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Multi-Way Conventional loudspeakers with crossovers

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Old 22nd May 2018, 10:07 PM   #401
bwaslo is offline bwaslo  United States
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Yeah, looks like something off there. Here are some horizontal curves I have from a few years back (done indoors, unsmoothed, angles are 0, 20, 30, 45, 60).

mid offaxis plots.png

What happens if you move the mic closer/further? (thinking cabinet edge diffraction maybe).
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Old 22nd May 2018, 10:15 PM   #402
bwaslo is offline bwaslo  United States
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To rule out cabinet effects, try to measure on-axis and watch that peak when you move the mic closer/further as well as higher/lower. See if it stays put or shifts around. I don't know why the peak should drop like that due to anything in the ports -- directivity effects near that frequency should be happening from more near to the end of the waveguide mouth.
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Old 22nd May 2018, 10:57 PM   #403
3ll3d00d is offline 3ll3d00d  United Kingdom
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OK I'll give that a go next time I get the mic out.
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Old 22nd May 2018, 11:29 PM   #404
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Bill, any chance that's a combination of a resonance (on-axis boost) and path-length differences (off-axis null) from the mid ports?
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Old 23rd May 2018, 12:14 AM   #405
bwaslo is offline bwaslo  United States
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Dunno, maybe. Horn Response (not sure I have the same model from then) shows if the port is too small/too short/too close to the throat that can give a peak about there. Maybe try some modeling clay to "lengthen" the ports and see what happens?

Doubt an off-axis null could be there, though. It could only happen from the distance of the ports from each other (tweeter isn't playing!), you'd have to get about 5 inches closer to one than the other from being off-axis for that to happen.
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Old 23rd May 2018, 01:31 PM   #406
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Quote:
Originally Posted by bwaslo View Post
Yeah, looks like something off there. Here are some horizontal curves I have from a few years back (done indoors, unsmoothed, angles are 0, 20, 30, 45, 60).

Attachment 682485

What happens if you move the mic closer/further? (thinking cabinet edge diffraction maybe).
Do you have any absorption in back of the cone? I had a dip like that in my first Synergy proto and it turned out to be a reflection from the panel in back of the driver coming back through the cone and nulling at the mid port hole. Does the null freq correlate with the distance?
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Old 23rd May 2018, 04:22 PM   #407
bwaslo is offline bwaslo  United States
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It's a sealed-back midrange driver (TF0410MR)
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Old 23rd May 2018, 04:25 PM   #408
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3ll3d00d - are you sure the midrange driver is sealed against its mounting surface? Maybe an air leak could do that (guessing)
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Old 23rd May 2018, 09:12 PM   #409
3ll3d00d is offline 3ll3d00d  United Kingdom
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3ll3d00d - are you sure the midrange driver is sealed against its mounting surface? Maybe an air leak could do that (guessing)
i'm not sure how to verify that definitively but it certainly seems a very firm/tight/complete seal

I took some more measurements, different location as I had to do it inside but with the mic on axis and then moving both left and right & up and down (to an extent of about +/- 1m). No obvious difference in that hump.

mic_move.png

so then I took some quick and dirty off axis measurements at ~40 and 60 degrees both left and right

mid_directivity_test.png

it was a bit rough and ready but still no sign of a dip, just a softening of the hump.
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Old 24th June 2018, 10:25 AM   #410
3ll3d00d is offline 3ll3d00d  United Kingdom
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I finally got one one up and running

syns.png

quick on axis FR in my kitchen to check it was wired up ok

smallsyns.png

and the xo I have atm (which was tweaked a bit from the original design as my measurements showed a slightly different response shape with that XO, particularly on the CD), sims maintain v similar directivity pattern to the original though which I figured was the thing to aim for.

syns_xo.png

I will be running this with DSP so decided to leave that peak for DSP to fix

need to get it outside to measure it properly but will need to leave that for later in the week
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