Expansion Cabinet Questions

Well, a doubling in speaker area would indeed double the volume, but when translated to maximum sound pressure level, it would only increase by 3 dB. Doesn't seem very much, however it is noticeable.

 

Although 3dB doesn't sound like much, the dB is a logarithmic scale! Which is why as Oysterman says the difference would be noticeable!

 

A perceived doubling of volume is an increase of 10 dB. This equals ten times the acoustic output power. Either you get an amp with 10 times as much power, or you stack about 10 cabs with the same amp.

3 dB is a clearly audible increase.

 

"Perceived doubling"... how can one tell that "that signal appears to be exactly twice as loud as the other one"?

 

This is an excellent question, and one whose answer I wasn't sure of myself. According to one of my noise control books, it says that "tests have shown" doubling of loudness occurs at *approximately* 10 dB increases in sound level. But they say this effect mainly occurs above 40 dB. Below that, perceived loudness increases more rapidly with sound level. Other than that, information seems sparse. I'm not sure what psychoacoustic tests had been done to come up with this. It's similar to asking what light level seems twice as bright. They might have done something like take a typical source and move it from a distance R from the listener to 1/2 R. If the source were perfectly omnidirectional, the increase would be about 6 dB. But if the source were somewhat directional, perhaps the sound level increased about 10 dB.

So maybe they had listeners blindfolded while moving a noise source closer to them and had them indicate when they think it sounds about half as far away. Just a guess, though.

- Mike

 

assuming that the speakers are stacked, wouldn't doubling speaker area cause a 6dB increase? 3 db from the doubled speaker area, and another 3db from mutual coupling? You are the techies, but that's what i had understood...

 

I think the doubling of cone area IS the actual mutual coupling. Just two different words for the same phenomenon.

 

Hey guys... aren't we forgetting something here ?

If his amp has 8 ohm speakers, and he adds an 8 ohm cab to it.. his wattage will be boosted.
Won't that increase his output too ?

 

No...mutual coupling is very, very different thatn surface area. But the way it works is kinda technical, actually it is wave physics, but I have enough of that at university everyday, so I feel inclined not too explain it.

DingZ

 

k hypothetical situation..i have one speaker on the right side of the stage, facing the crowd... if i add another speaker on the left side of the stage facing the same way, i double my volume, right? that's regardless of mutual coupling... then i move the two speakers closer to each other, say within 1/4 wavelenth of the fundamental on an open g string, that's like 4 feet or something.. then mutual coupling enters.... and it doubles again, right?

That would mean that the volume doubles twice.. once with the extra speaker, and again when they are moved closer to each other, right? hence the 6db increase...

I don't have a degree on this, so if i'm wrong please set me straight, but this is what i believe to be true..

 

I would say that the a 410 or a 115 are good to expand with. I actually have a super redhead, i bought it about a week ago, and I specifically tested it with other cabs so that I could get an idea if the cab could handle the extra cab well. It did, and if it hadn't been for the fact that I am getting a new bass I would have picked up a Triad. I tried it with a goliath jr210, goliath 410, big ben 18, son of bertha and a triad. I personally liked the triad and the 210 the best as they were both 4 ohm cabs, so I got 450watts out of the SR. I don't know why, but SWR doesn't list these two as suggested extension cabinets. I personally liked the way it sounded with the triad, that 3 way system is very nice, but I think you have to try anything that you think may work to see what will work best.