Re: Question re Subwoofer Connections, High-Pass, Low-Pass"JimC" <avocat5@sbcglobal,net > wrote in message
news:fr2eo101p06@news1.newsguy,com
> 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.