Keith G wrote:
"Serge Auckland" wrote in message
...
Eeyore wrote:
Don Pearce wrote:

I would add that finding an ideal position for one sub is hard, and
right positions for two are near enough impossible. Provided there is
very little distortion and the crossover frequency is sensible, there
is no benefit to having a pair of subs - you can't locate the sound
anyway.
Oh yes you can !

That's just an old wives' tale.

Graham

I'm not so sure. I did some tests a couple of months ago after reading
that in the early days of stereo, Philips reckoned that anything below 200
Hz was non-directional, and consequently, a sub and two satellites was
perfectly acceptable for stereo. EMI insisted on two full-range
loudspeakers.

Using sine waves into left only, right only or equally into both, below
220 Hz it was increasingly difficult to decide which was playing, and
impossible below 150 Hz. That of course is in my room, and other rooms may
be different.

However, when using a single subwoofer located to the right of the
right-hand 'speaker and with a crossover of 70Hz, it was disturbing to
hear the extreme bass separate from the 'speakers, possibly as a result of
hearing harmonics from the sub. The disturbing effect went away when the
sub was positioned between the main 'speakers.

I currently use two subs to fill in the bottom half-octave below my main
'speakers, and I have them located as close as possible to the mains to
create effectively a pair of larger 'speakers. Works for me.



This is interesting. This very thread has prompted me to set the 'sub ball'
rolling (finally) and I've scrounged a sub to play with for a few days:

http://www.apah69.dsl.pipex.com/show/subbie2.JPG

http://www.apah69.dsl.pipex.com/show/subbie3.JPG


...with a view to building one (or one like it) and am considering these
atm:

http://www.bkelec.com/HiFi/Sub_Woofers.htm

http://www.iplacoustics.co.uk/SW5%20...0subwoofer.htm


..unless anyone knows better?

But my point is that there is no way of locating the single sub by ear in my
small room and, as the sub in the photos (BK Electronics) has a *variable*
phase adjustment between 0 and 180 deg, is there not a danger of phase
cancellation with two subs, given that they seem to need a lot of adjustment
and faffing with to suit the various different types of music....??

IOW, is a pair of subs a possible complication that might be best *not*
bothered with....??




Should work wonderfully well using one of your 4W SETs............

Seriously, in your room, a single sub should be more than ample. As to
phasing, I really don't understand the point of a variable phase
control. 0 & 180 switched should be provided to phase up the sub with
the mains (which hopefully will be in phase with each other), but apart
from that, I can't see it's possible to match the phase of the main LF,
as it will be frequency dependant. As you suggest, with two subs, trying
to get the phase right would be a nightmare.

Other controls needed are a crossover frequency selector and a level
control. Ideally, if the main speakers are small (say don't go below
70Hz) then the extreme bass should be rolled-off to the mains
considerably improving their power handling and lowering distortion.



S.