# Comments on my first measurements?



## Guest (May 26, 2009)

Any thoughts on my first measurements. The first graph is sub only (custom built Rythmik set at 20Hz mid dampening), the second is sub+mains, and the third is a waterfall of the sub+mains. Any thoughts on how this looks?

One question that I have as an amateur... why is 10hz to 40Hz so much louder than 40Hz to 200Hz? Is this how it's supposed to be?


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## Wayne A. Pflughaupt (Apr 13, 2006)

> why is 10hz to 40Hz so much louder than 40Hz to 200Hz? Is this how it's supposed to be?


Every sub/room is different.

Impressive extension, for sure. Any other location options that might minimize that 55 Hz null?

Regards,
Wayne


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## Guest (May 26, 2009)

Thanks for the reply Wayne. I do have some other placement options. I'm mostly trying to confirm that I am using REW correctly. 

Is it true that I can put the sub in the primary seating position and then take readings at various spots in the room to see what it would like like if I placed the sub in that location? If so, does it matter which direction I point the sub when I put it in the primary listening position (I have a front-firing sub). 

Also, my primary use is for music listenting, with home theater a close second. As a result, I suspect I would prefer to focus more on that 30hz to 80hz region?

Oh, one other question for now... when I originally created my soundcard calibration file, I was connected to my pre-pro via the soundcard's analog outs. I have since switched to the soundcard's SPDIF output. Do I need to create a new soundcard calibration?

Thanks!


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## brucek (Apr 11, 2006)

> I have since switched to the soundcard's SPDIF output. Do I need to create a new soundcard calibration?


How do you propose to do that?



> I suspect I would prefer to focus more on that 30hz to 80hz region?


Your bottom end is a bit heavy for music.



> Is it true that I can put the sub in the primary seating position and then take readings at various spots in the room


Yes, read this.



> does it matter which direction I point the sub when I put it in the primary listening position


Not really. Put it on the floor in front of the couch and point it at your system. Once you find a good spot with the RTA, move the sub there and fine tune the position.

brucek


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## Wayne A. Pflughaupt (Apr 13, 2006)

elee,

brucek pretty much covered it. I'll just add:



> Also, my primary use is for music listenting, with home theater a close second. As a result, I suspect I would prefer to focus more on that 30hz to 80hz region?


Yup. Lots going on in that region with bass instruments, and your response there is pretty rough (as you can see). 

Regards,
Wayne


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## Guest (May 27, 2009)

brucek, Wayne,

Thank you for the replies! 

To the soundcard calibration question... I guess I hadn't quite thought it through all the way. I guess I MUST use the analog outs on the soundcard to do the calibration. :doh: 

Any thoughts besides placement as the reason for the lesser performance in the mid-bass region? I've done a fairly thorough job of treating room corners with superchunk bass traps. 

Thanks!


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## Wayne A. Pflughaupt (Apr 13, 2006)

> Any thoughts besides placement as the reason for the lesser performance in the mid-bass region?


Nope. You'll probably have to consult with the knowledgeable folks at our DIY Subwoofer Forum for that.



> I've done a fairly thorough job of treating room corners with superchunk bass traps.


Although traps can reduce the distance between the worst peaks and valleys, their main function is to reduce low frequency ringing. Your waterfall chart shows yours are doing that quite nicely. :T

Regards,
Wayne


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## weverb (Aug 15, 2008)

elee532 said:


> Any thoughts besides placement as the reason for the lesser performance in the mid-bass region?





elee532 said:


> (custom built Rythmik set at 20Hz mid dampening)


What about playing with the phase and crossover point? Also, can you change or try different settings. Maybe this one is boosting the 20Hz region too much. :huh: There is some eq reference here:

http://www.rythmikaudio.com/faq.html#eq


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## Saoof1 (May 29, 2009)

Make sure you have the crossover adjusted all the way up on the sub itself and adjusted accordingly on the receiver. Seeing your response on the low end try the 28hz mode as well.


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## Guest (May 29, 2009)

Thanks for the suggestion. The readings above do have the crossover turned all the way up. I'm hoping to make some adjustments this weekend and will try the 28Hz setting.


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## Guest (May 30, 2009)

Can someone confirm that I am using the RTA feature correctly to position my sub? Here's what I think...

Spectrum Tab
Mode: RTA 1/24 Octave
FFT Length: 65536
Averages: 2
Window: Rectangular
Y Axis: dB

Generator:
Pink Noise
Sub Cal
Set RMS Level to 75dB

Put sub in main listener location
Press play button on Generator
Press record button in Spectrum window
Move SPL meter around the room and look for flattest response


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## JohnM (Apr 11, 2006)

Pretty close, but you will get much more stable readings in the low frequency end by using Pink PN (Periodic Noise) rather than Pink Noise, you can get good results with Pink PN even without any averaging. You can also use a shorter FFT length for faster updates of the RTA display, 32768 is a good compromise between update speed and frequency resolution.


