Performance enclosures for Polk in-wall and in-ceiling speakers


Novice Member

I currently have a set of 4 Polk 265-LS and 1 Polk 255c-LS in-wall speakers in a 5.1 setup. They are great, but I am doing a rebuild/renovation and will be re-using them in a 7.1.4 atmos setup. I will be getting 2 more 265-LS speakers and 4 700-LS in-ceiling speakers.

My existing speakers were installed directly into the existing wall cavity by cutting through the plasterboard (dry-wall). This has worked fine and I have been happy with the sound.

In researching my new system I have come across people installing back-boxes behind in-wall speakers like mine when they are doing a new build. It makes sense to me that this would give better sound. It looks like it would also solve the problem I had with drafts coming through the bass ports of the 265-LS speakers!

It seems like Polk used to manufacture these boxes themselves but they have discontinued them. I found a link to an old product page here (Polk Audio Performance Enclosure Compatible with select Polk in-wall speakers at Crutchfield). It sounds like some people just build these themselves and that is what I hope to do (or at least get my builder to do).

I can build a basic box out of MDF or plywood using the dimensions shown here for the 265-LS speakers. I have a few questions though.

  • From reading around similar threads to this I have learned that I need to allow an internal volume of ~ 1.2 cu ft. Is that correct?
  • The Polk enclosure shows a series of wooden inserts. What do these do? Are they necessary?
  • What are the strips of black tape like material in the enclosure? What do they do? Are they necessary?
  • Why is there a square of insulation material in the bottom corner? Is this necessary?
  • Are there similar enclosure designs that exist for the 255c-LS or 700-LS speakers? If not, what size cavity should I aim for with these speakers?

Thank you for any input that you can provide.

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