In-Ceiling Backer Boxes

[GO-NAD!]

Any opinions on in-ceiling backer boxes? My kitchen speakers are Angstrom Ambientis in-walls, but I installed them in my ceiling, as there isn't any wall space available. I chose those, because I loved their sound and every other in-ceiling speaker I came across was a co-axial design and I'm biased against co-axials. Can't say why - maybe it's that I can't believe that a tweeter can be rigidly mounted in such a design. I could be wrong - I've been wrong before!

Anyway, right now, my speakers do not have backer boxes. I've stapled insect screen to the joists, just above the speakers, laid cheese cloth on top of that, with the ceiling insulation (fibreglass batts) laid on top. The screen and cloth are there to prevent the insulation from resting directly on the speaker backs.

I considered installing backer boxes at the time, but decided to leave them as is for a while, and consider it again later. I guess that would make them an infinite baffle installation - would that be correct?

I recently had a home energy audit conducted on the house, which included a door blower test to find where air leaks are located. Well, those in-ceiling speakers are not airtight. I e-mailed Angstrom for advice and received a reply as to the appropriate dimensions for an enclosure. Of course, the enclosure would be sealed - no porting, otherwise I would not acheive the aim of sealing my ceiling. He also said to fill the enclosure with pillow stuffing.

Now that you have the background, here's my question. Any ideas on how a sealed enclosure might affect the performance of my speakers - good or bad?

 

[highfigh]

Any opinions on in-ceiling backer boxes? My kitchen speakers are Angstrom Ambientis in-walls, but I installed them in my ceiling, as there isn't any wall space available. I chose those, because I loved their sound and every other in-ceiling speaker I came across was a co-axial design and I'm biased against co-axials. Can't say why - maybe it's that I can't believe that a tweeter can be rigidly mounted in such a design. I could be wrong - I've been wrong before!

Anyway, right now, my speakers do not have backer boxes. I've stapled insect screen to the joists, just above the speakers, laid cheese cloth on top of that, with the ceiling insulation (fibreglass batts) laid on top. The screen and cloth are there to prevent the insulation from resting directly on the speaker backs.

I considered installing backer boxes at the time, but decided to leave them as is for a while, and consider it again later. I guess that would make them an infinite baffle installation - would that be correct?

I recently had a home energy audit conducted on the house, which included a door blower test to find where air leaks are located. Well, those in-ceiling speakers are not airtight. I e-mailed Angstrom for advice and received a reply as to the appropriate dimensions for an enclosure. Of course, the enclosure would be sealed - no porting, otherwise I would not acheive the aim of sealing my ceiling. He also said to fill the enclosure with pillow stuffing.

Now that you have the background, here's my question. Any ideas on how a sealed enclosure might affect the performance of my speakers - good or bad?

How much more rigid could the tweeters be mounted? Most are mounted on a stalk that goes through the voice coil to the magnet and a screw holds it in place. The sound from the woofer sure won't make it move (although it can modulate it) and its own sound won't cause that. How many car speakers are coaxial? They have used that configuration for decades, although some used a metal plate or strap to suspend the tweeter (and sometimes three drivers).

If you know how large the enclosure needs to be for those speakers, MDF works well and is what many companies use to make the ones they sell. Some companies recommend a metal box, although many of those are made for 6-1/2" or 8" round speakers and they're expensive. As long as the back box has the correct internal volume, is sealed and installed properly, it will work fine. Some wall speakers, however, don't sound as good when installed in a ceiling but I guess you'll have to decide.

How will a sealed box affect your speakers? If they were designed to be used in a wall cavity, the bass response may not be what you thought it would.

 

[lsiberian]

Any opinions on in-ceiling backer boxes? My kitchen speakers are Angstrom Ambientis in-walls, but I installed them in my ceiling, as there isn't any wall space available. I chose those, because I loved their sound and every other in-ceiling speaker I came across was a co-axial design and I'm biased against co-axials.

Coaxials are great. The tweeter does act as a waive guide.

I can't suggest In-walls for a ceiling. There are a lot of issues that will introduce especially for a non-coaxial.

 

[GO-NAD!]

How much more rigid could the tweeters be mounted? Most are mounted on a stalk that goes through the voice coil to the magnet and a screw holds it in place. The sound from the woofer sure won't make it move (although it can modulate it) and its own sound won't cause that. How many car speakers are coaxial? They have used that configuration for decades, although some used a metal plate or strap to suspend the tweeter (and sometimes three drivers).

If you know how large the enclosure needs to be for those speakers, MDF works well and is what many companies use to make the ones they sell. Some companies recommend a metal box, although many of those are made for 6-1/2" or 8" round speakers and they're expensive. As long as the back box has the correct internal volume, is sealed and installed properly, it will work fine. Some wall speakers, however, don't sound as good when installed in a ceiling but I guess you'll have to decide.

