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Old 10th October 2012, 04:00 AM   #1
Lgrau is offline Lgrau  Denmark
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Default TPL150 DIY

Hi,

I've worked a bit on a TPL-150 diaphragm in my own Magnet setup.

I wanted to avoid the iron right in front of the diaphragm, do here's the magnetsystem in FEMM:
magnetsystem.jpg

in real life from Iron is 12mmx12mm:
magnetsystem billede.jpg

Made this small enclosure for the TPL:
Kabinet forfra.jpg
Kabinet forfra uden membran.jpg
Bagfra.jpg

It measures quite good, here compared to my accuton C30:
Playing at bit more than my maximum listening level, guess around 100dB, the 3'rd harmionic is actually decreased a bit compared to the aprox 85dB measurement(note my MIC is not linear above 13KHz)
3rd harmonic.jpg


The frequency responce is very smooth and the 3'rd harmonic distortion very low.
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Old 10th October 2012, 07:29 PM   #2
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This is the first AMT I've seen without iron in front of the diaphragm! Good work! And it measures very good, looks like a lot better than the stock TPL-150.

If I understand this correctly, you have two separate magnet systems that are not interconnected in any way?

What is the sensitivity of the TPL with this magnet system?
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Old 10th October 2012, 08:08 PM   #3
Lgrau is offline Lgrau  Denmark
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Hi,

Thanks.

The magnets are not interconnected, and the sensitivity is a bit on the low side, aprox 88dB/Watt, same as my accuton C30.

Mre powerfull magnets can of coarse be used to increase the sensitivity, but around 90dB/w is fine for my setup.

There's one problem though with the TPL-150, and it's the high resonance frequency around 1800Hz.

My first AIM was to use it down to 1KHz maybe by adding a horn loading, but the low fs, is preventing a fast impulse response. I'll add some measurements, showing the problem later.

But used over 2KHz, this seems to be nearly perfect with excellent impulse response and very low distortion.
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Old 11th October 2012, 06:46 AM   #4
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88 dB should be fine for domestic hifi. The TPL diaphragm can take quite a lot of power, so thermal compression should not be an issue at all.

There is a slight resonance. I measured it to 1700 Hz on the TPL's I have had my hands on. If you want perfection, then it should be crossed over around 2 kHz I guess, making it harder to find suitable large midranges ....
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Old 12th October 2012, 12:10 AM   #5
Lgrau is offline Lgrau  Denmark
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Default CSD plot

Hi Here's some of the CSD plots.

As wrote earlier the resonance is clearly visible, here's plot at 1KHz and 2KHz crossover points. 2KHz looks fine and usable, 1KHz is showing quite heavy resonance.

1KHz:
1k filter CSD.jpg

used at 2KHz it's fine:
2K filter CSD.jpg
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Old 12th October 2012, 12:26 AM   #6
ramallo is offline ramallo  Europe
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Quote:
Originally Posted by Lgrau View Post
Hi Here's some of the CSD plots.

As wrote earlier the resonance is clearly visible, here's plot at 1KHz and 2KHz crossover points. 2KHz looks fine and usable, 1KHz is showing quite heavy resonance.

1KHz:
Attachment 305933

used at 2KHz it's fine:
Attachment 305934
This resonance is in dipole mode or with the TPL cabinet?
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Old 12th October 2012, 06:41 AM   #7
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That's a very clean CDS when you XO at 2 kHz!

If I remember correctly, that resonance is more pronounced in dipole mode without the rear chamber.

Have you tried removing the rear felt damping pad? It looks like its there on your pics.
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Old 12th October 2012, 10:05 AM   #8
Lgrau is offline Lgrau  Denmark
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This i measured in the enclosure which is open at the back, so this is the CSD as dipole

@Stig Yes there's a damping filt in the picture, this was not used in this measurement. When adding the filt the resonance get dampened. I'm afraid that adding a heavy damping near the back of the diaphram will also dampen the dynamic of the tweeter a bit. Did you made tests with and without the damping?

My problem in the setup is that I like to keep it 3 ways, an I was hoping that the TPL could cover down to at least 1KHz for a smooth crossover to my 6 inch skaaning bas.
(using JBL2226 15" as bas)

My system is active using Thuneau digital filter, so it's a bit expensive to upgrade to four way. :-)

But let's see when I get the skaaning up working, it might go clean above 2KHz. It's underhung, and I'm getting a new diaphragm made with foam surrounding. It's also made without spider, which I'll replace by thread spider.
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Old 12th October 2012, 11:05 AM   #9
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Quote:
Originally Posted by StigErik View Post
That's a very clean CDS when you XO at 2 kHz!

Have you tried removing the rear felt damping pad? It looks like its there on your pics.
Without the felt damping pad, the 2 order distortion drops 20dB
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Old 12th October 2012, 11:30 AM   #10
Lgrau is offline Lgrau  Denmark
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Ok, then the issue is clear, no damping right behind the diaphram :-)
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