Which way to fire my sub?

[RobWells]

LOL

google is your friend.

[AndrewT]

Hi,
downfiring will cause some sag in the suspension.
I have seen the 5% figure quoted elsewhere.

If you can see/measure any sag difference between upfireing and downfiring, you have probably already exceeded the 5% limit on a low Xmax driver.

Stick with side firing except for a driver specially developed for vertical mounting.

[zenmasterbrian]

I've seen the 5% number too. But I don't know how it is derived.

It seems like it would be different for different drivers.

I have never before heard of drivers specially designed for vertical firing. That sound intriging.

I have also never seen anything in print which analyzes how long the legs need to be, and the effect of the design of being so close to the floor.

[Ap]

I think if the box is sealed, then sag would be minimal as the driver effectivley is held by the air pressure of the box - does that make sense?
Anyway I quite like the look of SVS subwoofers.
http://www.svsound.com/

[AndrewT]

Hi,

if the box is sealed, then sag would be minimal as the driver effectivley is held by the air pressure of the box

sorry, Rubbish.

[Ap]

Why is that rubbish?
The only way the driver can move is if the volume of air in the box increases, this can only happen if it is not properly sealed.
Of course the other way the driver moves is by the force applied to it from a signal applied to the voice coil, in this instance the air inside the box is being compressed - that is why a sealed box is often referred to as working like a spring.

[SY]

The only way the driver can move is if the volume of air in the box increases, this can only happen if it is not properly sealed.

That's not correct; the volume can (and does) increase with varying energy inputs. In the case of cone-down, the driver gives up an energy 1/2kx², balanced against the change in energy from expansion of the volume PdV. It's no different than any other mass-on-a-spring: if you exert a force mg, you'll get a response kx.

Now, you can argue that eventually, the box's pressure will equalize (no box is totally impermeable). And that's a correct argument. But it really means that the cone sag increases with time until that equilibration occurs.

[AndrewT]

and what if the air temperature in the box changes?

[Ap]

Hey good point - I haden thought of that!
(BTW I think Im completely wrong about sag).
I guess the trend nowadays is to go for forward firing because more drivers have very large soft surrounds & high xmax - maybe something to do with the low Q, low efficiency, low Fs woofers and therefore low Vb.

[AndrewT]

Hi,
you're allowed ONE. what is the sanction for a second?