build a VPR bass trap.uk

[OpusOfTrolls]

Originally Posted by Red Mastering

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

You NEED to be taking every possible measurement you can. If you don't, no one can help you.

I honestly think your 32hz resonance is not solely caused by the boundary dimension, but something else as well. In fact, I will go so far as to say it is structural. It could be the wall itself resonating. I told you to measure with the glass open to eliminate any resonance of it from the measurement. But since you are deadset on doing it your way, I will let you decide how to 'vpr'.

[Red Mastering]

I did test as you suggested
there are .mdat files and waterfalls
open doors, closed
l and r channels separate

'I will go so far as to say it is structural. It could be the wall itself resonating.'
you could be very right with this,
wonder if vpr traps can be solution for this,
thanks for help
(all files and .mdat are on previous pages)

[Syncamorea]

I'm going to remain skeptical of the need to have the plate unsupported and am assembling pieces and parts to make a few prototypes. I spent over 20 years doing research in adhesives and resins and am comfortable working with steel and melamine foam but I do not trust the long term integrity of an open cell foam to support loads of this magnitude. At the least, I'll have a fail safe catch for the plate as Murphy's Law would probably place my toe, hand or head under the plate when the assembly failed. I understand RPG's need for avoiding liability, but I don't believe they would try to sell a (significantly) compromised design. Their drawings don't even show any isolation between the folded plate and the wall mount. The wanna-be ME in me wants to believe that a compliant mount Rube Goldberg kind of device could allow for a tiny bit of reactivity for the plate.

[OpusOfTrolls]

Originally Posted by Syncamorea

I'm going to remain skeptical of the need to have the plate unsupported and am assembling pieces and parts to make a few prototypes. I spent over 20 years doing research in adhesives and resins and am comfortable working with steel and melamine foam but I do not trust the long term integrity of an open cell foam to support loads of this magnitude. At the least, I'll have a fail safe catch for the plate as Murphy's Law would probably place my toe, hand or head under the plate when the assembly failed. I understand RPG's need for avoiding liability, but I don't believe they would try to sell a (significantly) compromised design. Their drawings don't even show any isolation between the folded plate and the wall mount. The wanna-be ME in me wants to believe that a compliant mount Rube Goldberg kind of device could allow for a tiny bit of reactivity for the plate.

I am in agreement that the foam is not to be trusted for a long term mount. To anyone building a VPR in this way, please exercise safety and use common sense.

[G. E.]

Originally Posted by Red Mastering

... there are .mdat files and waterfalls ...

I think your measurements don't show enough detail in the bass range, it looks "noisy". Could you measure again at a higher speaker level?

I think the best way to check the room modes and the core bass decay of a room is to position the speaker in one tri-corner and the mic at the most opposite tri-corner.

[Red Mastering]

Originally Posted by G. E.

I think your measurements don't show enough detail in the bass range, it looks "noisy". Could you measure again at a higher speaker level?

I think the best way to check the room modes and the core bass decay of a room is to position the speaker in one tri-corner and the mic at the most opposite tri-corner.

thank you for this
I will try do measurements again, as you suggested

[JonW]

This is really great information and it is nice to see a thread I can participate in. (all the info I look up is years old). I have a couple questions for you guys:

1. The modex specifications state: "The face plate contains a regular array of 1.5 mm diameter holes spaced 2mm horizontally and vertically apart, with a non-perforated border of 25 mm." - Does this mean we have to drill a thousand little holes into the steel for it to function properly and what difference would it make either way?

2. Anyone know where I can get the Isobond stuff in Canada, eh?

Finally, thanks to all the regulars on here for all the great information.

Jon.

[hsal]

The modex specifications state: "The face plate contains a regular array of 1.5 mm diameter holes spaced 2mm horizontally and vertically apart, with a non-perforated border of 25 mm." - Does this mean we have to drill a thousand little holes into the steel for it to function properly and what difference would it make either way?

