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Post by patate91 on Jul 18, 2018 0:21:36 GMT
Patate91- I see that you're using REW. When you take measurements, you can set the software to take multiple sweeps per measurement. This is useful in a noisy environment (usually by "noisy" we mean HVAC but screaming kids count, too) because the test signal will sum coherently and the noise will not, so the signal-to-noise ratio of the measurement is increased. It's basically a mathematical way of lessening the impact of noise on your measurements. That being said, your data looks very good indeed. You're doing very well for a room of that size, far better than I would have expected based on your description. With the exception of the 68 Hz issue, your room is basically +/- 5 dB in the "modal" region (below Schroeder, if you're reading up on acoustics) so I think you should feel somewhat successful already. Really tough to tell given the available data, but I have a suspicion that the 68 Hz cancellation is an axial mode between the floor and the ceiling. If this is the case, it's going to be at ear height regardless of where you sit in the room, and I don't think there's much to be done about it. You can try to knock a few dB off the depth with some bass traps IF that's indeed what the issue is. You nailed it lol. I experienced the axial mode. With a tone set on the dip I hear it perfectly while standing up. The speakers are on 4' or 5' stands. First I was using a cushion to sit higher. If I remove it my ears are just above the backrest, where I'm now placing the mic. The response is better, and I'm more confortable. 4 inch higher and the dip is worst. I'll have to read about modal region, do you have a link or a suggestion? I'm very happy with my setup and improvement, I wish I discovered acoustic earlier, it would have saved me money lol.
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Post by Michael Lawrence on Jul 18, 2018 0:31:39 GMT
Sure, the Master Handbook of Acoustics by F. Alton Everest is exactly what it sounds like. Most libraries seem to have it, interestingly enough, although it's worth every penny. It's really the gold standard for learning about how sound waves behave in spaces. Also, if you don't have Ethan's book The Audio Expert, you should consider picking up a copy of that, too.
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Post by patate91 on Jul 18, 2018 0:34:45 GMT
Patate91- I see that you're using REW. When you take measurements, you can set the software to take multiple sweeps per measurement. This is useful in a noisy environment (usually by "noisy" we mean HVAC but screaming kids count, too) because the test signal will sum coherently and the noise will not, so the signal-to-noise ratio of the measurement is increased. It's basically a mathematical way of lessening the impact of noise on your measurements. That being said, your data looks very good indeed. You're doing very well for a room of that size, far better than I would have expected based on your description. With the exception of the 68 Hz issue, your room is basically +/- 5 dB in the "modal" region (below Schroeder, if you're reading up on acoustics) so I think you should feel somewhat successful already. Really tough to tell given the available data, but I have a suspicion that the 68 Hz cancellation is an axial mode between the floor and the ceiling. If this is the case, it's going to be at ear height regardless of where you sit in the room, and I don't think there's much to be done about it. You can try to knock a few dB off the depth with some bass traps IF that's indeed what the issue is. Do you think it will be possible to improved the +/- 5db with an EQ to +/-3 db?
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Post by patate91 on Jul 18, 2018 0:37:59 GMT
Sure, the Master Handbook of Acoustics by F. Alton Everest is exactly what it sounds like. Most libraries seem to have it, interestingly enough, although it's worth every penny. It's really the gold standard for learning about how sound waves behave in spaces. Also, if you don't have Ethan's book The Audio Expert, you should consider picking up a copy of that, too. My first language is french, so more technical books are harder to read. I'm still trying to find a french editor for Ethan's book. I sent a couple of emails but no success for now.
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Post by Michael Lawrence on Jul 18, 2018 0:42:07 GMT
Your English seems fine to me! You can certainly make improvements with EQ, but whenever you're dealing with system EQ, you have to look at the big picture. Pay attention to the general curve trends, not the details. I personally would only use a single low-q filter to bump that one range back down, see attached image. For more on this, check out my post here. One or two filters per channel, nothing severe. Attachments:
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Post by patate91 on Jul 18, 2018 0:53:53 GMT
Your English seems fine to me! You can certainly make improvements with EQ, but whenever you're dealing with system EQ, you have to look at the big picture. Pay attention to the general curve trends, not the details. I personally would only use a single low-q filter to bump that one range back down, see attached image. For more on this, check out my post here. One or two filters per channel, nothing severe. Thanks. I don't know if it's just the mic placement but all measurements I made during summer 2017 gave me this bump. Yesterday humidity level was lower and the bump wasn't that much. I tend to beleive that is mic related but I always wonder if humidity can have an impact. I'll try to find time for measurements during winter, humidity level is always low. I'll post new measurements soon, before I get the panels.