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## Guest (Jun 1, 2009)

I posted a quick reading of my sub+mains with the sub moved from the front to the back of the room. This looking like some improvement?

Thanks.


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## Guest (Jun 7, 2009)

I finally found some time today to play around a bit more. I tried to get my seating as close as possible to 38% from the back wall. 

The first graph below shows some readings in the locations that I have available... blue = back corner, brown = front left corner, green = front middle, and red = along side wall right next to seating (kind of like an end table). Unless I am misunderstanding, the side placement (red graph line) looks to be about the smoothest. 

The next graph shows the sub gain turned down a bit and the sub tuned to 28Hz Low Dampening. This seemed about as flat as I could get. Any thoughts on how this looks? I can't seem to do anything about that drop between 90 and 100. Is this something that I should worry about?

Thanks!!


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## weverb (Aug 15, 2008)

elee532 said:


> The next graph shows the sub gain turned down a bit and the sub tuned to 28Hz Low Dampening. This seemed about as flat as I could get. Any thoughts on how this looks? I can't seem to do anything about that drop between 90 and 100. Is this something that I should worry about?


Looking good. I would do a plot with the mains on and see if the dip goes away. Also, with the side placement, just make sure the bass is not localized when listening to anything. Other than that, that is a good looking graph.


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## Guest (Jun 9, 2009)

Thanks for the feedback! Unfortunately, it seems you're one step ahead of me... the bass is definitely localized now. I haven't made any adjustments to phase/distance settings. Maybe this will help? If not, are there other options for dealing with localization?

Thanks!


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## weverb (Aug 15, 2008)

elee532 said:


> Thanks for the feedback! Unfortunately, it seems you're one step ahead of me... the bass is definitely localized now. I haven't made any adjustments to phase/distance settings. Maybe this will help? If not, are there other options for dealing with localization?


Usually localization can some what be addressed by crossover points, but usually it is mostly based on location of the sub. What xo setting are you using? Looks like 80Hz. Try something lower like 60Hz. and see if you notice a difference. Can your mains go down to 60Hz.? It may be a good idea to do a graph of just your mains. Try them at different xo points and see what they can do. Since your Rythmik is doing a good job going so low and if your mains can handle it, you can try a xo as low as 40Hz. possibly.

Also try the "blue" location. You may still get "localization" of the bass when the sub is in the rear, but try it any way.


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## Guest (Jun 9, 2009)

Thanks. I'll experiment different crossover frequencies and see what I come up with. Can you tell me... when getting a graph of my mains, do I test with both of them connected or just one of them?

Thanks.


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## weverb (Aug 15, 2008)

elee532 said:


> Thanks. I'll experiment different crossover frequencies and see what I come up with. Can you tell me... when getting a graph of my mains, do I test with both of them connected or just one of them?
> 
> Thanks.


For what you are looking for, you can do both at the same time.


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## Guest (Jun 14, 2009)

I took a few more readings today...

The first is a graph of my mains. The red line is with my pre-pro crossed over at 80Hz and the blue is crossed over at 60Hz. There doesn't appear to be a much difference. However, I am surprised at how all over the place this reading is. Is this normal? (BTW, these are Salk SongTowers)

The next one is my sub + mains with my pre-pro crossed over at 60Hz. Looks like the dip around 100Hz from my earlier readings is pretty much gone. However, still a major dip around 167Hz. 

Any advice?


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## weverb (Aug 15, 2008)

Looks pretty good, but if you still have the localization problem then you might be better off moving the sub. Did you try the rear corner (blue response in previous graph) again?

Also, I am surprised there was no difference between 60 and 80Hz. Maybe brucek can shed more light on this.

The dip at 167 Hz. can probably be fixed with room treatments.


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## Guest (Jun 14, 2009)

Thanks weverb. After a brief listen, the localization seems less, but not gone, at 60Hz crossover. I have not tried the rear corner again, but I do plan to.

brucek, any light to shed?

Would I use a 2" or 4" absorption panel or some other type of treatment to address the dip at 167Hz? How would I go about determining the position for the treatment? 

FYI, I do currently have many of the room corners treated with superchunk bass traps. 

Thanks!


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## brucek (Apr 11, 2006)

I think the sub + mains looks fairly good.

At 60Hz, I can't imagine localizing a sub.

To determine if the 167Hz mains dip is a result of cancellation between the two speakers or between one speaker and the room, try measuring each one separately. A small movement of one might make a lot of difference.

brucek


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## weverb (Aug 15, 2008)

elee532 said:


> Would I use a 2" or 4" absorption panel or some other type of treatment to address the dip at 167Hz? How would I go about determining the position for the treatment?


