In-Ceiling Subwoofer

[annunaki]

I did some poking in the attic and realized that I would not be able to get a pair of subwoofers mounted 1/4 distance from each sidewall, which are 11.5 ft apart. The slope of the roof is too low on one side. I'd have to create an L-shaped design in order to fit in a joist bay, while being low enough to clear the rafters. I don't want to get into odd shapes, so I drew up a combined enclosure.

The drivers will be closer to each other than to each side wall - I don't know if that'll be a problem. What would be better - have the ports further apart? Or, the drivers? I can swap the port locations, so that that they are adjacent to each other and spread the drivers further apart, if that would be advantageous.

The reason for minimal bracing, is that I plan to install it in the ceiling, then attach massive bracing to the outside of the enclosure. Any thoughts?

I wonder about stuffing material as well, i.e. what to use and how much?

Thanks for any input!

While this would have lot's of output (doing 2 subs in one location) it will some what defeat the purpose of doing 2 subs to begin with.

One can do some bracing on the exterior of the enclosure, however it is rather difficult to tie all 6 panels together as one on the exterior of the enclosure as can be done rather easily internally.

Give me your maximum height allowed for the locations you want and I can design you an enclosure to fit where needed.

If you are going to go this far only to compromise because of a simple design modification, what is the point?

 

[GO-NAD!]

While this would have lot's of output (doing 2 subs in one location) it will some what defeat the purpose of doing 2 subs to begin with.

One can do some bracing on the exterior of the enclosure, however it is rather difficult to tie all 6 panels together as one on the exterior of the enclosure as can be done rather easily internally.

Give me your maximum height allowed for the locations you want and I can design you an enclosure to fit where needed.

If you are going to go this far only to compromise because of a simple design modification, what is the point?

Point taken. I'll get the dimensions and post them later this morning.

 

[GO-NAD!]

OK, the living room is 11.5' wide. So, the 25% distance point from each wall is 45". That raises a question. Is that 25% point supposed to be the centre of the driver? Centre of the port? Or, half-way between the driver and the port? Does the port location have any bearing on it?

The problem is the location closest to the outer wall. At that point, the height from the ceiling to the underside of the rafter is 27.5". The enclosure would have to extend several inches beyond that point, in each direction. At 36" from the wall, the height from ceiling to rafter is 22".

Of course, I could spread the drivers further apart by making the enclosure wider. That would allow me to lower the height proportionally.

On the other side of the room, height isn't a problem, as the roof is well above the height needed. That said, I'd like the enclosures to be of identical dimensions to ensure identical performance.

I don't know if you can understand that description, but what it boils down to, is that the maximum height for the enclosure would be about 20" (that would be at the outside corner, at the lowest part of the roof slope), to give me a fudge factor. The depth would be 13", giving me a port width of 11.5". If I added 9" to the width of each enclosure, for a total of 1.5', that would get me down to about 20" in height. That volume should account for lot's of internal bracing. I could shrink the enclosure somewhat, by using the external bracing.

An expansion in width will be a problem WAF-wise, as it will cover much more ceiling area than originally estimated. I'll have to deal with that...

One can do some bracing on the exterior of the enclosure, however it is rather difficult to tie all 6 panels together as one on the exterior of the enclosure as can be done rather easily internally.

I don't quite understand that. My idea was to use "T" or "L" type bracing that would overlap at the corners and be attached to each other, as well as the enclosure. The bracing could be massive and from a physics standpoint, would be just as strong as internal bracing. In fact, it would be stronger, because it could be bigger and I could use more of it. I came up with that idea, because the bracing "allowance" from the calculator you sent me was only about .05ft^3. That's just one brace, unless I make them really skinny - then I might get 2. The braces I have in my attached sketch use up that entire volume.

I just opened the attached sketch. I didn't realize how fuzzy it was. Can you read the dimensions? My apologies...

 

[GO-NAD!]

