The Quarter Wavelength Rule And How It Applies To Room Acoustics

[@CraigFlowersMusic]

I didn't understand what you meant. Yes, okay, 4.5ft is 1/4 of 18' which is a 60 wave. Ten minutes of saying that ten ways or more, yet nothing I could discern about anything you're applying that principle to. Add 4.5' to acoustic treatment how? Make acoustic treatments 4.5 feet in what way? What is the context of this principle you're trying to impart? This felt so incomplete as to lose the conception of the very premise.

[@AcousticFields]

C, Education of complex issues requires a step by step process. Our experience with illustrating complex subjects tells us no more than one main item per video. If you try and define and explain the issues and then offer the next logical step as you have illustrated, people get confused. A confusion that translates into numerous phone calls and emails for me that takes away from my available time with customers. We will be doing a follow-up series on this topic in 2019 taking this concept to the next step and applying it to small room acoustics.

[@CraigFlowersMusic]

Thx but I asked for elaboration not a defense; that in no way answers my question. 4.5 feet what? 4.5 feet in what way? In what regard? 4.5 feet from the short walls? 4.5 feet tall? 4.5 feet is 1/4 of 18 yes, but you can't just apply that to NOTHING and call it a rule.

[@matthewward5813]

It has to do with particle velocity when the strength of the wavelength is at its weakest then theoretically it should be easier to stop with velocity based absorbers such as broadband panels etc...so to trap 60 hz fully you would need 54 inches of pink fluffy stuff to completely trap the wavelength. Limp mass absorbers or helmholtz helps in this situation, but by all means look into it dont use pieces of charcoal briquettes to tey and fix it at over a thousand dollars a pop. A sealed cabinet with hardboard or mass loaded vinyl does wonders if tou know the math so you can build them deep enough etc...

[@rafalvarezsevilla]

@@AcousticFields but which video shall i watch next? step by step is the right way to walk, but where shall we step next? we get lost in youtube randomness if you don't lead us a little bit, maybe you could PIN a comment with a link to the following subject? would be dope! much love and thanks for your work, really appreciate it!!

[@basscat111]

There are 2 types of sound absorbers: pressure and velocity. At a physical barrier, the velocity of the air particles is zero and consequently the pressure is at a maximum. At 1/4 wavelength from the barrier, the velocity is at a maximum and the pressure is zero (in a perfect environment). Porous absorbers, like rockwool, absorb best at maximum velocity, so if you want to absorb the 60Hz wave that he is talking about, you will need to place your rockwool panel 4.5ft from the wall. This isn't practical in most situations, so the better solution is to go with a pressure-based absorber like a diaphragmatic panel absorber mounted on the wall where the pressure is at its maximum.

[@MrBonger88]

Definitely saving this video so that I can refer back to it in the future. Thank you

[@AcousticFields]

Glad it was helpful!

[@Arcygenical]

Thank you. Explained very well to my SO why we needed a few acoustic panels in our Sun Conure Parrot's room (95dba max screaming) and why they needed to be the size, shape, and offset from the wall that they are. FWIW, Sun Conure's scream biased in the 2k-4.5k hz range, so absorption is easy with 2" rockwool and a distance from the wall of 2.875cm. Cheers!

[@AcousticFields]

A, Building insulation will provide absorption in that frequency range. However, it does not provide the proper rates and levels for music and voice. The fibers are also lighter than air and can go through any fabric covering stretched over it. look at what those fibers are made of and then ask yourself if you want those in your bird's lungs and any other living thing in that room.

[@HollyWinn]

I can always go through your videos to check it you have one on this, but Id be interested to see the process of building and placing the treatments in a room based on this video. I'm unfamiliar with quarter wavelength bass traps, how they might be built and implemented. As I read, it was getting a bit confusing -- so it would be great to see one of those put together to resolve a similar issue to the one mentioned when trying to absorb bass. My understanding is it tends to bunch up in corners. I also know there's pressure-zone traps, functional traps, and active traps. Trying to learn the different use cases of each. Thanks for the video!

[@daniloviana8818]

At 1/12 wavelenght, wich is just 33% of the original impractical 137 cm of 1/4 wavelenght, you still have 50% of energy in speed form, and it's a practical distance of wall (46 cm) for hanging treatment. please correct my numbers if I'm not right.

