Be gentle please
looking for some advice on PVC pipe resonators 
Pipe dreams??????
Trying to get rid of this 50hz hang in the room. Got some PVC pipe and got them to resonate at the frequency I wanted. Three 10ft pipes basically cut in half and a neck added to lower frequency. Added some poly fill to see if it did anything. Do I do 3 more or am I just wasting my money?
https://vimeo.com/894328084/979b8b537f?share=copy
Pipe dreams??????
Trying to get rid of this 50hz hang in the room. Got some PVC pipe and got them to resonate at the frequency I wanted. Three 10ft pipes basically cut in half and a neck added to lower frequency. Added some poly fill to see if it did anything. Do I do 3 more or am I just wasting my money?
https://vimeo.com/894328084/979b8b537f?share=copy
I have built many PVC Helmholtz resonators, including an S shaped 9 ft. Long resonator, for which I used two elbow joints, two end caps and three straight pipes. 6” inch diameter. The finished resonator was closed at one end (end cap) with brass nozzle on other end cap. I also placed a grapefruit size ball of hollow fiber wool inside the resonator just prior to sealing, to absorb high frequencies. I used purple primer and PVC cement. You can fine tune resonant frequency by selecting desired nozzle length and or diameter. The nozzle of the finished resonator is placed where the standing wave or reflected wave of interest is located. There are Helmholtz calculators available on line.
I used the polyfill to stop the upper harmonics of the resonator, not the frequency it was tuned at. Do you still recommend using some left over rockwool instead?
Yes, this is what I used except I used a 4" to 3" coupler to a 3" pvc neck for the tuning. Do you think I would be better off with a chunk of mineral wool as opposed to my polyfil? I wasn't sure of the stuffing was to get rid of the upper harmonics of the resonant in the pipe itself (when I bang the pipe on the floor, before polyfil) it would ring at the resonant frequency but was also accompanied with some harmonics of the pipe resonance. When I put the polyfill in it no longer rings when I bang the end on the ground.
Do you really think the energy, that is in the modal space in your room, will suddenly decide to concentrate and magically jump into the 6" opening of your trap? Try to be realistic!
It is right that energy that you induce into such a "trap" will be converted to thermal energy, if you put some absorbing material inside.
It is wrong that it actively "suck's" energy out of the room. If there is no absorbing fiber inside, it will simply resonate at the tuning frequency.
Try an experiment: Blow over a bottle. This will produce a certain frequency. Now place some identical bottles near the bottle you use to make that sound. Does the sound get absorbed or do you hear it just as loud in the room? Repeat with fiber filled bottles. Any change in what you hear? No? Why not?
If you think this experiment is ridiculous, you now realize that the funny idea of "bass traps" doesn't work. Like a mouse trap without cheese.
There are people selling these for huge money. Now you know why this legend is told again and again...
Anyway, absorbent material, placed in the right places, is able to reduce reflections that are not wanted in a room. As people are not educated enough to understand the physics behind it, they can not differenciate between a working absorber for higher frequency and a snake oiled bass trap.
Last, people dislike to admit they have been fooled, so they tell you they work, a little. Maybe, they even hope to sell them to the next idiot. Not surprising, all commercial bass traps are "made to order", which excludes any right to return them.
It is right that energy that you induce into such a "trap" will be converted to thermal energy, if you put some absorbing material inside.
It is wrong that it actively "suck's" energy out of the room. If there is no absorbing fiber inside, it will simply resonate at the tuning frequency.
Try an experiment: Blow over a bottle. This will produce a certain frequency. Now place some identical bottles near the bottle you use to make that sound. Does the sound get absorbed or do you hear it just as loud in the room? Repeat with fiber filled bottles. Any change in what you hear? No? Why not?
If you think this experiment is ridiculous, you now realize that the funny idea of "bass traps" doesn't work. Like a mouse trap without cheese.
There are people selling these for huge money. Now you know why this legend is told again and again...
Anyway, absorbent material, placed in the right places, is able to reduce reflections that are not wanted in a room. As people are not educated enough to understand the physics behind it, they can not differenciate between a working absorber for higher frequency and a snake oiled bass trap.
Last, people dislike to admit they have been fooled, so they tell you they work, a little. Maybe, they even hope to sell them to the next idiot. Not surprising, all commercial bass traps are "made to order", which excludes any right to return them.
I'm curious. Did you read what I wrote or watch the video or did you simply read the title? I ask because you go on and on about bass traps but I actually don't mention a single bass trap in my post, aside from the tittle.
Helmholtz resonators are not bass traps. They do not trap the sound. They are also not snake oil as they have been used for millennia to tame sound in large churches and such in ancient days. They are used today to help tamp down the sound from our exhaust in our cars.
