Bare Speaker mounted in brick wall

[AndrewCollett]

Hey Peoples,

So, I have heard a theory that goes something like this. The best thing you can do to get clear and efficient sound is to mount your speak (the driver itself) into an infinite wall, where the front and the rear of the cone are on opposite sides. In essence, a closed speaker box, with infinite area inside. If that makes sense?

Anyway, the idea is this. I want to mount my speaker (the driver or bare "speaker" itself) into my brick wall on either side of my tv, such that both sides of the cone are open to air. The wall is an inner wall, (so both sides are inside) one brick thick, open to air, and is a fairly long wall.

The "speakers" I'm wanting to mount are mainly medium sized base's on either side.

I want to know if this is a good idea from sound perspective. Will I have better sound this way than from a ported box? Will the base be pure and true? What other things could anyone out there bring to the idea that would help understanding?

Thanks in advance guys!

 

[Budgie]

It's all about the design of the drivers - different speaker drivers are designed with different applications in mind. In wall speaker mounting can have some advantages, but also some disadvantages, over enclosure mounted speakers and neither one is a winner just because of the choice of in wall or not. No simple answer.

 

[AndrewCollett]

Specs?

It's all about the design of the drivers - different speaker drivers are designed with different applications in mind. In wall speaker mounting can have some advantages, but also some disadvantages, over enclosure mounted speakers and neither one is a winner just because of the choice of in wall or not. No simple answer.

Would some driver specs be useful?

 

[bear]

Actually this is known as an "Infinite Baffle" or "IB".

If you search here and on the web you will find a lot of information.

To some extent this is the ultimate "enclosure". Neglecting higher frequency diffraction problems that may come depending on the wall surface and the mounting, you will get the flattest response the driver is capable of, and output down to the Fs of the driver. Normally the F3 point is *higher* than Fs in an enclosure.

However the power handling and Qt of the system will be somewhat different than in a standard enclosure. The Qt of the system will now be exactly the Qt of the driver. The power handling and control of the cone depends on the suspension of the driver, there is no effect from the air in a finite sized enclosure at all. This is good or bad depending on the driver.

So, in the case where you have (for example) a 15" pro sound driver with a low Qt (like 0.29) and an Fs of 25Hz, but a high VAS that would only tune to something like 35-40Hz in an enclosure the size of a refrigerator, it will now tune to 25Hz...

Also due to the very large surface area of the wall, the mid bass response will be much closer to the published spec measured on an IEC baffle than any standard enclosure.

However, it will be impossible to adjust the acoustic centers, the physical relationship between the wall mounted drivers and the associated higher frequency drivers as one might be able to accomplish otherwise. Often, the higher frequency drivers need to be physically behind the woofer (front to back, on axis) for optimum alignment. Although many speakers don't take this into account.

_-_-bear

 

[chrisb]

yup, this is one of those cases where theory and practical application don't mesh perfectly for all cases


In-wall or shallow enclosures mounted on-wall often have all the deficits that bear describes - I certainly experienced that a couple of decades ago with on-wall design - great bass response relative to enclosure size, and fine for background, but so much for critical listening. And just to stir the pot, I'll posit that some of those issues are exhibited by large OB / planars as well.

ducking for cover now

 

[AndrewCollett]

Sooooo I think I'm going to try it. (gulp at though of the mess)

I'll post back with a few pictures of the project and some of my experiences. I'm going to compare it with the enclosure (ported) the driver was in, for sound, in a side by side comparison, see what happens.

I really hope I don't knock a hole in the wall for nothing. if nothing else, it'll look awesome. unless it sounds terrible. In which case i'll need to fix the hole. (Sorry dad...)

Thanks for the help, will do some more reading up too!

 

[Richard Ellis]

A side benefit might be......If it is new construction or an addition, you will have sound on both sides of the wall, IE you can have two rooms set-up for sound.
The room with the magnet side will require a different approach of course as the higher frequencies will be rather attenuated. ?????????



___________________________________________________Rick..........

 

[bear]

Depends on how high up you run the driver, if it is say <300Hz. then it makes not much difference at all...

IN the wall and through the wall are different things... IN the wall requires serious consideration of the wall behind the driver, whereas through the wall only requires minor concern with the opening behind the driver into the other room...

People have put woofers in the ceiling and the floors, fwiw...

