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Discussion Starter #1
Hi, I have been messing with my newly purchased MiniDSP and trying to setup an LT for my sealed SI 18"s. This is a close mic measurement of each sub, you can ignore the bottom two lines. I am trying to establish what the actual qtc is of my subs (in their boxes) so that I can experiment with the LT using the Mini. The issue I am having is the question of why the entire response rolls off above ~43hz? Why the "mountain" appearance? Is this the actual response of the sub/box or could there be something else at work? It almost looks like there is a low pass crossover applied above 50hz, which there is not. The system is Onkyo TX-NR808 -> MiniDSP 2x4 balanced -> Behringer NU4-6000 -> SI 18" in ~4.2 cu ft sealed boxes. These particular measurements were taken a while ago before the Mini was in the path. The results are the same with the Mini in place.

I am still learning much about REW and general measurement principles. These measurements were taken with Audyssey turned off, dynamic EQ turned off, my mains disconnected, and one sub measured at a time while the other is off.

 

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Here is the measurement of that driver in a 4.2 cubic foot enclosure from data-basss.com. It looks like your crossover is engaged.

 

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It looks like the XO is still set to 60hz or so.


If that's the case, then your results look about what I'd expect provided those are 5db or less increments.
 

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Discussion Starter #5
I'll get some more snapshots with nothing chopped out. The AVR crossover for bass management is set at 120hz. The amp has no crossover set. This response was taken from when I was using an EP2500 with no crossover, the NU4-6000 measures the same way.

I have seen native responses similar to this, as DD posted, but not to this extreme on the higher end. The setup for measurement is that I have the UMIK-1 into the computer, REW running, then a line out cable from the computer to the front Aux inputs on the AVR. Do I need to run into and out of the AVR in a different way? The AVR is set on Stereo mode which just enables the front L+R and the sub. No other processing is applied.
 

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Quote:
Originally Posted by tuxedocivic  /t/1526380/what-does-this-close-mic-result-mean/0_100#post_24582627


Unless those are 2db increments, there's no way that's a 120hz XO. Are you sure?? If so, there's gotta be something going on.

My vote is he has his LFE xo set to 120hz, but the mains set to small with a 60-80hz xo.
 

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Discussion Starter #8
Alright, here are some updated results and, YES, I was a dummy. That's what learning is all about, right?


After doing some thinking about it, I realized that when using any of the normal analog inputs, such as the front panel Aux input, and then running the line from the computer and REW into that, even set on "Stereo", the receiver is using bass management to cross from the fronts to the subs. This is obviously not the same as the settings for what the crossover freq for the LFE channel is (which is set to 120hz). So, with my AVR setup to cross to the mains at 80 hz, the sub(s) were being crossed there as well when using anything but a multichannel input that has a dedicated LFE channel. That is why my raw response looked so funny.

TL;DR:

I have been trying to do this wrong since the beginning.



NOW I have the computer running into the AVR directly into the analog multichannel subwoofer input (used for Bluray/DVD). This bypasses all processing AND bass management. The results now make much more sense.




Green is the CORRECT raw response close mic of one of the subs.

The others are some different Linkwitz Transform setups from the MiniDSP. I'm thinking that I'll go with the red one and give that a try.


I'm going to try and calculate my actual box volume, which is going to be difficult for me since they are curved cabs. What's confusing and I still need help with is interpreting the graphs to determine what the real raw qtc is. The red trace LT is using the parameters of qtc as 1.3 and the F as 40hz. I really don't think that the box is that undersized to produce such a high qtc, but that's why I need to calculate.

When looking at the graphs, what do you estimate the qtc is (green trace)? Thanks!
 

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Discussion Starter #10

Quote:
Originally Posted by notnyt  /t/1526380/what-does-this-close-mic-result-mean/0_100#post_24583183


My vote is he has his LFE xo set to 120hz, but the mains set to small with a 60-80hz xo.

Yep, you've got it. Using the Aux inputs, the AVR was using bass management and crossing to the mains at 80hz. I have been setting up to do measurements incorrectly ever since buying the iMM-6 mic from PE a few months ago. Fortunately, that was before having any external eq for the subs anyway so it didn't really matter what I was measuring since I couldn't do much about it anyway.
I just got my UMIK-1 from Cross Spectrum last week which is why I am now trying to measure -for real-.
 

