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build a VPR bass trap.uk
Old 28th September 2012 | Show parent
  #91
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Red Mastering's Avatar
 
🎧 10 years
Quote:
Originally Posted by JP__ ➡️
I´m not boggy nor my english is very good, nevertheless I will try:
If you don´t have physical a l/r symmetrie regarding your ls and listening postion no basstraps in the world can solve your problem.
This is the most important requirement in a room.
If you have found a place with best possible symmetrie you have to find the best place for your speakers (most less SBIR problems) and for your listening position (with best modal behaviour).
If these conditions have been created, you can think about absorbers.

But theres no way to make a step before the other.

The only consequence I see is to change your loudspeaker position. I would say 90° or 180° to the left.
hey, your English is much better then mine,
I understand everything except last sentence
thanks for info

PS, I know room is not perfect, and it's not even mine, I rent it
I hope to have a good room in 2 years time, but for now - I have to work with what I have
Old 28th September 2012 | Show parent
  #92
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boggy's Avatar
 
🎧 10 years
Quote:
Originally Posted by Red Mastering ➡️
hey Boggy,
could you explain it a little more, please ?
I am confused a bit
I draw simple illustration, for one example, I hope you will understand.
In short, you need to place your speakers in room where they will have possibility to be symmetrically placed in the room relative to you. Also you need to have approximately similar surfaces at your left and right sides. Especially for surfaces which will left reflective after treatment.
Also... if you have mixed walls, one built from bricks (or concrete)... and one part built from gypsum boards and rockwool (inside)... it is needed to have it at symmetrical places (or mirrored) at your left and right side...
If you aren't follow this you will never have same (or even similar) response from your left and right loudspeaker, no matter how it is expensive (or not), and this is basic request, needed for stereophonic reproduction in room, no matter whether it is for professional purposes or audiophile/amateur enjoyment, and it is prerequisite to real stereo image.

For example, if you have different stiffnes of walls at your left and right side, you will have extremely different low end response from left and right speaker, up to low mids... as you can see at your measurements already. Also, you don't have enough space in your room to cure this problem, so sometimes is only way to choose good room and right loudspeaker positioning. I already advise you about loudspeaker positioning (in already symmetrical plan) here:
https://gearspace.com/board/8296362-post53.html

Quote:
Originally Posted by JP__ ➡️
I´m not boggy nor my english is very good, nevertheless I will try:
Hey, I'm currently in your Frankfurt (am Main), and my english is ugly!
Quote:
Originally Posted by JP__ ➡️
If you don´t have physical a l/r symmetrie regarding your ls and listening postion no basstraps in the world can solve your problem.
This is the most important requirement in a room.
If you have found a place with best possible symmetrie you have to find the best place for your speakers (most less SBIR problems) and for your listening position (with best modal behaviour).
If these conditions have been created, you can think about absorbers.

But theres no way to make a step before the other.

The only consequence I see is to change your loudspeaker position. I would say 90° or 180° to the left.
I agree with JP__

And I will rotate whole listening axis for 45 degree to the right (clockwise), to the front of window, if drawings from the start of this thread are current. This way I believe we will have better starting point for positioning.




EDIT: on picture below is NOT a recommended studio layout, but only one possilbe example, as illustration of symmetry problem (which is not related only to visible surfaces, but also to room construction, wall structure, etc.)
Attached Thumbnails
build a VPR bass trap.uk-symmetry800.jpg  
Old 28th September 2012
  #93
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boggy's Avatar
 
