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Old 2nd February 2007, 09:33 AM   #11
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A dipole is the worst system to create bass; phasecancellation/low efficiency/need for equalizing, reflection of antiphase sound against backwall (also cancellation), no damping of fundamental resonance.
But a tower of 10 large woofers looks cool and impressive.

Just my opinion.
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Old 3rd February 2007, 06:25 PM   #12
Calvin is offline Calvin  Germany
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Hi,

@ APi
when You can hear so distintively each source, than I assume that there is something seriously wrong with the setup. Maybe some artefacts from filtering or whatsoever. I had never had anybody complaining about that point, when listening to my system and I can´t verify it either. I think that You´re right that 1kHz is too high as crossover freq and that could create probs the closer the istening distance becomes.

@MJ
does Your opinion base on any experience at all with dipole bass??
Sure, the efficiency seems to be low on first glance, but what do You compare??? Let´s have a look at a an example:
The AudioElevation Attac400 was a dipolar sub, measuring app. 70L of volume (which was actually even less than the shipping cartonage the drivers came in!!). It featured 2 15" drivers and a ~100W amp and a passive notch-filter for the upper resonance. No further equing was necessary but could be switched in (subsonic, up to +6dB possible).
It went right down to 20Hz (16Hz with subsonic) and levelled out at 106dB @40Hz. The linearity was outstanding, as several measurements in test magazines proved.
Sonically it was the most precise bass I ever heard. It even outperformed the aktive feedback subs of Backes&Müller.
Because of its outstanding linearity it was one of the very few subs that could be set up by ear in a few minutes. Since of its distribution character it excited the room resonances much less and thus was a solution for critical rooms where nearly every other sub failed.

Now find an equally compact woofer, that is able to play that deep down, still that loud and with just an 100W amp and comparable sonic quality.

phase cancellation:
takes mainly place perpendicular to the frontal axis of the dipole, thereby reducing the influence of the roommode of that room dimension. On axis there´s nearly no loss in efficiency!

need for equalizing:
oh come on, show me an completely unequalized Box!! Each and every passive box is one and You´d probabely a great fool not to use equing in an active box too!

reflection of antiphase sound against backwall/cancellation:
aah yes, I understand ... but what about those reflections from the backwall from a monopolic radiating driver? Are those better in any wayy and don´t they cancel out at certain freqs too?

no damping of fundamental resonance:
Well, damping is inversly proportional to the Q-factor. Since the Q-factor of any driver rises when it is built into a cabinet, damping decreases. In an open baffle or dipole cabinet the Q-factor nearly remains on its free-air value, which means that the damping is in fact the highest of all possible cabinet builds!! You usually need way overdampened drivers so that -after they are built into a cabinet- the damping sinks i.e the Qt rises to the neede value!
The dipole on the other hand doesn´t rely on the cabinet to beef up its performance, but You can use drivers with the right damping/Qts-value right from the start. Even closed boxes store and release energy, BR adds another resonator. With every resonanting mechanism (energy storage) I add the sound quality becomes worse. I find it totally logic, that the system with the lowest resonator count should be the potentially best.


jauu
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Old 4th February 2007, 08:28 AM   #13
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[QUOTE]Originally posted by Calvin
[B]Hi,


@MJ
It went right down to 20Hz (16Hz with subsonic) and levelled out at 106dB @40Hz. The linearity was outstanding, as several measurements in test magazines proved.

The dipole sub you mention; whatt freq.range does it have to cover?
The problem I see/hear with dipoles is in the 100-250 Hz region, where there is a severe suckout. You can boost bass below , say 200 Hz, but this will boost the fundamental resonance too, so things are getting complicated. If heard several dipoles but im still not convinced of their sonic superiority. Now there are dipoles and ther are dipoles. and I've never heard some really large arrays as you have build, Calvin. So maybe I can be convinced some day. Till then I am continuimg to experiment with transmissionlines which, according to R. Sanders, should be one of the best, non-resonant, system to marry the ESL.
By the way, with my dipoles esls, I still had some nasty room modes, just as my omni-dynamic speakers.

By,
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Old 4th February 2007, 11:34 AM   #14
Calvin is offline Calvin  Germany
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Hi,

the sub covered from <20Hz up to ~150Hz (depending on the settings of the woofer-amp.
See the tests
Click the image to open in full size.
another freq-resonse from a different test magazine
Click the image to open in full size.

without the passive notch-filtering there would be an rising response peaking at @250Hz.
Click the image to open in full size.
Very similar curves did I get with the A-shaped dipoles using the 6.5" drivers. The main difference beeing the higher peak-freqency at 350-400Hz and a higher Fs (~35Hz).
You simply don´t have the 100Hz to 300Hz suckout like with an open baffle and You can easily shape the response to Your needs with a simple 2nd order filter or with he help of an notch-filter.

