Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 346 - AVS | Home Theater Discussions And Reviews
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Old 06-05-2014, 10:35 PM
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Yes, sorry Jim, I was being pedantic.
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Old 06-06-2014, 08:48 AM
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Quote:
Originally Posted by 3ll3d00d View Post

Some more distortion graphs coming up which might be interesting on the subject of 2nd and 3rd harmonic distortion & quantities therefore, at least at sub bass frequencies anyway.

These are taken from the RTA using CEA-2010 tones centred at 18, 19 and then 20Hz. The level is ~110dB (musicians earplugs essential!), I have 2 reasons to take such measurements; firstly I had a problem that my old amp was rather optimistically rated so I have replaced it & want to be sure this one has the power required, secondly to decide how much of an LT is really feasible at my usual listening levels.

IMO, if increasing the SPL shows a substantial increase in distortion, then your either clipping the amp or exceeding the linear excursion limits of the bass driver (in the case of a sub where XO components are absent in lieu of active circuitry).

I am pointing this out because from 95db to 105db the THD increases from about 4% to almost 13% Somewhere in that region your running out of power or xmax. A 85db test may yield still more insight. Are you applying low end boost? Are these ported or sealed subs? How loud do you generally listen?

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Old 06-06-2014, 10:51 AM
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Originally Posted by jim19611961 View Post


IMO, if increasing the SPL shows a substantial increase in distortion, then your either clipping the amp or exceeding the linear excursion limits of the bass driver (in the case of a sub where XO components are absent in lieu of active circuitry).

I am pointing this out because from 95db to 105db the THD increases from about 4% to almost 13% Somewhere in that region your running out of power or xmax. A 85db test may yield still more insight. Are you applying low end boost? Are these ported or sealed subs? How loud do you generally listen?

yes I agree, the reason for these tests was to determine how much clean output my system is really capable of so I can decide whether to add more drivers or not. I am pretty certain I'm not running out of power (though am changing the amp again soon for other reasons). 

 

I rarely listen to music at more than -20 so transient peaks should be no more than 85dB, films are rarely more than -10 so LFE peaks of 105dB (though what the actual max peak might be with combined effects of other channels I don't know). Having said that, I don't watch many of the sorts of films that have peak LFE output (and if I do, I'm not convinced I'd hear even 20% 2nd harmonic distortion given the sort of soundtrack that is on such films :D).

 

It is a sealed sub, 15" Fi SP4 in a 65L cabinet with an LT applied that adds around 4dB by 20Hz (rising from ~35Hz) and adjusts theoretical Q from 0.71 to 0.5.

 

The high THD at 105dB is at 16Hz btw, the measurements suggest to me that a single 15" sub is not really capable of serious clean 16Hz output (not that this is a surprising fact but still nice to quantify it). I also noticed that my projector mount and/or screen was vibrating during some of these tests so I'm not sure the extent to which the measurements are distorted (no pun intended) by that. I did notice a comment in the PSA thread by Tom V that inroom THD measurements are inherently noisy.

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Old 06-06-2014, 11:03 AM
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Quote:
Originally Posted by 3ll3d00d View Post

yes I agree, the reason for these tests was to determine how much clean output my system is really capable of so I can decide whether to add more drivers or not. I am pretty certain I'm not running out of power (though am changing the amp again soon for other reasons). 

I rarely listen to music at more than -20 so transient peaks should be no more than 85dB, films are rarely more than -10 so LFE peaks of 105dB (though what the actual max peak might be with combined effects of other channels I don't know). Having said that, I don't watch many of the sorts of films that have peak LFE output (and if I do, I'm not convinced I'd hear even 20% 2nd harmonic distortion given the sort of soundtrack that is on such films biggrin.gif ).

It is a sealed sub, 15" Fi SP4 in a 65L cabinet with an LT applied that adds around 4dB by 20Hz (rising from ~35Hz) and adjusts theoretical Q from 0.71 to 0.5.

The high THD at 105dB is at 16Hz btw, the measurements suggest to me that a single 15" sub is not really capable of serious clean 16Hz output (not that this is a surprising fact but still nice to quantify it). I also noticed that my projector mount and/or screen was vibrating during some of these tests so I'm not sure the extent to which the measurements are distorted (no pun intended) by that. I did notice a comment in the PSA thread by Tom V that inroom THD measurements are inherently noisy.