This perforated steel plate with isobond behind it is an optional "add on" to the vpr absorber extending absorption to the mids/highs, making it a broadband absorber.

[DanDan]

There are lots of posts here and in the other threads.
Easy to lose sight of the wood for the trees.
I have distilled a pocket understanding from watching this over time.
I intend to act on it soon, so I offer the following in the hope of saving some of you time. Do remember that is is only my distilled understanding, G.E. is the one who has acted all this out. I would like to thank him again for sharing this extensive work with us.

EDIT
1 G.E.'s experiments come to a different conclusion than Dr. Fuchs.
i.e. Most importantly, the VPR does NOT have to be firmly bonded to a solid boundary. Plse remember that the patents prescribe Basotect, but Isobond was later found to be superior. So let's not over or underestimate the Fraunhofer work.

2 Caruso can be contacted by email and phone and will respond. Although english skills may be very limited I have had nothing but warm responses from them.
Shipping out of the EU is a headache, just as much as shipping outside the Continental USA. There must be Polyester Insulation available in the States.
3 I would go with their standard size, and probably chose the self adhesive version.
4 I would chose a size depending on steel availability. I found a local supplier where the steel is 1mm, on a 1.5M wide roll. I will of course get this cut to the 600mm size of the Iso and use 2x 1250. BTW the steel supplier could get a local facility to powder coat it with nice colours for very reasonable cost. Note I live in a very small City. So the steel is probably nearby. Remember HVAC.
5 I get the impression that 2.5mm steel will function at lower frequencies, but not as 'efficiently'. i.e. To really hit 30Hz will take a lot of surface area. At such frequencies, many of us turn to Eq.
6 I intend to try to hang the devices either flat to a wall in an alcove or staddling a corner. By chosing the hanging point I expect it possible to use the devices weight to exert a small pressure to the wall.
7 It is very likely that I will have to place a HF absorbent layer on the front. Maybe more Iso, or perhaps simply hang a drape in front of it.
8 Unless I have missed some important test, Corner mounting seems vastly superior to flat to the wall. Same as it ever was.

DD

[G. E.]

Originally Posted by DanDan

... G.E.'s experiments come to different conclusions than Dr. Fuchs. ...

I ("G. E." that's me = Gernot Ebenlechner on Gearslutz) don't agree with this sentence because I want the information that I share and the context in which I am cited to be as unmistakably as possible.

Here we go: the point is that I compared different mounting options (not described in the literature AFAIK) for the same VPR-style absorber in my room and found a configuration that worked best in my setup. I appreciate the work of Helmut V. Fuchs (namely his book "Schallabsorber und Schalldämpfer") and my private experiments with wall-mounted VPR-style absorbers fall in line with his published results.

[DanDan]

Hi Gernot, I will very gladly edit/ correct my comments to reflect reality exactly if you would be so good as to help clear up the matter in my mind.

I am particularly referring to just one aspect. A crucial one. Bonding to the boundary. This would be a go/no go issue for many DIYers IMO.

The Patents, as best I could read them, prescribe that the Basotect be firmly bonded to the wall.
Am I correct in understanding that your experiments show success without such bonding?
This is the different conclusion I referred to. Different, additional, and very welcome. As was the post- patent change from Basotect to Isobond.
Buy perhaps I have read too much into that spectacular corner mounted test which you showed us?
Was your success without bonding, only in this corner straddling position?
In other words, did you have 'flat to the wall' success without bonding? And if tested, did bonding increase the efficiency?
DD

[G. E.]

Originally Posted by DanDan

... The Patents, as best I could read them, prescribe that the Basotect be firmly bonded to the wall. Am I correct in understanding that your experiments show success without such bonding? ...

Indeed I couldn't prove any performance difference between glueing vs. not glueing in my tests using CARUSO-ISO-BOND® for the absorbent in a VPR-style basstrap.

Originally Posted by DanDan

... Was your success without bonding, only in this corner straddling position? In other words, did you have 'flat to the wall' success without bonding? And if tested, did bonding increase the efficiency? ...