Check out this other cool feature REW has. It is call Energy Time plots (ETC). brucek has some good info in this post:

http://www.hometheatershack.com/for...rew-analysis-voiceover-studio.html#post170156

It should help show if all your reflection points have been addressed.


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## Guest (Jun 19, 2009)

I took a few more readings. Any help understanding them would be most appreciated!

As suggested earlier, the first graph shows readings of each speaker. Red is the sub and mains together, green is the left front speaker, and gold is the right front speaker. Does this offer any insight into the dip around 169Hz? :dontknow:

The next graph shows my sub and mains with my pre-pro crossed over at 60Hz. The red line shows the crossover setting on my sub set at about one-o'clock (scale ranges from 40Hz to 160Hz). The gold line shows the crossover setting on the sub at about eleven-o'clock. The red line looks a bit flatter, but I wonder whether dialing up the crossover setting on the sub is contributing to my localization issue. I'm really confused by how the crossover setting on my sub works with the crossover setting of my pre-pro... and how do I go about finding the best setting for each?? :scratch:

The next graph shows my mains without the sub. Green is pre-pro set to large with no sub, black is 60Hz pre-pro crossover, and blue is 80Hz crossover. Not posting this one for any reason in particular, though it does seem an odd looking graph to me? ...actually, I just realized something, this contradicts my earlier posting showing no difference between 60Hz and 80Hz crossover setting. Guess I must have screwed up something the first time. Why do my mains dip like that between 30Hz and 80Hz?

Finally, I posted my first attempt at an ETC reading. To be honest, I have no idea how to read it. :huh:


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## weverb (Aug 15, 2008)

elee532 said:


> As suggested earlier, the first graph shows readings of each speaker. Red is the sub and mains together, green is the left front speaker, and gold is the right front speaker. Does this offer any insight into the dip around 169Hz? :dontknow:


Ok, I am going to take a stab at answering this but hopefully Wayne or brucek will give us better information. It looks like both of your mains may be causing the dip. I think you can address this by trying to move them around. If not, I still think it can be handled by a treatment panel. By the way, that is a good looking graph even with the 167Hz dip!



elee532 said:


> The next graph shows my sub and mains with my pre-pro crossed over at 60Hz. The red line shows the crossover setting on my sub set at about one-o'clock (scale ranges from 40Hz to 160Hz). The gold line shows the crossover setting on the sub at about eleven-o'clock. The red line looks a bit flatter, but I wonder whether dialing up the crossover setting on the sub is contributing to my localization issue. I'm really confused by how the crossover setting on my sub works with the crossover setting of my pre-pro... and how do I go about finding the best setting for each?? :scratch:


I would put the sub xo back to the red line setting. I would think you would want to bypass the sub xo and only use the pre-pro crossover.



elee532 said:


> The next graph shows my mains without the sub. Green is pre-pro set to large with no sub, black is 60Hz pre-pro crossover, and blue is 80Hz crossover. Not posting this one for any reason in particular, though it does seem an odd looking graph to me? ...actually, I just realized something, this contradicts my earlier posting showing no difference between 60Hz and 80Hz crossover setting. Guess I must have screwed up something the first time. Why do my mains dip like that between 30Hz and 80Hz?


That's what we should see. I think this is correct. :scratchhead:



elee532 said:


> Finally, I posted my first attempt at an ETC reading. To be honest, I have no idea how to read it. :huh:


You want to zoom in and only look at the first 10-20 milliseconds, not out to 2 seconds. You want to find all the major peaks in that time span and figure out the distances. Combinations of that distance will help you narrow down what surfaces need more absorption put on them. Here is an example of mine:



That second peak right after the initial one is either my back wall (couch is against my back wall) or the couch its self. The peak that I measured out to be 6 feet tells me something within 6 feet of the mains or mic needs to be addressed. I believe it is the ceiling. Then you can see the much smaller peaks that will then need to be address. This graph also helps when you trial place a panel to be sure you have it located correctly.

How did I do brucek/Wayne? :sweat:


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## brucek (Apr 11, 2006)

elee532, you have to switch the ETC plot from DBFS to %FS as weverbs plot shows.

The peaks will show the extra distance the signal had to travel to reach the mic. So a back wall at 3 feet from the mic will show up at 6 feet in the ETC.

brucek


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## weverb (Aug 15, 2008)

So my comments were correct? :rubeyes:


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## JohnM (Apr 11, 2006)

weverb said:


> So my comments were correct? :rubeyes:


Seemed reasonable to me 

The sub's own crossover should be set as high as it goes (or defeated if that is an option) so that the pre-pro is handling the crossover.

