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Old 15th December 2008, 10:22 PM   #31
Ziggy is offline Ziggy  Australia
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Changed the position of the sound pads so that I had them mounted in a straight vertical line. An improvement was noticed.

Here's an observation - two pads per channel is not sufficient in a large listening room unless you listen to your music at below normal or realistic levels. I was however, testing both channels on only one sheet of corflute(3 foot X 2 foot) which is far from ideal.

This was soon obvious when the pads were beginning to get warm as I increased volume and listened at a reasonably loud volume for about 30 minutes.

I think that four per channel(bearing in mind the resulting impedence change) at least is what's required to spread the power input between drivers to a safe level. Will do that tonight and run a mono (summed stereo) signal to the four pads wired up for eight ohms.

I'm not sure what the sensitivity rating of these pads are as they are not stated anywhere that I have seen? I presume that they would be in the low to mid 80's ?

Before I give the cardboard panel idea away, I might try to varnish with shellac to see what happens.
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Old 15th December 2008, 10:56 PM   #32
Damosan is offline Damosan  Australia
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Ziggy,
You could also try Modge Podge, which is available from Spotlight. Thin it a bit with water and paint on to the cardboard. Otherwise there are a number of PVA based solutions that you could try as well.

I have some if you want to use it.

Damo
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Old 16th December 2008, 12:49 AM   #33
Ziggy is offline Ziggy  Australia
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Thanks Damo.

The idea is that the cardboard needs to be hardened without adding too much mass.

I have been thinking along the lines of Shellac because it dries hard and there will be minimal, if any, shrinkage.

Some of these plastic based varnishes cause a considerable shrink on anything that's able to flex if forced to.
You should see what DOPE (used on model planes) does !!

Anyway, the whole project is on the line tonight (seriously !) if the 4 drivers still warm up at loudish levels. I mean they were not ''hot'' last night, but it's still a concern as to what it's doing to their life span.
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Old 17th December 2008, 05:07 AM   #34
Ziggy is offline Ziggy  Australia
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O.K............all is well no drivers cooking or smoldering at high levels. Only slightly warm to the touch. When the number of pads increases to 6 per panel this should be adequate and sensitive enough for most amplifiers.

I have ordered another 4 pairs of SOUND PADS just this morning and had an interesting conversation with the supplier. We talked about the various panel materials tried and he stated that the most adequate material that has been used is CORFLUTE.

Hmmmmmm???..........maybe, but I'm not convinced until I try a giant piece of it. I do know that some commercial ceiling panels and picture frame NXT products use it quite successfully.

Last night I heard some surprising and very low frequencies (but not at subwoofer levels) occasionally show up while listening to classical music on FM radio. That was with corrugated cardboard propped up with a balsa wood stick from behind, so it looks promising that low frequencies can be extracted from large panel sizes.

What was not so pleasant was some buzzing/resonances around the edges of the cardboard and one or more of the drivers. The drivers are only held in place temporarily by cheap paper masking tape(re-useable!!) so I don't expect a perfect coupling in that area

I'm also not surprised that the edges buzz either - the panel was hacked off the side of a rectangular box with a rather blunt knife!!
However, if corrugated cardboard wins the panel material game, the edges will need to be treated or sealed with some sort of rubber or similar compound. There's a lot of energy shooting towards these edges - trust me
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Old 17th December 2008, 07:57 AM   #35
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What type of corrugated cardboard are you using? The best type to use is very thin 5-layer double corrugate, like the example at this link.....

http://www.smurfitkappa-obalysturovo...ted+Cardboard/

Are you using the SoundPads as-is, or have you removed the exciters? The SoundPads are designed to dampen low frequencies to keep the excursion of the exciter in check. If you remove the exciter and build a frame that allows the motor to be firmly attached you will get much more low end. This way the exciter will act more like a conventional driver at low frequencies.
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Old 17th December 2008, 08:13 AM   #36
el`Ol is offline el`Ol  Germany
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Is it possible to remove the actuator from any piezo tweeter? On Ebay you get the "PT1-1016" from various shops. They claim it works from 1kHz on crossoverless.
http://cgi.ebay.de/2-x-Hochtoener-Pi...1%7C240%3A1318
Or is it just the horn flare that limits the operating range?
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Old 18th December 2008, 04:10 AM   #37
Ziggy is offline Ziggy  Australia
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The Anonymous1, I'm using just the standard 3 layer double faced cardboard about 4mm thick in total. It's interesting that you feel the 5 layer version is better and I can get hold of this locally.

The SOUNDPADS are being used AS IS at the moment.

Can you give me some tips on how best to dismantle them without causing damage as that would be much appreciated

I agree that used without the attached circular stick on cardboard disk and those stupid ''arms'' would result in better sound as you have previously implemented, similar to the PODIUM speakers?

Did you have the panel free floating but held at just the four corners or the entire panel?.
What do you think was the cause of the RESONANCES you spoke of??

elOL, the speakers on ebay are similar to the ones I pulled apart.

All you do is remove the screws at the driver end of the horn and the back will come off exposing the rear of the piezo driver.

To me the sound of the piezo cones mounted on the large boards went down to about 800hz, but that was not measured and is only subjective based on listening.

You will still need an impedence matching transformer to get these things to go loud.

PARTS EXPRESS sell large 4 inch diameter screw on horn drivers ''similar to KSN1188'' that have a built in transformer. You would be better off trying those. They are LOUD I know, because I have a pair.

Thinking of pulling them apart
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Old 18th December 2008, 08:00 AM   #38
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Quote:
Originally posted by Ziggy
It's interesting that you feel the 5 layer version is better and I can get hold of this locally.
This was actually a recommendation of NXT I had found in an article. I doubt I would be able to find the article again if I tried, it was a couple of years ago.

Quote:
Originally posted by Ziggy
Can you give me some tips on how best to dismantle them without causing damage as that would be much appreciated
I will take some pictures of an exciter so you can see what it looks like without the extra stuff attached. I believe they were just attached to the plastic shell with some double sided tape or glue on the back.

Quote:
Originally posted by Ziggy
Did you have the panel free floating but held at just the four corners or the entire panel?.
What do you think was the cause of the RESONANCES you spoke of??
The entire perimeter of the panel was attached to the frame with 1/4" expanded foam tape. I don't know what was causing the resonances. I don't have any sound measurement equipment and I didn't spend much time experimenting with it.
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Old 18th December 2008, 03:01 PM   #39
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You've posted in the wrong part of town speclcd.

Ziggy, here are the pics....

Click the image to open in full size.
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Old 19th December 2008, 02:20 AM   #40
Ziggy is offline Ziggy  Australia
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TheAnonymous1, Thanks!!!.......I'll go the 5 layer cardboard laminate route. Is 5mm (approximately) too thick?

Great photos - they will help.
How did you remove the central voice coil ''foot'' from the cicular pad and what did you use to stick the voice coil/foot on to the new 5 layer stuff?

Your advise is much appreciated
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