Both straddling and 'flat to the wall' configurations worked equally well without bonding compared to bonding with long-lasting flexible glue given the geometry of the setup being unchanged. Nevertheless straddling has the potential to show much better performance than 'flat to the wall' setups in my experience.

[DanDan]

Thank you for confirming that Gernot.

That seems to be the only difference between your findings and the patents.
So I will edit my earlier post to 'conclusion' rather than conclusions.

Are you OK with that?

DD

[G. E.]

Originally Posted by DanDan

Thank you for confirming that Gernot.

That seems to be the only difference between your findings and the patents.
So I will edit my earlier post to 'conclusion' rather than conclusions.

Are you OK with that?

DD

Excuse me if I don't get the English language right (it's not my mother tongue) but I'm still uncomfortable reading that I come to a different conclusion than Fuchs because one might think he is wrong with his conclusion. If I remember correctly he used a different absorbent so whatever he said is not directly comparable anyway.

[boggy]

Originally Posted by G. E.

Excuse me if I don't get the English language right (it's not my mother tongue) but I'm still uncomfortable reading that I come to a different conclusion than Fuchs because one might think he is wrong with his conclusion. If I remember correctly he used a different absorbent so whatever he said is not directly comparable anyway.

All absorbers are strongly dependent on placement in the real room (as you already prove in your experiments), so I believe that your findings can better fit to our needs... Fuchs is right too, but he has his own way, e.g. - not some particular room, but measurement reverberant room, which is hardly can be most relevant thing for our small rooms... and strategy of implementation of this construction.

So it's very easy to have different conclusion if we compare apples and oranges, and it is perfectly ok to prefer oranges (IMHO).

[OpusOfTrolls]

I don't want to jump to conclusions, because the work you have done G.E. has been valueable for us all. I do think your results could be based on a more macroscopic acoustic effect than the actual functioning of the VPR itself. Having the panel in the hemisphere (on the boundary) makes sense because with no airspace behind, more force will be encountered. The foam is porous, but provides plenty of resistance to airflow behind the plate. When the corner is straddled, with a significantly sized plate, the reflection path will change. This could be better or worse, but is not indicative of the resonant effect of the VPR.

[G. E.]

Originally Posted by OpusOfTrolls

I don't want to jump to conclusions, because the work you have done G.E. has been valueable for us all. I do think your results could be based on a more macroscopic acoustic effect than the actual functioning of the VPR itself. Having the panel in the hemisphere (on the boundary) makes sense because with no airspace behind, more force will be encountered. The foam is porous, but provides plenty of resistance to airflow behind the plate. When the corner is straddled, with a significantly sized plate, the reflection path will change. This could be better or worse, but is not indicative of the resonant effect of the VPR.

... from a phenomenological point of view I don't care what's the reason for the potential of enhanced efficiency of straddling VPR-style absorbers is (to know would be nice for sure). Though much has been puzzled about VPR-style mounting options here yet I've not come across a setup where the straddling didn't by far outperform the wall-mount setup.

[OpusOfTrolls]

Originally Posted by G. E.

... from a phenomenological point of view I don't care what's the reason for the potential of enhanced efficiency of straddling VPR-style absorbers is (to know would be nice for sure). Though much has been puzzled about VPR-style mounting options here yet I've not come across a setup where the straddling didn't by far outperform the wall-mount setup.

I can think of one, a big superchunk type trap with the same surface area as the plate.

EDIT: With the VPR to the side of it. In this way, there will not be phase cancellations in direct proximity to the it.

[boggy]

Originally Posted by G. E.

... from a phenomenological point of view I don't care what's the reason for the potential of enhanced efficiency of straddling VPR-style absorbers is (to know would be nice for sure).

I understand you, and I agree with you.

Originally Posted by G. E.

Though much has been puzzled about VPR-style mounting options here yet I've not come across a setup where the straddling didn't by far outperform the wall-mount setup.

Great!

