# help! MiniDSP causes big distortion on big bass hits



## MetropolisLake

I have four 18's with a Speakerpower amp. I got my response flat as a pancake with a MiniDSP. Problem is though, with big bass hits when several frequencies are being thrown around like with an explosion, I get all kinds of distortion. The bottom end falls off and it's almost like the equivalent of bass-y white noise with no treble. I don't know what to adjust. I'm not boosting much, only one frequency around 65 hz. Everything else is being cut, basically 3 major frequencies, everything else is fine tuning. Everything below 30 hz was already flat, so I'm not boosting that part in the MiniDSP. 

I have tried to bump down my output gain 10 db but I'm having to crank up the amp gain and crank up the receiver output to compensate, and the overall output is still too low. If there is a procedure I need to be doing to get it working right please let me know. I'm just kind of lost right now. With actual material playing at any volume, it actually sounds better with no DSP even though my frequency response is flat. 

Current frequency response at the seat, bottom end is 10 hz, top is 100:


----------



## tonyvdb

are you sure your amp has the headroom for all that? Sounds like something is running out of steam. (your input or output levels could be to loud and your overloading them but that would likely be a clipping sound not distortion).


----------



## MetropolisLake

tonyvdb said:


> are you sure your amp has the headroom for all that? Sounds like something is running out of steam. (your input or output levels could be to loud and your overloading them but that would likely be a clipping sound not distortion).


I have a 4,000 watt Speakerpower and I'm listening to stuff at -20 db. Yes, I have the headroom. The only time I can unleash the amp is when the MiniDSP is out of the mix. Amplifier output is not even on the radar.


----------



## Wayne A. Pflughaupt

Not much information to go on, not knowing what specific speakers or amp you have, how you have things connected, the amps configured, no details on the specific EQ filters in use, etc.



MetropolisLake said:


> I'm not boosting much, only one frequency around 65 hz. Everything else is being cut, basically 3 major frequencies, everything else is fine tuning. Everything below 30 hz was already flat, so I'm not boosting that part in the MiniDSP.


Ah yes, the old “cut don’t boost” myth. There’s no free lunch - any EQ sucks up headroom. The problem with cuts is that they lower the overall level of the bass, so you end up turning up the amp to compensate. See here and here for details.

Aside from that, your graph – well, it’s just too pretty . Either it’s smoothed (unsmoothed graphs are best for sub response) or you used like a million EQ filters, which is not a good way to go.




MetropolisLake said:


> The only time I can unleash the amp is when the MiniDSP is out of the mix. Amplifier output is not even on the radar.


What model miniDSP are you using? Some of them have severely limited headroom.

Regards, 
Wayne


----------



## MetropolisLake

Wayne A. Pflughaupt said:


> Not much information to go on, not knowing what specific speakers or amp you have, how you have things connected, the amps configured, no details on the specific EQ filters in use, etc.


It is four Ultimax 18's in sealed boxes but all under the screen. As mentioned before it is a Speakerpower 4,000 watt amp, the SP1-4000. I'd have to dive into the MiniDSP and type out all the filters for an exact list. As previously mentioned I'm only boosting one band significantly at all, I think around 65 hz, about 6 db. Everything else was just pulling down expected peaks from room mode issues. 




Wayne A. Pflughaupt said:


> Ah yes, the old “cut don’t boost” myth. There’s no free lunch - any EQ sucks up headroom.


I could live with "some" lower headroom but the action I took by both pulling down peaks and pulling down the output gain by 10 db does not seem to be a step in the right direction at all. It is so far off what I would consider to be even remotely correct that I even decided to make a post here.  





Wayne A. Pflughaupt said:


> The problem with cuts is that they lower the overall level of the bass, so you end up turning up the amp to compensate.


Yes but if you boost it aren't you potentially clipping the MiniDSP? I don't know what else would cause the bad distortion that I experienced. Also, my amp already has DSP programming in it to get the subs flat, otherwise sealed subs have a rolloff that you have to correct for. So realistically, the low end is already boosted to counteract this rolloff. If I see that area being flat like it should be, then I see a big boost where a known and expected peak from a room mode should be, what would be the correct action to take, boost the known to be correct low end even more, or kill the incorrect peak from the room mode issue? 




Wayne A. Pflughaupt said:


> Aside from that, your graph – well, it’s just too pretty.


Believe it or not, supposedly Dennis Erskine shoots for this same 1.5 db window, BEFORE he applies any DSP. I cannot confirm this. 




Wayne A. Pflughaupt said:


> Either it’s smoothed (unsmoothed graphs are best for sub response) or you used like a million EQ filters, which is not a good way to go.



It's not smoothed. With smoothing it's basically a flat line. It's probably 10 filters but most are very minor. Here is what it looks like before MiniDSP. Notice the "no smoothing" in the screenshot below. The MiniDSP was on here but I think I had all the bands bypassed. Don't pay attention to the big null on the right. The big dip was where my seats previously were, scooting the seats back 1' brought it up to the level of the other graph. I boosted this area to flatten it out. Also at the time I had a LFE boost on the amp which is why it was rising to the left. I turned that down and it flatted it out. Pretty much everything was brought down to the level of 28 hz here. That seemed to be where it was actually correct. This frequency happens to be exactly where my room gain kicks in. Regardless, not boosting the LFE knob on the amp makes everything from 28 hz on down be flat with no MiniDSP correction. 











This is what it looked like with only 3 DSP bands, cutting 37, 54, and I forget what else I did. Again, disregard above 65 hz on this one, there was a null, had to scoot my seats back to avoid it. Will have to add more subs to smooth this out. The other bands were minor touch-ups. 37 and especially 54 were pretty major comparatively being 6 db off. It sounded fine with only these 3 bands being active, I could live with that, but am unsure as to if the distortion I initially complained about would be an issue with 3 vs. all the ones I'm using now. 













