RPG Modex Plates-"Free" Bass Traps

dallasjustice

Member Sponsor
Apr 12, 2011
2,090
0
0
Dallas, Texas
#1
Okay. I don't mean they are free of cost. As a matter of fact, they are very expensive. They are probably the most expensive bass trap on the market. However, I think they are the best value going in room acoustic treatment. This last weekend, my dealer Scotty Warren and friend Bill Gainer installed 3 additional modex plates into my room. Before these 3, I already had 6 modex plates in my room. In the post below are some pictures of the side walls and and rear walls before the new modex plates were install. I am showing these photos to demonstrate how many "conventional" panels a modex plate can replace. Later on, I will explain AND demonstrate the advantages Modex Plates offer over fiberglass panels (even great ones like RPG BAD panels). You might also ask me; Why would you want to add 3 more Modex Plates to your room? Isn't 6 enough already? Before I do that, I think it's important to discuss how fiberglass panels work and how that's different from a VPR like the Modex Plate works.

PRESSURE VS. VELOCITY

The standard in room treatments has been fiberglass panels. They can be very effective at reducing low frequency ringing from about 100hz to 300hz. Their performance can even be extended below 100hz depending on their thickness and some other mounting tricks. Fiberglass works on velocity. Fiberglass can reduce the bass wave's velocity and thereby mitigate room ringing. Of course, velocity is at its greatest away from the walls in a room. So fiberglass doesn't work so well mounted directly onto a flat wall. However, fiberglass can be mounted on "off sets" which create a 4" air gap from the wall. This can greatly increase their performance along with using very thick panels.

There's a "cost" with fiberglass though. Fiberglass will absorb a lot of midrange and high frequencies. Moreover, the closer a panel is located to the speaker, the more the panel will color the speaker at the seated position. This is especially true if one elects to use absorption on sidewall lateral 1st reflection points. I know there's much controversy here and Floyd Toole has done some research suggesting that no panels should be used in this location. However, there's no universal here. In my case, I like to use absorption at these reflection points. I believe I can get a smoother midbass and the measurements bear that out. However, it takes a lot of fiberglass panels to do the trick. And even the best fiberglass panels will absorb a little too much midrange and high frequency. RPG BAD panels are designed to mitigate this effect with a perforated wood plate which is mathematically proven to diffuse the mid and HF much more evenly. However, even BAD panels aren't great and too many of them can reduce the decay times in a room to a VERY low level. So, that's the cost for fiberglass. You have to use sooooooo many of them to get great bass that you suck out too much HF and make the room sound a little unnatural.

RPG Modex Plates work by reducing bass wave pressure. I don't know how to build one and I can't give you a technical paper on how they are designed. I know that RPG sells them on license from a German manufacturer. I don't believe there are any other companies selling VPRs. Modex Plates must be mounted directly onto a wall wherein high pressure bass energy accumulates. So, knowing where to install the modex plate requires some basic room acoustics knowledge. In my case, my room is 14'6" wide, 24' long and 9'3" high. Of course, the lowest frequency ringing is length axial with the most dominate mode being 47hz and another half wave at 23hz. There would be many others as well if the room were untreated.

At this pointed, my room is very well controlled in the low frequencies. A few years ago I started getting room acoustics help from Nyal Mellor. This relationship started me on the path to room acoustics learning. I've learned a lot since then. I regularly use a mic and REW. Let's just say that the room treatment, my seated position, speaker positions, digital crossovers, DSP and subwoofers are not haphazardly setup in my room based on hand claps or listening to the soundtrack for The Movie U571 or Saint Saens Symphony No. 3. :D

Yes, I said it. Modex Plates are "free." They don't absorb midrange and high frequency. The absorb low frequencies better than any other product on the market. That's actually a fact and RPG has real data testing to prove it. So, I'm not blowing smoke here. These things work very well. I am going to post some pictures below starting with what my room looked like before I install these last 3 modex plates. Then I will show some photos of the install and finally some photos of what they look like now.

