¿? ¿? ~ 1x12 or 2x12 ~ open-back or closed-back ~ ¿? ¿?

ChrisMusic

Thanks ICBM, a good smile and a laugh, just what I needed today   

now, about that burning pain...

ChrisMusic

So does the larger cabinet volume, or tuning of some of these cabinet designs, change the frequency response or polar pattern, apart from extending the low frequency capabilities ?

I can understand how it may affect the loading and acoustic impedance of the cone somewhat.

As I meant to say in the OP, I am a total noob in guitar cab design and performance issues, and hungry to learn from the experience here.

ICBM

ChrisMusic said:

So does the larger cabinet volume, or tuning of some of these cabinet designs, change the frequency response or polar pattern, apart from extending the low frequency capabilities ?

Yes, definitely.

ChrisMusic

ICBM said:

ChrisMusic said:

So does the larger cabinet volume, or tuning of some of these cabinet designs, change the frequency response or polar pattern, apart from extending the low frequency capabilities ?

Yes, definitely.

A marvellous economy of words there @ICBM   

Care to elucidate ?

Pretty please  :o3

ICBM

As in, yes the cabinet volume or tuning does change the frequency response and polar pattern as well as just extending the low frequency capabilities.

Exactly *how* is somewhat more complicated…

There are no really easy answers actually. A lot of things can have a surprisingly large effect, at least partly because in a guitar cabinet there is usually no attempt to damp out resonance, so the whole thing vibrates and changes the response of the drivers as well. And that's even in a closed cab. Open the back and it becomes a whole lot more complex again, depending on where the cab is in its surroundings.

ChrisMusic

Cheers ICBM.

Yes that does make a lot of sense, as you always do.

"There are no really easy answers actually" ~ I feared as much when I posted the discussion, tricky little thing, all this inter-related acoustics stuff.  Challenging and intriguing in equal measure.  It is good to get some ball-park understanding to guide future projects though.

I am beginning to understand why you said a long time back, that wood was so much better for guitar cabs than more acoustically inert materials such as MDF or the like used in Studio Monitors, PA and HiFi applications.

There was an interesting 1980's Mesa 4x12 pictured in a discussion a while back, with two compartments, the lower sealed and the upper open backed, how about a punt on the probable performance goals and sound on that one ?

llew

I use a Dr z 2x10 open backed cab,sound's huge loads of thump and plenty of dynamics.

ecc83

What is this "destructive interference" occurring in a 2x12?

If the speakers are the same model (I won't say "identical" because no two ever are!) they are in phase and will simply radiate as a single larger surface. The directional property comes from the increase in size (which is why a 4 x12 CB is even more directional and, incidentally, more efficient than a single or double cone) 

Stood on end a 2x12 radiates in the same way as a single 12 in the horizontal plane. But all this is frequency dependant. All speakers are essentially Omni-directional up to a frequency where the wavelength is comparable to cone circumference and gets ever more directional as F increases. Mind you, this is pure theory in that it assumes the cones vibrate as pure pistons and don't break up, which of course they do! No wonder then that people's experiences differ so greatly as different cones are put in varying cabs and responses duck and dive all over the shop!

Size matter and not only at LF. The front/back dimension will determine a standing wave frequency which will pour out of paper cones with gusto.

Your observation about front loading was interesting ICBM. I was pulled up quite smartly for suggesting it once! "Should never front load guitar speakers!" (I am still not fully convinced mind!)

About the best one can say I think is that if you are building a cab, make it as big as reasonably possible and flexible as far as closed/open/part open backed.

Dave.