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DIY Tube Bass Trap and frequency tuning

MRC01

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No tube trap will provide sufficient absorption in the 75hz and 55hz range. They will work OK above 100Hz.

Define "sufficient". My 21" diameter traps measured in-room impact of 6 dB @ 50 Hz and 3 dB @ 40 Hz.
 

bo_knows

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Define "sufficient". My 21" diameter traps measured in-room impact of 6 dB @ 50 Hz and 3 dB @ 40 Hz.
Wow! I would say that is very "sufficient". LOL Care to share the design of trap, room dimension, before and after measurements?
 
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dougi

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Is anyone familiar with these commercial ones (Vicoustic Vari Bass)? It is hard to tell whether they are helmholz or wideband absorbers. Probably the former. Not outrageously priced compared with the cost of fixed foam based bass trap panels.
 

bo_knows

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Most of those details: construction, dimensions & measurements are in the link I posted.
I built those in the past (even larger diameter than yours) and experienced a strange feeling with the pressure in my ears when music was played. This was a long time ago and I didn't have REW or much knowledge about the measurements besides how to use the Radio Shack meter. Needles to say, I abandoned those traps and never looked back. I'm glad they are working for you. Now, I experiment with the use of MLV (mass-loaded vinyl) to deal with lower frequencies (40-80Hz). I also moved away from using the fiberglass in my room treatments and substitute it for eco-friendly material.
 

sarumbear

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No tube trap will provide sufficient absorption in the 75hz and 55hz range. They will work OK above 100Hz.

That is plain and in my case demonstrably wrong.

The link you supplied is not about Helmholtz Resonators but standard resistive absorbers in the shape of a tube. I will also think twice before relying on a source that says "Because of this design feature, the TubeTrap is more than 100% efficient." How can a trap be more than 100% efficient???
 

bo_knows

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That is plain and in my case demonstrably wrong.

The link you supplied is not about Helmholtz Resonators but standard resistive absorbers in the shape of a tube. I will also think twice before relying on a source that says "Because of this design feature, the TubeTrap is more than 100% efficient." How can a trap be more than 100% efficient???
I'm not sure how to take your response. You have a quite aggressive response style for some reason. I shared a link from the Tube Trap manufacturer because OP is interested in tube trap DIY design and wanted to address certain frequency issues in his room. I assume, that DIY build is/are based on the original design. I build DIY tube traps in the past and I personally don't like them and I expressed my opinion/concern about their ability to absorb in the 50Hz range. Helmholtz resonator was not mentioned in any of my posts (not sure why you brought this up and linked it to me).
 
OP
Razorhelm

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This has been a bit of an issues through out the thread! The term tube trap is used online to refer to both Helmholtz resonance absorbers and tube shaped absorbers filled with things like rock wool.

I had to check which people were refering to as it starts to get quite confusing!

@sarumbear is talking about helmholtz resonators generally, this is what he built and what i am trying to build. Tuned right you can affect any frequency you like but it is quite narrowband.

@MRC01 is generally talking about the rockwool filled type, he made some and they were effective for low frequencies but he had to make them with a 16inch diameter to be effective below 100hz.

Hope i have not garble that!
 
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sarumbear

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I'm not sure how to take your response. You have a quite aggressive response style for some reason. I shared a link from the Tube Trap manufacturer because OP is interested in tube trap DIY design and wanted to address certain frequency issues in his room. I assume, that DIY build is/are based on the original design. I build DIY tube traps in the past and I personally don't like them and I expressed my opinion/concern about their ability to absorb in the 50Hz range. Helmholtz resonator was not mentioned in any of my posts (not sure why you brought this up and linked it to me).
I am not sure how can I be seen as aggressive when I am simply correcting a false declaration? I said "That is plain and in my case demonstrably wrong." Which of my words are hostile, please show me; I correct them and apologise. Should I have said "I am very sorry dear gentleperson but I think your assumption may be wrong because I designed and then built three HR resonators in the shape of tubes that work at the the first and second audio octaves. I learned how to design them at school where they gave me a Masters degree in Acoustics."

You said "No tube trap will provide sufficient absorption in the 75hz and 55hz range." Now you are changing your "tune" and telling us that you have "concerns" and that you do not "like them". Can either of those be interpreted as your previous declaration that no tube trap can work below 100Hz?