_-_-bear

yes driver specs would be useful

 

[AndrewCollett]

Okay here's what I could find on the speaker:

First, a quote from someone on another forum who "tested" the same model speaker:


" Here follow the T-S characteristics of an Infinity Dynamic 20cm loudspeaker, model R8520, as determined 'on the bench' by me. (I have used several of these):

BL = 6,32 t.m fs = 36,7Hz Mmd = 22,1gm Mmr = 1,5gm Mms = 23,6gm Cms = 8,06 x 10(power -4) m/N Qes = 0,88 Qms = 3,3 Qts = 0,69 Levc = 1,1mH Revc = 6,9ohm Vas = 42 l (1,5 sq. ft)

It will be apparent that Qts is rather high for many uses, also there is bound to be a tolerance as Timber said. I did not test several examples for control.

Also to state that I am not an agent for Infinity Dynamic and have no connection with them. (In fact, I was rather disappointed by the scant attention received at my last visit to their Jo-burg agents.) But the above for comparison. "

From this forum: Speaker Kits

And here is what I can tell you myself from the speaker:

20cm ~ 7.87inch
8 Ohm
Max 200W

Infinity Dynamic
Model: R8520


Let me know if there is any other info I can tell you! I've already started the hole in the wall. About a meter off the ground, near the tv. Good? Bad?

 

[Richard Ellis]

Using WinISD Beta sim, My guess was right....this will function fine "Thru the wall" With the Qts of .69 it is just about perfect...
Recall, we are all shooting for a Qtc of .707 with our drivers...a middle ground of bass output vs. dynamics or transient response...go a little above .707 for more bass..with the threat of muddiness if too high (greater than 1.0 ), conversely at .5 we get good transients but sacrifice sheer output.
The sim calls for a sealed enclosure of 842 liters, a big box for a Qtc of .71 , the middle ground 37.5 Hz, -3Db But all I did was keep punching the keyboard with zeros for liter size & whadda-you-know......842 liters or 842,000 liters, the sim trying to work its way down down to a Qtc of .69, a hair away from .707......
Upshot? It'll work just fine "out in the open".

_______________________________________________________Rick.......

 

[bear]

with that Fs, it's not exactly a great driver for this application.
also you may find the suspension *may* not be up to handling that much SPL...

I urge you to read the other IB threads here to get some other ideas.

It's fine to go ahead and do this experiment, but I'd blast a hole large enough for at least a standard 12" driver and best, a 15". (we can skip the 18" drivers for now).

Also I don't recall reading what is on the other side of that brick wall?
Is it open to another space or is it a cavity between walls, with studs??
Big difference in what you need to do.

_-_-bear

 

[AndrewCollett]

The Finished product

Hey guys, so I went ahead with it, decided to see what would happen. Here's a few pictures, and a few questions at the end.

The driver sounds better, but that's not saying much, since the driver was in the box in the picture, which I put together myself with no calculations, just guess work. The volume is less, which makes sense since there's no port, but tit sounds more "accurate", and just generally a little better. Also, no vibrating at certain frequencies. Which is nice.

Question, what should I use between the wall and the speaker? The part that is screwed down, I have a bit of t shirt in there at the moment. Should I use something like silicone to glue it down? or what?

Once I have completed the cupboard on the other side of the wall, (I need to plaster the wall and build in the cupboard, no backing or siding will be used) I'll see what the speaker sounds like, and decide if I want to do the other, or seal up the hole.

Any other thoughts? advice?

 

[Andersonix]

We're afraid to give advice to someone who removes bricks from a load-bearing corner without checking with their parents first.

 

[AndrewCollett]

Um? Yes. It would be a very good thing to be hesitant to not give advice to those people.

However.

My parents do know My dad was keen on knowing how it'd work out.

More importantly, the wall is internal, and not load bearing. I checked this in the ceiling. Moreover, its a single brick divider wall, the load bearing walls are two bricks thick on the outer sides. Lol

I'm not that mad

Please do give what advice you guys have that horrible cupboard looking thing with bare walls is now plastered and being painted for a new cupboard to go in.

 

[bear]

You need a 100% seal.

I think you may have that... not sure from ur description. the back should be open to the air.

It looks like a smallish driver, and not a sub... so it ought to be pretty ok, but unless you know
the Qt and VAS plus the Xmax its hard to know what it will do in this IB set up...

_-_-