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Old 21st October 2013, 06:49 PM   #131
epa is offline epa  Netherlands
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Originally Posted by epa View Post
looks real good,nice job
btw you might want to delay the outer subs a bit,for better dispersion of the upper bass.
uhrm its exactly opposite front sub needs the delay, if any
but it needs some experimenting .
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Old 22nd October 2013, 02:29 PM   #132
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How do they integrate with tops in the midbass, and do the tops even come close to keeping up with them....?
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Old 22nd October 2013, 04:31 PM   #133
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Originally Posted by Trackzilla View Post

weltersys- I am looking forward to having a chance to do some final tweaking & measurements, looks like it'll be a few weeks til I get caught up enough. BTW, distortion measurements haven't been part of my normal procedure, and they should be...any suggestions for a process on a tight budget?
Distortion testing is easy with some measurement systems, but still can be done the hard way by looking at a sine wave signal and the resultant harmonics on an RTA, subtracting the difference in dB, then calculating the distortion percentage.
For " close enough for rock and roll" purpose I calculated distortion % on the calculator page below, the harmonic with the highest level pretty much determines THD, the contributions added by lower harmonics generally add only a fraction of a percent to the highest harmonic.

In the two examples below a Lab 2x12" push-pull bass reflex enclosure is compared to a Lab 2x12" Keystone tapped horn using a 49 volt sine wave input at 35 Hz and 50 Hz.
At 35 Hz, the push-pull (PP) third harmonic (105 Hz) is 20.9 dB below the 107.9 dB fundamental, around 8.9% distortion, the tapped horn (Key) second harmonic (70 Hz) is 30.5 dB below the 114.5 dB fundamental, around 3.2% distortion.
At 50 Hz, the push-pull (PP) third harmonic (150 Hz) is 22 dB below the 109 dB fundamental, around 8% distortion, the tapped horn (Key) second harmonic (100 Hz) is 16.4 dB below the 119.8 dB fundamental, around 15% distortion.

The difference in distortion at high drive levels gives different sub designs quite a different sound, even when equalized the same.

In post # 12 the distortion and output of Lab 12 and a BC18SW115-4 are compared in the same cabinet:

Keystone Sub Using 18,15,&12 Inch Speakers

When doing sine wave testing like this you must keep the individual tests short and allow time for cooling between each test, the higher drive levels I used would burn the voice coils if applied for extended time periods.

Art
Attached Images
File Type: png 35 Hz distortion.png (104.7 KB, 91 views)
File Type: png 50 Hz distortion.png (105.6 KB, 87 views)
File Type: png Distortion Calculator.png (55.6 KB, 85 views)
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Old 23rd October 2013, 12:32 AM   #134
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Thanks Art, that's intuitive enough that I should be able to zap off some useful data about distortion when I get a chance to tune & test.
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Old 23rd October 2013, 04:11 PM   #135
MemX is offline MemX  United States
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Thank you for those graphs, they look like a good illustration of the distortion differences of Push-Pull setups
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Old 24th October 2013, 03:55 PM   #136
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Originally Posted by Trackzilla View Post
Thanks Art, that's intuitive enough that I should be able to zap off some useful data about distortion when I get a chance to tune & test.
Cool, as a suggestion type up all the frequencies and voltage you plan to test prior so you can copy and paste them in as you go, and keep track of where you are.

The only time I burnt a speaker during distortion testing was when I was manually entering, made a mistake, deleted, re-entered, oops...

Although this way of testing is a PITA, it does show more information than the usual distortion tests which only show second and third harmonics- some times even the fourth or fifth harmonic can be objectionable, since they show up where our hearing is far more sensitive than in the LF range.

Art
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