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build a VPR bass trap.uk
Old 1st March 2013 | Show parent
  #181
Gear Head
 
🎧 5 years
Vibrating Metal = More Air Velocity?

Quote:
Originally Posted by G. E. ➡️
You wouldn't need the plate for the sound wave hitting the porous absorber "directly", would you? The reason for the resonating element always is to build up more air velocity (at the resonant frequency) than there would be without.
A resonating plate increases air velocity??? I didn't know a solid piece of vibrating metal increases AIR velocity...

interesting...
Old 1st March 2013
  #182
Gear Maniac
 
🎧 15 years
Depends on how you look at it. At the boundary's air particle velocity is at a minimum. The plate converts pressure to particle displacement but the speed of sound is a constant
Old 1st March 2013 | Show parent
  #183
Gear Guru
 
1 Review written
🎧 15 years
Acceleration

Might just be semantics at play. The speed of sound will increase dramatically from air to steel.
DD
Old 1st March 2013
  #184
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G. E.'s Avatar
 
🎧 10 years
Quote:
Originally Posted by Vank ➡️
Depends on how you look at it. At the boundary's air particle velocity is at a minimum. The plate converts pressure to particle displacement but the speed of sound is a constant
I totally agree that speed of sound (= speed of the wavefront) doesn't change because of a bass trap :-) ... I'm talking about the air particle velocity.
Old 4th March 2013 | Show parent
  #185
Lives for gear
 
G. E.'s Avatar
 
🎧 10 years
Sonic Velocity

Quote:
Originally Posted by G. E. ➡️
I totally agree that speed of sound (= speed of the wavefront) doesn't change because of a bass trap :-) ... I'm talking about the air particle velocity.
Another detail: the sonic velocity c_0 indeed does change within the porous absorber but again this is not part of the explanation how a VPR works.
Old 4th March 2013
  #186
Gear Maniac
 
🎧 5 years
hi Quick question
If I can build a framework for the VPR like rpg made
why not use 60-100 kg\3 Glass wool Glued to the 1/2,5 mm metal plate Instead of isobond or basotect?
Old 4th March 2013 | Show parent
  #187
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3 Reviews written
🎧 10 years
Quote:
Originally Posted by dor baruch ➡️
hi Quick question
If I can build a framework for the VPR like rpg made
why not use 60-100 kg\3 Glass wool Glued to the 1/2,5 mm metal plate Instead of isobond or basotect?
Just go for it and if it fails, call it "research". I had been thinking that one of the essential elements of the VPR was the difference in stiffness and density between the steel and the foam. Then I read here that folks are using rock wool in VPRs and now think other materials should be tested. If it wasn't such a mess to clean up, I'd try sticking a sheet of steel to drywall with green glue.
Old 5th March 2013
  #188
Gear Maniac
 
🎧 5 years
thanks Syncamorea
I thought exactly the same thing
Because I spend a lot of work and thought into the type of the frame,metal plate,size
and the Absorbent Material (basotect,sonex,roclwool,35kg\3 polyester polyurethane b1 and i have new 60kg polyester polyurethane ( a1 fire Safety)
if i know Exactly how to measure the absorption features
And compare them I can contribute alot to this topic
i hope 120\60 will work properly on low freq

+i Usually use 3m 90 for the plate to foem i can try use green glue and see...
Old 5th March 2013 | Show parent
  #189
Lives for gear
 
🎧 5 years
Glueing to glass fiber is pointless, because it will tear. And Green Glue is not GLUE despite the name, it's a mastic.

