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Re: Number of speakers affect on tone?

11/29/1997 9:24 PM
Re: Number of speakers affect on tone?
>>I was under the impression that higher frequencies are subject to more audible phase cancellation (to the human ear anyway) than lower frequencies. Maybe that's not true either. <<  
Phase cancellation is easier to get at highs because of the wavelength of sound in air. Speakers separated by less than 1/4 wavelength don't exhibit "lobing" and cancellation.  
>>One final thing I've noticed that I wish someone  
would explain to me: the smaller the speaker's  
diameter, the less "directional" it seems to be.<<  
If you consider that every point on a vibrating surface is an independent point source speaker, the math says that the waves that spread sideways are cancelled, and the ones all heading out in parallel are reinforced. Point sources are more omnidirectional, just as you observe.
12/6/1997 3:08 PM

Thanks RG, that makes sense. I can sort of almost vaguely picture why a bigger speaker would have more "parallel reinforcement." Makes sense.
11/29/1997 9:15 PM

>> In my humble experience the  
single 15 usually has a better  
bottom than the 2x12 combo. I did  
some fast calculation and I see that  
2x12 is about 225 sq in. vs 175 sq  
in. for the single 15. Thats a  
difference, but I'm not sure if it's  
a big enough one to matter. <<  
A single 15 DOES sound as if it has a better bottom - it does this by having a poorer top. Most 15's roll off the highs worse than 12's and so sounds more bottom heavy, like the tone control on a guitar - that's a treble cut.  
>> At low  
freqs, it seems like there must be  
some phase cancellation in the pair  
of speakers no matter how well  
matched everything is.<<  
Actually, for frequencies where the separation of the centers of the cones is less than 1/4 wavelength of the sound, there can be no cancellation. The cancellation is prominent for highs, not lows. This is one thing that leads to "beaming" of highs and "lobing" in multispeaker arrays.
11/29/1997 9:10 PM

Speaker low frequency cutoff is at least partially determined by the equivalent surface area of the cone. Bigger diameter speakers can reproduce bass to lower and lower frequencies. Think about it - making bass waves requires moving a lot of air, and this is much harder to do with a tiny "piston" than a big, wide one.  
The bigger speaker is not necessarily louder per electrical watt in because bigger also means heavier in many cases. and that can mean more losses to heat. Two 12's may be more efficient and hence "louder" than one 15 because of both the increased surface area / air moved and also because there are two smaller, more easily moved cones and drivers, the "drive" being distributed over the whole area.  
This last is important - electrostatic speakers combine in one speaker response from low bass to very high highs because the whole surface of the speaker is the "driver", driven by electrostatic fields.
11/26/1997 6:45 AM

Bingo! I took the amp to my practice space and connected the external speaker connection up to a 4 ohm cabinet. The two functioning speakers in my amp (8 ohms each, wired in parrallel) create a 4 ohm load, but when the ext. cab. was added (in parrallel) the impedance the "amp" was seeing was 2 ohms (the same as the three original speakers wired in parrallel). Boy what a difference! It sounds huge, with a lot more head room. I compared it with a Dual Showman a friend keeps there and I swear it's almost as loud. I can't believe I didn't find this out before.  

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