What does this close mic result mean? - AVS Forum
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post #1 of 30 Old 04-08-2014, 07:08 AM - Thread Starter
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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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post #2 of 30 Old 04-08-2014, 07:32 AM
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You chopped off your scale. Would help to include it. This naked response is not all that uncommon for sealed subs. What is the crossover in your receiver set to?
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post #3 of 30 Old 04-08-2014, 08:02 AM
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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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post #4 of 30 Old 04-08-2014, 08:04 AM
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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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post #5 of 30 Old 04-08-2014, 08:27 AM - Thread Starter
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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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post #6 of 30 Old 04-08-2014, 08:37 AM
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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.
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post #7 of 30 Old 04-08-2014, 10:21 AM
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Quote:
Originally Posted by tuxedocivic View Post

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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post #8 of 30 Old 04-08-2014, 10:21 AM - Thread Starter
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Alright, here are some updated results and, YES, I was a dummy. That's what learning is all about, right? tongue.gif
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. mad.gif

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! biggrin.gif
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post #9 of 30 Old 04-08-2014, 10:27 AM
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Quote:
Originally Posted by dtsdig View Post

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

0.65
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post #10 of 30 Old 04-08-2014, 10:27 AM - Thread Starter
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Quote:
Originally Posted by notnyt View Post

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. tongue.gif I just got my UMIK-1 from Cross Spectrum last week which is why I am now trying to measure -for real-. smile.gif
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post #11 of 30 Old 04-08-2014, 10:39 AM - Thread Starter
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Quote:
Originally Posted by tuxedocivic View Post

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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post #12 of 30 Old 04-08-2014, 10:47 AM
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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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post #13 of 30 Old 04-08-2014, 11:00 AM
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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...
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post #14 of 30 Old 04-08-2014, 11:10 AM - Thread Starter
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Quote:
Originally Posted by tuxedocivic View Post

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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post #15 of 30 Old 04-08-2014, 11:17 AM - Thread Starter
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Quote:
Originally Posted by notnyt View Post

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!!!! biggrin.gif
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post #16 of 30 Old 04-08-2014, 05:47 PM - Thread Starter
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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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post #17 of 30 Old 04-08-2014, 06:18 PM
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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?
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post #18 of 30 Old 04-08-2014, 07:03 PM - Thread Starter
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Quote:
Originally Posted by tuxedocivic View Post

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. smile.gif 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. frown.gif
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post #19 of 30 Old 04-08-2014, 07:48 PM
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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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post #20 of 30 Old 04-09-2014, 04:18 AM
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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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post #21 of 30 Old 04-09-2014, 04:20 AM - Thread Starter
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Quote:
Originally Posted by tuxedocivic View Post

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.

Sorry Tux, the terms I'm using are off of the MiniDSP site and worksheet. There's an excel sheet that you plug values into, F(O) and qtc and then it spits out values to copy/paste into the biquad filters of the mini interface.
I'll give what you suggested a try. Thankfully, the UMIK-1 makes setup quick and easy.

Thanks!
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post #22 of 30 Old 04-09-2014, 10:27 AM - Thread Starter
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Here are some more results. Firstly are some new measurements using various f and qtc parameters for the LT setup in the MiniDSP:



I left it set to the orange one. This was using 30hz for f with a qtc of .9 as the current parameters with the target f set to 20hz and qtc at .707. It seems to smooth it out nicely without an excessive amount of boost.
Also, in regards to guessing at the actual qtc, I did some measurements and my box comes in right around 4.1 cu ft. According to a few box calculators I tried out, the SI 18" would require a box size of 5.9 cu ft for a native .707 qtc. I think .9 seems about right but others have way more experience with this stuff than I do.

The next graph has measurements of just my right sub and includes the raw close mic response, the LT's close mic response and then both responses from the main listening position. Like I said, my room is a train wreck right now and I am not expecting this to look good. Over the next few months, the room(s) will be put back together and room treatments will be added as well as 2 more SI 18"s in the back of the room plus a trio of Tux 1099's up front and Volt V10's as surrounds. It's at that point that I will really be concerned about what the room is doing and how I can improve it.



Lastly, this one shows one sub's close mic raw response compared to both subs running the LT mentioned at the main listening position. This is with only the subs running with no Audyssey and no other eq.



You can see where everything completely tanks above 50hz.

Thoughts about the close mic responses and the LT setup are welcome. As far as the LP sweeps, there's nothing for it right now and it would be wasted effort to attempt any fixes at the moment. biggrin.gif
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post #23 of 30 Old 04-09-2014, 10:39 AM
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Nice. 25db room gain at 5hz biggrin.gif

The rest. Ugly cool.gif Haha...

Crossing over to your mains will likely smooth out the 60 to 100hz region. Depending on how that goes, you may end up pretty flat and smooth from 15 to 100hz. Just tweak from there and you'll be good.

Only one sub?
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post #24 of 30 Old 04-09-2014, 10:59 AM - Thread Starter
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Quote:
Originally Posted by tuxedocivic View Post

Nice. 25db room gain at 5hz biggrin.gif

The rest. Ugly cool.gif Haha...

Crossing over to your mains will likely smooth out the 60 to 100hz region. Depending on how that goes, you may end up pretty flat and smooth from 15 to 100hz. Just tweak from there and you'll be good.

Only one sub?

LOL, yeah, I know!
No, two subs up front. Two more will be in back.
Would you recommend crossing the 1099's at 60hz once they are built and running in a couple of months?

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post #25 of 30 Old 04-09-2014, 11:31 AM - Thread Starter
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Quote:
Originally Posted by Martycool007 View Post

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!

Marty, my computer does not have an HDMI either. I am running a headphone jack to RCA cable out of the laptop to the multichannel analog subwoofer input on the receiver, like you had guessed at. This is the only way I have to get the signal into the AVR while bypassing all crossovers and DSP settings.
Why do you need to call CSL? Just order online.
Yes, it can all be confusing. One step at a time. wink.gif
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post #26 of 30 Old 04-09-2014, 11:34 AM
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Quote:
Originally Posted by dtsdig View Post

LOL, yeah, I know!
No, two subs up front. Two more will be in back.
Would you recommend crossing the 1099's at 60hz once they are built and running in a couple of months?

Nice! I like that execution. cool.gif

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post #27 of 30 Old 04-09-2014, 11:39 AM
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Nice! I like that execution. cool.gif

Hell yeah. smile.gif

My Dual 18" LLT subs 120dB down to 10hz

 

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post #28 of 30 Old 04-09-2014, 11:46 AM - Thread Starter
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Thanks guys. Some day I'll put up a summarized build thread here. It's all over at HTS for now.
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post #29 of 30 Old 04-09-2014, 12:01 PM
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I'd try 60, 70, 80 and see what happens. How much power you putting on them (1099)? If receiver power a 60hz XO is probably just fine. Measure the results and see. An 80hz XO will still have added output down to 60hz and I wouldn't doubt if it ends up the best result anyways.
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post #30 of 30 Old 04-09-2014, 12:07 PM - Thread Starter
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I'll be running off the receiver. When the time comes, I'll try each option and measure.
Thanks!
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