Wally wrote:

Am I right in thinking that some sort of push-pull set up will give
me a shallower roll-off for a given size? What design approaches are
there, and how do they compare?

Been reading this...

http://www.maximacar.com/isobaric.htm

It says that having the drivers facing towards or away from each other, as
opposed to facing the same way, gives the "benefit of push-pull operation".
Does this have something to do wth the driver having a different response
when the cone moves away from the magnet compared to towards the magnet,
such that having the pair of drivers doing one half of each movenment
reduces the variation in a single driver. Ie, a bit like the idea of matched
valves in a push-pull amplifier giving less variation between the +ve
and -ve halfs of the waveform?


--
Wally
www.makearatherlonglinkthattakesyounowhere.com
Things are always clearer in the cold, post-upload light.

"Wally" wrote in message
...

Rather than the idea I mooted recently about making compact transmission
lines using Kef B139s and driving them with a filtered signal to provide
lift where the speakers roll off, I have another option - I have a total
of
four B139s, two in the existing speakers, and two bought as spares and/or
drivers for the future bass units.

Am I right in thinking that some sort of push-pull set up will give me a
shallower roll-off for a given size? What design approaches are there, and
how do they compare?

The simple fact is that by modern standards, B139s are pretty mediocre
subwoofer drivers. They were never much more than fairly good plain old
woofers.

*real* subwoofer drivers don't need kludges like "isobaric" cabinets to
outperform any reasonable requirements.

If money is tight, auction off the B139s and use the cash to buy a real
subwoofer driver.

Oh, and if you are building a subwoofer, forget transmission lines. They are
basically a waste of good box volume.

In article ,
Arny Krueger wrote:
If money is tight, auction off the B139s and use the cash to buy a real
subwoofer driver.

Oh, and if you are building a subwoofer, forget transmission lines. They
are basically a waste of good box volume.

More sacrilege from Arny. But true. I've never come across a pro
transmission line speaker, and for good reasons.

--
*It's a thankless job, but I've got a lot of Karma to burn off

Dave Plowman London SW 12
RIP Acorn

Dave Plowman wrote:
In article ,
Arny Krueger wrote:
If money is tight, auction off the B139s and use the cash to buy a
real subwoofer driver.

Oh, and if you are building a subwoofer, forget transmission lines.
They are basically a waste of good box volume.

More sacrilege from Arny.

Is that a synonym for 'trollage'?


But true. I've never come across a pro
transmission line speaker, and for good reasons.

For reasons of volume, as Arny states?


--
Wally
www.makearatherlonglinkthattakesyounowhere.com
Things are always clearer in the cold, post-upload light.

Dave Plowman wrote:
In article ,
Arny Krueger wrote:
If money is tight, auction off the B139s and use the cash to buy a
real subwoofer driver.

Oh, and if you are building a subwoofer, forget transmission lines.
They are basically a waste of good box volume.

More sacrilege from Arny.

Is that a synonym for 'trollage'?


But true. I've never come across a pro
transmission line speaker, and for good reasons.

For reasons of volume, as Arny states?


--
Wally
www.makearatherlonglinkthattakesyounowhere.com
Things are always clearer in the cold, post-upload light.

Dave Plowman wrote:

: In article ,
: Arny Krueger wrote:
: If money is tight, auction off the B139s and use the cash to buy a real
: subwoofer driver.
:
: Oh, and if you are building a subwoofer, forget transmission lines. They
: are basically a waste of good box volume.
:
: More sacrilege from Arny. But true. I've never come across a pro
: transmission line speaker, and for good reasons.

Well, more straight talk from Arny ... a loosely chosen entry point!
OTOH, I've been following the thread, as I've a pair of B139's too;-)

AAMOF I hauled them out of a pair of small "TL"s I bought (with early
T27 variant, B110 (unknown label-off variant)) and reduced the cases
to face-down "speaker stands" interim because they sounded so bad,
with old stuffing etc, and besides I needed a temporary replacement
for the one blown T27's in my kitchen Kef 104ab set - but I digress!

