|
|
Post by Boomzilla on Aug 15, 2017 8:39:52 GMT -5
I got my Umik microphone and software primarily to do near-field speaker measurements. But I'd also like to use the setup to evaluate the room itself. As I understand it, I'd do best to locate the microphone at the listening position and then run individual sweeps for the left and right speakers? When I run these sweeps, should the subwoofer be active also (as it would normally be for music listening)? Once the sweeps are completed, what do the curves and waterfalls mean? In other words, how would I convert a specific resonance-peak as seen on the sweep to a floor, ceiling, or side-wall reflection? My audio amigo, garbulky continuously encourages me to add more room damping. How can I tell from the measurements whether what I've already got is "enough" or not? And, perhaps more to the point, if I do need more, where should it go and why? In short, I think I have better tools than I can effectively understand. Is there an online "Audio Measurements 101 class?" Thanks - Boomzilla |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Aug 15, 2017 9:17:43 GMT -5
Hello,
The problem with microphones in general is they are pressure response devices. They typically can't give you any information about which direction a stimulus came from, only what the waveform (and thus SPL, spectrum, impulse) was at the measurement location. The UMIK-1 and most other measurement microphones are intended to be omnidirectional, and for the most part they are - that is, an electrical response can be generated from a stimulus that comes from any direction, even behind (though they can't "see" perfectly behind them - maximum deviation from the on-axis response will be seen at 180 degrees off axis, or "behind" the mic).
To determine which wall a reflection came from requires that the distance from the microphone to each wall is known, and that the flight time from the sound source, to the first reflection point, to the microphone has been calculated in advance. It also requires that the reflected energy be well organized enough that when you look at the impulse measurement, you will see a 'peak' or a group of ripples at or near the predicted flight time for a reflection from that direction in the room. You can then set the time window for the frequency response measurement so that it includes or excludes those reflection artifacts, and you can see what the effect upon frequency response is.
A waterfall plot is a group of impulse response curves generated for a single frequency or a group of frequencies (based on the FFT histogram bin width, measured in octaves). If your flight time for certain early reflections is known, and is different enough from the flight times of other reflections, then you can take a slice through the waterfall plot and see what frequencies the most reflected energy is concentrated near, and that can help you choose the type of treatment to install on that wall.
Take your time and play around with the tools to become familiar with them. Since you have the UMIK-1, you'll want to use Room EQ Wizard as your program of choice for data acquisition - it's free and reasonably easy to work with, and its layout and features are oriented around room measurements. For loudspeaker design, the Dayton Audio OmniMic is a better package, just in the way its software is laid out.
|
|
DYohn
Emo VIPs 
Posts: 18,493
|
Post by DYohn on Aug 15, 2017 9:34:27 GMT -5
Good advice above.
Waterfall plots show you many important things, the three most important to designing room treatments being the frequency of the mode or peak (the tops of the mountains) the Q or effective bandwidth of the mode (the width of the mountain) and the amount of ringing or reverb at that mode (how far the peak comes forward on the Z axis, which is time.) The "ideal" is generally to minimize the number and height and the ringing time of the peaks, and to maximize the Q or width of the peaks. The graphs really cannot tell you "where" the modes are coming from, which is why there is math and general rules of thumb about room treatments based on the geometry of the room which you can discover by reading a good book on acoustics or even by using your friend Google. Treat the "first reflection points" and add as many bass traps as you can handle is a general guide, and if you have high frequency issues think about diffusion not just absorption. And by the way you want to measure for the listening position with all channels active, not near field on individual channels. You are designing a room, not the loudspeakers.
