DIY Tube Bass Trap and frequency tuning

[Razorhelm]

Hi All,

I am having trouble with long decay times for bass in my listening room, an open plan living room and kitchen. I would like to build some bass traps and tune them to the frequencies where I have the most trouble. I think tube traps would be a good fit but I have struggled to find out what dimensions I need to deal with the frequencies which are causing my problem. the worst frequencies are 75hz and 55hz but a broadband absorption below 100hz would be great.

I feel like length, diameter, filling material and thickness of filling must matter but I can't seem to find how to work out what you need.

Does anyone know of a good guide to follow? or a calculator to work this out?

Thanks

Will

 

[DVDdoug]

I think you need a box with a tube (port) which is a Helmholtz Resonator, but maybe a big tube can be both.

 

[abdo123]

I think you need a box with a tube (port) which is a Helmholtz Resonator, but maybe a big tube can be both.

Do you have personal experience with Helmholtz resonators?

 

[sarumbear]

I think you need a box with a tube (port) which is a Helmholtz Resonator, but maybe a big tube can be both.

That’s what I use, three of them tuned separately. I hid them above the false ceiling.

I helped a friend a while back who has a barn conversion (high triangular ceiling) where we used two unit but he left them visible hanging from the apex. They look like the Bose Bazooka!

 

[abdo123]

That’s what I use, three of them tuned separately. I hid them above the false ceiling.

I helped a friend a while back who has a barn conversion (high triangular ceiling) where we used two unit but he left them visible hanging from the apex. They look like the Bose Bazooka!

I wonder if you filled them with porous material ( i read that helps increase the Q or the damping ability of the resonator further) whether it would work as a broadband bass trap as well above 100Hz.

 

[sarumbear]

I wonder if you filled them with porous material ( i read that helps increase the Q or the damping ability of the resonator further) whether it would work as a broadband bass trap as well above 100Hz.

Filling should reduce the Q, not increase it, as it adds resistance to the resonator. Lowering Q broadens the range the resonator works by reducing its efficiency at the resonance frequency (Q is Quality Factor, i.e. efficiency). However, the range increase is never as wide as an octave.

I didn’t use filling, instead I used multiple units, each tuned to different frequencies. I only treated major standing waves. The remaining smaller ones are treated with EQ.

 

[abdo123]

Filling should reduce the Q, not increase it, as it adds resistance to the resonator. Lowering Q broadens the range the resonator works by reducing its efficiency at the resonance frequency (Q is Quality Factor, i.e. efficiency). However, the range increase is never as wide as an octave.

I didn’t use filling, instead I used multiple units, each tuned to different frequencies. I only treated major standing waves. The remaining smaller ones are treated with EQ.

I know for porous absorption the more surface area available the better.

But how does that work for resonators? Should people have one big resonator for each frequency or should there be multiple ones spread around the room with more or less the same tuning?

Also does the material of the resonator impacts its Q or not really?

 

[Frgirard]

Hi All,

I am having trouble with long decay times for bass in my listening room, an open plan living room and kitchen. I would like to build some bass traps and tune them to the frequencies where I have the most trouble. I think tube traps would be a good fit but I have struggled to find out what dimensions I need to deal with the frequencies which are causing my problem. the worst frequencies are 75hz and 55hz but a broadband absorption below 100hz would be great.

I feel like length, diameter, filling material and thickness of filling must matter but I can't seem to find how to work out what you need.

Does anyone know of a good guide to follow? or a calculator to work this out?

Thanks

Will

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The calculator

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I forgot google bass trap tuned.

 

[Razorhelm]

Thanks for all this, is there any information about tube traps? I am starting to think they are just normal absorbers in a tube shape!

 

[abdo123]

Thanks for all this, is there any information about tube traps? I am starting to think they are just normal absorbers in a tube shape!

They are.

 

[sarumbear]

I know for porous absorption the more surface area available the better.

A resonator is not a surface absorber. It works by resonating the air at a set frequency.

But how does that work for resonators? Should people have one big resonator for each frequency or should there be multiple ones spread around the room with more or less the same tuning?

The job of a resonator is to cancel a standing wave. A resonator tuned to a wave's frequency will cancel or reduce the wave's amplitude. If you have multiple standing waves you need multiple resonators tuned to each frequency independently. A room has many standing waves but not all of them have large amplitude, hence you may only want to use a resonator for the ones that have a high multitude and leave the smaller ones to be treated by an EQ or other forms of acoustic treatment.

