My Tapped and Offset Driver Horn Build (with super slow motion driver footage)! - AVS Forum
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post #1 of 8 Old 08-29-2013, 03:30 AM - Thread Starter
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I made a thread asking what drivers would perform ok in a tapped and front loaded horn a few months ago. I ended up getting the Dayton 15" Ultimax, not an ideal driver for a tapped horn, I know. However, it ticked the most boxes and I wouldn't have to go with out food for a month to afford it.

To begin with, I decided that around 25Hz was where I was aiming for both enclosures.


The tapped horn


The front loaded horn



Folded up in AutoCAD


Since driver excursion plays such a big part in how an enclosure performs, I needed to be able to measure it.
To do that, I designed viewing windows into the throat of both enclosures.



I can do the the cutting myself, but my facilities are limited and since I was adding these windows I had a friend of my brother do it all on his CNC.









REW graphs for the tapped horn



and the front loaded

I used photoshop to overlay the REW and Hornresp curves



The tapped horn performed as expected. I'm unsure why, but the front loaded horn was a fair way off the projected result.
It was even more off in the excursion results.














these were all filmed at 400 frames per second
the gifs were made from a program called Tracker, which allows the measurement of motion in videos

when you look at Hornresp's displacement the tapped seems as predicted, but the front loaded is miles off.


tapped


front loaded

anyone have any ideas how it could be so far off?
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post #2 of 8 Old 08-29-2013, 04:27 PM
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Cool project.

Can you measure impedance?

If the impedance doesn't match well with the sims, I'd look for a leak.
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post #3 of 8 Old 08-29-2013, 10:54 PM - Thread Starter
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could a leak account for the discrepancies in excursion?
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post #4 of 8 Old 08-29-2013, 11:10 PM
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first...extremely cool work and post!!

second, the front loaded horn is a total malfunction. your frequency response is missing 8db or more vs model and that means something is wrong bigtime. massive air leak or something. no conclusions can be drawn until the horn is fixed and working properly.

"could a leak account for the discrepancies in excursion?"

yes. with a bad leak, the horn isn't loading the driver properly, so the driver ends up flopping around, not quite as bad as a ported cab under tuning, but that is kind of the idea of an unloaded driver.

Listen. It's All Good.
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post #5 of 8 Old 08-30-2013, 12:56 AM - Thread Starter
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I figured something had to be seriously wrong with how far down it was on the modelled.
Any tips on locating leaks?

Is there anything to be concerned about with the performance of the tapped?

Also, the driver is rated with 19mm xmax. Would I have damaged it with that amount of excursion?
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post #6 of 8 Old 08-30-2013, 11:01 AM
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smoke is good for seeing air move.

19mm of excursion is the listed xmax for that driver. I think it klippeled at 22mm or so. but in any case, most drivers have quite a bit of running room before their damage point which is known as xlim (excursion limit) or xdam (excursion damage point). just going to xmax won't cause any damage at all. I suspect the driver is fine.

I don't see anything wrong with the tapped horn at first look.
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post #7 of 8 Old 08-31-2013, 04:45 PM
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I don’t understand what you are doing with your speaker problem.

I am interested in high speed video, especially for the analysis of tennis strokes. I use a Casio FH100 camera, usually at 240 fps or 420 fps.

CMOS cameras have a ‘rolling shutter’ readout process. Individual sensor elemental detectors are exposed at the frame rate for the exposure time or shutter speed. However, these lines of detectors are exposed and readout one line after the other, for example, from top to bottom of the frame. There is a delay down the frame and it causes 'Jello Effect' distortion.

I measured the Jello Effect distortion by videoing straight bars on a rotation disc. The Jello Effect bends the bars is a characteristic way. It also changes the width of a rotating bar, in the videos below to narrower on the side where rising and wider on the side where going down.

See videos for a Casio FH100 at 240 fps:
9 rps
https://vimeo.com/21529497

21 rps
https://vimeo.com/25242212

330 rps
https://vimeo.com/25224520

For a Canon Powershot 110 HS / ELPH 125 at 240 fps, see also adjacent videos.
https://vimeo.com/73165190

If your camera is a high performance CCD, it probably has a Global Shutter and that process does not have the Jello Effect.

To check for Jello Effect distortion, rotate the camera, 90°, 180° and 270° and repeat the experiment. Changes to the same object movement are due to Jello Effect distortion. This effects bends golf club shafts during swings.

Some more discussion of Jello Effect distortions, see Kinovea. You may also want to look into Kinovea for video motion analysis. See reply #12.
http://www.kinovea.org/en/forum/viewtopic.php?id=435

If you want to measure position x & y as a function of t (time) with a CMOS video camera by measuring locations in the video frame, the effect of Jello Effect distortion has to be considered or determined to be negligible. Time is not simultaneous throughout the frame.
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post #8 of 8 Old 09-02-2013, 09:20 AM - Thread Starter
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ok?
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