Dave Plowman (News) wrote:
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?


'Don't worry, the two 12 inch holes are under the settee. You won't even
know they are there....hello, hello....anyone there?' fx:slam of door, car
engine starts up.

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


'Don't worry, the two 12 inch holes are under the settee. You won't even
know they are there....hello, hello....anyone there?' fx:slam of door,
car engine starts up.

You could put them under those massive cabinets you're going to build. And
use the cabinets for something useful.

--
*Procrastinate now

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

"TonyL" wrote in message
news
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.

Given the unknown nature of these drivers, there is very little that you can
reasonably assume if your goal is *not* a boom box.

Well, you could build 3 boxes with a 3:1 range of sizes and see which one
sounds best.

At some point, measuring T/S parameters starts looking good.

I don't know about the UK, but in the states you can get a USB gizmo with
software that does full relevant set of driver tests using your PC for under
$100.

Arny Krueger wrote:

Given the unknown nature of these drivers, there is very little that
you can reasonably assume if your goal is *not* a boom box.


Fair enough...which is why this project is not so serious and might not even
happen. I am just looking for opinions at this stage.

Are there any clues from a physical inspection that might indicate what I
can expect?

Well, you could build 3 boxes with a 3:1 range of sizes and see
which one sounds best.

At some point, measuring T/S parameters starts looking good.


Better than building 3 boxes, certainly.

I don't know about the UK, but in the states you can get a USB gizmo
with software that does full relevant set of driver tests using your
PC for under $100.


OK, but that would be somewhat more than I paid for the drivers. I do have
an amp module that goes down to DC as well as other bits of audio gear so I
might have a go at T/S parameters to give me a ballpark figure for the box
volume.

If I started this project would there be any benefit in placing two drivers
in one enclosure and on opposite sides? I know that KEF have done that in
the past.

"TonyL"

If I started this project would there be any benefit in placing two
drivers in one enclosure and on opposite sides?


** The same outcome as any other arrangement using two drivers in the one
box - means the box has to have twice the volume.

There * IS * a benefit to be had using two, low cost woofers by mounting
them face to face and connecting the terminals out of phase. The combined
unit has the same resonant frequency but twice the cone mass with the same
cone area, twice the power handling and usually much better linearity that
one woofer does. The box can be half the volume too.

This idea is known as " push pull" or "Isobaric".


..... Phil

In article , Phil Allison
scribeth thus

"TonyL"

If I started this project would there be any benefit in placing two
drivers in one enclosure and on opposite sides?


** The same outcome as any other arrangement using two drivers in the one
box - means the box has to have twice the volume.

There * IS * a benefit to be had using two, low cost woofers by mounting
them face to face and connecting the terminals out of phase. The combined
unit has the same resonant frequency but twice the cone mass with the same
cone area, twice the power handling and usually much better linearity that
one woofer does. The box can be half the volume too.

This idea is known as " push pull" or "Isobaric".


.... Phil





Presume that was where the Linn Isobarik was derived from?..
--
Tony Sayer

In article , TonyL
wrote:
Arny Krueger wrote:

At some point, measuring T/S parameters starts looking good.


Better than building 3 boxes, certainly.

I don't know about the UK, but in the states you can get a USB gizmo
with software that does full relevant set of driver tests using your
PC for under $100.


OK, but that would be somewhat more than I paid for the drivers. I do
have an amp module that goes down to DC as well as other bits of audio
gear so I might have a go at T/S parameters to give me a ballpark
figure for the box volume.

Someone else will know the details rather better than myself. But I think
you can estimate some of the basic parameters for a large bass speaker from
some quite simple measurements.

e.g. By using a ruler to measure the displacement of the speaker cone when
you apply a fixed dc voltage. And - with the speaker pointing upwards - how
much displacement a small weight produces. (Rotating from vertical to
horizontal and measuring the displacement will also let you estimate the
mass of the cone, etc.) None of that may be very accurate, but may still be
close enough.