🎧 10 years
I think about this image:
EDIT: I attached smaller picture....
Attached Thumbnails
build a VPR bass trap.uk-imag0061-800.jpg  
Old 28th September 2012 | Show parent
  #94
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🎧 5 years
Quote:
Originally Posted by boggy ➡️
I think about this image:
EDIT: I attached smaller picture....
From everything I have seen, the 5 sided clipped rectangle is a terrible room shape, acoustically. Not only does it skew node locations, but it also prevents good diffusion. While Boggy's suggestion is very good, there is still the lack of access to the balcony, but would provide good even sound with the right treatments.
Old 28th September 2012
  #95
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🎧 10 years
Quote:
Originally Posted by OpusOfTrolls ➡️
From everything I have seen, the 5 sided clipped rectangle is a terrible room shape, acoustically. Not only does it skew node locations, but it also prevents good diffusion. While Boggy's suggestion is very good, there is still the lack of access to the balcony, but would provide good even sound with the right treatments.
It's all about compromise. Even if we rotate listening axis for 45 degree, room remain asymmetrical, but this way, left and right speaker response may be at least similar, if not in +/- 1.5dB difference range. Second thing is sofa, which can become smaller, and more appropriate for current (bad) room shape.
EDIT: people are very sensitive to asymmetrical diffusers (or assymetrical placement of the same diffusers), so low end treatment, using VPRs, as already planned, may be only treatment I recommend here, and it is good to leave enough time for listener adaptation. It won't be easy.



Sent from my ST18i
Old 29th September 2012 | Show parent
  #96
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akebrake's Avatar
 
🎧 5 years
Quote:
Originally Posted by Red Mastering ➡️
ok. I did some more testing
separate L and R channel
with doors left open and closed...

...... Attachment 310959
This is an interesting thread with measurements and treatment in an asymmetrical room.
When I started to investigate your files I noticed a couple of things.

First you seem to have been using 22.05 kHz sampling frequency?
Better to use 44.1 or 48 kHz. I am not a computer guy so I don't know what will happen to the measurements...

Also you can export (in REW) measurements as an IR (.wav or .aiff ) a lot smaller than .mdat
You are using linear frequency scale on waterfall jpg:s (example above) which make the low end "crowded" for evaluation. Shift to log scale

I would love to see a couple of more measurements from your listening position with L spkr, R spkr and L+R (mono). If possible a couple of more positions around your working area.

Cheers
Old 29th September 2012 | Show parent
  #97
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boggy's Avatar
 
🎧 10 years
Quote:
Originally Posted by akebrake ➡️
.......
First you seem to have been using 22.05 kHz sampling frequency?
Better to use 44.1 or 48 kHz. I am not a computer guy so I don't know what will happen to the measurements...
......
For low frequencies (room measurements) this really doesn't matter ... even with 8bit 8kHz S/R (digital telephony, 3.5KHz Nyquist's frequency, 48dB theoretical Dynamic Range) measurements will works acceptable.
Old 29th September 2012
  #98
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Red Mastering's Avatar
 
🎧 10 years
I am sure I set up 44.1kHz in REW preferences,
thanks for chiming in,
I hope to do more measurements but not until I build vprs,
at the moment there's no sense in doing so without them

I sent 2 emails to Caruso, waiting for their answer
I don't know if they can cut different thickness and size of IsoBond
Old 30th September 2012 | Show parent
  #99
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akebrake's Avatar
 
🎧 5 years
I (akebrake) wrote:
Quote:
First you (Red Mastering) seem to have been using 22.05 kHz sampling frequency?
Quote:
Originally Posted by boggy ➡️
For low frequencies (room measurements) this really doesn't matter ... even with 8bit 8kHz S/R (digital telephony, 3.5KHz Nyquist's frequency, 48dB theoretical Dynamic Range) measurements will works acceptable.
Thank you Boggy, nice reminder...

Maybe the software is changing the sampling automatically to save BW when the user uses 2 kHz as upper sweep limit?

As long as communication is not corrupted, I am totally happy

Best
Old 30th September 2012 | Show parent
  #100
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akebrake's Avatar
 
🎧 5 years
Quote:
Originally Posted by Red Mastering ➡️
I am sure I set up 44.1kHz in REW preferences, ....
Good! That's interesting and I have to do some research how REW behaves when the bandwidth is restricted by user and exported in different ways.