How will a sealed box affect your speakers? If they were designed to be used in a wall cavity, the bass response may not be what you thought it would.

Oh, I'm well aware that co-ax speakers have been made for a long time; I won't claim that my dislike of them is logical.

I had already planned on MDF.

Why don't some in-walls sound as good when put in a ceiling? I certainly couldn't experiment - I'd have holes all over the kitchen. That would have a somewhat negative WAF...

My kitchen is galley-style and I really can't expect superior acoustics anyway. I installed the speakers about 42" either side of the spot where I normally stand, with the tweeters in-line with my noggin.

Are you saying that a sealed enclosure would decrease the bass response? Would it tend to flatten the FR as well, or should I expect variations? As an in-wall design, I assume it was meant to be in a sealed enclosure. The advantage of having them in a ceiling (with the attic above) is that the enclosure volume can be more easily fine-tuned for best response. If I was retrofitting them into a wall, the volume is what it is - unless I wanted to be really destructive. And in the kitchen, I don't have that flexibility.

I'm not questioning your statements - I really appreciate the input. I'm just trying to understand what I should expect.

Thanks!

 

[GO-NAD!]

Coaxials are great. The tweeter does act as a waive guide.

I can't suggest In-walls for a ceiling. There are a lot of issues that will introduce especially for a non-coaxial.

That's the problem with in-wall/in-ceiling speakers - they don't lend themselves well to "in-home auditioning". I could hardly buy several different models and install them in my ceiling.

So, when I auditioned several different models at a couple of dealers, these sounded the best to me. What's done is done.

And, they do sound quite good to my ear. But, I don't have anything to compare them against. I could go and get a different pair, put them in and they might put my Angstroms to shame. Who knows? I played a test CD and checked the FR from my normal listening position with my RS SPL meter. I certainly wouldn't call the response "flat", but it was better than I expected (I wrote down my readings, but I don't have them with me right now). The layout of my kitchen is long and narrow, with cabinets and countertops on each side, appliances and other assorted kitchen "stuff". I wonder if that helps or hinders SQ. It's all hard surface, but with so many angles, would it scatter reflections and tend to flatten the response. Or, would it tend to just screw things up royally?

 

[lsiberian]

That's the problem with in-wall/in-ceiling speakers - they don't lend themselves well to "in-home auditioning". I could hardly buy several different models and install them in my ceiling.

So, when I auditioned several different models at a couple of dealers, these sounded the best to me. What's done is done.

And, they do sound quite good to my ear. But, I don't have anything to compare them against. I could go and get a different pair, put them in and they might put my Angstroms to shame. Who knows? I played a test CD and checked the FR from my normal listening position with my RS SPL meter. I certainly wouldn't call the response "flat", but it was better than I expected (I wrote down my readings, but I don't have them with me right now). The layout of my kitchen is long and narrow, with cabinets and countertops on each side, appliances and other assorted kitchen "stuff". I wonder if that helps or hinders SQ. It's all hard surface, but with so many angles, would it scatter reflections and tend to flatten the response. Or, would it tend to just screw things up royally?

All that matters is how it sounds to you. It's your home and your setup.

Just make sure to share some pictures. I really want to see how it turns out.

 

[highfigh]

Oh, I'm well aware that co-ax speakers have been made for a long time; I won't claim that my dislike of them is logical.

I had already planned on MDF.

Why don't some in-walls sound as good when put in a ceiling? I certainly couldn't experiment - I'd have holes all over the kitchen. That would have a somewhat negative WAF...

My kitchen is galley-style and I really can't expect superior acoustics anyway. I installed the speakers about 42" either side of the spot where I normally stand, with the tweeters in-line with my noggin.

Are you saying that a sealed enclosure would decrease the bass response? Would it tend to flatten the FR as well, or should I expect variations? As an in-wall design, I assume it was meant to be in a sealed enclosure. The advantage of having them in a ceiling (with the attic above) is that the enclosure volume can be more easily fine-tuned for best response. If I was retrofitting them into a wall, the volume is what it is - unless I wanted to be really destructive. And in the kitchen, I don't have that flexibility.

I'm not questioning your statements - I really appreciate the input. I'm just trying to understand what I should expect.

Thanks!

The way our ears are oriented, we really need sound to come at them in a certain way in order to sound real. Also, crossovers can be designed for best phase alignment, best on-axis response and off-axis response.

In-wall and in-ceiling speakers are designed for infinite baffle use, but if they're in a box, the free air resonance will be affected by the box's internal volume.

