Speaker/Room calibration

[rbbert]

Almost identical to my listening room (166" x 274" with a slanting ceiling averaging 132"), so I'll be following your journey with great interest.

[NorthStar]

Even for a basement!

Well, the length is within 5% of the height's multiple (X2 = the only onion; oil in the ointment).

* http://www.silcom.com/~aludwig/Room_acoustics.html
* http://www.linkwitzlab.com/rooms.htm
* http://www.ethanwiner.com/acoustics.html

* http://www.tmlaboratories.com/RoomDi...alculator.html

P.S. My older room was 13.5' by 23.5' by 8.0'.
So, I'll be watching you. ...Except for the ceiling (height).

[Soundproof]

Definitely a thread to watch! Looking forward to following Bruce's investigation!

[Bruce B]

Well, the length is within 5% of the height's multiple (X2 = the only onion; oil in the ointment).
...Except for the ceiling (height).

Well the ceiling height is actually 2 levels. There is a center section that is 10.5', but there is a perimeter soffit, that serves as a bass trap, that is just over 8'. The center section is broken up with diffusors and the ceiling surface is 2" 703 covered with fabric.

[NorthStar]

WoW! Ok, you win!

[Bruce B]

First, the easy part. REW wants me to do a calibration of the soundcard via analog loopback (M-Audio Pro Track USB)

[jazdoc]

Bruce,

Could I ask a big favor...could you try and use English to explain for the 'technically challenged' audiophiles what the graphs are used for and what the data means to you. Thanks in advance!

[Bruce B]

Bruce,

Could I ask a big favor...could you try and use English to explain for the 'technically challenged' audiophiles what the graphs are used for and what the data means to you. Thanks in advance!

For any good engineer, you need to make sure the test equipment itself is within normal limits (WNL). This was the first part in making sure what I measured was actually happening. In the above graph, lets say the line dipped down -6dB at 100Hz. Well instead of thinking that is a room problem when I did the actual measurement, the software would take that into consideration and correct for that. The calibration file that you save in the program would say the "M-audio Pro Track" does not accurately track the signal and the software has to correct (raise the graph +6dB at 100Hz) for that deficiency.

Now, if I wanted to be anal, I could purchase the calibration file of the microphone that I'm using from Earthworks. Every measurement microphone they sell, they calibrate and have the freq. plot and such available, for a price!. You would then load in the calibration file for the microphone too and the software would correct for any variance of that particular microphone.

I don't think REW software does this, but some software even adjusts for elevation, humidity and temperature, all factors on the speed of sound. So the top green line in that graph above should be as straight across 0dB as possible.... especially in the audible band of 20Hz to 20k. Here you can see the test equipment in the chain is down maybe 0.1dB at 20Hz. If you want to measure below that, the calibration file would compensate for that downward slope.

[Bruce B]

Now this has been a pain in the arse...

Seems the M-Audio Fast Track Pro does not have enough gain for the Earthworks Mic. I'm just using USB bus power now, so I'm assuming that you need the AC/DC adapter to give it enough gain.
So.. I ended up using my Radio Shack digital SPL meter. Guess that's "good enough" for a down and dirty shot to see if this thing works.

There are several adjustments on the back of the speakers.

Bass Filter - regulates how much low freq. is sent to the woofers. Settings are 50 - 100 - 150Hz. Mine set at 100Hz

Bass Level - the loudness level of the bass. Settings are Off to 0 to +6dB. Mine set at 0 (Neutral)

Bass Quality - ?? Tight - Neutral - Full, Mine set at Neutral

Bass Extension - this is how low you want your speakers to go. Settings are 0 - 1- 2 octaves. Mine set at 2

Rumble Filter - can be used when playing vinyl. Factory default is Off.

Now the first graph is the initial sweep.

Though the first graph shows a nice bass extension from 20Hz all the way down to 4.5Hz? at -10dB. Don't know if I needed all that bass or not. I'm sure the Bass Pig would be proud!

I started playing around with some of the settings and the only thing I changed is Bass Extension. I turned it down to 1.5 This is shown in the second graph.

As you can see in the second image, the null at 40Hz and peak at 75Hz are less obtrusive.

The experts can chime in anytime now?? HELP!

[theguesswho]

hi Bruce, That looks like a great response! With bass extension down below the stated 10hz that the factory posts! I am jealous. My system barely manages 16hz. Your system goes down to the level of the rotary woofer!
I do have a few questions
1) can you post a picture of the controls on the back of the speakers, so we can see what is adjustable.
2) did you originally have the system tuned when the were originally set up?
3)Do you think you can eek out the last 1-3% with the controls?
4)What is your goal?
THanks,
Wendell