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Design Trade-offs (Read 207 times)
morpheous85
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Design Trade-offs
03/02/18 at 19:52:38
 
So I built my Wicked One back in 2005, with a pair of DHM-108b.  I was younger and less intelligent back then, and was not fully aware of the concept of design trade offs.  I somehow missed the line, "A direct parallel between the efficiency curve and the height dimension is eminent. The larger up to the full 36 inches, will be louder." I built my WO in the 24 x 36 size without realizing I was loosing efficiency and low end extension.

I did see in the plans that the throat opening can be increased from 1.25" to 2.5" to increase high frequency response, combined with facing the drivers towards the throat.  My original goal was a 5 kHz response, so I did so.  Steve later informed me that this is at the expense of low end response.

So my questions are:
1.  How much efficiency do I lose by making it 24x36 instead of 36x36?
2.  How much low end extension do I lose by making it 24x36 instead of 36x36?
3.  How much efficiency do I lose by making the throat opening larger?
4.  How much low end extension do I lose by making the throat opening larger?

For these questions, I prefer actual numbers as opposed to, "more efficiency", or "more extension".  How much more?

These all lead to the ultimate question:
5.  Is it worth rebuilding the box to 36x36 and throat opening of 1.25"?
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morpheous85
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Re: Design Trade-offs
Reply #1 - 03/12/18 at 16:03:49
 
I pushed my WO as close to the limit as I felt comfortable.  I have a 1050 Watt PA amplifier with a input limiter set at -3dB (~525 watts).  I ran it up to the peaks just barely engaging the limiters and I measured 110 dBC SPL standing about 4m away. I would calculate: 90.5 dB @ 1 watt @ 1m,  2 drivers = +3dB,  550 watt = +27.4dB, 120.9dB @ 1m, for a total of 108.9dB @ 4m.  That's actually surprisingly close to what I measured!  So it looks like I'm not gaining sensitivity from the box itself.

Would I gain dB from building it 36x36 with the smaller throat size?

I measured (in a 50ft x 120ft room) a 5 dB peak around 80-100 Hz and a roll off ~40 Hz.  I have a 6 string bass player with a low B tuned to 31 Hz.  Would I be able to reach 30 Hz with a 36x36 and smaller throat size?

Does this design completely unload the driver below its lowest frequency (like a ported enclosure) or does it behave more like a sealed enclosure that limits over excursion?
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« Last Edit: 03/12/18 at 19:43:41 by morpheous85 »  
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