**Re: Re: Technical Discussion about Frequency Dependent Terminal Impedance**
soongsc said:

The impedance has no direct relationship with the frequency response because there is no direct relationship between impedance and motor power. Motor power at different frequencies and the cone design determine frequency response. But it would be interesting to see what everone comes up with.

MJK said:

**Based on the original statement of the question, I assumed that the discussion was directed at low frequencies. I assumed that the discussion centered around T/S modeling and correlation of measured impedance plots with SPL response. That is what the plotted data also showed. **

soongsc,

I disagree with you on this one. If you look at the actual power delivered to the load (V*I*cos(Angle)), it varies geatly depending on the impedance of the load. Over one of the sweeps this was on the order of 6dB difference (min to max). If you change the amount of power deliverd to the cone by 6dB, I would expect a 6dB change in SPL on the output. I have not yet proved it to myself, but have a hunch that a (with virtually no research) a good portion of the frequency response curve is dictated by terminal impedance.

The question is, how would a speaker respond if the surround and spider had no restoring force?

MJK,

I figure the discussion to be full band and then some. (i.e. the reason the we're in fullrange). However, this discussion should also include Thiele-Small modeling and any other associated 'standard' parameters.

catapult,

Ahhh, interesting. I've never seen that model before. I'm going to have to wrap my head around that one for a few days.

However, I noted that the room is modeled as a CR load. That is, energy is coupled into the system through a capacitor. I find it interesting that there is no inductive component included there. maybe it should be an RCL, or multiple RCL's as the acoutic load can infact have it's own resonances (i.e. room with walls). Or are we talking acoustic load into free space? (Looking at ot more closely, maybe this is so.)

I would suspect that the coil should be modeled as having a capacitive value to account capacitance between turns of the coil. o. This would be to correctly model the self resonant frequency of the voice coil itself. Yes, this is a bit picky, and it's effects would be small at even 20Khz, but we are talking theoretical. What happens to a very wide bandwidth amplifier with poor phase margin at frequencies where this comes into play? (Even with input filtering, it may be an issue)

So, what I'm getting is Rma if the momentum of the air, and MmA is the mass of the air being driven and/or transferring the momentum? I would also suspect that the box would have some capacitve aspect as well. (Again, maybe at audio frequencies it's too small to worry about.)

Do you have any sources on where the acoustic load is modeled from?

-Dan