# miniDSP dropping subwoofer output



## Bear123 (Dec 31, 2013)

So I have a few days off work and am trying to dial in my sub(s) with the miniDSP. First thing I did was use it to hook up both my subs to get a non eq'd response, but noticed that it lowered the sub output ALOT. Had to turn up sub from 2:00 to max for similar output. Any ideas? I am thinking maybe low voltage to the miniDSP? I am powering it with a USB cable plugged into a cell phone type plug into ac outlet. Just wondering if this is normal or something that should not be happening.


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## alfa-74 (Aug 31, 2013)

Bear123 said:


> So I have a few days off work and am trying to dial in my sub(s) with the miniDSP. First thing I did was use it to hook up both my subs to get a non eq'd response, but noticed that it lowered the sub output ALOT. Had to turn up sub from 2:00 to max for similar output. Any ideas? I am thinking maybe low voltage to the miniDSP? I am powering it with a USB cable plugged into a cell phone type plug into ac outlet. Just wondering if this is normal or something that should not be happening.


I think you need to add more information, for example what mini dsp are you using, is it balanced or unbalanced, what receiver are you using, etc


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## Bear123 (Dec 31, 2013)

Version A .9Vrms Max, 2 x 4, with 2 way advanced 2.1 plugin. also, when playing the sweep for rew, it stutters rather than playing smoothly


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## Bear123 (Dec 31, 2013)

Here is an update with graphs. I really would like to get this sorted out, as you can see by my best eq'd graph, but I want to see if I need to fix my output issue first. I have been given the advice to just turn the sub gain up to compensate for the lost output, but I can't get past the feeling that something is not right. This graphs shows with and without the miniDSP inline, no eq, no filters, same volume, sub gain, and avr sub trim. Looks like a loss of about 8 dB.


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## Bear123 (Dec 31, 2013)

The last graph is what my eq looks like when I close both of my 5' french door openings. I get 10 dB of room gain below 20 Hz and actually have to cut 6 dB around 12 Hz to get flat. And this is with an open stairwell, 2525 ft3. GOGO XS30.


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## dboff01 (Feb 16, 2010)

I've recently added a MiniDSP 2x4 box to my system and am experiencing the same drop of signal level. For instance, I had to increase the volume on my AVR from -22dB (without DSP) to -12dB (with DSP) to achieve the almost equivalent levels shown in the below measurements.









I've got the 2x4 jumpered for RevA (0.9Vrms) and am receiving the signal from my Marantz SR7002 AVR. The BASH 500s subwoofer plate amp has sufficient gain headroom to compensate for the drop, but I am also dealing with an amplifier induced thump on transition to standby. The higher the gain knob on the amp, the louder the thump. So adding the MiniDSP to my system has now made my auto-sensing amp so annoying that I am switching it on and off regularly like a pro amp.

Like the OP, any suggestions as to improper use of MiniDSP or is the the nature of this device?


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## GCG (Aug 22, 2013)

dboff01 said:


> I've recently added a MiniDSP 2x4 box to my system and am experiencing the same drop of signal level. For instance, I had to increase the volume on my AVR from -22dB (without DSP) to -12dB (with DSP) to achieve the almost equivalent levels shown in the below measurements.
> 
> View attachment 47732
> 
> ...


I'm assuming an unbalanced MiniDSP. That's what I have. What I found when I checked the sub out on my AVR (see my signature) the output actually had a high end at "0" of around 2.0 vrms. I used a Fluke Scope Meter and a 10kΩ resistor on an old RCA cable. I set the jumper to 2V and adjusted the gain on the plate amp. That won't change the output range on the unbalanced version. It is 0.9 vrms.

I hear what you're saying about the thump, but mine obviously isn't as annoying as yours. I know on my next sub the amp will have a full ON setting either in combination with the standby or no standby at all.

Don't know if this helps but you might just try the 2V jumper to see. It can't hurt. If your sub out is in fact 0.9V then you'll just under drive the MiniDSP input. No harm.


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## dboff01 (Feb 16, 2010)

GCG said:


> I'm assuming an unbalanced MiniDSP.
> 
> Don't know if this helps but you might just try the 2V jumper to see. It can't hurt. If your sub out is in fact 0.9V then you'll just under drive the MiniDSP input. No harm.


Yes, an unbalanced using RCA connections.

I can try the jumper change for input sensitivity and see if any change, but I'm not sure why there would be. Intuitively I would think that could drop the relative input to output level even more. We'll see.


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## jtalden (Mar 12, 2009)

Bear123,
Since you are using REW it may be helpful to insert the MiniDSP in a loopback of the soundcard as the device under test (DUT). That way you can see the exact level difference across the freq range. You can see that now with the acoustic measurements, but it is not as clean as just measuring the MiniDSP directly. 

I'm just thinking that if you know the exact voltage offset across the freq range then it may provide some hints as to where to look for the problem. It may be a simple voltage offset setting on the input or output or some filter setting? Hopefully it is not a fault with the unit. If the as levels are set flat and all filters are off, I have no idea as to the problem is. I was just thinking of what I would do to investigate the issue in more detail. 

If you remove the REW mic cal and measure the soundcard with a loopback wire first you will establish a flat line level representing the soundcard loopback. Then insert the MiniDSP with all functions turned off and compare the result. The exact offset value is the difference in dB between the traces. REW will also provide the overall transfer function of the unit. You can check distortion and other characteristics see if there are any obvious problems. Then you can test all the level and filter functions in the MiniDSP to see if they are functioning normally.

It may not help, but it will provide a more detailed analysis.


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