[@chadbarker2316]

Damn. Finally somebody actually explains this shit instead of just throwing things up on a wall. As I'm building my wife a sound room in the basement. She has cancer and I want her to enjoy her music while she's still here. I'm just an old construction worker getting back into audio so I really appreciate your very imformadable videos man. Just got her a Sansui 9900,Luxman TT and Infinity Kappa 7s thay sound damn good. Ain't rich but think I did pretty good. Finishing the drywall tonight . Thanks again

[@AcousticFields]

C, let me know if you have any issues with your build. We have a whole DIY series of product build plans. www.acousticfields.com/product-category/d-i-y-acoustic-treatment/ You can buy the carbon and foam from us.

[@AtulJataayu]

Thanks for the valuable knowledge you are imparting. You are my Guru.

[@AcousticFields]

A, Thank you for your support. If you have a topic you wished covered in video format, let us know. Send to: [e-mail]

[@enriques8094]

Reales trustable info

[@TheTruthAlwaysAddsUp]

It wasn't clear to me what you were saying.
What if the room was 18' long?
What about if the room was 13.5' long?
Please explain what the 1/4 wavelength rule means.
Thank you

[@AcousticFields]

T, An 18' length would be best. Here is a different definition:
Quarter-wavelength rule : If a wall is a node, then the nearest other node at any frequency will be 1/2(wavelength) away from the wall. Given this, the antinode is midway between those two points, or 1/4(wavelength) away from the wall, for any given frequency. So, for example, if you want to filter out 60Hz, divide 18’ (the wavelength of 60Hz) by 4 = 4’6" and hang a thin layer of frictional material (acoustic foam) at that distance from the wall(s) and floor and ceiling.

[@NorthPoleJeff]

@@AcousticFields I really liked your video, It really opened up my eyes into how the acoustics works. But, here's another explanation from the wave sense. If you think of a sine wave, the positive peak is at the 90 degree point. That means that the highest amplitude or sound level will be at that point. If you want to quiet a room, then place the sound absorbent material at that 90 degree point and it will be the most effective in absorbing the sound. But, at the 45 degree point, the effectiveness of the sound absorption would be about fifty percent less. Thanks for making this video and it was a bit difficult to understand the directions of the wave in the drawings. Have a nice day.

[@grindingguru]

Denny... when you have said > the space between the front 2 channel speakers is hallowed ground, meaning nothing should be there... AND your hatred of glass also... what am I supposed to do if I want a monster 75" screen in between the R/L channels? Isn't that plexiglass in exactly the wrong place? I can't wait for your reply!

[@AcousticFields]

Cover the screen with sound absorption or sound diffusion technology when listening to two channel.

[@sarathsankar929]

Very helpful video Dennis Foley..

[@AcousticFields]

sarath sankar Thank you, much appreciated.

[@grindingguru]

If anything, should I place the the baffle of the speaks in front of OR behind the screen?

[@AcousticFields]

Neither. If you place them behind the screen, you attenuate 4 - 6 dB of sound energy from source. Never loose energy from source in order to manage it. Let source be source. In front of screen. I dont kknow what that means. Place them right and left of screen. Place them as close to screen as possible. Make sure the front edge of spaeker is ahead of the screen. Split the center channel signal into left center and right center.

[@J.RRandallIllinois]

Well explained, my buddy had me place my speakers according to the golden ratio of the room dimensions, not sure why. Is there a logical reason behind this ir is my buddy full of it, lol, thanks.

[@AcousticFields]

J, Its physics. Sound travels at a certain speed. It also takes that speed and travels over distance. In small room acoustics its all about the distance the direct energy (straight line from speakers to ears) and the reflected energy from walls must travel before it reaches our ears. Its a balance between straight line energy (speaker) and reflected (room) energy. The "Golden Ratio" is a starting point towards that goal.

[@manny_f]

Great video, as usual :)

[@AcousticFields]

Glad you enjoyed it!

[@esaugalindo4733]

Wouldn't you be seating facing the long wall and not the short wall direction? So you're saying it at least has 6 inches from the back walls/font or the side walls? I'm confused if we're facing the long wall it would be 6 inches from the front wall?

[@AcousticFields]

Rememeber the room does not care what you want. You must set up on the surface area that exhibits the frequency and amplitude issues that will best respond to treatment for the pressure issues. Along with this pressure consideration, you must then look to sidewall distance to manage primary, secondary, and tertiary reflections. The longer wall will satisfy the reflection issue but may not be the best pressure choice. Nothing in acoustics is easy.

