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loninappleton 17th April 2011 05:51 PM

Is this box building technique using scraps to avoid internal speaker resonance good?
Fostex FE127E DIY Bass Reflex Bookshelf Speakers

The link shows using circular cut outs and other scrap glued to the inside of a small BR for Fostex 127e.

I saw this the day after I pitched out (but did not discard) many circles and other small bits and was wondering if I should retrieve them for future projects?

Previously I had seen this random technique to avoid resonances and diffusion inside the box using foam which was in an old Speakerbuilder mag. I never had the choice foam shapes the author used, so never tried this tweak.


Richard Ellis 17th April 2011 06:10 PM

Yes , this is a viable technique to damp out resonances in an enclosure. Perhaps the key word here would be "randomness". Resonances occur when frequencies "pile up" by sameness. By being as random as you can...........with these 'random scraps' we can damp things out.

__________________________________________________ _____Rick.........

loninappleton 17th April 2011 06:27 PM

Thanks. I think I have a good application for this where I'm using a remaindered Roland full range electric piano speaker and sold on ebay. It will be interesting to see any improvements.

So far I have done Enabling with one and added a homebrew phase plug made from doweling and a wooden craft Easter egg. Very seasonal. In other years I've checked the craft stores around Easter for the right size of plastic Easter eggs which would be easier to work with. I never landed on the right dimensional size though.

Borus 17th April 2011 06:29 PM

Years ago I was involved in testing the vibration of some panels at work. We were using small accelerometers. I worked with them after hours to test some panels I was thinking of using for the sides of some speakers I was making. I altered the vibration (resonance frequencies) of the boards by gluing small blocks of wood to the areas of the most vibration until it was hard to measure them. One of the wizz kids that worked for me, did the math to find where to put the blocks afterwards. As I would not have the test tools or the accelerometers at home. I learned a lot about sound movement in different media back in those days. Still use these techniques when building speakers to this day. It can be done by hand with a stethoscope, test tone CD, and lots of patience.

loninappleton 17th April 2011 07:22 PM

I have a set of mp3 test tones and also the Marchand program (which I'd have to look up to link to. The Marchand free program uses a sliding frequency software to find out the Fs or resonant frequency if that number is not available. Marchand is fun to use. You can feel the air pushing through a port with your hand.

Here it s:

Look further down the page below the promotions:

Function Generator, Software for PC and Hardware models

The box I made for the Roland was salvage from other builds. So it is wide and shallow and tall.

I've only ever made two scratch builds with two speakers the same: BIB and GM designed MLTL for FE127e. The rest are experiments.

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