# my first measure for comments(Subwoof measurement)



## jianhua1975 (Sep 13, 2011)

hi, guys:
here is my first measurement
Hardware: Tascam US-144MKII, laptop, Cary cinema 12 Preamp, MKV1250 sub, Radioshack SPL 33-2055. 

here is the result for comments:
Pic1: SPL&phase
Pic2: Impulse 
Pic3:Waterfull
PIc4:Group delay


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## jianhua1975 (Sep 13, 2011)

add Pic5 Spectrogram and Pic6 Excess group delay


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## SAC (Dec 3, 2009)

Please make a _full range_ sweep and post the .mdat file.
Do not try to band limit the sweep!

This will allow us to convolve and window it as appropriate.
FWIW, the IR looks wonky.


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## aackthpt (Jan 24, 2011)

IR always looks weird like that in REW when it is a band-limited measurement. The band-limited measurement is perfectly acceptable if all you want to look at is the bass region.

However, your excess group delay plot looks VERY wonky.

Did you use the correct generic calibration file for the RS meter? Speaking of which, ditch that ASAP. You invested in a US-144mkII and are using an SPL meter (and an RS to boot) for input??? Seriously, buy a Dayton EMM-6, an XLR cable from monoprice and a cheap mic stand (e.g. http://www.amazon.com/Musicians-Gear-Tripod-Stand-Telescoping/dp/B001G457BQ ) stat.


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## SAC (Dec 3, 2009)

Use a full range sweep.
I know the IR looks like that with a LF band limited sweep- that is why we run a full range sweep.
Also, I hope that is a log ^2 impulse, otherwise we are missing the negative ranges of the IR....that is , unless you have one of those rare drivers that only move in the 'positive' direction and never in the 'negative' direction... (plus, per the display, you apparently have a driver that takes 3 cycles to reach its maximum peak output upon the initial application of the stimulus...fascinating! :rofl2: )
We will use windowing of the response to narrow our focus.


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## jianhua1975 (Sep 13, 2011)

thanks all for your reply. 

feel good anyway since it's a first "DONE" measurement. 
feeling better that i know where to go further 

i'll try and try.


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## jtalden (Mar 12, 2009)

It would be helpful to scale the SPL/Phase graphs using the recommendations per the Sticky Thread. The measurement looks fine however.

The IR looks normal, but the it is in the "dB FS" mode and I think SAC and aackthpt may have been looking to see it in the "% FS" mode. If the OP can hover their the mouse over the IR graph then the top left corner provides a dropdown box to switch between the 2 modes.

The GD is not a relevent issue for a single driver measurement. This is just some noise due to modal or boundry affects at the mic position.


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## jianhua1975 (Sep 13, 2011)

hi, i performed a full range Sweep testing last night( is that set freq from 0~48KHZ when start measuring). 
and i carefully compared the result with the measurement attached here , i found it's very consistantly the same. so i guess using band-limited sweep is not an issue for my testing. 

also this time i used radioshack 33-2055 SPL cal. 

here i attached the Mdata.


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## jtalden (Mar 12, 2009)

jianhua1975 said:


> hi, i performed a full range Sweep testing last night( is that set freq from 0~48KHZ when start measuring).
> and i carefully compared the result with the measurement attached here , i found it's very consistantly the same. so i guess using band-limited sweep is not an issue for my testing.
> 
> also this time i used radioshack 33-2055 SPL cal.
> ...


Okay, now it also looks to me like there may be something wrong with the measurement so I am on board. This is your IR:








This looks to me like a measurement error. Possibly may be getting loop back do your monitor setting. Be sure all monitor settings are turned off both on the sound card and your PC sound controls. I am not familiar with the settings needed for you particular equipment, but it is well documented in this forum.


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## jianhua1975 (Sep 13, 2011)

hi, Jtalden: really glad to see your reply with helpful comments. 

then i try to found out where exactly is the error located. and try to get rid of it. 

happy to know more!


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## aackthpt (Jan 24, 2011)

This sweep is only to 200 Hz. Please give us something to work with; run the sweep up to 5000 Hz. Higher is better but that is getting to the range of meaninglessness with the RS meter anyway.

Also, are you running your subwoofer only? The frequency response looks like it. Please perform the sweep with one speaker and all subwoofers running.

What sort of comments are you looking for / what is your goal here? The answers you get are often only as good as the questions you ask.


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## jianhua1975 (Sep 13, 2011)

hi, aackthpt: 
since i am eager to make right EQ on my Subwoof by using REW with needed hardwares, since i am feel
unconfortable with the Subwoof souding in the movie, and i know there must be something seriously wrong, and i know EQ mostly can make it better. 

so i am also interested in knowing how, that why i look into REW, and make measurements and learn to know why and how in the EQ area. 

then first thing first, i need help to secure that i make right set up as a base for right measurement result. 

now i got more and more valuable comments now even i didn't ask the right questions. 

