TPL150 DIY

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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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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?
 
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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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 ....
 
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 6½ 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.
 
Yes, is the one of lowest THD I could measure (The other was a Quad ESL 63). This measure was made in my garden with a Earthworks M30 microphone and a Sound Devices USBPre soundcard

So based on what you are showing, I really should remove the rear chamber! Just to make sure, both of those measurements were at the same SPL and under the same conditions? This is stock TPl versus dipole AND your magnet system or just the stock TPL run as a dipole?

I've played with the idea for a while, but never tried it. Hmmmmm, in my case I cannot leave it dipole, but I could make the chamber significantly larger and stuff well with Bonded Logic.

Greg
 
So based on what you are showing, I really should remove the rear chamber! Just to make sure, both of those measurements were at the same SPL and under the same conditions? This is stock TPl versus dipole AND your magnet system or just the stock TPL run as a dipole?

I've played with the idea for a while, but never tried it. Hmmmmm, in my case I cannot leave it dipole, but I could make the chamber significantly larger and stuff well with Bonded Logic.

Greg

By Removing the chamber and the felt mat.

Yes, at the same place and same SPL (ten minutes of difference).

The worst thing is the felt on the back of the TPL (is very dense), just removing this felt you can get better measures. Filling the camera with another material also improves a bit (foam).

Dipole mode is very good for THD, but the freq response is worse.
 
When placing absorber a couple of inch back, it measures same as dipole.(EDIT in my setup) So using a larger enclosure with good damping should be the right approach.
But please keep in mind when removing the felt pad, you'll get more pronounced resonance at 1800Hz.

I expect to keep the back opened, but with quite heavy damping of the sound from the back of the driver. Made a test filling with rockwool this gave aprox 30dB attenuation.
 
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