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Lenin21 2nd October 2011 09:53 AM

"Quick and dirty" sealed subwoofer - HELP!
 
Hi,
The 'household authorities' have decreed that I should be banished (along with dozens of boxes of hifi equipment, components, soldering and measurement kit, etc) to the garden shed. Incredibly, desperate to have the house looking like a home rather than a workshop, she even agreed to me getting a new, 20x12ft shed.

With a 10ft/3m internal height, I'm fitting ceiling speakers. (Available depth is only 5 inches/14cm). I'm using a simple sealed box approach. Speakers are full-range, with 8 inch main drivers. (I may add a sub at a later date so am also boxing off an enclosure suitable for a 10 inch sub).

The rough and ready approximations I've found so far suggest the following for sealed box designs:
  • 8 inch driver - 0.6 - 0.8 sq ft (17 - 22 sq l)
  • 10 inch driver - 1.0 - 1.5 cu ft (28 - 42 sq l)
Can anyone confirm that this is a good rough and ready starting point? (Before you ask the most obvious and sensible question, no, I don't have the T/S parameters!)

Even though this installation is hardly Hi-Fi, I'm keen to do as good a job as I can. I'm after a tight, detailed bass sound, with good transient attack and articulation.

Are 0.7sq ft/20 sq l (8 inch) and 1.2 sq ft/34 sq l (10 inch) likely to be near the mark?

The full-range unit I'm considering is here

Thanks in advance!

ODougbo 2nd October 2011 10:21 AM

I think I understand the question, but why would you build boxes for “ceiling speakers”? If anything, that would reduce the bass. Speakers designed for walls, ceilings and adjoining room (infinite baffle) will have very little bass in an enclosure.

A quick overview of speaker designs:

http://en.wikipedia.org/wiki/Loudspeaker_enclosure

Lenin21 2nd October 2011 03:43 PM

Thanks for the reply.
Unfortunately, I'm not sure I understand your answer.
What is it about a full-range driver (when mounted in a sealed enclosure) that results in reduced bass?Surely the standard laws affecting any driver mounted in a sealed enclosure applies?
What is it about drivers suitable for ceiling mounting that standard air loading effects don't apply?
(In the absence of T/S parameters, I'm presuming that it's high compliance will at least ensure that it's not completely unsuitable for sealed box loading).

Help!

ODougbo 2nd October 2011 04:58 PM

You wouldn’t want to stray too far away from a speaker’s purpose, especially without specifications.

E.g. I had a extra pair of ceiling speaker from a install, I thought they sounded great up in the ceiling so decided to try them in a bass reflex enclosure, even tuned them; it just didn’t work, no bass. I wasn’t that surprised, actually, I would have been more surprised if it worked.

They make subwoofers for “ceilings”, not that I know of any, but I do know they make them.

ODougbo 2nd October 2011 09:17 PM

In-Wall Subwoofers - Polk Audio

revboden 2nd October 2011 10:55 PM

I think what ODougbo is getting at is that those drivers may be setup for IB loading ie. they want to have a lot of space behind them to work right. For the 10" try 169L

Lenin21 3rd October 2011 07:34 AM

1 Attachment(s)
Thanks again for the replies so far guys.

Odougbo, yes, drivers are made for ceiling mounting - I prvided a link in my first post to the ceiling speaker that this post is about.

I very much doubt that that driver is specifically designed for IB loading though. It would be the logical thing to do - but at this price level, I suspect that price dictated the design (hence polyprop cone, compliant surround, etc). I'm attempting to take advantage of those key characteristics in order to optimise the potential performance of this driver, that's all.

In any case, proper IB loading (and this is where I crash and burn in flames) would see a volume of air behind the cone at least equibalent (and even greater than) the volume of air forward of the cone (but as i say, that's just one of my personal frustrations with so many people wh kid themselves that they have an infinate baffle design, when in fact, what the have is, at best, an oversized sealed enclosure, at worst an oversized and inadvertantly ported enclosure. Rant over...

In fact, Odougbo, your experience of ceiling speakers failing to work well in a bass reflex enclosure just confirms my suspicions that ceiling speakers are designed with the key characteristics I've mentioned, making tem most suitable for use in a sealed enclosure.

Revboden - a 169 litre sealed enclosure for a 10' driver?!!!
Are you sure you've not made an error there? That's 6 cubic feet!

Everything I've read indicates that my 1.2sq ft/34sq l is nearer the mark. Would you mind explaining why 6sq ft/169sq l would work better?

Meanwhile, I'm going to contact the manufacturer to try and get T/S parameters. I strongly suspect that they themselves will have no idea however. (I'm pretty sure they will know the precise buld cost per unit though - it's all to easy to know the cost of eberything and the value of nothing, to paraphrase Oscar Wilde).

For what it's worth - image of the unit below:

ODougbo 3rd October 2011 09:04 AM

There are ways to measure speaker parameters with computer programs and hardware, not that I know how. Good idea about contacting manufacturer, they may get back to you.

As a woodworker I shoot first then ask questions later; you could build a pair of test boxes and see how it goes. A sheet of MDF is about $30 bucks.

I’ve installed quite a few of ceiling and wall speakers (as a contractor) they work pretty well, a lot of bang for the buck. They have their limitations e.g. the mounting hardware can start to buzz, typically at higher levels.

The ceiling speakers I mentioned were bass reflex design. I just “copied” the size, and tuned them to the same box frequency. They ended up in the speaker bone yard.

tb46 3rd October 2011 02:12 PM

Hi,

Google for "measuring thiel small", or for starters try this link: Measuring Loudspeaker Driver Parameters

Regards,

art West-VL. 3rd October 2011 02:31 PM

I keep seeing this website coming up for T&S, a great site!
I have been trying to follow the step-by-step but, being non-English, it's pretty hard.
Is there a place with more info that you know of?


Quote:

Originally Posted by tb46 (Post 2733017)
Hi,

Google for "measuring thiel small", or for starters try this link: Measuring Loudspeaker Driver Parameters

Regards,



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