Thorn F1 - a learning experiance with Tapped Horn - Page 6 - diyAudio
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Old 23rd May 2013, 12:04 PM   #51
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Join Date: Aug 2010
I believe now the esteemed Mr. McBean has added Vtc and Ap1, so there is definitely a model for the cone volume. Theres now even a very friendly wizard to calculate how much volume your cone uses.

Quote:
Originally Posted by Djim View Post
Hi Forsman,

Sorry I didn't reply earlier but (enough) time is sometimes difficult to find...

To be honest I think (just my opinion) that using Resonators/absorbing techniques only increases losses. I prefer to optimise the design rather than creating more losses. To me your 'dip problem' is the result of the difference between sim and design, like I stated earlier. I think it would be helpful to have a more accurate model to see what’s going on. It also help me to explain what I meant with the cone volume correction.

The volume within the cone is usually the main reason why the dip is (usually) larger in measurements compared to the sim. In other words the volume at S2 in the original model doesn’t represent the volume in reality. In my post#23 of the "SS15 or Tham 15?" thread I showed an example of an alternative way of simming the THAM. The alternative model shows the dip pretty accurate and looks similar to what one can measure from a standard Tham.

To make such alternative sim for your Thorn F1, I used your measurements to go from. First, I implied your measurement within the graphic ratio of HornResp. This gives a much easier comparison tool between model and measurement. After that I made some small changes in the HornResp input parameters to correct the volume at S2 and S4 and some small changes for the correct position of the point source ( lays within the cone). When you increase the volume at S2 one needs to compensate at S4 in order to keep the correct total internal volume of the enclosure. By using the exact frequency location of the peaks and dips of your measurements I tried to improve the model further. In the next picture you see the result (black) in combination with your actual measurement (red), all in the same plot ratio.

Click the image to open in full size.

The input page looks like this:

Click the image to open in full size.



Now you have an more accurate model you can see that by making the S2 area smaller (Cone Volume Correction) you can optimise the model to what you have modelled in the first place. I did so by decreasing the volume of S2:

Click the image to open in full size.

This example of the cone volume correction should bring it back to what you have simmed (freqeuncy response) in your original model. What this Cone Volume Correction will do is increase the compression at S2. Therefore the pressure minimums at S2, those of the 1/2 wavelength and full wavelength, will rise.

If you decide to experiment with the cone correction I made a quick sketch of how to start. You can experiment with smaller and larger shapes until you find the best solution.

Click the image to open in full size.
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