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build a VPR bass trap.uk
Old 29th October 2012 | Show parent
  #151
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🎧 5 years
Quote:
Originally Posted by Syncamorea ➑️
Their resonant frequencies are very different. That may affect how energy is transferred to the foam?
The idea is to create a very heavy and rigid panel as a control. While the thicknesses would be different, a better control would probably be very expensive in comparison. A steel panel the same weight per square unit is more flexible than MDF because of the thickness. The control is getting rid of the flexural element of the panel.
Old 29th October 2012
  #152
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superwack's Avatar
 
1 Review written
🎧 10 years
Talking

I'm certainly no acoustician but I designed this VPR-Alliance diffusor for my api lunchbox so I'm pretty sure you could do a bass trap as well
Attached Thumbnails
build a VPR bass trap.uk-vpr_diffusor.jpg  
Old 30th October 2012 | Show parent
  #153
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G. E.'s Avatar
 
🎧 10 years
Resonating

Quote:
Originally Posted by OpusOfTrolls ➑️
... you might want to try a control experiment with a MDF panel (or better two screwed and glued) the same surface area as the metal panel, setup the same with CIB and all. I am thinking you will see very similar results. ...
The modal distribution (of modes perpendicular to the membrane surface) in the bass range is quite different for (in this example) 2,5mm [~0,1"] steel versus a MDF-plate of the same weight (24mm [~1"]). I expect heavier (higher mass densitiy) plates, plates with less inner damping, and plates with lower stiffness to enhance resonances in the bass range and to perform better as VPR resonators.
Attached Thumbnails
build a VPR bass trap.uk-2.5mm_steel.jpg   build a VPR bass trap.uk-24mm_mdf.jpg  
Old 30th October 2012 | Show parent
  #154
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1 Review written
🎧 15 years
Reminder

An alternative material might be useful. But I reckon Dr. Fuchs must have tried different materials or at least predicted their behaviour.
As ever, I remember that one of the greatest verbs, the EMT140, is a steel plate.

DD
Old 30th October 2012
  #155
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Red Mastering's Avatar
 
🎧 10 years
just got delivery from CIB
got a question though,
it seems CIB is very rigid from one side
and it gets softer to the other side (the one with adhesive)
I was sure it was very rigid, but possibly I am wrong and soft/rigid texture is important ?
Old 30th October 2012 | Show parent
  #156
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🎧 5 years
Quote:
Originally Posted by G. E. ➑️
The modal distribution (of modes perpendicular to the membrane surface) in the bass range is quite different for (in this example) 2,5mm [~0,1"] steel versus a MDF-plate of the same weight (24mm [~1"]). I expect heavier (higher mass densitiy) plates, plates with less inner damping, and plates with lower stiffness to enhance resonances in the bass range and to perform better as VPR resonators.
I agree, the wood is too stiff for good flexural resonance. The reason the modes spread apart per unit thickness is because of stiffness. Quality is reduced as well. Having a thinner panel allows more flexing per force unit.

Maybe my idea of a control panel wasn't good enough, but that still doesn't explain better performance of a corner straddle panel.
Old 5th November 2012 | Show parent
  #157
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Red Mastering's Avatar
 
🎧 10 years
success !

I would like to say I am so happy!
finished project Friday night, having flu and not feeling great,
I am not being able to do measurements, this has to wait

anyway, I can say, that even for my blocked and sore ears I can hear that VPR traps are fantastic solution
built was -
4 panels, 2m x 1m, CIB WLG-035 10 cm thick
plus 1mm thick steel plate glued to CIB,
mounted by the back wall (3 panels) and front wall
the one behind front wall gave great precision and punch in 60-150Hz (smaller dip probably?)
really big difference

and I also like the steel plate look

I promise to make photos, add more details and do measurements when I get better,
need to finish last touches here and there,
set up monitors again as they were moved during placing VPR panel behind them

I don't have a doubt VPR are very interesting solution
project is easy to build (stick steel plate to CIB, mount it in the studio, done!)
it's inexpensive considering other solutions
very important factor - foot print, thickness is 10 cm - in my case, as in many studios it's an air gap between bandtraps and wall
I added 8 square meteres of VPR panels, and literally it did not take space

most important - effects are amazing

big big thanks to anyone involved in this thread and involved in testing and measurement of VPR bass trap idea
Old 5th November 2012 | Show parent
  #158
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🎧 5 years
I am glad to hear it worked! I would have thought that 32hz resonance was caused by a large sympathetic vibration somewhere in the room, considering your test results. The Q didn't budge with all that rockwool, something had to be reinforcing it. Still, glad to hear it.
Old 5th November 2012 | Show parent
  #159
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1 Review written
🎧 15 years
Brill

Glad to hear that Red. I look forward to your measurements, but in the meantime your delight at the sonic improvement is palpable.
Might be worth considering that previous optimum speaker and listener locations may not apply in the new acoustic.

