Speaker ports
On Mon, 19 Jan 2015 06:24:18 +0100, "Peter Larsen"
wrote:
Hi Don,
I was going to ask. Why are you porting this at all? Bottom E on a
guitar is 82Hz, and the speaker cone is far better protected and
supported in an IB box.
It is a very low Qt unit, well into the "suited for horn loading range", so
yes, it should be vented, I think an IB with this unit will sound thin. So
I'll just re-iterate my suggestion of a slit shaped vent above and below the
unit.
A bit of finagling yields something like this as I see it early in the
morning:
box: 25 liters
tuning: 60 Hz
2 vents as slits 30 centimeters long, 1 centimeter wide, 9 centimeters deep.
The response should then be -5 dB at 80 Hz and sloping upwards to -1 dB
around 250 Hz, that is about as much bass as you can get from that unit. It
is not a standard tuning for the box, but as you said, too much bass in a
guitar box can end up muddy.
It is important to ensure a smooth inside finish of the vents. Box inside
walls should probably be felt covered, 1 cm thick felt stapled in place,
somewhat messy, not too flat and tidy. Make the box 32 liters to allow for
it and for the loudspeaker magnet.
Amplifier should if possible be highpassed at 60 Hz to protect loudspeaker
from "hit all strings tranasients", somewhat depending on how powerful it
is, RMS power for the unit is spec'd at 225 watts, the old JBL guideline was
assume 30% for instrument use because of low crest factor and the risk of
weird transients, ie. "somewhat safe to use with 60 watts amplifier".
d
Kind regards
Peter Larsen
Extra damping on the walls of the box shouldn't be necessary. The
internal Q is set by the driver and the port, so felt on the walls
would be an added and unknown extra source of loss. And of course this
is for sound production, not reproduction, so some character and
resonance is probably to be considered a good thing.
d
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