MJK's Fostex FF125wk BLH project - Page 6 - diyAudio
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Old 21st January 2013, 09:54 PM   #51
xrk971 is offline xrk971  United States
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Nice work Dr Boar, you work fast! I almost want to try this with foam... What driver are you using?
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Old 22nd January 2013, 05:27 AM   #52
DrBoar is offline DrBoar  Sweden
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Its a Tangband 4", that I bought back in 2002, look at page 2 in this thread for specifications, measured, official and compared to Kings Fostex driver. It is a pretty good match apart from surface area that is substantially smaller. Fr was way higher than specified out of the box but Rammstein really loud for hours on end have helped to both lower the Fr of the drivers and for me to discover many more good songs apart from Du Hast

Last edited by DrBoar; 22nd January 2013 at 05:43 AM. Reason: early morning spelling
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Old 22nd January 2013, 12:47 PM   #53
xrk971 is offline xrk971  United States
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Dr Boar,
OK, so the trick to quick break-in of drivers is to play Rammstein - would other metal bands work ? How loud do you play it - b'cuz around my house, I would have to put it in a sealed cooler with pillows and foam to absorb all the sound from breaking in. Otherwise, I do it slow and gentle with normal jazz or pop for days on end - which is not a problem.
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Old 22nd January 2013, 03:09 PM   #54
IG81 is offline IG81  Canada
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Don't you guys know that dubstep was originally created for the purpose of breaking-in drive units?

IG
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Old 22nd January 2013, 09:11 PM   #55
DrBoar is offline DrBoar  Sweden
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I play so loud that the cone move several mm, for some drivers I used ear protectors before entering the room. So I start the music then leave the house!

Today I have made impedance measurements and taken pictures
1. No damping
2. Damping as article
3-5 variants of removed damping.

At the end I discovered that it easy to get leaks as the newer clamps had to have their plastic feet removed to reach over the boxes and they can slide around a bit. I edited all the images but then Photobucket or my computer did something odd with the series of images so all the .jpg are now identical?

The impedance peaks are hardly changed by having the horn in a corner or in mid air. So tomorrow I will redo all the impedance measurements with the horn lying down on a flat surface with a gravity seal assisted by two 15" drivers to add some mass.
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Old 23rd January 2013, 09:27 AM   #56
DrBoar is offline DrBoar  Sweden
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Measurements!
As impedance curves with the horn in a corner, freestanding or sideways on a table overlap I have done all measurement using the table as a side wall and with me as weight. Using the cabinet alone or just a 15" driver as a weight was not enough. When using the horn freestanding and clamps great care has to be taken to make sure that everything is properly sealed.

The fluffy things are at 3x 25g(chamber, IPA and P3) one of 15 g (P2) and 2,6g (p1)
The IPA should have had 23 g but I did not think about using a marker on that one to keep it apart from the two 25 g ones. My kitchen scale goes all the way up to 5000 g I have not tried to calibrate it to see how accurate it is. As 1 ml= 1gram (and 1cc) it is not hard to do.

Click the image to open in full size.

Just to make clear what I mean by chamber, IHR and P1-P3

Click the image to open in full size.

Then for the impedance measurements. First out is with no damping what so ever. This curve is then in as a green reference curve in the other measurements

Click the image to open in full size.

Adding 25 gram of fibers to the driver chamber
Click the image to open in full size.

And then 25 g to the IHR as well
Click the image to open in full size.

And some few grams in P1
Click the image to open in full size.

15g in P2
Click the image to open in full size.

fully stuffed
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Old 23rd January 2013, 12:15 PM   #57
IG81 is offline IG81  Canada
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Nice, did you also listen and found one the damping schemes to perform better?

Also, while 1ml does equal 1cc, it's not automatically 1g, as this depends on the material's density.

I'll be looking forward to the frequency response measurements!

IG
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Old 23rd January 2013, 12:46 PM   #58
DrBoar is offline DrBoar  Sweden
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Regarding density I ment water

These are the measurements for a full damping of the pipe

I run a impedance sweep before before measurements to make sure that the box is properly sealed.

Driver 10 on axis
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.

Increasing the distance to 30-50 cm increase the output above 10 kHz, the 6 kHz peak remain. Note the dip in the driver around 75 Hz

Pipe output in the middle of the opening
Click the image to open in full size.

With the horn in a corner at 1 m in front of the driver
Click the image to open in full size.

The clutter around is reflected in the poor water fall response
Click the image to open in full size.

In Kings simulation if I read it correctly the pipe output has - 6dB points at 40 and 200 Hz, I get more like 65-150 Hz and about 12 dB down at 40 and 200 Hz.

Time to investigate what that IHR is doing and the damping material in the pipe
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Old 23rd January 2013, 01:31 PM   #59
xrk971 is offline xrk971  United States
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Very nice work Dr Boar. Perhaps the most exhaustive set of measurements I have seen on any project. That seal is pretty important it looks like. Do you have horn pipe output with no stuffing in P2 or P3? That should boost SPL.
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Old 23rd January 2013, 01:40 PM   #60
IG81 is offline IG81  Canada
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Waddya know, water is ~1g/cc - probably something I've known at some point, thanks for specifying!

Overall response is quite decent IMO. You're getting the typical BLH suckout right below 200Hz. Naturally, the horn's upper cutoff rolls-off quite smoothly with all the damping, it will be interesting to see if that's what you find sounds best in the end.

IG
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