Frequency Response Measurement - First Attempt
- Thread starter BmWr75
- Start date
Zilch,
Mic stand and adapter are the next step on this science adventure.
Thanks to all involved for the continuing guidance.
BMWR75
Most likely a hard surface that's causing a 1st reflection to cancel the initial wave. At 100Hz you're looking at ~10' wavelength so a pathlength difference of ~5' will be the culprit. If the measurement is made at (or near) 1m then find something that's a pathlength of 8' from the speaker to the mic. Is it 4' away from a wall? The floor? Throw together a quick and cheap sound deadening panel and put it there and see if it goes away. Chances are at that frequency it won't totally go away but you can probably knock it down some.
Note: that's why we measure the low end in the near field (~1/4") and also where MLS and gating come into play.
Ray
Does the RS "calibration" file take the C-weighting into account? IIRC, C is down 3dB at 31Hz on the low end and 8k on the top and down 6dB at 12kHz. That looks to be about how far it's off from "flat".
Ray
whoaru99
Epic Member
As far as I know, the cal file for this RS meter does not include C-weighting correction. So, there is a checkbox in the Mic/Meter tab that should be marked for correction.
My listening space (the basement) is probably far from ideal. It is 18 feet wide and 33 feet long. On the end where the speakers sit, there is an additional enrty way area (4.5 ft x 10 ft) that adds 4.5 feet to the width of the 18 ft wall. The door to the garage is there and stairs going up to the main floor.
The basement has a 7.5' drop acoustic tile ceiling and has heavy wall-to-wall carpet, except in the 4.5'x10' entry way, which is ceramic tile.
There are two support posts in basement that run from the floor to ceiling, they have been enclosed with wood and measure 8"x12" square on the cross section. The one on the listening area end is 9.5 feet from the 18' wall and about 3 feet diagonally from the listening position.
Is the column in the picture the likely culprit?
Plan to get a mic stand for the SPL meter this week per Zilch's recommendation.
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Let's back up a sec...When you're measuring, where is the mic? And are you playing one speaker or both? If you're using the right speaker then I'd say the vanity/dresser/workbench/whatever that is on the right hand wall is causing a reflection. If you're using the left then there's a chance the pillar could be a problem. If you're testing with both then there could be a bunch of things going on.
Mic is right in front of the recliner sitting on a speaker stand as shown in the 2nd picture. Playing both speakers then doing the measurements.
tooloud62
Active Member
Go to the web and put in Real RTA. If you have a laptop use this program about $99 dollars. You would need a small USB mixer and mic. Behringer makes a mic for $50 that is pretty flat or if you want a A+ mic try a Earthworks the best, you would have to dig deep for the Earthworks. That is the best way to tune the room. Add a 1/3 octave Eq and cut the bad frequencys
Your mic must be at the precise acoustic center between the speakers to measure the two of them concurrently; I mean within 1/16". One speaker at a time, moved out from the wall 1M, and mic 1M in front of it, in line with the tweeter, is the preferred measurement methodology.
The test signal is mono. You're doing the "two sources playing simultaneously WILL interfere with each other" thing playing the same signal through both speakers.
Keyword "Axiomatic" by Zilch will tell you why not to do that until you know how to find the precise acoustic center.... :yes:
Not tuning the room here, rather, measuring frequency response.
Yes, TrueRTA will do that, and the Behringer ECM8000 is a rational mic choice, but we're learning using available resources and free downloads here.... :thmbsp:
MOPAR3
Super Member
This looks interesting. How accurate is it? I've got a speaker project in proress will this help? What about this page is this the correct way to design a crossover? http://sound.westhost.com/lr-passive.htm
On Zilch's recommendation, I got a boom mic stand, mounted the RS SPL meter on it, and placed the meter 3 ft from the tweeter on the same level as the tweeter centerline. Speaker being measured today in an honorary econowave that was designed by Zilch using 1960s vintage Heath AS-10 cabinets I picked up for $20.
All measurements are made using the REQW software (free download) and a Soundblaster Audigy 4 soundcard in my PC. Left speaker only being measured, right speaker is off.
The attached graph shows how making system changes affects the frequency response. Look at the 4k Hz level to see how the highs are reduced with each adjustment described below in an attempt to flatten the frequency response. This is a one variable at a time audio experiment.
Measurement #1 - dark green line - baseline measurement
Measurement #2 - blue line - padded down the horn 100%, probably was already l-padded down 80% on #1
Measurement #3 - magenta line - lowered tweeter level by -1 dB on active crossover
Measurement #4 - gold line - lowered tweeter leve by -2 dB more on active crossover
Measurement 5 - light green line - raised crossover point from 1.8k Hz to 2.0k Hz on active crossover. This change can be seen as in increase in the 1.2k-2.2k Hz range.
All measurements are made using the REQW software (free download) and a Soundblaster Audigy 4 soundcard in my PC. Left speaker only being measured, right speaker is off.
The attached graph shows how making system changes affects the frequency response. Look at the 4k Hz level to see how the highs are reduced with each adjustment described below in an attempt to flatten the frequency response. This is a one variable at a time audio experiment.
Measurement #1 - dark green line - baseline measurement
Measurement #2 - blue line - padded down the horn 100%, probably was already l-padded down 80% on #1
Measurement #3 - magenta line - lowered tweeter level by -1 dB on active crossover
Measurement #4 - gold line - lowered tweeter leve by -2 dB more on active crossover
Measurement 5 - light green line - raised crossover point from 1.8k Hz to 2.0k Hz on active crossover. This change can be seen as in increase in the 1.2k-2.2k Hz range.
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Thanks for the recommendation on the REQW software.....I'm having fun with it.
Does HF Comp = CD Horn button? If yes, it is off.
The tone is a sweep from 30 to 20,000 Hz, don't see that there is an option to do anything else in the software.
No problem with that, actually; just wanted to know what methodology was employed.... :yes: