I'm looking to calculate VAS .from the formula that is in Rod Elliot's ESP website. The formula is Vas = Vb × (( Fb / Fs )² - 1 ). I plan on making a box and inverting the speaker so it faces into the box, as per Rod's Instructions. How is Fb calculated? I don't want to calculate VAS using the added mass method. I can't find a formula anywhere to calculate FB.
Fb/Fs would be how much the resonance goes up once you put it in the box.
I presume you intend to measure it?
I presume you intend to measure it?
You actually want to measure Fs, Qes and Qms in free air and in the box. In the box call these Fb, Qeb and Qmb.
The "correct" formula is Vas=Vb*(Qeb*Fb/(Qes*Fs)-1)
The "correct" formula is Vas=Vb*(Qeb*Fb/(Qes*Fs)-1)
I have had a quick look, but could not find much. Qeb and Qmb would be best measured with the dats, or is there a better way?
You measure them the same way you measure Fs, Qes and Qms in free air. You just measure them when the driver is in the box.
You can also make a simple jig and let REW do the measurements for you as long as you have a soundcard wiht a line out and line in. REW = Room Equalization Wizard
I am on a crash course at the moment. I learn one thing and forget another. Im reading rod elliotts page on T/S parameters. Talks about r0 f1 anf f2 which are used in formulas to get Qms and Qes. Does anyone know how to measure these? Thanks in advance.
I'm having problems. Unless I missed something, Rod states two frequencies, either side of Fs. I believe these frequencies are not given the values of F1 and F2 specifically. From what you've now written, I presume that R0 is Fs. If this is the case, then you have unlocked some major understanding issues. Thank you for the input. It's great that, however dumb a question may sound, the members seem to help in answering the questions.
The link is https://sound-au.com/tsp.htm. Getting a good grasp of the terminology is the challenge. Thanks
Ro is Zmax/Re
https://sbacoustics.com/wp-content/uploads/2021/01/Measuring-Thiele-Small-parameters.pdf
Seriously, a little time spent making a jig and using REW with your sound card will pay dividends.
On the page you are following: I means a current measurement and V means a voltage measurement. So R0 (r0) is the reference value below.
I don't think this method of measuring voltages and currents is an "accepted" method and you are better off using the one at the PDF above.
=====================================================================================
First, measure the resonant frequency. Adjust the frequency until the voltage across the resistor reaches a null (minimum level). Without changing anything, carefully measure the frequency and voltage across the resistor ...
Calculate the following ...
https://sbacoustics.com/wp-content/uploads/2021/01/Measuring-Thiele-Small-parameters.pdf
Seriously, a little time spent making a jig and using REW with your sound card will pay dividends.
On the page you are following: I means a current measurement and V means a voltage measurement. So R0 (r0) is the reference value below.
I don't think this method of measuring voltages and currents is an "accepted" method and you are better off using the one at the PDF above.
=====================================================================================
First, measure the resonant frequency. Adjust the frequency until the voltage across the resistor reaches a null (minimum level). Without changing anything, carefully measure the frequency and voltage across the resistor ...
| Frequency | Fs |
| Voltage across the resistor | Vm |
Complete the measurements for Fl and Fh, for which the voltage across the source resistor is equal to Vr, and as a sanity check (to ensure that your calculations and measurements are accurate), calculate the resonant frequency based on these last two measurements. Note that these measurements are critical, and even a small error will cause large deviations in the driver parameters.
If the above checks out (within 1Hz or less), then Qes, Qms and Qts can be calculated as follows ...
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