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Discussion Starter #11

Quote:
Originally Posted by tuxedocivic  /t/1526380/what-does-this-close-mic-result-mean/0_100#post_24583224


0.65

Can you explain why? And would you call the F(O) 40hz or lower? I've only been looking at pictures like this (from the MiniDSP worksheet) that show the rise just before the fall on alignments with qtc's higher than .7, and my green response seems to do that but I'm most likely viewing it wrong.

 

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In my experience, they always have a hump, even when sized right. Just Le or something, but I couldn't tell you for sure. What I was looking at was the roll off. I looked at 20 to 40hz. That was 1 octave for 9 or 10db. And 15 to 30hz. That was 1 octave for about 10 or 11db. So just under 0.707, which would be 12db/oct. But it would be interesting to hear an opinion from Ricci or someone with better knowledge of this sort of thing.
 

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Discussion Starter #14

Quote:
Originally Posted by tuxedocivic  /t/1526380/what-does-this-close-mic-result-mean/0_100#post_24583329


In my experience, they always have a hump, even when sized right. Just Le or something, but I couldn't tell you for sure. What I was looking at was the roll off. I looked at 20 to 40hz. That was 1 octave for 9 or 10db. And 15 to 30hz. That was 1 octave for about 10 or 11db. So just under 0.707, which would be 12db/oct. But it would be interesting to hear an opinion from Ricci or someone with better knowledge of this sort of thing.

Thanks Tux!
 

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Discussion Starter #15

Quote:
Originally Posted by notnyt  /t/1526380/what-does-this-close-mic-result-mean/0_100#post_24583414


Careful, you're boosting 12db @ 10hz and 8db @ 20hz. That's a good deal extra excursion. I'd run the blue curve there anyway... flatter...

Thanks notnyt! Based on Tux's estimate, I will rerun the parameter's in the worksheet and re-measure based on an initial qtc of ~.65. Over the weekend, I ran based on a qtc of .7 and a F(O) of 40hz with the target being .707 and an F of 20hz. The measured response looked very good and it sounded fantastic. Since I finally got the Mini, I've been getting much more out of my SI's than before. I really had been missing out with no EQ, bigtime.

At this point, I think I am staying within limits pretty well since each sub is only getting ~640 watts @ 4 ohms from 2 channels of my NU4-6000. They have never looked distressed or overdriven even on the craziest of scenes.


Congrats on making Home theater of the month!!!!
 

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Discussion Starter #16
This is what I set up tonight. The LT is set up for an initial F(O) of 42hz with a qtc of .65 and a target F(p) of 20hz with a qtc of .707. This seems to apply a significant amount of gain, but I am amp limited and as I said before, I really don't think I could put these drivers into the danger zone with my normal listening habits of -10 to -5 ref. Thoughts? How does this look?

Green is raw, blue is with LT:

Ignore the spl numbers, they are not accurate.

 

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Discussion Starter #18

Quote:
Originally Posted by tuxedocivic  /t/1526380/what-does-this-close-mic-result-mean#post_24585598


That is a lot of boost. Maybe set Fc lower. Seems to boost up high where it's not needed.


What is your room response?

Do I set the initial Fc lower or the target Fc?


I'm finding that the MiniDSP documentation leaves a lot to be desired. I thought that I'm supposed to enter the initial Fc into the worksheet by looking at where the peak is in the raw measured response.


Yeah, I can't talk about my room right now.
It's a complete train wreck. I had a thread about it a while back but at the moment, I've been repainting the rooms and everything is a disaster. No pictures or artwork on the walls, no room treatments, not even any curtains on the windows in the last couple of weeks. I sold all of my Polks, have no surrounds and I'm waiting for my pair of Tux 1099's to arrive. Everything is temporary right now.
 

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Sorry, you're calling it Fo. Lower that and it should lower the starting point of the LT. If I'm thinking about it right. I don't know. I did mine in my head using PEQ.
 

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I am still trying to understand how you have the line out from you PC connected to your AVR. Do you have line out from the PC to the analog DVD input on your AVR? What do you mean by the analog multi-channel subwoofer input? I know that some AVR's have multi-channel inputs for AVR's that don't have HDMI to connect to a BluRay players multi-channel analog outputs, but, I was unaware that there is a separate analog multi-channel subwoofer output on an AVR in addition to the subwoofer pre-out jack.


. Can you or someone else clarify this? I ask this mostly because I have been trying to understand how to properly setup the measurement gear that I bought off another forum member. My computer does not have HDMI and I am unsure what to hook it up to. I have a Behringer UCA-202, a phantom mic power source, and a mic. This stuff is so confusing! I am trying to get ahold of CSL to order a USB mic, but, they never answer the phone!
 
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