RPG Modex Plates-"Free" Bass Traps

dallasjustice

Member Sponsor
Apr 12, 2011
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Dallas, Texas
#21
I have to say that QRD diffusers might be the one of the most overrated type of room treatment I've used. I think maybe in really huge rooms, they make some sense. I think intelligibility is decreased using them anywhere close to seated position. Looking at the Magico sound room, it looks like they mounted many QRDs at the sidewall first reflection. I wouldn't do that.


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.
View attachment 21245
 

spiritofmusic

Member Sponsor
Jun 13, 2013
6,225
11
38
E. England
#22
How many panels are you likely to use Keith in your room (which I am familiar with)? Price per panel? Do the UK suppliers provide an expert measuring service, or is this best done y'self/DIY or via a specialist, and then just order the stuff?
 
#23
When it came to bass measurements in my room my response was pretty bad. My acoustician had me take measurements with an SPL meter in 6 different locations in my room at 40Hz and 80Hz. This gave us the pressure points in the room and guided us to where the Modex Plates needed to be. We came up with four Type 1's and one Type 2. The Type 2 is located on the front wall where it meets the ceiling and the two Type 1's are mounted high in the corners. The other two Type 1's are mounted vertically beside and slightly behind each speaker. I don't have my measurements handy, but it drastically smoothed my bass response. I was simply blown away with the sound and love the look of the Modex Plates.

DSCF2738.JPG
 
#24
Practice Makes Perfect :D

The Modex Plates are relatively easy to mount(see statement above). If the Modex plate is standing vertical it has two horizontal metal brackets that mount on the wall. The MP is lifted over the bracket and gently pulled down which seats small knobs into the bracket. If I don't find a stud I use a type of toggle bolt called a Toggler.

Toggler.jpg

These hold about 238lbs per anchor and make installing Modex Plates easy and safe.

I did have an issue in my room with the front wall being bowed a bit :( so I had to use a 4x6 and make a spacer to bring the MP about 3/4" away from the wall. I was told this would not affect the performance of the MP one bit.
 
#25
Nyal is right about the price of the Modex Plates. They vary according to quantity and fabric choice. In my opinion RPG makes the finest room treatments available, but their main customers are Symphony Halls, Church's and Recording Studios so us stereo room treatment guys are not at the top of their list. Now this is not to say they don't take care of us, they really are great to deal with, we just have to wait and be patient for our Modex Plates :).
 

Nyal Mellor

Industry Expert
Jul 14, 2010
591
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SF Bay Area, CA, USA
#26
I have to say that QRD diffusers might be the one of the most overrated type of room treatment I've used. I think maybe in really huge rooms, they make some sense. I think intelligibility is decreased using them anywhere close to seated position. Looking at the Magico sound room, it looks like they mounted many QRDs at the sidewall first reflection. I wouldn't do that.
Not QRDs, Abfussors. A hybrid absorber / diffuser.
 

mep

Member Sponsor & WBF Founding Member
Apr 21, 2010
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#27
I have to say that QRD diffusers might be the one of the most overrated type of room treatment I've used. I think maybe in really huge rooms, they make some sense. I think intelligibility is decreased using them anywhere close to seated position. Looking at the Magico sound room, it looks like they mounted many QRDs at the sidewall first reflection. I wouldn't do that.
You should give Alon a call and see if you can be a sound consultant for Magico. :D
 

dallasjustice

Member Sponsor
Apr 12, 2011
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Dallas, Texas
#29
Not QRDs, Abfussors. A hybrid absorber / diffuser.
The RPG website says they are a QRD and absorber. If so, there's still phase grating in the mid and higher frequencies since they are partially QRDs. Aren't QRDs designed for far field?

As you know, I had QRDs on back wall about 6 feet from seated position. I felt that BAD panels were better there instead and the Modex plate better yet. I moved them to side walls adjacent to listening position. My room is 14'6" wide. The QRDs greatly reduce soundstage precision and vocal intelligibility in that position. I never tried them any closer to the speaker but I bet they would create more problems. Maybe in a huge room they could be okay but they aren't for me.
 
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#31
Scott W, where were the six locations you measured with your SPL meter and what exactly were you measuring for? Thanks.
The 6 locations were given to me by my acoustician that I work with. They were based on possible bass pressure zones. I measured 40 and 80 at the listening position with an SPL meter, then at each location. I was measuring for a major increase in volume of these two frequencies in relation to the listening position reading. This then gave me the possible locations for the Modex Plates.
 
#33
Mainly where you see the Modex Plates :D They were at the front of the room corners, up high and front center ceiling/wall intersection. And beside each speaker.
 

