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Old 27th October 2006, 12:52 AM   #1
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Default Why rebate speaker cut-outs?

Hi, Just wondering why most speaker cut outs are rebated using a router? Is there an improvement in sound?
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Old 27th October 2006, 01:13 AM   #2
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Yes.

The techies can take it from here.
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Old 27th October 2006, 01:49 AM   #3
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Greetings fellow Digger. I'm ex-Melb' myself many moons ago. Re; your question. What happens is this. As the wave of sound (which is an alternate compression and expansion of the air) comes off the face of the cone/dome etc it can interact with any physical object in it's path. This causes distortion of the waveform. I forget whether these are just refraction effects or defraction aswell (I think it's diffraction), (and I can't spell). Illustrations in the standard texts show that angular surfaces such as the join between the front and sides of a conventional box will create this effect. The result is a series of small additional waves that will effect the purity of the original signal. They "muddy" the result. Not a techical term but quite descriptive. Actually, a classic retangluar box is not a good shape from a theoretical point of view. Hence you see various attemts to move away from this type of enclosure. (i) The first move is to chamfer the edges at say, 45 degrees. (ii)Then to make them round ie a smooth curve. (iii) Thirdly, a designer will have non-parrallel sides ie a tapered tower and eventually (iv) curved sides. So being in Melb' you'll understand when I say that a "Sherrin"* is an ideal shape for an enclosure!!!!! Sometimes they place a mat of felt or other acoustic absorbent material on the front face of the enclosure. Now all these work but also incur penalties of cost and sometimes aesthetics, although that is of course v.subjective. That is one reason why DIY speakers can be so rewarding. We have more time and less commercial restraints on our work.
I'll never forget the first time I rebated a 5" Philips mid-range and took the plasitc suround off the 1" tweeter. My wife and I did a comparison with the unmodified enclosure and that was my first DIY improvement. A very noticible difference. (1975 in Fenwick St. North Carlton for the history buffs/trivia freaks amongst us!) Now you'll see the sort of modifications I've mentioned in various speakers around the place. Another technique is to offset the drives so that they are not equidistant from the two sides. This tends to smooth the on-axis response but others have criticised it for reducing stereo image (debate starts at this point). There's good stuff around on this. Try "diffraction effects in speakers" in Google and see what pops up. Also just a simple tute on "wave theory" be it water or air, its all the same, will prove rewarding. You may well have done it in high school physics!!!!! Martin Collums (High Performance Loud Speakers) states that a potruding screw head can make an audible difference.

*For the unbelievers amongst us a "Sherrin" the oval shapped football much loved by all right thinking Aussies! "Go the Bombers"
(which hasten to point out is a football team and not a terrorist group).










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Old 27th October 2006, 01:59 AM   #4
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Hi Jonathan, thanks for your lengthy reply. Actually I'm building a 3 way truncated Pyramid design and I'm alkready thinking about the next design which will be a curved sides enclosure.
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Old 27th October 2006, 02:06 AM   #5
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And I take from you name that you're a class A convert....congratulations.
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Old 27th October 2006, 02:08 AM   #6
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lol yes I am, but Solid State not valves (not yet) I can use a little heat from amp, its cold today in Melb.
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Old 27th October 2006, 02:43 AM   #7
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I'm solid state too, Linsley Hood 10 watts. can't beat it. Yes, we have three daughters in Melb', can get cold. Long hot one up here this year.
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Old 27th October 2006, 09:05 AM   #8
sreten is offline sreten  United Kingdom
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http://www.zaphaudio.com/mtg-surface.html

/sreten.
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Old 27th October 2006, 09:37 AM   #9
AndrewT is offline AndrewT  Scotland
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Hi,
build some JLH 20W for 5.1 surround and you'll never be cold again.
On second thoughts a JLH on each driver would be even warmer.
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Old 27th October 2006, 09:43 AM   #10
AndrewT is offline AndrewT  Scotland
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Hi,
the last three lines of post3 include many words that get past the "banned" dictionary
i.e. football, bomber, terrorist, right thinking Aussie.

Moderators!! where are you?
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