DD
Old 5th November 2012
  #160
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Red Mastering's Avatar
 
🎧 10 years
thanks,
like I said, no proper measurements, just my ears (and they aren't up to task right now)
I think that 32Hz issue hasn't gone completely, but it is really well minimized
in general low end is so precise, punchy and tight
didn't expect such a great results
Old 6th November 2012 | Show parent
  #161
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3 Reviews written
🎧 10 years
Quote:
Originally Posted by Red Mastering ➑️
I added 8 square meteres of VPR panels, and literally it did not take space
That's great news. I'm looking forward to photos. From your comment above, I take it you didn't straddle corners with your VPRs? I wish the foam you used was available in the US!
Old 6th November 2012 | Show parent
  #162
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Red Mastering's Avatar
 
🎧 10 years
Quote:
Originally Posted by Syncamorea ➑️
That's great news. I'm looking forward to photos. From your comment above, I take it you didn't straddle corners with your VPRs? I wish the foam you used was available in the US!
yes, all panels stand against the wall (back and front)
in US there is only Basotec for my knowledge,
here in EU, you have Caruso IsoBond in Germany
Old 6th November 2012 | Show parent
  #163
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3 Reviews written
🎧 10 years
Quote:
Originally Posted by Red Mastering ➑️
here in EU, you have Caruso IsoBond in Germany
I have tried to navigate my way to a US supplier but apparently, the stuff is as inaccessible as the holy grail.
Old 6th November 2012 | Show parent
  #164
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G. E.'s Avatar
 
🎧 10 years
Mounting

Quote:
Originally Posted by Red Mastering ➑️
... project is easy to build (stick steel plate to CIB, mount it in the studio, done!) ...
How did you mount these Absorbers to the wall?
Old 6th November 2012 | Show parent
  #165
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Red Mastering's Avatar
 
🎧 10 years
Quote:
Originally Posted by G. E. ➑️
How did you mount these Absorbers to the wall?
I just stick them against the wall,
3 at the back are behind hanging bandtraps and sofa - it secure it very well
and 1 on front is behind 2 massive bass traps, just standing against wall
Old 31st December 2012 | Show parent
  #166
Gear Head
 
🎧 5 years
Any news or pictures of your VPRs?
I'm interested in the way you mounted them!?
Old 5th January 2013 | Show parent
  #167
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Red Mastering's Avatar
 
🎧 10 years
Quote:
Originally Posted by JochenM ➑️
Any news or pictures of your VPRs?
I'm interested in the way you mounted them!?
I hope to do it very soon....
just need some time to do it,
anyway here is the photo of 1 2x1m vpr panel, behind monitors
DSC_0094_bis | Flickr - Photo Sharing!
it is freely standing behind 3 bass traps (0.8x0.4x0.8m filled with rockwool
3 others vpr are at the back wall (1 in the corner) also covered by 'standard' rockwool panels
Attached Thumbnails
build a VPR bass trap.uk-dsc_0094_bis.jpg  
Old 3rd February 2013
  #168
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Bilou's Avatar
 
🎧 10 years
Very interesting thread here !

Hope to see more pictures soon.

I didn't understand how you fix the panels. Did you glue the isobond to the wall ? Or are they just standing with the side touching the floor ?

I was wondering about making 2 holes in the plate, add 2 silent blocs and fix with 2 screws on the wall. Would it affect the resonance of the plate by much ?

