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Multi-Way Conventional loudspeakers with crossovers

In Pursuit of a 20-20k Dipole Loudspeaker
In Pursuit of a 20-20k Dipole Loudspeaker
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Old 2nd January 2019, 05:09 PM   #11
John Busch is online now John Busch  United States
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Charlie, interesting negotiating point! Let me think about it!!
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Old 2nd January 2019, 06:25 PM   #12
Gerrit Boers is offline Gerrit Boers  Netherlands
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Directivity and other measurements of the B&G Neo10 can be found in the thread on my 'Totem of Tone' dipole system.
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Old 2nd January 2019, 07:34 PM   #13
CharlieLaub is offline CharlieLaub  United States
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Originally Posted by Gerrit Boers View Post
Directivity and other measurements of the B&G Neo10 can be found in the thread on my 'Totem of Tone' dipole system.
Yes, I have read over your project. It's a great build and you got pretty much everything right. Nice job! You also figured out (via measurements) the problem(s) that arise when you start to add wings to a driver in an effort to reduce the low frequency dipole losses.

I think the post below taken from that thread captures a lot about why I am also striving for dipole and CD behavior over as much of the audio range as possible:

Quote:
Originally Posted by Gerrit Boers View Post
So, was it worth the effort? Yes, definitely yes! Iíve been listening to this system for over 6 months now and I havenít yet detected anything problematic, as far as Iím concerned it is a blameless loudspeaker. The nearly constant horizontal directivity and perfect dipole symmetry (at least above 400Hz) results in an exceptionally focused and stable stereo image. Because the system is so narrow at the top it also does not stand in the way of itís own back-wave reflection, I think this is very important for a dipole. A wide baffle will cast a shadow so to speak which will make it possible for your auditory system to (more easily) detect its position.

Yes, the system is horribly inefficient but the amplifiers and power supplies are all very efficient so the total power consumption in rest is just above 100W which is not bad for a system with a peak power of well over 3kW. The enormous peak power capability does provides horn like dynamics and ease of presentation. The operating temperature is somewhere between 30 and 40 degrees Celsius depending on output power. The system is very, very quiet, you have to press your ear against the Neo10 to be able to hear a faint noise. No hum, no clicks, no pop or crackle. The system is also free of any mechanical noise (humming or whistling).

So whereís the catch? Well, it wonít do an orchestra at full concert level despite the enormous amount of power available. The maximum SPL I measured on the my listening couch (3m distance, with acceptable distortion) was about 103dB which is more than enough for me and it also is enough for SMPTE RP 200, 83dBSPL average at the listening position with 20dB headroom (83dBSPL = -20dBFS). The limited vertical dispersion requires a minimum listening distance of 3m for proper integration of low,mid and high frequencies and sufficient high frequency dispersion. The system is certainly not child or pet proof and I would expect the WAF to be close to 0. And then thereís the cost, this particular implementation with the AT drivers and Ncore amps is very expensive but even with other amps and drivers this kind of system will never be cheap.
I noticed that you mentioned that the system is inefficient. I am trying to avoid this problem in my own systems by (A) using high sensitivity drivers such as pro audio woofers when possible and (B) using drivers close to their dipole peaks so that they are used where they are most efficient. To do this I need to construct a 3-way dipole plus a separate subwoofer for frequencies less than 100Hz. My 2017 nude 3-way test system was plenty loud (although I did not measure the SPL level), so I think I am on the right track.

I would not say the "WAF is near zero" as you claim. There is only so much WAF for these kind of systems, and they are DIY after all. I am a terrible wood worker and lack both tools and talent, but I can do basic cutting and routing. Luckily I don't need to do much of that sort of thing, but this leaves me with some basic wooden "frame" and drivers dangling by wires. I would say this provides much less WAF that you own effort!
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Old 2nd January 2019, 07:50 PM   #14
augerpro is offline augerpro  United States
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Aurum Cantus AST2560 is a fantastic tweeter to run fully dipole.
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Old 2nd January 2019, 08:21 PM   #15
John Busch is online now John Busch  United States
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The OB efficiency topic is always interesting.... And we are talking below 80 Hz. What sets final efficiency is based on what frequency, effective cancelation path distance, and to some extent, the woofer or woofers used.

