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Old 25th April 2007, 07:51 PM   #301
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Actually, a thin constrained damping layer can be quite effective. I don't know at what point the damping is at a maximum, but I'm pretty sure efficiency doesn't scale linearly with thickness...
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Old 26th April 2007, 06:36 AM   #302
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Default PVDF Accelerometer

/quote/
PS: when John Atkinsom measures panel rsonances with his little device... what kind of device is that and where would one get one (or get something to repurpose)?
/quote/


This was posted a few days ago...I'm just not around every day or I would have responded. The following links may help you out:

Measurement Specialties, Inc.
http://www.meas-spec.com/myMeas/default/index.asp
http://www.meas-spec.com/myMeas/sensors/piezo.asp
http://www.meas-spec.com/myMeas/sens...ezoSensors.asp

Piezoelectric Film Transducers
http://www.pages.drexel.edu/~st96p2ha/piezo.html
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Old 26th April 2007, 06:36 AM   #303
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Default What to build speakers out of... multilayered construction?

I was thinking about building speakers using a multi-layered construction. Does anyone have any feeling one way or the other with regard to the construction of the Pioneer TAD Model 1 or speakers like it?

The layers would be made out of material similar to Russian Baltic Birch plywood. I know that the cost would be exorbitant but I'm looking into this method for all the reasons everyone is discussing herein.


http://tadhomeaudio.com/images/CabinetInterior.jpg

http://tadhomeaudio.com/images/cabinet-exp.jpg

http://tadhomeaudio.com/images/CoverSpeaker.jpg
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Old 26th April 2007, 07:52 AM   #304
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Default Re: PVDF Accelerometer

Quote:
Measurement Specialties, Inc.
That is VERY helpful, thanx.

dave
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Old 26th April 2007, 08:03 AM   #305
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Default Re: What to build speakers out of... multilayered construction?

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Originally posted by showflash
I was thinking about building speakers using a multi-layered construction. Does anyone have any feeling one way or the other with regard to the construction of the Pioneer TAD Model 1 or speakers like it?
Called translam construction (or layertoning)... other than having huge waste and the need to have access to a CNC this technique is very good.

You can use all sorts of material (stay away from all mdf / Rob Well's story tells why), and even use different materials and in different thicknesses. Walls can vary in thickness, and can be made very irregular inside (check out seven veils)

One thing too note in the exploded pioneer/TAD ... they could have done the braces better -- braces should run in the longest direction....

Another trick you could do, would be to purposely build up a very holey, open cel structure in the middle of the box -- this should have a dramatic effect on stide-to-side standing waves

Not as stiff as doing it the way B&W does....

dave
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Old 26th April 2007, 03:03 PM   #306
Geoff H is offline Geoff H  Australia
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Re: PVDF Accelerometer

A couple of days back I was probing with a screwdriver between an ear and a baffle, with some interesting results. Not very scientific, thinking about a DIY solution, the best idea to date is a magnetic phono cartridge mounted on a stand, with suitable mass, with the stylus positioned on the baffle in question.

The results could be observed on a CRO, studied on a storage CRO, or just fed to a level meter. A mic pre-amp should do the job - no need for RIAA eq.

Another possibility could be using the receiving end of a guitar reverb unit. Instead of springs, attach a high tensile wire, the other end going to the framework. A small block could couple the wire to the baffle.

The unit would be placed in front of the baffle, such that the wire was parallel to the surface under test.

None of those methods will give absolute data, only comparative.

Back to the screwdriver in the earole. The big surprise was the amount of energy transferred was from the edge of the baffle, not the front. That was on MDF.

Cheers,
Geoff
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Old 26th April 2007, 03:50 PM   #307
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Geoff,

Was that a box or OB? Imagine the noise at the edges with real wood instead of MDF. Typical approaches do little to address what we're hearing at the edges other than decoupling the driver frame from structure. I'm sure that something more is needed to prevent sound from entering the structure at the driver cutout where SPL's are their highest by using some damping material there and/or dissipating the energy that enters the baffle there.

The problem is very driver dependant, because with some drivers the frame itself will block much of the radiation toward the edge of the cutout

I plan to first try damping the cutout with clay or duct seal, but I think something like the mounting rings I mentioned before will be needed to cure the problem.
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Old 26th April 2007, 04:37 PM   #308
Ricky is offline Ricky  United Kingdom
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Hi.

I've been following this thread with loads of interest. I'm going to try a 2 layer cabinet using 12mm MDF veneered one side and then cold press it, using a PVA, to 18mm high density particle board with a balance veneer on one side.

I'll let you know how I get on.

Ricky.
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Old 26th April 2007, 06:38 PM   #309
tinitus is offline tinitus  Europe
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The ressonanse in the middle of the plate will move outwards towards the corners, just like rings in the water
When all the ressonanses from all sides meet in the corners I would expect all sorts of nasty things to be going on

Thats why, in my next speaker, I will use soft wooden lists in all corners inside the box - like in the old days, only differense.... it will be glued with a thin layer of some sort of acrylic glue
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Old 26th April 2007, 07:00 PM   #310
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Default soft wood

Tinitus:
By soft wood do you mean pine or softer like balsa? Should they be corner gussets?

Ricky:
I am recycling some Bozak cabinets for use as subs and intend the identical two-layer treatment since the cabinets are made of high density patricle board. Why did you choose PVA over some of the other glues/adhesives mentioned and what is the "cold press" process?

Ray
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