"Jim Lesurf" wrote in message
...
In article , Peter Scott
wrote:

Hence what we get may be nothing like either 6dB or 3dB. Depends on the
details.

In practice, the speaker designer is probably trying to get a given
response, but has to worry about the user-choice of speaker and listening
locations and room acoustics all being outwith his control, and varying
from one user to another. Thus the designer has to make a 'guess' as to
what will suit enough people to make a speaker a commerical success!

Thanks for clarifying that. The more you think about it the more of a
compromise loudspeaker design is. Bit like designing a vehicle that might
run
on a road or perhaps on fields or up mountains, or maybe on water or.....
This must also be true for high-end speakers unless the designer exactly
specifies the room, speaker positions and surfaces. Going back to another
discussion perhaps there ought be a test criterion along the lines of
'performs well in a wide range of environments'? This might prove to
be a crucial, if not *the* crucial, factor for speakers.

In my question I was thinking of a simpler matter. According to Behringer
two speakers next to each other, so acting as a single point-source, would
show 3dB gain at low frequencies. I should have specified the frequency.
This region is on my mind because I'm pondering what to do about
the design for a sub-woofer. B says you need four drivers for 6dB.
Clearly this will not be the perceived gain throughout the listening
area but just that near the speakers.

Peter Scott

In article , Peter Scott
wrote:

"Jim Lesurf" wrote in message
...

[snip]


Thus the designer has to make a
'guess' as to what will suit enough people to make a speaker a
commerical success!

Thanks for clarifying that. The more you think about it the more of a
compromise loudspeaker design is. Bit like designing a vehicle that
might run on a road or perhaps on fields or up mountains, or maybe on
water or.....

Yes. FWIW When I worked at Armstrong mumble-mumble years ago I used to
get into conversations and work with a speaker designer[1] who developed
the Armstrong 602 speaker. This rapidly convinced me that designing
commercial speakers for domestic use is an absolute nightmare. Designing
amps is child's play in comparison. :-) A lot of the design decisions tend
to be based on experience and judgements of what will be most acceptable to
a given target audience of customers.

[1] Bill Perkiss. Came to Armstrong from Goodmans. Wonder what happened to
him after he left Armstrong?...

This must also be true for high-end speakers unless the designer exactly
specifies the room, speaker positions and surfaces.

The advantage of the 'amateur' is that they generally only have to develop
speakers for their own use, to suit themselves and their listening room.
The disadvantage is that they may lack to experience and knowledge and test
kit of a professional.

Going back to another discussion perhaps there ought be a test criterion
along the lines of 'performs well in a wide range of environments'? This
might prove to be a crucial, if not *the* crucial, factor for speakers.

The problem here is defining the relevant set of conditions and then
testing them all. This brings up once again that magazines and reviewers
generally simply don't have the time, money, skills, etc, to do this on a
routine basis.

In my question I was thinking of a simpler matter. According to
Behringer two speakers next to each other, so acting as a single
point-source, would show 3dB gain at low frequencies. I should have
specified the frequency. This region is on my mind because I'm pondering
what to do about the design for a sub-woofer. B says you need four
drivers for 6dB. Clearly this will not be the perceived gain throughout
the listening area but just that near the speakers.

I am not sure why they say the above. There are some other complications
which I didn't mention, though... :-)

One is that the pressure variations produced by one speaker may 'push on'
the other, thus altering its ability to move.

In general, conventional 'cone in a box' speakers have movements that are
mass-controlled. So the main force limiting their movement when driven is
that required to accellerate their mass. The air load is relatively small,
so they tend not to be affected much by the presence of a second unit.

However the same may not be the case at LF as the main force opposing
movement becomes the springiness of their support, and the air inside and
outside the cabinet.

Hence - for example - if two speakers are sharing the same box, at LF, and
the LF compliance (springiness) is mainly that of the air support, then
they might affect each other quite noticably. Even in different cabinets
they may do this.

The division between 'mass controlled' and 'compliance controlled' tends to
occur at the basic resonance frequency of the speaker system. For LF
systems this is typically well below 100Hz somewhere.

But I am not clear why this would mean the result would be a 3dB increase.
It only obviously implies that it may not be 6dB. I'd expect the results to
depend on the specific details of the situation.

Would need more information to know what B are specifically referring to
and why they say the change is 3dB. Or perhaps someone else can explain why
B say this?

Slainte,

Jim

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Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html