I have been taking REW measurements and I am confident in saying two things.
1. The3 Modex Plates (1 type two Modex Plate and 2 type one Modex Plates) installed easily perform as well or better than all of the 8 very thick fiberglass panels and two QRD diffusers (6 of which were BAD panels). Most of these panels were at least 5" thick, some thicker.
2. The decay time in my room is greatly improved since I've removed these numerous fiberglass panels from my room and replaced them with 3 "free" Modex Plates.
IMG_0351.JPG
 
Last edited:

dallasjustice

Member Sponsor
Apr 12, 2011
2,090
0
0
Dallas, Texas
#5
I will post REW plots tomorrow. The overall SPL will be virtually identical. However, I expect to see longer decay times in midrange and high frequencies.

Subjectively, the longer mid and HF decay was the first and biggest impression. The sound is so much more open. The soundstage is wider, deeper and inner nuance is heightened. The bass sounds just as great as before. So, it's a win-win!!
 
Last edited:

dallasjustice

Member Sponsor
Apr 12, 2011
2,090
0
0
Dallas, Texas
#6
Here is right channel before and after the three new modex plates at 1/12th per octave resolution. The before is a stereo sub measurement, so the very low bass is smooth with two mono subs versus two stereo subs. I prefer listening with the mono subs. It sounds much better. Green is before and yellow is after. These are actual measurements from the seated position after Audiolense digital crossover and target curve application.
yellow after green before.jpg

You can see that the SPL and especially the bass matches my target curve very well. I prefer a downward sloping target curve. This is perceptually flat and the most subjectively desirable target. Overall, the sound quality is mega; never-heard-before; whatever else you want to call it. :D

The following is RT60. RT60 tells us how long it takes for a signal to fall by 60db. Its not the perfect measurement for small room decay. But it IS very useful in comparing different setups. There is a sweet spot for decay; no doubt about it. If you want to read more about where the sweet spot should be and how decay should be shaped, I highly recommend Nyal Mellor's article he recently published on the topic.
http://www.acousticfrontiers.com/un...il&utm_term=0_9f30f97542-0a1da279b6-408472965

Again, green is before and yellow is after.
yellow after green before rt60.jpg

These graphs tell us two things.

1. The bass is just as good, if not better, after the 3 modex plates were installed and the 8 fiberglass panels removed.
2. The decay time is greatly improved in two ways. First, the decay is smoother without all of the fiberglass panels and the three modex plates installed. Second, the decay time in the midrange and higher frequencies are significantly increased. Previously, the room was on the edge of acceptable decay time. Some folks may have thought the room sounded a little to anechoic, if you will. I personally felt the room sounded great but I also knew it could be improved.

Now, with the longer and smoother decay times, its the soundstage that gets the mega upgrade. The soundstage is much wider and deeper. Also, the smaller high frequency details like the nylon tipped drum stick tapping the high hats, are so much more clear. Also, I was surprised to discover that vocalist intelligibility is greatly enhanced with slightly longer and smoother decay times.

Was it worth all the money and trouble? Absolutely! I could have spent that money on a new DAC/ADC or a fancier speaker cable. Would I have been able to get the same level upgrade in my system had a spent that money on something else? No way, no how.

Michael.
 
Last edited:

Nyal Mellor

Industry Expert
Jul 14, 2010
591
0
0
SF Bay Area, CA, USA
#7
Great posts!

Worth mentioning there are three different types of Modex Plate.

Type 1 works from 65-300Hz. Uses a 1mm steel plate. Steel plate is the outermost layer facing the room. 4" of absorption behind that.
Type 2 works from 40-100Hz. It uses a thicker 2.5mm steel plate than the Type 1. Steel plate is the outermost layer facing the room. 4" of absorption behind that.
Broadband works from 65-5000Hz. It uses the same steel plate as Type 1 but sandwiched between two layers of 2" absorption.

