What exactly happens when yu don't match box size?

[jamo]

What happens when your box size is different from the box size specification on p.149 of the PE catalogue -which, I presume is derived from a T/S calculation?

So, f'rinstance, what happens if a 12" RSS-HF, which is listed a sealed box colume of 1.64 cu.', or a 12" TI looking for 1.45 cu.' is put in a 3 cu.' box?

What if a 15" DVC with a 3.5 cu.' spec is put in a 3 cu.'?

And what if power handling maximums are not met, so that a 15" TI that can handle 800 watts RMS only meets 240 watts RMS, on top of the box size discrepancy?
Well, what?

[damkor]

12"
> RSS-HF, which is listed a sealed box colume
> of 1.64 cu.', or a 12" TI looking for
> 1.45 cu.' is put in a 3 cu.' box?

Bass will drop off higher in frequency, at a more gradual rate. Depending on the parameters, the deepest bass will suffer too. No reward here.

> What if a 15" DVC with a 3.5 cu.' spec
> is put in a 3 cu.'?

Sealed, I assume.

Maybe not a whole lot of difference, but the reverse: Bass will drop off lower in frequency, but at a steeper rate. You will get a higher F3. You may get a peak of a few dBs above that.

Use this site:

<A HREF="http://www.mhsoft.nl/spk_calc.asp">http://www.mhsoft.nl/spk_calc.asp</A>

[Pete Schumacher ®]

> 12"

> Bass will drop off higher in frequency, at a
> more gradual rate. Depending on the
> parameters, the deepest bass will suffer
> too. No reward here.

Not quite right. Qts is lowered which causes the bass to have a shallower roll-off, actually allowing slightly deeper bass.

Power handling is reduced somewhat, but peak SPL is unaffected.

[damkor]

With a bigger box:

Qts is lowered which causes
> the bass to have a shallower roll-off,
> actually allowing slightly deeper bass.

That's only true if Q is above 0.5. You are making that assumption. As soon as Q is below 0.5, F3 (the low limit) starts to rise again, although F10 will still be lower. It depends what we mean by deep bass.

[Pete Schumacher ®]

> With a bigger box:

> Qts is lowered which causes

> That's only true if Q is above 0.5. You are
> making that assumption. As soon as Q is
> below 0.5, F3 (the low limit) starts to rise
> again, although F10 will still be lower. It
> depends what we mean by deep bass.

You described it exactly except in calling F3 the "low limit" which it is not. F3 is F3, nothing more. Many would consider F10 the true in-room low limit.

Regardless, your description of the response is dead-on. The lower the Qts, the shallower the slope and more extended the F10 point of the curve.

[jamo]

I don't get it. Still a jigsaw puzzle. Can you possiblt restate the entire proposition, using words rather than the terms 'Qts' and 'Q'?

> Qts is lowered which causes

> That's only true if Q is above 0.5. You are
> making that assumption. As soon as Q is
> below 0.5, F3 (the low limit) starts to rise
> again, although F10 will still be lower. It
> depends what we mean by deep bass.

[jeffman]

It'll make a lot more sense if you just look at the frequency plots generated by some box design software. The link Damkor suggested isn't perfect (and he knows that) but it'll bring you up to speed very quickly if you input different values and see how they affect the curves.

FWIW, it's not as important to know what the different TS parameters mean as it is to know what kind of effect they'll have on a project.

Here's that link again. Just scroll down to the sealed box calculator. It's all online. <A HREF="http://www.mhsoft.nl/spk_calc.asp">http://www.mhsoft.nl/spk_calc.asp</A>

[damkor]

...the woofer cone is allowed to passively wobble back and forth under its own momentum and inertia, every time it is energized by the motor, rather than having its movement damped by the air in the box, among other things. You have to look at the curves.

BTW, sometimes seemingly large differences in volume have a surpisingly small effect on response.