[@esaugalindo4733]

@@AcousticFields i understand it not easy. Besides having s small room ( thats the biggest complaint for everyone) I purchased the diy kit made two bda and still i cant get or understand your concept. I challange you to make me a Believer. At this point all the money i spent on these BDA. Im starting not to have faith in what your saying

[@ronkalvaitis4199]

Ok. I went back to this one to try to understand it better. I understand the blow back of the energy and therefore it will stack up (I believe that's what you're telling us). In a practical sense are you suggesting we measure the room and figure out what the maximum wavelength is that will fit in the room so we know we need to especially work toward treating the frequencies below that?

[@AcousticFields]

R, There are many variables we must look at in room size and volume. Quarter wavelength, half wavelength, SPL levels, and a host of others. If you use full wavelength you have a good start towards ideal. The compromises from that ideal start point will determine the quality level we have to start with when we face the reality of small room acoustics.

[@monetize_this8330]

Do you always treat the shortest wall-wall distance?
Wouldn't floor to ceiling be shorter. My rooms are 8' 6" high, isn't there a build-up of energy if the shortest wall to wall and floor to ceiling are almost exact. (or a multiple such as 17' 2")?

[@AcousticFields]

D, Shortest distance largest problems below 100 Hz.

[@juststuff5216]

Interesting video!

[@rahulraj-us9er]

sir thank you for the info and I also have question : how to design a quarter wavelength trap for 500hz?
what are the steps involved in designing it?

[@AcousticFields]

A 500 Hz, issue can be resolved with a 2" think piece of open celled foam

[@westikle]

ok. but what about the thousands of other frequencies that are generated when you play music?

[@AcousticFields]

All energy goes into the room. This 1/4 rule is showing what will fit and what will not.

[@TelstarElectronics]

Good video. Let me add that 1/4-wavelength effects are far-reaching. They can be applied to transmission lines and antennas in electronics... and also apply to light/optics!

[@AcousticFields]

Wavelengths come in sound and light. I would be interested in the color associated with the wavelength for light.

[@claudevandarn8083]

Dennis, I really enjoy your video's as you are great at breaking things down for newbies like myself. I have a question about seating position and the frequency to diffuse.
If I am diffusing both the front and rear wall in a critical listening room, should the diffusers used have matched frequency given that the distance to the rear wall is much closer than that of the front? In my case, I'm on the short side of a 7x22 room with the seated position being up against the back wall. From this video, I know that we could safely go down on the front diffuser to 282Hz but unsure of the rear given that it's directly behind my head when seated.
Any help would be appreciated.

[@AcousticFields]

You will have to use two dimensional diffusion on the rear wall due to proximity.

[@claudevandarn8083]

@@AcousticFields Should I build the rear diffusers with the same 282hz goal in mind? As I understand it, the target frequency depends on distance from listening position. With the rear diffusers being so close to that position would that number rise for the rear diffusers only?

[@ibad1352]

plzz share a link after this video.to understand the process.As you have told in this video

[@AcousticFields]

I, There is plenty information on the net that you can use.

[@RichTeer]

An interesting video, but I just get my head around an acoustician referring to "cycles" instead of Hertz (Hz)!

[@AcousticFields]

Energy moves in repetitive cycles. A 60 hz. energy wave cycles 60 times per second.

[@Altuz]

Hi Dennis, thank you again for your insight. When a single 60Hz wave is formed from the driver of the speaker, what happens at 18' away from the speaker once the wave completes it's cycle? Does it decrease in amplitude(is that the correct term?), thus making it easier to manage if the room is larger than 18'? If so, by how much does it decrease in amplitude (if that's the correct term)?

[@AcousticFields]

A, Remember that waves oscillate through the air in cycles. Each wave has frequency and amplitude. If you look at a 18 8' wave individually, you would have to know the ending point of the wave as a result of boundary interference.

[@Arcygenical]

Assuming a constant 60hz wave, with an amplitude of 1 unit, and a wavelength of 18', at both 0' and 18' the wave will be at full amplitude (1). The wave will also be at full amplitude at 9' due to the way a sin wave works. 18' away will sound as loud as 0' away, as will 9'. These are maximum pressure modes for a single wave. This is assuming a perfect room with no absorption factors (couches... Cushons... Curtains... Etc.) and a single source of sound. After 18' the cycle repeats (with peak modes at 18', 27', 36') at a reduced amplitude due to a function of distance. The general rule is that, every doubling of distance, you lose 6db. That's not actually a lot. A subwoofer dumping 100db into a room at 60hz, at 1, 9 and 18 feet, will only be attenuated to 94db at 18, 27, 36 feet. As a general averaging rule.
And unless you're playing single tones of music, harmonics play a large factor as well. A tone of 60hz, with harmonics at 120hz, 180hz, 240hz etc. will greatly complicate the dampening effect of distance.
realtraps.com/art_rear_wall.htm

[@hugovejar6960]

great explanation! thanks a lot, what happens with monitor position? I know it is also applied this theory to know which frequency will be affected

[@AcousticFields]

H, Why be concerned about speaker placement by dodging modes and looking for places where there is minimum pressure issues. Why not treat the room to minimize these issues throughout the room.

