Sound variation depending on cab positioning

gearaddict

Last night I was happily playing in my usual position - standing right in front of my cab. I then walked across the room to look at something until I was standing in front of the cab a few metres away...and the sound was completely different. What had perviously been full and deep and rich was suddenly thin and tinny and harsh.

I've not noticed that level of variation before...are these sorts of effects amp dependent?

Danny1969

The higher the frequency the more directional it becomes, plus once you step away from the direct beam you also get all the reflected sound from surfaces in the room, which is why in studios they use a lot of diffusion to break these reflections up. Cab design also plays a part, some are far more direction than others. 

ICBM

Amp-dependent in the sense that the brighter the amp, the worse it tends to be - but more down to the cab usually. Also sometimes due to the room acoustics.

If the cab was on the floor, you really need to get it up off the ground to where you can hear it properly. That will also make it project better out into the room, and decouple the bottom end so it won't conflict with the bass as much. This will give you a better mix overall even if you like bassy guitar sounds.

Some people like to point the cab up at their ears, but I think that gives too much of a good thing and you end up dialling the amp in too dark because the speakers sound brighter on-axis at short range than they then do out in the room.

Waist height or just above with the cab level seems to be the best, to me.

Cirrus

This might be bollocks and I welcome anyone who knows better to challenge me... but I seem to remember there being some correlation between directivity (is that a word?) and speaker size.

With a typical 12" speaker frequencies with a wavelength below 12" pretty much eminate evenly out from the speaker. So if you're standing off-axis (ie not dead on centre) you can hear those frequencies pretty much ok.

However, once you get to sounds with about a 12" wavelength and less (say 2,500-3kHz... basically upper mids/ treble on a guitar) if you're standing off axis you encounter a problem because the sound coming off one side of the speaker and the sound coming off the other side of the speaker cancel out or at the very least interfere with each other due to phase cancellation. There's not a lot you can do about it, it's just the physics of a 12" wide disk having to reproduce the full frequency range. It means that the more off axis you are, the more complete any phase cancellations are and this mostly affects higher frequencies. But if you're right in line with the direction the speaker is pointing, all frequencies from all parts of the speaker get to your head at the same time so there's no phase cancellation and treble comes through nice and clear.

It's very much a problem of perception though, and you just need to work out where in the room the sound matters to you then adjust your tone for that. If you want it to sound good where your head is, turn dem knobs. If you want it to sound good right in front of the speaker where a mic might go, because you're recording or being miked up for a gig, turn dem knobs. If you want it to sound good out in the room,  turn dem knobs but just be aware that it'll be brighter directly on axis - I usually point my amp a bit away from the crowd when I'm having to use it to fill the room.