DIY design for KEF B139

[Per Stromgren]

Cheers!

I have a transmssion line subwoofer that uses a KEF B139 unit. I have
had this for years, and used it for pop recordings together with my
Quad 63's. Well, we did some moving around of furniture and the
transmission line became just to large and ugly to fit anywhere.

Can you recommend a reflex design no more than 100 litres that I could
build instead? Or should I drop the KEF for a modern unit? My
requirements are really not that big, just adding a little bit of omph
for the electric and synth bass of pop CDs. I use the 63's alone for
anything else. I have an 85Hz 4:th order Butterworth filter to go with
the sub.

(In an ideal world of would like to build myself Gradient SW63
look-alikes including electronics, but I'm too lazy to do that, and
too poor to buy the Gradients... Or a pair of Quad 989, for that
matter.)

Per.

[François Yves Le Gal]

Post by Per Stromgren
Can you recommend a reflex design no more than 100 litres that I could
build instead?

Try 85 to 90 litres net internal volume with a large port tuned to 32 Hz.
This will give you a nice so-called EBS (extended bass shelf) response.

Post by Per Stromgren
Or should I drop the KEF for a modern unit?

The B139 is still a really nice (sub)woofer if you're not into headbangin'
or wall shakin'.

[Per Stromgren]

On Mon, 22 Dec 2003 12:06:19 +0100, François Yves Le Gal

Post by François Yves Le Gal

Post by Per Stromgren
Can you recommend a reflex design no more than 100 litres that I could
build instead?

Try 85 to 90 litres net internal volume with a large port tuned to 32 Hz.
This will give you a nice so-called EBS (extended bass shelf) response.

Thanks. That should fit nicely.

Post by François Yves Le Gal

Post by Per Stromgren
Or should I drop the KEF for a modern unit?

The B139 is still a really nice (sub)woofer if you're not into headbangin'
or wall shakin'.

No, I'm neither. When they say that if they're too loud, I'm too old,
they are right.

Per.

[Peter Larsen]

Post by François Yves Le Gal
Try 85 to 90 litres net internal volume with a large port tuned to 32 Hz.
This will give you a nice so-called EBS (extended bass shelf) response.

Hmm ... I would have thought the 4'order tuning to end up around the box
the factory made with it, I think that was 40-some liters.

Post by François Yves Le Gal
The B139 is still a really nice (sub)woofer if you're not into headbangin'
or wall shakin'.

I think Per will miss the ole' box ... don't discard the old box Per,
you may want to perform what is technically known in XP lingo as a
driver rollback into the old version, if not now then perhaps later.


Kind regards

Peter Larsen

[Per Stromgren]

On Mon, 22 Dec 2003 18:07:14 +0100, Peter Larsen

Post by Peter Larsen

Post by François Yves Le Gal
Try 85 to 90 litres net internal volume with a large port tuned to 32 Hz.
This will give you a nice so-called EBS (extended bass shelf) response.

Hmm ... I would have thought the 4'order tuning to end up around the box
the factory made with it, I think that was 40-some liters.

Could you guys settle for something? Is this perhasp just a matter of
looking up the T/S spec and compute an ordinary B4?

Post by Peter Larsen

Post by François Yves Le Gal
The B139 is still a really nice (sub)woofer if you're not into headbangin'
or wall shakin'.

I think Per will miss the ole' box ... don't discard the old box Per,
you may want to perform what is technically known in XP lingo as a
driver rollback into the old version, if not now then perhaps later.

Thanks, Peter! We have a rather large house, it can sit in the attic
for a while.

Per.

[François Yves Le Gal]

Post by Per Stromgren
Could you guys settle for something? Is this perhasp just a matter of
looking up the T/S spec and compute an ordinary B4?

Standard Kef-style alignment:

Vb = 49,64 liters
Fb = 36,4 Hz
QL = 6,84
F3 = 44,4 Hz

Not very extended, can sound quite boomy.

EBS:

Vb = 88,41 liters
Fb = 31,6 Hz
QL = 6,541
F3 = 35,6 Hz

More extended, with an initial gentle slope, no boom.

[François Yves Le Gal]

On Mon, 22 Dec 2003 18:07:14 +0100, Peter Larsen

Post by Peter Larsen
Hmm ... I would have thought the 4'order tuning to end up around the box
the factory made with it, I think that was 40-some liters.

Yes, but it's a less than optimal alignment, which isn't really extended and
can sound quite boomy. As the original poster has room for 100 l, going EBS
is IMO a much better option, particularly considering his main speakers...

[Geoff Wood]

Post by Stewart Pinkerton
On Mon, 22 Dec 2003 11:07:38 +0100, Per Stromgren

Post by Per Stromgren
Can you recommend a reflex design no more than 100 litres that I could
build instead?

