On 12/09/2014 07:08 AM, gregz wrote:

I would be more concerned with the crossover. Is it going to br MTM ?
I made a center design over 15 years ago. It worked well, and I got my
desired pattern. I didn't use it as a bass though. They were a bit smaller
than 4 inch. I used a common enclosure, sealed, with plenty of interior
damping, and front panel antidefraction.

Likely MTM - unless there is a brighter idea. Got a large CRT TV at
present. Will likely look at size suitable to stand a likely LCD on it
for the day when the CRT breaks. Of course acoustic parameters are a
prime driver for box size as well.

Crossover Mk1 will be some caps I have in the garage and some wire
likely wound around a cardboard former. However, in future I can have a
play with active, actually designing it properly etc. 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. Small is good for this case.
Bass/Tweeter as normal.

I have a 2 channel power-amp spare - but 3 would be ideal if active!


antidefraction? Do you mean round the edges and stand the grill off of
the front baffle?


Pete

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.



..... Phil

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

Peter Chant wrote:


** 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

** Nonsense.

The two drivers do not act independently so no such scenario can exist.


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


** Read it all again if you ****ing like.

Won't mean a thing to a narcissistic, know nothing nutter like you.




.... Phil

In article ,
Peter Chant wrote:
Likely MTM - unless there is a brighter idea. Got a large CRT TV at
present. Will likely look at size suitable to stand a likely LCD on it
for the day when the CRT breaks. Of course acoustic parameters are a
prime driver for box size as well.

You might find it a problem sighting a speaker with a powerful magnet
close to a CRT set.

--
*Can atheists get insurance for acts of God? *

Dave Plowman London SW
To e-mail, change noise into sound.

On 12/10/2014 12:44 AM, Dave Plowman (News) wrote:
In article ,
Peter Chant wrote:
Likely MTM - unless there is a brighter idea. Got a large CRT TV at
present. Will likely look at size suitable to stand a likely LCD on it
for the day when the CRT breaks. Of course acoustic parameters are a
prime driver for box size as well.

You might find it a problem sighting a speaker with a powerful magnet
close to a CRT set.

The bass drivers are sheilded.