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Re: Cab for EV12L

6/10/2003 4:48 PM
Re: Cab for EV12L
Well that's comparing a speaker with a cabinet to one without a cabinet. Again it's not a fair comparison because there is no cabinet. The reason for the lack of output is the cancellation of the positive pressure from the front by the negative pressure from the rear of the cone.  
it would seem to me that the whole purpose of a cabinet is to isolate the two sides of the cone from each other to eliminate this cancellation and improve efficiency.
6/10/2003 5:27 PM
To a large extent that is true at low frequencies but the efficiency at higher frequencies is largely unchanged. I'm not intending on playing with words here. The box changes the low frequency response but the efficiency at higher frequencies is largely unchanged. The problem with an open speaker is the bass response is so cut-off that it would give the impression of being less "efficient" with low frequency signals, it's an extreme case. You can lower the cut-off frequency, and get more bass, by putting the speaker on an open baffle-the bass improves but the high frequency stay at the same level. A closed cabinet like a sealed or ported cab doesn't have the cancellation issue and for typical sized cabs bass cut-off isn't so high that it gives the impression of bass cut. It's not that the enclosure has no effect at all, the enlosure controls the shape of the bass response but whatever speaker you use the output at higher frequencies plateaus off to the same level.  
6/6/2003 1:55 AM

"Anyone have dimensions?"
I built a pair of 1x12" cabs for a pair of similar speakers (Mesa's original 150W Black Shadows) that I have, and I used 22" wide x 16" tall x 12" deep so that if I eventually get enough cash for a quad of good 10"s, I could switch over by just making new baffles. I am probably not going to do this now, though, since they are pretty nice as 1x12" cabs, and if I have the scratch later on, I'll pick up a Marshall 4x10" and stick some Weber Blue Pups in it....  
Anyway, I used 1/2" plywood all around (with 1"x2" corner pieces inside), and then screwed & glued a decent sized rectangular scrap (leaving about 2" all the way around it) to stiffen each of the back panels and hopefully eliminate any bad resonances. It seems to have worked. I'm eventually (hopefully soon) going to get a second Weber P12B to match the one I already have, and stick *them* in the cabs. That'll be a killer sound! :D  
They sound great with a pair of 1.25" ports in the lower portion of the otherwise closed back panels. The ports loosened up the sound of the cabs, which were originally completely closed-back and damped the speakers a bit too much, and really made them have the best of the open and closed cab sounds. Even with the fairly large volume for a 1x12", the speakers, which were designed for an open-backed Boogie cab, sounded a bit tight and bass-shy in the sealed back cab.  
They project fairly well, and are still quite directional, which is good if you have problems getting into volume wars with a drummer who plays louder if he can hear the guitar.... Open-backed cabs tend to disperse sound in a much less directional way, and have a lot of sound coming out the back that can set those volume wars off....  
One of these days I ought to finish those cabs up with nice quarter-round edges/corners and some tolex, but maybe I'll just round the edges/corners and throw a little Minwax stain on 'em (maybe PURPLE! :)) and then poly coat 'em....  
C ya,  
6/18/2003 5:18 PM
I just finished a pair of cabs for JBL K120's and a pair of Celestion G70M's. I built 2 Chieftains and I wanted to build a pair of combo's but when I calculated the weight I was looking at greater than 70lbs each. So I opted for the best of both worlds. I made a pair of heads 20.5W X 9.0H X 12.0D I was looking at SMF amps and noticed they have a trap door on the cabinet back. What a great idea!. I ended up with a cabinet 20.5W X 16.0H X 12.0D.  
1.63Cubic feet. I split the cabinet back into 3 pieces. a 2in strip across the top to mount the speaker jack. then a 6 inch fixed piece across the bottom , I screwed a piano hinge I bought at Home Depot and mounted the 6 inch trap door to that in the middle of the cab. I have always been a closed back guy. This combination gives the best of both worlds. There is quite a difference in sound with the door open and closed. There are some great benefits to doing this. I spent quite a bit of time laying out the amp and cab dimensions on 5 yards of 54in W tolex. I ended up with 2 heads including backs, and 4 speaker cabinets within the layout. I estimated 97% tolex material utilization. The front of the amp heads are of a different colour of tolex and doesn't count for the 5 yard material utilization. The fact that the cabinet backs are 3 pieces helped greatly in the material utilization.  
One other tidbit. I used 3/4 inch birch veneer plywood for the cabs. 4X8 plywood weighs roughly 25lbs per 1/4 inch thickness or 0.016276042 lbs per square inch for 3/4 inch thickness of 75 lbs.  
I can use one, 2 or 4 cabs and a combination of open or closed back configurations . I recommend this to all you cab builders. If you don't like the trap door cab just replace it with a fixed piece. I think Mark Sampson has come up with yet another masterpiece.  

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