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Old 1st September 2013, 01:21 PM   #11
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MJK's alignment table document contains the following regarding stuffing:

"Classic transmission lines exhibit ripples in the pass-band. This is a property of
the design that can be mitigated by the driver placement and the location and density of
the fiber stuffing. Adjusting the amount and location of fiber stuffing helps reduce the
ripples but at the expense of bass performance. One scheme is to place stuffing only at
the locations of the highest air velocities for the quarter wavelength modes targeted for
suppression. This usually means stuffing the first 2/3’s to 3/4’s of the transmission line
length and leaving the last 1/3 to 1/4 of the length nearly empty. In general, add or
remove fiber stuffing to tune the final enclosure to your system, your room, and your
personal taste."

To me, stuffing 2/3 to 3/4 of the line seems a significant amount. Again, here, stuffing should be done with a combination of imp. measurements and listening tests - all to suit the builder's voicing preferences of course.
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Old 1st September 2013, 06:35 PM   #12
DrBoar is offline DrBoar  Sweden
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I mesurements hand written as Google Draw is "waiting for connection". The leftmost box is the DaLine in 11mm OSB the other two in 12mm MDF.

I am not sure what you mean by backwall. With the microphone in the nearfield the room does not enter the equation.

I typed a much longer reply but then my token had expired and I had to start all over



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Old 1st September 2013, 07:03 PM   #13
DrBoar is offline DrBoar  Sweden
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The one fold pipe.
The first I notice is that the signal sweep in Omnimic sounds way less hollow. If this is due to change in harmonics or the fact that the opening is at the opposite side of the box I do not know.

If we normalize the harmonics to the fundamental peak the 3rd: is about + 6dB and that is 4-5 dB better than the IMF, the 5th is the same as the IMF and the 7th harmonic is worse by a couple of dB. I think this is a better folding than the IMF, not as dramatic as in Tyrlands measurements but still.

Stuffing at the first 40-50% of the pipe shold be enough. The fundamental that has it velocity maxima at the opening is left alone. You catch the 3rd harmonic at ⅓ of the length you catch the 5th harmonic both at ⅕ and ⅖ of the lenght and the 7th at 1/7 ⅖ and 3/7. That should be a pretty good start!

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Last edited by DrBoar; 1st September 2013 at 07:10 PM. Reason: damping of harmonics by stuffing
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Old 1st September 2013, 07:09 PM   #14
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by DrBoar View Post
I mesurements hand written as Google Draw is "waiting for connection". The leftmost box is the DaLine in 11mm OSB the other two in 12mm MDF.

I am not sure what you mean by backwall. With the microphone in the nearfield the room does not enter the equation.

I typed a much longer reply but then my token had expired and I had to start all over



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Click the image to open in full size.
What is the final vent dim on the IMF ? 40 or 46 mm? Could not quite make out your writing. I only wanted the back wall distance for he final integrated output from driver port and reflected from back wall.
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Old 1st September 2013, 07:48 PM   #15
DrBoar is offline DrBoar  Sweden
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40 mm it is. ( I also have trouble reading my writing)
How about having the rear of the box 300 mm in front of the back wall?
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Old 2nd September 2013, 05:09 AM   #16
xrk971 is offline xrk971  United States
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Default Sim of DaLine

Dr Boar,
Here is the simulation of the Daline TL. I am not sure which one to compare to because you say to ignore the previous post? If I compare with your Daline measurements:

Click the image to open in full size.

I get this:

Click the image to open in full size.

The harmonics seem to match but the fundamental is off (meas is 40 Hz, sim is 50 Hz)??

Anyhow, let me know what you think. I color coded it the same as yours: black is driver direct radiation and red is the emission from the port. Green is the overall combined output at 1 m away.

- Freq response
- Impedance
- Cone displacement
Attached Images
File Type: png DrBoar-DaLine-Freq.png (26.2 KB, 138 views)
File Type: png DrBoar-DaLine-Impedance.png (20.6 KB, 7 views)
File Type: png DrBoar-DaLine-Displ.png (20.2 KB, 3 views)

Last edited by xrk971; 2nd September 2013 at 05:14 AM.
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Old 2nd September 2013, 08:26 AM   #17
DrBoar is offline DrBoar  Sweden
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Now I have made som final measurements on the DaLineR with the Peerless driver. At the moment I am listening to The Commitments the original soundtrack, one chanel only and through that Peerless, no crossover no tweeter. It sounds good

On the floor 300 mm in front of concrete wall measured 1 m in front of driver. Unsmoothed and to 1/6th octave.
Click the image to open in full size.

This is the data for the acual driver used as measured by Woofer Tester 3.
* Manufacturer: Peerless
* Model: 830343
* Piston Diameter = 108.0 mm
* f(s)= 63.93 Hz
* R(e)= 3.31 Ohms
* Z(max)= 22.26 Ohms
* Q(ms)= 2.951
* Q(es)= 0.515
* Q(ts)= 0.439
* V(as)= 7.868 liters (0.278 cubic feet)
* L(e)= 0.55 mH
* n(0)= 0.38 %
* SPL= 87.90 1W/1m
* M(ms)= 9.29 grams
* C(ms)= 0.67 mm/N
* BL= 4.90

The impedance curve in the model is not far of from the acual curve apart from that the real one has a much lower peak at 30 Hz of 10 Ohms instead of 20 Ohms.

Click the image to open in full size.

Also the predicted frequency cuves are quite close
Click the image to open in full size.

As is the pipe and driver output
The real measurements show lower Q than the predicted model with less sharp dips in frequency dip at the fundamental and less deep at the harmonics. The fundamental also looks flatter (lower Q) IRL than model, the Q of the harmonics are in closer agreement. At normal listening levels the cabinet OSB parts vibrates to a degree that is easy to feel with a hand on front or back panel. Could it be losses in the cabinet that lower the Q of the fundamental? This box has sides of 12 mmMDF but all other parts of 11mm OSB. The other boxes are all made of 12 mm MDF

Last edited by DrBoar; 2nd September 2013 at 08:28 AM. Reason: adding box info
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Old 2nd September 2013, 09:05 AM   #18
DrBoar is offline DrBoar  Sweden
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My morning coffe kicked in.
If I do the same in room measurement with the pipe open and stuffed close, the differences will show how the pipe output contribute regardless of room resonanses.

Compared to the closed pipe I get +5dB around the fundamental, +10 dB at the third harmonic at 150 Hz and then a sharp peak followed by a dip at the 5th harmonic at about 250 Hz. Time to add some external braces to the cabinet to see of that will bring up the Q of the fundamental.

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Old 2nd September 2013, 11:44 AM   #19
xrk971 is offline xrk971  United States
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Dr Boar,
What software are you using to get your frequency response predictions? I thought your earlier plots were measurements, but now not sure if they were measurement or prediction.
Nice deep bass extension you have on your measurement at 1 m.
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Old 2nd September 2013, 01:42 PM   #20
xrk971 is offline xrk971  United States
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Default Sim of IMF with measured driver T/S params

Dr. Boar,
Here is the sim of the IMF speaker. Let me know what you think...

Here is your measurement:

Click the image to open in full size.

Here is the AkAbak sim:

Click the image to open in full size.

second plot below is impedance, last is the cone displacement.
Attached Images
File Type: png DrBoar-IMF-Freq.png (26.3 KB, 123 views)
File Type: png DrBoar-IMF-Impedance.png (20.6 KB, 3 views)
File Type: png DrBoar-IMF-Displ.png (20.5 KB, 3 views)
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