Basics of Acoustic Engineering (Full Article)

acoustics
Basics of Acoustic Engineering (Full Article)
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#43

+1 for believing in Global Warming, thank you I have hope for this world.

I am like a gas pump, always open. Always behind on paperwork


#44

Could you provide a link to the literature where you gathered these diagrams from ?


#45

I found them here…the math itself is valid. This basic equation for notes and antinodes is commonly accepted. But I’m not sure what or how or why this relates to the speed of sound divided by 30 assertion.

https://physics.info/waves-standing/

AlphaVictor said he was a little intoxicated at the time he posted this. He didn’t give an explanation of this 37 foot theory, which parts of Boz’s response he found incorrect, or why his response was incorrect. Rather he told him to go read a book which is really a full-blown add hominem. It really does no good to tell someone this…

…without giving at minimum, a rebuttal of what they think was incorrect. Quite frankly, when someone posts all that stuff, then someone challenges it, then the other person says “well, I don’t have time to explain it”…it raises one of 2 questions: 1 - If the person truly understands it or 2 - if they completely lack skills necessary to accurately and concisely communicate this to people to whom they are trying to share information with. (For the record, I think Dave is brilliant at doing this, hence the reason he runs his own department at NASA).

So hopefully AphaVictor can clarify some things today, because there are a good number of people here (like myself) who do understand basic math, and are willing to think about what is being discussed here if there’s meaningful content up for discussion.


#46

Those images come from here: https://physics.info/waves-standing/

They show a standing wave with a fixed end and a free end. Room modes happen with two fixed ends, so the correct images would have been these:

https://physics.info/waves-standing/harmonics-1.svg


#47

lol…I found this video while I was digging through materials trying to follow along with this discussion :smiley:


#48

I’m sitting trying to figure out why I just watched that entire video. (??) I kept waiting for something to happen… Maybe this will help. Play this in the background while watching @Jonathan 's video. It’ll make sense at the end. :face_with_raised_eyebrow:


#49

I was really really hoping he would have started spinning it and flames would have been thrown in all directions. I almost feel like I should go remake that video exactly the way it is with the ending I was hoping to see, just to scratch that itch.


#50

was not talking about room modes, and of course you are correct about room modes.

(misunderstanding on resonant boundary distortions vs room modes cleared) << cleanup

Aside from basic phenomenon like room modes, there are millions of things happening in a room, millions of reflections, many different types of acoustic challenges, some predictable and some unpredictable. Unpleasant harmonics can very well be generated based on the materials, vibrating structures and geometry of the structure alongside other issues.


#51

I looked back over this and I don’t see where Boz said it was (the only think happening in the room)…did he?


#52

(offtopic ) cleanup


#53

boz and I were talking about different details, I came to know of it when he was talking to Michelle. I had not even yet begun explaining room modes, I was talking some other basics of wave collisions before that… that do happen in a room


#54

Nobody disagrees with that. Nobody ever did disagree with that.


#55

People are going back over some of what you have wrote and how Boz has replied out of sheer curiosity. This is how people learn things. I could rant off a hell of a lot things about music history, music theory, or music copyright law that you won’t understand, and if you wanted to follow the conversation, you’d need to take a quick look over my sources to re-acquaint yourself with the content. Its not a “I doubt this” thing going on here. Its about people trying to follow the conversation.


#56

(misunderstanding cleared) - off topic cleanup


#57

I think where you are looking for more explanation is if it is important for room size to be around the wavelength of the schroeder freq… let me try to explain it one more time.

lets say 100 hz is the crossover freq, you have an alto flute player and a bass flute at one end of the room.
one thing though I want to clarify, its not so much as the room size as opposed to distances to different types of surfaces, materials etc. These vary based on room to room. The “room size” itself is a generic term that relates to “unhindered space” really.

wavelength of 100hz is around 1130/100 = 11.3 ft lets say roughly 12
there are vibrating surfaces located at 3ft at 45 degrees, resonating surfaces located around 9ft relatively perpendicular
the waves from the bass flute are going to hit those surfaces with partial collisions , partial collisions generate in-harmonic and odd overtones. Some overtones are pleasant , some are problematic. That is what I was referring to.

Now if there were no obstacles in an ideal world, if the room had around 12-14 feet of unobstructed passage, the collisions would generate even harmonics. It would still generate some inharmonics but overall result is a bit pleasant.

Now if the room were to be treated properly, room size would become immaterial (and room ratios with a minimum size contingency come into play more) and yes in that sense you are correct. But an ideal treatment is unlikely, budget restrictions etc.

I should have worded my premise a little differently. To add to this, I started the topic at a much more basic level , geared towards those who are totally unfamiliar with it, hence I talked about very basic stuff first. Different priorities and different orders.

As the article is developed, I will evolve it so both a beginner and an expert level of knowledge would be able to relate to it.


#58

The only two things I’ve said from the beginning and haven’t seen any answers for

  1. “to be an effective studio, we must be able to handle low frequencies, lets say 30hz. By handle, I mean “room to breathe” or flow unrestricted.

    In an ideal world, 37 feet of room, is important to let the sound flow unrestricted inside a room for low frequencies such as 30hz, which means an effective studio must be 37 feet long in the direction of the sound source.”

The way you are saying this, or the way I’m understanding that you are saying this, is that once you get beyond 1 wavelength of the room in size, it suddenly becomes easy to handle because the wave has “room to breath”. All I’m saying is that 37 feet is not any sort of hard line of good above/bad below (for a 30Hz wave). As you get larger, it gets easier to manage, but not in any sort of hard line fashion like you are implying here.

If what you are saying is in fact true, I would love to see a source. That’s all I’ve been saying the whole time.

  1. when a wave collides against a resonating structure at a premature cycle, it generates higher frequency harmonics (odd harmonics) that pool up together and eventually create higher intensity standing waves than it would if they were even harmonics.

    here is a diagram where waves that collides at maximum amplitude generating higher frequency overtones (odd ones), generating more overall reflected intensity and harshness.

I’m sure boundaries do create distortions. I’m willing to believe that even without a source. But it seems pretty far fetched to me that the boundaries will create such high levels of distortion at normal listening levels that it’s of any significance at all. Again, if you have a source for this that shows otherwise, I would be more than happy to see it.

Also, I think it’s strange that you are using a diagram of a standing wave to show an illustration of this fact, when the image you used would not ever take place in a room as a standing wave.


#59

resonant boundary distortions

Here is a simple experiment, hang a wind chime in your studio (metallic and good quality). and clap about 10 ft from it and record the result near the wind chime. If your studio is perfectly treated, thats another story. Then you may want to hang it in an empty room, and then clap loud from around 9-10 feet.


#60

ok, now it’s making more sense what you are talking about with this one. When you first posted the idea of waves creating harmonics at a boundary, you didn’t mention the boundary being a resonant boundary. It sounded like you were saying it’s a byproduct of a wave reflecting off any material. Reflecting off a resonant material changes it completely (which is why I mentioned rattling walls).


#61

yeah, I was pretty drunk yesterday and I think I was playing tug of war with you but from a different rope altogether while still writing the article. I will add more details and polish the article a bit better over time. I personally have no need to spread any kind of misinformation and I appreciate the indepth questioning :slight_smile:


#62

Note to self … things alcohol doesn’t go good with: driving, tightrope walking, stomach ulcers, counting backwards from 999, headstands, javelin throwing competitions, horseshoes, internet forum debates. :upside_down_face: