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RE: What is the best 30-300hz bass cab solution?

"PPSL stands for push-pull slot-loaded and is done to reduce distortion. Art Welter did a test at DIYaudio and got a 30dB reduction in 2nd harmonic and a 20dB reduction in 4th harmonic in the bottom octave at full power. 20dB is a 100:1 reduction!"

For those interested in more detail:
http://www.diyaudio.com/forums/subwoofers/191833-push-pull-vs-normal-distortion-compared.html
Dennis,
Although 2nd, 4rth, sixth (even order) harmonics were greatly reduced by push pull loading, the third harmonic sometimes increased, resulting in the THD (total harmonic distortion) not always significantly changing, as can be seen in the 20 Hz 49 volt test results .
That said, distortion figures were reduced by 50% or more at some frequencies.

Since the frequency response and output of both the PP and standard cabinets were almost identical, an A/B listening test was simple, just swap the speaker cord and short out the unused cabinet.

At lower power levels, where the Lab12 is quite clean, no difference could be detected. When pushed at a power level where distortion could be noticed, the most distracting artifact was the audible vent noise from the reversed cone of the PP.
The lack of the second harmonic, an octave, made the now predominant third harmonic distortion more apparent in the PP cabinet. This is music related thing, the third harmonic , being a perfect fifth, may sound OK with some compositions, while sounding “wrong” with others.

Although the technical side of me says reduction of distortion of any sort is a good thing as far as a reproduction system is concerned, both my old ears, and a college freshman apprentice thought the push pull cabinet sounded less “musical” when pushed hard.




Doing another far more extensive test between six different HF drivers all on the same type of horn now, they sound quite different at different levels..

Art


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