Does butt-jointed assembly geometry matter?

[Brisso57]

I'm about to construct a pair of boxes for full-range drivers. Peak (Coral) 8CX-501's.
I'm using 25mm MDF butt-jointed. The joint edges will be routed so you can be sure they'll be dead-square. The cabinet will be taller than it is wide.
Now to the question ...
There are two options:
1. Have the top "capping" the two sides; or
2. Have the two sides "sandwich" the top.

I plan to veneer the cabinet, so the joint won't show either way.

They will be similarly fixed, with a reinforcing strip glued & screwed inside.

Is there any sonic benefit to be gained by choosing one arrangement over the other?

I'm thinking that the arrangement which results in a shorter side piece will provide less vibration in the cabinet. Is this the only consideration? What other factors are at work?

Which would you recommend?

cheers

Doug

[Scottmoose]

Either will be OK, but a top tip is to double the top panel. Internal bracing is good, as you've noted. Best is to brace the rear of the magnet against the rear panel. Dave's Swiss cheese bracing is best for that, like the attached:

[Brisso57]

Originally posted by Scottmoose
Either will be OK, but a top tip is to double the top panel. Internal bracing is good, as you've noted. Best is to brace the rear of the magnet against the rear panel. Dave's Swiss cheese bracing is best for that, like the attached:

Yes. Actually I was sharing a beer with Greenie512 last night and he was telling me about the swiss cheese brace Dave recommended he put in his remodelled (small) Thor's. He's very impressed with the result.

I've already cut & routed the front baffles so I'll need to ponder how I can fit in a brace without reducing the volume too much.

Doug

[Scottmoose]

It doesn't need to be full height, so even 1/2 or 1/3 should do the trick pretty well.

Best
Scott

[vitalstates]

Originally posted by Scottmoose
Either will be OK, but a top tip is to double the top panel. Internal bracing is good, as you've noted. Best is to brace the rear of the magnet against the rear panel. Dave's Swiss cheese bracing is best for that, like the attached:

Just a thought... I have discovered, but not proved, that the resonance in the side panels can resolve into the top panel. Remember the vofo 2 Scott?
If you stop the resonance in the top you may find that the resonance will migrate back to source, i.e the sides. My advice would be NOT to double the top panel but concentrate on the bracing.

Thinking back to building light aircraft, the idea was to sink vibration and not to stop it. If you stop it, it only moves somewhere else.

fwiw to answer the original question, I have always capped at the top and inserted at the bottom. Its always worked for me.

Ed

[Brisso57]

Originally posted by vitalstates


fwiw to answer the original question, I have always capped at the top and inserted at the bottom. Its always worked for me.

Ed

Cap top & insert bottom was exactly what I had planned originally, but I didn't want to pre-empt answers.

That, PLUS 2 swiss cheese mini braces - 1 fore&aft & 1 side2side should be good.

Thank you all. I'll try to post some progress pictures in due course.

Doug javascript:smilie('')

[Scottmoose]

Originally posted by vitalstates
If you stop the resonance in the top you may find that the resonance will migrate back to source, i.e the sides. My advice would be NOT to double the top panel but concentrate on the bracing.Ed

Good plan Ed. My only slight concern is that the MDF is not as sonically forgiving as the BB ply. On the whole, like yourself I prefer resonance control rather than attempted erradication, but if this is what's used in the construction, then the material's sonic properties tend to sway toward pushing it below the operational passband.

[Pit Hinder]

Originally posted by Scottmoose


Good plan Ed. My only slight concern is that the MDF is not as sonically forgiving as the BB ply. On the whole, like yourself I prefer resonance control rather than attempted erradication, but if this is what's used in the construction, then the material's sonic properties tend to sway toward pushing it below the operational passband.

Yup. MDF resonances ares smallband peakish and have a decay time you nearly need a calendar to measure. Good old crude chipboard (I have to use it for the invisible parts, BB is ~40€/sq.m hereabouts) is much more forgiving if you don't mind the odd slipped disc when handling larger boxes .

Cheers,
Pit