Yes, i am only using Subwoof, and use my Cary12's dSP working on bassmanagement(crossover), not useing any main speakers: connect TASCAM US144's left lineout into Cary12's stereo L input, and connect
Cary 12's SW out to my subwoof.
and the latest measurement, i selected Sweep from 0~Maximum, and the actual measurement result should be only valid/meaningful bellow 80Hz i believe, since my Preamp's bass management. 

now i really don't know where is the error comming from, wrong config of my Tascam144 soundcard? sweep selection? not using main speakers? using Pre-amp's bass management? something wrong with my 
radioshack SPL?

BTW: i am using sample rate 96KHz, tried 512K and 1M sweep. does these choice make difference? 

also hope someone can share the setting/config of Tascam 144MKII in Windows system( i'm using Vista)


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## jianhua1975 (Sep 13, 2011)

hi, Jtalden: 
i already turn the knob(see attached pic) on TAS 144 sound card to only output signal from computer(REW) during measuring, so that shall not cause any loopback as you suspected. 
but for the setting in computer, i may need to check to make sure any enhancement shall be checked OFF.


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## jtalden (Mar 12, 2009)

jianhua1975 said:


> hi, Jtalden:
> i already turn the knob(see attached pic) on TAS 144 sound card to only output signal from computer(REW) during measuring, so that shall not cause any loopback as you suspected.
> but for the setting in computer, i may need to check to make sure any enhancement shall be checked OFF.


I am no expert in resolving setup issues for various hardware, but I think I remember that someone else was having issues when the hardware and REW were not sampling at the same rate. You may want to try to set both the soundcard and REW to 48k. I think there is a fair chance that that may resolve the issue. There is normally no advantage in sampling at 96k anyway.


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## aackthpt (Jan 24, 2011)

jtalden said:


> I am no expert in resolving setup issues for various hardware, but I think I remember that someone else was having issues when the hardware and REW were not sampling at the same rate. You may want to try to set both the soundcard and REW to 48k. I think there is a fair chance that that may resolve the issue. There is normally no advantage in sampling at 96k anyway.


Actually I think 44.1 is optimal. I think John has stated that is what REW uses, therefore if you cal and test at 48 the data has to be resampled before analysis which can cause some errors.

I suspect his sweeps are fine. Excess group delay looked more normal on the file he posted, iirc, than the original images. I think the reasons his sub sounds weird are either that the levels and delays are not properly set up or just the clearly massive amount of modal activity in his room. Having a full range sweep would at least give some idea if the sub level is reasonable. 

jianhua, did you set the channel levels and delays in your processor using the SPL meter before running REW?

Use the 1M sweep. Also, compare the result of a measurement with 1 sweep to the result with 4 sweeps to verify they are the same. If you have continuous noise in your listening area, it might help to always run the measurement with 4 sweeps.



> actual measurement result should be only valid/meaningful bellow 80Hz i believe, since my Preamp's bass management.


The measurement will be valid and meaningful through the entire range, up to the limit of good response for your mic (SPL meter). The bass management in your AVR acts the same as a crossover in a speaker. Full range signals come from a DVD player into the AVR the exact same way REW test signals do. The subwoofer doesn't act alone, its output actually only makes sense in context with the other speakers, hence the need to set the levels and delays to try to get everything to integrate properly - and do a larger sweep including the higher speakers. Fixing your bass sound problem might (or might not) be about making the sub work properly with the rest of the system.

Also please tell us more about your listening area. What size is the room and what materials are the walls/ceiling/floor made of?


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## aackthpt (Jan 24, 2011)

Also you may want to review this thread. The default REW input and output is on the right channel, so you should have your mic going to the right channel input, and be feeding the AVR from the right channel output. When you did your soundcard calibration you should have done it with a cable from the right channel output to the right channel input. You can use either right channel or left channel input on the Cary AVR.

Left channel connections on your soundcard/mic pre are used when running REW in a more advanced fashion that is not really essential for you at this time.

I should also have asked in my last post... have you set the small/large settings for speakers in your AVR? How are they set?