[Red Mastering]

been struggling with personal and other problems,
which took all my time..:(
hence my lack of involvement in this thread
just ordered CIB 4x 2mx1m
I order steel when I get info about CIB delivery
I will do testing without a panels and then with 1, and 2, etc (I hope)
possibly next week,
very, very curious about the outcome,
CIB, plus delivery, plus steel and delivery and VAt, and other fees - ca £600
well, not really cheap,
hope it resolve the issues with low freq rumble

[DanDan]

Great stuff Red. That sounds cheap if it works. Plse keep us in the loop.
If you need help/advice with the testing process, feel free to PM or consult here.

DD

[Syncamorea]

Originally Posted by G. E.

Though much has been puzzled about VPR-style mounting options here yet I've not come across a setup where the straddling didn't by far outperform the wall-mount setup.

I'm really glad you posted this as I misunderstood, thinking that flush wall mounting was preferred. I have purchased foam and steel for VPRs and once I'm finished with my LMV builds, I plan to jump into VPR assembly. I'm still puzzling over the pros and cons of having the plate attached directly to the walls (now in straddle configuration) although in straddle configuration, I guess gluing the foam to the walls is not an option!

[DanDan]

Welcome clarity indeed.

I intend making some VPR's in due course. My plan is to hang them from the ceiling or from stalks attached to the wall.
If the hang point is slightly towards the wall the weight should cause them to hang inwards with a little pressure.

DD

[OpusOfTrolls]

Originally Posted by Syncamorea

I'm really glad you posted this as I misunderstood, thinking that flush wall mounting was preferred. I have purchased foam and steel for VPRs and once I'm finished with my LMV builds, I plan to jump into VPR assembly. I'm still puzzling over the pros and cons of having the plate attached directly to the walls (now in straddle configuration) although in straddle configuration, I guess gluing the foam to the walls is not an option!

IF you do it this way, 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.

If you want to focus on a corner VPR, why not flush mount it directly on the wall, also butted into corner? What is the difference?

[G. E.]

Originally Posted by Syncamorea

I'm really glad you posted this as I misunderstood, thinking that flush wall mounting was preferred. ...

Mounting a VPR on the wall is no misunderstanding -- that's the way it is described in the patent.

Originally Posted by Syncamorea

... I'm still puzzling over the pros and cons of having the plate attached directly to the walls (now in straddle configuration) although in straddle configuration, I guess gluing the foam to the walls is not an option!

The "plate" is the absorbent not the steel, right? Maybe you find another way of securing your basstrap against moving away from the wall.

[G. E.]

Originally Posted by DanDan

... I intend making some VPR's in due course. My plan is to hang them from the ceiling or from stalks attached to the wall. If the hang point is slightly towards the wall the weight should cause them to hang inwards with a little pressure.

I guess anything else than the absorbent touching the steel might result in reduced performance (some modes might be "locked").

[G. E.]

Originally Posted by OpusOfTrolls

... If you want to focus on a corner VPR, why not flush mount it directly on the wall, also butted into corner? What is the difference?

In my experience the difference is the potential of the straddling configuration (according to the enhanced porous absorber scheme) to clearly outperform the wall-mount configuration.

[mhch]

Originally Posted by OpusOfTrolls

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.

Interesting idea, worth to give it a try since it's much easier for many people to buy and cut MDF than Steel.

However, I'm surprised no see no mention of that from the VPR inventors, if only to mention it doesn't work as well.

The main physical differences between MDF and Steel are density & rigidity but I don't see which physical effects make Steel better than MDF.

[Syncamorea]

Originally Posted by mhch

The main physical differences between MDF and Steel are density & rigidity but I don't see which physical effects make Steel better than MDF.

Their resonant frequencies are very different. That may affect how energy is transferred to the foam?

[mhch]

Originally Posted by Syncamorea

Their resonant frequencies are very different. That may affect how energy is transferred to the foam?

Understand but for what oscillatory mechanism ? standing oscillation waves of a flat panel ?