Trick to test for cabinet leaks

If you're building a 3-way where you have a sealed midrange chamber and want to test if there are any air leaks with the bass chamber (which will influence the fidelity of the mid), try this:

Put a voltmeter across the terminals of the midrange unit (via its leads) and then gently move the woofer with your hand. If your voltmeter shows any voltage it means the movement of the bass unit (via air pressure) is leaking into the midrange chamber and moving the midrange driver, thus producing a voltage in its coil which you are reading.

You could try it with the tweeter as well although I think the danger there is more from mechanical vibration through the cabinet than from air movement.
 
Mos Fetish said:
If you're building a 3-way where you have a sealed midrange chamber and want to test if there are any air leaks with the bass chamber (which will influence the fidelity of the mid), try this:

Put a voltmeter across the terminals of the midrange unit (via its leads) and then gently move the woofer with your hand. If your voltmeter shows any voltage it means the movement of the bass unit (via air pressure) is leaking into the midrange chamber and moving the midrange driver, thus producing a voltage in its coil which you are reading.

You could try it with the tweeter as well although I think the danger there is more from mechanical vibration through the cabinet than from air movement.


Awesome tip/trick! That is a great idea, one I will have to remember!

Justin
 

Svante

Member
2004-02-01 11:17 pm
Stockholm
... and the voltage is the velocity of the cone, multiplied by Bl.

v=U/(Bl)

So if Bl is known, the cone velocity can be calculated.

And from the velocity, the sound pressure generated by the cone can be calculated as:

p=Sd*v*rho0*f/(2*r)

where rho0=1.2 kg/m³, f is the frequency and r is the distance.

The sound pressure level generated by the mid driver is:

Lp=20*log10(p/pref)

where pref=20 µPa.