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Spice Modeling Acoustic Properties of Speakers
Spice Modeling Acoustic Properties of Speakers
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Old 18th April 2018, 12:38 PM   #1
jelanier is offline jelanier  United States
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Default Spice Modeling Acoustic Properties of Speakers

Did you know that you can model electro-acoustic properties of loudspeakers? I use LTSpice for my simulations. I create a circuit based on the electro-mechanical properties of a woofer, and an enclosure. It takes the form of a high pass filter of sorts. Using Thiele-Small parameters, you can convert them into a circuit. I am attaching a screenshot example acoustic suspension speaker system with a system Q of .707. You can plot frequency response, impedance, phase or anything you wish. This model has an amplifier with a damping factor of about 300. I also model ported systems. I can show an example of that if there is any interest.

Jim
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File Type: jpg AS_Plot.jpg (226.9 KB, 126 views)
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Old 18th April 2018, 12:55 PM   #2
IG81 is offline IG81  Canada
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I've never tried to include the enclosure in the model, but I did mess about with this in AIMSpice many years ago. Without using the T/S parameters, I just adjusted the various RCL values until the impedance plot matched a driver I had (Pionneer A11 IIRC) and played around with adding crossovers, zobels and Z-peak correction circuits. It was quite educative.
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Old 18th April 2018, 01:27 PM   #3
jazbo8 is offline jazbo8
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Spice Modeling Acoustic Properties of Speakers
Jim - you showed a pretty simplified model of the loudspeaker, how close would it match the actual measured results? Dr. Leach back in 1991 was already working with more complex models, which no doubt were subsequently incorporated into the modern speaker design programs.
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Old 18th April 2018, 02:47 PM   #4
jelanier is offline jelanier  United States
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The model can be made as complex as you want, but it will have little effect on the box volume and/or tuning condition IMHO. Thiele showed more complex models in 1971 but opted for the simpler model for design.

The ported model is similar to the one shown but contains 2 more elements that are of consequence. Since there is a vent capacitance, there is also a resistance associated with it. This is used to calculate the box leakage Q.

Tuning conditions for ported designs are selected based on Butterworth, Chebyshev, or whatever filter you prefer. Again, the simple model is best for these calculations. The other elements will have little effect on box and tuning conditions.

More complex models can be created based on actual measurement of specific drivers. From this you could get more accurate impedance/phase plots.


Jim
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Old 23rd April 2018, 12:29 PM   #5
jelanier is offline jelanier  United States
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Examples of a ported system.
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Old 23rd April 2018, 01:11 PM   #6
xrk971 is offline xrk971  United States
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Spice Modeling Acoustic Properties of Speakers
It’s good to do this to show that all this theory comes down to networks of RLC lumped elements. It works of course, but Spice really is best left for the design of the electronics and amps.

Akabak is a scripting language for modeling acoustic systems using lumped element and is basically doing the same thing but has all the functionality of modeling speakers built in. It also handles the diffraction, wave propagation in horns waveguides, velocity, etc. In the end, T/S parameters are just RLC equivalents of a driver. Sure we can do it in a Spice, but let’s use the optimal tool for the job.

One can use a pipe wrench as a hammer, but we have hammers for the job.

Akabak also has electrical elements like RLC, and opamps, etc and ok to use for occasional BSC or XO. But a power amp should be modeled on LTspice. Same thing.

Akabak
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Old 23rd April 2018, 02:19 PM   #7
jelanier is offline jelanier  United States
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I think you missed the point of this. A.N. Thiele solved the mystery of ported loudspeaker design by converting the electro-mechanical properties of a speaker system into a circuit. The idea being that once these parameters are known, the values can be calculated for known filter types. As an example, a ported system can be designed as a Butterworth filter as quasi third order (QTS less than .383) or a forth order if Qts is .383. The poles are zero for orders 1 and 2 in first case and zero for 1,2 and 3 in second case. SPICE is great for modeling filters.
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Old 23rd April 2018, 03:06 PM   #8
chrisb is offline chrisb
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If Thiele solved the mystery of ported loudspeaker design, why are there still so many horrid sounding examples inhabiting modern showrooms?

Perhaps there’s an element of art to balancing the numerous comprises involved in creation of a musically pleasing sounding system than just crunching numbers?
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Old 23rd April 2018, 03:10 PM   #9
jelanier is offline jelanier  United States
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Maybe you should you read the paper . There are an infinite number of "designs" that can be derived from the mathematical model.
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Old 23rd April 2018, 03:16 PM   #10
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Jim, perhaps you missed my point, but there’s far more important things for all of us to worry about.
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