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How to avoid too high excursion figures with folded or taped horn subs


Lasse223
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Im pretty new to the DIY subwoofer thing and ran into a few problems I couldn't find an answer to online.

I want to bould a tapped or folded horn sub with the Eminence-15LFA Driver for home audio use at partys, so I calculated both boxes in hornresp and managed to get frequency responses and SPL I was very satisfied with, with the enclosures tuned to 30Hz (folded Horn) and 35Hz (tapped Horn). 

 

Hornresp_SPL1.JPG.a464fc8339e11fae8e0ead5884043784.JPG

 

However when I started looking at the displacement graph, I realized that the excursion was way too high and more than three times Xmax (5,5mm), even at the peak above the cut off frequency.

 

Hornsresp_Exc1.JPG.dd3d80d325437c8ba4a3aa3951a56752.JPG

 

I tried adjusting the enclosure parameters, but nothing changed it that much without completely altering the frequency response. I had to reduce the Power from 600W RMS to 50W to get to numbers under Xmax. But the Sub would still get above 125 dB at 100 Hz and 122dB at 30Hz (1,0 x Pi, half space). I mean fine, thats more than enough for my application, but it sounds really unrealistic to me.

Could these figures really be true? I think I haven't messd up some of the Input parameters (I tripple checked). I also thought that the driver just may not be suted for use in a horn sub, but I've read about many succesfull projects using this driver.

I would really appreciate if someone knows whats going on.

 

Hornresp_Input1.JPG.eff63b691b3dba61c7cf5abf7557d926.JPG

 

(sry for the bad English, its not my first language)

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Yes all of your results make sense.  The basic issue is that your using a driver with relatively low xmax in a low tuned box and as such its excursion limited rather than power limited.  There exist drivers with 15-20mm of linear excursion capability that would be able to get much louder in a low tuned box.  The Hornresp simulation assumes linear behavior whereas in real life increasing the drive voltage beyond which causes xmax will result in less than the predicted excursion.  So when you observe 13mm peak excursion its unlikely the driver would get that far and may be undamaged, it probably won't sound great though.   The xmech for this driver is listed as 16.5 mm but it might be almost impossible to reach as the coil will be far beyond the magnetic gap and thus subject to little force before excursion reaches this point.

In this thread I measure the excursion capability of a driver, you can see on the scope screen that the driver position measurement starts to 'flat top', increasing drive beyond this point just doesn't result in anymore excursion, just more heating in the voice coil.

 

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