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MiniDSP 2x4 gain for subs

5K views 11 replies 4 participants last post by  MetropolisLake 
#1 ·
So basically I got a flat response with minidsp, but, I pulled down my peaks so much that it squished the entire output. Now, my subs are really quiet. Tried to increase gain on the amp and increase output on the receiver but its not enough plus its picking up noise. I thought I could bump up the overall output but I guess not, can only cut it I guess.

Am I missing something or do I need to redo everything and bring levels up rather than cut my peaks down to the baseline on the low end of the spectrum? Attached is my before and after response. The flat line is with REW 3 db higher and I think a couple of clicks on my amp. I just want to make this line be at a higher output level.
 

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#2 ·
Your target level was set too low so the filters ended up being used as a volume control. Probably need a target level around 62 dB with that response, but difficult to be sure without seeing what it does a little further up. It also looks like a sub + main measurement rather than sub only, unless there is no crossover applied. Bear in mind you can't use filters to make a sub that rolls off at 35 Hz into one that is flat to 10 Hz, filters are really only good for dealing with the peaks above the sub's low end roll-off - to address the low end try different positions (e.g. sub in a corner), but ultimately for very low extension a sub that has a very extended low end response is required, which typically means big.
 
#3 ·
Your target level was set too low
I had no target level set period as far as I know. I just plugged it in, played it at a comfortable level that didn't wake anybody up, then adjusted the response manually. I didn't export any curves or anything from REW and as far as I know MiniDSP has no target SPL or anything of the sort.


looks like a sub + main measurement rather than sub only, unless there is no crossover applied.
This is my laptop being plugged straight into the sub amp. I didn't want to blend in the mains yet. The receiver wasn't even on.


Bear in mind you can't use filters to make a sub that rolls off at 35 Hz into one that is flat to 10 Hz, filters are really only good for dealing with the peaks above the sub's low end roll-off - to address the low end try different positions (e.g. sub in a corner), but ultimately for very low extension a sub that has a very extended low end response is required, which typically means big.
These are four 18's sitting in a granite covered box that weighs 800 pounds. That big enough? They're just not spread out, they're all under the screen so I still have nulls and peaks due to room modes, and no I'm not going to run sweeps 100 times at full blast so that's why it's not 115 db.


It seems that my mistake was to bring everything down to the level of what it is around 20 hz but the more I pulled down, the more the entire volume was pulled down, and now that I'm done there's just no saving it. Looking for specific alternatives and advice to this situation because I'm afraid I'm going to have to start over and adjust with a different strategy.
 
#10 ·
Where is the LP, and have you measured other spots around the LP just to see how the room responds? If the subs can't move, try moving the LP. (If only to see). Mode calculators leave out a couple things(IME), and those are where the subs are and where the listener is. For example, you may have subs that are flat to 7hz if you're 2' off the back wall, but might have a huge peak or null if you're more towards the canter of the room. (That part was arbitrary so don't hold any numbers against me lol)


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#11 · (Edited)
Where is the LP, and have you measured other spots around the LP just to see how the room responds? If the subs can't move, try moving the LP. (If only to see). Mode calculators leave out a couple things(IME), and those are where the subs are and where the listener is. For example, you may have subs that are flat to 7hz if you're 2' off the back wall, but might have a huge peak or null if you're more towards the canter of the room. (That part was arbitrary so don't hold any numbers against me lol)
Room is 15x20 with 9' ceilings. Subs are on one long wall. Seats are 4' from the back of the other long wall. Eventually there will be two more there for nearfield but not for now.

To visualize what I was saying about room gain vs. raw response, you can see it here, second one down on the right.

http://www.data-bass.com/data?page=content&id=80#!prettyPhoto

That's a DIY sealed 12" with a raw frequency response rolloff similar to most other sealed subs, even very large ones. Notice what happens when you put it in a room. There are multiple 10-13 db peaks as well as a 25 db null, with the overall response vaguely following the ground plane response. Perfectly normal and expected in my opinion. Yeah ideally you'd spread the subs around and also use EQ but to just look at that response in the room and say something is wrong with the sub, just isn't reality. If that's all that four 18's could put out, sure, but that's not the conversation here. Every sealed sub or even multiple sealed subs with no DSP magic is going to have similar issues.
 
#12 ·
As a follow up, this is my last sweep. Almost 115 db at 12 hz. It's usually flatter but I was kind of cranking it, probably kicked in some soft limiters on the amp. Got it to look this good by taking the MiniDSP out of the equation. I'll keep studying on it but at this point it is doing more harm than good.

 
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