Try 85 to 90 litres net internal volume with a large port tuned to 32 Hz.
This will give you a nice so-called EBS (extended bass shelf) response.

Post by Per Stromgren
Or should I drop the KEF for a modern unit?

The B139 is still a really nice (sub)woofer if you're not into headbangin'
or wall shakin'.

"It isn't the size, it's how you use it" is a saying often encountered in
many situations. A handy response is "... but a large one used well is
always better than a small one used well !".

Use your B139 TL as a stand for something. You will regret it if you
replace it. And you'll never get cone break-up unlike other cones - or if
you do you're in trouble !

geoff

[Arny Krueger]

Post by Stewart Pinkerton
On Mon, 22 Dec 2003 11:07:38 +0100, Per Stromgren

Post by Per Stromgren
Can you recommend a reflex design no more than 100 litres that I
could build instead?

Try 85 to 90 litres net internal volume with a large port tuned to 32
Hz. This will give you a nice so-called EBS (extended bass shelf)
response.

Post by Per Stromgren
Or should I drop the KEF for a modern unit?

The B139 is still a really nice (sub)woofer if you're not into
headbangin' or wall shakin'.

IOW, as a mid-bass driver it's not totally obsolete.

I've found sources that say its Xmax is only about 3 mm, which is
ridiculously small for a driver in this size class by modern standards.

http://members.aol.com/NmacSmith/f3ported.htm

[Stewart Pinkerton]

Post by Arny Krueger

Post by Stewart Pinkerton
On Mon, 22 Dec 2003 11:07:38 +0100, Per Stromgren

Post by Per Stromgren
Can you recommend a reflex design no more than 100 litres that I
could build instead?

Try 85 to 90 litres net internal volume with a large port tuned to 32
Hz. This will give you a nice so-called EBS (extended bass shelf)
response.

Post by Per Stromgren
Or should I drop the KEF for a modern unit?

The B139 is still a really nice (sub)woofer if you're not into
headbangin' or wall shakin'.

IOW, as a mid-bass driver it's not totally obsolete.
I've found sources that say its Xmax is only about 3 mm, which is
ridiculously small for a driver in this size class by modern standards.

Yes, but first breakup is around 1200 Hz, which is pretty good for a
3-way bass driver. Agreed that it's a woofer, and in no way qualifies
as a subwoofer driver.

[Tony Pearce]

Post by Stewart Pinkerton
Agreed that it's a woofer, and in no way qualifies
as a subwoofer driver.

Just like 90% of the commercial "sub woofers" then.

TonyP.

[Fernando]

Hi,

I would think twice before adding a bass reflex subwoofer to
Quads, as transmission line subwoofers are usually considered a
good match with electrostatics and dipoles. Although the
B139 can have a good performance in a transmission line,
its berformance as a bass reflex is "boomy" and will be
a poor match with the Quads. I do not know why, but KEF B139s
are usually sold for high values at eBay - better selling
them and buying a new subwoofer for a different project!
best regards
Happy New Year
Fernando

Post by Tony Pearce

Post by Stewart Pinkerton
Agreed that it's a woofer, and in no way qualifies
as a subwoofer driver.

Just like 90% of the commercial "sub woofers" then.
TonyP.

[Dick Pierce]

Post by Fernando
Hi,
I would think twice before adding a bass reflex subwoofer to
Quads, as transmission line subwoofers are usually considered a
good match with electrostatics and dipoles. Although the
B139 can have a good performance in a transmission line,
its berformance as a bass reflex is "boomy" and will be
a poor match with the Quads.

If it's performance in a bass reflex is boomy, that's a sure
sign that whoever designed the bass reflex enclosure did it
wrong.

A KEF B139 has a free air Qt of around 0.37, which is slightly
overdamped for a lossless B4 alignment. Over size the enclosure
slightly, and you're in the realm of of the upper end of QB3
performance, which is hardly "boomy" at all.

Post by Fernando
I do not know why, but KEF B139s
are usually sold for high values at eBay - better selling
them and buying a new subwoofer for a different project!

And, whatever driver you use, don't use whatever was used to
design the system alluded to above.

[Ian]

Post by Dick Pierce

Post by Fernando
Hi,
I would think twice before adding a bass reflex subwoofer to
Quads, as transmission line subwoofers are usually considered a
good match with electrostatics and dipoles. Although the
B139 can have a good performance in a transmission line,
its berformance as a bass reflex is "boomy" and will be
a poor match with the Quads.

If it's performance in a bass reflex is boomy, that's a sure
sign that whoever designed the bass reflex enclosure did it
wrong.
A KEF B139 has a free air Qt of around 0.37, which is slightly
overdamped for a lossless B4 alignment. Over size the enclosure
slightly, and you're in the realm of of the upper end of QB3
performance, which is hardly "boomy" at all.