How much power do you have?

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Old 06-06-2014, 11:19 AM
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Not to say that this is all there is, but very few manage a clean output @ 16hz > 100db.


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Old 06-06-2014, 11:32 AM
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Originally Posted by jim19611961 View Post


How much power do you have?

The amp used in these measurements is a Focux D12. There are no reviews of this anywhere though so the only spec available is the rating for an 8ms burst at 1kHz and allowing 1% THD (i.e. about as generous as you can get), on this basis I have 7.2kW available. My winisd model says the driver needs ~2.5kW to reach xmax.

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Old 06-06-2014, 11:47 AM
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Quote:
Originally Posted by 3ll3d00d View Post

The amp used in these measurements is a Focux D12. There are no reviews of this anywhere though so the only spec available is the rating for an 8ms burst at 1kHz and allowing 1% THD (i.e. about as generous as you can get), on this basis I have 7.2kW available. My winisd model says the driver needs ~2.5kW to reach xmax.

http://www.focux.us/support-doc/spec/D_amps_spec_v2.pdf

http://store.ficaraudio.com/sp415/

1 ohm or 2 ohm version?

I modeled your driver and box:



This says you run out of xmax at about 105db @16hz. Not sure the accuracy here though.

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Old 06-06-2014, 11:53 AM
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2 ohm wired to present a 4ohm load, I can post my model & precise LT/correction filter later. I am swapping this amp for a speakerpower SP1-6000 though, the focux appears to be a hairdryer in disguise (audible from a few rooms away)

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Old 06-06-2014, 12:00 PM
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Quote:
Originally Posted by 3ll3d00d View Post

2 ohm wired to present a 4ohm load, I can post my model & precise LT/correction filter later. I am swapping this amp for a speakerpower SP1-6000 though, the focux appears to be a hairdryer in disguise (audible from a few rooms away)

Thought of making a muffler for it? biggrin.gif

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Old 06-06-2014, 01:19 PM
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Is there a way to get the sweep for ONLY the Left or Right speaker without unhooking them speaker itself with HDMI, also sub only? My AVR can't turn off the Mains just turn them down.

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Old 06-06-2014, 01:29 PM
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Originally Posted by mijotter View Post

Is there a way to get the sweep for ONLY the Left or Right speaker without unhooking them speaker itself with HDMI, also sub only? My AVR can't turn off the Mains just turn them down.
Use asio and pick channel 1 (for L) or channel 2 (for R). I am not sure what HDMI does via the Java driver if you are using that.
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Old 06-06-2014, 03:35 PM
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Originally Posted by mijotter View Post

Is there a way to get the sweep for ONLY the Left or Right speaker without unhooking them speaker itself with HDMI, also sub only? My AVR can't turn off the Mains just turn them down.

 

The instructions for which channel to select are in the guide.  If you read the appropriate Guide section, then you should not be having an issue.  Can you be more specific as to what problems you are encountering?

 

If your HDMI supports only two channels, then the only way to isolate the sub for measurements is to disconnect the speaker wires to the left and right channels.  I believe you mentioned earlier that this might be difficult for you, but that is the way to do it.  Unhook the speakers carefully either at the AVR side, or at the back of the speaker.  If your HDMI supports a full 7.1 configuration, then simply select the LFE channel as described in the guide.

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Old 06-09-2014, 08:13 PM
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Hello

Last year I started using REW, discovered unacceptable inadequacies and soon spun off into DIY world where I built 3 BF THTLP's , a 24" and 2 30' for my LR.
My current and maybe last (ha-ha) sub in the Submaximus" a thread over in the DIY section. It's BIG . . .there's lots of pictures
So now I'm testing it inside the house and expect to be able to integrate it into the rest of the system, excluding for now, the BF subs.
I usually post my REW data files so others may examine/manipulate them and I try to be inclusive of details, though you may need to look through some of the earlier post in the build thread for some of the references

6-9PEQandHPFsweepsforMAX.zip 499k .zip file

Some folks without REW wanted just a chart to look at so here is a sample from today



there is some commentary for those posts from today over in that thread.

enjoy,

suggestions, comments welcomed,

if you have something , let me know, PM's are o.ok.

