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Multi-Way Conventional loudspeakers with crossovers

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Old 19th June 2007, 05:07 AM   #1121
Pano is offline Pano  United States
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Hey guys.
I'm glad the Horn Honk thing caught your interest - but woudn't it be better to discuss it over in This Thread?

There seems to be enough going on here, already.
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Old 19th June 2007, 07:23 AM   #1122
Salas is offline Salas  Greece
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Default Opinion on Gunness work?

Would you like to comment on Gunness Mr. Geddes? EAW approach
Would be interesting.
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Old 19th June 2007, 07:54 AM   #1123
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Getting back to the topic of OBs with previously stated objectives....

Quote:
Originally posted by Lynn Olson
As mentioned earlier, the simplest - and most compact - way to realize the MB/B is a single 21" driver. The biggest drawback of the 21" is poor response above 200 Hz, since these are designed as subwoofers, not woofers, and certainly not midbass drivers. This implies a steeper slope for the LPF for the 21", making integration with the WR driver a bit more challenging, not to mention side issues of different driver colorations.
Do you think that an adequatley chosen 21'' could deliver proper dynamics / linearity down to -- say -- upper mid 30s without the need of a sub ? Can the WR integration and driver coloration be addressed by e.g. proper driver selection ?

I am thinking about the aforementioned 21LW1400 physically decoupled from the OB and driven by a plate amp with a 4th order LR LPF set to about 200Hz. Suggestions for other readily avail 21'' highly appreciated (the Executioner-X21 sure looks nice, but sadly unobtainum for those on the other side of the pond).

Lynn, I know you stated in the beginning of this thread -- and multiple times after that -- that the last two octaves would be driven by a Rythmik or similar sub, but such less ambitious design variant might appease the "middle of the road" crowd with smaller rooms, smaller budgets and lower SPLs reqrmnts...

That is, in case you care about them / such a design offshoot, of course...
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Old 19th June 2007, 09:02 AM   #1124
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It's a pretty simple allocation between dynamics vs bass depth. To expand a bit (I'd illustrate this if my big G5 computer were up and running, but it is still awaiting repair), a closed-box monopole speaker has a 12 dB/octave increase in excursion vs frequency - above Fs. It's this area-under-the-curve that limits dynamics and creates the majority of the IM distortion we have to contend with.

The situation is a bit worse with dipoles - in the region between the 1/f transition and Fs, in an equalized, flat-response system excursion increases at a 18 dB/octave rate, not merely 12 dB as it is with a monopole.

The area under the curve is much greater than a monopole, and this limits dynamics and creates more distortion. The only cure is more surface area - and more Xmax, and lower distortion, don't hurt. But the biggest useful gain is in simple surface area, since it doesn't require extremely long voice coils, exotic magnetic drive, and associated lowered efficiency.

One extreme is the Bastanis, with a very high crossover (220 Hz) to a monopole bass unit. Linkwitz leans on equalization, amplifier power, H-baffles, and the lowest-distortion drivers he can find. One corner of the triangle that hasn't been as well explored is a large amount of surface area that also takes full advantage of the floor image.

The key point here is the spectral distance between the lower frequency limit (of the dipole) and the 1/f transition frequency. The greater this distance, the more surface area and/or equalization is going to be required. No free lunch here.

If the baffle is big enough for a movie theater, the 1/f frequency essentially becomes low enough to treat the speaker as an infinite baffle - literally, wall-sized. If the baffle is this petite, decorator-friendly little thing, well, it's going to need an awful lot of equalization, or a very high subwoofer crossover frequency.

Equalization has the terrible drawback of tremendous driver excursion, many times worse than an equivalent monopole system, There are very real limits to what can be achieved with exotic low-distortion drivers, or even servo feedback.

Equalized H and W-baffles increase the effective baffle size, but at a cost: restricted bandwidth, since the H and W-baffles suffer from the same annoying box modes - as well, a box, a monopole. Linkwitz sidesteps this by sharply restricting the bandwidth of the H-baffles so they cut off before reaching the first mode. If you want a compact dipole speaker with any degree of LF extension, I can't see any other solution than a narrow-bandwidth, equalized, H or W-baffle. A Linkwitz system, in other words.

The same tradeoffs are on the horn side of the fence, too. A truly low-excursion, high-dynamic deep-bass horn is the size of a single-car garage. The more typical approach transitions to a direct-radiator driver anywhere between 200 and 800 Hz, depending on whether there are midbass horns or not. A big speaker like the Klipschorn takes advantage of the room corners to expand the mouth size, and operates the bass horn right through the cutoff region.