For less than fifteen bucks and a little time, you could build a mockup of a wall with enough width that you could find out how the response changes as you move around the speaker (visualize a cone). If you measured the response perpendicular to the tweeter's dome or cone, you'd see one response curve but as you move more off-axis, this can change drastically. If you have seen a graph for speakers that has concentric rings and a wavy circle with degree markings and a decrease in distance at the bottom (usually where 180 degrees to the speaker is), that's a polar response graph and will tell you how much the speaker's response varies with the angle to the mic.

 

[GO-NAD!]

The way our ears are oriented, we really need sound to come at them in a certain way in order to sound real. Also, crossovers can be designed for best phase alignment, best on-axis response and off-axis response.

In-wall and in-ceiling speakers are designed for infinite baffle use, but if they're in a box, the free air resonance will be affected by the box's internal volume.

For less than fifteen bucks and a little time, you could build a mockup of a wall with enough width that you could find out how the response changes as you move around the speaker (visualize a cone). If you measured the response perpendicular to the tweeter's dome or cone, you'd see one response curve but as you move more off-axis, this can change drastically. If you have seen a graph for speakers that has concentric rings and a wavy circle with degree markings and a decrease in distance at the bottom (usually where 180 degrees to the speaker is), that's a polar response graph and will tell you how much the speaker's response varies with the angle to the mic.

I really appreciate the input Highfigh! Although building a mockup to test the response of a particular speaker would be be an interesting exercise, I just don't have that kind of time. Besides, if I did that and didn't like the speaker, I would think it unlikely that a dealer would take it back. I can tell you that I have not been disappointed with mine - but as I said before, I could put a different pair in and think they were much better. It's probably best that I don't know, eh?

I made my decision to purchase the Angstroms, based on what I heard from each dealer's installation. It's not the best way, but in the circumstances, it was the only practical way for me.

Thanks again!

 

[GO-NAD!]

All that matters is how it sounds to you. It's your home and your setup.

Just make sure to share some pictures. I really want to see how it turns out.

I hope that's not what you say to Bose owners - then I would think you were patronizing me!

Everyone who has heard them, makes complements on the sound. But then, everyone who has heard them, knows even less than me about how a good speaker should sound!

I will post photos, when/if I install the enclosures. I'm still wondering if it's a good idea. But, I'd like to reduce the air leakage through the ceiling as well. If I knew that the sound wouldn't be adversely affected, it would be a no-brainer. But, I'd hate to do all that work and have the speakers sound terrible.

 

[annunaki]

To truly do this right, ask the manufacturer to provide the Theile-Small parameters for the woofer of your in-wall speakers. Once you have that, you can get them to me and I will model it for you determining the best enclosure solution. If you are familiar with modeling software, of course you could do this yourself as well.

If they will not provide you this info, I would; #1 be disappointed in the manufacturer, & #2 purchase the Dayton woofer tester to get the T/S parameters (assuming you want to do this correctly) yourself.

If all else fails, build the sealed enclosure to manufacturer specification. Be sure to brace it well and seal it on the back side around the speaker opening. I would suggest using 1"-2" rockwool/mineral wool sheets on three of the six internal surfaces to absorb reflections.Also be sure to decouple the enclosure from the drywall so as to prevent vibration.

 

[GO-NAD!]

Just to beat a dead horse a bit more, this is the response I received from Angstrom, when I initially inquired about enclosing the speakers:

"Enclosing the speaker allows control of the back pressure and should make the speaker more defined and quicker in the bass and mid/bass,more control of the bass reduces intermodulation of the cone allowing the mid response to improve."

Any opinions on that statement? I'm no expert on speaker design, but I understand physics a bit. By "quicker in the bass and mid/bass", does he mean that the enclosure acts somewhat like a spring? As the driver moves back, the air compresses and returns the driver to neutral more quickly and when it moves forward, it creates a vacuum, pulling the driver back to neutral more quickly as well. Would that be correct? And if so, is that desireable?

It just occured to me - a completely sealed enclosure would not make the speaker airtight. Should I apply a bead of caulk at the speaker frame/ceiling joint and at the baffle/frame joint? I know those seams are miniscule - I just don't know if they are important. Actually, sealing those seams would seal the ceiling - no more draft! Maybe I don't have to build enclosures....

I apologise for being such a pain, but I do appreciate the help!

I can't find a definition for "intermodulation" either.

 

[GO-NAD!]

To truly do this right, ask the manufacturer to provide the Theile-Small parameters for the woofer of your in-wall speakers. Once you have that, you can get them to me and I will model it for you determining the best enclosure solution. If you are familiar with modeling software, of course you could do this yourself as well.

If they will not provide you this info, I would; #1 be disappointed in the manufacturer, & #2 purchase the Dayton woofer tester to get the T/S parameters (assuming you want to do this correctly) yourself.

