Sound (bass) coming from back of cabs

Why do some cabs do this?
I've heard scoops do it, Quakes when on their side do it, T18's can do it when cone facing out.
Sound better on stage so to speak.
Technical reasons??

yeah good question....... the t18's in one of the venues i dj at sound better from behind!!!!!! i.e. the bass is lower...... smiley29

bee wrote: yeah good question....... the t18's in one of the venues i dj at sound better from behind!!!!!! i.e. the bass is lower...... smiley29

this could be because the lower (in frequency) you go, the coverage becomes more omni-directional. A bass note, which is probably at the -6db point of the Sub's capability, will usually appear to be louder behind the Subwoofer in relation to the higher bass notes which overpower the speaker's response while you are in front of it.

In large venues, cardioid subwoofer arrangements are sometimes used to control the bass spill on to the stage.

Sher Singh wrote:
this could be because the lower (in frequency) you go, the coverage becomes more omni-directional.

This does make sense.

Why do some 18" drivers manifest this phenomenon more than others ?

In the same cab, have seen driver A project huge amounts of SPL to the rear of the cab with acceptable SPL at the front,
Driver B provided excellent SPL at the front, with lesser SPL to the rear.

Driver B was definetly known to be more efficient.

All cabs will be affected by Defraction. As soon as the waves reach the edge of the cab they would want to rap themselves around because the cab is too small to contain the wavelength produced. However, we do have to consider why some cabs are more prone than others. I think that the design of the cab would be the least cause of the problem, because you can't alter wavelength V frequency whatever the design. A badly built cab that resonates will produce a sound all around the cab, because anything that moves will send out sound waves. Could this be a contributor to the problem?

so by adding more bracing Tony, could this help to reduce this problem.......

It's got to help. If you think about the debate with scoop bin performance, I am always amazed by the different sounds from one to the other. To me they should all sound very close to each other, because, as I have said before, small differences in the shape of the horn should make little or no difference to the sound waves which travel around the bends. So therefore, I have always concluded that it must be the build quality of the cab that makes the difference, i.e. the stronger and more rigid the build, the better the sound will be, because there will be less energy lost through the cab itself.
I think that if you were using a poorly built cab, it may stand there like a giant radiating machine, sending sound in all directions.

I've just designed a double 21'' BPH and a single BPH with a double back, 36mm

I'll let you know how I get on with them as far a bass leakage

the idea was to achieve what often happens when I enclose subs in a concrete dj stand, obviously no bass out the back and all out the front

so 36mm should help a LITTLE smiley24

Beginning to think, after certain cab build quality is reached, driver behaviour is still a factor.

Backward motion on some 18" drivers (except PD), often seems excessive in comparison to forward motion.

Could this not be contributory?

no way, should be equal

unless they are really old and called Wembly B lines