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Author Topic: Help setting HP filter for bass cab  (Read 6631 times)

john lutz

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Help setting HP filter for bass cab
« on: July 27, 2010, 04:03:10 pm »

What data should I be looking at to find a proper HP for these boxes?

I have some DIY JBL dual 18s w/2241Hs in a vented box tuned to 33hz and have just been using LR24 @30hz.  

Power is CE4000 stereo - so possible 1200w max into nominal 4 ohms.  Is the HP I'm using too conservative or too risky?  

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Duane Massey

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Re: Help setting HP filter for bass cab
« Reply #1 on: July 27, 2010, 09:08:00 pm »

Depends....how loud do you run the rig? What type of program?

I'm very conservative, so I'd run it at 40hz if you're pushing the system very hard. And, as always, don't clip the amp...
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Duane Massey
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Paul O'Brien

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Re: Help setting HP filter for bass cab
« Reply #2 on: July 28, 2010, 11:08:42 am »

john lutz wrote on Tue, 27 July 2010 16:03

What data should I be looking at to find a proper HP for these boxes?



You need to model the boxes in something like WinISD Pro to find the system tuning frequency, and to do that you need the TS parameters for the drivers(available from JBL), and the internal box volume and port dimensions. This software is free to download from here.. http://www.linearteam.dk/default.aspx?pageid=winisdpro
When done properly this software can also show you how much power the speakers can actually take before over excursion.
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Paul O

Silas Pradetto

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Re: Help setting HP filter for bass cab
« Reply #3 on: July 28, 2010, 11:32:38 am »

LR filters are 6dB down at the knee, so you'd be 6dB down at 30Hz. Usually a high pass at box tuning is quite safe, so you're probably fine. Modeling it would obviously be a more accurate way to determine this, but often the physical piece doesn't match the model.

I think Butterworth filters are usually used for high passes because they are only 3dB down at the knee. They stay flatter in their passband.
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Evan Kirkendall

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Re: Help setting HP filter for bass cab
« Reply #4 on: July 28, 2010, 11:42:01 am »

Silas Pradetto wrote on Wed, 28 July 2010 11:32

LR filters are 6dB down at the knee, so you'd be 6dB down at 30Hz. Usually a high pass at box tuning is quite safe, so you're probably fine. Modeling it would obviously be a more accurate way to determine this, but often the physical piece doesn't match the model.

I think Butterworth filters are usually used for high passes because they are only 3dB down at the knee. They stay flatter in their passband.


+1

I'd use a 3rd order BW at your tuning frequency.

As always, keep an eye out for signs of stress during use. Bottoming out, distortion, ect. You may need to play with it a little... What JBL driver are you using?


Evan
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Silas Pradetto

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Re: Help setting HP filter for bass cab
« Reply #5 on: July 28, 2010, 11:44:59 am »

Evan Kirkendall wrote on Wed, 28 July 2010 11:42

Silas Pradetto wrote on Wed, 28 July 2010 11:32

LR filters are 6dB down at the knee, so you'd be 6dB down at 30Hz. Usually a high pass at box tuning is quite safe, so you're probably fine. Modeling it would obviously be a more accurate way to determine this, but often the physical piece doesn't match the model.

I think Butterworth filters are usually used for high passes because they are only 3dB down at the knee. They stay flatter in their passband.


+1

I'd use a 3rd order BW at your tuning frequency.

As always, keep an eye out for signs of stress during use. Bottoming out, distortion, ect. You may need to play with it a little... What JBL driver are you using?


Evan


He mentioned the 2241H so he should be set.
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John Roberts {JR}

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Re: Help setting HP filter for bass cab
« Reply #6 on: July 28, 2010, 12:27:42 pm »

john lutz wrote on Tue, 27 July 2010 15:03

What data should I be looking at to find a proper HP for these boxes?

I have some DIY JBL dual 18s w/2241Hs in a vented box tuned to 33hz and have just been using LR24 @30hz.  

Power is CE4000 stereo - so possible 1200w max into nominal 4 ohms.  Is the HP I'm using too conservative or too risky?  




As others have mentioned the LR alignment is not intended for simple HPF. The LR alignment is basically two Butterworth alignments stacked (added) in series, and the -6dB at tuning is only useful for combining with a symmetrical LPF where the relative phase shift rotates through a full 360' and back to in phase again.

For a single ended HP filter, there in no other bandpass to mate with, so tuning should be based on complementing the box driver needs.

Other speaker guys can give useful specific advise. My experience is more with the filters than boxes and drivers.  

JR
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Paul O'Brien

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Re: Help setting HP filter for bass cab
« Reply #7 on: July 28, 2010, 12:54:31 pm »

I have this software so I ran a simulation quickly just to see for myself. Using a 15 cu ft box(for a pair) tuned to 42hz these drives reach xmax at 900w, the LR24 HPF at 30hz actually does appear to limit excursion below tuning to the same amount that occurs above but it also moves the -3db point a little higher too. These numbers are only valid for this particular combo but as expected it demonstrates that over excursion begins to occur at relatively low power levels. Increasing power handling involves using smaller enclosures and higher low-cut filters.. though that also decreases low freq response.
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john lutz

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Re: Help setting HP filter for bass cab
« Reply #8 on: July 28, 2010, 01:41:51 pm »

Thank you all for replies - plenty for me to digest.  Here is the data I have on these boxes so far.index.php/fa/31645/0/
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john lutz

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Re: Help setting HP filter for bass cab
« Reply #9 on: July 28, 2010, 01:43:26 pm »

john lutz wrote on Wed, 28 July 2010 12:41

Thank you all for replies - plenty for me to digest.  Here is the data I have on these boxes so far.index.php/fa/31645/0/

index.php/fa/31647/0/
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