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).
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).
/sreten.Hi Andrew, would it make it worse if I admitted to also being a "Sassenach" prior to 1957! Yes, you have to be careful when trying to find the "Bombers" football club on the Net. All sorts of things turn up. Their site is actually called "Bomber Land" which is not much better! Their nickname derives from the fact that their home suburb of Essendon used to be the main international airport of Melbourne; planes everywhere. While on that topic why is one of the UK Sheffield teams called "Wednesday"? It's puzzled me for a while. You know Australia is an interesting place from the point of view of football as it has four significant codes, Rugby Union, Rugby League, Soccer and Australian Rules. I'm not sure that there are many other places where that is true. Ireland is one......any others? It is also one of the rare places where a League is more popular than Union. Aussie Rules is perhaps unique in being played on an oval and not a rectangle. Anyway I still maintain a Sherrin is an ideal type of paradigm for a speaker box (enclosure) so there!!!!!! BTW if Tony Blair can get you guys out of Iraq before us then I'll give you bragging rights on "right thinking". Best wishes from Australia.......Take care, Jonathan.
BTW Andrew re: post #9 that is my plan except I've now got the raw material together for seven amps (plus some more for the children). A "sub" plus a pair of threeway satelites is the plan. In my neck of the woods, where it is subtropical, I'll have to consider liquid cooling with the heat exchanger under the house. The recently set overnight minimum record was 28C. (well, the highest o/night minimum if that makes sense) Not sure what that is in Farenhiet but it is warmish. If it works I'll bring it in during the winter when it can get down to 5-6C. Usefull then, as heaters.
Hi,
a router may not be required.
If the speaker chassis is the same thickness as the baffle, then plant a second baffle board behind the driver flange and mount the driver to that.
The front baffle can have a hole that is a close fit to the chassis od.
Joining the two baffles are down to choice.
Screws only,
Screw & glue,
Joint with a damping medium (maybe non setting bitumen),
Bond with a thick resilient layer of silicone sealer.
Take care to allow any/all solvents to evaporate before mounting the driver.
a router may not be required.
If the speaker chassis is the same thickness as the baffle, then plant a second baffle board behind the driver flange and mount the driver to that.
The front baffle can have a hole that is a close fit to the chassis od.
Joining the two baffles are down to choice.
Screws only,
Screw & glue,
Joint with a damping medium (maybe non setting bitumen),
Bond with a thick resilient layer of silicone sealer.
Take care to allow any/all solvents to evaporate before mounting the driver.
The other thing that hasn't been mentioned are the acoustic benefits of rebating on what happens on the INSIDE of the box. If you look at some of the pressed steel mids (old KEF B110 are a case in point) there is not much clearance for the sound waves from the back of the speaker to emerge unhindered. Various people have done tests that show that reflections immediately behind the cone can be bounced back thru' the cone and further hinder the clarity of reproduction.
Doing something like Andrew mentions in his last post will allow the greatest space for the sound to dissapate inside the box which is where you want it.
BTW~Andrew, What's 'ceroq'?
Doing something like Andrew mentions in his last post will allow the greatest space for the sound to dissapate inside the box which is where you want it.
BTW~Andrew, What's 'ceroq'?
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