Wayne A. Pflughaupt said:


> What model miniDSP are you using? Some of them have severely limited headroom.


The common 2x4.


----------



## Wayne A. Pflughaupt

MetropolisLake said:


> I'd have to dive into the MiniDSP and type out all the filters for an exact list.
> 
> It's probably 10 filters but most are very minor.


Minor filters are of no value and indeed can cause problems. I’d suggest reviewing my Minimal EQ article.




MetropolisLake said:


> Wayne A. Pflughaupt said:
> 
> 
> 
> What model miniDSP are you using? Some of them have severely limited headroom.
> 
> 
> 
> The common 2x4.
Click to expand...

There’s your choke point. If it’s the unbalanced version, IIR its maximum input headroom is only .9Vrms. Speakerpower specs the SP1-4000’s input sensitivity as 4 dBV, which translates to 1.6 Vrms. What’s probably happening is that at the point you get enough signal from the receiver to get the subs singing, the mini is clipping. And as you’ve experienced, clipping in the digital realm is especially nasty.

Regards, 
Wayne


----------



## MetropolisLake

Wayne A. Pflughaupt said:


> There’s your choke point. If it’s the unbalanced version, IIR its maximum input headroom is only .9Vrms. Speakerpower specs the SP1-4000’s input sensitivity as 4 dBV, which translates to 1.6 Vrms. What’s probably happening is that at the point you get enough signal from the receiver to get the subs singing, the mini is clipping. And as you’ve experienced, clipping in the digital realm is especially nasty.


That seems like it would be an issue with any amp, not just Speakerpower. Audessey on my Marantz actually set the subs to be -12 db. If a MiniDSP can't handle a very common receiver's output at -20 db with the subs at -12 db, then what good is it? Is there a more appropriate one?


----------



## Wayne A. Pflughaupt

MetropolisLake said:


> Audessey on my Marantz actually set the subs to be -12 db. If a MiniDSP can't handle a very common receiver's output at -20 db with the subs at -12 db, then what good is it?


A receiver’s level indicators have no meaning in absolute voltage output (Vrms). The figures are referenced only to the maximum output of the unit itself: A -20 dB setting on any receiver basically means “we’re at 20 dB below our maximum output.” 

As an example, take two receivers, one with a maximum output of 1 volt and one of 5 volts. Even if you set them both for “-20 dB” (or any other figure), you still have a 4-volt output differential between the two. 



> Is there a more appropriate one?


MiniDSP offers a balanced version of the 2x4 that has 2 volts headroom (it can be used unbalanced). Or, get a professional-grade device like the Yamaha YDP2006.

Regards, 
Wayne


----------



## MetropolisLake

Yeah I just got off the phone with Seaton, he acted like the balanced version would do what I want. Also thought the normal version could be made to work though. This would require boosting the gain on my Speakerpower though, and when I do that I'm picking up way more noise than I believe is acceptable. This isn't exactly my favorite idea.

He also more or less said knock it off with the smoothing of every little anomaly.


----------



## Wayne A. Pflughaupt

MetropolisLake said:


> Yeah I just got off the phone with Seaton, he acted like the balanced version would do what I want. Also thought the normal version could be made to work though.


You could get a signal booster and insert it after the mini, which would allow you to boost the signal coming into the amp and run its gains lower.




> This would require boosting the gain on my Speakerpower though, and when I do that I'm picking up way more noise than I believe is acceptable.


If that’s happening with a subwoofer, either Speakerpower's S/N noise figures (95 dB) are bogus, or the miniDSP has is generating a lot of noise on its outputs.




> He also more or less said knock it off with the smoothing of every little anomaly.


Sounds like he’s read my stuff - hee hee! 

Regards, 
Wayne


----------



## MetropolisLake

> If that’s happening with a subwoofer, either Speakerpower's S/N noise figures (95 dB) are bogus, or the miniDSP has is generating a lot of noise on its outputs.


Before this, what I've experienced with sub noise is that you either have a high pitched hiss, which I've experienced with Crown XLS and Behringer iNukes, or you have a ground loop. The noise I'm getting is in between these tones, have no idea how to describe it but it's more of a low midrange thing.


----------



## MetropolisLake

Here's what I'm dealing with here, and I'm just totally lost. The blue is what my raw response looks like when plugged into my receiver. The rest of the lines that are 30 db down are what happens when I simply plug the MiniDSP in. I don't understand this. I have been watching both the input and output gain and they stay below -10 which is in the green, which supposedly means it is good to go. All filters are bypassed, this is nothing but sending the signal through the MiniDSP. According to the blue, basically all I need to do is bump down 40 hz somewhat and I'm golden. Then I plug in the MiniDSP and I have other issues that need attention. It just gets worse with louder levels. If I had not been watching the input gain it might be a different story. I'm literally ready to throw that thing in the trash. At this point it sounds best not EQ'ing it at all. I can't even plug in the DSP without it wrecking the response. 

Why on earth is it making that null way worse? Why is it dropping 30 db on the low bass?


----------



## JohnM

Looks like there are crossover filters active in the miniDSP for the output(s) you are using. There are several sections where filtering can be applied in the miniDSP plugin configuration so make sure you check them all.


----------



## MetropolisLake

JohnM said:


> Looks like there are crossover filters active in the miniDSP for the output(s) you are using.


Strange, I can't recall setting up such a thing and have no idea why I would.


----------



## JohnM

A crossover may be on by default depending on the type of plugin.


----------



## MetropolisLake

There was a 1,000 hz low pass filter in place. Not sure why that would cause the null to be worse or for below 30 hz to look like a ski slope. Guess I'll play with it some more and see if it is correlated.


----------

