrankWW  Canada
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Scot, why don't you let Earl and John sort each other out?

They get to some interesting things and I don't really care how they get there.

You are being "tiresome". The extra personal attack is unnecessary.
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Old 27th April 2008, 08:32 AM   #85
Graham Maynard is offline Graham Maynard  United Kingdom
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But why 90 degrees - which is quadrature ?

Even when the drivers/cabinets are specified we still have significant transduction phase variation through the resonant frequencies as well; whereupon any circuitry must be driver specific.

This is becoming more complex than audio is meant to be.

Yes phase/frequency tracking filters are possible, or drivers can be used in resistively small enclosures below their imposed system resonance only, but a filter which develops a quadrature output (90 degrees represents amplitude differential in time) takes time (variable with frequency) to modify output. The waveforms/pressures are modified in 'music time' after the music event has driven the filters, and this cannot fail but to distort any eventually reproduced leading edge impulse events, as well as muddy a composite in-room response.

The same would apply when a separately boxed monopole is used to generate cardioid when the monopole waveform is filtered to phase match the output of a dipole. Only an optimum range of frequencies for the cardioid pattern can be assured, which must then become 'cottage loaf' like either side of that optimum frequency.

I cannot help become distracted by un-neccessary argument, and I think it was Earl who broached the subject that cardioid can only be LS-position-room specific.

Cardioid is no more than a balancing of figure of eight plus 2pi output to null the rear output. The rear output of a dipole is going to be completely different in an open field compared to when in a room with corner/wall reflections modifying level/phase of rear output at the very point where it these must combine and null to generate the cardioid response.

However, when the cardioid is passively generated without electrical signal mixing between a dipole and a monopole then the rear null can be physically adjusted to suit any room corner, or even a field, and I think JohnK uses his circuit for the LF amplifier crossover and corner response filtering only.
Also I believe that JohnK's 'mechanical' cardioid (no electrical filter induced leading edge distortions) is optimised for lower frequencies only, such that the response of his design gradually reverts back into full dipole operation with increasing frequency.

Maybe JohnK's cardioid dipole plus one of Earl's separately positioned bass monopoles would be an excellent working compromise ?

Cheers .......... Graham.
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Old 27th April 2008, 11:36 AM   #86
john k... is offline john k...  United States
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Well, Grahm and Earl have touched on my next question or suggestion. Earl's set up seems to consider placement, LF cut, amplitude and phase, anything else?

So, why not add source directionality to the list. Say we position 3 cardioids or dipoles so that they are at the intersections of floor/side wall, floor back (or front) wall, and side/back wall. All sources would be away form the corners and would have their axis aligned with the line formed by the intersection of the surfaces. Using dipoles, for example, since they couple strongly only to modes which propagate in the direction of the dipole axis such a set up would allow individual control of front to back, side to side and vertical modes. Cardioids would couple differently.
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Old 27th April 2008, 12:53 PM   #87
MaVo is offline MaVo  Germany
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@ John k, is there a difference in exciting all modes just as gedlee describes and your idea to controll all modes? do you mean no mode is excited with this setup? And if thats the case, what will be the difference in perceived sound? The double bass array i posted earlier also seems to want to controll the modes instead of exciting them. Maybe my question boils down to something like "Is it possible to excite no mode in a room?".

@ Gedlee, i would really like to see a closer description of your woofer setup process. intuitively i would put the woofers in the room like you described. then at first let the one in the corner play a pink noise sample at full volume and look at the rta. while the first one plays, i would raise the second subs volume until its about the same at listening position and play with the phase, until the rta shows the smoothest response and finally repeate that for the third sub. Another question would be, do you mean a simple allpass phase controll like most cheap subwoofer amps have or something more sophisticated?
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Old 27th April 2008, 02:06 PM   #88
gedlee is offline gedlee  United States
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Quote:
Originally posted by MaVo
@ John k, is there a difference in exciting all modes just as gedlee describes and your idea to controll all modes? do you mean no mode is excited with this setup? And if thats the case, what will be the difference in perceived sound? The double bass array i posted earlier also seems to want to controll the modes instead of exciting them. Maybe my question boils down to something like "Is it possible to excite no mode in a room?".

@ Gedlee, i would really like to see a closer description of your woofer setup process. intuitively i would put the woofers in the room like you described. then at first let the one in the corner play a pink noise sample at full volume and look at the rta. while the first one plays, i would raise the second subs volume until its about the same at listening position and play with the phase, until the rta shows the smoothest response and finally repeate that for the third sub. Another question would be, do you mean a simple allpass phase controll like most cheap subwoofer amps have or something more sophisticated?
John - I have said many times, but I guess that I'll say it again. Talking about directionality of the source in a frequency range of the room where the sound CANNOT travel in arbitrary directions is pointless. You can talk about LF sources in a free field or in a room, but the two things are completely different and there is no reason to believe that what happens in one will happen in the other. Thus, I think that your "test" is based on the false assumption that the free-field directivity will still hold in the closed room. It won't.

MaVo your procedure is pretty close. I am reluctant to to give a "simple" overview of the technique, but here it is (there will be some details missing and the devil is in the details). The one source (two or three actually) that has to be fixed in the room are the mains. They have to be positioned for best MF -> HF response at the seats. Thus their response, phase, and amplitudes are a given. The rest of the subs need to augment those.

Playing a noise signal I measure the sound field by spatially averaging (simply move the mic by hand over the seating area while the Analyzer averages. This give a good approximation of the power response at LF, but will not be accurate at HF (unless your analyzer can do a dB average as opposed to a spectral average). I add one sub at a time, usually starting with the lowest frequency one. I just use simple plate amps with a phase switch, gain control and LF cutoff control - nothing fancy. Try adjusting these settings until you reach the best response with the first sub and the mains all playing at the same time and the response spatially averaged.

Then add one sub at a time. Adjust the gain and the LF cutoff for best overall response and try the phase switch to see the diffrence. The phase switch should be a large difference for the first sub (pick the "better" one), a lessor difference for the second and so on. Add one sub at a time.

While this procedure cannot be proven to lead to the optimal response, it always leads to a very good response. Remember that the subs and the mains all overlap each other to some extent.

On occasion we have seen modes in the room that we just cannot get the response down at without deflating the neighboring response. In these cases some EQ helps. I have never used more than two bands of EQ and even then only less than 1/2 of the time. If you are using more EQ than this then something is wrong.

It is also possible to start all over if the end response is not as good as you think that it should be. If you end up with the same response two or three times then you have it as good as it gets and EQ is going to be required, or maybe another sub.
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Old 27th April 2008, 02:51 PM   #89
MaVo is offline MaVo  Germany
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Thanks for the long response. It sounds pretty straight forward and i hope the devil of the details can be tamed with more iterations of this process.
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Old 27th April 2008, 03:15 PM   #90
gedlee is offline gedlee  United States
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Quote:
Originally posted by MaVo
Thanks for the long response. It sounds pretty straight forward and i hope the devil of the details can be tamed with more iterations of this process.
Its obvious that the above procedure could be automated and improved by just taking transfer functions from each source to the listening positions. Then the computer picks the best settings. This is what I had hoped to do some day. A computer with sound card and a mike would be all that was required. Everyone has these tools these days.
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