SubMaximus -- A Large Front-Loaded Horn for UXL18 and Stereo Integrity HT 18" - Page 17 - AVS Forum
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post #481 of 485 Old 07-23-2014, 07:47 PM - Thread Starter
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posted.

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post #482 of 485 Old 07-31-2014, 05:00 PM - Thread Starter
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post mortem

a couple of things have had me concerned about how close the actual measurements were to the model.

first, there seemed to be a little more 'chop' in the frequency response than in the model.
second, there seemed to be more "ripples" under 100hz than the model predicted.
third, and of primary concern was the larger drop at the last leg of about 8db or so where the model forecast about 6db or so.
fourth, the low corner seemed lower than the low corner in the model. the target low corner was around 14-15hz and actual ended up around 10hz or so (which is getting into likely signal chain rolloff).

so with all that considered, and after reviewing the layout again, I think what has happened is that with three 180 degree turns, the effective path length has been extended by about 50% relative to the model. this is good news and bad news. it means that with three 180 degree turns, a horn can be shortened by about 33%, which in this case would provide a good deal of space savings. that however is just a theory for the moment.

in order to test the 50% "effective increase in length" hypothesis, I went back to the original hornresp model and increased each leg by 50%. the picture below shows the original target in red and the 50% longer horn in black. the 50% longer horn in black exhibits all four characteristics that were noted above.

as everybody who followed along knows, the construction was a masterpiece, so I don't think any concerns rest there.

the design just missed the mark by coming in with a lower effective tuning than plan.


original hornresp model (red), 50% increase in path lengths (black):




actual measurement with low pass filter in place:






edit: updated initial 25% number to 50%.
Attached Images
File Type: png submaximus actual vs model.png (37.9 KB, 17 views)
File Type: png actual with low pass submaximus.png (35.6 KB, 86 views)
File Type: png target vs model with 50 percent increase in path lengths.png (39.6 KB, 77 views)
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post #483 of 485 Old 07-31-2014, 05:27 PM
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So design up another... and I'll build it and test it. How's that ? But make it even more awesome so I can wreck my house with a few of them. The only issue I have is one dimension needs to be like 30" to fit behind screen wall. A few more inches probably ok. But the other dimensions can basically be about as big as you want. If you walk me through folding process that would be super cool.

This idea and subwoofer is just too awesome to let it die. It needs a version 2.0

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post #484 of 485 Old 07-31-2014, 06:06 PM
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SUBMAXIMUS V2.0: "home wrecker"

What drivers would work in this monster? Anything other than UXL18 ? (that driver is fine with me btw)

also, what low pass filter was in place? It doesn't look so strong...

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post #485 of 485 Old 07-31-2014, 08:23 PM
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Quote:
Originally Posted by maxmercy View Post
The model is wrong. Make all the hornresp segments PAR in the model (according to post 1, the segments are EXP) and you will see the results meet the model much more closely w/ regards to the ripple amount. I didn't notice this until after I looked at it when I entered the model into hornresp myself a few days ago. If you will build a re ?horn with a rectangular cross-section, always use PAR.

The lower corner is because of horn length/x-section areas not accounted for in the corners by hornresp.

JSS
Can you explain this more?

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