[Arny Krueger]

"JimC" wrote in message


My question is: Assuming the low-pass crossover is set to
40Hz, and the high-pass filter is set to 80Hz, what
happens to the frequencies between 40Hz and 80Hz
(Ignoring signals that are outside the roll-off curves)?

They get attenuated.

Are they simply lost?

Well, reduced.

In this system, the mains are
Maggie 3.6 planars, with response extending somewhat
below 40Hz, and I would prefer to feed bass above that
frequency to the Maggies rather than have them reproduced
by the subwoofer.

Why?

But with the above system, it seems
that they would not receive any substantial bass below
80Hz.

Most analog filters such as these have relatively gentle roll-offs. At the
corner frequency (in this case 80 Hz) the filter response is only 3 dB down.
Below that frequency, response rolls off fairly gently. It's not like
signals below 80 Hz are lost - they are simply attenuated a modest amount.

Any discussion of filters for the purpose of crossing-over loudspeakers has
to include the acoustic response of the loudspeakers, which includes room
effects. I don't think that those are exactly known at this time.

For example, if there is a peak in room response in the 40-60 Hz range, the
slight depression caused by the separation of crossover frequencies might be
filled-in by the peak.

Also, what happens to signals sent to the mains
when the Velodyne low-pass crossover is adjusted, e.g.,
adjusted between 40Hz and 80Hz or above?

Usually, there is no effect at all.

Presently I am not using the high-pass connections, and
instead feed the full audio frequency spectrum directly
to both the sub and the power amp (the preamp output is
connected directly to the power amp and to the sub).

That seems to avoid some of the benefit of the subwoofer. I would expect a
peak in response where the subwoofer and the mains overlap, unless there was
a polarity problem. Then there would be a dip. But, I don't know anything at
all about room response, and it is very significant.

This
is because I had concluded that signals fed directly from
the preamp to the power amp, without any processing or
filtering, would be cleaner and provide a more
transparent sound from the Maggies.

Maybe yes, but probably no.

On the other hand, it
might be beneficial to remove the very low frequencies
from the amp and the Maggies for greater efficiency.

More to the point, the maggies may not be as linear at low frequencies. As a
rule, most speakers sound cleaner and tighter when the very lowest
frequencies are filtered out. Applying a low pass filter to a subwoofer
often helps reduce thuddiness and boominess. Usually, low pass and high
pass filters used in a situation like this are set to the same frequency.

Any advice or suggestions? Do I need an external
electronic crossover to resolve this issue?

It seems like the crossover on the Velodyne would be adequate for many
applications. I think you should try to exploit it before buying more
equipment. As a rule, low and high pass filters are set for the same corner
frequency.