The technology was developed by Fraunhofer, it is also known as a VPR. Fraunhofer license to Renz who manufacture the product, RPG import from Renz. RPG will wrap the Modex in any fabric, or you can get it without a fabric wrap, in which case the finish is white perforated metal.

They are very good products, and work as advertised. The only downside is their expense. However you need to factor into that their size and compare that to the 2'x4' standard acoustic panel size. The Modex are 3'3" x 4'11". Pretty much double the surface area of a 2x4 panel.

To deal with the sub-100Hz range I advise a combination of proper shell design ("floppy walls"), multiple subs and EQ. See a blog article I wrote called Five Steps to Amazing Bass.
 

dallasjustice

Member Sponsor
Apr 12, 2011
2,090
0
0
Dallas, Texas
#9
How much is each one of those
They are priced by RPG based on the order. The prices don't include shipping, which isn't cheap. The type 2 is usually listed around $1,500 and the type 1 is usually listed around $1,200. So, they can really add up fast. IMO, they are well worth it since there's zero competition in terms of performance or aesthetics. They are only 4" deep so they look very nice.

In my room, I have 3 type 2s and 6 type 1s. I bought them at three different times because I could really afford to buy all at once, I thought. When Nyal first advised me to buy them a couple of years ago, I think he told me I could easily use 9 in my room. I almost fell out of my chair. Looking back, it would have been wise to just bite the bullet.
 

dallasjustice

Member Sponsor
Apr 12, 2011
2,090
0
0
Dallas, Texas
#10
I also want to mention something about installation. Scotty has probably installed 20 plates now. He uses a special type of lag bolt which works super on drywall. There's no need to drill into studs. Hopefully Scotty can chime in here. My room has pretty flat and symmetrical walls. But Ive seen a few problem installs in cases where the wall isn't totally flat. You'd be surprised how often walls aren't totally flat.
 

dallasjustice

Member Sponsor
Apr 12, 2011
2,090
0
0
Dallas, Texas
#12
Indeed it can add up fast. That's why I asked. Did you consider other options?
I removed 8 RPG BAD panels and two qrd diffusers and replaced them with 3 Modex plates. IME, the RPG BAD panel is the best fiberglass panel on the market because of how diffusion works on the front wood plate. But even BAD panels require many more to equal the performance of a Modex plate so decay time suffers with too many BAD panels.

There are a few other companies who make pressure based bass absorbers. As you can see in my photos, I do use some GIK pressure absorbers. I've taken more of them out of my room than I use. I think that is a pretty low performance product. I don't recommend them. I think Stillpoints makes a product called aperture. Of course, we have already seen that thread. I'm not sure you want me to get started on the aperture. It could get ugly.
 

ddk

Industry Expert
May 19, 2013
3,431
2
38
Utah
#13
I removed 8 RPG BAD panels and two qrd diffusers and replaced them with 3 Modex plates. IME, the RPG BAD panel is the best fiberglass panel on the market because of how diffusion works on the front wood plate. But even BAD panels require many more to equal the performance of a Modex plate so decay time suffers with too many BAD panels.

There are a few other companies who make pressure based bass absorbers. As you can see in my photos, I do use some GIK pressure absorbers. I've taken more of them out of my room than I use. I think that is a pretty low performance product. I don't recommend them. I think Stillpoints makes a product called aperture. Of course, we have already seen that thread. I'm not sure you want me to get started on the aperture. It could get ugly.
Please expand on the GIK product Michael, what's actually wrong with them? They seem to be popular these days and I never actually heard them.

david
 

dallasjustice

Member Sponsor
Apr 12, 2011
2,090
0
0
Dallas, Texas
#14
Please expand on the GIK product Michael, what's actually wrong with them? They seem to be popular these days and I never actually heard them.

