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Twelve 10" NHT Subwoofer Build. - Page 7

post #181 of 274
Quote:
Originally Posted by Erich H View Post

If I'm just testing the subs, is there any reason to set 'Large full range speakers'?

That's to get a good calibration loop-back, because you are using the AVR as the "sound card". Once you've got that done you should switch to the AVR's sub-out and run a sweep to see if the low end of the curve is flat. If the AVR had a way to defeat the crossover on the sub-out you could just use that for the calibration, but most AVR's don't offer that option.
post #182 of 274
Thread Starter 
First let me warn you guys that I doubt this is done properly.

On the REW site, I downloaded the calibration file for my meter. When I open REW, it flashes something saying that the calibration file has been loaded. So I assume it's ready to go? Under settings....under the soundcard tab, there is a 'calibration' tab to select a file. Should I select the file I downloaded for my specific meter?


Also, understand, I don't have my system set up properly for refrence level. I have changed so many things that it wasn't important yet. I will learn how to do that tonight. This was just a quick test to see if I'm getting something.



Okay, so here's what I did. Made sure the receiver was set to pure stereo (no other eq stuff running). I ran an optical from the computer into the Denon. Then ran a single RCA line into the input on my computer. Is that it?

At first I had no idea how loud the test tone was going to be so I set it at -45. Ran the test and got an error telling me to crank it up. So I just settled with -20. I don't know how important the correct volume needs to be.


This is what I got:





And here is my screen shot because I don't know if I should be looking at something else.








Can anyone tell me if I'm doing that right? It seemed louder than the 70 something decibles it showed. But maybe not.
post #183 of 274
I would turn up the gain on your Denon until the SPL from REW shows between 85-90dB on the response curve. Then remeasure. Overlay your new curve at 85-90dB with your 70dB curve. I strongly suspect that the near flat response down to 10Hz is just low frequency noise in the room.
post #184 of 274
Thread Starter 
Quote:
Originally Posted by Jack Hidley View Post

I would turn up the gain on your Denon until the SPL from REW shows between 85-90dB on the response curve. Then remeasure. Overlay your new curve at 85-90dB with your 70dB curve. I strongly suspect that the near flat response down to 10Hz is just low frequency noise in the room.


I'll give that a try.

What do you mean by 'low frequency noise' in the room?

When nothing is on, I think the meter is hovering around the 40 db mark.

I'll go work with it some more.
post #185 of 274
Thread Starter 
Okay, I just had 2 things that were pretty exciting. (for me anyway)

#1. I forgot that I was just listening to music last night and only had the bottom 6 on! I just now turned them all on a minute ago. So those tests above are only with 6.

#2. I set REW to sweep from 8hz to 30 hz. My meter was reading when I couldn't hear anything on the low end of that sweep. I was watching the meter. I also went to look at my subs and they were moving very slow and I couldn't hear anything real low, but I did hear some things shaking somewhere. I've never seen subs move that slow with no sound! I can't hurt them can I?



It's not calibrated for the proper SPL at all. I think it's about 20 db's off, and obviously, I'm no where near max anyway. I will need to figure out how to calibrate.

I'm hooked up from the computer using an optical cable. So I guess I need to change that to calibrate? I don't understand why it's not calibrated right because I am using the file that is suppose to correct it for my exact meter.
post #186 of 274
Erich,
There are two different processes going on in to set this up correctly, first the soundcard cal process and then you can load in the Meter's .cal file.

So you just need to run a rca from the Left channel out back to the PC and calibrate the loop and generate a soundcard .cal file.

Once you have that you connect to the LFE out and see if it's still flat in the lowend, but now showing the Low Pass setting for the LFE crossover.

At that point you load the .cal file for the meter and connect to the amp, then you can calibrate the level with the meter.
post #187 of 274
Thread Starter 
Quote:
Originally Posted by NEO Dan View Post

Erich,
There are two different processes going on in to set this up correctly, first the soundcard cal process and then you can load in the Meter's .cal file.

Okay, I know what you mean there.


So you just need to run a rca from the Left channel out back to the PC and calibrate the loop and generate a soundcard .cal file.

I'm dumbing it down a bit....Do I need a 1/8" to double RCA cable? Then run the left RCA to the meter and the right one to the Denon?

Once you have that you connect to the LFE out and see if it's still flat in the lowend, but now showing the Low Pass setting for the LFE crossover.

I'll need to think more on that sentence....


I will start gathering up all my cables.


Like this?

post #188 of 274
Erich,
your picture did not show up.

To calibrate you will be making acontinous loop from PC optical out back to the PC mic input, so it's a rca from the AVR's Left ch out into the L ch of the RCA to stereo 1/8" adapter plugged into the PC's mic input.

Once you've generated the .cal file switch the RCA cable over to the LFE out on the AVR and look at the FR with the filter.

Basically you can't calibrate the loopback off the AVR's LFE out because it will attempt to compensate for the roll off of the LFE's crossover. That's why you need the Left channel out on the AVR.
post #189 of 274
Thread Starter 
Okay, I'll start working on that tonight. I need another splitter.

