Modifying BBC LS 5/8
 

Just to follow on from my post about the crossovers, thought I'd tell you
what I've been up to.

Bought a total of three LS 5/8 with BBC modified Quad 405s a few months
back. This design is post my time at the BBC, so I'd never used a pair for
work monitoring - but had been impressed on the occasions I'd heard them.
However living with a pair for day to day use is often not the same.

Also, on chatting to some retired BBC TV sound supervisors at a reunion,
it became clear the 'pop' boys loved them, but drama ones didn't.

Which is what I'd been finding. Sound great at high levels on most types
of music, but not good at low levels - and more so on speech at 'natural'
levels. And since they are to be used for everything including TV and
radio, not so good for my use. If I had to put a finger on it I'd say
something not right in the midrange. The design uses a 12" bass unit to
2kHz, and a single dome tweeter above that. The bass is superb, though.

AB tests between a single LS 3/5a and a single LS5/8 showed the mid range
voicing to be very different at normal domestic listening levels. So they
both couldn't be correct. ;-)

Now the B110 was always highly regarded so I decided to fit then to the
5/8 covering the critical midrange of 300 - 3kHz. Falcon Acoustics make
new FB110 units which they claim are as near identical as possible. Adding
an extra amp to the 405 and of course a new crossover.

Which is what I've done.

I made a new baffle and moved the tweeter to one side with the B110 on the
other side in its own 0.004 cu.mtr enclosure - this is what KEF
recommended for mid range use. When I do the other one it will be mirror
image.

Fitted a Maplin 150w MOSFET alongside the treble amp in the 405, a
separator PS for the crossover between the mains transformer and smoothing
caps, and the crossover where the BBC one was - alongside the other 405
power amp. (My thinking was the original 405 PS should be ok as I'm not
actually expecting more total 'watts' out of the system.

I'm listening to the prototype at this minute here in the worskshop and am
very pleased with it. (I used the third speaker as a prototype, so still
have the main pair in the living room.) Doing an AB between it and a 3/5a
shows them to be very similar in the midrange.

I have lots of pics I can put on Photobucket if anyone's interested.

--
*He who laughs last, thinks slowest.

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

Modifying BBC LS 5/8
 

Dave Plowman (News) wrote:

Now the B110 was always highly regarded so I decided to fit then to
the 5/8 covering the critical midrange of 300 - 3kHz. Falcon
Acoustics make new FB110 units which they claim are as near identical
as possible. Adding an extra amp to the 405 and of course a new
crossover.

What is the frequency of the baffle diffraction step? - life can be easier
with the cross-over frequency right on it.

Kind regards

Peter Larsen

Modifying BBC LS 5/8
 

If you want *good* speakers, buy a pair of good speakers.
If you want an antique, don't modify it.
You can't sell them to wealthy Japanese collectors now.

Thanks for the description. Most informative.
Isn't it time Stuart popped up to mention that
Bextrene cones are rubbish at low levels?

--
Eiron.

Modifying BBC LS 5/8
 

In article ,
Eiron wrote:
If you want *good* speakers, buy a pair of good speakers.

When you get to the pro monitor end, that can be difficult. And
horrendously expensive. The total I will have spent (excluding labour)
will be well under 2 grand.

If you want an antique, don't modify it.

Why? it's not irreversible - I have kept all the original bits for that
express reason. And they weren't in mint condition originally anyway.

You can't sell them to wealthy Japanese collectors now.

I didn't buy them to sell on.

Thanks for the description. Most informative.

Thought it might get some discussion going - it's a bit quiet here.

Isn't it time Stuart popped up to mention that
Bextrene cones are rubbish at low levels?

Everyone has an opinion.

--
*Why 'that tie suits you' but 'those shoes suit you'?*

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

Modifying BBC LS 5/8
 

In article ,
Peter Larsen wrote:
What is the frequency of the baffle diffraction step? - life can be
easier with the cross-over frequency right on it.

What little I've read about that says you do all the calculations then add
your own fiddle factor. ;-)

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

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

Modifying BBC LS 5/8
 

"Dave Plowman (News)" wrote in message
...
Just to follow on from my post about the crossovers, thought I'd tell you
what I've been up to.

Bought a total of three LS 5/8 with BBC modified Quad 405s a few months
back. This design is post my time at the BBC, so I'd never used a pair for
work monitoring - but had been impressed on the occasions I'd heard them.
However living with a pair for day to day use is often not the same.

Also, on chatting to some retired BBC TV sound supervisors at a reunion,
it became clear the 'pop' boys loved them, but drama ones didn't.

Which is what I'd been finding. Sound great at high levels on most types
of music, but not good at low levels - and more so on speech at 'natural'
levels. And since they are to be used for everything including TV and
radio, not so good for my use. If I had to put a finger on it I'd say
something not right in the midrange. The design uses a 12" bass unit to
2kHz, and a single dome tweeter above that. The bass is superb, though.

