ok, let's start from this - I read and studied many threads&post here about VPR (so called) bass trap. Thanks to few great folks here and after some thoughts I decided VPR panels are way to go in my situation.
I want to build them myself, and before asking questions first, let me describe my situation quickly.
I have heavily trapped working space. I will drop some photos with more details asap.
Monitors I used 2 weeks ago were PMC TB2, and those sounded in my room excellent.
The outcome of REW test was also very good.
Situation has changed since I got new monitors PMC IB1 (passive). Room nodes became evident and low end became boomy:(
I mean 32-40Hz is kind of a pain now...
My room doesn't like peter's gabriel 'up' album (great album btw), and many lowest notes resonate
Well, hence it's my working space and it's my day job, I need to put old TB2 when working, and then remove them when testing setup IB1...and the latter are not very light
Anyway, after mounting additional broadband absorbers at the backwall (most offending), in the sweet spot/listening position, is almost perfect, although a little move of head (10-20cm) and the problem is there.
Situation is I work here and rent this flat, can't move walls, or even pay acoustic designer to design this room for me, as I will move out in 2 years for sure (I hope. I have to work with what I have, space is as it is.
I can fit 2 big vpr panels at the front (between and behind monitors) and at the back (behind a sofa).
2m per 1 m, will easily fit and won't take much space (10 cm).
I thought it over and I could actually make bigger VPR panels, only thing worries me is a weight of that thing...

my question regarding building an vpr panel would be:
1. weight of 2m x 1 m build panel (steel+foam)
2. I am still not sure should I go for 1mm steel or 2.5mm or maybe both for 2 panel
3. I know I need to ask DanDan about purchasing the foam (Iso Bond right ?)
4. what kind of steel to buy ?
5. where buy steel in uk/babylondon ?
6. prices for foam (2m x 1m x 10 cm, I presume ?), steel sheet, transport, anything else (price per 1 2x1m panel)
7. why there's no sticky about VPR panel? - wiki about it, sort of

if anyone who build them have anything to add, to encourage me or warn me - please go ahead,
I need those panels very badly asap!

peace

First things first, you want to use a VPR for behind the monitors and at the back of the room.

Do you have solid wallspace to mount them? The foam needs to be glued to something with a high strength surface, and it also needs to be heavy. Normal drywall will not work. Something must be placed on the boundary to reinforce the foam and panel.

The weight of the units (2m x 1m) is something like 80lbs at 1mm and 200lbs at 2.5mm. The Basotect VPR design is perfectly capable of supporting this amount of weight, but I couldn't tell you if the IsoBond is.

You will need 4 inches of foam standoff for the panel to work. This 4 inch standoff will create more leverage for the plate to sag, which will compress the foam more and change how resistive it is. I get the intuition that Caruso IsoBond is the better material in this regard, but there is still the question of if it can support the weight. The Basotect has already been tested and shown to work.

If you have devices sensitive to magnetic interference, the metal plates will pull magnetic fields towards them, which can change any interference pattern in the room, depending on proximity to the magnetic source. Before mounting any panel permanently, place the panels in there position and test everything susceptible to magnetic interference.

Unless you are a genius such as Helmut Fuchs, don't think you can change things about the design, like using aluminum instead. The VPR is steel, and intended to work with steel. Anything else is a different design with it's own parameters.

Aluminium will increase the frequency peak, this could be beneficial or not depending on the target range.

As always measure during the building construction.

firstly, big thanks for chiming in

yes. both front and backwall are solid.
This is very important info from you, I didn't ask. How to mount them ??
Well I thought I could slip it behind a sofa and just lean on the wall a bit. I hoped sofa is heavy enough (without my presence
On the front wall I have a big bass trap, but it's not as heavy as sofa for sure, so maybe I'd have to mount VPR panel to the wall somehow (?)
Anyway I think now my idea about 'slipping' it behind the sofa may not work.
if I remember correctly on G.E. thread, he didn't mounted his VPR panels, just lean them on the wall (?)


thanks for this info, now it changes a lot, 200lbs is over 90kgs, it's just impossible to get it into my space, too heavy.
only option left is 1mm steel (is it the weight of just steel panel, or steel plus foam?)
I am in EU so i will go for IsoBond, if I understand correctly this could weight a lot too ?

I am not sure I understand it fully:( sorry, English isn't my first language

that's very important factor, I completely overlooked.
in short, if i understand it correctly - mounting VPR panel in close proximity to big monitors, could be very bad idea

I won't do any experimentation, simply I don't have a time for doing this,
1mm steel is the way to go, and I will stick to it

big thanks for you help above

Hi Red M,
great questions!

My modest contribution:
1. Spec sheet from Fraunhofer Institut. (Smaller units 1x1.5 m) 21 and 39 kg respectively.
Technical Data

2. The 2.5mm is much heavier but goes lower in frequency. Imagine how to handle that bastard...
3. Ask DD
4. This is a tricky one I asked a friend who is working for a big steel company and he laughed... "We have hundreds of different kind of steel. Can you specify?"..
5. My be a friendly GS member in London knows.
6. It depends how big, how far, how heavy. Not cheap.
7. You might start one...heh


30-40 Hz are difficult to tame. Rigid walls...hmmm. What are your room dimensions? Listener distance from rear wall?