I have posted earlier how that will be possible, how I achieved it and attached a calculator to design it yourself.

Furthermore, you are confusing a resonant bass trap and a resistive one.
 
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sarumbear

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This has been a bit of an issues through out the thread! The term tube trap is used online to refer to both Helmholtz resonance absorbers and tube shaped absorbers filled with things like rock wool.

I had to check which people were refering to as it starts to get quite confusing!
If there is a single frequency mentioned it is a Helmholtz Resonator. If a broad range of frequencies displayed on a chart then it is a passive (resistive) absorber.
 
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bo_knows

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I am not sure how can I be seen as aggressive when I am simply correcting a false declaration? I said "That is plain and in my case demonstrably wrong." Which of my words are hostile, please show me; I correct them and apologise. Should I have said "I am very sorry dear gentleperson but I think your assumption may be wrong because I designed and then built three HR resonators in the shape of tubes that work at the the first and second audio octaves. I learned how to design them at school where they gave me a Masters degree in Acoustics."

You said "No tube trap will provide sufficient absorption in the 75hz and 55hz range." Now you are changing your "tune" and telling us that you have "concerns" and that you do not "like them". Can either of those be interpreted as your previous declaration that no tube trap can work below 100Hz?

I have posted earlier how that will be possible, how I achieved it and attached a calculator to design it yourself.

Furthermore, you are confusing a resonant bass trap and a resistive one.
"The link you supplied is not about Helmholtz Resonators but standard resistive absorbers in the shape of a tube." I replied to OP in the middle of the night (have difficulty sleeping) and admittedly didn't read every single reply. But here you are and in some other previous thread, correcting me or replying in what I consider a rude way.
I don't need it and if you have a problem with me, reach out to me via PM.
 
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bo_knows

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This has been a bit of an issues through out the thread! The term tube trap is used online to refer to both Helmholtz resonance absorbers and tube shaped absorbers filled with things like rock wool.

I had to check which people were refering to as it starts to get quite confusing!

@sarumbear is talking about helmholtz resonators generally, this is what he built and what i am trying to build. Tuned right you can affect any frequency you like but it is quite narrowband.

@MRC01 is generally talking about the rockwool filled type, he made some and they were effective for low frequencies but he had to make them with a 16inch diameter to be effective below 100hz.

Hope i have not garble that!
Cool, now I fully understand what you are looking for. I have no clue about helmholtz resonators. I have never built one or planning to build one in a near future and can't provide any more meaningful info. I wish you good luck.
 

sarumbear

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"The link you supplied is not about Helmholtz Resonators but standard resistive absorbers in the shape of a tube." I replied to OP in the middle of the night (have difficulty sleeping) and admittedly didn't read every single reply. But here you are and it some other my previous tread, correcting me or replying in what I consider a rude way.
I don't need it and if you have a problem with me, reach out to me via PM.
I am sorry that you made a mistaken post while trying to sleep. Insomnia is not a nice symptom. I hope you will not suffer long.

My reply was "That is plain and in my case demonstrably wrong." There is nothing rude in that sentence, nor there is anything personal. You mention me being rude on other thread(s). I appreciate if you show them to me. I do not want forum members think that I am a rude person.
 

MRC01

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...

@sarumbear is talking about helmholtz resonators generally, this is what he built and what i am trying to build. Tuned right you can affect any frequency you like but it is quite narrowband.

@MRC01 is generally talking about the rockwool filled type, he made some and they were effective for low frequencies but he had to make them with a 16inch diameter to be effective below 100hz.

...
Yep, that's about right. I built my tube traps with 21" diameter which is better for the bass frequencies you want.
Tube traps for a band of roughly 2 octaves, resonators for narrower.
In my room, I used big tube traps to improve the bass overall, then added bass traps and tuned resonators to weaken a specific null at 70 Hz.
 

sarumbear

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Yep, that's about right. I built my tube traps with 21" diameter which is better for the bass frequencies you want.
Tube traps for a band of roughly 2 octaves, resonators for narrower.
In my room, I used big tube traps to improve the bass overall, then added bass traps and tuned resonators to weaken a specific null at 70 Hz.
May I ask why you needed absorbing for a two octave range, and what is the frequency range of them?
 

