Jim Lesurf wrote:

The point to bear in mind that the overall frequency response may be
different now for a combination of reasons:

1) Removal/bypass of the original networks. These may not just have
acted as crossovers. They may have alttered the in-band levels and
shapes of response.

I've been doing some browsing, and it would seem that the KEF B110 has a
one-octave-wide lift at about 1.5KHz. I don't know how big a lift it is.
When I do my baseline measurement, I'll be paying close attention.


2) The power amps may have different gains.

They have, but, as I said to Stewart, they each have volume controls, none
is turned up full, and the crossover provides +/-6dB on each band.


3) Your 'crossover' points and slopes may be different to before.

The points are dialled in to match those used by KEF, although I dare say
the active xover has steeper slopes. A steeper slope is generally a good
thing, isn't it?


4) The effective gains for the active crossover may now be different
in the various bands.

As I say above, they're settable - even if there are discrepancies between
bands when the gains are set to zero, there's scope to compensate in any
case.


Hence it remains plausible that you might have obtained much the same
effect by using the active crossover simply as a 'tone control' whilst
using the speakers with fewer amps and leaving the passive networks in
place.

Maybe so, but part of the aim of this is to double up the bass drivers by
making isobaric subs. The main reason for doing this is to get substantially
smaller cabinets - the existing boxes are way too big, and moving them
around simply isn't practical. I also wanted better bass than the lumpy
response I had (the cabinets are 'wrong' for the drivers), and better power
handling. Since I already had two B139s in the speakers, and two spares,
this would seem a reasonable way to go.



Indeed, of the passive networks included arrangements to deal
with some detailed aspects of the speakers, the results *might* have
been better in some way. Problem is that we can't tell without a
suitable comparison test.

As I said, the tri-amped set up is the baseline. The way I see it, it's
easier for me to make changes and assess their effects. For example, if
there are shortcomings in the midrange drivers, I'm not averse to trying
something more modern that has a flatter 'natural' response (and,
intuitively, this seems to be a better approach than taking a driver with a
lumpy response and trying to flatten it with reactive components). FWIW,
I've never been overly happy with the midrange - comments here a few months
ago, about bextrene cones, rang true with my experience of them.


How are you defining "available power" here? It may not be as simple
as just adding together the ratings for the individual amps.

I don't know what I'm talking about, so I'm being simplistic. :-)


That is fair enough from your point of view. You have spent your
money, put in the effort, and obtained a result which you prefer.
That seems an excellent result to me, and clearly justifies the
effort.

No doubt about that - the tonal character is much the same, but the overall
change is, to me, a step-change improvement.


However I am simply trying to point out for consideration by
yourself and others that there may well be a cheaper and easier way
to get similar 'improvements'. This may save others some cost and
effort.

I appreciate your point, but I freely admit that the tri-amp thing is as
much about curiosity as anything. If I discount the digital EQ for the bass,
the actual spend has been about 200 quid for the active crossover and a
second Cyrus. IOW, I would have added the EQ regardless of what system
configuration I was using - the bass was a mess, and I think the room will
always conspire to keep it that way whatever speakers I have. All-in, the
spend, including connectors and cable, has been around 300-odd quid, spread
around bits that are relatively cheap, and easy to sell on if I want to
change the overall approach.


[1] In this context it does not matter much if the sound meter is a
cheap/poor one, or if the room has an odd acoustic. The aim is to do a
'before/after' comparison and have the info as a reference.

Yup. I'll be doing a full range frequency response test sometime fairly
soon.


--
Wally
www.artbywally.com/FiatPandaRally/index.htm
www.wally.myby.co.uk