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#521 | |
diyAudio Member
Join Date: Jan 2008
Location: Florida
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Quote:
1) Yes. 2) The Keystone has a more rapid drop in frequency response below F3 than the TH18 or DSL TH118, indicating the loading is a bit different. 3) The differences you notice could be due to flex or the effect of different dispersion due to proximity of the exit to the ground plane. There was a fairly significant difference in the smoothness of the upper response of the Keystone when measured on it's side or upside down compared to the "normal" apex up configuration. |
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#522 | |
diyAudio Member
Join Date: Nov 2007
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Quote:
Panel flex however will introduce some changes, which should show up in the distortion plot as well as FR. Here's a quick and dirty FR I did of my POC3 (which shares a similar layout to the TH* designs) in upright and sideways position. FR seems to be basically identical up to 150 Hz, but the distortion curve is different. Above 65 Hz, the distortion is actually HIGHER for the "sideways" position, but that may be due to the fact that I've done some changes to my PC to ensure that the mouth's bottom panel only touches the ground on one edge, which should minimize any additional distortion caused by the panel slapping against the ground. Or who knows - maybe the change in distortion is due to the change in orientation of the driver ![]()
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#523 | |
diyAudio Member
Join Date: Jan 2008
Location: Florida
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All the subs I have tested have progressively less distortion in the upper passband, in the range of 1-2% above 100 Hz. Distortion exceeding 100% above 130Hz indicates something is definitely wrong with the POC3 or the test gear. Art Last edited by weltersys; 13th May 2015 at 08:51 PM. |
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#524 |
diyAudio Member
Join Date: Nov 2007
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The only thing I changed during the testing was the orientation of the subwoofer.
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#525 | |
diyAudio Member
Join Date: Jan 2008
Location: Florida
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Quote:
A slow sine wave sweep makes either of the above mentioned problems easy to identify. |
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#526 | |
diyAudio Member
Join Date: Nov 2007
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#527 | |
diyAudio Member
Join Date: Jan 2008
Location: Florida
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1) Distortion relative to the fundamental signal means when they are equal level, distortion is 100%. Your graph displays THD crossing the fundamental signal both in the low range (expected) and in the upper range (unexpected). -10 dB is 31.62% distortion, -20 is 10% and -40 =1% etc. The Keystone (or bass reflex) loaded with the B&C or Lab 12s has distortion around -40 dB in the upper range. 2)Your graph does not appear anything like "48dB/oct LP signal @ 100 Hz or thereabouts." That said, panel flap or rubbing voice coils don't really care what the electrical crossover does. Art |
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#528 | ||
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Join Date: Nov 2007
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Note, both tests were done indoors, so there may be some in-room resonances that are adding their character to both the FR and distortion graphs.
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#529 |
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Join Date: Nov 2007
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As a sanity check, here's a TrueRTA measurement at 138 Hz, just above where the FR and distortion curves cross. Notice the level of the distortion components next to the fundamental. I moved the mic a bit closer to the subwoofer to get the level up a bit. Ain't no way that could be "100% distortion".
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#530 |
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