RPG Modex Edge a Resonator Bass Absorber

[TitaniumTroy]

https://www.rpgacoustic.com/modex-edge/

I see RPG has a new to me product, any inputs would be appreciated. It looks to me like it is some kind Hemholtz Resonator type product.

The Modex Edges are dedicated, broadband, low frequency sound absorbers designed to balance the modal distribution of small rooms such as studio control rooms and home theaters down to 20Hz. The damped chamber system is able to offer bass control over several octaves while not contributing to mid or high frequency absorption.

• High-pass resonator design.
• 30 – 500 Hz absorption efficiency.
• Modular free-standing unit.
• Fabric upholstered exterior with decorative trim.
• Corner and Mid-wall mounting.

 

[March Audio]

no performance data below 100Hz where in typical sized rooms your problems will lie.

 

[Bounce44.1]

Agreed. Unfortunately to attack the below 100hz issue costs. The smaller the room the more it costs. Acoustic Fields has some good information on this.

 

[pozz]

I'd like to know more about the RPG Modex series myself. Particularly if they work as advertised for low frequencies. I've only encountered a few other products designed this way. The GIK Acoustics T40, T70 and T100 and MSR Springtrap are the only ones I know of.

There aren't many with facilities certified to test below 100Hz using the established ASTM C423 methods. The official results will simply stop at the lowest certified band, although they will provide the bass readings with an attached list of caveats. Many manufacturers won't include this information since it's unreliable (no known error tolerances, for example).

And I have a bone to pick with Acoustic Fields.

Agreed. Unfortunately to attack the below 100hz issue costs. The smaller the room the more it costs. Acoustic Fields has some good information on this.

Acoustic Fields tutorials are unreliable, and at best inconsistent. It's a polite way of saying that they are the equivalent of cable companies and the like for audiophiles interested in acoustical treatments. They have a forum and Dennis responds personally to emails, but in both cases the messages are brief and cryptic. Same goes for their marketing materials: a lot of disorganized information, just educational enough to get you interested, but not enough to put together an informed buying decision.

Take the attached single-page RAL report for the ACDA-10 broadband/membrane trap. Total absorption for 8 units placed flat on the ground (which is called A mounting) averages to around 10 Sabins across the entire frequency range, and 17 for 100Hz and below. The full RAL report will contain the entire testing procedure, including pictures and other figures. One of the common items is total absorption per unit, which for the ACDA-10 roughly translates to 1.25 Sabins broadband, and 2.125 Sabins for sub-100Hz bass. This is disappointing. Broadband traps can easily perform at 10—20 Sabins per unit for the midrange. I don't know what the equivalent would be for bass traps.

Keep in mind that Acoustic Fields advertises the ACDA-10 to target the 30Hz—200Hz range and charges a minimum of $1050 USD. Each 27"x48"x8" unit is 137 pounds! Compare that to the report for the attached GIK T100 membrane trap ($190 USD, half the height/thickness and only 24 pounds). Looking at 100Hz, which is the T100's resonant frequency, you have:

• GIK T100: 6.98 Sabins per unit
• ACDA-10: 1.77 Sabins per unit

You may wonder if the comparison is fair given that the T100 report shows J mounting. J mounting indicates that something unusual or atypical was done. There is no associated standard, as there is for A mounting (flat on the ground) or E mounting (like A, but with brackets that hold up the tested unit, typically with 400mm spacing, and skirting around the resulting air gap to prevent absorption by the back of the tested unit). In the case of the T100, J mounting was described as wall mounted and no air gap. So all in all largely similar.

Acoustic Fields is likely going for low-level but linear absorption. As is, you'd have to cover the ceiling and every wall with these traps to make an appreciable difference. But even then the actual effectiveness is hard to guage since they don't post before/after acoustic results for their studio or listening room builds. The activated charcoal used for the trap interiors will also likely saturate over time with humidity.

It would be much cheaper, simpler and more effective to use targeted absorption with a number of different trap types.