Quote:
thanks for chiming in,
I hope to do more measurements but not until I build vprs,
at the moment there's no sense in doing so without them
You are welcome! I fully understand.

I am curious to see your VPR in action

Cheers

Ake
Old 30th September 2012 | Show parent
  #101
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Red Mastering's Avatar
 
🎧 10 years
now I still cannot decide on few things...
the size of a VPR absorber (steel) -
after re-reading 100s posts about vpr here on GS
I came to the conclusion 1m x1.5m is minimal size
Renz use also bigger ones 1mx2m,
and as my biggest problem lays in lowest octave (it's exactly 32Hz)
I think it could be better to have a bit bigger panel

the thickness of steel is still on the table
I was almost 100% convinced to go for 1mm
4 1x2m panel in corners (one instead of corner - behind the sofa)
all of them would be covered by 'classic' rockwool 120x60x10cm panels
now I presume with 4 big panels like this, low end have a chance to even,
but what if I am mistaken :( ?
and I should go for more thick steel instead to 'catch' that 32Hz ??
when I get info from Caruso (I will call them on Monday) about sizes of IsoBond
I will be ready to decide on size of steel
order everything in few days and hopefully mount it on following weekend

if anyone would like to advise me about steel thickness and 32Hz problem -
please be very welcome!

thank
Old 30th September 2012 | Show parent
  #102
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3 Reviews written
🎧 10 years
If I was making 4 panels and was seduced by the thicker steel, I'd probably do half thicker, half 1mm. You're going to be adding some mass to the room!
Old 1st October 2012 | Show parent
  #103
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Red Mastering's Avatar
 
🎧 10 years
I just called Caruso
they told me thickness is from 10mm to 200mm
but if I order only small amounts (anything below 100 sq meters)
they can offer me only 'standard' cuts
which will be 1250 x 625 mm
now it's kind of bummer as it means more troubles with my VPR panels:(
I will have to sit down and make a calculation
and then cut IsoBond and glue few pieces per panel...:/

if anyone who have experience with cutting CIB into smaller pieces and mounting it on the steel plate - please give me a hint

thanks
Old 1st October 2012
  #104
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JP__'s Avatar
 
🎧 10 years
I think there will be no problem using a good scissor. Caruso Isobond is a very soft material.

But I think it would be wiser to rethink your room concept and optimize your listening and loudspeaker position, do some more measurements and then, go on from there. Maybe priorities will change.
Old 1st October 2012 | Show parent
  #105
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Red Mastering's Avatar
 
🎧 10 years
Quote:
Originally Posted by JP__ ➡️
I think there will be no problem using a good scissor. Caruso Isobond is a very soft material.

But I think it would be wiser to rethink your room concept and optimize your listening and loudspeaker position, do some more measurements and then, go on from there. Maybe priorities will change.
thanks for answer, but there' no really room to re-think my situation
I am not able to re-setup room, it's out of question,
all I can do is move monitors bit left/right forward/backward
and eventually move listening position
that's it.
I did measurements,
and although there's a large peak at 32Hz and few steep peaks/dips - the waterfall looks good (except 32Hz
in current position, according to all measurements is as best as it could be at the moment
I expect 4 big VPR panels to take care of 32Hz issue and minimize the other few peaks/dips in low end
although my knowledge and experience in this area is minimal
I am very happy to be corrected as for the size of the panel
and thickness of the steel

thanks
Old 1st October 2012 | Show parent
  #106
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JP__'s Avatar
 
🎧 10 years
Ok, regarding placement it´s up to you. But can´t really accept this...

I´ve no direct experiences with vpr, but I would think the bigger the better. But I know someone who has good results with 1x0,75 m.
For 32Hz I would go with 2mm steal.
Old 1st October 2012 | Show parent
  #107
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Red Mastering's Avatar
 
🎧 10 years
Quote:
Originally Posted by JP__ ➡️
Ok, regarding placement it´s up to you. But can´t really accept this...

