[SoCalWJS]

Finally got around to swapping a few things around, moving speakers a bit, re-arranging room treatments, then taking a few measurements using OmniMic.

Including a Waterfall plot - which I freely admit to not fully understanding. I took a snapshot of the readings and am posting it here.




If I am reading this right, it looks like I have a bit too much Bass treatment, and not enough treatment above 2khz or so.

Is that right?

[FullRangeMan]

These waterfall charts show the spectral decay or harmonics of musical notes or in this case a sine wave. In this case you can treating the enclosure or the listening room, I do not know which one you are referring to.

[poseidonsvoice]

SoCalWJS,

Any luck using REW with a calibrated mic and boom mic stand at the listening position?

REW would be much easier to interpret and analyze.

If you are having trouble, send me a pm.

Best,
Anand.

[SoCalWJS]

SoCalWJS,

Any luck using REW with a calibrated mic and boom mic stand at the listening position?

REW would be much easier to interpret and analyze.

If you are having trouble, send me a pm.

Best,
Anand.

I'm trying to read through the "Simplified" REW procedure and see that the UMM-6 from Parts Express is now supported - that looks like the USB Mic I have, but I can't confirm it. My eyes go crossways real quick though. I'm out of practice with much of the lingo and I have to go through each step a couple of times. I probably need to download REW again because the version I have (but never successfully used) has got to be 5+ years old.

Also reading about this 0. 90 & 45 degree thing for angles. I don't have anything but the original calibration file. Have to read through the procedure and see if it really makes a difference.

[poseidonsvoice]

Hi!

For measurements from 20Hz to 300 Hz you want to load up the 90 degree calibration file for the microphone and have the microphone either pointing directly up (the ceiling) or down (the floor). Play both your speakers or play both your speakers and your subs together, to see how they all mesh together. The microphone should be placed at the listening position.

For measurements from 300Hz to 20khz, you want to load up the 0 degree calibration file for the microphone and have the microphone pointing directly in between your speakers. Play one speaker at a time. Take a right speaker measurement. Then take a left speaker measurement. The microphone, again should be placed at the listening position.

These 3 measurements (Low frequency, right speaker and left speaker) should have sufficient data to give us an idea of what areas we may need to concentrate on. Who knows, everything just might be perfect!

This document is an excellent read, but I am almost afraid that your eyes may cross even more: https://www.avnirvana.com/resources/getting-started-with-rew-a-step-by-step-guide.19/

There are also guides on Youtube and multiple other informative guides right here: https://www.avnirvana.com/threads/some-guides-to-rew-and-acoustic-measurement.121/

Best,
Anand.

[Hipper]

Regarding microphone position, I conducted some experiments on the differences microphone orientation has on REW readings. I used a calibrated Earthworks M23 mic..





Light brown - at my ear pointing to speaker
Green - in the middle pointing at speaker
Purple - in the middle pointing down the middle of the room
Red - in the middle pointing upwards
Turquoise - in the middle pointing downwards

The first FR is up to 500Hz, no smoothing. The second is full range at 1/24 smoothing.

The makers of my Earthworks microphone say to point it to the source, but I’ve seen other recommendations to point mics up or down. It seems to make a bit of difference in actual measurements.

I suppose all we can do is be consistent so that you can see the changes you are making. I think it's best not to get too carried away by graph accuracy but rather do your best and then use listening to music as the final arbiter.

[Hipper]

This is a guide to Waterfall graphs:

http://www.gikacoustics.com/understanding-decay-times/

It's most useful for decay time performance.

The noise floor you set has a bearing on things as there will always be noise of some sort. I set it at 30dB.

I'm of the school that thinks you can never have too much bass trapping but you can overdo the higher frequency absorption, and I probably have!









The 40Hz problem is traffic noise as I live on a busy High Street. When playing music it's not noticeable but it does make it difficult to measure that region.