In my case the ESL-panel´s lower cutoff-freq nicely corresponded with the woofers upper cut-off. Since both drivers feature steep slopes below/above this cutoff-point, I got similar and steep acoustical filter orders. ML -and basically everybody else- had always had the prob that their panels acoustical filter curve was much steeper than their woofer´s and that made the sound ´typical´ Hybrid.

This prob also remains when using a TL. So the TL is way away from beeing the optimum partner for an ESL. There are several points in Sanders book he wouldn´t do the same nowadays, and even some minor failures. When he wrote his book, dipoles were simply not in fashion and everybody thought they couldn´t work properly because of the nasty nasty phase cancellation.
The second point is,that Sanders proposed crossover-freqs around 500Hz. You will only get that high in frequency with an openbaffled dipole to which the problem of suckout applies again. Keeping the crossover-freq below ~300Hz You can use other shapes for the dipole cabinet, thereby solving this problem elegantely as long as the ESL panel doesn´t suffer too much from its own suckout-prob (i.e. as long as the equing can be kept small).

jauuu
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Old 4th February 2007, 12:32 PM   #15
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Quote:
Originally posted by Calvin
Hi,

There are several points in Sanders book he wouldn´t do the same nowadays, and even some minor failures. When he wrote his book, dipoles were simply not in fashion and everybody thought they couldn´t work properly because of the nasty nasty phase cancellation.

jauuu
Calvin

Hi,

Are these personal assumptions or did you have some conversation with R. Sanders?
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Old 4th February 2007, 06:31 PM   #16
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I'm not sure R. Sanders would do dipole bass even today. His innersound speakers were designed and produced during a time when Linkwitz's Orion speakers showed the practicality of dipole bass.

The cost of doing dipole bass is significantly higher than a TL. and that's a real issue when trying to sell a product that is already a white elephant in the speaker world.

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Old 5th February 2007, 03:42 PM   #17
Calvin is offline Calvin  Germany
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Hi,

of course personal "assumptions", if You want to call careful reading and watching and some experience assumption
One point for eg. is, that RS obviously changed his mind about insulating the stators. I admit, I rather could have written minor flaws instead of failures. One shouldn´t forget that english is not everybodys native tounge here.

@sheldon
Yes, Your argument is right. Cost is a rather negative point about dipole basses. They need more complex cabinetry and more membrane area and should preferabely be driven actively and thus are more costly. Additionally You still have to ´convince´ people -as can be read in this thread again ;-) It´s much easier to sell the ´well known´ stuff, even if it were inferior in a certain application.
Trying selling a ESL is hard enough, selling a ESL and dipole bass is double hard.
But aren´t we talking about DIY-here, where the complexity of a cabinetry is rather a matter of effort and time and not money?

jauu
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Old 5th February 2007, 11:48 PM   #18
thadman is offline thadman  United States
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After reading my post concerning the RS390HFs and the review attributed to them...can you explain to me why they wouldnt reach 200/300hz? It would save me a LOT of money...$700-800 worth if I could simply use a line array of them to cover the midbass also.

Im not exactly sure why Roger Sanders recommends the TL. Sure it is an excellent way of reproducing the frequencies with high fidelity...but it falls miserably short in mating with the ESL.

First off its going to have lots of floor/ceiling reflections since the ESL will be operating as a line source and the TL will be operating as a point source. Second the horizontal dispersion patterns would be incredibly different. Third a line sources operates at -3dB for every doubling of distance, whereas a point source operates at -6dB for every doubling of distance.
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Old 6th February 2007, 10:45 AM   #19
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Hi,

The dercrease in loudness as a function of distance (doubling) is supposed to be 3 dB versus 6 dB for linesource and pointsource respectively. However this is based on a theoretcal model where there are no boundaries which influences the decrease in intensity. If your speaker hangs under the Eiffel tower, than 6 dB decrease/doubling distance may be a reasonable aproximation. But speakers are set up in small listening rooms where sound bounces against the wall very soon. So you won't get that 6 dB slope, in fact you will have some room gain! So the whole story of 3 dB vs 6 dB slope makes no sense in real world situations. I would like to see some measurements in real-world listening rooms which show the exact difference between linesource-dipole vs pointsource.

Another thing is that an ESL will work as a line source only if the wavelength is smaller than the height dimension. Low bass has such large wavelength compared to the seize of the ESL that it will not be beamed like the high freq. It will behave more like a (large) pointsource than a line source. So the advantage regarding room interaction in the bass region is widely overrrated while the antiphase sound only causes a lot of trouble.
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Old 6th February 2007, 01:50 PM   #20
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I agree with Dijkstra's points but wanted to add:

If a line source reaches from floor to ceiling, and if the floor and ceiling are reflective, then the line source is effectively extended in length upward and downward by the images in the floor and ceiling, ad infinitum, reducing wavelength sensitivity to a great degree. However, the side walls muddy everything up!
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