Testing Harmonic Distortion in a enclosure

[ocool_15]

I realize most harmonic distortion testing is done on a infinite baffle but was wondering if the tests would be valid between drivers if done in the same enclosure.

F3 and QTC will vary with the different drivers. The Qtc varies from about .0703-1.07 in the test enclosure.

I have a 0.3 cu ft enclosure I can mount them in for testing and will build the proper enclosure once a driver is chosen.

I have a couple pairs of 6.5" and am looking at using a pair for midbass/bass duty for my moderate home theatre. Frequency response will be F3-120Hz.

[MaVo]

a closed volume generates its own distortion due to air compression. look at linkwitz site for details.

[Michail Bugaria]

But also work as HPF for driver and reduce some HD in low end.
It will be interesting to look and compare behaviour HD loudspeakers in the enclosure and without it.

[Ron E]

Originally posted by ocool_15
I realize most harmonic distortion testing is done on a infinite baffle but was wondering if the tests would be valid between drivers if done in the same enclosure.

Just do it. The true test would be if they were each in the enclosure size you would use with them. I wouldn't agree that distortion tests are usually infinite baffle....

Originally posted by MaVo
a closed volume generates its own distortion due to air compression. look at linkwitz site for details.

This is important only when the enclosure stiffness dominates and when the displacement volume of the driver exceeds 15% of the total volume. Otherwise the air spring is usually considerably more linear than the driver's own Cms.

[ocool_15]

Originally posted by Ron E

Just do it. The true test would be if they were each in the enclosure size you would use with them. I wouldn't agree that distortion tests are usually infinite baffle....

Since the systems Qtc and F3 will vary from each other and from their final alignment doesn't that make the information of limited or no use in their intended range( up to 120Hz)?

Would the comparison be accurate at frequencies well above the enclosures high pass filter effect like 250 Hz-20kHz?

[ucla88]

See my dipole-monopole comparison graphs

See the posts for Sept 19th.

http://www.markk.claub.net/whats_new.htm

To be fair, this is a 4 vs 1 comparison and a host of changed variables. Nonetheless, the distortion pattern is clearly different for the open baffle vs the closed box.


Ideally, if you're going to use a driver in an open baffle configuration, that's the way you should test it. Same for the closed box. However, that's just not always practical. You should still be able to get a reasonable idea of driver nonlinearities as long as they are compared in the same way.

[Ron E]

Originally posted by ucla88
See my dipole-monopole comparison graphs
Ideally, if you're going to use a driver in an open baffle configuration, that's the way you should test it. Same for the closed box.

Very interesting! Even order is what would typically be generated in an enclosure. It would be neat to see the test rerun with one driver in each enclosure at the same drive level, and perhaps in different sized closed boxes.