I´ve no direct experiences with vpr, but I would think the bigger the better. But I know someone who has good results with 1x0,75 m.
For 32Hz I would go with 2mm steal.
placement is really limited as I said, only left/right, forward backwards -
not even up/down, as I use original PMC stands, and those have their own height
my logic/simply thinking, tells me
the bigger panel - the better
but steel thickness.....its still on the table
..
I plan to fit panels behind monitors and on the backwall (corner and behind sofa)
there's also another important factor,
I plan to move in 2 years time to 'proper' big room
and I would like to use all my acoustic treatment
at the moment costs of the material itself - would be around 2k£
and 4 new VPR add another .4k£
simply, I cannot afford right now to hire a professional for acoustics
and I am not sure I will be able to hire one in future,
as for my knowledge it's a massive amount of money to rent a pro lad
Old 1st October 2012
  #108
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JP__'s Avatar
 
🎧 10 years
When only low bass is your aim I will go with thicker steel.
Old 2nd October 2012 | Show parent
  #109
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G. E.'s Avatar
 
🎧 10 years
Cutting

Quote:
Originally Posted by Red Mastering ➡️
... if anyone who have experience with cutting CIB into smaller pieces and mounting it on the steel plate - please give me a hint ...
They sell a knife for €10 if I remember correctly (you're going to ruin your bread knife pretty fast). I had no luck with Stanley knives.
Old 2nd October 2012 | Show parent
  #110
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G. E.'s Avatar
 
🎧 10 years
Quoting

Quote:
Originally Posted by Red Mastering ➡️
... I have read several G.E. posts and he supports 1mm over thicker steel ...
You cited me without the context for the second time. I'm disappointed because I want my posts on gearslutz.com to be clear for all readers. Please stop quoting me out of context.
Old 2nd October 2012 | Show parent
  #111
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Red Mastering's Avatar
 
🎧 10 years
Quote:
Originally Posted by G. E. ➡️
You cited me without the context for the second time. I'm disappointed because I want my posts on gearslutz.com to be clear for all readers. Please stop quoting me out of context.
ok. my apologies,
could you, please advise on following

1. size of the VPR panel (I'd like to get 4panels 2mx1m)
2. thickness of steel plate

considering main problem is 32Hz resonance

your answer is much appreciated
thanks
Old 2nd October 2012
  #112
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Red Mastering's Avatar
 
🎧 10 years
and just 1 very quick and fast question
I planned to buy CIB about 5cm bigger then steel plate
assuming then when glued and mounted vertically - the foam will crumple
under the weight of steel plate
If CIB is super hard, this shouldn't be an issue,
Am I correct ?
Old 2nd October 2012
  #113
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gullfo's Avatar
 
🎧 10 years
if the CIB is the correct density and the thin steel plate is glued on so it's mass is evenly distributed, why would the CIB crumple?
Old 2nd October 2012 | Show parent
  #114
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Red Mastering's Avatar
 
🎧 10 years
Quote:
Originally Posted by gullfo ➡️
if the CIB is the correct density and the thin steel plate is glued on so it's mass is evenly distributed, why would the CIB crumple?
because 2mm steel weight 20kg ?
I dunno how rigid is the foam,
that's the reason I ask
Old 2nd October 2012 | Show parent
  #115
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3 Reviews written
🎧 10 years
Quote:
Originally Posted by Red Mastering ➡️
because 2mm steel weight 20kg ?
I dunno how rigid is the foam,
that's the reason I ask
In the context of being glued to a 20kg plate of steel, the foam is not rigid. It is an open cell polymeric foam. The RPG Modex Plate has the steel formed such that it wraps around the foam and the sides are the mounting surface that mate with metal attachments on the room wall. The point I'm trying to make is that for the RPG device, the strength and rigidity of the foam isn't an issue - it just needs to be in intimate contact with the steel.