I'm retired and have a good amount of time to try things wrt overall optimization of it all

thank you,

Wil
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Denon X5200 , Emotiva UPA7, for 7.3.4 ATMOS/DSU
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Old 06-09-2014, 08:46 PM
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The graph doesn't look right. How could you be measuring upwards of 200dB? And it would be nice if the vertical scale actually showed the top of the measurements. It is impossible to draw any conclusions from the graph you posted.
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Old 06-09-2014, 10:38 PM
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AustinJerry

thank you for taking a look

could my UMM-6 mike not be using its calibration file 1/3 octave 90 degree correctly?

my ambient is high 40's yet after setting the spl, the large window on top is showing 128 and the "real time' display in the same spl window is bouncing around about 85.

if there is any suggestions for correction there, i'll do it

this chart, no HPF or PEQ with the Inuke6000DSP with the laptop output reduced from 100 to 50% so it would "fit"



this is the data file

jjerrylate6950percentsweep.zip 101k .zip file

the sub is at the distance for the sweeps #3 & #4 from earlier today wrt to front wall doorway.
as i said earlier, the 87 hz dip will be addressed with YPAO or a Berry 1124.

tell me more

thank you
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Old 06-10-2014, 03:00 AM
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Something is definitely off with the levels. If you really were hitting those SPLs, you'd be deaf and bleeding from your ears.

BTW, that 87Hz 'dip' looks like a room induced null. Narrow range, high Q. If so, EQ will do no good except overdrive the system.


Max
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Old 06-10-2014, 05:22 AM
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Quote:
Originally Posted by jim19611961 View Post

A 85db test may yield still more insight. 

I took some more measurements including some at 85dB 

 

    

 

 

I then summarised the results to approximately get the points at which I pass various distortion thresholds by frequency which gave me this. Some of the numbers are a bit inconsistent, I'd need to be a bit more methodical to get it completely consistent and fill in the gaps but the pattern seems pretty clear.

 

 

 

Combining this with an estimate for room gain & my winisd model suggests 10% limit is persistently breached somewhere around the 25-28mm excursion (when xmax is 33mm). The main question mark being my measurement of room gain (which seems quite tricky). I'm not sure I've gained anything from this other than verifying that the model of my sub looks pretty accurate but still.

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Old 06-10-2014, 07:32 AM
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Will,  the good news is that the actual response curve looks pretty good, with the exception of the dip at 85Hz.  As Max says, if this is a room mode, DSP isn't going to resolve it.  Please provide your listening room's dimensions, including height, so we can take a look at where the modes fall.  I looked at your postings in the DIY thread and didn't see dimensions.

 

I'm a bit puzzled at why the measurement levels are showing to be so high.  BTW, you should be using the "narrow_band_response_90_degree.frd" calibration file, not the 1/3 octave file.  However, this is not the cause of the skewed levels.  Please review the section in the REW guide regarding USB mic sensitivity parameters, starting on page 51.  Make sure your calibration file has the correct sensitivity parameter.  Better yet, if you have an external hand-held SPL meter, run a manual calibration as described on page 46.

 

As I am sure you already know, the frequency response curve is only one part of assessing the sub's bass performance.  The other measurements look at bass resonance.  Here are the graphs from the file you provided:

 

 

 

 

The waterfall shows some significant ringing below 50HZ, and at ~70-80Hz.  For the Spectrogram, we like to see the "flames" terminate below 450ms.  This is just another way of looking at the same information as the waterfall, and both show that you could make some improvement.

 

So, based on this preliminary information, I suggest exploring placement options based on where your room modes fall in order to address the 85Hz dip, and then seriously considering bass traps to lower room resonances.

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Old 06-10-2014, 09:25 AM
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Quote:
Originally Posted by 3ll3d00d View Post

I took some more measurements including some at 85dB 


 
 
 
 



I then summarised the results to approximately get the points at which I pass various distortion thresholds by frequency which gave me this. Some of the numbers are a bit inconsistent, I'd need to be a bit more methodical to get it completely consistent and fill in the gaps but the pattern seems pretty clear.