I'm beginning to come to the view that controlling decay time evenly across the frequencies is even more important then a flat frequency response.

[SoCalWJS]

Thanks for all of the input Anand & Hipper.

When I installed the newest version of REW, I saw that A/V Nirvana was the first resource listed, so I've been working my way through that a little at a time.

I am used to the procedure that OmniMic uses, where all of the Test Tones are on a CD which I place into my Player and proceed from there. When I read through the REW process, I get the impression that the Test Tones are inside the software and there is no procedure to burn them to a disc.

I'm trying to figure out my next step, and I want to make sure I understand how REW works, with respect to hardware. I know that they say the easiest/best way to use REW is via a Digital USB Mic and HDMI cable. It appears the Test Tones are then sent to the music system via the HDMI cable. My 2 channel setup does not have HDMI inputs. I believe that means I need to get the external processor that then sends the Test Tones out via RCA cables.

Is that correct? Is there any way to get the tones onto a disc or a USB drive?

[sledwards]

Hello SoCalWJS:

You do not need an external processor to run REW. Assuming you are running REW on a laptop, the USB Mic attaches to a USB port, and you can use the Headphone output jack on the laptop (most have this, typically a 3.5mm phono jack) run into your preamp. You can get a simple phono jack to RCA adapter cable such as this from Amazon: https://www.amazon.com/AmazonBasics-3-5mm-2-Male-Adapter-Cable/dp/B01D5H8KO2/ref=sr_1_8?ie=UTF8&qid=1530299626&sr=8-8&keywords=rca+adapter

Regards,

Steve

[Hipper]

REW doesn't play test tones but uses what's called a logarithmic sine sweep. This is a long single signal starting low and going right through to the top frequencies. You can control this signal in various ways: to only do from 0-500Hz for example, or to repeat the sweep any number of times to average the results.

Indeed there are so many options on REW that it requires patience to learn how to use it. The bonus though is that this one measurement can yield a range of graphs to help discover what is going on. If you plan on regularly improving your listening experience - new gear, room treatment, different set ups, different rooms etc. - it will serve you well over the years.

I don't know of any good way to put the REW signal on a CD, and don't see the need to do so.

What I've found is a useful CD is one from RealTraps which has lower frequency test tones going up in 1Hz stages:

https://realtraps.com/test-cd.htm

It helped me correct the frequencies around the traffic noise I mentioned earlier.

[SoCalWJS]

SoCalWJS,

Any luck using REW with a calibrated mic and boom mic stand at the listening position?

REW would be much easier to interpret and analyze.

If you are having trouble, send me a pm.

Best,
Anand.

OK, finally broke down and ordered the UMIK-1. It arrived yesterday and I am starting to play around with it this morning. Took a couple of attempts to get things squared away (it didn't automatically locate the CAL file) and it took a few attempts. Updated to the latest version of REW (5.19) and I think it's now happily calibrated (I think)

Wow. Lots of info available. Need a good starting point to work with.

Biggest problem right now is that the Housing development I am in is starting a new Phase and I've got multiple Earth Movers and large Bulldozers, literally across the street from me.

Think I should wait until they stop so my background rumble stops.

Need to read up a bit more (OK - a LOT more) about how to run REW

[Hipper]

Out of interest you could measure the builders rumble.

Set up the microphone and play the sine wave but turn the volume of your playback gear to 'off' so no sound is heard. Do this when the builders are working and again when they're not and check the differences. A waterfall plot and spectrogram would be good here too.

[SoCalWJS]

Out of interest you could measure the builders rumble.

Set up the microphone and play the sine wave but turn the volume of your playback gear to 'off' so no sound is heard. Do this when the builders are working and again when they're not and check the differences. A waterfall plot and spectrogram would be good here too.

I'm not sure about the FR, but the background noise floor goes up by 10-20 db. Figure it's pointless. 

[dB Cooper]

A friend just told me about This app for FR and waterfall measuremnts in case any are interested.