About the foam, I understand Basotect is not the best material for that. It's not really flexible (if you try to bend it, it breaks), so flexibility properties shouldn't be optimal to damp plate resonances. Isobond seems better but I think any open-cell PU foam about 20-30kg/m3 will have better flexibility than Basotect. Melamine is often selected by manufacturers for its flame ******ant properties.
Old 3rd February 2013 | Show parent
  #169
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akebrake's Avatar
 
🎧 5 years
Quote:
Originally Posted by Bilou ➑️

....About the foam, I understand Basotect is not the best material for that. It's not really flexible (if you try to bend it, it breaks), so flexibility properties shouldn't be optimal to damp plate resonances. Isobond seems better but I think any open-cell PU foam about 20-30kg/m3 will have better flexibility than Basotect. Melamine is often selected by manufacturers for its flame ******ant properties.
It seems like there is a choice between Isobond and Basotect. At least from an acoustical view. (Fraunhofer link, figure 1)

IBP - Compound Baffle Absorbers

ake
Old 4th February 2013
  #170
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Bilou's Avatar
 
🎧 10 years
I'm pretty sure Caruso has been chosen for flame properties too.
Do you see any reason why standard acoustic PU foam would not work as good ?
If not, I would be interested in testing that configuration.
Old 22nd February 2013
  #171
Gear Head
 
🎧 5 years
Hi G. E. ! I'm posting my question here now .

I was a little confused by a post you made when you said "Remember that since VPRs are "reactive" devices they'll do more to the release of the room response than the frequency response."


If I'm interpreting your meaning of "reactive" correctly, aren't all bass traps (porous absorbers, limp mass, helmholtz, etc) "reactive" devices in that they react to a frequency and absorb it? So is it pointless to try and fix frequency response with bass traps??

Then how do you recommend fixing frequency response in a small room then? Adjusting speaker placement?

Thanks a lot, and thanks for all the great posts!
Old 22nd February 2013 | Show parent
  #172
Gear Head
 
🎧 5 years
Sorry, here's the quote

Sorry, I forgot to include the quote from page 1

Quote:
Originally Posted by G. E. ➑️
Can you post an Impulse Response (or a REW .mdat file) of your room?

Personally I would take 2 VPRs with 1mm over a single one with 2,5mm any day. You'll probably need more than two VPRs anyway to tame the last octave. I've had good results using VPR-like absorbers straddled in the vertical corners behind the speakers. Remember that since VPRs are "reactive" devices they'll do more to the release of the room response than the frequency response.
Old 22nd February 2013 | Show parent
  #173
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🎧 5 years
Quote:
Originally Posted by Brian_SLS ➑️
Hi G. E. ! I'm posting my question here now .

I was a little confused by a post you made when you said "Remember that since VPRs are "reactive" devices they'll do more to the release of the room response than the frequency response."


If I'm interpreting your meaning of "reactive" correctly, aren't all bass traps (porous absorbers, limp mass, helmholtz, etc) "reactive" devices in that they react to a frequency and absorb it? So is it pointless to try and fix frequency response with bass traps??

Then how do you recommend fixing frequency response in a small room then? Adjusting speaker placement?

Thanks a lot, and thanks for all the great posts!
Porous absorbers (or also called passive absorbers) are resistive. The sound energy is lost in them. Reactive absorbers respond to sound stimuli and reverse the phase of the reflection, causing a nulled reflection. The energy still exists in the room, but is not heard as a function of pressure. Almost all bass traps are a mixture of the two types, because of energy conservation.
Old 22nd February 2013 | Show parent
  #174
Gear Guru
 
1 Review written
🎧 15 years
Frequency Response

Quote:
Then how do you recommend fixing frequency response in a small room then? Adjusting speaker placement?
Hi Brian. Frequency Response graphs depict a moment in time.
Roughly speaking a Waterfall kinda presents a montage of these slices as time passes. Some frequencies die away quickly, others ring on. Others are nulled in the first moments, but fill in later as the burgeoning modes develop.

Music is composed of tonal pulses. So the sound we hear in the room is a flow of musical tonal pulses into a room full of bells. Albeit damped bells.

If the number of bells is enormous and their tuning random, all equally damped, then all tones will be reinforced by the room equally. Wouldn't that be heaven!

Shorter answer:- Traps, particularly LF ones will shorten modes to a decent extent. Quite often there will be little or no change in the FR graph.
BIR and other Speaker and Listener Position optimisation can have radical effect on FR with sometimes no cost. See the last graph here.
https://gearspace.com/board/studio-b...er-v2-1-a.html

DD
Old 22nd February 2013
  #175
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🎧 10 years
dan, this is one of the best short answer I have ever read
by the way, was he calling you? DAN
Old 24th February 2013
  #176
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G. E.'s Avatar
 
🎧 10 years
Quote:
Originally Posted by OpusOfTrolls ➑️
Porous absorbers (or also called passive absorbers) are resistive. The sound energy is lost in them. Reactive absorbers respond to sound stimuli and reverse the phase of the reflection, causing a nulled reflection. The energy still exists in the room, but is not heard as a function of pressure. Almost all bass traps are a mixture of the two types, because of energy conservation.
I don't agree with the "reactive absorbers" part of this post -- maybe I used an inappropriate term calling VPRs "reactive". Point is what we call energy "loss" (here: sound energy dissipated to thermal energy) always happens in the "passive" parts (porous absorbent) of an absorber.