Jeff Hedback

[Industry Expert]
Feb 9, 2011
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Indpls, IN
www.HdAcoustics.net
#34
Hi Scott...thought I'd jump in on our analysis process. The SPL in-room studies were used to compare/contrast with acoustical pressure mapping simulations (BEM). Those studies defined the optimal type and location for the low freq control products. Here is a graph of the results. The room is still a situation of making the right compromises/choices (between spkr/listener locations for LF response vs locations for soundstage and imaging. post_fullrange_1-third oct smoothed.png
 
#35
Awesome Jeff! Thank you for that info. And as always you are the MAN!
 

Bjorn

New Member
Oct 12, 2010
140
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0
Norway
#37
The RPG website says they are a QRD and absorber. If so, there's still phase grating in the mid and higher frequencies since they are partially QRDs. Aren't QRDs designed for far field?

As you know, I had QRDs on back wall about 6 feet from seated position. I felt that BAD panels were better there instead and the Modex plate better yet. I moved them to side walls adjacent to listening position. My room is 14'6" wide. The QRDs greatly reduce soundstage precision and vocal intelligibility in that position. I never tried them any closer to the speaker but I bet they would create more problems. Maybe in a huge room they could be okay but they aren't for me.
Just came over this thread. I sell RPG products in Europe.

Diffusers need space between the listener and the units to work well. The general rule is that the distance should be minimum 3 wavelengths of the diffused energy. That means if the QRD diffuses down to 500 Hz, the wavelength is 2.2', and thus the minimum distance should be 6.57'. Some argue that 2xwavelength is also fine but 3x or more is definetly better. Sitting closer to a diffuser will result in one hearing comb filtering instead of proper diffused energy.

Also, when three or more of the traditional RPG QRD diffuser are placed next to each other it will cause lobing due to periodicity. The new RPG Modffusor and Modffractal are built after an aperiodic model which minimizes lobing greatly and are better products.


BAD panels/BAD Arc don't diffuse as low, approximately down to 800 Hz, so these work better closer. However, if one desires the absolute best clarity, intelligibility, and localization, it's better to attenuate reflections that arrive soon after the direct signal with only absorbents. If the aborbents are thick and big enough to work down the schroeder frequency and combines them with bass trapping, one avoids much of the typical deadening of the room. Absorbents need to be a minimum of 6" thick (either flushed or with an airgap) to get this low. And surface must be bigger than the typical 2x4'.

When you have Modex Plate on the rear wall, you will end up with specular reflections at you seating position. I would advice you to place either some absorbents or BAD Arcs at the reflection points in front of the Modex Plates.
 

Nyal Mellor

Industry Expert
Jul 14, 2010
591
0
0
SF Bay Area, CA, USA
#38
Just came over this thread. I sell RPG products in Europe.

Diffusers need space between the listener and the units to work well. The general rule is that the distance should be minimum 3 wavelengths of the diffused energy. That means if the QRD diffuses down to 500 Hz, the wavelength is 2.2', and thus the minimum distance should be 6.57'. Some argue that 2xwavelength is also fine but 3x or more is definetly better. Sitting closer to a diffuser will result in one hearing comb filtering instead of proper diffused energy.

Also, when three or more of the traditional RPG QRD diffuser are placed next to each other it will cause lobing due to periodicity. The new RPG Modffusor and Modffractal are built after an aperiodic model which minimizes lobing greatly and are better products.


BAD panels/BAD Arc don't diffuse as low, approximately down to 800 Hz, so these work better closer. However, if one desires the absolute best clarity, intelligibility, and localization, it's better to attenuate reflections that arrive soon after the direct signal with only absorbents. If the aborbents are thick and big enough to work down the schroeder frequency and combines them with bass trapping, one avoids much of the typical deadening of the room. Absorbents need to be a minimum of 6" thick (either flushed or with an airgap) to get this low. And surface must be bigger than the typical 2x4'.

When you have Modex Plate on the rear wall, you will end up with specular reflections at you seating position. I would advice you to place either some absorbents or BAD Arcs at the reflection points in front of the Modex Plates.
Or you could use Modex Broadband on rear wall!

The general rule about distance from diffuser to listener I have found only applies to aggressive QRD phase-based diffusion. Less aggressive quasi-diffusers like Auralex T'Fusor or the Harmonix K you can sit closer to without aural weirdness. Amplitude based diffusion like BAD or slat diffusers you can sit even closer to.

BTW my wife is Norwegian!
 

Bjorn

New Member
Oct 12, 2010
140
0
0
Norway
#39
Modex Broadband would be better, but the absorption stops around 5KHz. So there would still be some high frequency specular reflections.
Absorbents in front of Modex Plate (type 1) don't need to be very thick though, considering the Modex Plate absorbs well up to around 300 Hz. I've done this in my home theater room where a Modex Plate where placed on the sidewall at a first reflection point. The absorbents in front actually increased the low frequency absorption a little.

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