What do you mean "usually use 3m 90 for the plate"? Have you built one already?
Old 5th March 2013
  #190
Gear Maniac
 
🎧 5 years
no opusof trolls
I glued mlv and metal plates of different sizes to compressed mineral wool(100kg\3+)
at My friend's house Without an understanding of the vpr subject and use 3m as ethan winer Proposed, Now I'm trying to build vpr elements at Various sizes
And check them with various methods proposed by this forum and by the experts Who invented them (piezo accelerometer,rew 5 with ecm8000 or other,5,4,3,room,4,4,3,room,lab room, room with only rockwool or without rockwool bass traps and
In the distant future large impedance tube and acoustic camera )
According to my current understanding the metal plate Does not have to be glued
to the absorber You are absolutely right Green Glue is mastic,I do not want to use it because of its adhesive properties But because the rest of its features
Maybe they will contribute in some way to the vpr Performance

+ i am thinking of a combination Between 5 cm 9kgm\3 sonex to 5 cm 100+kgm\3 rockwool

12 kilo mlv wont tear So I do not see why the metal plate thus
Old 5th March 2013
  #191
Gear Maniac
 
RickD's Avatar
 
🎧 5 years
Will my studio have these problems too? (plan included)

This thread is particularly interesting to me because i own a pair of PMC TB2i and hope to get a pair of PMC IB1 passive.
I am also to start building a studio.
Rough plans here: Remarks needed on studio plans

Question:
Is there any risk that i will have the same problems as Red Mastering in my studio ? ie 30-40 Hz issues.

Thanks a lot.
Old 5th March 2013 | Show parent
  #192
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Gdupproductions's Avatar
 
🎧 10 years
Quote:
Originally Posted by dor baruch ➡️
i hope 120\60 will work properly on low freq
I'm wondering this aswel..My room is only 1.90m wide and 4m long.
So 120/60 already takes alot of space.
Old 6th March 2013 | Show parent
  #193
Gear Guru
 
1 Review written
🎧 15 years
Big

The commercial VPR's from RPG, Renz, and others, are minimum 1.5M x 1M.
I think that kinda says it all. As ever with LF, big is king.
Although these devices have shown great results straddling a corner, I fully expect them to perform very well flat to the wall IN a corner also.
And for that matter, flat to a wall for Axial mode absorption.
While they are big, they are much thinner than any other type of enhanced LF absorber afaik.
DD
Old 7th March 2013 | Show parent
  #194
Lives for gear
 
🎧 5 years
Flat in the corner is good. I have been wondering if both sides of the corner edge would work even better.
Old 7th March 2013
  #195
Gear Addict
 
PaulRain's Avatar
 
1 Review written
🎧 10 years
of course it will be better because you double the number of vpr
Old 7th March 2013 | Show parent
  #196
Gear Addict
 
Bobecca's Avatar
 
🎧 5 years
Sorry for my ignorance and not understanding what direction this thread is heading. What Im missing greatly here is the after measurements, if any, cant be presented here.

I read a lot of positive words about VPR but still very little data of measurements done after they have been installed. Especially in this very long thread. I could have missed it somewhere then please point me out where it is.

Is there any, at all, before and after measurements when using these trapps? Any in room measurements?

My understanding is that Red Mastering has installed a x pcs of them but not presenting any after measurements results that can be compared to before, is very odd.

Question is why not??
Old 7th March 2013 | Show parent
  #197
Gear Addict
 
Bobecca's Avatar
 
🎧 5 years
Quote:
Originally Posted by DanDan ➡️
The commercial VPR's from RPG, Renz, and others, are minimum 1.5M x 1M.
I think that kinda says it all. As ever with LF, big is king.
Although these devices have shown great results straddling a corner, I fully expect them to perform very well flat to the wall IN a corner also.
And for that matter, flat to a wall for Axial mode absorption.
While they are big, they are much thinner than any other type of enhanced LF absorber afaik.
DD
How can it take Axial mode when it is an membrane that has to be tuned for that problematic freq? It is afterall an broadbsnd type of absorption. If you mean that it dosent matter to tune then please clarify what you mean here or provide some data that this is the case.
Old 7th March 2013 | Show parent
  #198
Gear Guru
 
1 Review written
🎧 15 years
Modes

Bobeca. Lets consider a Mode, say a width one in a very approx 10 foot room, there will be a 60Hz mode with a strong null room centre.
However axial modes are not just one frequency , there will be another at 120, 160, 240, and so on.
VPR's at the side walls, should absorb a whole range of these modes very well, still 0.6 at the x8 mode, while taking only 100mm a side.
build a VPR bass trap.uk-screen-shot-2013-03-07-15.37.18.png
There is a variation on the VPR, where the steel is sandwiched in foam. This would absorb HF side reflections also.
Here are some more absorption graphs from the people who invented VPR. The thicker but very heavy device covers down to 40Hz.
IBP - Compound Baffle Absorbers

It would be difficult to the point of unrealistic to attempt to tune the absorption peak these devices.
So for clarity. Axial modes have multiple frequencies. VPR's are not tuned in any way similar to devices that are tuned.

