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From: Steve M on 28 Feb 2010 11:10
I need a bit of a refresher WRT sub box specs. When a driver spec states the
Vas, is that the maximum, minimum, or "ideal" volume of the enclosure? I'm
about
to build two pairs of 10" subs intended for small system rentals.
I searched the web for free box design software, and found that the data I
have on hand
for the drivers in question is not sufficient to make the box builder
programs workable.
Too many blank fields. The drivers I'll be using have a Vas spec of 1.89
cu/ft. One program
I tried said the box should be .4 cu/ft, and showed a response curve that
fell off drastically
below 100hz. Doesn't look like a workable sub, to me.


--
Steve <snip> McQ


From: Leon on 28 Feb 2010 12:21
On Sun, 28 Feb 2010 11:10:04 -0500, "Steve M" <mcsteve1350(a)verizon.net> wrote:

>I need a bit of a refresher WRT sub box specs. When a driver spec states the
>Vas, is that the maximum, minimum, or "ideal" volume of the enclosure?

The VAS has nothing to do with recommended volume of the box, it is a
measurement of the speaker itself. It is a measure of the 'looseness' of the
cone, compared to a box of air!

If you put a membrane the same size as the speaker cone over a sealed box and
push on it, it will be the same as pushing on the speaker itself, so to speak...
so since your spec is 1.89 feet, that means a box of that size with a membrane
the size of your speaker, would have the same stiffness or compliance. (Thats a
fairly stiff speaker.)

It's weird, I know, but it a spec that is used to determine the way the speaker
behaves. It is not a universal spec, since it varies as the size of the speaker
varies. Bigger speakers have a higher VAS since they are easier to push... in
simple terms... your program knows how to handle this.

I recommend WinISD for a good program...

> I'm
>about
>to build two pairs of 10" subs intended for small system rentals.
>I searched the web for free box design software, and found that the data I
>have on hand
>for the drivers in question is not sufficient to make the box builder
>programs workable.
>Too many blank fields. The drivers I'll be using have a Vas spec of 1.89
>cu/ft. One program
>I tried said the box should be .4 cu/ft, and showed a response curve that
>fell off drastically
>below 100hz. Doesn't look like a workable sub, to me.

Very few, if any, 10" speakers can be used as a sub... especially in pro sound.
You also need to know the resonant frequency of the speaker, and it's Q, or
tendency to resonate.

The resonance will tell you the general low freq. limit of the driver. A 50hz
spk for example is not good as a sub. In a sealed box it will usually start to
drop in output at 1.5x the rs. and in a reflex box any bass below that will be
'forced' and any power applied below system resonance will destroy the driver.

The Q of the speaker determine what kind of box is best... high Q needs a sealed
box to tame it, and low Q works well in a reflex box.

I am building a few small subs right now, and I am using the Eminence LAB12,
which will produce sub base in a small 2' box. These spks are fairly low output,
and are either used in small venues or else in multiple installs of 4 or more
cabs.

They go lower than almost any speaker I've seen, and were designed for large
horns, although they work fine in reflex boxes.

These are the specs of the LAB12 for you to compare:

Rs 22 hz
Qt 0.38
VAS 4.4 ft

2' test box low frequency -3db = 30hz.


From what you say about your 10", I would give up the idea of a sub...

From: Arny Krueger on 28 Feb 2010 12:43
"Steve M" <mcsteve1350(a)verizon.net> wrote in message
news:hme4gt$gf4$1(a)speranza.aioe.org
> I need a bit of a refresher WRT sub box specs. When a
> driver spec states the Vas, is that the maximum, minimum,
> or "ideal" volume of the enclosure?

None of the above. Vas usually ends up being about 3 times the ideal volume
of a box, subject to some other assumptions:

How flat the bass response?

Vented box?

Unvented box?

What sort of space are you using with the speaker?

> I'm about
> to build two pairs of 10" subs intended for small system rentals.
> I searched the web for free box design software, and
> found that the data I have on hand
> for the drivers in question is not sufficient to make the
> box builder programs workable.

Measuring the T/S parameters of raw drivers is not mission impossible. For
example, Parts Express has a little USB gizmo that does the deal. I think
that George has one, so he can say more from personal experience.


> Too many blank fields. The drivers I'll be using have a
> Vas spec of 1.89 cu/ft. One program
> I tried said the box should be .4 cu/ft, and showed a
> response curve that fell off drastically
> below 100hz. Doesn't look like a workable sub, to me.

If you follow the usual rule of thumb of Vas = 3 times the size of a good
box, you might conclude that 0.4 cu/ft is a bit small. Too-small boxes tend
to stifle the bass extension of a driver, again subject to some other
conditions.

Not all 10 inch drivers are designed to be subs. Also, the F3 of good subs
for live sound and hifi are quite a bit different.


From: Steve M on 28 Feb 2010 16:52
<Leon(a)nospam.com> wrote
> The Q of the speaker determine what kind of box is best... high Q needs a
sealed
> box to tame it, and low Q works well in a reflex box.
>
> Rs 22 hz
> Qt 0.38
> VAS 4.4 ft
>
> 2' test box low frequency -3db = 30hz.
>

Specs for the drivers I'm talking about:
Power handling: 300 watts RMS/600 watts max
Fs: 41 Hz
Qms: 6.78
Qes: .26
Qts: .25
VAS 1.89 cu ft

I'm guessing your "Rs" spec is the same as Fs?
And, "Qt" = Qts?

My plan is to use these for small-system bass content roughly
50hz to 100hz. At low to moderate SPL. I have single 15, double 15,
and single 18 boxes for jobs that require real thump.


--
Steve <snip> McQ


From: Leon on 28 Feb 2010 19:25
On Sun, 28 Feb 2010 16:52:47 -0500, "Steve M" <mcsteve1350(a)verizon.net> wrote:

><Leon(a)nospam.com> wrote
>> The Q of the speaker determine what kind of box is best... high Q needs a
>sealed
>> box to tame it, and low Q works well in a reflex box.
>>
>> Rs 22 hz
>> Qt 0.38
>> VAS 4.4 ft
>>
>> 2' test box low frequency -3db = 30hz.
>>
>
>Specs for the drivers I'm talking about:
>Power handling: 300 watts RMS/600 watts max
>Fs: 41 Hz
>Qms: 6.78
>Qes: .26
>Qts: .25
>VAS 1.89 cu ft
>
>I'm guessing your "Rs" spec is the same as Fs?
>And, "Qt" = Qts?
>
>My plan is to use these for small-system bass content roughly
>50hz to 100hz. At low to moderate SPL. I have single 15, double 15,
>and single 18 boxes for jobs that require real thump.

A 0.4' box is the optimum according to software, and it does show a roll off
below 100hz, with the f3 point (-3db) at 80hz...

However, if you put it into a 1.5 cubic foot reflex box, tuned to around 50hz,
you can get a bass extension down to 50hz.

Just make the box about 20% bigger than you want to accommodate the volume of
the speaker and port and bracing and whatever...

The box would be about 16"x25"x10" or similar, with 1 port, 3.5" diameter by 4
1/4" long.

This will work as a "sub" for your limited requirements.

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