Straight talk or not, I've total sympathy with the OP's desire to do
what he can with what he has, especially with budget considerations,
and I'm saving the B139's (and the B110's in case an alternate idea
for a better cabinet arrangement .... looking at the really basic TL I
bought, it could be turned sideways and possibly extended ... as per
http://www.t-linespeakers.org/design/foldings/tttl.html ... maybe ...

But my main point was going to be ... and I hold this out as a
potential future project of my own, all comments appreciated;- -
what about considering the "coffin" dual TL supposedly sub at
http://www.t-linespeakers.org/classics/coffin/
and especially, obviously the details at the "Perfectionist Audio"
link therein,
http://www.hogheaven.com/diyaudio/su...PATL/patl.html
as a possibility for using a spare pair of B139's up?

OK, it requires a little work in the timber dept, but why not?
It might seem to have capabilities beyond the usual, anyway.

[Cheers!]

RdM

"Big is better, and biggest is best" (;=}))
William S. Burroughs as lead dinosaur in some song skit, somewhere

[and the reason I'm delaying mine is because I'd never get it down the
stairs on a move ... but it's definitely a considered future project!]

Dave Plowman wrote:

: In article ,
: Arny Krueger wrote:
: If money is tight, auction off the B139s and use the cash to buy a real
: subwoofer driver.
:
: Oh, and if you are building a subwoofer, forget transmission lines. They
: are basically a waste of good box volume.
:
: More sacrilege from Arny. But true. I've never come across a pro
: transmission line speaker, and for good reasons.

Well, more straight talk from Arny ... a loosely chosen entry point!
OTOH, I've been following the thread, as I've a pair of B139's too;-)

AAMOF I hauled them out of a pair of small "TL"s I bought (with early
T27 variant, B110 (unknown label-off variant)) and reduced the cases
to face-down "speaker stands" interim because they sounded so bad,
with old stuffing etc, and besides I needed a temporary replacement
for the one blown T27's in my kitchen Kef 104ab set - but I digress!

Straight talk or not, I've total sympathy with the OP's desire to do
what he can with what he has, especially with budget considerations,
and I'm saving the B139's (and the B110's in case an alternate idea
for a better cabinet arrangement .... looking at the really basic TL I
bought, it could be turned sideways and possibly extended ... as per
http://www.t-linespeakers.org/design/foldings/tttl.html ... maybe ...

But my main point was going to be ... and I hold this out as a
potential future project of my own, all comments appreciated;- -
what about considering the "coffin" dual TL supposedly sub at
http://www.t-linespeakers.org/classics/coffin/
and especially, obviously the details at the "Perfectionist Audio"
link therein,
http://www.hogheaven.com/diyaudio/su...PATL/patl.html
as a possibility for using a spare pair of B139's up?

OK, it requires a little work in the timber dept, but why not?
It might seem to have capabilities beyond the usual, anyway.

[Cheers!]

RdM

"Big is better, and biggest is best" (;=}))
William S. Burroughs as lead dinosaur in some song skit, somewhere

[and the reason I'm delaying mine is because I'd never get it down the
stairs on a move ... but it's definitely a considered future project!]

Dave Plowman wrote:

More sacrilege from Arny. But true. I've never come across a pro
transmission line speaker, and for good reasons.

Err, PMC make rather a lot of them. But I guess you've never come
across one, so...

Andrew.

Dave Plowman wrote:

More sacrilege from Arny. But true. I've never come across a pro
transmission line speaker, and for good reasons.

Err, PMC make rather a lot of them. But I guess you've never come
across one, so...

Andrew.

In article ,
Arny Krueger wrote:
If money is tight, auction off the B139s and use the cash to buy a real
subwoofer driver.

Oh, and if you are building a subwoofer, forget transmission lines. They
are basically a waste of good box volume.

More sacrilege from Arny. But true. I've never come across a pro
transmission line speaker, and for good reasons.

--
*It's a thankless job, but I've got a lot of Karma to burn off

Dave Plowman London SW 12
RIP Acorn