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## jianhua1975 (Sep 13, 2011)

hi, aackthpt: 

before running REW, my Cary pre amp has been set up with 75Db level each 5 channel, and 76DB subwoofer by using my SPL. for delay parameter(distance), i set by measuring the actual distance from 
each speaker to main LP. and set Xover 80HZ for L/C/R/SL/SR/SW. 

then i'll try to make different measurement with different size and qty of Sweeps, also i'll also use Right Line/mic in and right Line out on my soundcard for REW measurement. also use 44.1Khz for sample rate. 

regarding to my listening environment, it's quite unregular. about 35squaremeter. 3.5m high, right side with a big window with 2layer glass and heavy curtain(occupy almost 60~70% of total wall area), left side with also a big window (60% of the total wall ) but without glass&curtains(directly a through window from my listening area to another area). left side also with a 2squaremeter size entry (with steps up into another area).

all surfaces are not sounding processed. most are hard surfaces, stone type material on the floor, painted walls.

that's rough description of my listening area.


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## jianhua1975 (Sep 13, 2011)

hi, now i just completed a new measurement.

3 measure results are included, 
1st: 1M full range sweep, and 1 sweep only, Sub with FR main speaker, 
2nd:1M full range Sweep, and 1 sweep only, only Sub 
3rd: 1M full range Sweep, and 4 Sweeps, only Sub

and this time i set sample rate to 44.1Khz, and using right in&out of soundcard for calibration and measurement. 

what's your comments on this measurement? is the setup right this time according to the result. and 
how does this measurement result say about my environment? 
i read it sounds not good at all.


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## JohnM (Apr 11, 2006)

Your measurements are fine, but when making sub only measurements it is better to limit the upper end of the sweep to (say) 200Hz, otherwise much of the test signal is outside the range the subwoofer can reproduce and the signal-to-noise ratio of the measurement is degraded.

You can save some time by using a 256k sweep, the results will be just as good for this purpose.

It is not surprising you are unhappy with the subwoofer's contribution, as the response is very uneven. Here it is with 1/6 octave smoothing:








Where is you sub located? It might gain some low end if placed in a corner, allowing the level to be reduced and better match the mains.

What main speakers are you using? From the combined plot they may benefit from a higher crossover setting, a measurement of a main speaker on its own (sub turned off) would make it easier to see whether that is the case.


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## aackthpt (Jan 24, 2011)

JohnM said nearly everything I would. The measurements look entirely normal now, which is good. Your 1 and 4 sweep measurements look the same - another confirmation that your equipment is working properly.

Remember, when taking a sub-only sweep, only do it up to a little above the crossover frequency, so for 80Hz cross go to 100 or 120 Hz. With what you are doing now you do not need sub-only sweeps. When taking a full-range measurement use the sub AND a speaker. It's a good idea to do this for all three LCR.

To me it looks like you subwoofer level is just way too high (which is why you need to take full range sweeps including another speaker) ... 20 dB up at 50-60 Hz is obviously incorrect. John's recommendation to try other positions is great, also maybe double check the manual for what level you are supposed to set it to when you do the AVR calibration. Also you should have the low pass filter on the sub in "bypass" mode. That sub has a "bass level" adjustment, what I like to do on those is leave the AVR sub level at 0 and set the level using the noise from the AVR with the knob on the sub. What is the sub level in the AVR, and in what position is the knob on the sub?


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## jianhua1975 (Sep 13, 2011)

OK, 
then i got motivation to go steps further now. happy to know that there shall be no error setup last night.

currently, i put my Sub at front left corner. and M&K LCR 750 speakers are my main speakers, together
with M&K V1250 Subwoof. and the suggested CrossOver is 80HZ, which is what i am seting with. 

i need some time to practise with the measurements with adjustments. and more important to me, i need to learn and know. so my plan is to invest also a MIC with good full range performance say 20~20Khz.


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## jianhua1975 (Sep 13, 2011)

aackthpt said:


> Also you should have the low pass filter on the sub in "bypass" mode. That sub has a "bass level" adjustment, what I like to do on those is leave the AVR sub level at 0 and set the level using the noise from the AVR with the knob on the sub. What is the sub level in the AVR, and in what position is the knob on the sub?


hi, aackthpt: the Knob on Sub is on 10:00~11:00AM position. and i always use AVR level adjustment to get right level instead of Sub. but i'll try ur suggestion for sure.


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## aackthpt (Jan 24, 2011)

jianhua1975 said:


> hi, aackthpt: the Knob on Sub is on 10:00~11:00AM position. and i always use AVR level adjustment to get right level instead of Sub. but i'll try ur suggestion for sure.


That's a reasonable position for the sub level knob (not for the crossover knob); as long as the level in the AVR doesn't have to be too crazy (like not more than perhaps +6 dB) then you should be fine. Most of the chances for problems in these things are are extreme settings in either direction.

If you want to learn more accurately and specifically about level setting, you should read Wayne's article on gain structure as well as the ensuing debate in the rest of the thread (so you can understand different positions or methods and decide for yourself which way you like with your equipment).


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