Prev: Creditors driving you mad?
Next: For Sale: Premodded Video Game Consoles, Backups & Retro Stuff
From: Phil Allison on 28 Feb 2010 19:33

"Steve M"
>
>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.


** Programs like " WinISD " sometimes need a bit of driving to get the
result you need.

Using the TS numbers you gave in a later post - the automatic result is an
11.1 litre ( 0.4 cu ft ) box tuned to 67 Hz with a -3dB point at 82 Hz.

What you do next is click on "Box" in the parameters window and simply
*tweak* the volume and tuning frequency numbers. The results of doing this
will immediately show up on the main response plot - this is the BEST
feature the program has !!!

For example - when I changed the volume to 40 litres and the tuning
frequency to 60 Hz and the new response curve peaks by just 1dB at 67 Hz and
is 3 dB down at 54 Hz.

Much better !!

The problem is that WinISD always calculates the box size and tuning
frequency to get as flat as possible curve.




..... Phil









From: Phil Allison on 1 Mar 2010 17:10

<Leon(a)nospam.com>

> 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...


** Not generally the case.

For a given suspension stiffness, Vas goes up by the *square* of the cone
area.

So, a 12 inch speaker is likely to have 4 times the Vas figure as an 8 inch
one with the same stiffness.


> I recommend WinISD for a good program...

** Yep.


...... Phil


From: Leon on 1 Mar 2010 19:38
On Tue, 2 Mar 2010 09:10:11 +1100, "Phil Allison" <phil_a(a)tpg.com.au> wrote:

>
><Leon(a)nospam.com>
>
>> 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...
>
>
>** Not generally the case.

You are right, Phil, I meant that speakers of the same design, would show higher
VAS in the bigger speaker.


>For a given suspension stiffness, Vas goes up by the *square* of the cone
>area.
>
>So, a 12 inch speaker is likely to have 4 times the Vas figure as an 8 inch
>one with the same stiffness.
>
>
>> I recommend WinISD for a good program...
>
>** Yep.
>
>
>..... Phil
>

From: Steve M on 2 Mar 2010 19:03
Thanks to Leon and Phil A.
I will let you know how these boxes work out.


--
Steve <snip> McQ


First  |  Prev  | 
Pages: 1 2
Prev: Creditors driving you mad?
Next: For Sale: Premodded Video Game Consoles, Backups & Retro Stuff