The picture in my last post was just the setup photo copied from this page:

http://www.hometheatershack.com/foru...on-basics.html


Not sure why it didn't show up for you though.

Well, I'd love to stick around and chit chat, but I have cables to buy and calibrations to get worked out, then light fixtures to vibrate!!
post #190 of 274
Erich,

By low frequency noise, I mean just that. In all environments, there is a certain amount of background noise in the room. If you are in a closed room, the walls and door will filter out most of the external sound above 100Hz. Below 100Hz, there will be some amount of noise that gets into the room because the walls are not stiff enough to stop it. How much low frequency noise you have will be a function of how close you are to roads, what AC there may be in your building, etc. Generally as frequency goes down, the noise level goes up.

Once you get both calibrations done for REW (SPL meter and soundcard) click on the Spectrum tab in REW, then click the start record button in the bottom right corner. This puts REW in an RTA (Real Time Analyzer) mode. This will show you in real time what the noise spectrum in the room looks like. Do this with everything turned off. You can also play music or movies back and see in real time what the frequency content is. The results will surprise you.
post #191 of 274
You probably have everything you need to make the calibration loop.

post #192 of 274
Thread Starter 
Thanks for the info guys. Jack, I'm curious about that lower end stuff as well. Looking directly at my meter, it was registering pretty high for those frequencies that I couldn't even hear. When nothing was on, REW (calibrated in that above graph) was showing over 20 db lower than when 10 hz was played. I guess tomorrow will tell because the calibration isn't right yet.


Dan, you're right, I did have everything I needed. I went looking for a decent splitter at an open store but couldn't find one. Stopped at a friends and he couldn't find one. Geeze.


Now I see that I could have just kept the optical on it. Looks fairly simple now that you put up that editted drawing.
post #193 of 274
Tech Support Operators are standing by
post #194 of 274
Quote:
Originally Posted by NEO Dan View Post

Tech Support Operators are standing by


One of these days when I get to my subs, you are going to have to drive to my house and do all this for me. That is the Tech Support I expect from you!

BTW, nice setup you got there Erich. I really need to show this to my wife, prove to her I am not the only one who likes bass.
post #195 of 274
Thread Starter 
Okay, there might be another piece of the puzzle I'm missing......sorry. I know this is easy for most of you guys, but it's a first time for me.


I have it all wired up correctly. I hit the calibrate button and it runs the subwoofer signal, it says to adjust the number (default was 75) to match what the meter shows. Well, my actual meter was showing well over 80 db, but the live meter reading in the program (red flashing numbers) was only showing around 72? But what good is that if the program doesn'ty know what volume I am set on?

So do I adjust the Denon's volume to bring the db down to 75db on my meter? Or do I just not even look at the actual meter and only pay attention to what the reading is flashing in the program?

Did that make any sense?? I'm not so sure it did, so you might have to read that again!



Or do I actually need to set my Denon at the 75 db reference level BEFORE doing any of this? And then test at reference level?




P.S. - you guys should be laughing because I had my Denon at -15 and then hit the calibration button. It sent the sub frequencies through and the entire room started to shake. I hit cancel pretty quick!
post #196 of 274
Thread Starter 
Quote:
Originally Posted by Aiden Chase View Post

One of these days when I get to my subs, you are going to have to drive to my house and do all this for me.



Dan only does first class airline flights with the limo waiting for him outside on arrival. All expenses paid, with free beer of his choice.
post #197 of 274
Quote:
Originally Posted by Erich H View Post

Or do I actually need to set my Denon at the 75 db reference level BEFORE doing any of this? And then test at reference level?

That's what I did to take my measurements.

Run the test signal and adjust the volume of your AVR so that your meter is reading as close to 75db as possible. Then go to REW and set the level on the meter calibration box to match what is being displayed in REW.

Give that a whirl then post up results.
post #198 of 274
Thread Starter 
Quote:
Originally Posted by Jailer View Post

That's what I did to take my measurements.

Run the test signal and adjust the volume of your AVR so that your meter is reading as close to 75db as possible. Then go to REW and set the level on the meter calibration box to match what is being displayed in REW.

Give that a whirl then post up results.


I'll give that a shot. The only thing is, for my subs to be at 75 db, they Denon volume is like -40 or something like that! And when the meter says 75db, the REW meter is showing much lower.

Damn, looks like I may need to actually read the manual!!! I'm surprised no one has yelled "RTFM" yet!
post #199 of 274
Alright, I'll give this a shot (I've only done this a few times myself). Go into Settings, under the "Mic/Meter" tab next to where you load the Cal file is a button for "Calibrate SPL". I think you need to press that then it will play a test tone and allow you to tell REW what the SPL meter is reading.
post #200 of 274
Quote:
Originally Posted by Erich H View Post

I'll give that a shot. The only thing is, for my subs to be at 75 db, they Denon volume is like -40 or something like that! And when the meter says 75db, the REW meter is showing much lower.

Damn, looks like I may need to actually read the manual!!! I'm surprised no one has yelled "RTFM" yet!

Mine was pretty close to that too (Onkyo 805) IIRC.

