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Compression Ratio for Bass Horn

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DMorison View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Topic: Compression Ratio for Bass Horn
    Posted: 14 March 2007 at 9:51am
Hi all,
Does anyone know of any reliable guidelines for appropriate compression ratio's for bass horns please?
 
Also, what are the likely results of using a high-ish ratio (eg 3:1)
 
I'm playing around with Hornresp and have what seems to be a useful design, but want to be sure I'm not leaving myself open to bad things happening.
 
Cheers,
David.
 
EDIT - corrected typo.


Edited by DMorison - 14 March 2007 at 9:52am
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mark68 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mark68 Quote  Post ReplyReply Direct Link To This Post Posted: 14 March 2007 at 8:03pm
keep in mind that with high compression ratio you could have high pressure in the throat and in the front chamber and so more distortion, someone suggest more than half of SD  for the throat but for me I think that maybe could change by using a right driver.

I used the ratio 3:1 with a PD1550  and I have a Bang sound and air  overload in the throat but maybe beacause my driver  move to much air.

if you use hornresp you could see  what happens by changing the throat area with the 2 armonic distortion, but there are also other type of distortion like doppler effect



bye Marco
 
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unclejam View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote unclejam Quote  Post ReplyReply Direct Link To This Post Posted: 14 March 2007 at 11:43pm
check mobile enneid's post on win isd and horn response thatt should help some i think meybe i dont kno
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tb_mike Quote  Post ReplyReply Direct Link To This Post Posted: 24 March 2007 at 4:56am
mark68 I think you should diagnose the cause of the distortion before attributing it to a high compression ratio - which should only produce distortion if the bandwidth is too high.which on a basshorn,it isnt.

There is an equation to calculate approximate 2HD on a particular horn,but the version I had,was misstyped.Mentioned on audioasylum.

eg
http://db.audioasylum.com/cgi/m.mpl?forum=hug&n=40053&highlight=throat+distortion+Tomservo&r=&session=

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mark68 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mark68 Quote  Post ReplyReply Direct Link To This Post Posted: 24 March 2007 at 9:35am
I know that  but for the



2° HD   I had used this formula for exponential horns:


2° HD = 0,00173 x (F/FC) x RADQ(PAR/ST)


Where :

F= generic frequency in Hz

FC= Cut off of horn in Hz

PAR = acoustic power irradiated in Wac

ST= area of throat in mq


You will notice that if you have very small ST the 2°HD will rise and of course if you have large bandwidth 2°HD will rise too.

There is a table also taken from Beranek that explains this.

In Horn resp program is possible to estimate 2°HD

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JD01 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JD01 Quote  Post ReplyReply Direct Link To This Post Posted: 25 March 2007 at 3:31pm
A high compression ratio needs speakers able to handle the load (As do big stacks of horns... it all comes down to load). The bang mark68 described could well be the cones outer parts slapping back because of the pressure.... (but it's a PD1550, so this is not THAT likely.... I have seen this on speakers like Kappa15lf, mainly intended for BR use).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tb_mike Quote  Post ReplyReply Direct Link To This Post Posted: 26 March 2007 at 6:50am
Doesnt seem to change much with practical 2:1 and 3:1 compression ratios and two octave bandwidths with hornresp 2HD.

Problem with strong cones,how do you tell without trying one?Apart from building a labhorn.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JD01 Quote  Post ReplyReply Direct Link To This Post Posted: 26 March 2007 at 9:14am
There are some 'obvious' characteristics.... they aren't THAT exact, you can still have a speaker that looks extremely stiff and sucks and you can have a speaker that looks fragile and won't break. But for starters the look is ok. Deep cone, not too hard surround (no hard plastic filled into the surround), and depending on the application (kick or 'infra') a progressiv suspension that kicks in slightly above Xmax (kick lower xmax, infra depending... 'big stack' with similar speakers as kick, 'small stack' with high xmax speakers).
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mark68 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mark68 Quote  Post ReplyReply Direct Link To This Post Posted: 27 March 2007 at 3:52pm
>Doesnt seem to change much with practical 2:1 and 3:1 compression ratios and two octave bandwidths with hornresp 2HD.

Problem with strong cones,how do you tell without trying one?Apart from building a labhorn. <


I Don't know with the formula I had different value  little more higher.
 
In hornresp with a PD1550
with Eg=63V    in the frequency of 150 Hz

I see that for compression ratio 1:3        I Have the 2° HD    2,10%

I see that for compression ratio 1:2        I Have the 2° HD    1,50%

I see that for compression ratio 1:1        I Have the 2° HD    0,70%




 

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