|
|
|
|
Post by novisnick on Aug 15, 2017 9:39:22 GMT -5
Good advice above. Waterfall plots show you many important things, the three most important to designing room treatments being the frequency of the mode or peak (the tops of the mountains) the Q or effective bandwidth of the mode (the width of the mountain) and the amount of ringing or reverb at that mode (how far the peak comes forward on the Z axis, which is time.) The "ideal" is generally to minimize the number and height and the ringing time of the peaks, and to maximize the Q or width of the peaks. The graphs really cannot tell you "where" the modes are coming from, which is why there is math and general rules of thumb about room treatments based on the geometry of the room which you can discover by reading a good book on acoustics or even by using your friend Google. Treat the "first reflection points" and add as many bass traps as you can handle is a general guide, and if you have high frequency issues think about diffusion not just absorption. And by the way you want to measure for the listening position with all channels active, not near field on individual channels. You are designing a room, not the loudspeakers. Thanks for this information! 👍👍👍👍👍 |
|
DYohn
Emo VIPs
Posts: 18,493
|
Post by DYohn on Aug 15, 2017 9:45:47 GMT -5
And by the way number two, I highly recommend Ethan Winer's book "The Audio Expert" as relatively easy reading for anyone who wants to learn more about acoustics.
|
|
|
|
Post by foggy1956 on Aug 15, 2017 9:59:35 GMT -5
Hello, The problem with microphones in general is they are pressure response devices. They typically can't give you any information about which direction a stimulus came from, only what the waveform (and thus SPL, spectrum, impulse) was at the measurement location. The UMIK-1 and most other measurement microphones are intended to be omnidirectional, and for the most part they are - that is, an electrical response can be generated from a stimulus that comes from any direction, even behind (though they can't "see" perfectly behind them - maximum deviation from the on-axis response will be seen at 180 degrees off axis, or "behind" the mic). To determine which wall a reflection came from requires that the distance from the microphone to each wall is known, and that the flight time from the sound source, to the first reflection point, to the microphone has been calculated in advance. It also requires that the reflected energy be well organized enough that when you look at the impulse measurement, you will see a 'peak' or a group of ripples at or near the predicted flight time for a reflection from that direction in the room. You can then set the time window for the frequency response measurement so that it includes or excludes those reflection artifacts, and you can see what the effect upon frequency response is. A waterfall plot is a group of impulse response curves generated for a single frequency or a group of frequencies (based on the FFT histogram bin width, measured in octaves). If your flight time for certain early reflections is known, and is different enough from the flight times of other reflections, then you can take a slice through the waterfall plot and see what frequencies the most reflected energy is concentrated near, and that can help you choose the type of treatment to install on that wall. Take your time and play around with the tools to become familiar with them. Since you have the UMIK-1, you'll want to use Room EQ Wizard as your program of choice for data acquisition - it's free and reasonably easy to work with, and its layout and features are oriented around room measurements. For loudspeaker design, the Dayton Audio OmniMic is a better package, just in the way its software is laid out. Good luck convincing Boom on the use of REW😂 |
|
|
|
Post by Boomzilla on Aug 19, 2017 16:28:42 GMT -5
OK - The speed of sound in air is a constant, regardless of frequency. I can back-calculate the distances from the peaks. I've got a laser distance measure & a calculator. What I can't do is tell if the peak is being caused by a floor or a ceiling reflection (pretty close to equidistant) or a right-wall / left-wall reflection (ditto). So if I were to line one side-wall with absorbers, and then find that the actual reflection was coming from the other side, I'm left with a bunch of holes in the wall or some windows covered with absorbers. It's also going to be hard to sell the WAF for ceiling absorbers (again). Really, really hard... The thing is, I've previously TRIED both side wall and ceiling absorbers with no audible differences. My audio amigo, Mr. garbulky, says it's because I didn't use enough of them. Maybe he's right, maybe he isn't. The problem is - there's no "try them for 30 days & send them back if you're not impressed" offers for room treatment panels (that I recall). As to REW software, I really don't see anything that it claims to do (that I'd even care remotely about) that my current software (FuzzMeasure) doesn't already do. And foggy1956 hit the nail on the head concerning my proclivities regarding REW. I will, however, look into Ethan Winer's book "The Audio Expert" (thanks DYohn). As with most of us, the worst "component" in our system is the listening room itself, and also like most of us, I may just have to live with what I've got. Boomzilla |
|
DYohn
Emo VIPs
Posts: 18,493
|
Post by DYohn on Aug 19, 2017 16:43:56 GMT -5
The problem is that even if you could calculate the approximate distance from the mic that is probably causing the peak or null, you still cannot tell in which direction. Audio is 360 degrees, it might be up, down. forward or sideways.
