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Lgrau 10th October 2012 05:00 AM

TPL150 DIY
 
6 Attachment(s)
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:
Attachment 305599

in real life from Iron is 12mmx12mm:
Attachment 305601

Made this small enclosure for the TPL:
Attachment 305602
Attachment 305603
Attachment 305604

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)
Attachment 305606


The frequency responce is very smooth and the 3'rd harmonic distortion very low.

StigErik 10th October 2012 08:29 PM

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?

Lgrau 10th October 2012 09:08 PM

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.

StigErik 11th October 2012 07:46 AM

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 ....

Lgrau 12th October 2012 01:10 AM

CSD plot
 
2 Attachment(s)
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

ramallo 12th October 2012 01:26 AM

Quote:

Originally Posted by Lgrau (Post 3198340)
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?

StigErik 12th October 2012 07:41 AM

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.

Lgrau 12th October 2012 11:05 AM

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.

ramallo 12th October 2012 12:05 PM

Quote:

Originally Posted by StigErik (Post 3198524)
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

Lgrau 12th October 2012 12:30 PM

Ok, then the issue is clear, no damping right behind the diaphram :-)


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