david
The problem with the GIK pressure traps is they have very narrow bandwidth and it takes a lot of them. So you could fill a whole wall up with them to get only a very narrow bandwidth handled. For me, the big ones work okay. Putting up treatments is exactly like putting a puzzle together. :)
 

spiritofmusic

Member Sponsor
Jun 13, 2013
6,225
11
38
E. England
#15
New to this thread.
I'm pretty much where I want to be re components, not looking to upgrade further (just a final decision on sticking w/my Zu Definitions 4 spkrs, or moving to Sadurni Staccato horns/Behringer DCX dsp'd subs)
Have maxxed out on my final choice of accessories (Sablon Reservas cable loom/Westwick 8kVA balanced power/Entreq grounding/Symposium Acoustics Isis rack), w/some remaining expenditure on Shun Mook Diamond resonators, and possibly a Spiers And Robertson Air Table for my tt.
I'm moving house in the next 12 mnths, and am looking to max out the new room acoustically as my Final Frontier series of upgrades. I'm wary of dsp, but acoustic panels are more in my comfort zone, and Dallas' strong recommendation of these means it'll be the brand I investigate.
So a couple of qs to kick off:
How do you go about measuring accurately and getting the most of this expensive item? Can I rely on a specialist distributor of Modex in the UK providing a bespoke measuring service that I can trust?
And when one identifies the area needing treatment, does it need to be floor to ceiling in that zone (esp in corners), or just half way up the wall, or just at ear level when sitting?
 

steve williams

Site Founder,Co- Owner, Adminisrator
#16
Indeed it can add up fast. That's why I asked. Did you consider other options?
I removed 8 RPG BAD panels and two qrd diffusers and replaced them with 3 Modex plates. IME, the RPG BAD panel is the best fiberglass panel on the market because of how diffusion works on the front wood plate. But even BAD panels require many more to equal the performance of a Modex plate so decay time suffers with too many BAD panels.

There are a few other companies who make pressure based bass absorbers. As you can see in my photos, I do use some GIK pressure absorbers. I've taken more of them out of my room than I use. I think that is a pretty low performance product. I don't recommend them. I think Stillpoints makes a product called aperture. Of course, we have already seen that thread. I'm not sure you want me to get started on the aperture. It could get ugly.
I went with fabric and drapes and the Lumitex linking as well as Noiseout under the sub carpet and I a wondering if is cost me less and our rooms are very close
 

Nyal Mellor

Industry Expert
Jul 14, 2010
591
0
0
SF Bay Area, CA, USA
#17
They are priced by RPG based on the order. The prices don't include shipping, which isn't cheap. The type 2 is usually listed around $1,500 and the type 1 is usually listed around $1,200. So, they can really add up fast. IMO, they are well worth it since there's zero competition in terms of performance or aesthetics. They are only 4" deep so they look very nice.

In my room, I have 3 type 2s and 6 type 1s. I bought them at three different times because I could really afford to buy all at once, I thought. When Nyal first advised me to buy them a couple of years ago, I think he told me I could easily use 9 in my room. I almost fell out of my chair. Looking back, it would have been wise to just bite the bullet.
The price varies depending on whether you want a fabric wrap or not and how many you order.

I have four Type 1 in our showroom which is 12x16.

The Magico showroom at their new factory has a bajillion of them! Plus some Modex Edges (not shown) and a bunch of Abfussors and Modfussors as well as some Waveform Monoradials on the ceiling.
Magico%20Demonstration%20Room_Abffusor%20BAD%20Panel%20Modex%20Plate%20Modffusor%20Waveform%20Mo.jpg
 

dallasjustice

Member Sponsor
Apr 12, 2011
2,090
0
0
Dallas, Texas
#18
I went with fabric and drapes and the Lumitex linking as well as Noiseout under the sub carpet and I a wondering if is cost me less and our rooms are very close
I don't know. But I bet the bass could have been more cost effectively handled had I customed designed the walls like yours. My attic has turned into an acoustic treatment graveyard.

I think decay times are tricky and can come down to personal listening preference as well as type of music.