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Old 11th December 2012, 08:01 PM   #1221
mortron is offline mortron  Canada
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Originally Posted by StigErik View Post
All dipoles have an upper frequency limit where they no longer behave any good; the dipole peak. XO should be at or below the dipole peak if you want good polar pattern and frequency response. The peak is where the front and rear radiation sum in-phase, and is determined be the front-rear distance.

There is no "resonance" in the H-baffle itself, just a response peak (the dipole peak actually). The peak is more pronounced with a H-baffle than with a flat baffle.

A dipole covering up to 6-800 Hz would need to be small, and not at all suited for bass.... you should prepare for a 3-way.
StigErik, what is the dipole peak of a given driver? Do you need to model it, or can it be derived through using some combination of TS parameters? I am planning some open baffles, and am trying to figure out how the dipole peak variable can be addressed in my design. I understand that we want to crossover at this point or have it outside of the band we are utilizing. Is that correct?
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Old 11th December 2012, 09:01 PM   #1222
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I'm not Stig but I've been playing with dipoles for a while now. The peak is determined by the baffle the driver is on (or the driver itself if no baffle). I usually figure on good dipole response up to the freq dictated by the baffle (or driver) width. A 10" wide baffle works out to 1350hz (speed of sound is 13500 in/sec, so 13500/10=1350). In practice the peak comes out lower than that. This is roughly where the driver begins to "beam" and dispersion narrows considerably compared to below the dipole peak.

The Edge baffle simulator is good for simulating baffles: Tolvan Data

It's desirable to use a dipole driver below the peak if constant directivity is one of the your goals for speaker design. There are many open baffle speakers out there that don't follow this and they make people happy too
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Old 21st December 2012, 08:24 PM   #1223
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Originally Posted by sendler View Post
This was an interesting thread that didn't get the interest it deserved. He is using a unique test signal/ analysis to study room modes where he eventually found that a dipole line has measured advantages up into the midrange.
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Measured monopole and dipole room responses
.
I sure resurrected this thread which had intense arguments and posters included Dr. Geddes and JohnK of Nao. No real conclusion at the end..which is unexpected as the dipole bass was "supposed" to win on the measurements too.
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Old 22nd December 2012, 06:30 AM   #1224
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Yeah, that was a "my d*ck is bigger than yours" kind of thread.... too bad.
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Old 22nd December 2012, 09:50 AM   #1225
Rudolf is offline Rudolf  Germany
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Originally Posted by soundaatma View Post
I sure resurrected this thread which had intense arguments and posters included Dr. Geddes and JohnK of Nao. No real conclusion at the end..which is unexpected as the dipole bass was "supposed" to win on the measurements too.
There can't be one "real" conclusion. It depends too much on the individual room situation. There are room proportions and listening situations where "monopole" will be the clear winner and others, where "dipole" will be the best solution. We shouldn't think of "monopole against dipole" bass concepts, but simply of distributed point sources with whatever polarities or positions that suite the room best.
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Old 22nd December 2012, 01:55 PM   #1226
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Originally Posted by Rudolf View Post
There can't be one "real" conclusion. It depends too much on the individual room situation. There are room proportions and listening situations where "monopole" will be the clear winner and others, where "dipole" will be the best solution. We shouldn't think of "monopole against dipole" bass concepts, but simply of distributed point sources with whatever polarities or positions that suite the room best.
This makes more sense then anything I have read here. Cheers.
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Old 22nd December 2012, 04:48 PM   #1227
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Default Best of both worlds...

Quote:
Originally Posted by Rudolf View Post
There can't be one "real" conclusion. It depends too much on the individual room situation. There are room proportions and listening situations where "monopole" will be the clear winner and others, where "dipole" will be the best solution. We shouldn't think of "monopole against dipole" bass concepts, but simply of distributed point sources with whatever polarities or positions that suite the room best.
From my own experiments with dipole and monopole bass, and works of SL and MJK, postings by Dr. Geddes and many others, I guess that it is a combination of both dipole and monopole that provides the most bang for the buck, in every room.

Distributed multiple monopole sources for the lowest frequencies from
10-40hz does not seem to have any drawback compared to dipoles, sound quality wise. However using dipoles in this frequency range needs huge space, equalisation, amplification and resultant expense.

From 40-200 hz, a MJK style H-frame with large high Qtc woofers (like the inexpensive eminence alpha 15), needs no bass equalisation and definitively 'sounds' better to my ears than every monopole I have tried, sealed or ported. Having dipole bass in this range also allows for a seamless transition to a dipole arrangement of drivers for the range above 200Hz.

Higher than 200 Hz a dipole on the thinnest baffle (or no baffle) with a small amount of low end bost, like StigErik seems to be the obvious choice for most.

In huge rooms dipole bass "may" have some benefit as low as 30 hz and in very small rooms, dipoles may loose their radiation benefit a lot higher than 40Hz compared to monopoles.

So at the end, a dipole above 40Hz and monopole multiple subs below 30-40Hz seems to be best of both worlds IMHO.

Last edited by soundaatma; 22nd December 2012 at 04:57 PM.
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Old 22nd December 2012, 10:46 PM   #1228
Rudolf is offline Rudolf  Germany
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Originally Posted by soundaatma View Post
From my own experiments with dipole and monopole bass, and works of SL and MJK, postings by Dr. Geddes and many others, I guess that it is a combination of both dipole and monopole that provides the most bang for the buck, in every room.
That is exactly what I'm saying too.

But you go on with too much thinking in boxes and baffles, imho. If you feed a monopole next to your listening position and another monopole at 3.4 m distance from you with the same sound signal, they will work as a perfect dipole at 50 Hz for you. At another position, distance and frequncy they will act as a cardioid for you.

One could say that the optimal placement of some distributed monopole bass sources in a room provides the best ratio of omnipole, dipole and cardioid behaviour - hopefully leading to the best sound.
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Old 23rd December 2012, 12:59 AM   #1229
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That is exactly what I'm saying too.

If you feed a monopole next to your listening position and another monopole at 3.4 m distance from you with the same sound signal, they will work as a perfect dipole at 50 Hz for you. At another position, distance and frequncy they will act as a cardioid for you.

.
You are right
Never thought multiple monopoles with different phases and delays will be like a combination of dipoles, cardioids..

very similar to the DBA concept actually !!
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Old 23rd December 2012, 07:48 AM   #1230
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For a time I tried this: dipole 3-way with closed box subwoofers. I did not manage to integrate the subs properly, regardless of crossover frequency. They just sounded different than the dipoles.
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Last edited by StigErik; 23rd December 2012 at 07:51 AM.
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