DD
Old 10th March 2013 | Show parent
  #199
Gear Addict
 
Bobecca's Avatar
 
🎧 5 years
Quote:
Originally Posted by DanDan ➡️
Bobeca. Lets consider a Mode, say a width one in a very approx 10 foot room, there will be a 60Hz mode with a strong null room centre.
However axial modes are not just one frequency , there will be another at 120, 160, 240, and so on.
VPR's at the side walls, should absorb a whole range of these modes very well, still 0.6 at the x8 mode, while taking only 100mm a side.
Attachment 333665
There is a variation on the VPR, where the steel is sandwiched in foam. This would absorb HF side reflections also.
Here are some more absorption graphs from the people who invented VPR. The thicker but very heavy device covers down to 40Hz.
IBP - Compound Baffle Absorbers



It would be difficult to the point of unrealistic to attempt to tune the absorption peak these devices.
So for clarity. Axial modes have multiple frequencies. VPR's are not tuned in any way similar to devices that are tuned.

DD
So VPR is basically a broadband type of absorber, yes. Are you saying that it is enough to just take the second or third harmonics and at the same time dealing with the first? One should deal with the first harmonics of that specific room mode problem.

Im still missing the measurements when the trapps are installed. There should also be a pressure change in the freq response at that room mode in question let say at 60 Hz.

I dont follow you when saying axiall mode have many freq? If you mean the first, second and so on, then agreed but there would not be second if the first has been taken care of, or at least minimized. Then the second harmonics would be of less importance. But the question is if it can be the other way around?

And remember that we are talking about the pressure build up when we are dealing with our types of room modes.

http://www.sengpielaudio.com/StandingWaves.htm

Some readings, especially number 3.

Last edited by Bobecca; 10th March 2013 at 12:09 PM.. Reason: added link
Old 10th March 2013 | Show parent
  #200
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Red Mastering's Avatar
 
🎧 10 years
Quote:
Originally Posted by Bobecca ➡️
...
Is there any, at all, before and after measurements when using these trapps? Any in room measurements?

My understanding is that Red Mastering has installed a x pcs of them but not presenting any after measurements results that can be compared to before, is very odd.

Question is why not??
answer is very simple,
I don't have a time or facilities&knowledge to present measurements, in a way other folks here did
I run mastering studio, and I had to re-setup my room in no time to be able to continue working
I am very sorry about that, although, when I find few free hours,
I will gladly put info about all I achieved
Old 10th March 2013 | Show parent
  #201
Gear Guru
 
1 Review written
🎧 15 years
Generous

That would be most welcome Red, and thanks for all you have shared so far.
I would make the point that not many commercial facilities, nor designers, publish their results. Newell being the only one I have seen.
Also, reality check, many if not most of us have to work in spaces which are frankly embarrassing on paper.

Quote:
I dont follow you when saying axiall mode have many freq? If you mean the first, second and so on, then agreed but there would not be second if the first has been taken care of, or at least minimized. Then the second harmonics would be of less importance. But the question is if it can be the other way around?
OK, I see two things here, a good question, and a fundamental misconception regarding harmonics, which I once had also.

I think a realistic example will help. This is my White Room.
First Length Mode is 35Hz. Note well that such modes have bandwidths of typically 5Hz or so (Everest). Note also that the room is mostly treated. this mode has been reduced from 1.3S to 0.6S by three large SSC's.
I have a big 'alcove' at the back corner. Currently not treated as I have tried and then removed two different types of trapping. While this 35Hz looks big on graphs, it is not at all as musically and sonically damaging as it's harmonics particularly when they all gang up causing nulls 70-100Hz.

So the treatment choices.

