# What do you think is the max size for surround speakers?



## robbo266317 (Sep 22, 2008)

I have been modelling these for use as surround as I can get them to go down to 30 Hz which suits a 60-80 Hz crossover to the sub. 
My question is if the box size is too large at 4 cu feet?







:scratch:


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## atledreier (Mar 2, 2007)

I'd say there's not much point in going larger than your fronts, but other than that, larger is better!


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## Andre (Feb 15, 2010)

Seems to me that If you system is crossed over at 80hz to the sub there is no need to have speakers that can play down to 30hz, 60hz maybe considering rolloff.


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## koyaan (Mar 2, 2010)

Being large shouldn't hurt surrounds, but they really don't see nearly as much bass as your main speakers on any recording that I'm aware of. Rear speakers see even less than side surrounds.


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## GranteedEV (Aug 8, 2010)

Keep in mind that most receivers and processors use thx style crossovers...

This means a 24db/oct lowpass cutoff on the sub and a 12db/octave electronic highpass cutoff on mains/surrounds.

To get a smooth response and ideal symmettrical blend, a 12db/octave natural rolloff starting near the crossover frequency is necessary. This means either a classic stylw transmission line (as per george augspurger's modeling software) or acoustic suspension box (sealed). It also means you want a sub roughly flat to 160hz. This will get you 24db/oct rolloff both ways.

THX Speakers are sealed and rolloff at 80hz btw.

If going the less desired ported route, an sloped tuning near 55hz is suggested by me. I always reccomend as large a box as you can get good performance out of. It will subjective sound least influenced by the box.


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## robbo266317 (Sep 22, 2008)

GranteedEV said:


> This means a 24db/oct lowpass cutoff on the sub and a 12db/octave electronic highpass cutoff on mains/surrounds.
> 
> THX Speakers are sealed and rolloff at 80hz btw.


OK thanks. 
So how does this look If I do it sealed?


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## GranteedEV (Aug 8, 2010)

robbo266317 said:


> OK thanks.
> So how does this look If I do it sealed?
> View attachment 29958


first what is the Qtc of that driver?

second, I would want to get that f12 a bit higher.. into the upper 30s ideally. not a huge deal by any means though. In this current scenario i think a 60hz crossover might sound just a tad bit better than an 80hz XO

third, I would get the box bigger for a q from .45 to .6 or so... although that contradicts the above goal of getting the F12 higher... this IS more my preference on damping so take it with a grain of salt. 

but yea, based on that model, this would work rather well indeed. :T

An alternative is to make that 4 cu ft ported box from earlier, with port plugs!


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## robbo266317 (Sep 22, 2008)

I think I will try the 3 cu ft that rolls off at 33 Hz (half of 66) with the option to seal the port(s)
I will build a test box and see. (mdf is cheap!)


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