THAM18 - new and traditional THAM folding compared 
Wednesday, November 28, 2012, 19:47
Posted by Anders
When looking at designing an 18" (and and above) tapped horn you might notice challenges not previously encountered, this is how the new version of the THAM folding came to be.

In order to sort out if this new folding really is an improvement upon the traditional THAM folding in an 18" TH case a simple comparison was needed, and I have to stress that this is an exercise in theory, and not practical findings, at least not yet.

First we start of by designing a compact and efficient traditional THAM folded 18" tapped horn, and we spend some time trying to optimize it until a satisfactory result is achieved (see drawing below).

Then we take the same enclosure restrictions (above) but swap the folding to the new version, first seen in the THAM18 proposal, and optimize that until a satisfactory result is achieved (see drawing below).

Next we take a decent but not over the top standard 18" like the B&C 18TBX100 and simulate the two foldings in the same way (4 segment), and compare the results.

The drawing :

Traditional THAM folding inputs :

New THAM folding version :

The simulation results :

The simulations with descriptions :

The results show both a higher sensitivity (approx 2-4 dB) and a wider range for the new folding version, but remember, this is theory, but the differences seen in the simulations makes me think there is something to this.

If the theoretical performance gain is the same for smaller drivers are not yet clear, nor is it for larger ones even if this seems more likely.

The THAM18 using the new folding version seen in the drawing above is a size optimized version of the THAM18 proposal published earlier, although not yet finetuned it still shows the potential of the new folding version (or NFV for typing convenience).

The theoretical results also points to that this might be the way to go for a future 21" version, below you can see two examples of THAM18 simulated with the 18TBW100 and THAM21 simulated with 21SW115.

Regarding simulation method, below is the difference between 3 and 4 segment simualtions :

And a Akabak response curve of the THAM21 NFV from hornresp export script for comparison:

But I'm also working on getting the THAM18 simmed up in AkAbak, this is the dimensions required (just for testing, not for final result) :

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