One thing the ETC highlights is fairly high distortion - those smaller peaks that happen before the main peak are distortion harmonics. Suggests your sub may be working fairly hard even though the measurement levels don't look especially high.


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## Guest (Jun 20, 2009)

JohnM said:


> The sub's own crossover should be set as high as it goes (or defeated if that is an option) so that the pre-pro is handling the crossover.


This is still confusing me. :dizzy: My pre-pro is set for 60Hz crossover. As the two measurements below show (red line shows the crossover setting on my sub set at about one-o'clock (120Hz?) - the dial on my sub ranges from 40Hz to 160Hz - and the gold line shows the crossover setting on the sub at about eleven-o'clock (80Hz?).) 

This higher crossover setting on the sub shows a flatter response line. Doesn't this reflect that the sub is now producing output all the way up to 120Hz? Wouldn't this be contributing to my localization issue? If my pre-pro is set to 60hz crossover, shouldn't the sub only be getting signal at 60hz and below? :dizzy:



JohnM said:


> One thing the ETC highlights is fairly high distortion - those smaller peaks that happen before the main peak are distortion harmonics. Suggests your sub may be working fairly hard even though the measurement levels don't look especially high.


This is really vexing as well. The gain on my sub is at about 50%. Moreover, the bass extension frequency switch on the sub is set to 28Hz and Damping is set to Low. I would think these settings would reflect about the easiest load possible on the sub?

Thanks for any additional info!


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## JohnM (Apr 11, 2006)

elee532 said:


> This is still confusing me. :dizzy: My pre-pro is set for 60Hz crossover. As the two measurements below show (red line shows the crossover setting on my sub set at about one-o'clock (120Hz?) - the dial on my sub ranges from 40Hz to 160Hz - and the gold line shows the crossover setting on the sub at about eleven-o'clock (80Hz?).)
> 
> This higher crossover setting on the sub shows a flatter response line. Doesn't this reflect that the sub is now producing output all the way up to 120Hz? Wouldn't this be contributing to my localization issue? If my pre-pro is set to 60hz crossover, shouldn't the sub only be getting signal at 60hz and below? :dizzy:


Crossovers provide a smooth transition, not a sharp cutoff. If you play with the target settings in REW you can see (in the target curve) what the crossover response looks like for various crossover frequencies for a subwoofer or non-full range speaker. For a 60Hz crossover the sub's output is down 6dB at 60Hz and down 25dB at 120Hz. By bringing the sub's own crossover into play as well you speed up the rolloff of the sub's output but create a dip in the transition between sub and mains. 

The localisation issue may be a result of the distortion. The ETC shows significant harmonics from 2nd right up to 6th (so for a 50Hz input that means distortion products at 100, 150, 200, 250 and 300Hz), and these are at the output of the sub, they are not reduced by changing the crossover setting. It does seem odd, as high distortion would typically be seen in a sub being driven past its capabilities but from the extension you have your sub seems very capable - unless that extension is being achieved by boosting the sub's low end and that boosting is contributing to the distortion.


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## Guest (Jun 20, 2009)

OK, as if I'm not confused enough already... :gah:

It seems I am getting completely different results depending on the Start and End Frequency that I use for my sweep. The blue line is when I use 0 to 200Hz for my sweep. The purple line is when I use 0 to 15,000Hz for me sweep. 

The results are obviously dramatically different up to about 20Hz. Any insight as to what's going on? 

Thanks!


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## JohnM (Apr 11, 2006)

That is very odd. You don't have a procesor that applies any sort of dynamic EQ or dynamic loudness do you?


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## Guest (Jun 21, 2009)

No dynamic EQ or loudness on my pre-pro (Emotiva LMC-1). When I take my readings, pre-pro reads "bypass mode, PCM48k." Sounds Effects are checked as disabled on the Enhancements tab for the playback devise in Windows. Here's another graph using various sweep settings.

Red = 0 to 200Hz
Gold - 0 to 500Hz
Green = 0 to 1,000hz
Aqua = - to 5,000Hz
Black = 0 to 15,000Hz

I have no idea what to make of this?? :gah:


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## JohnM (Apr 11, 2006)

The difference in the various sweeps is how long the signal spends at the lowest frequencies. If the sub is very non-linear below 20Hz changing the time spent there would affect the level of distortion products. You may get a sense of that from watching the driver as the sweep progresses. You might get more consistent results by changing the sweep start frequency to 10Hz or higher.


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## Guest (Jun 22, 2009)

JohnM, thank for the reply! I understand what you are saying re: the length of time at each frequency during the sweep might differ depending on the sweep range. However, I'm kind of lost after that (i.e. non-linear sub?). I'm pretty much an amateur at this stuff. 