VPR (s) filling the entire alcove 2.4x1.6M BUT only 100mm thick. (Plus 2.5 mm steel)
From the published tests IBP - Compound Baffle Absorbers I have some doubt that this will help the 35Hz which is massively loud in that whole alcove. We can see the performance of the tested devices is great at 40, but falls off rapidly and is not looking so good at 35. Maybe if I used 3mm steel.
Hmmm.

Helmholtz. Seal the alcove with perforated sheet or wide slats. I would ask Jens or some other experienced HH expert to do the numbers and to help with practical details. Let's say we end up with a device 200mm deep.
If it is indeed tuned efficiently to the 1st axial, 5Hz wide, it will have virtually NO effect at 70-80. Where I have much more serious problems than the 35.
That is the problem with tuned devices, they are tuned to one frequency. They do not do harmonics.

Grunt Fibre.
We have seen a welcome reduction in the 35Hz mode, from 1.3S down to 0.6. This was caused by three SSC's with a maximum corner depth of 43cm.
i.e. 1/22 of Wavelength. (I often get numbers wrong, so plse do check)
So, I would install 40cm of fibre. This has the advantage of dealing with ALL the harmonics and ALL the other modes that gather in this corner.
It also does not create a flutter echo issue back there and can be HF slatted for a bit of HF scatter.

A long way round Bo, but I hope this gives you an insight into the balancing act when choosing treatment.

DD
Old 11th March 2013 | Show parent
  #202
Gear Addict
 
Bobecca's Avatar
 
🎧 5 years
Quote:
Originally Posted by Red Mastering ➡️
answer is very simple,
I don't have a time or facilities&knowledge to present measurements, in a way other folks here did
I run mastering studio, and I had to re-setup my room in no time to be able to continue working
I am very sorry about that, although, when I find few free hours,
I will gladly put info about all I achieved
Thats understandable
Old 11th March 2013 | Show parent
  #203
Gear Addict
 
Bobecca's Avatar
 
🎧 5 years
Quote:
Originally Posted by DanDan ➡️
That would be most welcome Red, and thanks for all you have shared so far.
I would make the point that not many commercial facilities, nor designers, publish their results. Newell being the only one I have seen.
Also, reality check, many if not most of us have to work in spaces which are frankly embarrassing on paper.



OK, I see two things here, a good question, and a fundamental misconception regarding harmonics, which I once had also.

I think a realistic example will help. This is my White Room.
First Length Mode is 35Hz. Note well that such modes have bandwidths of typically 5Hz or so (Everest). Note also that the room is mostly treated. this mode has been reduced from 1.3S to 0.6S by three large SSC's.
I have a big 'alcove' at the back corner. Currently not treated as I have tried and then removed two different types of trapping. While this 35Hz looks big on graphs, it is not at all as musically and sonically damaging as it's harmonics particularly when they all gang up causing nulls 70-100Hz.

So the treatment choices.

VPR (s) filling the entire alcove 2.4x1.6M BUT only 100mm thick. (Plus 2.5 mm steel)
From the published tests IBP - Compound Baffle Absorbers I have some doubt that this will help the 35Hz which is massively loud in that whole alcove. We can see the performance of the tested devices is great at 40, but falls off rapidly and is not looking so good at 35. Maybe if I used 3mm steel.
Hmmm.

Helmholtz. Seal the alcove with perforated sheet or wide slats. I would ask Jens or some other experienced HH expert to do the numbers and to help with practical details. Let's say we end up with a device 200mm deep.
If it is indeed tuned efficiently to the 1st axial, 5Hz wide, it will have virtually NO effect at 70-80. Where I have much more serious problems than the 35.
That is the problem with tuned devices, they are tuned to one frequency. They do not do harmonics.

Grunt Fibre.
We have seen a welcome reduction in the 35Hz mode, from 1.3S down to 0.6. This was caused by three SSC's with a maximum corner depth of 43cm.
i.e. 1/22 of Wavelength. (I often get numbers wrong, so plse do check)
So, I would install 40cm of fibre. This has the advantage of dealing with ALL the harmonics and ALL the other modes that gather in this corner.
It also does not create a flutter echo issue back there and can be HF slatted for a bit of HF scatter.

