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Modal Testing Speaker Enclosures
Modal Testing Speaker Enclosures
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Old 12th June 2019, 06:30 AM   #1
George Schmermund is offline George Schmermund  United States
diyAudio Member
Join Date: Mar 2011
Default Modal Testing Speaker Enclosures

The modal analysis hardware has made some more progress lately, so I thought I'd start a new thread to post the updates. There have been a number of upgrades and improvements in this version of the hammer and it's about ready for a market test on eBay.

The photos show one of the latest versions of the hammer and its different tips. The tips include a choice of rubber, Nylon, or stainless steel. There is also a detachable added mass for the back of the hammer to improve the signal output of the soft rubber tip when needed.

The other attachable item in the photo (not included with the hammer) is a Bruel & Kjaer 8200 force transducer that can be mounted on the front of the hammer and behind the selected tip. This adds an extra comparison calibration for the hammer's installed force transducer.

The calibration test stand consists of a cylindrical test mass supported on thin Inconel wires. The mass has a calibrated B&K 4384 accelerometer installed on its backside as a further calibration point.

The accelerometer design and testing is also close to the finish line and should be ready soon as a compliment to the modal hammer. The plan is to offer the pair as an entry level front end set of transducers for those who want to move up to the next level of speaker enclosure testing and evaluation.
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Last edited by George Schmermund; 12th June 2019 at 06:35 AM.
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Old 16th June 2019, 06:21 AM   #2
George Schmermund is offline George Schmermund  United States
diyAudio Member
Join Date: Mar 2011
I think I've finally arrived at the last accelerometer design and a working prototype for the time being. This one weighs in at 11 grams and should work well with any speaker enclosure that's out there. Typically an accelerometer should not weigh more than 10% of the structure that is being tested. That would limit this ones practical use to a panel weighing no less than about 4 oz. I don't think there will be any mass loading problems with most enclosure tests.

I've just finished the final assembly tonight so the full characterization won't be done for a couple of days. The basic design incorporates a magnetic base for attachment to any ferromagnetic structure. Otherwise the attachment can be done with things like super glue, double backed tape, or microcrystaline wax. I'm a big wax fan! It's easy to use, very tenacious, and cleans up easily.

The photos indicate the size of the device.
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