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Discussion Starter #1
Hello people.

I have finally got my sub, amp and power supply but I have an issue that I need to limit my sub for anything less than 16hz because the drivers are going beyond excursion

Any idea how I would start to make one or better yet one I can buy off the shelf, ideally an adjustable HPF?

Thanks

Craig
 

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An unbalanced miniDSP or a Reckhorn B-2 would do the trick. The miniDSP would have many more options, but is a bit more expensive. I have both and would get the miniDSP 10:1 if you like to tinker.
 

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What's the input impedance on the amplifier? (And is the amp just for the sub?)

Could easily put a capacitor on the input.
 

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What's the input impedance on the amplifier? (And is the amp just for the sub?)

Could easily put a capacitor on the input.
+1. I have done this before with accurate results.

If a 1st-order filter is all you need, this is by far the simplest and cheapest solution.
 

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+1. I have done this before with accurate results.

If a 1st-order filter is all you need, this is by far the simplest and cheapest solution.
This is interesting. I'm also looking for getting a minidsp, but this could be a short term solution. looking forward for more details
 

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Using the formula for HPF and a spreadsheet you get the following results for a 16 Hz cutoff and assuming your amp's input impedance is 47 kΩ or greater, then the combined impedance of R1 and R_amp (R2) is 8.25kΩ
Then using the info from here: http://www.t-linespeakers.org/tech/filters/passiveHLxo.html you get R1 as 10 kΩ and C1 as 1.2 micro Farad

Passive hpf.PNG


-Bill
 

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Discussion Starter #7
Thanks guys, I am not mega clued up on the elctronic side of things so I am unsure of input impedance, is there an easy way to find out?

The amp is dedicated only to the subwoofer.

As above if a 1.2Micro farad will do, how would I connect it, across the lines or in series?

Thanks for the help

Craig
 

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Most modern amps will have an input impedance of at least 47 kΩ so you can ignore it.

The setup would be: Sub Output from receiver goes into the capacitor with the resistor after it connected to earth. (As per the picture, the sub out is on the left and the power amp input is on the right.)

-Bill.
 

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Yes, if you go with a single component filter. Which is what I would do probably. And Fusseli too. You would need a .211 uF capacitor. (Someone please check my math and correct me if I'm wrong!)
 

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Discussion Starter #11
Thank you, above said it should be a 1.2microfarad? (uf)
What resistor would I need and where on the line would I place it, across the positive and negative lines?

Thanks again

Craig
 

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Those bigs caps and resistors are overkill, and I believe you are confusing the op. For a hpf, all he needs in an inline cap, as in the drawing he posted. Where does the 10K ohm resistor come into the picture for a simple 1st order hpf? The cap value is calculated based on the input impedance of the amp he's using, which the op really should try to identify.

Remember, we are dealing with line-level inputs here. A small smd 50V cap will do the trick, maybe even 25V depending on his source. NOTE: I haven't calculated the cap value needed for a typical 47kohm input impedance amp, so I'm not sure if a value close to needed is even available in smd form.
 

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I would agree that those are way bigger than necessary. But I also don't think the op wants to get into soldering any smd components.

I also agree that the resistor is unnecessary, but since he isn't sure what the impedance is, going with the resistor will reduce the error.

If it was me, I'd do it your way. Or Fusseli's way. But for someone who doesn't really know what he's doing: the most recent suggested components will be just fine.
 

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A .21 microfarad cap will work if the impedance is 47 kΩ.
However, not knowing the exact impedance it is easier to add the 10 kΩ resistor with the 1.2 uF cap to guarantee you get the desired results.

If you have ways of measuring it then I would suggest trying the .21 alone as per above.
 

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That is correct IF (notice the big "if") your amp impedance is about 8-10Kohm. Since we don't know, you will need the resistor.

How about you tell us what amplifier you are using, and maybe we can figure out a simpler filter for you.
 

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Discussion Starter #20
That is correct IF (notice the big "if") your amp impedance is about 8-10Kohm. Since we don't know, you will need the resistor.

How about you tell us what amplifier you are using, and maybe we can figure out a simpler filter for you.
Thank you.

I did give it a try and it didn't work correctly the freq drop was WAY high.

The amp is an onkyo nr1007 and the sub amp is actually a modified car amp to work on mains power using a PC psu

Craig
 
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