On 12/09/2014 11:06 PM, Phil Allison wrote:
Peter Chant wrote:


My thinking for
the future would be that a plan might be to run the two bass speakers as
one up until they hit a frequency where their distance apart might
become problematic, then roll one off.

** If you put the two woofers in series, that will make the impedance 16 ohms and increase effective the amplifier power rating - then put say a 20uF cap across one of them. The impedance will drop towards 8ohms above 1 kHz and the no cap driver gets 6dB more level - just what you need to maintain flat response.

Interesting thought. Does that not kill the electrical damping from the
amp, as at resonance each speaker sees mainly the impedance of the other
speaker rather than the low impedance amp output. Or if using a ported
enclosure does that not matter?

Just found my copy of the Loudspeaker Design Cookbook. Perhaps I ought
to re-read part of it.

Hmm, if I don't care about looks I could use a push pull format with the
driver facing towards me being the one with the mid frequency roll off.
Also, if it is going to be ugly then I can just glue and screw some MDF
or ply and do it in a day!

More thoughts - once going unsymmetrical why not go isobaric? Do I want
to roll off the rear - hidden driver? Given the calcs give a 3.5lt
enclosure can I keep a small enough volume between the two drivers for
it to not be significant? If I want to stand a TV on it it may be too small.

Another design issue has surfaced. Usual practice seems to be to mount
the flange of the speaker on the front face of the fron baffle - so the
speaker is not recessed. However, the spider is so shallow that 1/2 of
ply/ MDF will largely block off the holes in the spider!

Pete