Ideas on ceiling-inset sub-woofer (infinite baffle)

[drew3945]

Hi all,

In the quest for optimal hi-fi sound in my bedroom, I am thinking of refining my setup by mounting a 12" sub-woofer in the ceiling right above my headboard so that it can enjoy the benefits of an 'infinite baffle' situation (with my house's loft being the rear airspace). Has anyone else tried this? Without having ever tried this before, I am hoping that it should result in optimal low-frequency response. In my case, the bedroom is where I do my movie-viewing and music-listening (while lying down during rest-periods and prior to sleep). My hi-fi speakers are positioned on a shelf opposite my bed, beyond the foot of the bed. My plan is to cut a hole in the ceiling and mount the sub-woofer directly above my pillow. This means that the subwoofer will also be about the same distance from my listening-position as the two bookshelf hi-fi speakers beyond the foot of my bed. Does this sound like a good plan? I thought I'd ask, before cutting holes in my ceiling! The reason I am eager to try this 'infinite baffle' approach is that I gather it should result in the most uncoloured sound, with the lowest frequency response that the driver is capable of. The driver I have at my disposal is a German 'Magnat Classic Sub 300' (12" sub-woofer) which is supposed to be capable of audio reproduction down to 20Hz. The added advantage of having the thing pointing directly at my pillow is that (a) the obvious advantage of hearing the sound waves directly rather than indirectly reflected and (b) the double bed will hopefully absorb most the sound which might otherwise be reflected back at the ceiling resulting in undesirable room resonances. Comments, suggestions and advice would be much appreciated.

Al

[bobbasrah]

Hope you live in the countryside, at least any snow you get could be dealt with via the volume control...
Swapping a smaller box for which the drive is designed for a bigger box (loft) with presumably glass wool and nightlife visiting is not a clever idea IMHO...

What makes you think sub-bass is detectably directional, other than when it crashes through the plasterboard at 9.81 m/s2 at 3am with a big magnet trying to connect with your cranium?

[drew3945]

Thanks for the comments. Yes, I live in the countryside, but I only use my system at low volumes anyway. Good point about the wildlife, so placing a wire cage over the thing would be advisable. There's no chance of it crashing through the ceiling in my case - but if I had a weak ceiling I'd think twice! I know people often say that subwoofer frequencies are non-directional and I know what they are talking about, but I still believe that sound waves travel from A to B and reflect off surfaces, no matter what the frequency.

[Macca]

Should work well but as ever the only real way to find out is to try it. Keep the cut-out and if it doesn't work out you can bodge it back in again.

[drew3945]

Martin - yes indeed about the cutout (especially since the ceiling is artexed). Yes, I guess that trying it is the only real way to find out. I wonder if positioning the subwoofer in the corner of the ceiling would be a better bet. One thing I am a little unsure about is whether there is any significant risk of damaging the driver by running it without an enclosure. The driver's handbook doesn't actually specify that it must only be used within a cabinet, so perhaps it'll be OK. I will not be using it at more than a few watts - probably 45 watts max, though the driver is rated at 300W.

[Macca]

No reason why it should damage the driver. In principle the whole idea should work pretty well.

[stewartwen]

Quite a few years ago, when IAS was in production, Allan Willis and I were prototyping a type of cab just the same as you are describing.
We decided on a small infinite baffle style of cabinet. The cab was not the difficult part! The power amplifiers were. You have to remember this was before the introduction of "T" amps. We came to the conclusion that they would have to be powered l/s. As we planned on using Volt bass drivers we required amplifiers that could deliver current, loads of it! But the amps psu was sooooooooooooo large we decided to drop the project.
But we decided to put 8 cabs into the listening room, this was to recreate a bass field! So we put four into the ceiling and four into the floor!
The results were stunning, even at low levels the music was much much better................and they measured well, an added bonus. We measured sub 20 Hz on the full installation!
The powered protos were built as mono units that took their feed from the pre outputs, we used a pre which we used to make for sale to the general public.
So to the OP I would go for it!!!!
S

[drew3945]

I decided to build a regular ported bass reflex cabinet, to see if it would give satisfaction. Luckily, the sub's paperwork included plans for a cabinet designed to suit the sub. I think I improved on the plans by adding cross-struts made of triangular-section pine: one going from front to back, and one going from side to side. to reduce resonance. I also lined the interior with rubber-backed carpet. Now, if you thump any surface of the cabinet, there is virtually no resonance; it's almost like thumping a block of concrete! I'm totally satisfied with the result; the bass reproduction is fantastic and totally uncoloured by the cabinet. The only disadvantage is that it creates an additional large piece of room clutter. However, the pros outweigh the cons: One of the main 'pros' is that I can move the cabinet from room to room if necessary - and from house to house, when I move. I'm now using a hi-fi amp with a dedicated subwoofer output now, which eliminates the need for a crossover. If I make any further improvements, it is more likely to be concerning the top end of the frequency range. I may try adding a graphic equaliser first.