AB tests between a single LS 3/5a and a single LS5/8 showed the mid range
voicing to be very different at normal domestic listening levels. So they
both couldn't be correct. ;-)

Now the B110 was always highly regarded so I decided to fit then to the
5/8 covering the critical midrange of 300 - 3kHz. Falcon Acoustics make
new FB110 units which they claim are as near identical as possible. Adding
an extra amp to the 405 and of course a new crossover.

Which is what I've done.

I made a new baffle and moved the tweeter to one side with the B110 on the
other side in its own 0.004 cu.mtr enclosure - this is what KEF
recommended for mid range use. When I do the other one it will be mirror
image.

Fitted a Maplin 150w MOSFET alongside the treble amp in the 405, a
separator PS for the crossover between the mains transformer and smoothing
caps, and the crossover where the BBC one was - alongside the other 405
power amp. (My thinking was the original 405 PS should be ok as I'm not
actually expecting more total 'watts' out of the system.

I'm listening to the prototype at this minute here in the worskshop and am
very pleased with it. (I used the third speaker as a prototype, so still
have the main pair in the living room.) Doing an AB between it and a 3/5a
shows them to be very similar in the midrange.


There are comments on this speaker
http://www.harbeth.co.uk/usergroup/s...5-12A-monitors

Given the age of the design, the crossover is probably the weakest link.
Speaker drivers from the 70s are generally down on power handling and linear
SPL generation, but their response can be good. Crossovers from that era
tend to be oversimplifed and less than modern SOTA with regards to issues
like off-axis response,

Modifying BBC LS 5/8
 

In article ,
Arny Krueger wrote:
There are comments on this speaker
http://www.harbeth.co.uk/usergroup/s...5-12A-monitors

Yes - I've seen that before, although it's more about the 5/9 - a very
different beast.

Given the age of the design, the crossover is probably the weakest link.
Speaker drivers from the 70s are generally down on power handling and
linear SPL generation, but their response can be good. Crossovers from
that era tend to be oversimplifed and less than modern SOTA with
regards to issues like off-axis response,

I did have a quick play simply replacing the crossover with a modern
design - and it didn't make a significant difference. My gut feeling is
2khz is way to high for a 12" high power unit.

--
*Warning: Dates in Calendar are closer than they appear.

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

Modifying BBC LS 5/8
 

Fitted a Maplin 150w MOSFET alongside the treble amp in the 405, a
separator PS for the crossover between the mains transformer and smoothing
caps, and the crossover where the BBC one was - alongside the other 405
power amp. (My thinking was the original 405 PS should be ok as I'm not
actually expecting more total 'watts' out of the system.

I'm listening to the prototype at this minute here in the worskshop and am
very pleased with it. (I used the third speaker as a prototype, so still
have the main pair in the living room.) Doing an AB between it and a 3/5a
shows them to be very similar in the midrange.


There are comments on this speaker
http://www.harbeth.co.uk/usergroup/s...d.php?172-BBC-
LS3-5-LS5-8-LS5-9-LS5-12A-monitors

Given the age of the design, the crossover is probably the weakest link.
Speaker drivers from the 70s are generally down on power handling and linear
SPL generation, but their response can be good. Crossovers from that era
tend to be oversimplifed and less than modern SOTA with regards to issues
like off-axis response,




Heres some other interesting stuff on the 5/8 and 5/9 .

There is a bit more to this than meets the eye regarding the amplifiers
in use., It does seem to be agreed that the original Quad's which were
very good for their time did have some shortcomings and over time there
have been mods that do improve them.

Note the comments on the Chord amps used on later designs and the better
reviews they attract..

Also the 5/8 seems to be better regarded than the 5/9 also..


http://www.mhennessy3.f9.co.uk/rogers/ls58.htm
--
Tony Sayer

Modifying BBC LS 5/8
 

In article ,
tony sayer wrote:
There is a bit more to this than meets the eye regarding the amplifiers
in use., It does seem to be agreed that the original Quad's which were
very good for their time did have some shortcomings and over time there
have been mods that do improve them.

That's why I chose to use the MOSFET for the midrange - it's what I listen
to a lot in the workshop and sounds very clean.

--
*Support bacteria - they're the only culture some people have *

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

Modifying BBC LS 5/8
 

"tony sayer"


Heres some other interesting stuff on the 5/8 and 5/9 .

There is a bit more to this than meets the eye regarding the amplifiers
in use., It does seem to be agreed that the original Quad's which were
very good for their time did have some shortcomings

** Bet you cannot identify even one real example.


and over time there
have been mods that do improve them.

** The Quad 405 design lent itself to part swapping around the op-amp input
stage.

So of course audiophool ******s had to try it and then publish all kinds off
bull about it on the net.

None of the mods does anything worthwhile - audiophool mods never do.


Note the comments on the Chord amps used on later designs and the better
reviews they attract..

** Groannnnnn....

Audiophool reviews read by audiophools.

The blind leading the blind.

**** off Tony.


.... Phil