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previous: Mike What tonal differences are there in... -- 6/21/1999 10:20 PM View Thread

Re: Cabinet Design

6/29/1999 1:11 PM
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Re: Cabinet Design
When a speaker vibrates, the cone makes the air move in waves. That's how the sound is propagated. When the cone is moving forward, the air in front of it is pushed while the air behind it is being pushed. The result is that the air in front of the speaker is being compressed while the air behind the speaker is being expanded - in other words, the waves in front and behind the speaker are OUT OF PHASE.  
 
 
 
If two out of phase waves are added they cancel each other. In an open back cabinet this cancellation is not total because the wave from behind has to travel some distance (the cabinet baflle dimensions) before it gets "mixed" with the "front" wave, so you cancel just the BASS. So an open back cabinet has less bass than a closed cabinet.  
 
 
 
The 3/4 cabinet is a way to make the "back" wave travel a greater distance before mixing with the "front" wave without having to build a bigger box. It's ecquivalent to have a larger baffle. The cancellations occur at lower frequencies and you have more bass.  
 
 
 
In a closed cabinet you have even more bass because there's no cancellation. Also, since the air behind the speaker is enclosed inside the cabinet, it will have a different behave when compressed or expanded (in comparison with open air). If the cabinet is very big you won't notice any difference. As the internal volume of the cabinet gets smaller you will notice the resonant frequency of the speaker increase and also the "Q" of the resonant peak will increase. In other words, if two closed cabinets use the same speakers, the smaller will have more "boominess".

 
Replies:
Gary C Interesting thoughts regarding the ... -- 6/29/1999 3:21 PM
John K. Are there formulas for specific dimensions? -- 6/29/1999 6:09 PM
Earl Re: Cabinet Design -- 6/29/1999 8:36 PM