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MiniDSP 2x4HD, Output HPF affects FR above Filter 2 years 9 months ago #47796

  • spearfish25
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I've been using a 2x4HD to time align and PEQ 4 subwoofers. It worked great for the time align and PEQ from REW. To allow some other PEQ in the input channel, I applied the subwoofer PEQ to each of the 4 output channels. I then wanted to make a high pass filter for each output channel so that I wasn't sending signal to the subs below their tuning frequencies. No issues using the Xover tab in each output to apply the HPFs. I chose 20hz and used a LW 48db/oct curve. Filter looks as I want in the displayed FR above the settings in the Xover window.

The problem arises when I go and use REW to view the results. I've attached a screen grab of the subwoofer FR curve without the HPF and then again with the HFP enabled.

The RED trace is my subwoofer FR (all 4 together and PEQ'd) WITHOUT the miniDSP Xover HPF enabled. The GREEN trace is everything exactly the same but with the miniDSP Xover HPFs taken off bypass. Why is the FR changing above the HPF?
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MiniDSP 2x4HD, Output HPF affects FR above Filter 2 years 9 months ago #47799

  • Ultrasonic
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My bet is you've not got things set up as you think on one of the channels.

Rather than looking at all 4 subs together it would be interesting to check with/without the HPF on each channel on its own.

Edit: for info. you can use the camera icon at the top-left of graphs in REW to save them as pictures.

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Last edit: by Ultrasonic.

MiniDSP 2x4HD, Output HPF affects FR above Filter 2 years 9 months ago #47802

  • spearfish25
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My bet is you've not got things set up as you think on one of the channels.

Rather than looking at all 4 subs together it would be interesting to check with/without the HPF on each channel on its own.

Edit: for info. you can use the camera icon at the top-left of graphs in REW to save them as pictures.


Good idea. So here's what I get when I apply the HPF on only one output channel at a time. The other 3 have the filter bypassed. Interesting that it still impacts the overall FR. I have two sealed subs and two ported subs. Depending on where the HPF is placed, it affects the FR differently. The two curves with big dips at ~22Hz are when the HPF is on one of the ported sub outputs. The curves with a smaller dip from 32-50Hz is when the filter is on a sealed sub output. If I put the filter on all 4 outputs, the FR is similar to having the HPF on one of the sealed sub outputs.

Changing the HPF cutoff frequency drastically changes the impact on the entire FR curve too. So picking 14hz or 30Hz leads to a completely different curve.

I've included a screen shot of the filter I'm placing in the Xover portion of the output channel in the miniDSP.

No clue what's going on here.
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Last edit: by spearfish25.

MiniDSP 2x4HD, Output HPF affects FR above Filter 2 years 9 months ago #47803

  • Ultrasonic
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Sorry, I think you misunderstood me there.

I meant make measurements with only one sub running at any one time. So for example mute channels 2, 3 and 4 and then make measurements for channel 1 with and without the HPF applied.

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MiniDSP 2x4HD, Output HPF affects FR above Filter 2 years 8 months ago #48235

  • andrewjaye
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Adding another filter ie high passing the subs adds additional latency so you need to time align to bring your stopband back into time with the mains.

Also the roll off rate of ported enclosure bottom end is steeper than sealed enclosure, applying the same high pass filter to the different enclosures in different locations in the room are not going to have the same effect across all the subs. This is probably exacerbated because the bottom of the first octave is both where the port tuning freq is and right in the area where you are seeing the greatest amount of room gain.

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Last edit: by andrewjaye.
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