True active absorbers indeed generate sound with inversed polarity to cancel out standing waves (at least in some places in the room) using a microphone, electronics, an amp, and a woofer.

The way pressure based absorbers (membrane, Helmholtz, VPR) work is different: basically they turn air pressure to air velocity at the resonant frequencies of their mechanical system. They have in common that the resonance (and therefor the absorption as well) builds up with every wavecycle, so they need some cycles to get into action, it takes time (depending on the wavelength, for example 5 cycles at 40Hz = 125ms).
Old 25th February 2013
  #177
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boggy's Avatar
 
🎧 10 years
Quote:
Originally Posted by G. E. ➑️
I don't agree with the "reactive absorbers" part of this post -- maybe I used an inappropriate term calling VPRs "reactive". Point is what we call energy "loss" (here: sound energy dissipated to thermal energy) always happens in the "passive" parts (porous absorbent) of an absorber.
.....
I agree with Opus, description is basically ok, in regards to acoustical impedance, or impedance in general. Absorption may be basically passive (strictly porous), reactive (resonant, but still absorbers), and active (feedback controlled active subwoofer, basically).
"delay" between moment when stimulus is started and when we reach steady-state response, is normal for reactive systems, and this is called transient response (natural response, etc.) . For resistive systems (strictly porous) response is instantaneous... no delay. It is also needed to tell, that we can't strictly differentiate all types of absorbers, because only implementaton may change its nature. This differentiation is more figurative IMHO.

EDIT1: Changing pressure to velocity then absorbing, is also common for reactive systems... Passive absorbers won't work, in place where velocity is low...

EDIT2: Without metal sheet, used porous absorber glued to it can't do anything below 100Hz alone...

Sent from my ST18i
Old 25th February 2013 | Show parent
  #178
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🎧 5 years
Well it's safe to say SOME devices are in one category. Helmholtz resonator is the best example, using no passive absorption but the air itself.

There are many small details of acoustics which may or may not be calculated, but are measured either subjectively or objectively. Working off of known principles is a good way to avoid unexpected behavior.

Back on topic, I can't see only a metal plate working well to predictably change room response. The passive component is a very important part of the device. But stranger things have happened, and every system has it's irregularities. One thing the mass of steel can do is break and modify reflection paths. In addition to this is the reactivity of what encounters the plate, and what transpires on the other side. Very complex.
Old 25th February 2013 | Show parent
  #179
Gear Head
 
🎧 5 years
Air pressure to air velocity...?

Quote:
Originally Posted by G. E. ➑️
I don't agree with the "reactive absorbers" part of this post -- maybe I used an inappropriate term calling VPRs "reactive". Point is what we call energy "loss" (here: sound energy dissipated to thermal energy) always happens in the "passive" parts (porous absorbent) of an absorber.

True active absorbers indeed generate sound with inversed polarity to cancel out standing waves (at least in some places in the room) using a microphone, electronics, an amp, and a woofer.

The way pressure based absorbers (membrane, Helmholtz, VPR) work is different: basically they turn air pressure to air velocity at the resonant frequencies of their mechanical system. They have in common that the resonance (and therefor the absorption as well) builds up with every wavecycle, so they need some cycles to get into action, it takes time (depending on the wavelength, for example 5 cycles at 40Hz = 125ms).
Correct me if I'm wrong, but I thought VPRs work not by turning air pressure to air velocity; instead, they take the energy from sound waves and transfer them (through the metal plate's modal resonances) directly to the porous material. In turn the, energy is turned into heat within the porous absorber. There's no transfer from air pressure to air velocity.

I could be wrong though...

Last edited by Brian_SLS; 25th February 2013 at 11:46 PM.. Reason: Typo
Old 27th February 2013
  #180
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G. E.'s Avatar
 
🎧 10 years
Quote:
Originally Posted by Brian_SLS ➑️
Correct me if I'm wrong, but I thought VPRs work not by turning air pressure to air velocity; instead, they take the energy from sound waves and transfer them (through the metal plate's modal resonances) directly to the porous material. In turn the, energy is turned into heat within the porous absorber. There's no transfer from air pressure to air velocity. ...
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.
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