I have a couple of 12" drivers sitting around doing nothing in the loft.
They are of unknown manufacture with rubber surrounds and (from memory) are
rated at 100Watts or similar. I forget the nominal impedance but they were
fairly standard. I was wondering if it is worthwhile installing them in a
sealed (not ported) enclosure and driving them from a couple of proprietary
ss modules and lp filters as a subwoofer system. I don't especially want to
get involved in T/S parameters and volume calculations and I don't want a
'boom box'...just clean extended bass. Can I just assume the bigger the
better for the enclosure? I would probably use MDF or plywood with braced
sides.

On Fri, 6 Apr 2012 19:43:25 +0100, "TonyL"
wrote:

I have a couple of 12" drivers sitting around doing nothing in the loft.
They are of unknown manufacture with rubber surrounds and (from memory) are
rated at 100Watts or similar. I forget the nominal impedance but they were
fairly standard. I was wondering if it is worthwhile installing them in a
sealed (not ported) enclosure and driving them from a couple of proprietary
ss modules and lp filters as a subwoofer system. I don't especially want to
get involved in T/S parameters and volume calculations and I don't want a
'boom box'...just clean extended bass. Can I just assume the bigger the
better for the enclosure? I would probably use MDF or plywood with braced
sides.


Unidentified drivers? Have a good look at them first, particularly the
cone surround. If they are of corrugated paper, you are unlikely to
get any useful bass extension out of them. If they are foam or a
rubber roll, give them a go. You won't go far wrong with a large box,
although you might get better results from measuring the Thiele-Small
parameters and designing a proper box.

How involved do you want to get?

d

In article ,
TonyL wrote:
I have a couple of 12" drivers sitting around doing nothing in the loft.
They are of unknown manufacture with rubber surrounds and (from memory)
are rated at 100Watts or similar. I forget the nominal impedance but
they were fairly standard. I was wondering if it is worthwhile
installing them in a sealed (not ported) enclosure and driving them
from a couple of proprietary ss modules and lp filters as a subwoofer
system. I don't especially want to get involved in T/S parameters and
volume calculations and I don't want a 'boom box'...just clean extended
bass. Can I just assume the bigger the better for the enclosure? I
would probably use MDF or plywood with braced sides.

If you have a wood floor you could try just mounting them in that, using
it as an infinite baffle.

--
*I don't suffer from insanity, I enjoy every minute of it *

Dave Plowman London SW
To e-mail, change noise into sound.

"TonyL"

I have a couple of 12" drivers sitting around doing nothing in the loft.
They are of unknown manufacture with rubber surrounds and (from memory) are
rated at 100Watts or similar. I forget the nominal impedance but they were
fairly standard. I was wondering if it is worthwhile installing them in a
sealed (not ported) enclosure and driving them from a couple of proprietary
ss modules and lp filters as a subwoofer system. I don't especially want to
get involved in T/S parameters and volume calculations and I don't want a
'boom box'...just clean extended bass. Can I just assume the bigger the
better for the enclosure? I would probably use MDF or plywood with braced
sides.


** There is always an optimum size box for a given bass driver - too big
and you actually loose low frequency efficiency.

Using a free program call " WinISD beta " I tried a few brand name, 12 inch
roll surround, woofers ( with free air resonances between 24 and 32 Hz ) and
found that they all performed OK in a 100 litre sealed box = a cube with
45cm sides.

A nice ball park to be in.


...... Phil

Don Pearce wrote:


If they are foam or a
rubber roll, give them a go. You won't go far wrong with a large box,
although you might get better results from measuring the Thiele-Small
parameters and designing a proper box.

Rubber.


How involved do you want to get?


It is just a vague idea right now. They were bought as replacement drivers
for a very old pair of Wharfedale speakers a couple of years back and they
were fine. But then I found some replacement surrounds for the Wharfedale
units and restored them.

Would knowing T/S parameters help much in the case of a sealed enclosure?

My initial idea was just a big rigid box, stuffed with wadding. Box volume
being constrained by the fact that I want to stay married.

Dave Plowman (News) wrote:

If you have a wood floor you could try just mounting them in that,
using it as an infinite baffle.


'Hello darling, how did the shopping go? By the way I just cut a couple of
holes in the floor. Mind you don't step in them. The lounge carpet needed
replacing anyway'

On Sat, 7 Apr 2012 08:50:33 +0100, "TonyL"
wrote:

Don Pearce wrote:


If they are foam or a
rubber roll, give them a go. You won't go far wrong with a large box,
although you might get better results from measuring the Thiele-Small
parameters and designing a proper box.

Rubber.


How involved do you want to get?


It is just a vague idea right now. They were bought as replacement drivers
for a very old pair of Wharfedale speakers a couple of years back and they
were fine. But then I found some replacement surrounds for the Wharfedale
units and restored them.

Would knowing T/S parameters help much in the case of a sealed enclosure?

My initial idea was just a big rigid box, stuffed with wadding. Box volume
being constrained by the fact that I want to stay married.

For a sealed box, no you don't need to know the T/S parameters. The
question is really one of diminishing returns as you make the box
bigger. This is determined by the stiffness of the speaker suspension
which is specified in T/S as an equivalent box size (smaller box =
stiffer suspension). There is no point making the box much bigger than
this, as the suspension stiffness will take over control.

The advantage of doing the measurements and making a ported box is
that it makes use of the speaker's resonance, coupled to the box/port
resonance to prop up the natural low frequency roll-off for a while,
extending the bass response. The cost is that once roll-off inevitably
sets in, it is much steeper, and the residue of the resonances can
make the bass a bit flabby unless it is all configured just right.
That can always be a future project, of course.

d

Don Pearce wrote:

which is specified in T/S as an equivalent box size (smaller box =
stiffer suspension). There is no point making the box much bigger than
this, as the suspension stiffness will take over control.


Understood, thanks.

I do have the basic kit to do T/S so I may have a dabble just to give me a
rough idea of optimum box volume.

In article ,
TonyL wrote:
Dave Plowman (News) wrote:

If you have a wood floor you could try just mounting them in that,
using it as an infinite baffle.


'Hello darling, how did the shopping go? By the way I just cut a couple
of holes in the floor. Mind you don't step in them. The lounge carpet
needed replacing anyway'

Your room is totally bare of furniture?

--
*If you must choose between two evils, pick the one you've never tried before

Dave Plowman London SW
To e-mail, change noise into sound.

On 07/04/2012 08:53, TonyL wrote:
Dave Plowman (News) wrote:

If you have a wood floor you could try just mounting them in that,
using it as an infinite baffle.


'Hello darling, how did the shopping go? By the way I just cut a couple of
holes in the floor. Mind you don't step in them. The lounge carpet needed
replacing anyway'

"Don't use the downstairs toilet. I've converted it into a transmission line
and the pipe is stuffed with optimally-damped wadding."

--
Eiron.