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Multi-Way Conventional loudspeakers with crossovers

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Old 25th May 2007, 09:11 PM   #881
Pano is offline Pano  United States
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Old 26th May 2007, 07:57 AM   #882
mige0 is offline mige0  Austria
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Default Re: hyper-vivid tonality

Hi

Quote:
WRT the nonlinearity of air: not sure if this is a factor. IIRC it leads to distortion in sealed boxes, via addition of 3rd harmonics. And seeing how compression driver manufacturers like to claim if the 3rd harmonic is well behaved it must also be an issue there. But, 3rd harmonics would rather indicate a compression effect, not an extension..
I guess it's rather 2nd harmonics involved as there is no symmetry around anything and IM would be an even better start for description.

In addition to that there also should be found kind of delay or phase shift involved due to the difference in the speed of sound.
In this respect it is also different to something created by simple electronics as the "signature" is created along the way when passing compressed or expanded air along the horn and within the compression chamber. This takes some time depending on the distance the waves have to travel through.

The result should have quite a unique sound pattern, actually nothing else than a specific kind of distortion we are all familiar with from real world but is not specified in technical terms yet.

Just my private not fully thought through theory!

Greetings
Michael
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Old 27th May 2007, 05:41 AM   #883
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Been thinking about a 4-driver version, with two 18Sound 12NDA520's and two 18Sound 15NMB420's. I figured out how to do a series-parallel crossover for all 4 drivers, so the impedance stays between 4 and 8 ohms - although multi-amping is still preferable, and certainly more flexible in terms of room EQ and control of driver overlap. I should add the 4-driver version would work with almost any sets of 12 and 15-inch drivers, most certainly including Tone Tubby's.

In terms of the low Qts of the 18Sound drivers, my friend John Atwood is working on a Class D subwoofer amplifier with variable damping, yes, re-visiting the old Fisher "Z-Matic" circuit. Actually, it's not that hard to do with any feedback amplfier - the amp is re-configured to sense current as well as voltage.

There's a reasonable chance this is the one I'll build - the more I've thought about the "issues" of OB speakers, over-equalization has to be at the top of the list. This is where the horn guys have it all over us. Compare the surface areas of midbass horns to dipoles - well - most dipoles lose out, particularly when you think of just how much EQ the commercial systems are using (a lot). This system has a surface area equal to a 27-inch driver; when you add the floor image for the closely-coupled 15-inch drivers, it equals a 34-inch driver - Hartley territory. The Variable-Geometry concept means the surface area decreases with increasing frequency, so we're back to the single 12" driver by 400~500 Hz.
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Old 27th May 2007, 06:45 AM   #884
Variac is offline Variac  United States
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That fits most of the things you've mentioned. And the driver layout is about the only one that works.

One of my thoughts is that these dipoles start to get a comparable area ,and advantages of, a flat panel speaker but a whole lot more excursion if needed. At normal volumes they'll barely move most of the time.. While not cheap, they won't be as expensive as many high end projects, and you sure get an impressive speaker!! Very little doubt that it has the basics for good sound. At this point it makes sense to go for the best drivers possible. I suspect that having identical 12" drivers will be best- think of single malt vs. blended scotch. The blends seem logical, but the single malts have the character. Soon you will find out though, I could be wrong.

A much cheaper version might be doable later. As you mentioned this basic approach will work with many other drivers of the same size.

Nelson Pass had a current amp design published here, but possibly less power than you have in mind..

Congratulations- I really like it!
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Old 27th May 2007, 02:29 PM   #885
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Quote:
Originally posted by Lynn Olson
There's a reasonable chance this is the one I'll build
To quote Borat "you can barely see the horns..." But then again you're on the record of trying CD and the new RAAL for HF

Any specific wide ranger you're considering ?

Rgrds,

Florian
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Old 27th May 2007, 02:50 PM   #886
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Quote:
Originally posted by Lynn Olson
Been thinking about a 4-driver version, with two 18Sound 12NDA520's and two 18Sound 15NMB420's. I figured out how to do a series-parallel crossover for all 4 drivers, so the impedance stays between 4 and 8 ohms - although multi-amping is still preferable, and certainly more flexible in terms of room EQ and control of driver overlap. I should add the 4-driver version would work with almost any sets of 12 and 15-inch drivers, most certainly including Tone Tubby's.
I'd be interested in hearing the details of this, for both the passive and the active versions.
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Old 27th May 2007, 09:02 PM   #887
mige0 is offline mige0  Austria
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Hi


Lynn, this concept looks impressive! Nothing for small rooms!

Double 15" bass seems to be the minimum needed for what you are looking for in SPL (assuming around 5-10mm linear X-max).

What exactly do you expect to be the benefits from the second 12"?
Do you expect the max excursion of the WR to drop enough to balance the additional cost and size or is it for a possibly less complex crossover?


Greetings
Michael
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Old 27th May 2007, 10:05 PM   #888
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Quote:
Originally posted by mige0
Hi

Lynn, this concept looks impressive! Nothing for small rooms!

