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-   -   Help me, I feel dumb. (http://www.diyaudio.com/forums/subwoofers/1899-help-me-i-feel-dumb.html)

 BAM 14th January 2002 03:02 AM

Help me, I feel dumb.

For those of you who are mathematically-inclined, I need help converting something. I was using Mr. Linkwitz's closed-box spreadsheet to determine how much EQ I would need to make an ELF sub sound OK.

The spreadsheet asks for mechanical resistance in Ns/m and the Peerless web site only delivers it in Kg/s. I'm not in Physics yet, and I don't have a clue what to make of this and I'm hoping that someone here may know how to convert:

1.87 Kg/s to Ns/m

If someone knows how to do this, please help me, or show me how to help myself. I will be very grateful.

~BAM

 subwo1 14th January 2002 03:43 AM

BAM, below is a link where to find out that a newton is a unit of force. I used Google to find the site. It says:
"force push, pull, or weight newton= kg m/s2"

"1.87 Kg/s to Ns/m" If you multiply both sides by m/s, you get

1.87 kg m/s^2,
the same units that it says above are newtons.
That means both of the expressions are of the same thing.
I am not too good with math either, but I think I figured it right. Give Physics your best shot, I made it through 2 years, maybe you can go all the way.

http://www.essex1.com/people/speer/units.html

 paulb 14th January 2002 03:48 AM

A Newton is a kilogram-meter per second squared = kg.m/(s^2). So,
N.s/m = (kg.m/s^2)(s/m) = (kg.m.s) / (s^2.m) = kg/s.
Voila! They are the same units.

 Pete Mazz 14th January 2002 06:15 PM

This is a great utility for those type of conversions:

http://www.joshmadison.com/software/...t/download.asp

Pete

 BAM 15th January 2002 01:58 AM

Hey, thanks. I may feel even dumber, but at least I have my answer. Thanks for showing me what was what.

Best wishes,
~BAM

 BAM 15th January 2002 11:07 PM

Duh...

What is meant by Qb?

I've never seen this referred to anywhere, on any DIY sites or in my DIY book from RadioShack.

 Cloth Ears 17th January 2002 06:41 AM

BAM,

http://www.audiobuilder.co.uk/ has most of these elements, but not Qb (yet).

It's the Q of the enclosure with the speaker attached, like Fb is the box resonance frequency and Vb is the box volume. I've only really seen it used for sealed enclosures. For them:

Qb=.707
This is supposed to be the ideal. The Fb should be at the same frequency as the F3, the F3 should be the lowest possible for the particular driver and transients should be 'good'.

.5<=Qb<.=707
These alignments generally have better transient response than their higher Qb cousins, but have a higher F3 point (although the bass rolls off more slowly). You can strike problems with excursion at the bottom of the drivers' range, as you don't get much suspension from the air in the box behind the driver.

Qb>1.0
These alignments are affected by the space (or lack of it) behind the driver. An example is Bob Carver's little sub. The air acts like suspension, as the amount of air being moved by the driver has become a significant percentage of the box volume. For this reason, you get 'not so good' transients, the F3 is higher than most lower Qb alignments, and there starts to be a 'peak' in the response just above F3 (it's about +1dB for Qb=1.0, maybe +3dB for Qb=1.2). Generally these alignments need a bit more amplifier power to drive the speaker and need a bit of EQ somewhere to smooth out the peak.

Qb<.5
We are getting into 'Infinite Baffle' territory here. Some of the larger sub-woofers run this sort of alignment - but I don't know much about it. Have a look for those sub-woofers that are set up in a basement and you'll be on that track (I've seen one called 'Dancing Shivas', which is definitely I/B.

But in the end, it's just a figure...

 AudioFreak 17th January 2002 06:53 AM

boy ... Qb sounds an awful lot like Qtc :)

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