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Controlling Excursion

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tommysb View Drop Down
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    Posted: 24 August 2008 at 5:56pm
When messing around with HornResp etc, I seem to be able to get a nice 1w/1m response out of certain designs, however, when you look at what happens putting a few hundred watts through them, I end up with high excursions at LF. Obviously reducing the rear chamber size can help control this, but what other ways are there to control high excursions, or what parameters in a driver can help prevent this? 
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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 24 August 2008 at 7:36pm

You can use a step slope to reduce the frequencies below the horns cut off. 

Best Regards,

Elliot Thompson
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tommysb View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tommysb Quote  Post ReplyReply Direct Link To This Post Posted: 24 August 2008 at 8:17pm
Do you mean on the x-over?

Tom
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Deadbeat Quote  Post ReplyReply Direct Link To This Post Posted: 24 August 2008 at 8:24pm
Here's a small excerpt from the diyaudio wiki:


If you use a high pass filter with an fc @ F3, the excursion will decrease approx
30% at that point. If you use a 2nd order high pass, then half an octave below fc
the excursion will be reduced by at least half. After such a high pass filter is
used, the excursion limited power will increase so that the power handling will be
limited by excursion at fc. The actual power handling will be typically 140% of
the excursion limited power hanlding at the F3 point without the filter.
Away on extended leave.
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tommysb View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tommysb Quote  Post ReplyReply Direct Link To This Post Posted: 24 August 2008 at 10:02pm
Interestingly...The predicted excursions for the 'same' model in Akabak and HornResp are quite different
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Post Options Post Options   Thanks (0) Thanks(0)   Quote David McBean Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2008 at 8:22am
Originally posted by tommysb tommysb wrote:

Interestingly...The predicted excursions for the 'same' model in Akabak and HornResp are quite different
 
Hi tommysb,
 
If you are seeing differences then it can only be because the models you are comparing are not the same :-).  Hornresp and AkAbak diaphragm displacement predictions are normally identical.
 
Kind regards,
 
David
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tommysb Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2008 at 1:40pm
Thanks David, I'll look into that :) - I think it's to do with front chamber approximations
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AndyWave View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndyWave Quote  Post ReplyReply Direct Link To This Post Posted: 29 August 2008 at 6:00pm
Hi

Look at driver cms value. Stiffer suspension will help when X linear starts to run out. I allways try to use driver (and enclosure design) which can take full RMS(or AES) power without exceeding X lin. Usually you can't destroy drivers in such design (except with insane power).

I've also found out that different cabs like different slopes on filters. As I'm after a clear kick I allways try different filter types when doing my own presets. Many times the filter/cab combination sounds best with least phase jerks.

Andy
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Post Options Post Options   Thanks (0) Thanks(0)   Quote minaximal Quote  Post ReplyReply Direct Link To This Post Posted: 30 August 2008 at 11:31am
dont forget fourth order 24db LR is effectively two 180deg filters and therefore 360deg (in phase again) and -6db at xo point, unlike others being -3db at xo. 
Subs + Barges = :)

www.metaacoustics.com

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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndyWave Quote  Post ReplyReply Direct Link To This Post Posted: 01 September 2008 at 4:40pm
I should be more spesific. While I know phase rotation to be 90deg/6dBoct., the filter slopes and group delays are looking different on each filter type. For example compare chebychev and bessel types (them being the useful extremes). Both of them should be the same dB/oct.

I wanted to say that I listen how loudspeaker/filter combination sounds, like in active 3-way system, listen only mids and try different slopes or orders on highpass or lowpass.

You could make ruler flat system with horrible sound? Yes? No? I think impulse response is equally important.

LR filters are cascaded 2nd order butterworths, mkay. You could even ask from mrHat mkay.

Suddenly there was room for fine tuning. I smell bit OT hereEmbarrassed.

Andy
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Post Options Post Options   Thanks (0) Thanks(0)   Quote _djk_ Quote  Post ReplyReply Direct Link To This Post Posted: 02 September 2008 at 12:38am
"Obviously reducing the rear chamber size can help control this, but what other ways are there to control high excursions, or what parameters in a driver can help prevent this?  "
 
In order to produce sond, the driver diaphragm must move.
 
To produce the same sound level an octave lower, a given driver must move 4X as far (assuming the design is driven within its pass-band).
 
Driven below its design pass-band, the excursion increases rapidly (that's why we use a high-pass filter).
 
Resonant loading (tuned chambers, etc) reduce excursion at that frequency only, the same genaral 4X rule applies.
 
If you want loud sound, you must have a large excursion, if you want deep frequency, it must excurd even more (4X for one octave).
 
There is no such thing as a free lunch!
 
djk
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