So I go back to my original thought. A waterfall plot by itself cannot tell you *where* a problem is originating, it can only show you *what* is a problem. Yur best bet is a gross sledgehammer approach to big issues: EQ.
|
|
|
|
Post by foggy1956 on Aug 19, 2017 16:57:23 GMT -5
OK - The speed of sound in air is a constant, regardless of frequency. I can back-calculate the distances from the peaks. I've got a laser distance measure & a calculator. What I can't do is tell if the peak is being caused by a floor or a ceiling reflection (pretty close to equidistant) or a right-wall / left-wall reflection (ditto). So if I were to line one side-wall with absorbers, and then find that the actual reflection was coming from the other side, I'm left with a bunch of holes in the wall or some windows covered with absorbers. It's also going to be hard to sell the WAF for ceiling absorbers (again). Really, really hard... The thing is, I've previously TRIED both side wall and ceiling absorbers with no audible differences. My audio amigo, Mr. garbulky , says it's because I didn't use enough of them. Maybe he's right, maybe he isn't. The problem is - there's no "try them for 30 days & send them back if you're not impressed" offers for room treatment panels (that I recall). As to REW software, I really don't see anything that it claims to do (that I'd even care remotely about) that my current software (FuzzMeasure) doesn't already do. And foggy1956 hit the nail on the head concerning my proclivities regarding REW. I will, however, look into Ethan Winer's book "The Audio Expert" (thanks DYohn ). As with most of us, the worst "component" in our system is the listening room itself, and also like most of us, I may just have to live with what I've got. Boomzilla Quite possibly, we are the worst component in our system😎 |
|
hemster
Global Moderator 
Particle Manufacturer
...still listening... still watching
Posts: 51,952
|
Post by hemster on Aug 19, 2017 20:53:09 GMT -5
OK - The speed of sound in air is a constant, regardless of frequency. I can back-calculate the distances from the peaks. I've got a laser distance measure & a calculator. What I can't do is tell if the peak is being caused by a floor or a ceiling reflection (pretty close to equidistant) or a right-wall / left-wall reflection (ditto). So if I were to line one side-wall with absorbers, and then find that the actual reflection was coming from the other side, I'm left with a bunch of holes in the wall or some windows covered with absorbers. It's also going to be hard to sell the WAF for ceiling absorbers (again). Really, really hard... The thing is, I've previously TRIED both side wall and ceiling absorbers with no audible differences. My audio amigo, Mr. garbulky , says it's because I didn't use enough of them. Maybe he's right, maybe he isn't. The problem is - there's no "try them for 30 days & send them back if you're not impressed" offers for room treatment panels (that I recall). As to REW software, I really don't see anything that it claims to do (that I'd even care remotely about) that my current software (FuzzMeasure) doesn't already do. And foggy1956 hit the nail on the head concerning my proclivities regarding REW. I will, however, look into Ethan Winer's book "The Audio Expert" (thanks DYohn ). As with most of us, the worst "component" in our system is the listening room itself, and also like most of us, I may just have to live with what I've got. Boomzilla Quite possibly, we are the worst component in our system😎 I'm the worst component in anyone's system!    I tend to look for opportunities to improve the SQ and make suggestions.. often it's futile. But still.. life's too short for bad audio. Just not convincing some people.. you know the types...with scratchy CDs and mp3s... |
|
|
|
Post by Boomzilla on Aug 20, 2017 5:50:10 GMT -5
Constructive criticism never makes you a bad component.
|
|
