[Dick Pierce[_2_]]

Doug McLaren wrote:
On 2011-08-12, Dick Pierce wrote:

| -- make it more efficient -- use less power for the same volume
| (the power limited is limited, so this is a concern.)
|
| Porting an enclosure WILL NOT make the system any more
| efficient. Not in the least. Ported systems CAN be more efficient,
| not because they have ports, but because they have drivers suited
| for the enclosure that result in electromechanical parameters that
| mke the DRIVERS more efficient to begin with. ...

So I have even more to learn about this than I thought -- and I
thought I had a lot to learn before.

I'll go ahead and not add a port then.

| You simply cannot just take a pair of speakers, jam them
| in a box, stick a port in it, and expect 1) for it to work
| reasonably well, 2) for it to have "better low frequency
| response and 3) more efficiency. It simply does not work
| that way.

Sorry I used the wrong terminology. I was under the mistaken
impression that adding a port could help alleviate the limitations
imposed by the overly small case to some degree -- especially for
lower frequencies -- but at the cost of some sound quality.
(Obviously it's not so simple.)

It CAN, but you have to know a bit more about
the specific physical parameters of the components
of the systems to 1) determine if it''s possible,
2) figure out how to do it and 3) know when you've
done it.

My goal is five hours run time, with the volume being as loud as it'll
go and still achieve that goal with the energy available. At least I
assume that the battery capacity is the limitation -- it may not be.
The batteries should be able to provide 20 watts for 8 hours if the
rated capacity can be trusted, though in my experience it rarely can.

Let's assume it can. Let's also assume your T-Amp has
an efficiency of, oh, 75%. If you assume the 20 watts
figure as your draw, then you can reasonably assume only
15 of those watts could possibly make it to the speakers.

And let's further assume the speakers are ideally suited
to the amp, in terms of havimg an effective impedance
that draws the most effective power from the amplifier.

Now, there is a notable lack of real and reliable technical
information on the drivers, but let's assume my original
guesstimate of a reference efficiency of about 89 dB is
TRVTH (tm) (and so it shall remain until B3TT3R TRVTH
comes along). That means that, at best, your system could
produce on the order of about 101 dB or so AT BEST 1 meter
on axis of the drivers. And the actual average sound level
will be substantially less than that, unless your only
musical interest is ultra-compressed pop stuff.

So, again, you have to come up with some acceptable
definition of "loud" that can be turned into some real
design goals. "Loud" doesn't make it.

And, lastly, making it as loud as possible for you also
makes it, likely, TOO loud for those near you who don't
share you particular musical and audio proclivity.

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+ Dick Pierce |
+ Professional Audio Development |
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