FYI, I did try starting my sweep at 10Hz instead of 0, but the results were the same as above. 

What does all of this say about my sub? Which results, if any, results are accurate?

Thanks!!


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## weverb (Aug 15, 2008)

It almost looks like your amp is switching through the different damping options. It looks similar to the last three graphs on this page:

http://www.rythmikaudio.com/eq.html

:huh:

Is there a way to check the incoming signal response to the sub to eliminate it as the cause? This might help narrow down where the problem is coming from. You know, test something like:

1. Signal coming out of the computer before the pre-pro.
2. Signal coming out of the pre-pro before the sub.
etc.

brucek has mentioned similar tests to others. If I remember I did something like it to test if my pre-pro's xo was working properly.


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## brucek (Apr 11, 2006)

> Is there a way to check the incoming signal response to the sub to eliminate it as the cause?


Test the receivers response out the LFE port by using REW.

Just as you would test a loopback cable from line-out to line-in to get a flat response, simply include the receiver in that loop and take a measure. You have to fuss with the levels a bit when doing the Check Levels routine, but it's easy enough.

Connect soundcard line-out to receiver AUX-in, and receiver Sub-out to soundcard line-in, and measure.

Be sure the meter cal file is cleared and the soundcard cal file is loaded.

The response should be just like one of the REW targets, except it will roll off down low. Measure from 0Hz.

brucek


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## Guest (Jun 23, 2009)

brucek,

I'm think I am misunderstanding your instructions. When I follow what I think are the connection instructions you provided above, the output meter reads about -15 but the left/right input meters read nothing. Is the SPL meter supposed to be connected in the mix somewhere?

Thanks and sorry for my ignorance here!


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## brucek (Apr 11, 2006)

> Is the SPL meter supposed to be connected in the mix somewhere?


No, you're measuring the electronic frequency response of your receiver by itself, just as if it was a loopback cable. No meters, no speakers - you're measuring the electronics. 

Connect soundcard line-out right channel to receiver AUX-in right channel, and receiver Sub-out to soundcard line-in right channel. Run the Check Levels and Calibrate routine and Measure.



> but the left/right input meters


You'll only be looking at the right channel input meter. The left channel is not used.

brucek


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## Guest (Jun 24, 2009)

Thanks brucek. I'm a little closer now, not sure what I was doing wrong before. However, when running Check Levels, nothing I seem to can get the Output and Right Input meters to balance. The output meter is always louder than the input meter by something like 12db. 

Also, can you confirm for me that "soundcard line-out right channel" is the same as the right Front speaker connector?

Thanks for any advice!


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## Ricci (May 23, 2007)

So this is a Rythmik sub? Which one 12" or 15"? 

I've seen artifacts like that below 15hz before but not that dramatic:scratchhead:. Looks almost like a cal file got added or something.You will get different results depending on your sweep range and duration. From what I have seen the longer the sweep stays in that range the more accurate it will be. A 1M 0-200hz sweep is going to be better than a 128k 0-24000hz sweep for the bass range. The very short sweeps seem to exaggerate the bass below 15hz a little. THIS IS OPPOSITE OF WHAT YOU ARE SEEING THOUGH! You usually have a LOT of compensation added to the readings in that range, which can do some screwey things from multiple cal files. I've never seen it affect things all the way up above 23hz though and with that big of a difference. Usually it's just a few db. 

How hard is your sub being driven on these sweeps? Looks almost like a limiter is kicking in or something. The Rythmiks are small sealed subs and they are servo controlled and eq'd flat down to the really deep bass. That would cause the driver to be pushed very hard below 20hz even with a moderate volume sweep. What length were those sweeps? Can you keep the sweep range the same like 0-200hz and run one at each length and see if there is a difference there between the shorter and longer ones?


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## brucek (Apr 11, 2006)

> can you confirm for me that "soundcard line-out right channel" is the same as the right Front speaker connector?


Yep, usually.



> However, when running Check Levels, nothing I seem to can get the Output and Right Input meters to balance. The output meter is always louder than the input meter by something like 12db.


I'm a bit confused by that statement. It makes no sense to me. You use the receivers volume control to set whatever level you desire on the soundcards input meter.

First connect a single loopback from line-out (right) to line-in (right) and do a Check Levels and Calibrate @75 and a Measure to be sure you get a flat line. 

Now all your levels are setup in the soundcard. Then insert the receiver into that loopback and fuss with the receivers volume control when you run the Check levels routine. Don't touch the soundcards input or output levels, because you already have them in a good spot as if you were measuring a cable, but instead you've placed a receiver in the loop.

