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Old 25th January 2005, 03:03 AM   #361
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Quote:
Originally posted by MarkMcK
I am rather skeptical of a 200 hour break in period. Think about it. First, if the driver continues to change over the first 200 hours, what possible reason do we have to believe it will stop changing after 200 hours?

Mark

Hi Mark. The FE127E is my first Fostex driver so I do not know how long break in will take. However, I have read on several occasions that the break in time is in the order of about 200 hours!

Since you have measurements at 20 hours, I think it would be great to get more measurments at 200 hours and compare the two. Since we are all human, I think there is a possibility that after 200 hours, people become acustomed to the sound and say it sounds better.


Quote:
Originally posted by MarkMcK
I assume ML stands for mid line.

Mark

The ML stands for Mass Loaded.

Keep up the GREAT work!

Gio.
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Old 25th January 2005, 03:09 AM   #362
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Quote:
Originally posted by MarkMcK
I assume ML stands for mid line
ML stands for mass loading. The restricted terminus does this. Augspurger showed that the mass loading increases the amount of suppresion of higher order resonant modes (ie increased the performance of the low pass function on the output of the terminus)

Quote:
If it does, then the testing is showing a possible problem with MLs. When fully damped, it is small and therefore probably can be ignored. When fully damped, however, low frequency output is way down. Reducing damping brings up the bass, but also shows much increased magnitude of a spectral repetitive narrow bandwidth dip and then peak. First instance occurs around 400 to 500 Hz.
The position along the line of the driver is used to cancel some of the TLs ripple. It properly positioned it will almost completely kill one of the harmonics -- usually one goes after the 1st undesirable one because it has the largest magnitude. In an ML-TQWT this is most often halfway. On an ML-TL is is usually closer to a 1/3. Tim has choosen 1/2 in this design. For folding it is quite convienient -- especially in a bi-pole.

dave
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Old 25th January 2005, 03:13 AM   #363
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ML = Mass Loaded, a term coined by Martin King for his work on a restricted terminus quarter-wave pipe. I chose to use Martin's MathCAD worksheets because of it's availability to everyone on this forum and for the accurate modeling it can produce. This also gives everyone here the opportunity to try out the worksheets for themselves using the numbers provided and hopefully offering new and better ideas.
Dave's T-line website, Martin's Quarter-Wave website and G.L. Augspurger's articles for Speaker Builder are excellent places to do some reading on the subject.
My primary goal when using these tools is maximally flat bass response and good phase response while attempting to reduce harmonics in the pipe, in particular the third, first by driver placement then with stuffing.
Secondary goals may include the visual impact of the enclosure and ease of construction.
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Old 25th January 2005, 03:18 AM   #364
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Don't ya' just love overlapping posts!
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Old 25th January 2005, 03:41 AM   #365
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Quote:
Originally posted by Timn8ter
Dave's T-line website, Martin's Quarter-Wave website and G.L. Augspurger's articles for Speaker Builder
Don't forget Bob Brine's site http://geocities.com/rbrines1/

The best version (subtly) of Augspurger's paper is the revised one published in the AES journal.

dave
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Old 26th January 2005, 02:41 PM   #366
MarkMcK is offline MarkMcK  United States
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Here is the first of several posts about the test results.

The first set of graphs show the interaction of the enclosure with the driver. That interaction continues up until about 4. 5 kHz. Please do not overreact to the results. All enclosures interact, even open back baffles with wings will interact by backside loading the driver diaphragm.

I suppose one thing to take from these tests is that stuffed or not stuffed, the sound of the loudspeaker will be a combination of the driver and the enclosure. A lot of the interaction goes away with stuffing, but not all.

Good designing and good building,

Mark
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File Type: gif fe127boxandfill.gif (30.0 KB, 1474 views)
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Old 26th January 2005, 02:44 PM   #367
MarkMcK is offline MarkMcK  United States
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This next set looks at the impact of the vent or open aperture on the driver response. The comparison is between the vent closed or open.
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Old 26th January 2005, 02:51 PM   #368
MarkMcK is offline MarkMcK  United States
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Today's last post shows the far field, free space response of the loudspeaker comparing vent closed with vent open. The results shown here are repeatable, yet the differences shown are at the low frequency resolution limit of my chamber. While I believe the loss of low frequency output is a function of the loudspeaker and not the test set up, I have little confidence that the amount of difference shown is an accurate reflection of the actual acoustic performance. It may be less or it may be more. The magnitude reduction seen with vent open is likely a notch or dip with the response rising again at even lower frequencies. Few testing labs have the far field low frequency resolution to get the desired detail on this phenomena.

Mark
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Old 26th January 2005, 06:46 PM   #369
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Without fill, all the enclosures should be showing some ripple... did Tim ever give a specified amount of stuffing (i remember putting ??? in the drawings when i indicated it -- 0.25 to 0.5 lbs/ft^3 is fairly standard)

Unfortunately the linear scale charts make examing the LF results almost impossible and remove any easy way of seeing the periodic pattern any ripples make. Can you repost the results with a log scale?

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Old 26th January 2005, 07:03 PM   #370
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Quote:
did Tim ever give a specified amount of stuffing
IIRC, I used .25 lbs per cu. ft. I usually don't go much higher than that.
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