In article , Wally
wrote:
Jim Lesurf wrote:

Also, if you are simply splitting the links I assume the internal LP
and HP filters in the speakers are still in the signal paths. Thus the
'best' setting for your active crossover/filter may be quite different
to that specified for the speaker when used 'normally'.

No links as such - 3-way speakers with the bass drivers disconnected
from the passive crossovers and wired straight to the bass amp. The
remaining two-way pair are still connected to a single amp, going
through the full 3-way crossover (with the LF output open circuit).

IIUC the above means that the HF signals now go through the same network as
before, but with the LF speaker disconnected from that network.

Two comments on that:

1) If the LF speaker was previously connected via that network, it may now
be producing a different frequency response than before.

2) Removing the impedance of the LF speaker from the network may also
change the response of the network/HF speakers.

Hence in addition to other factors, the changes indicated above may change
the frequency response of the system.

I'm thinking of converting to the two-way Kef crossover for splitting
the B110 and T27 (this version has no high-pass element on the B110 cct,
since the B110 is acting as bass and mid in a two-way set up). The B110
is in its own IB sub-enclosure within the main cabinet. Do you think
this is worth pursuing, or would there be some sort of 'conflict' of
B110 roll-off in the sub-enclosure, compared with the 24dB/octave
low-pass that the active crossover applies to the bass driver?

Not sure what might be meant by 'conflict'. However the B110 and its
enclosure presumable have a given frequency response and set of
resonances, etc. Just driving directly from a flat amp with a LP roll-off
may not deal with this. Hard to say as I'm afraid I don't know the
specifics of the actual arrangement. Rolling away the HF will avoid things
like cone breakup resonances. However in the region where both the LF and
HF speakers are active their outputs will combine and this will also have
effects that will be quite specific to the individual arrangement.

The above is a long-winded way of daying "Dunno". :-)

TBH though, personally I would not embark on speaker development/design
without having access to some kit to measure the response, etc. There are
simply too many variables and potential problems which I'd find too hard to
disentagle simply 'by ear'.

If you can make up CDs of test sinewaves, etc, and have access to a
reliable sound pressure meter, then it would be interesting to see to
what extent the differences you hear correlate with any changes in
overall frequency response being produced by the active crossover,
differences in gain of the two power amps, and effects of the output
impedances of the amps.

Urrr..., I can make test CDs of sine waves. :-) (With a bit of software
I had on my old computer - would need to find it and reinstall.) Don't
have a sound pressure meter, I'm afraid. I suppose the Cyrus 2 has more
gain than the valve amp. I think their input sensitivities are roughly
similar (200-300mV for full power). The valve amp (20-ish Watts) is set
to half volume, the Cyrus (50W) at about '3', and the gains/cuts on the
active crossover are all set to 0dB. This seems to produce a balanced
sound. The overall volume is controlled by a preamp.

The problem here is not just that the two power amps may have different
gains. They may also have different output impedances. In particular if the
valve amp has a 'high' output impedance this will produce a different
frequency response to an amp with a 'low' output impedance.

It's all calibrated with the indubitably dubious power of the human
lug-'ole - but it's my lug-'ole, and that's the one that matters. :-)
My impression of the Behringer is that it's essentially flat - without a
set of before and after measurements, I'm assuming that the feeling of
better clarity and improved bass is down to having more power available,
and perhaps splitting bass and mid/top to separate amps.

Alas, I have my doubts that the reason you assume is the correct one.
Unless the amps were seriously current limiting I doubt that the biamping
will have had very much effect on the power levels available. Could you
hear previously clear signs of clipping?

The problem is that the changes you perceive may simply be due to you
altering the overall frequency response. This seems particularly likely
(and your assumption unlikely) if you hear the benefits at moderate to low
sound levels as well as at peak levels.

If the results sound better to you, that is fair enough as you have a
result you prefer. For that your lug-ole is king.

However it means that if that *is* the reason, then similar results might
be obtained by much cheaper and easier means. This may not matter to you at
this point, but if it were the case, knowing this might save others time
and money. :-)

Slainte,

Jim

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