Speaker soffit construction

[ggegan]

If one wants to use soffit mounted speakers in order to avoid SBIR issues, what type of construction is required? I have seen plans that specify a concrete wall with a sealed speaker cavity, but I have also seen soffits made of OSB and drywall with a lot of pink fluffy in the cavity. Does OSB and drywall have enough mass to eliminate SBIR? If using OSB and drywall, should the speaker cavity be walled off from the cavity and sealed?

[boggy]

Originally Posted by ggegan

If one wants to use soffit mounted speakers in order to avoid SBIR issues, what type of construction is required? ....

"Baffle step" is solved with LP shelving EQ filter in crossover circuit in all comercially available free standing loudspeakers.
If you like to build a real soffit mount to convert full space response of loudspeaker to half space, it's best to use concrete.

When you do soffit mount with free standing loudspeaker, you must disable shelving filter or attach external one with inverse characteristic to cancel it.

In all cases with soffit mounting you change frequency response of loudspeaker, and if it's not planned for soffit mounting, you probably must do some correction.

If you make "soft" soffit mount (with materials you suggest)... response wouldn't be changed too much, I mean, not 6dB bass/low mid gain, but about 2-4dB, depending of stiffness (reflection) of material for soffit, and in way that cannot be easily predicted. Then, you must live with that (new) response, and I recommend that, or you must tweak loudspeaker response with EQ filter... in room, and.... I don't recommend that.

Second opinion is to use a serious bass trap for soffit mount and air transparent diffusers in front for edge diffraction "smearing"... something from our "MyRoom" acoustic design. You will get a stronger bass response again... but not that much (1-2db), possibly something you would like....

Hope this helps!

EDIT: it's very good to read excellent paper "Direct Radiator Loudspeaker Enclosures", Harry F Olson, JAES Vol. 17, No. 1, 1969 ... if you like to understand "baffle step"compensation, "SBIR" issues, and diffraction...

[ggegan]

Originally Posted by boggy

Second opinion is to use a serious bass trap for soffit mount and air transparent diffusers in front for edge diffraction "smearing"... something from our "MyRoom" acoustic design. You will get a stronger bass response again... but not that much (1-2db), possibly something you would like....

I've been thinking about what this would look like and am a bit confused. I searched the internet for an example of what you seem to be describing, but can't find anything, so maybe I'm misunderstanding. Are you suggesting building a totally absorptive soffit out of say 703 and pink fluffy and then mounting the speakers in it so they are surrounded by the resulting trap? I've read the MyRoom white paper, but the speakers are freestanding in front of the bass trap/diffusers.

I can live without increased bass response as long as I can flatten it out and reduce SBIR influence.

[boggy]

Originally Posted by ggegan

I've been thinking about what this would look like and am a bit confused. I searched the internet for an example of what you seem to be describing, but can't find anything, so maybe I'm misunderstanding. Are you suggesting building a totally absorptive soffit out of say 703 and pink fluffy and then mounting the speakers in it so they are surrounded by the resulting trap?

I'll use P. Newell (T. Hidley) type of wideband absorbers, but this is my personal preference. You may have different experience... then build whatever you think that might absorb efficiently down to the lowest frequencies as possible.
It's may be a problem with ventilation (cooling) of active loudspeakers, but I think that this isn't impossible to solve.

Originally Posted by ggegan

I've read the MyRoom white paper, but the speakers are freestanding in front of the bass trap/diffusers.

Not in Studio Pressed Lizard...
Sorry, I still don't have a real pictures from there, then, please, try to imagine what I'm talking about, from this "picture" I attached below. This is a left loudspeaker in a smallest control room that we ever built, and it's analysis is included in our AES paper too, published last year: Acoustical Design of Control Room for Stereo and Multichannel Production and Reproduction - A Novel Approach

Originally Posted by ggegan

I can live without increased bass response as long as I can flatten it out and reduce SBIR influence.

You will have increased bass response but not too much (1-2dB, sorry for inaccuracy), and not like soffit with concrete wall (6dB)

Do you have commercial loudspeakers, or something without baffle step compensation?

Cheers.

Bogic

[ggegan]

Originally Posted by boggy

Do you have commercial loudspeakers, or something without baffle step compensation?

Cheers.

Bogic

I am using 5.1 Blue Sky System Ones in my current room, but would probably go passive 8" or 10" mid-fields in the new room.

[boggy]

Originally Posted by ggegan

I am using 5.1 Blue Sky System Ones in my current room, ....

They have baffle step compensation for sure.

[ggegan]

Thank you for your advice, Boggy.

One question: Are there similar bass traps below and between the speakers as well?

And a comment - I absolutely love the look and feel of the MyRoom installation! If it sounds as beautiful as it looks, it must be truly amazing.

[boggy]

Originally Posted by ggegan

Thank you for your advice, Boggy.

You are welcome.

Originally Posted by ggegan

One question: Are there similar bass traps below and between the speakers as well?

Yes.

Originally Posted by ggegan

And a comment - I absolutely love the look and feel of the MyRoom installation! If it sounds as beautiful as it looks, it must be truly amazing.

It's sounds beautiful, really.

Bass trap for soffit mount may be a good beginning for implementing overall MyRoom acoustic design principle.

It's a way to spare some space in room, where you can't have exceptionally good bass trap AND a free standing speakers in same time. Soffit mount is a much better compromise.

Don't forget to find a best possible position for loudspeakers and seating place before all... when you find it... build soffit mount with this info in mind.... loudspeaker positions stay fixed.

You may use a "plummet" to transfer position of speaker corners to floor, then measure coordinates from walls... and import this in 3D.... etc

Try to reach a mechanical (build) precision for reflection/diffuse surfaces symmetry better than +/-1/4"... it's not very easy... I know.

Good luck!

Boggy

[jhbrandt]

+1 - It works well!

We use a similar flush mounting approach with a stone facade - and still utilize the surrounding space for trapping.

Cheers,
John

[DanDan]

Gary, When selecting your new speakers, I strongly encourage active with onboard level/Eq. Fixed half step compensation is a bit restricted, a fully variable shelf can be used to adjust for the various pseudo soffits, half soffit half bass trap (see johnlsayers.com).
Such controls on the speaker are eq'ing the speaker rather than the room.
I encourage using them to achieve a response in the room like that at Understanding RTA at studiotips.com or the remarkably same one here
http://www.bksv.com/doc/17-197.pdf
Some speakers (e.g. ADAM) have controls, bass ports, and amps/heatsinks on the front. Wise eh?

DD

[ggegan]

Originally Posted by DanDan

Gary, When selecting your new speakers, I strongly encourage active with onboard level/Eq. Fixed half step compensation is a bit restricted, a fully variable shelf can be used to adjust for the various pseudo soffits, half soffit half bass trap (see johnlsayers.com).
Such controls on the speaker are eq'ing the speaker rather than the room.
I encourage using them to achieve a response in the room like that at Understanding RTA at studiotips.com or the remarkably same one here
http://www.bksv.com/doc/17-197.pdf
Some speakers (e.g. ADAM) have controls, bass ports, and amps/heatsinks on the front. Wise eh?

DD

My favorite speakers for film work are Blue Sky because they translate so well to large rooms for me, but I had assumed that the built in amps were going to cause a heat problem, so I was looking at other alternatives in case I do a soffit mount. I would love to get the new SAT 8 midfields for the front if I can, or even the SAT 12's if I win the lottery. Too bad the controls and heat sinks are in the back, but I may be able to run an AC vent into the soffit, which would probably do the trick.