Post by Fernando
I do not know why, but KEF B139s
are usually sold for high values at eBay - better selling
them and buying a new subwoofer for a different project!

And, whatever driver you use, don't use whatever was used to
design the system alluded to above.

As a fully qualified OF, I recall that the B139 had the best on-axis
square wave response ever seen, subject to ringing at around 1kHz.

Regards
Ian

A happy new year to all.

[Geoff Wood]

Post by Ian
As a fully qualified OF,

OF - "Old F........, um, 'Fella' " ???


geoff

[Ian]

Post by Geoff Wood

Post by Ian
As a fully qualified OF,

OF - "Old F........, um, 'Fella' " ???
geoff

"Old F*rt", sometimes preceded by a "B" for "Boring" ;-)

Regards
Ian

[Geoff Wood]

Post by Ian

Post by Geoff Wood

Post by Ian
As a fully qualified OF,

OF - "Old F........, um, 'Fella' " ???
geoff

"Old F*rt", sometimes preceded by a "B" for "Boring" ;-)

There are a number of other possibilities ;-)

geoff

[Ian]

Post by Geoff Wood

Post by Ian

Post by Geoff Wood

Post by Ian
As a fully qualified OF,

OF - "Old F........, um, 'Fella' " ???
geoff

"Old F*rt", sometimes preceded by a "B" for "Boring" ;-)

There are a number of other possibilities ;-)
geoff

Indeed ;-)

Regards
Ian

[Geoff Wood]

Post by Fernando
a poor match with the Quads. I do not know why, but KEF B139s
are usually sold for high values at eBay - better selling
them and buying a new subwoofer for a different project!

I guess because there are a lot of TL cabinets in existence, the B139 is no
longer made , and has a distinctive physical cut-out shape, they command a
"captive audience" price premimium for those who have blown or might blow
their drivers.


geoff

[John Walton]

This is a very easy speaker to repair if the VC is blown. The BL product,
for its day, was untouchable in a speaker of its size.

Here's a design for the PRO9-TL from about 30 years ago:
http://www.tech-diy.com/pro9.htm

Post by Geoff Wood

Post by Fernando
a poor match with the Quads. I do not know why, but KEF B139s
are usually sold for high values at eBay - better selling
them and buying a new subwoofer for a different project!

I guess because there are a lot of TL cabinets in existence, the B139 is no
longer made , and has a distinctive physical cut-out shape, they command a
"captive audience" price premimium for those who have blown or might blow
their drivers.
geoff

[Geoff Wood]

Post by John Walton
This is a very easy speaker to repair if the VC is blown.

Not so easy to repair when cats or childrem dig chunks out of the
'diaphram' though ...!

geoff

[Stewart Pinkerton]

On Mon, 22 Dec 2003 11:07:38 +0100, Per Stromgren

Post by Per Stromgren
Cheers!
I have a transmssion line subwoofer that uses a KEF B139 unit. I have
had this for years, and used it for pop recordings together with my
Quad 63's. Well, we did some moving around of furniture and the
transmission line became just to large and ugly to fit anywhere.
Can you recommend a reflex design no more than 100 litres that I could
build instead? Or should I drop the KEF for a modern unit? My
requirements are really not that big, just adding a little bit of omph
for the electric and synth bass of pop CDs. I use the 63's alone for
anything else. I have an 85Hz 4:th order Butterworth filter to go with
the sub.

Why not just buy a compact modern powered sub like a REL Q201? It will
handily outperform your TLs, while taking up less room than an average
footstool. Tuck it in a room corner, where all subs should live, and
you'll hardly notice it.

[Per Stromgren]

Post by Stewart Pinkerton
On Mon, 22 Dec 2003 11:07:38 +0100, Per Stromgren

Post by Per Stromgren
Cheers!
I have a transmssion line subwoofer that uses a KEF B139 unit. I have
had this for years, and used it for pop recordings together with my
Quad 63's. Well, we did some moving around of furniture and the
transmission line became just to large and ugly to fit anywhere.
Can you recommend a reflex design no more than 100 litres that I could
build instead? Or should I drop the KEF for a modern unit? My
requirements are really not that big, just adding a little bit of omph
for the electric and synth bass of pop CDs. I use the 63's alone for
anything else. I have an 85Hz 4:th order Butterworth filter to go with
the sub.

Why not just buy a compact modern powered sub like a REL Q201?

To save some 725£? :-) The B139 just sits there, the amp and filter as
well. Maybe even the MDF is somewhere in the house. Leaves the reflex
port and a new terminal plate.

But yes, a REL would be fine for this purpose. I am not familiar with
the Q201, though.

Post by Stewart Pinkerton
It will
handily outperform your TLs, while taking up less room than an average
footstool. Tuck it in a room corner, where all subs should live, and
you'll hardly notice it.