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Author Topic: z-fold sub design  (Read 2721 times)

Phil Pope

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z-fold sub design
« on: July 13, 2005, 05:24:48 am »

Hi

I am about to make a prototype of this sub (McBean input attached hopefully) but am still a little unsure of whether the size of the throat is OK.  I am not sure how a rubber throat loads the driver.  Below the rubber throat cutoff freq does the first section load the driver or does it just act as an extra large front chamber?

It seems to be accepted that increasing the compression ratio increases stress on the driver but I am not understanding quite how this works.  Is it at lower or higher frequencies where the compression driver stresses the driver?  Is it just the pressure on the driver or does the difference in pressure across the surface of the cone induce standing waves?  If it is is simply a matter of pressure is having a very small rear chamber equally as dangerous?  Does matching the size of the rear chamber to the throat properly reduce stress on the driver as well as reducing harmonic distortion and boosting output just below Fo?

sorry for all the questions Smile

cheers
Phil
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Mike MacWillie

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Re: z-fold sub design
« Reply #1 on: July 15, 2005, 12:24:12 am »

beware that you are modeling in 1/8th space.. ie corner loaded.. you'll probably want to model in 2pi (half space) Smile
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Phil Pope

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Re: z-fold sub design
« Reply #2 on: July 15, 2005, 06:40:50 pm »

was modelling in 1/8th space to simulate multiple boxes in full space.  even 1 or 2 boxes in half space looks pretty good to me though.

thanks
Phil
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Michael_Elliston¶

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Re: z-fold sub design
« Reply #3 on: July 28, 2005, 08:55:24 pm »

Hi Phil
Also it helps if you convert pictures to jpg or line drawings to GIF as it saves alot of space.

Quote:

Hi

I am about to make a prototype of this sub (McBean input attached hopefully) but am still a little unsure of whether the size of the throat is OK. I am not sure how a rubber throat loads the driver. Below the rubber throat cutoff freq does the first section load the driver or does it just act as an extra large front chamber?

Rubber throat is a different flare rate near the driver,to reduce 2HD from a lack of expansion(from memory).Seems more applicable to HF horns than basshorns.

Quote:


It seems to be accepted that increasing the compression ratio increases stress on the driver but I am not understanding quite how this works. Is it at lower or higher frequencies where the compression driver stresses the driver?

Sound pressure is just pressure.

Quote:

Is it just the pressure on the driver or does the difference in pressure across the surface of the cone induce standing waves?

The wavelengths here are 8metres long,dont think of light waves bouncing around(HF horns),think of waves of pressure emanating from the driver and being transmitted relatively un adulterated from the horn mouth. Think of the acoustical dimensions.

Quote:


If it is is simply a matter of pressure is having a very small rear chamber equally as dangerous? Does matching the size of the rear chamber to the throat properly reduce stress on the driver as well as reducing harmonic distortion and boosting output just below Fo?

I dont see a problem with a tiny rear chamber. Bear in mind that the heat from the driver will heat this rear chamber and a small chamber may not be ideal. Matchign the volume of the rear chamber to the horn does result in a less reactive horn and more flatter response(note excursion vs BLH)YOu dont really want to 'boost output' below Fc as excursion will be high and relies on high BL driver/subsonic filtering.

You dont have any ridiculous values in hornresp. Bear in mind that its easier to model an exponential horn and approximate it while folding and then remodel as conical when your done(actually parabolic sections assuming 2 panels constant,2 expanding)rather than try and fold the horn in the first place in the prescribed conical sections.

I fold from the mouth and work backwards,deciding on external dimensions as I go. After many iterations it becomes easy.

- http://www-ccrma.stanford.edu/~dpberner/Defense/pres.html

http://www.diyaudio.com/wiki/index.php?page=basshorn

http://www.audioroundtable.com/HighEfficiencySpeakers/messag es/495.html
Mike.e
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