Here's a sketch of an idea that I had previously cast aside as being a huge PITA. The advantage would be far less visiblility. I'd have to cut out a huge chunk of plastered wallboard in order to get the enclosure up into the attic. I'd have to avoid destroying the removed piece, as I'd need to put a piece back in place to seal up the hole. You may think that it would be simple to just cutout some gyprock and put a piece back in. Well, this house was built 50 years ago. It's plaster on drywall, weighs a ton and the thickness won't match modern drywall. A single layer is too thin, a double layer is too thick. So, I would have to try not to destroy the piece that I cut out.

Or, cut one small hole, shove the enclosure up through vertically, then lay it down horizontally. To do that, I'd have to ensure that I have sufficient attic height to insert the enclosure vertically. I'll have to measure it. I have my doubts though...

 

[GO-NAD!]

Just to add to my last post, it just dawned on me that I can build the enclosures separately and join them in the attic. Silly me...

 

[annunaki]

OK, the living room is 11.5' wide. So, the 25% distance point from each wall is 45". That raises a question. Is that 25% point supposed to be the centre of the driver? Centre of the port? Or, half-way between the driver and the port? Does the port location have any bearing on it?

The problem is the location closest to the outer wall. At that point, the height from the ceiling to the underside of the rafter is 27.5". The enclosure would have to extend several inches beyond that point, in each direction. At 36" from the wall, the height from ceiling to rafter is 22".

Of course, I could spread the drivers further apart by making the enclosure wider. That would allow me to lower the height proportionally.

On the other side of the room, height isn't a problem, as the roof is well above the height needed. That said, I'd like the enclosures to be of identical dimensions to ensure identical performance.

I don't know if you can understand that description, but what it boils down to, is that the maximum height for the enclosure would be about 20" (that would be at the outside corner, at the lowest part of the roof slope), to give me a fudge factor. The depth would be 13", giving me a port width of 11.5". If I added 9" to the width of each enclosure, for a total of 1.5', that would get me down to about 20" in height. That volume should account for lot's of internal bracing. I could shrink the enclosure somewhat, by using the external bracing.

An expansion in width will be a problem WAF-wise, as it will cover much more ceiling area than originally estimated. I'll have to deal with that...



I don't quite understand that. My idea was to use "T" or "L" type bracing that would overlap at the corners and be attached to each other, as well as the enclosure. The bracing could be massive and from a physics standpoint, would be just as strong as internal bracing. In fact, it would be stronger, because it could be bigger and I could use more of it. I came up with that idea, because the bracing "allowance" from the calculator you sent me was only about .05ft^3. That's just one brace, unless I make them really skinny - then I might get 2. The braces I have in my attached sketch use up that entire volume.

I just opened the attached sketch. I didn't realize how fuzzy it was. Can you read the dimensions? My apologies...

If one is using window type braces, as seen in many of my designs, bracing rarely exceeds .07ft^3. This amount of volume is rather quite small. The vents displace significantly more volume. External bracing will not allow the enclosure to be much smaller, perhaps a 1/2 inch on one or two of the dimensions. To brace a system externally, the enclosure would become significantly larger. I am also doubtful that it would be as effective as well.

The enclosures do not need to be the same dimensions so long as they have the same internal volume with the same vent area. That being the case there will be identical performance.

 

[annunaki]

Just to add to my last post, it just dawned on me that I can build the enclosures separately and join them in the attic. Silly me...

I was going to say that.

 

[GO-NAD!]

If one is using window type braces, as seen in many of my designs, bracing rarely exceeds .07ft^3. This amount of volume is rather quite small. The vents displace significantly more volume. External bracing will not allow the enclosure to be much smaller, perhaps a 1/2 inch on one or two of the dimensions. To brace a system externally, the enclosure would become significantly larger. I am also doubtful that it would be as effective as well.

The enclosures do not need to be the same dimensions so long as they have the same internal volume with the same vent area. That being the case there will be identical performance.