Double 15" bass seems to be the minimum needed for what you are looking for in SPL (assuming around 5-10mm linear X-max).

What exactly do you expect to be the benefits from the second 12"?
Do you expect the max excursion of the WR to drop enough to balance the additional cost and size or is it for a possibly less complex crossover?

Greetings
Michael
We're doing pretty well for linear Xmax. The 12NDA520 has 8mm total linear Xmax, and 22mm total peak-to-peak excursion. The 15NMB420 has 13mm total linear Xmax, and 36mm (!) total peak-to-peak excursion.

The Eminence 15" mentioned earlier has an Xmax one-third the 15NMB420 - not a small difference in terms of SPL at midbass frequencies. Then again, guitar speakers like the Tone Tubby frequently have Xmax so small it can't be measured ... 1~3 mm in the real world.

The second 12-incher (which can be replaced with a third 15-incher, possibly with some benefit) gave noticeably smoother transitions in the midbass region when I looked at the far-field in Edge. The vertical array of three drivers seems to be the minimum for smooth transitions from midrange to close-to-floor bass drivers - and if I want to have TWO bass drivers close to the floor, well, that's four drivers overall, like it or not.

In terms of size, the tradeoff between four 12-inch, two 12 & two 15's, and one 12 and three 15's, probably comes down to a tradeoff of LF extension vs baffle width. All of the variations use a singe Widerange, one Midbass, and two Bass drivers, with the lowpass filters for the MB and B drivers adjusted to the baffle width and room.

What I'm aiming for is a fairly steep area-doubling with frequency, instead of a sudden "step" at one frequency. I think this, combined with over-equalization, is one of the potential faults of OB design. I'm particularly wary of EQ response boosting.

I like EQ notch-filtering, since it withdraws energy from a frequency region where the driver is departing from constant-acceleration operation and entering an ultrahigh gain near-oscillation - mechanical resonance, which is a special-case operating region, with different rules. Thanks to resonance, you can have psuedo-efficiencies that exceed Theile-Small theoretical limits - that's what's happening with 10~15 dB peaks in metal-cone and the really wild guitar speakers. I feel it is quite reasonable practice to (greatly) reduce the power going into these frequency regions.

But boosting power - I don't feel so good about that. Drivers in the ideal case are already constant-acceleration, which means excursion going up at a 12 dB/octave rate, and LF boosting increase this slope to an astonishing 18 dB/octave!

This seems to be just asking for trouble from IM distortion at LF, cross-modulating with higher frequencies. This crossmodulation is especially malign since the maximum audibility of distortion follows the Fletcher-Munson curve, peaking at 1~5 kHz. So excursion that's been electronically boosted in the 100~200 Hz region is going to crossmodulate with 1 kHz and higher frequencies, where distortion products are much more audible.

That's the main reason Linkwitz uses multiway crossovers with high slopes - to control IM distortion from good, but low-efficiency, drivers that are being pushed really hard. This is a legitimate approach for both dipole and horn speakers - partition the spectrum to protect from out-of-band IM products, which also gives an additional degree-of-freedom to select drivers optimized for fairly narrow bands.

Speaking only for myself, it has been my experience that true multiway speakers are very difficult to integrate sonically, especially at low and high sound levels. If a complex system been optimized for 70~90 dB SPL, it probably won't sound good at less than 50 dB, or more than 100 dB. The real attraction of simple 2-ways is that system integration is much simpler, and you don't get that terrible "falls apart and lies on the floor" sensation with overly complex systems. I never really liked my 3 and 4-way systems - they just sounded too "busy" and never as natural and relaxed as the simpler systems.

This system is a 2.5 ... N design, with large, intentional overlap regions, and only one true highpass filter (for the tweeter). If there's a key design principle, that's it. I think 2.5 ... N is an interesting alternative to 3 and 4-way systems with high-slope crossovers, and I expect the new system will sound quite different than more traditional multiway designs.

The thing to be watched are the polar patterns from all those drivers. What makes it even possible are the low frequencies involved, frequencies that are well into the 1/f rolloff region. It also makes it hard to simulate and measure, since I'm bringing in addition drivers in the same region where the velocity component is getting large, and room interaction is becoming significant in terms of wavelengths. I'm pretty sure the "simulated" models will dictate excessive bass compensation - as it is, the Edge sim is showing a response down to 75 Hz for the system, a surprising result.
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Old 28th May 2007, 08:07 AM   #889
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Lynn,

I'm curious as to why you don't extend the baffle upwards to include the horn.
In your drawing you have a freestanding, round horn, that would be like sort of
like a speaker in a circular baffle, wouldn't it?

cheers
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Old 28th May 2007, 09:23 AM   #890
SunRa is offline SunRa  Romania
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I'm curious as to why you don't extend the baffle upwards to include the horn.
Well, as far as I remember, the ideea was that a freestanding horn allows you to move it along the baffle edge, for the best audible configuration.
One of the ideas was to strap the horn in a set of hinges. This way the vibrations from the massive midbas and bass units will not affect the compresion driver.
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