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Old 5th May 2008, 10:30 PM   #1
blue934 is offline blue934  Canada
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Default midrange box Q.

how high in the FR does the box Q. affect tonality? i am asking in regards to mids in a three way with most mids running approx. 300hz-5khz. go sealed(at what Q.) or TL.?

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Old 5th May 2008, 11:09 PM   #2
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If i understand your question right, you want to know
what the best Qt for a midrange box is ?

If you use a passive highpass for your midrange, there is
probably not enough electro mechanical damping, because
the midrange does not fully see the amplifier at fr .

( e.g. Midrange builtin fr=120 Hz , 1. Order highpass with crossover frequency = 300 Hz )

In practice Qt should be around 0.6 ... 0.8 . If the system lacks
electro mechanical damping via back EMF, you can adjust
the mechanical damping by adding flow resistance behind
the midrange cone, by placing absorbent material there.

Cabinet must be of sufficient size. "Acoustic swamp"
or tapered and damped Transmission Line may work fine for
a midrange cone, but a sealed cabinet of appropriate size
is OK too.

The Qt of each system affects tonality. This is valid for
Midrange and Tweets as well as the Woofers Qt.

I had very good experience with labyrints of foam rubber placed
in the midrange cabinets, diffusing the reflexions inside the
cabinet. Stuffing too much absorbent material like polyester
wadding or wool into the cabinet may tend the sound into
"dull" .

Cheers Oliver
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Old 6th May 2008, 05:03 AM   #3
blue934 is offline blue934  Canada
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thanks for the reply. i am more interested in whether the box Q of .5 would have different tonality at say 500hz from a .7 box tuning? at what FR does the box Q not affect the sound anymore?
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Old 6th May 2008, 07:42 AM   #4
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Between Qt 0.5 and 0.7 there will be a significant
difference in frequency response up to
6 x resonance frequency.

So if resonance is at 50 Hz, above 300Hz a "steady state"
signal (say steady state part of organ pipe sound
with fundamental FR of 300 Hz) should sound very similar with both alignments.

But music does not consist of steady state signals.
In fact both alignments will sound different, not only in bass
but also for voices etc. This is why i think a Qt of 0.5 is to low.

As far as i remember there has been some research, that
Qt lower than 0.6 does not improve performance subjectively,
even though a Qt of 0.5 (aperiodic damping) has shortest decay.

Hope answer hits better this time ...

Cheers Oliver
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Old 6th May 2008, 02:27 PM   #5
blue934 is offline blue934  Canada
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thanks linearray,

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Old 8th May 2008, 07:50 AM   #6
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.707 on an appropriate open baffle is hard to beat in 'theory'
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Old 8th May 2008, 01:20 PM   #7
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Quote:
Originally posted by LineArray
Between Qt 0.5 and 0.7 there will be a significant
difference in frequency response up to
6 x resonance frequency.

So if resonance is at 50 Hz, above 300Hz a "steady state"
signal (say steady state part of organ pipe sound
with fundamental FR of 300 Hz) should sound very similar with both alignments.

But music does not consist of steady state signals.
In fact both alignments will sound different, not only in bass
but also for voices etc. This is why i think a Qt of 0.5 is to low.



Cheers Oliver
all depends on the filter slope thus the spl level at mid's resonance frequency and...the resulting or not resulting IM distortions.
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