I have since made 6 more of these for a total of 12 in my room and they definitely brought some of the decay time down at the frequency they were tuned at.
Very intuitively, I would think about the damping inside the pipe as an attenuation of its efficiency to absorb the resonance...
I mean : assuming that the annoying "50Hz peak accident" is high and narrow (chances are...), then a fine-tuned pipe prone to resonate generously and sharply to that frequency (without damping...) would be more efficient to "null" the 50Hz accident by a deep and narrow "50Hz hole accident", if I can say so...
In other words : the sharp 50Hz "peak" would be better absorbed by the matching 50Hz "depth", that is to say a sharper resonator, with a higher resonance factor Q, so less to no damping inside it (like a flute or an organ pipe).
OK : my point of view here is purely empiric ! But, by chance, did you made the test damped vs. empty ?
T
Yes, that all seems to make sense to me. I tried to put just enough in to stop the other notes from ringing out of the tube when I would bang the capped end on the floor.
Isn't that what we are both talking about?Ah, OK - Honestly, I have no experience in pipe traps... More in resonant pipes !
Another thing to consider is that resonators, including Helmholtz resonators, must be place precisely where the anomaly is in the room, the anomaly can be any point or area where peak sound pressure is 6 dB or higher than the average sound pressure in the room. The general idea is to smooth out or neutralize these high peak SPLs. But if a resonator is placed somewhere else, arbitrarily, then the sound can and will suffer. That’s why tube traps sometimes should be placed away from a room corner, for example. It depends on where the standing wave is located. That’s why I suggest mapping out the room with sound pressure meter and test tone or tones, to establish the number of room abalomalies before building any resonators. Helmholtz resonators are not the only game in town, not by a long shot.
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Just moving a few of them changes decay times at different frequencies. I'm trying to figure out if they work better all co-located or spread out along the wall. That 50hz sound pressure wave is strongest in the corners I think but also has some spots along the walls that are pretty high. I have them spread all around right now. I wonder if they get in each others way and are less efficient and affective if placed too close to each other.
Deffinitely not the only game in town but, holy crap so quick and dirty. Grab pipe from Home depot, cut in half (almost resonates at 50hz right there) add a little neck, add a fistfull of polyfill and done.
I don't notice much change in the SPL peaks but more in the decay times.
I imagine it is much easier to deal with issues and decay times in the nearfield. The percentage of room involvement is greatly reduced.
Of course yes ! Moreover my room has a slanted ceiling and is (unpractically) crammed with stuff (in storage) that - for the occasion - provides enough sound neutrality...
Incidentally yes, many of my Audio pals are often fronting some resonances problems with their much larger listening rooms - usually their living room, shared with the rest of the family - and this complicates the possibilities of acoustical treatment and speaker placement, de facto...
T
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I read it even twice...
Bass traps are Helmholz resonators, as far as I can see. The things you see in churches are organ pipes. They work because they produce resonances, but you can not get the resonance back inside...
Anything else will not take up energy at all. Anyway, with your two measurements I see nothing that may not be the cause of two measurements, some time appart. Repeat them 15 times and average them. Do not touch the microfone, do not change your position. Even the simple existance of a larg object in a room or an open door will cause differences like you see in your plots. Even the software induces differences.
Even if you change nothing in the room, there are always measuring tollerances of a few dB. Try it.
In most cases what you belive to hear is what you would like to hear. You think it will work, otherwise you would not wast time and money for this "experiment". So you are subjective and fool your self.
I have been to audio trials, where the charismatic instructor could convince a majority of listeners of audible differences, even when nothing was changed at all. If you objected, others would comment like "wash your ears" or "get a hearing aid". The harder you try to hear a difference, the more likely it is you do.
To hear a difference is good, not hearing one is disapointing. Like failing a test.
I for example, have very simple, cheap A-B switching devices. Remote controlled, the last build even wireless, so you don't have to move your body for an objective A-B comparison. I use to it to compare amplifiers, CD player and DAC's, and while improving speakers
Such a device should be the minimum hardware for anyone who has an opinnion about any gear. Not many posting here have something like that. I add a picture of mine.
Decades ago I had to realize that recognizing small differences by listening was impossible if you had to get up, switch some gear and change some wires. Like when you wanted to know which type of capacitor sounded better in a crossover or even a RCA cable. With a break of only 30 seconds, things got inconclusive. If there is a 5db peak in the midrange instead of a flat, you can easily hear it if you hit the note, same with 2% distortion to 0.1%.
Anyway, when you start to fine tune things, your audio memory is very,very limited and dependent on your personal mode, concentration, time of day and outside noise.
Always try to stay on a foundation of physics.