Take a look at Absorption curves and discussion of measurements at RPG Europe site
http://www.rpgeurope.com/products/pr...odexplate.html

Have you tried finding the optimal loudspeaker/listener position?
https://gearspace.com/board/8058693-post1.html

The magnetic issue complicates the situation. Solution: Take a look at Tim's Limp mass thread. Long thread with several examples of successful LF treatments. Smaller sized boxes (still a little deeper than 10 cm) are easy to move around, but you still need a big surface area for trapping 30 Hz.

Cheers

great!, big thanks

ad 1.
well, according to Fraunhofer institute 1mm steel works with 63Hz, and I have 40Hz problem:( (anyway I will check it more precisely tonight, most offending freq, and places in the room)
anyway I am still confused about the weight, 1,5m x 1m with 2.5mm steel - 40 kg (I presume it is foam plus steel ?)

ad2 .
I always thought that it has to be big, min 2mx1m to really 'work',
but weight...well 2.5mm steel plus 2m x 1m x 10 cm panel in theory should be around 52kg! (39kg+1/3=52 ca)
anyway carrying 52 kg is no fun,
I know cause I move PMC IB1 left and right for some time and my back suffers
so maybe another options -
2 'smaller' panels 1m x 1.5 m plus 25mm steel, instead of 1 big one ?
hope to get involved in this thread folks who build VPR' and can share their opinions

ad 3. I will asap
ad 4.
well, after reading some posts here, I am also confused about the steel, hence my thread
ad5 . - please London mates who knows, get involved
ad 6. I am sure some folks in uk/eu built one, so I am counting on them to chime in with their experience
ad 7. - it would be better if someone like DanDan or G.E. started thread like this, as they have knowledge and experience

as for speaker setup, obviously I am limited by a space,
I spent a lot of time moving around the room, and anything around 38% backwall distance sounds best

and I almost forgot,
I would like to focus first on vpr, as it seems the best solution for many reasons
if it won't help, I will be moving further, (limp mass), etc
or maybe selling some stuff to afford at least some basic acoustic consultation

ok,
sorry for my 'nonpro' sketch
ok first 2 drawings is a room plus room with sofa, desk and monitors

here are photos of the walls and traps:
back wall first, you can see sofa (I am going to add 2 more panels there)
in the right corner, there is 1 trap just left for testing purposes
behind it is also 1 bass trap, temporary (80cm x40cm x40 cm filled with rockwool)
I should add, there are 4 traps hanging on the wall, plus 3 traps on top of them,
all traps are 120cm x60cm x10cm
corner trap is filled with rockwool from floor to top (superchunks)
I want to made another 2 panels on top of 'yellow ones', as the back wall is the most booming place,
panels are spaced 10cm off wall, the 'lighter ones' are actually 20 cm off wall

here is the left wall (this one is not solid brick or concrete)
there are 1 panel on the doors and back wall,
but also front wall corner - superchunks, and the yellow one (where is mpc)
is actually 10cm trap plus another 10cm trap (without a frame) and some old table top in between of them

now, front wall:
there is heavy trapping, 2 superchunks in both corners, 3 traps angled on front wall and also 3 bass traps, together bass traps are 200cm x80cm x40cm (the black thing behind monitors)
there is also a 4 panels cloud (awaiting for fabrics, so looking kind of ugly now

last photo is of non existing wall on my right (there is empty frame, but I am not sure this place needs trapping, I will check it)

my apologies, for some reasons photos gone, so one more try:

I overestimated the weight, sorry. A 2.5mm panel is 41kg and 1mm is 17.8, give or take the metal you use.

I am not sure behind the sofa is a good spot. You really should sweep the room with a dB meter or take measurements to compare loudness in different areas of the room. The VPRs work where the SPL is. The more SPL, the better.

You seemed to leave out a picture of one corner of the room. This corner might be a good location. Another good location is on the ceiling.

hey, thanks for update!
I think that maybe 2.5mm steel sheet is back on 'the table'
I did some basics (I hope to do proper testing tomorrow) test, and it seems back wall is the place, literally when I move my listening position at the back, it's just bad resonance...
anyway, I hope to get better (got fever now, so no testing) and check what exactly is booming and where,
the last corner is a 'office' area, a desk and laptop, not really entertaining
and also there's no chance to fit there anything, as my better part wouldn't agree
Although I checked 28Hz yesterday, and in that particular corner is resonating really badly, from another hand, I need to prioritize my work, and take care of 40Hz rumble first.
I forgot to add my room height is 8ft, or 245cm, exactly

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.

great!
thanks G.E
important info - why you think 1mm would be more suitable ? ( I obviously read all your posts about vprs, 1mm is more efficient, but does not sort out below 50Hz issues)
another thing - about putting big steel plate behind the monitors - what about magnetic implications mentioned by akebrake ?

hmmm, your last sentence worries me a bit, as I think I have more freq. response problem then decay time, but I could be wrong
I just installed REW ( I haven't used this for few years so I need to re-learn it, it's new version 5.0
I hope to make measurements very soon, need to buy ecm 8000 first,
as previously I just used standard spl meter.
I got cold, not feeling well, today, shame as I planned to do proper testing, firstly with test tones and spl meter, seems I have to postpone it

Red asked me to chime in here.
I don't really have the experience to add much other than reiterate some points already made plus the deceptively powerful Sine Method. (tm)....

