Peter Chant wrote:
On 12/09/2014 12:22 PM, Phil Allison wrote:
Probably making a vented enclosure. Is it better put the drivers in a
single enclosure or to make essentially two separate enclosures side by
side? Can't really think of any pros and cons except to do the sums and
see if the box sizes are realistic.
** Long as the 4 inch drivers are closely similar, using a common
enclosure and one port is the way to go.
Two Audax AT100M0 drivers. Found data sheets on-line last night.
http://www.audax.com/archives/AT100M...gue%201994.pdf
I love the internet, that info would have been harder to get hold of
when I bought the drivers. Don't speak French so ringing them up might
not have gone well.
The Bose 802 ( pro audio version of the 901 ) used 8 x 4 inch drivers
and two ports - not that it is any shining example of design.
Seriously, one large port IS better than two smaller ones - less losses
and wind noise ie chuffing.
Less surface area of the port compared to its volume / area - makes
sense. Suppose front / back is unimportant. Back is probably neater if
I have one port only.
If you have the basic TS parameters for the drivers ( Vas,Fs and Qs) and
pop them into WinISD Beta you can easily see how altering the box volume
and port frequency changes things.
Don't run windows if that is a windows program. Probably could run it
under wine. There seem to be plenty of on-line calculators. I have a
few 'cookbook' type design books as well, so if I have the parameters I
could also try them.
Given that these two tiny 4in paper drivers are a lot smaller than the
twin 6.5in polypropylene ones in my mains and that the centre is running
speech not full range I wonder if I ought to try something else? I
wonder what happens if build some sealed enclosures which are slightly
larger than normal to give a Q of around 1 so there is no rise in the
bass before they roll off. Would that avoid boominess that I might get
with ported boxes or if I used a Q of 0.7?
http://www.diyaudioandvideo.com/Calculator/Box/
I've worked this out* for a _single_ driver.
(* got someone else's website to do it for me)
Sealed Box Q=1
Vas = 4.41 lts
fs = 64 Hz
Qts = 0.48
Qtc = 1
Dimensions
Vb = 0.05 ft3 = 1.32 lts
= L x W x H
f3 = 104.82 Hz
fb = 133.33 Hz
That seems rather
With the more normal Q of 0.707 I get:
Sealed Box Q=0.707
Vas = 4.41 lts
fs = 64 Hz
Qts = 0.48
Qtc = 0.707
Dimensions
Vb = 0.13 ft3 = 3.77 lts
= L x W x H
f3 = 94.28 Hz
fb = 94.27 Hz
Vb: Speaker Box Internal Volume
f3: 3dB Cutoff Frequency
fb: Enclosure Resonant Frequency
Annoyingly I can't find my books.
Website recommends a ported enclosure - perhaps I should follow that advice:
http://www.diyaudioandvideo.com/Calc.../SealedPorted/
Ported. Guess cone dia at 3.5in.
(can't be bothered to find a rule right now)
Ported Box
Vas = 4.41 lts
fs = 64 Hz
Qts = 0.48
D = 3.5 in
Dimensions
Vb = 0.28 ft3 = 7.83 lts
= L x W x H
f3 = 49.72 Hz
fb = 53.57 Hz
Dv = 1 in = 2.5 cm
Lv = 1.85 in = 4.53 cm
Or I could just read the datasheet which gives various box volumes and
port sizes underneath a chart showing the various frequency responses...
Volume anywhere between 1.7 and 10lt! I suppose the
manufacturerintended this to be used in ported boxes.
This is of course for a single driver. So I do need to do the sums for
a twin driver enclosure - unless I simply make two single driver boxes
side by side.
Assuming doubling Vas is all I need to do then running that through the
last website gives:
Ported Box
Vas = 8.82 lts
fs = 64 Hz
Qts = 0.48
D = 3.5 in
Dimensions
Vb = 0.55 ft3 = 15.65 lts
= L x W x H
f3 = 49.72 Hz
fb = 53.57 Hz
Dv = 1 in = 2.5 cm
Lv = 0.53 in = 1.26 cm
Hmm. Double the size but I do save 1/2p making a shorter port...
You could try a little series resistance on the woofers to push up the Qts
and be more suitable for closed box?
This probably will not help you, but here was my quest. 15 years ago ?
http://www.pitt.edu/~szekeres/center.htm
Greg