Get it?

brucek


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## Guest (Jun 27, 2009)

brucek said:


> First connect a single loopback from line-out (right) to line-in (right) and do a Check Levels and Calibrate @75 and a Measure to be sure you get a flat line.


brucek, I'm sorry, but I'm confused. When I connect line-out to line-in, I don't actually get any sound from my sub or speakers. So, what/where am I looking to get a 75db reading?

Thanks!


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## brucek (Apr 11, 2006)

> When I connect line-out to line-in, I don't actually get any sound from my sub or speakers. So, what/where am I looking to get a 75db reading?


After you run the Check Levels routine, you run the Calibrate routine. You don't hear any sound (of course), but you set the level to 75dB with the thumbwheel in the Calibrate routine to _ fool_ REW's SPL meter into thinking the level is 75dB. How else would REW know where to place the trace on the graph. You have to tell it that the level of the loopback signal is 75dB, so that's where the trace will lie. The advantage of doing the loopback first before you insert the receiver in the loop is to first verify that a cable without the receiver is indeed flat, and to get a good setup of the soundcards line-in and line-out before the receiver is inserted in the loop.

Then you remove the loopback and connect the receiver and go through the Check Levels routine using the receivers volume control to get the correct input level.

brucek


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## Guest (Jun 27, 2009)

Thanks brucek! This is hopefully a correct attempt at measuring my pre-pro's response...


I set Windows Volume to 100. 
I connected soundcard line-out (front right speaker) to soundcard line-in right channel. 
I cleared meter cal file and kept soundcard cal file loaded. 
I ran check levels. 
I adjusted the sweep level to -20 which is where the out and right meters werer equal
I ran "Calibrate" using REW subwoofer cal signal as signal source
I set to 75 and clicked finished
I took a measurement using 0 to 15,000Hz, -20 level, 256k length, 1 sweep. 
.
The result is shown in the first graph below (green line). Does it look as it's supposed to?


Next, I connected soundcard line-out right channel to pre-pro aux-in right channel, and pre-pro sub-out to soundcard line-in right channel and ran Check Levels. 
I kept all settings the same as described above and only adjusted my pre-pro volume until out and right were equal (at around -20). I had to crank the volume on my pre-pro up to about 95%. Is this common?
I ran a measurement using the same settings as above. The results are shown in the second graph (red line). 

Do these both look as they should?

Thanks!


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## weverb (Aug 15, 2008)

Looks correct to me. brucek will have to verify. It looks to be doing just like John stated:



JohnM said:


> For a 60Hz crossover the sub's output is down 6dB at 60Hz and down 25dB at 120Hz.


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## brucek (Apr 11, 2006)

> Do these both look as they should?


Yep, they look correct.

I would display the measurement graph with an upper limit of 200Hz to get a better look, and I might add the 60Hz REW target line to give yourself assurance that it's tracking close to spec, but it looks fine. There's nothing wrong with your receiver....

brucek


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## weverb (Aug 15, 2008)

Would you say brucek that this pointing to the sub as the problem with his graph variances?


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## Guest (Jun 28, 2009)

Here's a closeup. Any idea what that weird "blip" is about at 120Hz? Also, is it normal that I needed to crank my pre-pro's volume up to 95% to get the output and input levels even?

I'll work on some of the measurements suggested above by Ricci next. 

Thanks again for all the help!!


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## brucek (Apr 11, 2006)

> Any idea what that weird "blip" is about at 120Hz?


It would not be the receiver. It would be your computer and REW causing a small hitch in the signal sweep at that point.



> is it normal that I needed to crank my pre-pro's volume up to 95% to get the output and input levels even?


I would set the REW sweep level up to a higher level (~-6dB) to offer the receiver more voltage, so you won't have to turn its volume up so high during the test.

BTW, turn on the REW target @60Hz to observe how the receiver tracks. Match it's passband level to the target for a good comparison.



> Would you say brucek that this pointing to the sub as the problem with his graph variances?


The sub or the room. It's almost never the receiver...

brucek


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## weverb (Aug 15, 2008)

brucek said:


> The sub or the room. It's almost never the receiver...


So now he should do a nearfield plot of the sub using the same testing he did post #34 correct? Basically place the mic a few inches from the driver and do the same sweeps in post #34 to see if it is the sub. This should help remove the room correct?


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## brucek (Apr 11, 2006)

> So now he should do a nearfield plot of the sub using the same testing he did post #34 correct?


Yeah, that's correct, although doing it outside would be even better. I take it this is a servo type sub - so he wouldn't need to check a port nearfield.

brucek


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## weverb (Aug 15, 2008)

brucek said:


> Yeah, that's correct, although doing it outside would be even better. I take it this is a servo type sub - so he wouldn't need to check a port nearfield.
> 
> brucek


Yes it is a servo sub.


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## brucek (Apr 11, 2006)

> it is a servo sub.