The readme file is pretty good but a little on the vague side. But it does have lots of pictures. The REW forum at HT shack is a good place to go for info.

It took me a few tries to get it right. If you check my sub build thread you'll see I was way off base until I got it figured out. Just keep playing around with it and you'll get it eventually.
post #201 of 274
Thread Starter 
Okay, looks like more reading is in order for me. Sorry guys.

Here's what I saw. Denon set at -34. Sub calibration is being sent out. My meter is showing 94 db but REW is telling me it's only 55. It asks me to select the number matching my meter, but does that mean my actual meter, or what REW is showing me my reader is hearing?



I'll keep reading.


By the way, I was not given an option to save the calibration. So I don't know. I'll be back shortly.
post #202 of 274
Erich,

When your SPL meter shows 94dB and REW asks for the meter reading, you enter 94. Done, finished. After doing this, your SPL meter and REWs metering function should show the same SPL. Make sure that the settings on your SPL meter are correct. I believe that it should be set to C weighting, slow, but I would check the REW documentation to be sure. I believe that REW saves the calibration value. Once entered, you won't need to do anything even if the program is shut down.

You should probably have the output level from your sound card/REW up near full. Then adjust the volume control on your Denon to get the actual SPL you want to take the measurement at. About 85dB at 1m should be fine. This will give you a good signal to noise ratio in the measurement chain.
post #203 of 274
Thread Starter 
Jack, I was able to just lower everything down and make it match at 75db. Thanks.

I'll go through my method. If anyone's still with me on this, please find any faults if you have the time.


#1. Fronts set to 'Large' on Denon.

#2. Optical cable from computer to Denon.

#3. RCA from 'front left' into stereo 'Y' to computer input.

#4. RCA from SPL meter into other side of 'Y'.

#5. Under soundcard settings -
a. I select 'use left channel for calibration reference?
b. hit 'check levels' and adjust Denon volume so meter reads 75db

#6. Under mic/meter settings -
a. Select 'C' weighted ?????
b. for calibration, load the correct radioshack meter file (33-2055)

#7. Main menu - hit 'measure' go from 10-200 hz

#8. Save that curve and load it into the sound card calibration setting?

#9. Uncheck 'C weight' and retest. This should give a flat line.

#10. Unhook loop, deselect 'use left channel for calibration', then run again to find the final outcome???



If that's correct, here is what I have:

The blue line was the sound card calibration. Looks odd to me.

The green line was to test to see if it worked. It's flat like it should be, so maybe it's okay?

The red line is the final result. My subs are crossed over at 90 I believe.







At no time did I change the SPL meter, it was left at the 70 'notch' on the wheel the whole time. But when I was done, I decided to change the actual meter's knob up to 90, then measured again with everything else the same. The graph looked different, but why should it?
post #204 of 274
That looks better
post #205 of 274
Looks like the c weight option is selected for the cal file, mabey

at least you get a flat loopback on the left RCA
post #206 of 274
Try looping back from the LFE RCA out to see if the curve is flat into the lowend and showing the roll off of the LFE x-over

don't forget to clear the cal file for the meter and uncheck the c weight, but leave the one for the soundcard loaded.

Please show the FR plott down to 5Hz or lower


LFE out should look like this:
post #207 of 274
If that turns out to be your FR at the listening position, you should consider your self extremely lucky. Is there any smoothing applied to the measurement?
post #208 of 274
Thread Starter 
Dan, I'll try to reload those graphs and then do what you said with the LFE. I did hook the LFE up for a second, but doing so introduced a bit of hum that I've never heard yet. So I just stopped.


I'm not sure what you mean by 'smoothing'. I don't have any EQ's on, it's set to stereo. The meter is in the primary listening position.
post #209 of 274
Quote:
Originally Posted by Erich H View Post

Dan, I'll try to reload those graphs and then do what you said with the LFE. I did hook the LFE up for a second, but doing so introduced a bit of hum that I've never heard yet. So I just stopped.

I didn't mean to the amp, this is for confirming the Left channel loop back calibration is OK for use with the LFE out on your AVR. run the RCA from the LFE out to the MIC input on the PC. No connection to the amp or meter is needed for this.

FYI none of the sound card loop back calibration needs a connection to the meter or amp, no meter correction file, make sure to unchecked c weight.

A good idea for when you making a cal file is to mute the main speakers by selecting the B speaker outputs on your AVR. That way your not bugging SWMBO whilst she is getting her beauty sleep You should also mute the mains when you are making actual measurements of the subwoofer to avoid picking up output from the mains.

Quote:
Originally Posted by Erich H View Post

I'm not sure what you mean by 'smoothing'. I don't have any EQ's on, it's set to stereo. The meter is in the primary listening position.

Now that look at the graph I don't think there is any applied, the control is located in the trace adjustments for the measurement.
post #210 of 274
Thread Starter 
Well darn, I just put a RCA splitter for the LFE. Sent one side to the amp, the other side back to the computer for the loop. So the amp was still getting the signal and playing.

Here's what it was overlayed on top of the previous chart:




So having the subs playing was no good in the LFE test? Back to the drawing board.....
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