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Post by Michael Lawrence on Jul 18, 2018 1:08:08 GMT
The effects of humidity on sound have mostly to do with the attenuation of the highest frequencies over long throw distances. It becomes an issue primarily over 4 kHz, and in rooms much much larger than yours.
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Post by Ethan Winer on Jul 18, 2018 20:16:18 GMT
I'll just add this link to my Density Report that answers some of these questions. You'll see that having 12 3-inch thick bass traps beats six much thicker traps because more surface is covered, as pasim mentioned.
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Post by patate91 on Jul 18, 2018 20:47:26 GMT
I'll just add this link to my Density Report that answers some of these questions. You'll see that having 12 3-inch thick bass traps beats six much thicker traps because more surface is covered, as pasim mentioned. Great I missed that one. I'm tempted to try a diy FRK. I have a big craftpaper roll and some 1$ survival blanket (looks like foil).
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Post by patate91 on Jul 19, 2018 13:01:05 GMT
I would say no, but do I need frk at first reflexion points? Should I add my frk layer on all my panels?
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Post by Michael Lawrence on Jul 19, 2018 13:41:15 GMT
FRK is reflective at HF. Do not use it to treat first reflections.
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Post by Hexspa on Jul 21, 2018 23:23:59 GMT
I think that notch at 68Hz is also a candidate for corrective EQ. It's worth giving a shot, anyway. Just remember to take a few measurements in your seating radius to determine its balanced effect.
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Post by Michael Lawrence on Jul 22, 2018 13:20:25 GMT
Yes, Hexspa is right - corrective EQ is a potential solution (or at least part of one). When response dips are caused by a reflection, more energy at that frequency also gives more energy to the reflection (yell louder, echo gets louder) so it's important to kill the reflection as much as possible with acoustic treatment before using EQ. In the worst-case scenario, an infinitely deep dip caused by a 'perfect' reflection would never get any better regardless of how much EQ you boosted. All you're doing in that case is reducing the headroom of your system. For this reason, a very common approach in the live sound reinforcement side of the field is to use "subtractive EQ" only - only cuts, no boosts. If a part of the system is deficient, they will cut away other things to bring the rest in line with the response dip, so you gain headroom instead of losing it. Going more than maybe 6 dB in either direction is bad news. (That's 4x the amplifier power, a valuable commodity in the live world.) This is a little bit of a controversial topic in the audio community, and was just addressed in the SynAudCon newsletter this month. Here are some research papers to check out: www.prosoundtraining.com/2018/06/25/1993-tech-topic-on-equalization/
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Post by Hexspa on Jul 24, 2018 3:37:44 GMT
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Post by Michael Lawrence on Jul 24, 2018 14:00:00 GMT
Hexspa, thanks for the links. It's a bummer that those are paid papers. I don't know of anything similar that's free to access off the top of my head. All, in a live sound situation, the main effect of humidity that's relevant to large concert environments is HF absorption in the back of the audience, for which we use a hi-shelf EQ to correct. This is a great chart from Bob McCarthy's treatise, Sound Systems: Design and Optimization. I think it is based on data gathered at Meyer Sound. Note that we're talking about being 100m away. So the back of a festival or an arena can really be affected by this. Not ten feet away on your couch. You can be a few dB down in the back of a large movie theater, as I learned doing some research for Ethan's book - this is mentioned under "Room Curve." In live, we don't tend to concern ourselves too much with how the absorption coefficient of boundaries changes with humidity because we try not to hit them in the first place. In a small room, however, it's a different story. Even an RT60 of 0.3 seconds means that sound waves follow a 339 foot path. So you'll see all the effects of air absorption in the chart, PLUS the effects of hitting a boundary 15 times (or so. You could calculate "Mean Free Path" based on the room dimensions and figure out how many times you're hitting the walls, on average). The effects compound and start to matter more. (In theory. In practice, you're 60 dB down at the end. Realistically, once a wave is 12 dB or so below the direct sound, it's incapable of contributing much. A quick vector summation will confirm this.) Regardless, you're talking about numerous boundary reflections vs maybe one, which is why we can usually ignore it in big rooms (or deal with it in different ways) as opposed to small rooms. The obvious exception to this is non-amplified (natural) transmission in large rooms, like concert halls. They have really long reverb times and thousands of reflections. So I would expect there to be some data on that in the large-room acoustics literature. Maybe Beranek? As has been said by Hexspa and myself, though, we're dealing with a strictly HF phenomenon. In a live reinforcement situation, I would ignore the effects of humidity below 4 kHz or so unless we're out in the desert. I agree with Hexspa that if you have 500 Hz problems, they're not caused by humidity.
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