# First measurement



## johnnybregar (May 8, 2013)

Hi all,

I tried hard to read all the rules and I've created my first graph. How does my room look? I have a small recording studio, about 34' x 22' and I was very concerned about low end - but it appears that I actually have a dip at 40 Hz. Looks like I have a peak at 60 Hz relative to the low end, a dip around 1K and a peak around 7K.

Am I reading this right? Is it anything to worry about? I get pretty similar results from different places in the room - off by a few dB here and there, but it follows the pattern.

I have windows, and I'm wondering if I should cover them - which might kill some of the high freqs.

Thoughts?

Thanks in advance for any advice!


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## JohnM (Apr 11, 2006)

Welcome!

It is worth checking out the sticky on posting graphs for some tips on scales etc. 

If you attach the .mdat file for your measurement we can have a closer look at it to check all is well - there are some odd features in the plots posted, like the substantial rise in the noise floor at high frequencies and the rise at very low frequencies.

What are you using to make the measurements?


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## johnnybregar (May 8, 2013)

Thanks - I'll spend more time looking at how to post graphs. I've attached the .mdat.

I measured it using a radio shack dB meter, with the correct calibration file. I used a Steinberg CI2 2 ch. USB audio interface and played the sweep through a pair of Yamaha HS80m studio monitors. The mic was positioned approximately in listening position at my mixing console. Not sure why the noise floor would be going up - that's weird. Aside from that, are the frequency dips and peaks unusual?

Thanks,

jb


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## johnnybregar (May 8, 2013)

Is it possible that someone can look at my measurement, or should I re-upload jpg images? 

Thanks - I really do appreciate the help. 

In fact, I appreciate it so much, that I'm willing to *pay* someone to work with me on this, it's important to me and I'd gladly PayPal someone who would be willing to take a little extra time to work with me and help me understand where my room needs treatment.


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

Hey Johnny,

The sound level meter was not designed for frequency response measurements, and the calibration file is only accurate up to about 3 kHz. I’m going to hazard a guess that the noise is coming from the meter itself. Aside from that – yes, the dips and peaks in response are typical.

Regards,
Wayne


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## EarlK (Jan 1, 2010)

Hi JB !

- I'll suggest ( respectfully ) that you direct your monies toward  *GIK Acoustics * and the purchasing of , their room treatment products ( or at least the ones you can't effectively build your-self ) .

- ( So you know ) getting a pro involved will ultimately save you time, money & head-ache .

- One of the principals of that enterprise ( Bryan / "BPape" ) hosts the  *Acoustics forum ( here at HTS )*  .

- Please read ( & digest the hidden info within ) * this thread ( by Brian of GIK ) !*  ( a hint ; even after some typically modest, yet "standard" room treatments, the bass "nulls" are left effectively untouched, by the type of treatment that you can typically build on your own ) . 

- In a nutshell, ( once you ) agree to procure their ( effective ) products, you'll be directed ( on how to use REW to get meaningful measurements ) to help you choose the most appropriate treatments for your space .

- Apart from that , I can certainly direct you towards the necessary books ( for you to buy ) so that you can self-study and take the DIY path if that's the direction you want to take .

:sn:


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## JohnM (Apr 11, 2006)

The peak around 7k is typical of the RS meter, the cal file data is for low frequencies only as the meters are too variable above a few kHz.

What range was the meter set to for the measurement? The signal-to-noise ratio is very low, which would typically be due to input levels too low.


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## johnnybregar (May 8, 2013)

Thanks y'all - 

Off to performances today - will do another run later this afternoon with a Neumann TLM170, which is very flat. Hopefully I get a better result.


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## morca (Aug 26, 2011)

odd result,s, lets see what the other mic make,s of it.
That is no mic for measurement i think ?


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## johnnybregar (May 8, 2013)

The TLM170 is not a measurement mic, but is very flat from 40 - 5K, with a couple dB bump between 5 and 10K. I think it will be sufficient - no?


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## EarlK (Jan 1, 2010)

The TLM170R is certainly a pro recording mic .

So far ( from the sounds of it ) I'll venture that it'll likely be good enough for your initial use of REW ( ie; to get some room acoustics data, for you to think about ) .



Note how the response ( in the above link ) at say 12K , turns into a figure eight pattern ( even in omni mode ) .

:sn:


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## johnnybregar (May 8, 2013)

OK. Finally had a spare moment to set up the measurement again. I hope this graph is what you want to see - I also attached the measurement file. I smoothed at 1/3 octave for the attached jpg.

This one was made with the Neumann TLM170. Looks to me to be more even, but I'm surprised a the mid-bump. Do you think there is sufficient data here to suggest that I try to absorb lows in my room? If so, I know what material I need to shoot for, but is there something specific I can use to get 70 Hz and below?

Thx.


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## johnnybregar (May 8, 2013)

Here's the waterfall from that one.

BTW - it was measured with the mono output (L) of my soundcard feeding a single mono input into my music computer, panned center for output. The mic was at listening position, set to omni.


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## Phillips (Aug 12, 2011)

johnnybregar said:


> Here's the waterfall from that one.
> 
> BTW - it was measured with the mono output (L) of my soundcard feeding a single mono input into my music computer, panned center for output. The mic was at listening position, set to omni.


Waterfall graphs are only useful up to 200 - 300hz.


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## johnnybregar (May 8, 2013)

Phillips said:


> Waterfall graphs are only useful up to 200 - 300hz.


I'm curious why that is?

Can anyone give me an indication on whether my graph looks ok? It if you need more data?

Thx.


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## Phillips (Aug 12, 2011)

You say the mic is flat, according to who?

I am not familiar with this mic.

I have learn't not to change anything in my system without accurate hardware, i thought the my mic was flat as well, but instead it was a mess. 

Spending little money getting accurate calibrated mic was a great investment. Know when i measure i know the data is accurate. You would be really surprised the difference.

At the end of the day do you want accurate or just ok results?


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## JohnM (Apr 11, 2006)

Looks like a good measurement, low noise levels, plenty of signal. You should clear the RS meter cal file now that you are no longer using it (for existing measurements use the Change Cal button on the measurement panel, for new measurements clear the file on the mic/meter preferences tab). Also make sure 'C weighted SPL meter' is not selected in the preferences. Might want to update to the latest REW V5.01 beta also.

Measuring with both speakers playing is OK to see how mono bass content will be reproduced, but for full range measurements and to look at individual low frequency behaviour you want one speaker playing at a time - the smallest difference in distance from the mic to either speaker will cause a lot of additional comb filtering at high frequencies.

The waterfall graph is good for spotting which low frequencies are slow to decay, above the bass range there is too much going on for the waterfall to provide useful info with its default settings (which are aimed at studying low frequency behaviour). 

That 59 Hz peak is a very dominant feature in your measurement, with not much happening below it. If you have any scope for moving the listening position or speakers around it is worth trying some different positions to see how the response changes. You can do that by taking lots of measurements, or you can set up REW's signal generator to play its "Pink PN" test signal and the use the RTA, with the settings below, to watch the response change live as you move about.








If you are thinking about treatments and the like, the folk in the Home Audio Acoustics forum have the expertise to offer great advice on how to proceed.


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## johnnybregar (May 8, 2013)

Thanks - I will goof around with moving the mic around as well as going one speaker at a time. As long as my measurement looks good, I'm happy to draw my own conclusions.

Thanks for the tip on where to get treatment info.


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