Also does the material of the resonator impacts its Q or not really?

Different metals and different thickness of tubes are used for different church organ pipes but overall the sound of church organs are pretty same. You can make the same analogy that the material of the resonator tube is pretty much immaterial to its effect.

 

[sarumbear]

Thanks for all this, is there any information about tube traps? I am starting to think they are just normal absorbers in a tube shape!

I think you are mistaken. They are not related. They do not absorb sound waves, they instead do the opposite, they excite sound waves. However, by tuning you can cancel an existing wave.

 

[Razorhelm]

Do you have any links to help me understand this?

Just to check When you say tube trap, could you explain the device you are describing?
The one i have seen are basically rock wool in a tube. And i thought they could be tuned but it doesn't seem to be the case.

I have seen helmholtz resonators but assumed they are different, the one build guide here shows a simple box not a tube, and the tube helmholtz resonators i have seen just use the the main tube for a volume of air, the shape seems unimportant.

 

[sarumbear]

Do you have any links to help me understand this?

I suggest reading general physics tutorials where sound waves are explained. Here is a good resource. It has a section on resonance.

Good physical knowledge is fundamental in understanding how speakers work and how sound behaves within spaces (rooms). I urge any H-Fi enthusiast to spend time to learn or refresh their knowledge on vibrations & waves.

 

[abdo123]

A resonator is not a surface absorber. It works by resonating the air at a set frequency.

The job of a resonator is to cancel a standing wave. A resonator tuned to a wave's frequency will cancel or reduce the wave's amplitude. If you have multiple standing waves you need multiple resonators tuned to each frequency independently. A room has many standing waves but not all of them have large amplitude, hence you may only want to use a resonator for the ones that have a high multitude and leave the smaller ones to be treated by an EQ or other forms of acoustic treatment.

Different metals and different thickness of tubes are used for different church organ pipes but overall the sound of church organs are pretty same. You can make the same analogy that the material of the resonator tube is pretty much immaterial to its effect.

Thanks for sharing, I’m still not sure if it is possible to determine how many resonators are necessary for a certain space and whether a resonator with a particular Q would translate 100% acoustically to the space.

 

[Razorhelm]

Seems we posted at the same time! Thanks for the resources. Could you explain your concept of a tube bass trap?

I suggest reading general physics tutorials where sound waves are explained. Here is a good resource. It has a section on resonance.

Good physical knowledge is fundamental in understanding how speakers work and how sound behaves within spaces (rooms). I urge any H-Fi enthusiast to spend time to learn or refresh their knowledge on vibrations & waves.

 

[sarumbear]

Seems we posted at the same time! Thanks for the resources. Could you explain your concept of a tube bass trap?

What do you mean by my "concept"? Its already built, in place and working.

 

[Razorhelm]

Their composition, what are they made of? Does it have an opening tuned to the wavelength or a membrane? How big are they? That kind of info.

I have with more research seen many products called tube bass traps and so want to check what yours are.

 

[sarumbear]

Thanks for sharing, I’m still not sure if it is possible to determine how many resonators are necessary for a certain space and whether a resonator with a particular Q would translate 100% acoustically to the space.

You may not be sure but thankfully many people are. We have calculations and theories in place for a good few decades -- for some even more than a millennia! I was sure enough to design and built mine and it works as expected.

Standing waves are easy to measure. Helmholtz resonators are also easy to design and built. The secret of resonators had been out for a pretty long time

Pipe organs invented by the Greek in the 3rd century BC. They were called hydraulos and the air was piped in via water pressure. However, they had open pipes that work on the same physical principal as a Helmholtz resonator, which is what a closed pipe organ use. Since the 5th century AD organs are operated by bellows and their numbers increased. By the 9th century pipe organ was part of the music scene. Lots and lots of people learned how to design, build and repair them.

 

[sarumbear]

Their composition, what are they made of? Does it have an opening tuned to the wavelength or a membrane? How big are they? That kind of info.

I have with more research seen many products called tube bass traps and so want to check what yours are.

They are standard plastic pipes of 10" diameter. They are much, much bigger version of these.