# Passives in L/R?



## icor1031 (Mar 24, 2011)

When I build my L/R speakers, I want to make sure the drivers in each cabinet have minimal space between them, so it sounds like it's one source.

I have three questions:

Would adding 2 or 3 passive radiators to my tower, destroy the above goal?

My understanding is that, when you add a passive, the woofer pushes in which causes the passive to push out.. Doesn't this mean they're out of phase, and it'll create nulls?

*Last, is there any other advantage, except a few Hz of bass extension, to having multiple passives and a woofer, instead of just a single woofer? It's for movie use, primarily.*

Thanks.


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## Zeitgeist (Apr 4, 2009)

Ok... so you're trying to create the most cohesive sound possible? That makes sense.

The difference between higher frequencies and those that most ports are tuned to (30-40-50 hz), and nearly all subs -- is that the low frequencies are relatively non-localizable. A great example being a dual opposed sub. You can't tell if it the source is from 1 driver or the other, unless you're inches away.

So no, adding PRs will not destroy your goal. And the PRs are out of phase -- just like the noise out of a port would be out of phase. 

Passive radiators are sometimes used instead of ports -- since there is no port noise. However, a passive radiator can cause mechanical noise (minimal generally). You can generally get similar results with ports or PRs depending on what you're trying to achieve. I think that (done right) you can squeeze out more output with PRs.

For movies, generally the extension is important. The end results depends largely on what size enclosure you can tolerate - and what driver you're using.

Plenty of commercial speakers that have a build in sub have it firing on the side......... and plenty of speakers have rear ports as well.


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