If all else fails, build the sealed enclosure to manufacturer specification. Be sure to brace it well and seal it on the back side around the speaker opening. I would suggest using 1"-2" rockwool/mineral wool sheets on three of the six internal surfaces to absorb reflections.Also be sure to decouple the enclosure from the drywall so as to prevent vibration.

I will make inquiries and see if they will provide that answer. When I asked about an enclosure before, I was told that 3 cubic feet would be appropriate. Would that seem like a proper answer, or just a convenient round number?

 

[highfigh]

Just to beat a dead horse a bit more, this is the response I received from Angstrom, when I initially inquired about enclosing the speakers:

"Enclosing the speaker allows control of the back pressure and should make the speaker more defined and quicker in the bass and mid/bass,more control of the bass reduces intermodulation of the cone allowing the mid response to improve."

Any opinions on that statement? I'm no expert on speaker design, but I understand physics a bit. By "quicker in the bass and mid/bass", does he mean that the enclosure acts somewhat like a spring? As the driver moves back, the air compresses and returns the driver to neutral more quickly and when it moves forward, it creates a vacuum, pulling the driver back to neutral more quickly as well. Would that be correct? And if so, is that desireable?

It just occured to me - a completely sealed enclosure would not make the speaker airtight. Should I apply a bead of caulk at the speaker frame/ceiling joint and at the baffle/frame joint? I know those seams are miniscule - I just don't know if they are important. Actually, sealing those seams would seal the ceiling - no more draft! Maybe I don't have to build enclosures....

I apologise for being such a pain, but I do appreciate the help!

I can't find a definition for "intermodulation" either.

What they said is true but they didn't say anything about how much internal volume is good or bad.

Look at the air in a sealed box as a spring that can control the speaker cone. The smaller the internal volume, the stiffer the spring and the larger, the less tension/control it will have. This affects the frequency response, bass output and tightness of the bass response. You could also think of it as a balloon. More pressure=tighter skin/more control and less pressure=softer skin/less control.

I would use rope caulk- it would be easier to remove and cleanup if the speaker has to be removed but sealing the edge isn't a bad idea.

 

[lsiberian]

I will make inquiries and see if they will provide that answer. When I asked about an enclosure before, I was told that 3 cubic feet would be appropriate. Would that seem like a proper answer, or just a convenient round number?

That's pretty large. My sub will be a little larger than that.

Lets get those T/S parameters if possible. I'd like to model this in a reasonably sized box if possible.

Get box notes to come up with the dimensions of the box.

 

[GO-NAD!]

Well, I sent an e-mail to Angstrom - just waiting for a reply. In the meantime, can I expect an audible improvement in SQ by installing a backer box? Are there any trade-offs, i.e. lower sensitivity, loss of lower bass response, etc?

If there are more minuses than pluses, is it worthwhile? I might be able to make the speaker airtight with the ceiling by fitting a gasket and/or applying caulk to the seams. That was the original goal of installing the backer box. If I can acheive an overall improvement in SQ, I'm all for it.

 

[annunaki]

To start, I would apply some rubberized foam weather stripping to the backside of the speakers frame that meets the drywall. This will seal the front wave from the back.

Strip caulk is messy and a pain to clean up once it has been compressed.

 

[GO-NAD!]

Received an answer, but....

...not quite what we were looking for. Here's the reply to my last inquiry:
" I don't have the Theile/Small parameters but I know that the speakers optimal enclosure size is 0.25 Cubic feet."

Here's what I received a few months ago when I made my initial inquiry:
"If you make a box 36" inside the joists and bolt a board across the
joists the box would be 3 cubic feet. Put the insulation around the out
side and stuff some pillow stuffing inside the box."

I have to admit, I didn't quite understand the dimensions in the first response.
Anyway, does 0.25 cubic feet (432 cubic inches) seem to be in the ball park? Plus, would I need to add the volume occupied by bracing to that number? How about the sound absorbant insulation - does that affect the volume of the enclosure as well?

 

[highfigh]

I will make inquiries and see if they will provide that answer. When I asked about an enclosure before, I was told that 3 cubic feet would be appropriate. Would that seem like a proper answer, or just a convenient round number?

Are the back boxes made for 2x4 or 2x6 walls? 3ft³, assuming the inside is 3-1/2" deep and 14" wide, comes to about 109" long.

3ft³ doesn't sound right.

 

[GO-NAD!]

Are the back boxes made for 2x4 or 2x6 walls? 3ft³, assuming the inside is 3-1/2" deep and 14" wide, comes to about 109" long.

3ft³ doesn't sound right.

I'm assuming the 3 cubic feet figure is a typo and the real volume is supposed to be 0.25 cubic feet.

 

[annunaki]

.3ft^3 would make sense from what they were describing in your post.

You would need to account for bracing in that figure, if you use rock wool or compressed mineral wool, you will want to add about 50% of their volume into that as well.