A long way round Bo, but I hope this gives you an insight into the balancing act when choosing treatment.

DD
What is an SSC??

So you mean that when dealing with higher harmonic you will at the same time deal with the first?

If this is the case then one never have to bother about the first harmonic.
Som measurements would be nice representing the improvement in decay.

How do you know that it will not have an effect at 70-80 Hz region? Has it been seen in your measurement.

Ive seen quit the opposite when doing my own measurements using tuned HH.
Old 15th March 2013 | Show parent
  #204
Here for the gear
 
🎧 15 years
You can go and have a listen to how 2 vpr 0,9 mm steel with isobond is performing when recording an upright bass. I just made the recordings so feel free to coment to the sound difference. The room is my musicroom at home. It´s 3,5x3,5x2,5m big.

Here´s the site, it´s in swedish but you see the links,hopefully.

Produkter | akustikdesign
Old 15th March 2013 | Show parent
  #205
Gear Addict
 
Bobecca's Avatar
 
🎧 5 years
Quote:
Originally Posted by balluda ➡️
You can go and have a listen to how 2 vpr 0,9 mm steel with isobond is performing when recording an upright bass. I just made the recordings so feel free to coment to the sound difference. The room is my musicroom at home. It´s 3,5x3,5x2,5m big.

Here´s the site, it´s in swedish but you see the links,hopefully.

Produkter | akustikdesign
But you offer measurements on your website. Why dont provide with some measurements instead. With and without VPR.

That is what I want to see.

Vad kostar de?
Old 18th November 2013 | Show parent
  #206
Here for the gear
 
🎧 10 years
How to bond

I am using 5 vprs in my small rectangular room with a strong 38hz mode with less than stellar results. (Measurements posted here.) Two vprs are straddling in corners and the other three flat against the wall. No mounting used (free standing) and no glue used between steel and cib. Should I try glue? What kind of glue?
Old 18th November 2013 | Show parent
  #207
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Mctwins's Avatar
 
🎧 5 years
Quote:
Originally Posted by dapost ➡️
I am using 5 vprs in my small rectangular room with a strong 38hz mode with less than stellar results. (Measurements posted here.) Two vprs are straddling in corners and the other three flat against the wall. No mounting used (free standing) and no glue used between steel and cib. Should I try glue? What kind of glue?
I see the Decay time has reduced in mid/upper freq but that 38Hz mode will not be fixed with those VPR's you have. Glued or not.

But you are right about less than stellar result.

Yet another prove that it is not working for killing the room modes.
Old 18th November 2013 | Show parent
  #208
Gear Guru
 
1 Review written
🎧 15 years
Sheep

dapost, did you expect the VPR's to work down at 38Hz?
build a VPR bass trap.uk-screen-shot-2013-11-18-10.21.44.png
Your linked post shows very great improvement in the range where they do work. If you wish, post the .mdat here and I will show you just how stellar they are.
McT, do you take pleasure when someone fails due to unrealistic expectations?


DD
Old 18th November 2013
  #209
Here for the gear
 
🎧 10 years
Well, 3 of my 5 VPRs use 2.5mm steel, so, yes, I was expecting more in the sub 50Hz region. My main goal is to improve the ca 50Hz suck-out, the actual 38Hz mode is less of a concern to me because it can be tackled with PEQ. At the moment my room has no kick drum punch. Any suggestions to improve this are welcome.

P.s. I will post a clean mdat file asap.
Old 18th November 2013 | Show parent
  #210
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Red Mastering's Avatar
 
🎧 10 years
Quote:
Originally Posted by Mctwins ➡️
...Yet another prove that it is not working for killing the room modes.
I beg to differ,
on the opposite, vpr changed my room from bad to very good
although there are many of them, 6 large ones (2000x1000mm x 100mm)
and 24 smaller ones (although a bit different materials)
plus 3 bass traps 800x800mmx400mm also with steel plates
and 14 'ordinary' 1200x600mm 100mm rockwool filled broadband traps
yes, that's a lot, but you cannot expect to even a problematic room with 6-10 panels, you need a lot of them and a lot of measuring and 'dancing' with panels from left to right
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