Combining this with an estimate for room gain & my winisd model suggests 10% limit is persistently breached somewhere around the 25-28mm excursion (when xmax is 33mm). The main question mark being my measurement of room gain (which seems quite tricky). I'm not sure I've gained anything from this other than verifying that the model of my sub looks pretty accurate but still.

I think the moral to this story is we dont want to clip our amps or exceed excursion limits for our drivers at levels we typically listen to. Either is stressful on the hardware, not to mention diminished audio quality. Once one knows where your at, you then can assess if you have enough woofage and power to satisfy those needs, or whether an upgrade is in order.
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Old 06-10-2014, 11:50 AM
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Submaximus room layout



PIc of MAX at the 2 meter mark




position is now 31" toward the rear of the room beyond that 2 meter mark and tight to that right wall

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Old 06-10-2014, 12:06 PM
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No offense, but it is difficult for me to decipher that sketch and derive the nominal LxWxH dimensions of your room.  Can you provide these, please?

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Old 06-10-2014, 12:54 PM
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Submaximus LR dimensions

sorry about the lack of clarity . .

at the front wall about 12'6" then opens to 14' 8" at just over 8' from that front wall and a total depth of 28' 2".

total volume with attached hallways, kitchen and dining room is close to 5K ft^3

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Old 06-10-2014, 02:10 PM
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Ok guys, help a noob out here. I cannot seem to get windows sound settings to recognize the AVR via the HDMI cable. .

I did read thru many of the pages in the first half of the thread and have still been unable to get the HDMI port to show as highligted.

I even put in another video card to see of it may have been the prot on my original card.

I am thinking it is some simple setting that I am missing? May be the cable is bad?

Thanks!
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Old 06-10-2014, 03:37 PM
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Ok guys, help a noob out here. I cannot seem to get windows sound settings to recognize the AVR via the HDMI cable. .

I did read thru many of the pages in the first half of the thread and have still been unable to get the HDMI port to show as highligted.

I even put in another video card to see of it may have been the prot on my original card.

I am thinking it is some simple setting that I am missing? May be the cable is bad?

Thanks!

You said you read through the thread. Did you read the Guide (link in my sig)? On the AVR, you must configure the HDMI port you are using. For example, on my Denon, I use the HDMI port on the front panel. I needed to go into the configuration menu, select Inputs, and configure the AUX1 input to use the front panel HDMI connection.

Then, launch REW, select AUX1 on the AVR, and plug the HDMI cable in. You should get an HDMI handshake, and then the PC desktop should display on your TV monitor.
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Old 06-10-2014, 07:26 PM
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Quote:
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Getting Started with REW:  A Step-by-Step Guide

 

The purpose of this document is to provide a step-by-step guide for novice users of Room Equalization Wizard, freeware audio measurement software authored by John Mulkahy. This guide focuses on the recent enhancements to REW that support the use of USB microphones. You are encouraged to visit the REW forum, and to thoroughly read the REW Online Help documents.

 

 

Link to REW 101 v3.5.pdf (April 6, 2014)

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Old 06-10-2014, 08:01 PM
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Old 06-12-2014, 07:12 AM
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How good or bad is this for my sub? I am learning about REW

sub8.jpg I don't know much about graphs.

Last edited by asere; 06-12-2014 at 10:18 AM.
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Old 06-12-2014, 10:58 AM
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Originally Posted by asere View Post
sub8.jpg I don't know much about graphs.
That's looking fairly decent. You've got a couple of humps at 30 and 75hz. Is this pre or post room correction? What room correction does your AVR use?
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Old 06-12-2014, 11:34 AM
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That's looking fairly decent. You've got a couple of humps at 30 and 75hz. Is this pre or post room correction? What room correction does your AVR use?
Thank you! This is after Audyssey correction. Before Audyssey the graph was all over the place.
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Old 06-12-2014, 12:24 PM
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Quote:
Originally Posted by asere View Post
sub8.jpg I don't know much about graphs.
If you are just getting started, did you read the Guide? If you had followed the guide recommendations, you would know that for graphs showing bass response:

- The measurements should be 15-300Hz, so we are all looking at similar graphs.

- You should specify what speakers are included in the measurements--is it sub only, sub+mains, etc.

Having said that, your output below 30Hz is not that good. And the severe dip at 100Hz is bad, but we don't know if the curve includes the main speakers or not.
AustinJerry is online now  
 

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