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Francis Vaughan · 13th March 2010

A few thoughts from the theoretical side of things. This is a lovely example of the symmetry of the physics. This symmetry goes quite deep. A mentioned earlier, the Q of the system will influence the sound. The Theile-Small parameters or the driver, the enclosure, and the electrical environment will all influence this.

A modern dynamic speaker is designed to be driven from a voltage source. This is essentially one with zero output impedance. This looks to the speaker as if you short the input out. Running the speaker into a low level input will pretty much look like an open circuit. This can mean a quite substantial difference in final system Q. This leads to an interesting tweakable parameter. Add a variable resistance between the speaker input terminals. Varying from about 1 ohm to about 20 odd should make for a noticable change in system Q and overall character of the sound. Just playing with a few fixed value resistors might be all that is needed to tune in a desired Q. A low load impedance will begin to drop the output, but since you need to pad it anyway this isn't exactly a problem.

Speaker drivers designed for different purposes have quite dramatically different physical charateristics. In particular those designed for use in an enclosure, versus those designed to be installed in a baffle only. The obvious source of the latter being car audio. IB drivers depend much more on mechanical stiffness, whereas boxed speakers rely more on the air inside the box. IB drivers tend to have higher mechanical Q, and thus will tend to be less affected by load issues. This is also true of most sound reenforcement drivers.

Symmetry of the physics would suggest that the sonic charater of the speaker when listening to music will in some form translate to a similar character when used in reverse - with the caveat that the Q may be different due to the different load impedance as described above.

In principle you can use a multiway speaker - the crossover will work in reverse - again with an assumption of the impedance of the los being zero to get the same crossover behaviour. However the physical location of the different drivers will mean phase issues. Speakers are designed to have correct phasing of the drivers at the listener. Any other location typically isn't going to work out. Coaxial drivers tend to avoid this.

Just some very late at night ramblings.

13th March 2010	#28
Francis Vaughan Lives for gear Join Date: Jan 2008 Posts: 745	A few thoughts from the theoretical side of things. This is a lovely example of the symmetry of the physics. This symmetry goes quite deep. A mentioned earlier, the Q of the system will influence the sound. The Theile-Small parameters or the driver, the enclosure, and the electrical environment will all influence this. A modern dynamic speaker is designed to be driven from a voltage source. This is essentially one with zero output impedance. This looks to the speaker as if you short the input out. Running the speaker into a low level input will pretty much look like an open circuit. This can mean a quite substantial difference in final system Q. This leads to an interesting tweakable parameter. Add a variable resistance between the speaker input terminals. Varying from about 1 ohm to about 20 odd should make for a noticable change in system Q and overall character of the sound. Just playing with a few fixed value resistors might be all that is needed to tune in a desired Q. A low load impedance will begin to drop the output, but since you need to pad it anyway this isn't exactly a problem. Speaker drivers designed for different purposes have quite dramatically different physical charateristics. In particular those designed for use in an enclosure, versus those designed to be installed in a baffle only. The obvious source of the latter being car audio. IB drivers depend much more on mechanical stiffness, whereas boxed speakers rely more on the air inside the box. IB drivers tend to have higher mechanical Q, and thus will tend to be less affected by load issues. This is also true of most sound reenforcement drivers. Symmetry of the physics would suggest that the sonic charater of the speaker when listening to music will in some form translate to a similar character when used in reverse - with the caveat that the Q may be different due to the different load impedance as described above. In principle you can use a multiway speaker - the crossover will work in reverse - again with an assumption of the impedance of the los being zero to get the same crossover behaviour. However the physical location of the different drivers will mean phase issues. Speakers are designed to have correct phasing of the drivers at the listener. Any other location typically isn't going to work out. Coaxial drivers tend to avoid this. Just some very late at night ramblings. __________________ The night is coming, and its filled with dark surprise.