[@hugovejar6960]

@@AcousticFields Thanks a lot!

[@sergejharres7932]

Thank you so so much for all this great videos!! My Gury aswell!

[@AcousticFields]

S, You are welcome. If you have any topics you wish covered in this video format, send us email to [e-mail]

[@renegiasson3492]

Hi i have a room that is 24f x17 f whith a vallt 10f at the cener of the room yousing the quarter langth rule for placing my moniters Iam lost about placing the furst reflektion absorbing I want to use the room for recording and mixing what do I do Rene

[@AcousticFields]

Hi Rene Giasson
Thanks for the comment. Please complete this form on our site so I can better understand your room layout: www.acousticfields.com/free-acoustic-treatment-room-analysis-tell-us-about-your-room/
I will be better able to advise you with this information to examine.
Thanks
Dennis

[@rodriguez.fernando]

Hi! Great video, thank you for sharing your knowledge. One question: Does this mean that you should place your acoustic treatment for that frequency (in this example, diaphragmatic absorption for treating the 60Hz) at the 1/4 distance? Or at every 1/4 distance of the wave length? Will the position of the, say, mixing desk interfere with the placement of the absorption?

[@AcousticFields]

F, Yes and no. Yes, placing the treatment at 1/4 wavelength distances is desirable for low performing absorption technologies, but not practical. It is best to use a technology that can absorb at 60 Hz. with the rates and levels you require regardless of where you place it.

[@rodriguez.fernando]

@@AcousticFields Thank you for your reply! This is very helpful.

[@kerryeblen189]

do u have any reason to be coming to Northern Wyoming or close? we are a small {483seat} Vaudevillian house {1930 Streamline Moderene} space with acoustic needs between musical fidelity and speech clarity. non-profit with limited funds. Kerry

[@AcousticFields]

K, No plans at the moment. Fill out the information in this link: www.acousticfields.com/free-room-analysis/

[@dukepalk6324]

Thankyou for the lecture. I can imagine this formula is similar to EMF disbursement. ₩"Thanks Old school pitbull's"₩

[@user-fb1fs8by8e]

Why don't we go from room sizes instead of going from frequencies/cycles?

[@AcousticFields]

B, I do not understand your question.

[@user-fb1fs8by8e]

Acoustic Fields, sorry. I mean, do we have to find the frequency, don't we? Should we take that 60Hz frequency as an example or to be treated in any room?

[@AcousticFields]

B, The video is about quarter wavelength theory. You can use any frequency to illustrate.

[@user-fb1fs8by8e]

Acoustic Fields, thank you for the answer!

[@mickywes3733]

Why is 60 cycles so important?

[@AcousticFields]

Take the length of a 60 Hz. wavelength and compare it to an 8' ceiling height.

[@stevemorgan6946]

Dennis with thi equation would a 30hz cycle be 36ft long?

[@AcousticFields]

Hi Steve Morgan
How are you? You are correct: 1132 / 30 = 34.40'. Now, here is a good question for you. What do you know of that will stop a sound wave of energy 34.40' long?
Thanks
Dennis

[@stevemorgan6946]

Diaphragmatic absorption device placed at 1/4 lenths along the wall?

[@stevemorgan6946]

What are you doing up so early? All nighter?

[@AcousticFields]

Steve Morgan I'm an early riser :)

[@AcousticFields]

Hi Steve Morgan I answered your question on the quarter wave length rule in greater detail in yesterdays Google Hangout. You can see the part where I answered your question here ua-cam.com/video/eVzFJYai0s0/v-deo.html. I also answered your question re: diaphragmatic absorber placement here ua-cam.com/video/qhNXi4cpVMM/v-deo.html
I hope they help. Please let me know if you have any follow up questions I can help with.
Thanks
Dennis

[@greganikin7003]

Can it be applied in the metric system?

[@AcousticFields]

G, Yes, it is the distance that matters, not the unit of measurement.