IIRC The "Loudspeaker Design Cookbook" by Vance Dickason explains this in
an appendix. But I may have actually read the details somewhere else. Not
really my topic.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

On Sun, 08 Apr 2012 16:46:17 +0100, Jim Lesurf
wrote:

In article , TonyL
wrote:
Arny Krueger wrote:

At some point, measuring T/S parameters starts looking good.


Better than building 3 boxes, certainly.

I don't know about the UK, but in the states you can get a USB gizmo
with software that does full relevant set of driver tests using your
PC for under $100.


OK, but that would be somewhat more than I paid for the drivers. I do
have an amp module that goes down to DC as well as other bits of audio
gear so I might have a go at T/S parameters to give me a ballpark
figure for the box volume.

Someone else will know the details rather better than myself. But I think
you can estimate some of the basic parameters for a large bass speaker from
some quite simple measurements.

e.g. By using a ruler to measure the displacement of the speaker cone when
you apply a fixed dc voltage. And - with the speaker pointing upwards - how
much displacement a small weight produces. (Rotating from vertical to
horizontal and measuring the displacement will also let you estimate the
mass of the cone, etc.) None of that may be very accurate, but may still be
close enough.

IIRC The "Loudspeaker Design Cookbook" by Vance Dickason explains this in
an appendix. But I may have actually read the details somewhere else. Not
really my topic.

Slainte,

Jim

I've found a very good explanatory web page which describes in fair
detail how to measure the T/S parameters. There is a downloadable
spread sheet to put the measurements in and produce a full T/S
parameter set.

http://sound.westhost.com/tsp.htm

I've fed some dummy data in, and the answers are very believable.

d

Phil Allison wrote

There * IS * a benefit to be had using two, low cost woofers by
mounting them face to face and connecting the terminals out of
phase. The combined unit has the same resonant frequency but twice
the cone mass with the same cone area, twice the power handling and
usually much better linearity that one woofer does. The box can be
half the volume too.

This idea is known as " push pull" or "Isobaric".


.... Phil


Thanks Phil, just looked it up. Seems like a good way to 'use up' my two
drivers.

Don Pearce wrote:
On Sun, 08 Apr 2012 16:46:17 +0100, Jim Lesurf
wrote:

In article , TonyL
wrote:
Arny Krueger wrote:

At some point, measuring T/S parameters starts looking good.


Better than building 3 boxes, certainly.

I don't know about the UK, but in the states you can get a USB
gizmo with software that does full relevant set of driver tests
using your PC for under $100.


OK, but that would be somewhat more than I paid for the drivers. I
do have an amp module that goes down to DC as well as other bits of
audio gear so I might have a go at T/S parameters to give me a
ballpark figure for the box volume.

Someone else will know the details rather better than myself. But I
think you can estimate some of the basic parameters for a large bass
speaker from some quite simple measurements.

e.g. By using a ruler to measure the displacement of the speaker
cone when you apply a fixed dc voltage. And - with the speaker
pointing upwards - how much displacement a small weight produces.
(Rotating from vertical to horizontal and measuring the displacement
will also let you estimate the mass of the cone, etc.) None of that
may be very accurate, but may still be close enough.

IIRC The "Loudspeaker Design Cookbook" by Vance Dickason explains
this in an appendix. But I may have actually read the details
somewhere else. Not really my topic.

Slainte,

Jim

I've found a very good explanatory web page which describes in fair
detail how to measure the T/S parameters. There is a downloadable
spread sheet to put the measurements in and produce a full T/S
parameter set.

http://sound.westhost.com/tsp.htm

I've fed some dummy data in, and the answers are very believable.


Thanks all. I'll drag one of the units from the loft and try the T/S 'added
mass' measurement method, not having a ready made box yet.

Great site, BTW.

Anybody like to comment on how T/S params translate to box volume if I tried
an isobaric design as mentioned by Phil? Just divide enclosure volume by 2?