[Adrian Tuddenham[_2_]]

geoff wrote:

On 16/07/2020 8:53 pm, Don Pearce wrote:
On Tue, 14 Jul 2020 21:08:39 -0700 (PDT), James Price
wrote:

How do manufacturers ensure a high degree of sonic consistency (eg.
frequency response, max peak SPL, etc.) between studio monitors of the
same make and model? *Is* there a high degree of sonic consistency
between two seemingly identical studio monitors/playback systems?

If you take as an example the LS3/5A BBC monitor speaker, the B110
bass drivers were selected to have a resonance frequency within 5Hz
for a matched pair. The internal resonance of the cabinet will pull
the speakers into line from that tolerance.

d


My (self-built, complete with auto-transformer) LS3-5As are lined,
instead of with bitumous sheet, lead !

I used the B110 and a soft-dome SEAS H881 tweeter with a pair of B139s,
each unit driven by its own amplifier in a closed cabinet design; the
four amplifiers and their power supply are built into the cabinet. The
B110's aren't called on to go down as far as their resonance frequency,
so matching between them isn't quite as critical. They are mounted in
fairly stiff enclosures damped with sandwiches of bitumen and
galavanised steel plates. The enclosures are tapered to reduce the
'organ pipe' effect and they also served as bracing members between the
front and back panels of the outer L.F. cabinets.

The main cabinet is divided into three unequal sections by two
perforated shelves which break up longitudinal air resonances and brace
the side and back panels. The panels are further damped by a sandwich
of galvanised steel plates and roofing felt. Knocking anywhere on them
wth the knuckles produces a dead 'thunk' (followed by "ouch!"). They
weigh 1 cwt (50kg) each.

The crossover is an 'active' design with cascaded state-variable
filters. It is interesting to note that the LS3/5a used twin amplifiers
and an active crossover during the design phase and was only fitted with
a passive crossover when it went into production (the BBC had to farm
out the design of that because it was so complex).


--
~ Adrian Tuddenham ~
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