Inspiration : a TQWT for Fostex FX120 and Fe127e - diyAudio
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Old 26th November 2005, 01:20 PM   #1
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Post Inspiration : a TQWT for Fostex FX120 and Fe127e

This design is the result of three prototypes and over 10 months of listening/adjustment work.

It is a folded ML-TQWT designed using MJK's excellent worksheets.

I wanted an enclosure that would bring the FX-120 driver to a true fullrange speaker, i.e having a convincing bass extension without sacrificing the outstanding refinement of the FX-120 driver.

Everything has been done to keep the frequency response flat, and to avoid port noises pollution.

Damping and port position have been optimized for a minimal midrange output through the port, keeping the driver the only sound source above 200Hz.

The port has been flared and its length corrected within 1/100mm precision to avoid chuffing issues.

The cabinet is made out of 19 and 22mm MDF and has been built by a carpenter on a CNC machine.

Every angle on the front has been flared to avoid edge resonnances.


When I plugged them for the first time, without any damping, I was struck by the bass reproduction.
It was clean and surprinzingly tight for such a small driver ! I experimented further with damping and got an even cleaner bass.
As I wanted it, the port is totally silent above 200Hz.
Everything that comes out from the driver is crystal clear, very well defined and detailed.
Coherence is a strong advantage with this enclosure, and imaging is ultra-precise.

I rediscovered my musics !

Now a few specifications :

BW : 47Hz - 20kHz -3dB
SPL max = 100dB 10W/1m (downside of the very large cabinet)
THD+N = 0.15% 3W/1.5m (including amp, soundcard, microphone etc...)
cost : 260/pair max


I decently think it is one of the best designs possible for those drivers

Enjoy
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Old 26th November 2005, 01:34 PM   #2
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An extensive work has been done on damping to find the best compromise between bass impact, clean impulse response, midrange output and bass extension.

Measurements and listening sessions with a friend led me to this :
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Old 26th November 2005, 01:39 PM   #3
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And finally, the plans. Note that the port dimensions are given for an unflared port !

With a 9.6mm flare radius, the length must be increased to 32mm.

WARNING : this plan is only intended for DIY purposes ! Any other use, including commercial use and profit making is strictly forbidden !
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Old 27th November 2005, 09:02 AM   #4
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Do you have the MathCad predicted response curves at all?
Cheers
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Old 27th November 2005, 05:59 PM   #5
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Yes, here they are : simulated far field response, port response and pulse response.


I'll soon publish real measurements, I currently only have the pulse response of the port and the frequency response in my little bedroom.
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Old 27th November 2005, 09:25 PM   #6
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Pretty good for an So=0 pipe design. Good job. I look forward to seeing the finished measurements. (I may be shoving a pair of these into some BIB boxes at some point -oh for the lost FX200s though!)
Best
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Old 30th November 2005, 12:12 PM   #7
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Had time to measure the port response and the port impulse response.

The microphone was placed right at the output of the port, aligned with the front plate. I hope it doesn't modify the port response too much because we can see a peak at 1kHz. It could also be the signal coming from the driver itself, as it is not that far from the port.
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Old 30th November 2005, 12:20 PM   #8
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... and the pulse response. I find it to behave quite well for a ported design. The main pulse is damped in 4ms, far better than my home theater JBL subwoofer !

I did measurements of the frequency response but lost all the data due to a battery failure of my laptop

It showed a ruler flat response from 800Hz to 50Hz, but seemed to have a "bump" of +3dB between 1kHz and 2.5kHz that rather comes from the driver (it did the same in my previous enclosures)

Now I have the speakers in my little listening room, I will remeasure them but it will be likely to look awful
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Old 3rd December 2005, 02:47 PM   #9
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Finally, I were able to take a far field frequency response graph :

the measurement was made in the middle of my bedroom, at 1m of the speakers.

My room is 4.3m*3.8m, and it is not acoustically treated.

Click the image to open in full size.

As I assumed, it needs some BSC if used in a big room. a cap+8ohms in parallel with the driver should do the trick.

Probably due to the room, bass surprizingly extends down to 43Hz.


Any comment, suggestions ?
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Old 6th December 2005, 02:03 PM   #10
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Hmm, not bad at all, especially in the middle of a fairly normal room. One suggestion -what speaker wire and amp are you running? Part of the slump below 1Khz is Baffle-Step loss, but if you're running solid state amplification a quick tip would be to go for a very thin gague wire. I use 24AWG magnet wire with my FF165Ks and it works very well -basically, it's adding some series resistance. You can get the same effect by adding a resistor in parallel, but this is the easier way! Cheapest way is to buy a single piece of Cat5, then extract 2 of the twisted pairs from it, and use one pair each side as the cable. That's 24AWG and will do the job. Interesting effect that's worth experimenting with if you haven't already as it's very cheap to achieve and invariably lifts the bass performance.

Best
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