Speaker Attenuation...

jakelm

But also, like you said, the effect will be different on different frequencies, right? or will all frequencies be attenuated the same?

It wont be -3dB's @ 500hz and -6dB's @ 12khz? They will all be attenuated @-3dB's

ShinAce

One way to look at it is to imagine the speaker as a short circuit and then an open load and see how that effects the L-pad.

With a 1.2 ohm series and 9.8 ohm shunt resistor, the highest resistance possible is 11 ohms when the speaker presents an open loan. A purely inductive or capactive component complicates this scenario, so we'll stick to the easy stuff.

Now the short circuit. The total reistance offered by the speaker and L-pad is the shunt resistor only, so 1.2 ohms.

The overall resistance of the circuit can only vary from 1.2 ohms to 11 ohms. Realistically, we set the limits as 3 ohms(lower limit) and 30 ohms(upper limit) for the speaker.

edit: Remember that a woofer's highest impedance is near the resonant frequency. All subs are getting less power when playing notes near resonance, yet they are still plenty loud. This is because the efficiency tends to go up in a region of rising impedance. So you don't need a flat impedance plot to yield a flat frequency response. But if you can achieve this ideal, it makes passive crossovers that much more powerful and trustworthy.

jakelm

Gotcha, open speaker is the sum of the 2 resistors. A closed speaker is the shunt value.

So from 1.2ohms - 11ohms.

But since the speaker is not open or short, then its 1.2(series) , 9.8 (shunt), 3.9 (speaker), so the lowest is 3.9ohms. The highest is 3.9 x 11ohms (sum of series and shunt) = 42.9 ohms.

ShinAce

For the given example, 1.2 ohm series and 9.8 shunt:
-A 3 ohm speaker resistance gives a load to the amp of 3.5 ohm
-A 30 ohm speaker resistance gives a load to the amp of 8.6 ohm

For a 10 fold increase in resistance for the speaker, the amp sees just a bit more than double. Not bad at all. I haven't checked the attenuation for each case.

jakelm

I knew there was more to it than just putting a resistor in seires with the speaker. This thread proves it.