I wonder if the servo mechanism is acting up. Certainly, he shouldn't be experiencing the high distortion that is revealed in his ETC plots shown in earlier posts.

brucek


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## Ricci (May 23, 2007)

Yep. My guess is that it's the servo or some form of limiting going on in the response below 25hz. 

Elee532,

Try a moderate volume 0-200hz sweep set at 128K and then follow up with a sweep at each setting up to 1M, keeping everything else the same when you get a chance. My guess is that the longer sweeps will show a decrease in the lowest bass. After that start at a very low volume and do a few sweeps while increasing the volume 3db at a time and keep the sweep used exactly the same in between. (just turn your reciever up, be careful so you don't overdrive your sub) This should reveal whether it is some form of limiter in the sub or a problem with it.


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## Guest (Jul 2, 2009)

The first graph shows four tests. Each was run using a 0 to 200Hz sweep. I used the "seperate traces" option to make for easier reading.

Green=128k
Red = 256k
Gold=512k
Aqua=1m

Graph two shows 0 to 200Hz sweeps set at 128k length with my pre-pro set increasing volume levels. The pattern doesn't seem to change much despite the change in volume.

What can you make of this?

Thanks!


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## weverb (Aug 15, 2008)

Have you tried doing any nearfield plots of the driver also?


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## Ricci (May 23, 2007)

Good suggestion Weverb.

Elee532,

Seeing as the 3 longer sweeps all correlate really well and have the lower bass represented well, I'd hazrd to say that you should probably stick with the 512K sweep length from now on. I think that your sub is fine.


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## brucek (Apr 11, 2006)

> I think that your sub is fine.


Why is the 128K sweep so poor?

brucek


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## JohnM (Apr 11, 2006)

brucek said:


> Why is the 128K sweep so poor?


Definitely the $64,000 question! Could the sub have some sort of auto standby that is not turning it on in time for the faster sweep? Certainly very odd.


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## brucek (Apr 11, 2006)

My initial thought was that the subs servo-mechanism was acting up whenever a fast attack signal was applied.

Then I wondered if it was perhaps his computer that was a bit challenged and couldn't handle the start of the faster sweep.

It's the first time we've ever seen this though.

brucek


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## Guest (Jul 3, 2009)

weverb said:


> Have you tried doing any nearfield plots of the driver also?


I wasn't positive about how to do a nearfield measurement, but I took a shot...


I couldn't get the sub outside, so I just left it where it was in the room.
I put the SPL meter mic about 3" from the center of the sub cone.
I ran Calibrate and set my pre-pro until I got a reading of about 75db. This led to my pre-pro volume being set at about 8.0 (max setting is 80.0). I took a reading using 128k and 256k sweep lengths. Just for the of it, I turned the volume control up to 15 and took the same two readings again. Here's what I got...

Green = volume 8.0, 128k
Red = volume 8.0, 256k
Gold = volume 15.0, 128k
Aqua = volume 15.0, 256k

FYI, the sub is set to the Always On setting. 

Also, can someone confirm... I've been setting my SPL meter for C Weighting, Slow Response. Is this correct?

Thanks.


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## brucek (Apr 11, 2006)

> I've been setting my SPL meter for C Weighting, Slow Response. Is this correct?


Yes....


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## Guest (Jul 3, 2009)

brucek said:


> Yes....


Thanks. Were my nearfield readings done correctly? Do they offer any insight?


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## brucek (Apr 11, 2006)

> Were my nearfield readings done correctly? Do they offer any insight?


It looks like you did everything correctly, although I am a bit confused by the statement:_I ran Calibrate and set my pre-pro until I got a reading of about 75db._

Generally, you first run the Check Levels routine (during which time the pre-pro volume is adjusted to get a reading of 75dBSPL on the RadioShack meter).

Then the Calibrate routine is run to match the REW SPL meter to the 75dB reading of the Radio Shack meter.

Anyway, there's no way to establish what's wrong without substituting one of the possibilities. You have to substitute either the measuring computer or the subwoofer.

brucek


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## Guest (Jul 3, 2009)

brucek said:


> It looks like you did everything correctly, although I am a bit confused by the statement:_I ran Calibrate and set my pre-pro until I got a reading of about 75db._
> 
> Generally, you first run the Check Levels routine (during which time the pre-pro volume is adjusted to get a reading of 75dBSPL on the RadioShack meter).


Yeah, I meant to say Check Levels not Calibrate. 

I do have a second computer that I can give this a try with. Will try to do so over the weekend. 

Thanks!


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## Guest (Jul 4, 2009)

I gave this a try on another computer... 0 to 200Hz sweep using 128, 256k, 512k, and 1M sweep lengths (graph 1, seperated traces is turned on). Graph 2 shows 0 to 20,000Hz sweeps at 128k and 1M. 

