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Author Topic: Help setting HP filter for bass cab  (Read 6629 times)

john lutz

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Re: Help setting HP filter for bass cab
« Reply #10 on: July 28, 2010, 01:44:33 pm »

and thisindex.php/fa/31648/0/
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john lutz

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Re: Help setting HP filter for bass cab
« Reply #11 on: July 28, 2010, 01:46:35 pm »

john lutz wrote on Wed, 28 July 2010 12:44

and thisindex.php/fa/31648/0/

and finally:
index.php/fa/31649/0/
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Evan Kirkendall

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Re: Help setting HP filter for bass cab
« Reply #12 on: July 28, 2010, 01:53:44 pm »

John,
Did you get all these graphs with the driver cool? Once you heat up the voice coil and apply some power to it, those graphs can change drastically. You'll get a much more realistic view of what's going to happen to those boxes when you start moving air.



Evan
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Not all change is good change.

Art Welter

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Re: Help setting HP filter for bass cab
« Reply #13 on: July 28, 2010, 02:05:48 pm »

The 2241H has a 35Hz FS, X max of 7.62 mm.
At 1000 watts, the model shows over Xmax from 48-60 Hz.

Tuning so low in the relatively small box is causing low output, almost 10 dB down at FB.

Why would you choose a Fb below Fs?

Have you tried a higher Fb, like 35, 40 Hz, 45 Fb for comparison?

Is the 10.7 cubes for one or two speakers?

Have you checked the actual Fb of the box by sweeping with a sine wave to see where the excursion minima (Fb) is ?
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john lutz

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Re: Help setting HP filter for bass cab
« Reply #14 on: July 28, 2010, 02:21:03 pm »

Thanks Evan.  The Win ISD graphs are predictions before box was built.  The WT3 impedance grarh is an actual measurement of the box at rest (cool).  The predicted tuning was 39hz - the measured tuning is 33hz.  I will remeasure with it heated up a bit.  I'm curious now.  It's all a learning expierience for me.  Once I fully grok the response form JR, Paul, and Silas I think that is basically what I was looking for....thank you all.  
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Art Welter

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Re: Help setting HP filter for bass cab
« Reply #15 on: July 28, 2010, 02:35:21 pm »

john lutz wrote on Wed, 28 July 2010 12:21

Thanks Evan.  The Win ISD graphs are predictions before box was built.  The WT3 impedance grarh is an actual measurement of the box at rest (cool).  The predicted tuning was 39hz - the measured tuning is 33hz.  I will remeasure with it heated up a bit.  I'm curious now.  It's all a learning expierience for me.  Once I fully grok the response form JR, Paul, and Silas I think that is basically what I was looking for....thank you all.  

39 Hz sounds like it would work a lot better than 33 Hz.
Shorten up the ports a bit and you will probably  hear a big increase in low end.
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john lutz

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Re: Help setting HP filter for bass cab
« Reply #16 on: July 28, 2010, 03:30:20 pm »

Art Welter wrote on Wed, 28 July 2010 13:35

john lutz wrote on Wed, 28 July 2010 12:21

Thanks Evan.  The Win ISD graphs are predictions before box was built.  The WT3 impedance grarh is an actual measurement of the box at rest (cool).  The predicted tuning was 39hz - the measured tuning is 33hz.  I will remeasure with it heated up a bit.  I'm curious now.  It's all a learning expierience for me.  Once I fully grok the response form JR, Paul, and Silas I think that is basically what I was looking for....thank you all.  

39 Hz sounds like it would work a lot better than 33 Hz.
Shorten up the ports a bit and you will probably  hear a big increase in low end.


Thanks Art, I was just thinking the same thing (more or less but not as clearly).  This little project came from having 4 drivers and 2 small sturdy boxes laying around - and playing with software.  In real use so far they do OK.  The size is a trade off in output for portability.  I started to wonder if I could get more out of them with proper HP filter and then I realized I didn't actually know what that should be - hence my query.

I think the WT3 impedance sweep tells me actual Fb is 33hz.
Modeling in  Win ISD, I chose a port size to tune to 39hz but the final result has drifted a bit.
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Art Welter

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Re: Help setting HP filter for bass cab
« Reply #17 on: July 28, 2010, 08:04:18 pm »

john lutz wrote on Wed, 28 July 2010 13:30

Art Welter wrote on Wed, 28 July 2010 13:35

john lutz wrote on Wed, 28 July 2010 12:21

Thanks Evan.  The Win ISD graphs are predictions before box was built.  The WT3 impedance grarh is an actual measurement of the box at rest (cool).  The predicted tuning was 39hz - the measured tuning is 33hz.  I will remeasure with it heated up a bit.  I'm curious now.  It's all a learning expierience for me.  Once I fully grok the response form JR, Paul, and Silas I think that is basically what I was looking for....thank you all.  

39 Hz sounds like it would work a lot better than 33 Hz.
Shorten up the ports a bit and you will probably  hear a big increase in low end.


Thanks Art, I was just thinking the same thing (more or less but not as clearly).  This little project came from having 4 drivers and 2 small sturdy boxes laying around - and playing with software.  In real use so far they do OK.  The size is a trade off in output for portability.  I started to wonder if I could get more out of them with proper HP filter and then I realized I didn't actually know what that should be - hence my query.

I think the WT3 impedance sweep tells me actual Fb is 33hz.
Modeling in  Win ISD, I chose a port size to tune to 39hz but the final result has drifted a bit.

Port shape and proximity to the walls of the cabinet can change the Fb quite a bit, as you have found out.

After a few cabinets not performing as they should, I always measure the cone excursion and adjust the port depth accordingly.

Port size is quite important too, and is a “catch 22”. A big port is needed for high excursion, but the pig port chews cabinet size, and you don’t get good LF from a too small box.
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John Robson

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Re: Help setting HP filter for bass cab
« Reply #18 on: September 15, 2010, 05:09:46 pm »

30hz would be a safe place to be at. A lot depends on what you pushing through them and at what level. You want to make sure that you don't go to low that cone is no longer loaded by the box if the cone become unload you can damage the speaker.
I suggest that you use test tones at a low power level and slowly go down from 35hz and watch the cone of the speaker. If the cone stats moving a lot farther at 25hz than it did at 30hz then you know the frequency that the cone is not loaded. John
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john lutz

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Re: Help setting HP filter for bass cab
« Reply #19 on: September 16, 2010, 01:40:09 pm »

John Robson wrote on Wed, 15 September 2010 16:09

30hz would be a safe place to be at. A lot depends on what you pushing through them and at what level. You want to make sure that you don't go to low that cone is no longer loaded by the box if the cone become unload you can damage the speaker.
I suggest that you use test tones at a low power level and slowly go down from 35hz and watch the cone of the speaker. If the cone stats moving a lot farther at 25hz than it did at 30hz then you know the frequency that the cone is not loaded. John


Thank you for input, John.  I'll try the visual sweep.  I did end up shortening the ports to the thickness of the baffle board just to get closer to the design target tuning of 39hz.  Interesting how drastically proximity to cab walls affected the ports.  I know I've read it and heard it, but seeing it and measuring it made it sink in.  

FWIW the result was a lot more output but not as nice a sound.  Now they sound like you might expect, two 18s shoehorned in to a small cab.  Of course that only made me wonder how to find 18s that really like a small box.   Smile    
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