How leaky is too leaky

[moonfly]

Hi all,

Has anyone got any experience of installing IB drivers into a manifold where the rear wave space has a route back into the main listening room? Essentially the room the drivers will service is in a basement and the cinema room is a kind of room built within a room. The ceiling has fabric that is somewhat acoustically transparent. I will take steps to isolate the front and rear waves as best as possible, most of the side walls of the room a timbered out and plasterboarded off, the screen is acoustically transparent with speakers behind it but this space is filled with insulation and will largely be isolated from the space behind the IB drivers.

My options are essentially to make a couple of baffles and install 2 x 15" drivers in the front left and right corners of the room (effectively 2 subs, each being a dual 15), and hope the rear space contains the rear wave sufficiently, or build some very large boxes into the front of the room that will actually be just under 2 x total Vas of the drivers. This will essentially be slightly leaky IB vs large sealed and eq'd boxes using IB drivers.

FYI - the drivers are AE IB15's. Any input or experience welcome.

[ThomasW]

Cancellation will occur where ever the front and rear waves meet.

If the ceiling is fabric that's a major problem solved by putting blocking plates to seal off each joist bay.

The baffle idea will only work if it isolates the front and rear waves. Otherwise the large sealed box is probably your best solution.

A picture or drawing of the room might help us come up with other ideas..

[moonfly]

I'll try and get some images tomorrow, but this is a finished room that's being retrofitted as part of an upgrade, hopefully with minimum interruption. I'm probably going to make some test baffles and try that tomorrow anyway as the work involved isn't nearly as involved, but I would need to do these initial bits in order to fit large sealed boxes anyway. The room is a sort of room within a room construction so the joist have already been covered and there is just a suspended framework for the sealing that was covered in fabric and has rockwool behind it. This roof void space does bleed into the cavity behind the side walls of the room, with this cavity serving as the rear space. Im concerned about cancellations, but it shouldn't cause to much work to try so I'm going to give it a shot anyway seeing as I'm more or less at that point. I'll feedback the results.

My concern with the sealed boxes is that they will be an inherently high Q system that only something like a Linkwitz filter is likely to help resolve, so this may be a case of leaky vs sealed high Q (I have a mini DSP), but I will reduce the leak factor as much as I possibly can do.

[moonfly]

Some general images of the room

Attachments:

[moonfly]

As best as I could manage, here are a couple internal shots of the void between the actual room, and the internal constructed room. The image with the pipes is behind the side wall.

Attachments:

[ThomasW]

I think that a large box with a Linkwitz Transform circuit is your best bet. That way you don't need to worry about all the possible leaks.

[moonfly]

Just as a follow-up, I've completed the install and went with the open back solution first to test the performance of a 'leaky' IB. In short, the system performs perfectly and doesn't seem to suffer anything by the rear wave not being perfectly sealed off. I have gone to some effort to ensure the area immediately around the rear of the drivers has been sealed off and isolated as best as is possible, but beyond that, there are routes where the sound could potentially leak back into the room. In practice, the construction is such that this really doesn't happen and the IB performance is as intended and comparable to other 'perfect' installs I've done.

My take away point from this is that the IB installation is more flexible than one might consider. Sound quality is spot on, performance is as you would expect from an IB, and Im quite pleased that I dont have to go to the considerable extra effort of fitting really quite large boxes into the room.

[ThomasW]

If you're happy that's all that counts, thanks for the follow-up ....