base cavity?

[anonymoose]

Hey,

I'm building what I suppose would be very large bookshelf speakers and beginning to think they will look stupid on stands as well as unstable. I don't want to alter the depth/width to get them higher so can I make a second cavity under the primary one so they look like floorstanders?

The upper enclosure would have at least 3.6cm (1.4"?) of MDF seperating it from the lower cavity and will be lined with bitumen sheeting.

Will the bottom cavity effect the sound? Should it be sealed or open at the back?

The bottom cavity will be around 35-40cm high and around 10 liters.

TIA,
Anonymoose

 

[inertial]

(sorry for my english)
Hi anonymoose,
Yes, The "base" affect the sound but it is inevitable. Sometimes people
put the crossover in the bottom box and I think it is a good solution
if you must "to adjust" the filter for a long time. When the filter will be ok you can to fill with fine sand.
If you are very exacting you can also seriously decoupling the box from the base but it is very expansive ( see Newport air spring and similar
devices).
regards

 

[anonymoose]

Thanks for the input Inertial. Don't apologise for your english, its a hundred times better than my Italian .

I was thinking about filling it with sand, but a 10+liter cavity filled with sand would make the speakers very heavy. What about something dense but lighter? I've heard of people using cat litter and even that expanding builders foam.

 

[mike.e]

Cat litter,I dont think its very dense.You have two approaches
High mass or low mass + damping(thin ply+ bitumenous stuff)

Mike.e

 

[GM]

Greets!

Kitty litter is massive enough and my fave. The insulation foam is great for keeping cavities from resonating, but isn't suitable for mass loading. Sand, Portland cement, etc., is overkill so you could fill it partly with sand or cement and finish off with the foam.

GM

 

[Bill Fitzpatrick]

I was thinking about filling it with sand, but a 10+liter cavity filled with sand would make the speakers very heavy.

10 liters of sand is only about 35 pounds. That's not heavy.

 

[GM]

Greets!

True, but the cab itself isn't particularly light for those of us with bad backs/hands/whatever, so the ~32% less weight of kitty litter can be the difference between moving it around ourselves or getting someone to do it for us.

GM