Before we design anything, we need to set the woofer panel dimensions. After that, how low do we want or need to go before roll off begins. And how loud to we need to play where the roll off begins. The laws of physics take over and we have an answer. We may not like the answer, but we will have one. Passive, dsp, whatever it does not mater. The key element of the three above, is the path difference and that is more or less set by the baffle dimensions.

So, Charlie, what are your maximum baffle dimensions. Face & wing depth?
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Old 2nd January 2019, 08:40 PM   #16
Scott L is offline Scott L  United States
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In Pursuit of a 20-20k Dipole Loudspeaker
Default Finally !

Bravo !
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Old 2nd January 2019, 09:00 PM   #17
CharlieLaub is offline CharlieLaub  United States
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Quote:
Originally Posted by John Busch View Post
The OB efficiency topic is always interesting.... And we are talking below 80 Hz. What sets final efficiency is based on what frequency, effective cancelation path distance, and to some extent, the woofer or woofers used.

Before we design anything, we need to set the woofer panel dimensions. After that, how low do we want or need to go before roll off begins. And how loud to we need to play where the roll off begins. The laws of physics take over and we have an answer. We may not like the answer, but we will have one. Passive, dsp, whatever it does not mater. The key element of the three above, is the path difference and that is more or less set by the baffle dimensions.

So, Charlie, what are your maximum baffle dimensions. Face & wing depth?
That's a good approach. I have a sligthly different, but related one. It's explained HERE under "Load That Bass" but I will repeat the essence of it now.

I use an H-frame subwoofer. I would like this to go as "low" as possible and this in turn means I want the front-to-back pathlength to be as long as possible. But how long is "too long"? In an H-frame, a resonance forms in both front and back tunnel. It's a 1/4 wave resonance, and it forms a null. Given where I know the woofer (the driver in the band above the H-frame subwoofer) can play (down) to in frequency, I choose the length of the H-frame so that the response is just starting to turn down into the null at the frequency where I want to cross over to the woofer. Then I can use that as part of the H-frame low-pass function. Make the H-frame any deeper/longer and the null would move down into the H-frame's desired passband. This also gives me as much air loading as possible on the H-frame's driver and as I mentioned it helps to raise Qts and lower Fs.

So that's the basic approach I use. I end up with H-frames that are, front to back, around 24-36". I use an 18" woofer in the H-frame and the height and width is also around 24". This keeps the aspect ratio of the tunnels around 2:1 length to width, which helps to keep the Q of the 1/4-wavelength resonance down to a reasonable value. This kind of structure is getting a bit large, so I use one central H-frame and then I can use the top for my amp(s) and other gear. It's like a big table. You can put a granite top on it if you want it to look fancy - some weight to the H-frame is not a bad idea to counteract the force from the cone movement.
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Last edited by CharlieLaub; 2nd January 2019 at 09:21 PM.
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Old 2nd January 2019, 10:17 PM   #18
John Busch is online now John Busch  United States
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OK... Would you consider a 1% (92 dbw) a usable half space efficiency target assuming a 23"-25" net baffle width and a max effective overall depth (path difference) of approximate 15"-16"?

Also will assume 107 db clean output at or above 28-30 Hz half space per speaker would be low enough and loud enough to qualify as a full range residential speaker? At 32 - 33 Hz we can produce 1 acoustic watt per speaker, (109 db/mtr forward radiation) again in residential half space. At 20 Hz a pair can still reach 100 db. Those last 12 Hz (from 32 Hz to 20 Hz) are a real output killer! This I have built before.
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Old 2nd January 2019, 10:35 PM   #19
scottjoplin is offline scottjoplin  Wales
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There's no advantage to using dipoles where room modes can't exist? THOR - subwoofer
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Old 2nd January 2019, 11:01 PM   #20
CharlieLaub is offline CharlieLaub  United States
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The situation is not as cut and dry as it once seemed. Even at very low frequencies, dipole bass is still palpable as long as the dipole source can deliver the desired SPL target. As John Busch mentions above, getting below 30Hz or so is a real challenge...

Let me as you this: does Linkwitz's ultimate loudspeaker, the LX521, have a dipole source in the lowest band? That should tell you something. He was working on the Thor many years before the LX521 came along.
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