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-   -   6th order bandpass subwoofer (http://www.diyaudio.com/forums/subwoofers/10048-6th-order-bandpass-subwoofer.html)

Ilianh 18th January 2003 08:18 AM

6th order bandpass subwoofer
 
I was experimenting with a 6th order bandpass system, when using those chambers sizes,

chamber 1 : 2cuFt fB: 19hz

chamber 2 : 0.2 cuFt fB: 500hz

Using a Max pentivent pv-1030 10" driver

I got the same results in phase response and impedance responce when using the same driver in a vented box
the only thing is a spike at 500 hz with the bandpass, but the woofer will have a 100 hz LP filter so im avoiding that.

Even the f3's are about the same, the bandpass one is 1 hz lower at -3dB

The only different thing between the vented design and the bandpass one is.. about 6db more at 2.83 volts, about everywhere.
and 6 dB is alot..... that makes it 102 dB at 27 hz, the vented box is 95.8 dB at same frequency.

I was curious about 2 things, is it ok to use a so high second chamber tuning fB?
and is it ok to use such a small second chamber size?

Ilianh 18th January 2003 09:19 AM

2 Attachment(s)
here a pic of the graphs
blue line is the 6th order bandpass, red line is the vented box

kelticwizard 18th January 2003 09:35 AM

2 Attachment(s)
I tried that woofer in WinISD and got very similar results for each enclosure.

Isn't this the woofer that different programs gave you different readings for SPL? One program gave you 6 dB higher than another, even though both were modeling identical boxes.

Something is incomplete about these numbers, they don't add up. Programs take some numbers and compute others from those according to a formula. I think these numbers are contradictory. I think that is what the programs are reacting to.

Maybe your program, having problems dealing with contradictory numbers, simply "flipped" SPL ratings from one enclosure to another.

At any rate, here is what WinISD gives for the 6 th order bandpass and a vented box, 2 cubic feet, tuned to 19 Hz.

The 6th order bandpass is in red.
The vented box is in blue.

Ilianh 18th January 2003 07:47 PM

yep, thats the same driver, i just tought i'd use jbl speaker shop for when using it, as the company uses that same app.

I'm trying to get the same resultes as you did in winisd, and I cant... something is strange here

djdan 18th January 2003 08:18 PM

Yes , it is something wrong with this speaker parameters ( or database maybe ).

My WIN ISD give a strange result for 6 order bandpass.

kelticwizard 18th January 2003 08:24 PM

2 Attachment(s)
WinISD has one nifty feature that can make life easy for you, or work against you. That is the feature where by clicking on the measurement, you can change from liters to cubic feet, from centimeters to inches, etc.

When you input your numbers for the driver, be certain that you use the right units. I think I might have added the 8 ohms for Z.

I decided to model the 8 ohms version-same numbers as the 4 ohms.

Below is a shot of the numbers I filled in.

Oops! I didn't get the whole box. Oh well, the section where the numbers are put in is all there on the screen.

kelticwizard 18th January 2003 08:35 PM

Anybody who wants to join this discussion should get some background on obtaining Ilianh's difficulties getting SPL ratings for this woofer in this thread:
http://www.diyaudio.com/forums/showt...ight=pentivent

And for the specs, just go here and then click on "Max Pentivent Specs". The 1030 is the speaker in question.
http://www.maxspeakers.net/products/pentivent/

Ilianh 18th January 2003 08:40 PM

ah, i see now, i was using winisd pro, wich seems to giving somehow different results.
anyway, at about same size boxes, i get 3hz lower at F3 for the bandpass... you think its worth the try?

kelticwizard 18th January 2003 09:02 PM

Quote:

Originally posted by Ilianh
ah, i see now, i was using winisd pro, wich seems to giving somehow different results.
anyway, at about same size boxes, i get 3hz lower at F3 for the bandpass... you think its worth the try?

Do I think It's worth a try? I think it might be fun.

Err, one question. How exactly do you plan the execute that .2 cu ft box tuned to 500 Hz? What will be your port size and length?

kelticwizard 18th January 2003 09:28 PM

You might have to use a Passive Radiator to tune the 0.2 cu ft box. Pioneer sold a really cheap passive radiator-like under $10-that was just a round piece of foam with a surround. You can cut a round piece of foam yourself, if you just want to experiment, and place a loosely attached piece of Saran wrap as a suround.

I've done it. Looks like hell, but it functions.

Make sure it is Saran Wrap, not any other brand of plastic wrap. Saran, and only Saran, is PVC-you can use vinyl glues on it and it will work fine. Poly wrap-most every brand except Saran-is essentially ungluable.

If it tunes out nicely, you can send away for speaker surround kits and attach the foam more professionally. If it doesn't work out right, then you saved the $20 for a speaker surround kit.


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