Computer 1 is my HTPC... 2.5ghz dual core, Gigabyte GA-E7AUM-DS2H motherboard using the onboard Realtek Digitial Input and Output. 

Computer 2 is a Lenovo ThinkPad X61T, Core2Duo 1.6Ghz, using USB Soundblaster X-Fi. 

As you recall, my initial question surfaced when my results from a 0 to 200Hz sweep were different from the results from a 0 to 20,000Hz sweep between 0 and 20Hz (graph 1 below for reference). 

Anyway, comparing these with the earlier readings, it looks the computer was the source of the difference and not the sub or pre-pro. Is my understanding correct? (I suppose if I was really motivated, I'd connect the X-Fi to Computer 1... just don't have the time or energy right now.). Any thoughts on why this might be the case?

Thanks!


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## brucek (Apr 11, 2006)

> Any thoughts on why this might be the case?


It does look like the computer is the source of the problem. I made the suggestion to check that because before I got my fancy new laptop, I use to have a second computer that I would use for REW, and it was certainly challenged by REW and would always stumble at the start of a sweep and I would have to try quite a few times before it didn't hitch at the beginning.

I'm surprised that the computer giving you the problem is the faster one of the two you've tried, but who knows what other resources you have tying up the bus besides running REW.

Anyway, looks like you should use the thinkpad for your testing from now on....

brucek


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## Guest (Jul 12, 2009)

I did some tweaking today using the ThinkPad for my readings. Not surprisingly, I now have more questions. 

1. The first graph below shows a major dip at around 150Hz from my right front speaker. It seems to even out when both speakers are on. Is this kind of thing to be expected?

Blue = Sub + Both mains
Gold = Sub + RF
Red = Sub + LF
Green = Sub only

2. I also played around with moving my seats and front speakers. The green line in graph 2 shows my seats moved forward about 12" and my front speakers moved about 24" closer to the front wall. Better?

3. All of my readings thus far were taken with my sub set at 28Hz/Low Damping. The purple line in graph 2 shows my sub setting changed to 20Hz/Low Damping. Looking better?

4. Is there something that I can do to address those dips at 71Hz and 172Hz? Should I just keep trying different speaker/seating/sub locactions? Is there any method to narrowing in on the seemingly infinte number of combinations of these three factors?

5. Graph 3 shows a reading from 200Hz to 2,000Hz. This is clearly way choppier. Is this normal?

6. How does the waterfall graph look? Are my bass traps paying off?

Thanks!!


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## Wayne A. Pflughaupt (Apr 13, 2006)

> 1. The first graph below shows a major dip at around 150Hz from my right front speaker. It seems to even out when both speakers are on. Is this kind of thing to be expected?


It happens, especially in asymmetrical rooms. 



> 2. I also played around with moving my seats and front speakers. The green line in graph 2 shows my seats moved forward about 12" and my front speakers moved about 24" closer to the front wall. Better?


Not really – levels below 30 Hz are significantly reduced.



> 3. All of my readings thus far were taken with my sub set at 28Hz/Low Damping. The purple line in graph 2 shows my sub setting changed to 20Hz/Low Damping. Looking better?


If you mean “better than graph 1,” the answer is yes.



> 4. Is there something that I can do to address those dips at 71Hz and 172Hz? Should I just keep trying different speaker/seating/sub locactions? Is there any method to narrowing in on the seemingly infinte number of combinations of these three factors?


The only problem is 71 Hz. The rest of it is perfectly normal.



> 5. Graph 3 shows a reading from 200Hz to 2,000Hz. This is clearly way choppier. Is this normal?


Yes.



> 6. How does the waterfall graph look? Are my bass traps paying off?


Looks good, but we’d have to see a “before” waterfall to say for sure.

Regards,
Wayne


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## brucek (Apr 11, 2006)

> major dip at around 150Hz from my right front speaker. It seems to even out when both speakers are on. Is this kind of thing to be expected?


Of course. You can add the red and gold line together yourself and end up withe result of the blue....



> The green line in graph 2 shows my seats moved forward about 12" and my front speakers moved about 24" closer to the front wall. Better?


No, it's worse.



> Is there any method to narrowing in on the seemingly infinite number of combinations of these three factors?


Fourth factor. Adjust your subs phase control, since 71Hz is at your crossover area.



> Graph 3 shows a reading from 200Hz to 2,000Hz. This is clearly way choppier. Is this normal?


It's called comb filtering. Normal. Turn on the smoothing feature to reveal the underlying trend.



> How does the waterfall graph look? Are my bass traps paying off?


Compared to what?

brucek


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## 1972nosay (Jul 20, 2009)

I think ,all is too difficult to undestand!I need to study the software and I'll make my first test.
:hide:


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