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Old 20th August 2006, 06:48 PM   #1
ch83575 is offline ch83575  United States
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Default Is this normal diffraction?

Ok, this is my first project and I am moving allong VERY slowly. I am confused by my tweeter responce. I think that the baffle diffraction looks very exagerated (ie +/- 3db) and it is making the tweeter crossover very difficult. I have the tweeter recessed, but the rebate ended up a little too shallow, so there is a little lip. Also I am not flush mounting the driver because I dont know how. I guess my question is, is this normal? Do I just have to design around this, or am I doing something wrong?

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Front baffle

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Close-up of tweeter rebate.

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Tweeter responce in question.

So, do I just rebuild with tighter tolerances on my woodworking (again this is my first time at this) or is there a bigger problem here that I am missing?

Thanks in advance.
Chad
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Old 20th August 2006, 06:52 PM   #2
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are you sure that's not your mic??
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Old 20th August 2006, 06:54 PM   #3
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Well you could try experimenting with felt strips around the tweeter like this site. And see if that smooths out the response. Personally I've had my own disaster at flush mounting since I only have the Dremel router. So from now on i just surface mount then put on a block of felt around the drivers.

http://www.speakerdesign.net/home.html
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Old 20th August 2006, 06:58 PM   #4
ch83575 is offline ch83575  United States
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I do not think it could be the mic, as when I do a nearfield, it looks a lot like the seas spec sheet... also the same pattern does not show up on the woofer responce. I guess that also confuses me, why doesn't it show up on the woofer... they are on the same baffle. Is it because of their diameters relative to the baffle size?

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Old 20th August 2006, 07:05 PM   #5
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are you talking about the 25kHz peak??
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Old 20th August 2006, 07:07 PM   #6
ch83575 is offline ch83575  United States
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No. I am not worried about the ultrasonic breakup (well I at least expect it, it does kinda worry me). I am referring to the peeks and dips throught the pass-band. Peaks at aprox 2k, 5.2k, and 11k. They look like baffle diffraction only exagerated.
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Old 20th August 2006, 07:17 PM   #7
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my guess is "no". It looks more like a boundery reflection interferring with the primary signal. Is the mic on a tripod and the baffle isn't near any reflective surfaces?
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Old 20th August 2006, 07:23 PM   #8
Tenson is offline Tenson  United Kingdom
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The response looks perfectly fine to me apart from the HF peak. Unless you have an anechoic chamber, what do you expect? What was the set-up of the speaker, mic and surroundings when measuring?
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Old 20th August 2006, 07:38 PM   #9
ch83575 is offline ch83575  United States
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I am stuck in a closet sized room and I can not get more than 1.5m from the side wall. I just thought that heavily windowing the impulse would take care of that (2.4ms). It looks like I have windowed out the first major reflection, but is it possible that it is still a boundry reinforcement issue? The mic is on a grip arm also about 1.5m from the nearest boundry (in its case a corner).

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Tweeter Impulse responce

Perhapse I am just expecting too much from my measurement closet? I realize it is less than ideal, but it will really suck to have to move my big computer to another location, plus the only larger room is the living room... that might not go over very well with the wife! Is that the direction I should be moving though? Faulty measurements due to poor room?
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Old 20th August 2006, 07:44 PM   #10
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Hmmmm, it might be related to the windowing and mic position. Can you get the speaker outside, aim it at the heavens and hang the mic vertically? Then rewindow the MLS. It does sound like cramped quarters related.
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