# Problem with resonance tone in DIY spray bar



## TimT (1 Dec 2013)

Does anybody have any experience the with these resonance tones in the spray bars? DIY or not? It can't be stopped by fixating the spray bar firmly. It seems to be more flow dependent and you can play it like a flute by covering the holes  Often I can stop it by blocking 2-3+ holes in a not obvious configuration. The combination varies a little from time to time.




I don't know that much about acoustics. Is there a simple way of stopping this and also making sure that they don't keep reappearing as the flow changes due to how dirty the filter is?

Thanks


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## Samuran (2 Dec 2013)

I don't know if it's just me but the only noise I can hear on that video is white noise... and a few pops and clicks...


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## TimT (2 Dec 2013)

I have tested on two additional Pc's now. I can easily hear it on both. It's a whistling sound. Somewhat deeper than when a human is whistling. And the tone is changing depending on which holes I cover. But thanks for the feedback on the video quality. Unfortunately I only have my mobile to do the video.


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## GreenNeedle (3 Dec 2013)

The sound is fine. I can hear it through my laptop's tinpot speakers  Can't help you with a solution though. seems strange.  Are you sure the end is completely sealed.


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## OllieNZ (3 Dec 2013)

Is it glass or plastic? If its plastic try opening the holes up 0.5mm at a time till the sound stops. If its glass you could try fine sand paper wrapped around a dowel. Before you get the tools out have you tried slowing the flow? If this fixes the noise then enlarging the holes will work


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## TimT (3 Dec 2013)

@Ollie: Thanks for the advice. It is made from Plexiglas. But lowering the flow is asking for trouble as my Eheim 2076 is already at the limit for running a tank of that size with any equipment attached. I hope that my CO2 reactor will solve it as that will change the flow compared to when I shot the video.

I could also bevel the inside edges of the holes. The sound is similar to what you will hear when making a whistling sound by blowing over the opening of a bottle. Perhaps rounding of these inside edges will stop it.



SuperColey1 said:


> Are you sure the end is completely sealed.


Thanks, yes it is completely sealed (and I have build in a little plug that allows me to open it later for cleaning)


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## ian_m (3 Dec 2013)

You need to add some damping of some form to stop the tube resonating (after having been involved in sorting industrial problems like this).

1. Try wrapping a bunch of elastic bands around the tube in various places to stop it vibrating
2. Make the end plug out of silicone rubber.
3. Put a layer of rubber between the tube and its supports.
4. Put a short length of PVC tube at the end then the end plug.
5. Make the holes spacing uneven and random.
6. Only have a prime number of holes.
7. Make a plug that can be inserted into various depths of the end of the tube, like a swannee whistle, you might find a position where it doesn't hum.
8. Make tube out of PVC pipe.
9. Flame round the holes to make them smooth.

Just a few thoughts...


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## TimT (3 Dec 2013)

ian_m said:


> You need to add some damping of some form to stop the tube resonating (after having been involved in sorting industrial problems like this).


Thanks Ian for putting your expert knowledge at work here!
I think I might have been imprecise when naming the thread. I begin to suspect it might be more of a 'standing wave' phenomenon' in contrast to a resonance one where it is the object itself that resonates. Holding the tube very firmly or even fixating it against something rock solid doesn't stop the sound. I guess a flute would behave a similar way. In a flute It is the air splitting on some edge that create standing waves and you can still play and hear the flute even though you hold it very tightly or even fixate it 100% I will play around with your options 2, 4, (6), 7 and especially 9 which I guess would have the same effect as making bevels. If it is a flute like situation then this could actually be the solution!
Thanks again Ian, really appreciate it!


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## OllieNZ (3 Dec 2013)

Just to clarify I meant to slow the flow as a test only. If it works then enlarging the holes will have the same effect as slowing the flow by reducing exit velocity


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## John S (2 Jan 2014)

Any resolution to this?

I've just made an acrylic spray bar and have the same issue but it goes by covering one of the holes


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## John S (2 Jan 2014)

John S said:


> ........ but it goes by covering one of the holes


 
Actually that's not true, it just raises the pitch so its less audible. Turning the flow up and down just changes the pitch so I think I might have to increase the hole size.


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## TimT (2 Jan 2014)

Hi John,
Sorry, no definitive solution. I added a CO2 reactor that changed the flow but that only covers the problem instead of solving it.
Good luck!


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## John S (2 Jan 2014)

Ok thanks Tim.

I'm going to try increasing the hole sizes.



Sent from my iPad using Tapatalk


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## John S (6 Jan 2014)

Well I tried increasing the hole size up to the point where the pressure was unequal across the spraybar and it failed to have any real impact

This is so annoying


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