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Old 8th April 2007, 12:07 AM   #121
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Quote:
Originally posted by BudP
Hi Lynn.

I wonder if the enclosures you mention could be terminated with some modification of the Mamboni pattern, perhaps extended into three dimensional shapes of some size and made from a material that eats energy by vibrating small kinked bits of fiber?

There is a material of merit, the replacement carpet underlayment used by auto interior restoration folks. About an inch thick, with a tightly interlaced body of various length and diameter, kinked, moderately stiff fibers and small pieces of a rag like material. Has a shorter, more densly packed face, on one side, with the other face more open and with larger kinked fibers. Easily the most linear damping material I have found and good from infrasonic to about 2 k or so. Very linear in this range too.

Perhaps a Mamboni ring applied just before and entering into the peg board mesh area?

Bud
Hmm, I'd like to hear more about this interesting material. Where do you get it, what is it named, etc. "Good from infrasonic to 2 kHz" sounds pretty awesome to me, and certainly good enough for the purposes of edge termination on the HF dipole and bass units.

Reflecting on the previous mini-essay, we see the same kind of topological tricks used in microphones to create the desired polar pattern. Omni mikes have small enclosed chambers on the back side of the diaphragm, dipoles are left open on both sides, and cardioids use damping techniques on the back side of the diaphragm - and for variable-pattern mikes, anything from variable shutters to two sets of diaphragms and an electrical adjustment.

The real issue is edge termination, regardless of enclosure type. Loudspeaker designers who avoid the time domain like to dance around this, but I now think it's a combination of mind-set (freq resp uber alles), unwillingness to work in another domain, and unfamiliarity with the tools of the time domain - MLS, TDS, etc. The frequency-only mindset has significantly retarded progress in loudspeaker design over many decades - I can now understand better why Dick Heyser of Cal Tech met nothing but 100% opposition in his native Los Angeles, the home of Altec, JBL, and Cerwin-Vega. His work met a more receptive audience in the UK and Europe, but I'm still surprised how alien working in the time domain is for many high-end designers.

When you visualize the driver as a wideband pulse-emitting device with a dipolar radiation pattern, it's easier to see what the enclosure is really doing - storing and re-radiating energy. There are two things making this challenging relative to other fields: the awkward requirement for three decades of bandwidth - extraordinarily wide by RF standards - and the extreme dynamic range of the ear, which is very sensitive to the faintest decay products. The only reason we don't object more to the grossly artificial sound of hifi systems is we've been listening to these things for a long time.
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Old 8th April 2007, 02:33 AM   #122
Geoff H is offline Geoff H  Australia
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Hi Lynn, and thanks for starting this thread. Pity about the leg, hope it mends well. But your pain has become our gain.

"Not to tease you guys too much" May not be the intention, but I think it's happening.

You have pointed out some interesting things often overlooked. In regard to stored energy in baffles, I was thinking only last week that the baffle could be tapered at the edges. But now I think that was wrong. The energy has only one place to go - air. You mentioned a conduit fixed to the baffle edge. It could be filled with something like cement or sand, to provide some mass to terminate the baffle.

Also, the whole concept of stored energy gets me thinking. This energy starts at the magnet. If we have a lot of mass at that point, less energy will go through the basket, which should be cast, with no sharp edges. File carefully!

Baffle treatment is also a problem. Nice high gloss finishes show off the quality of the timber, and radiate more....You mentioned a rough or textured surface. I wonder if a mix of bitumen paint and sand would help, how would you determine the size of the "lumps" in the texture?

I am very close to fitting some phase plugs to some little wide-rangers. Now I am wondering if I really want a reflective surface so close to the cone.

Regards,
Geoff
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Old 8th April 2007, 02:36 AM   #123
BudP is offline BudP  United States
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Lynn,

I can certainly attest to a mind set among transducer designers. NIH is the prevailing attitude and none of the designers I got to talk to over the life of the EnABL process had a clue what phase and time coherence might mean, and this includes some well regarded "designers" with published works and large followings. Might as well have been discussing making ice sculptures in Hades.

I am embarrassed to admit I do not know the commercial name of this damping pad material. At Perfect Fit McDonald, the local wholesaler to the auto interior restoration / repair industry in Seattle, they just call it carpet underlayment and ask you how many yards of it you want. I am sure Denver will have it's counterpart and I will call PFMcD and ask to talk to the purchasing people to see if I can get a line on trade names, grades, etc.

I use this material for selective damping in cabinets that have full EnABL pattern drivers installed. They are quite transparent to back wave energy from reflections and the damping pad material, just applied to discrete cabinet surfaces, rather than as a filler, effectively eliminates these reflections. I use 3M 99 spray adhesive to attach the pads in place.