I've looked at all the builds you have linked. They all seem to contain a lot more bracing than your stated .07ft^3 (to my eye, anyway). How do you calculate your brace volume? And, how thick are the "frames" of your window bracing - I've been going by .75" x 1.5". Is that too much?

I wasn't sure if different shapes would have any effect on the sound, so thanks for the info. I wanted to keep the same dimensions anyway, to keep production simpler.

 

[GO-NAD!]

I was going to say that.

Smarta**!!

I'm going to try to find time this evening to crunch some numbers, to make sure that shape will give me sufficient volume and still fit. I wanted to do it last night, except the bathroom sink drain pipe plugged up and it took me hours to clear it with a snake. Then, I had to go out to Home Depot to get a new sink drain assembly, because I managed to break the old one during my plumbing efforts. Bad words were spoken...

 

[annunaki]

I've looked at all the builds you have linked. They all seem to contain a lot more bracing than your stated .07ft^3 (to my eye, anyway). How do you calculate your brace volume? And, how thick are the "frames" of your window bracing - I've been going by .75" x 1.5". Is that too much?

I wasn't sure if different shapes would have any effect on the sound, so thanks for the info. I wanted to keep the same dimensions anyway, to keep production simpler.

All of my braces are from .75" MDF stock. I calculate their volume by figuring the gross volume (.75 x L x D) less 65% since I am cutting most all of it away except for about 1" in most cases. It is not exact but it comes out very close depending upon the size of the brace. It becomes very strong as it is all interlinked tying all 6 panels together.

For larger pieces i figure the volume of the stock and then calculate the volume of the piece or pieces I cut from it and subtract it from the original volume. Actually, this way may work much better for you for calculation as it is more exact.

 

[GO-NAD!]

All of my braces are from .75" MDF stock. I calculate their volume by figuring the gross volume (.75 x L x D) less 65% since I am cutting most all of it away except for about 1" in most cases. It is not exact but it comes out very close depending upon the size of the brace. It becomes very strong as it is all interlinked tying all 6 panels together.

For larger pieces i figure the volume of the stock and then calculate the volume of the piece or pieces I cut from it and subtract it from the original volume. Actually, this way may work much better for you for calculation as it is more exact.

That's how I calculated my brace volume as well. But, to get a bracing arrangement tied together in a similar fashion to your "Build Thread 1", I end up with at least .15ft^3. Does that make sense?

 

[annunaki]

That's how I calculated my brace volume as well. But, to get a bracing arrangement tied together in a similar fashion to your "Build Thread 1", I end up with at least .15ft^3. Does that make sense?

That seems high to me. Send your bracing pieces dimensions. I will see what we are looking at there.

 

[GO-NAD!]

That seems high to me. Send your bracing pieces dimensions. I will see what we are looking at there.

Well, here are the sketches of the double enclosure that I was considering. I haven't had a chance to sketch a wider enclosure, of lower height, with the drivers more widely spaced. However, I would imagine that the bracing volume wouldn't change much. My calculations are based on the "window frames" being .75" x 1.5". My total brace volume is actually 0.267ft^3! When I stated 0.15ft^3, I wasn't looking at the sketch and was going by memory.

I haven't crunched the numbers, but making the frames .75" x 1.0" would reduce volume by a third, I guess? That would still be about 0.176^3. Am I calculating correctly?

 

[annunaki]

I used all of your drawings and put in all of the dimensions into my calculator. Using your interior dimensions I get a net volume of 2.690ft^3. I came up with .201 net displacement from bracing and the sub itself using your sketches. I also used the original vent calculation of 2" x 12" x 45.19". This gives a net tune of 22hz.

I don't see any issues with displacement in the current setup.

Like I stated though. I do suggest that you test as well for optimal locations prior to cutting your holes.

Let me know if you have any other questions.

Well, here are the sketches of the double enclosure that I was considering. I haven't had a chance to sketch a wider enclosure, of lower height, with the drivers more widely spaced. However, I would imagine that the bracing volume wouldn't change much. My calculations are based on the "window frames" being .75" x 1.5". My total brace volume is actually 0.267ft^3! When I stated 0.15ft^3, I wasn't looking at the sketch and was going by memory.