EDIT: It would be interesting to dissect a Modex Plate to see how the internals are designed, but my personal R&D budget will not allow it.
Old 2nd October 2012 | Show parent
  #116
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🎧 5 years
Quote:
Originally Posted by Syncamorea ➡️
In the context of being glued to a 20kg plate of steel, the foam is not rigid. It is an open cell polymeric foam. The RPG Modex Plate has the steel formed such that it wraps around the foam and the sides are the mounting surface that mate with metal attachments on the room wall. The point I'm trying to make is that for the RPG device, the strength and rigidity of the foam isn't an issue - it just needs to be in intimate contact with the steel.

EDIT: It would be interesting to dissect a Modex Plate to see how the internals are designed, but my personal R&D budget will not allow it.
If you look at the Renz PDFs, you will notice that the free floating plates are superior for very low frequencies, such as 32hz. The RPG Modex is a manufactured product which comes with liabilities for RPG. The safety of the customer is insured by using the steel frame for mounting.

The reason I cannot answer any questions about CIB is a lack of data. But I can sense given the density and type of material that there is no need to worry about the compression of the CIB, if the whole surface of the plate is glued. What is most important is the tensile and shear strength of it. If the CIB is too fragile, the plate could rip it's bond and cause an accident. Any impact into the plate could cause a rip if it is large enough. There is a failure point to a surface bond which has to be considered.
Old 2nd October 2012 | Show parent
  #117
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Red Mastering's Avatar
 
🎧 10 years
Quote:
Originally Posted by OpusOfTrolls ➡️
If you look at the Renz PDFs, you will notice that the free floating plates are superior for very low frequencies, such as 32hz. The RPG Modex is a manufactured product which comes with liabilities for RPG. The safety of the customer is insured by using the steel frame for mounting. There is a failure point to a surface bond which has to be considered.
thank you for this,
if I understand it correctly, better idea in my case would be to do not glue it to CIB, and just lean it freely ?
hmmm, interesting,
but now I will have to figure out how to mount/setup whole thing...
my previous idea was to glue it to steel and then just stick against the wall,
that's it.
with 'floating steel plate (if it's 2mm steel it will be heavy)
it has to be secure properly or it could fall on my poor head any moment
Old 2nd October 2012 | Show parent
  #118
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🎧 5 years
Quote:
Originally Posted by Red Mastering ➡️
thank you for this,
if I understand it correctly, better idea in my case would be to do not glue it to CIB, and just lean it freely ?
hmmm, interesting,
but now I will have to figure out how to mount/setup whole thing...
my previous idea was to glue it to steel and then just stick against the wall,
that's it.
with 'floating steel plate (if it's 2mm steel it will be heavy)
it has to be secure properly or it could fall on my poor head any moment
No, the Renz VPR IS glued to the CIB. And then it is glued to the proper wall attachment.
Old 3rd October 2012 | Show parent
  #119
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3 Reviews written
🎧 10 years
Quote:
Originally Posted by OpusOfTrolls ➡️
There is a failure point to a surface bond which has to be considered.
There's no way I'd glue a 1 x 2 meter sheet of steel to melamine, then the melamine to the wall. That's a temporary situation.

Quote:
Originally Posted by OpusOfTrolls ➡️
If you look at the Renz PDFs, you will notice that the free floating plates are superior for very low frequencies, such as 32hz.
Do you know if that's been corroborated? I seem to remember GE standing his VPR in the room, presumably with the plate touching the floor? And his worked well at LF? GE: Correct me if I'm mistaken.
Old 3rd October 2012 | Show parent
  #120
Lives for gear
 
🎧 5 years
Quote:
Originally Posted by Syncamorea ➡️
There's no way I'd glue a 1 x 2 meter sheet of steel to melamine, then the melamine to the wall. That's a temporary situation.
It is a stretch of the material's capability, but more than adequate for gravity's effect. My concern would be a large impact such as a person falling or an earthquake or such. A failsafe could be installed with hooks in the ceiling and rope through holes in the plate.
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