One of the reasons I am interested in the Mamboni / EnABL experiment currently gong on in Tennessee is the likely hood of reducing the back wave transparency, without compromising room emitter surface coherence. The wave tank experiments I conducted years ago indicated that the waves emitted from an EnABL treated driver are phase and time coherent, as the wave tank pulses act just as Soliton waves do, in Norwegian Fjords. Having them terminate on the driver surface, on the back side of the driver, rather than emit into a box full force is quite an attractive possibility.

Another thought arises concerning the phase angle of energy emitted from back wave resonance couplers from bass reflex cabinet design. It appears that the energy being emitted is phase coincident to the energy emitted from the driver directly into the air. Can this same event be used with a back chamber scheme of Mamboni / multiple tuned vents to effect a Bipolar radiator of Bass?

Bud
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Old 8th April 2007, 02:52 AM   #124
BudP is offline BudP  United States
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Geoff,

May I suggest that you think about how you can get the energy off of the baffle plate without attenuating it, without mass "STORAGE" damping, without any ringing of transient standing waves, without any diffraction artifacts and in phase and time coherence with the expanding polar wave front from the driver. That will get you much farther than damping of any sort and I believe is the point Lynn has been pushing towards with his comments. Unless you have a "perfect" damping scheme you will have reflected energy.

You might also look at the thread on Walsh drivers for some interesting information on wave termination from a surface without damping.
OHM Acoustics "Walsh F" Speaker remakes

For your phase plug concern I would personally urge you to make a smooth flat surface with a flat acrylic paint, or study and apply either the Mamboni or EnABL edge termination process, one will apply, and will satify your concerns.

Bud
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Old 8th April 2007, 03:27 AM   #125
Geoff H is offline Geoff H  Australia
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Thanks Bud.

I understand the requirement of absorbing the energy before it travels, hence the large mass at the magnet. It will only absorb a percentage of the energy, depending on how much mass we can have without it effecting the radiation of the sound wave off the back of the cone, and it becoming another source of reflection.

Thanks for the links.

Geoff.
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Old 8th April 2007, 07:43 AM   #126
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Hi Lynn,

I guess you are discussing aperiod/resistive driver loading. Car audio exponents mount drivers in rigid containers little larger than the driver itself, the rear load with home made mesh enclosed glass fibre ARUs of half driver dia and vent externally to the cabin.

I guess we could cut 'vents' in wooden floors but not solid, so whether a graduated series of ARUs with the rear residual venting into a listening room would sound acceptable via a more normal sized cabinet might be worth considering.

Also I cannot begin to emphasise how simple rolls of dense carpet two to three turns thick and either side of a mounting baffle really do improve reproduction.

Cheers ........ Graham.
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Old 8th April 2007, 08:23 AM   #127
terry j is offline terry j  Australia
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hi lynn

am enjoying the thread, tho I will readily admit that the majority of it goes WAY over my head ha ha. Only recently discovered your ariels, but alas those vifa mids seem to be over the hills and far away.

Can I quickly make a clarification/correction?? Back in post 111 you cautioned against using a low fi device like the Behringer deqx in any application other than bass duties. (However, I have heard the Behringer DEQ 2496 make significant improvements in systems, yet admit that there would certainly be systems in which you wouldn't use it!)

There is no such unit as the Behringer deqx, there is for example a dcx(2496), or a deq(2496).

However, there is a unit (company) known as deqx, which do indeed do active eq and room correction. I think would be unfair on this unit to describe it as low or mid fi, indeed it is used in many very expensive and high end systems. Unless it indeed was the deqx you were referring to, what seems to have happened is that the two were somehow mixed together into some hybrid beast now known as the behringer deqx, which could be unfortunate on the deqx as it is a very good system indeed.

I use the deqx in my tri amped system and so can vouch for it's quality. That, of course, is only my opinion.
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Old 8th April 2007, 12:18 PM   #128
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Quote:
Originally posted by terry j
hi lynn

am enjoying the thread, tho I will readily admit that the majority of it goes WAY over my head ha ha. Only recently discovered your ariels, but alas those vifa mids seem to be over the hills and far away.


did you mean you can't locate them????..
if so, heres an example
http://www.speakercity.com/Merchant2...ry_Code=VifaCL

Regards

Ed
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Old 8th April 2007, 07:03 PM   #129
fred76 is offline fred76  Philippines
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Interesting links...

http://translate.google.com/translat...language_tools

http://translate.google.com/translat...language_tools
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Old 8th April 2007, 08:06 PM   #130
agent.5 is offline agent.5  United States
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Default Re: More Thoughts ...

Quote:
Originally posted by Lynn Olson

I'm visualizing a pair of drivers side-by-side in the front, another driver on the left side of bass unit, and another driver on the right side of the bass unit....

Gary Pimm is using modestly priced MCM or Parts Express 15-inchers for his high-Q subwoofers.
Having the bass drivers on the side minimizes visual impacts. You may as well go crazy and have a pair of 18". After all, 18" woofers have lower Fs than their 15" brothers.
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