I haven't crunched the numbers, but making the frames .75" x 1.0" would reduce volume by a third, I guess? That would still be about 0.176^3. Am I calculating correctly?

 

[GO-NAD!]

I used all of your drawings and put in all of the dimensions into my calculator. Using your interior dimensions I get a net volume of 2.690ft^3. I came up with .201 net displacement from bracing and the sub itself using your sketches. I also used the original vent calculation of 2" x 12" x 45.19". This gives a net tune of 22hz.

I don't see any issues with displacement in the current setup.

Like I stated though. I do suggest that you test as well for optimal locations prior to cutting you holes.

Let me know if you have any other questions.

Thanks for checking it out! You suggested that my enclosures not be joined because of the possible vibratoin issues that might crop up. My thinking, which could be quite erroneous, was that if both subs are operating in phase with each other, than vibrations between the two would be cancelled out. Besides, they'll be sitting on the same pair of joists, so any vibration will be transmitted to each other anyway. If that's wrong, I'll just make each a bit higher and narrower, to leave a gap between them.

 

[annunaki]

Thanks for checking it out! You suggested that my enclosures not be joined because of the possible vibratoin issues that might crop up. My thinking, which could be quite erroneous, was that if both subs are operating in phase with each other, than vibrations between the two would be cancelled out. Besides, they'll be sitting on the same pair of joists, so any vibration will be transmitted to each other anyway. If that's wrong, I'll just make each a bit higher and narrower, to leave a gap between them.

When two items are operating in phase with each other, vibrations or other, becomes amplified. When out of phase they would cancel.

 

[GO-NAD!]

When two items are operating in phase with each other vibrations or other becomes amplifier. When out of phase they would cancel.

I understand what you mean. I thought that applied to the pressure waves in open air. Correct me if I'm wrong.

I was just thinking that in this case, with enclosures securely attached to each other, pressure waves that are in phase would act on the sides of each enclosure simultaneously. And, if those waves are equal, there would be no pressure differential, just as if there was no wave at all. That was my logic in thinking that there would be no extra vibration caused when attaching them together. Vibration emitting externally to the ceiling joists is a different issue that I hope to reduce, if not eliminate, with good bracing and isolating foam between the mounting brackets and the joists.

I figured that I may as well join the 2 enclosures, as they would be so close together in the attic and that they could actually reinforce each other structurally.

Do you still think it's a bad idea?

 

[annunaki]

I understand what you mean. I thought that applied to the pressure waves in open air. Correct me if I'm wrong.

I was just thinking that in this case, with enclosures securely attached to each other, pressure waves that are in phase would act on the sides of each enclosure simultaneously. And, if those waves are equal, there would be no pressure differential, just as if there was no wave at all. That was my logic in thinking that there would be no extra vibration caused when attaching them together. Vibration emitting externally to the ceiling joists is a different issue that I hope to reduce, if not eliminate, with good bracing and isolating foam between the mounting brackets and the joists.

I figured that I may as well join the 2 enclosures, as they would be so close together in the attic and that they could actually reinforce each other structurally.

Do you still think it's a bad idea?

You can join them in the attic, but I would isolate them from each other with a layer of foam. Does that make sense?

 

[GO-NAD!]

You can join them in the attic, but I would isolate them from each other with a layer of foam. Does that make sense?

Sure, that actually crossed my mind.

 

[GO-NAD!]

Well finally! I started cutting MDF this past weekend. And, my wife just called - my drivers have arrived! It's a pair of Dayton 10" RSS265HF's. Thanks Annunaki, for all you help!

Can't wait to get home and fondle, er, uh, I mean examine my drivers for shipping damage. Yeah, that's what I meant....

Should I start another build thread for this project? This one is a bit long and unwieldy now. Anybody...Bueller?