G.E. did not glue or attach his devices to a solid boundary, which is completely opposite the patented design. Furthermore audiothings I think it was, constructed a standalone device with a substantial backplate. That worked well too. Seems hard to get it wrong.
Caruso Isobond performs a little better in tests and they do appear willing and able to ship EU. They also can supply a self adhesive version. (for the steel side).
The best test result I have seen (there may well be many others) was with the VPR in a corner.
It might be worth stating the obvious here, i.e. all Bass traps behave say 3 times better in corners. Parallel to one of the corner boundaries should be good also, if perpendicular to targeted modes or SBIR 'trajectories'.

While the data says that 2.5mm traps should effectively target lower frequencies, there is no 'efficiency' comparator. As we can see here G.E. would take two 1mm any day over one 2.5.
I am quite sure this view is the results of test and experience. Perhaps 1.5mm would be a useful compromise.
Full-on testing is not mandatory. One could play sine waves in the room, tuning them carefully when resonance is heard. Then one can search the room for hotspots suitable for placing treatment. This is diagnosis and prescription in one. DAW gennies are generally too rough. The frequency jumps in steps. The REW generator is very good as is SignalSuite.

DD

thanks DanDan,
do you know what is the price for 10cm x150cmx100 cm Isobond foam ?
I presume delivery won't be cheap either

You are welcome Red. This is an extract from a note from a J. Fischer, I am sure he won't mind.

we send today by DHL 3 plates CARUSO-ISO-BOLND WLG 035 = 40 kg/m³ in a
thickness of 100 mm in whidth 625 x 1200 mm = 2,25 m².
Price 33,00 €/m² = 74,25 € plus 30,00 € for freight = 104,25 € total.

DD

So let's see your measurement results first. Actually straddled VPRs behind the speakers have the potential to sort out dips in the FR in the ~80Hz-100Hz area -- I just don't know why.

thank you very much!
this does not look as bad as I though
may I ask you why size of 625x1200 mm ?
I am still trying to figure it out how to mount it

The magnetic interference I was referring to was not only the monitors. The monitors themselves are magnetically 'sunk' by the pole piece. As a result, the spread of gauss into the surrounding area is minimized. Not all drivers are the same.

It should be safe to have a VPR within a foot of a standard monitor. Anything exceptionally larger should have more distance. Your monitors look pretty beefy, but if they are designed right, they should still not be losing magnetic flux because of a small pole piece. My only recommendation for making the distance certain is to measure the gauss at that location and do the necessary calculations.

The other form of magnetic interference would be conduit currents, which can effect small devices like guitar pickups or possibly dynamic mics.

hey,
thank you for this,
I would have to check with PMC, although G.E. mounted them close to monitors, so maybe it won't do any trouble...
I don't use microphones in the room, and don't record guitar,
but what about valve compressor and culture vulture (valve saturation) ?
sorry my knowledge in this field is equal 0.
measuring gauss does not ring any bells in my head:(, so it has to be something I never done before

ok, so we are getting closer
1. weight is known
2. 2x1mm - I fully trust G.E
3. thank you DanDan, it's all clear, apparently it's not as expensive as I thought it could be
4. steel - what kind and where to buy in uk - still open questions

I will add 1 more question, about mounting
but let's first establish above, and then I will worry about mounting

I hope to do some basic testing (testing tones and ear+spl meter for more precision) tomorrow
and after weekend, I'd like to use REW and drop here exact data

I have found this :
1mm thick Mild Steel Sheet Free Cutting Service | Nationwide Delivery

could anyone who build VPR panel, tell me if it's ok steel for such a purpose ?

Maybe because of reducing sbir? The steel is a concrete boundary for reflections.

Maybe thats the solution for my problems too...

Yes this steel should work fine. But it is a matter of debate if annealed steel is better for this. The flexural modes in cold sheets are not the same, because one direction gets more stiffness from the work hardening.

ok, thanks,
so what would be better shot on steel ?

I bought ecm8000, and should have it around Wed.
need to re-learn REW and go ahead with testing
so far, basic tests show that 32-40Hz is the biggest problem
I have a peak from 33Hz, and around 35-37 it's over 12 dB (simple spl meter test),
the worst offending are back wall and corners
I put 20 slabs of rw3 (60kh/m3) rockwool (120x60x5cm) behind sofa
and this helped a lot, leaving 'only' problem in lowest octave

Simple answer, I don't know. The thickness is most important. Here in the states, you can't even buy 1mm hot rolled sheet because it's not made by AK steel anymore. But cold roll is.