It's not very pretty: big baffles, big cone area, big horn size, or smaller sizes and more amplifier power (and more excursion in direct proportion). The old AR-1W vs Klipschorn or E-V Patrician tradeoff.

Dipoles make this tradeoff worse, not better. It's Hoffman's Iron Law with an extra twist. At some point you have to stop swimming upstream and turn around. The "turn-around" is a subwoofer of some type, either heavily equalized W-baffles or less heavily equalized monopoles.

Our friend johninCR has come up with a novel, transitional solution, combining a partial open-baffle with something like a TQWT. A split-path rear wave, in other words. No measurements so far, but he reports good results.
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Old 19th June 2007, 09:32 AM   #1125
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Quote:
Originally posted by gedlee


Well thats enough "lecturing" for tonight.
But genuinely appreciated by yrs truly.

A vivid demonstration that horn theory has plenty of controversy in it, seventy-plus years after the first theater and studio-monitor horns. It also says volumes about the sound quality of contemporary constant-directivity horns in movie theaters. I'm enough of an old-timer to prefer the sound back in the Todd-AO 70mm mag-track days.
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Old 19th June 2007, 12:01 PM   #1126
Paul W is offline Paul W  United States
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Earl,
What is your preferred method for identifying -and measuring- HOMs?
Thanks,
Paul
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Old 19th June 2007, 12:38 PM   #1127
gedlee is offline gedlee  United States
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First - The Gunness approach is interesting, I've read this before. The measurements get my attention the most as they do seem to show an effect that I would say could well be HOM. But I disagree that HOM can be controlled with DSP. The manner in which this is suppossedly done is not at all apparent from the write-up which is much more of a marketing document than an engineering one. EAW has never really done an engineering description of this technology.

Second - I don't have a tried and true way of measuring the HOM, but I do have a very good handle on how they are generated and hence what one can do in the design to minimize them. I have focused on minimizing them. Theoretically, the HOM would not be readily apparent in the frequency domain, but should be in the time domain, i.e. the impulse response. This is in essence what Gunness has done - looked at the frequency domain in time slices (also known as time-frequency analysis in the literature) - another form of waterfall plot, but with much better resolution in time and frequency. Resonances and HOMs will both appear as time delayed signal content, but will difer in that resonances will be minimum phase while HOMs will not. I am not sure that this difference would be readily apparent in the Gunees plots or if it is even important. I have found that a properly designed waveguide and driver (with foam plug), properly EQd, will have an almost perfect impulse response (actually a doublet since there cannot be any LF content) at any angle with virtually no tail - a very compact impulse response in time.
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Old 19th June 2007, 01:20 PM   #1128
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Quote:
Originally posted by Lynn Olson
One extreme is the Bastanis, with a very high crossover (220 Hz) to a monopole bass unit. Linkwitz leans on equalization, amplifier power, H-baffles, and the lowest-distortion drivers he can find. One corner of the triangle that hasn't been as well explored is a large amount of surface area that also takes full advantage of the floor image.
IMHO a notable omission from that list is John Kreskovsky NaO speaker with the damped U-frame woofer. His study on the interaction btw dipole bass and in room response was a real eye opener for me, together with the problems in attempting to presurize a room below the room fundamental.

Unfortunately it seems that one has to accept the back side of the OB coin, just like you detailed (thanks again)

Quote:
Our friend johninCR has come up with a novel, transitional solution, combining a partial open-baffle with something like a TQWT. A split-path rear wave, in other words. No measurements so far, but he reports good results.
John's waveguides definitively match the "think outside the box" approach of this thread... Looks promising.

Again, thanks for the input. Best regards and a speedy recovery (we are all eagerly waiting for the first builds, afterall...).

Florian
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Old 19th June 2007, 01:28 PM   #1129
gedlee is offline gedlee  United States
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I did an AES paper on the subject of monopole, dipole and cardiod responses in rooms You can see it in the journal some years back.

The paper referenced above must be in error since it shows a flat response to DC from a dipole. This is not possible as the front and rear radiation must cancel and hence the DC response must go to zero. I am surprised that this was missed.
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Old 19th June 2007, 02:54 PM   #1130
kevinh is offline kevinh  United States
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IIRC this project is basically a knockoff of the Orion John starter putting some damping materials on the mid-hi panels, it seems he is trying a different woofer arrangement than the H used by Linkwitz.

I don't think he adds anything beyond what Linkwitz does on his site.


This thread is a lot of fun to follow. Building on what Linkwitz does and developing a High Efficiency OB that used cone area instead of EQ is very interesting.
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