What happens if I do this?

JohnR · « **on:** 1 Nov 2007, 11:34 pm »

Suppose for the sake of the discussion that the baffle goes from floor to ceiling. And the drivers are subs. This is a dipole, right?

JohnR · « **Reply #1 on:** 2 Nov 2007, 01:00 pm »

No takers? OK, well, I think it's kindof a dipole but the nulls are not exactly to the sides, but shifted towards the front.

JohninCR · « **Reply #2 on:** 2 Nov 2007, 01:43 pm »

John,

Yes, that shape would shift the area of greatest null somewhat forward, and result in lower overall output in the listening area. A few small changes that I would suggest:

Alternate the driver mounting, so half of your magnets are in the center manifold for push/pull operation.

Add 2 more pieces of wood perpendicular to the baffle to form 2 rear facing channels, which summed together equal the volume of the front facing channel. The reason for equal dimensions of the 2 combined rear pathways to the front is to create an equal air mass load on both sides of the drivers. If those channels are equal to the front channel depth, then you have a dipole. If you extend them deeper, then you begin to shift the null rearward, giving you broader dispersion in front.

Rudolf · « **Reply #3 on:** 2 Nov 2007, 07:28 pm »

Quote from: JohninCR on 2 Nov 2007, 01:43 pm

Add 2 more pieces of wood perpendicular to the baffle to form 2 rear facing channels, which summed together equal the volume of the front facing channel. The reason for equal dimensions of the 2 combined rear pathways to the front is to create an equal air mass load on both sides of the drivers. If those channels are equal to the front channel depth, then you have a dipole.

What does "which summed together equal the volume of the front facing channel" mean? Many people erroneously think that each back channel cross area should be half the front channel cross area. JohninCR correctly states that the volumes should be equal. Which means, that you have to add both in-cone volumes to the front channel and subtract the same cone volume (and some of the magnet volume) from the back channel volumes. I would not follow Johns recommendation to alternate the driver mounting because this would result in very different air mass loads on both sides of the drivers.

Rudolf

JohninCR · « **Reply #4 on:** 2 Nov 2007, 09:20 pm »

Rudolph,

If you have multiples of 4 drivers (4,8,12), then getting the pathway volumes becomes easy. Each of the 2 rear pathways just needs to have 1/2 the width of the larger front pathway. That gives you equal air mass on both sides of the drivers as long as you don't create multiple pathways using full shelf bracing.

JohnR · « **Reply #5 on:** 3 Nov 2007, 12:59 am »

Hm. Thanks! What would be the effect of not having the air mass loads equal?