MRC01

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Bass below 200 Hz was all over the place with long decay times. So I tamed it with tube traps first, then applied resonators to tackle specific resonances that remained. I posted in-room measurements before/after in that first link. Here it is again. In summary, a pair of tube traps 21" diameter and 7' tall had a measured difference from about 40 to 200 Hz. In that range, they raised troughs and lowered peaks.
 

sarumbear

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Bass below 200 Hz was all over the place with long decay times. So I tamed it with tube traps first, then applied resonators to tackle specific resonances that remained. I posted in-room measurements before/after in that first link. Here it is again. In summary, a pair of tube traps 21" diameter and 7' tall had a measured difference from about 40 to 200 Hz. In that range, they raised troughs and lowered peaks.
Thank you. Excellent report.

What was the cause of the almost 10dB dip around 2-4kHz?

The red dashed line is with the speakers 1" further from the rear wall

In above, may I assume that you meant feet (single quote) instead of inch (double quote)? And, what was the total distance?
 
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MRC01

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Thank you. Excellent report.

What was the cause of the almost 10dB dip around 2-4kHz?
The Y axis scale is half that - the 3k dip measured 3.5 dB dip in absolute terms, but the tube traps lowered it 2 dB more. I don't know why, assume they're absorbing some reflection. They also have reflective material around half of one side, so they should increase dispersion of mid-high frequencies.
In above, may I assume that you meant feet (single quote) instead of inch (double quote)? And, what was the total distance?
It's a pair of traps, each having diameter about 2', height about 7'. I didn't do any acoustic frequency band calculations before building them. I knew I needed them to be big as possible to affect low frequencies, so I made them as big as would fit into the available space. I got lucky that they were just the right size to affect the frequencies I needed.

Oh, you meant regarding wall distance. These are Magnepan 3.6/R speakers, dipoles very sensitive to room placement. 1 inch did make a difference, but that "red dashed" line it refers to isn't in the graph because it wasn't different enough to be worth reporting and complicating the graph further.
 
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sarumbear

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The Y axis scale is half that - the 3k dip measured 3.5 dB dip in absolute terms, but the tube traps lowered it 2 dB more.
I'm confused: In your blog you said "The vertical scale (each horizontal line) represents 2 dB." but on the chart you show marked them as 1dB and above you imply that the lines are at 1dB. Can you verify which value is correct, please?

InRoomFreqResp.jpg




These are Magnepan 3.6/R speakers, dipoles very sensitive to room placement. 1 inch did make a difference, but that "red dashed" line it refers to isn't in the graph because it wasn't different enough to be worth reporting and complicating the graph further.
You answered many of my questions why I am seeing such odd behaviour. You are using a dipole system and such wild anomalies are what to expect from a dipole in a habitable room. As you said even an inch movement alters the response and as wild as yours.

However, if I may analyse your before (blue dotted) and after (blue solid line) this is what I see.

1- You have successfully eliminated two prominent standing waves at 30Hz and 70Hz.
2- However, you have not been able to tame the standing wave at 450Hz. Your treatment have simply moved its frequency up to 600Hz and lower Q. I assume due to the big masses added to the room.
3- The dip at 2500Hz is also not tamed but like above its Q is lowered, most likely for the same reason above.
4- I am ignoring the anomalies between 200-400Hz, and above 2000Hx because they seem to be caused by the dipole speaker's position rather than standing waves.
5- However, I would pay attention to the peak at 250Hz as it nay well be caused by a standing wave.

If I been presented with the blue dotted curve and asked what do I suggest in terms of acoustical treatment here is what I would suggest.

1- Employ two Helmholtz resonator tuned to 30Hz and 68Hz.
2- Place an absorber that has coefficient of at 0.8 at the 300Hz-1000Hz range.
3- Once the above in place test to see if there are any more important standing waves, especially the one at 250Hz. If found and if they are higher than 100Hz, employ a single resistive (absorber) tube trap.

Once again, I congratulate you for the work you have done and the fact that you thought of treating a room before using an EQ. Bravo!
 

voodooless

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So how does one determine the size of a resonator? I can tune 50l box to the same frequency as a 200l box. Intuitively I would think the bigger box has more efficiency, but how much? Also filling the box with usual speaker damping material should virtually increase the size by a bit I guess (next to broadening the damping)?

Next up: what about a single box with various lengths of pipes, giving multiple tunings? Seems to me that this might be more efficient than multiple boxes with different tuning?
 
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