 

[mitchco]

RPG makes excellent, albeit expensive products. My exposure to them is in a variety of studio control room environments from years ago. Unfortunately, to get any control under 100 Hz requires either stuffing the room with so called bass traps. with the disadvantage of the room sounding too dead at higher frequencies. Even Helmholtz resonators targeted at a narrow band may take a peak down, but doesn't do much for the dip.

I worked in a couple of LEDE control rooms where it is a room within a room, where the symmetrical inner room gradually becomes transparent at lower frequencies which pass into an outer asymmetric shell for low-frequency control. Tightest bass response I have heard. But a very expensive room!

If you have REW and a measurement mic, one can look at waterfall to get a handle on low frequency decay and the inevitable up and down frequency response due to small room acoustics below transition/Schroeder. Personally, the best bang for the buck is employing some DSP room correction below 500 Hz. Here is a practical example:

Top measurement is a typical small room where we are seeing about 25 dB in low frequency variation below 100 Hz. The bottom trace is with Audiolense room correction in play below 500 Hz and leaves the response above alone. And it is not at just one mic position either.

While one can move speakers around, it typically just moves the peaks and dips around a bit, as one is bound by the physical dimensions of the room. Multiple subs strategically located can distribute the modes and even them out if you look at Todd Welti's paper and likely still need DSP correction like Andy's multi sub optimiser.

Sorry @TitaniumTroy to be a bit off topic, but dealing with room modes below 100 Hz either requires an acoustically designed room to take that into play, including preferred room ratios to better randomly distribute the modes, and even then it is not a guarantee due to small room acoustics where there may not be enough modes to distribute... But if into computer audio, the power of DSP at a minimal cost, will likely have the most bang of the buck for smoothing out the low frequency response around your listening area.

 

[Krunok]

Top measurement is a typical small room where we are seeing about 25 dB in low frequency variation below 100 Hz. The bottom trace is with Audiolense room correction in play below 500 Hz and leaves the response above alone. And it is not at just one mic position either.

While one can move speakers around, it typically just moves the peaks and dips around a bit, as one is bound by the physical dimensions of the room.

If I understand corretly Audiolense, like most other Room EQ solutions, requires multiple measurements from various points around the LP to be taken to calculate filters. Does it calculate filters based on the measurement taken from the central point of the LP while using other measurements only to analyze peaks and dips or it calculates some kind of average of all the measurements from which it then derives the filters?

 

[Bounce44.1]

I'd like to know more about the RPG Modex series myself. Particularly if they work as advertised for low frequencies. I've only encountered a few other products designed this way. The GIK Acoustics T40, T70 and T100 and MSR Springtrap are the only ones I know of.

There aren't many with facilities certified to test below 100Hz using the established ASTM C423 methods. The official results will simply stop at the lowest certified band, although they will provide the bass readings with an attached list of caveats. Many manufacturers won't include this information since it's unreliable (no known error tolerances, for example).

And I have a bone to pick with Acoustic Fields.

Acoustic Fields tutorials are unreliable, and at best inconsistent. It's a polite way of saying that they are the equivalent of cable companies and the like for audiophiles interested in acoustical treatments. They have a forum and Dennis responds personally to emails, but in both cases the messages are brief and cryptic. Same goes for their marketing materials: a lot of disorganized information, just educational enough to get you interested, but not enough to put together an informed buying decision.

Take the attached single-page RAL report for the ACDA-10 broadband/membrane trap. Total absorption for 8 units placed flat on the ground (which is called A mounting) averages to around 10 Sabins across the entire frequency range, and 17 for 100Hz and below. The full RAL report will contain the entire testing procedure, including pictures and other figures. One of the common items is total absorption per unit, which for the ACDA-10 roughly translates to 1.25 Sabins broadband, and 2.125 Sabins for sub-100Hz bass. This is disappointing. Broadband traps can easily perform at 10—20 Sabins per unit for the midrange. I don't know what the equivalent would be for bass traps.

Keep in mind that Acoustic Fields advertises the ACDA-10 to target the 30Hz—200Hz range and charges a minimum of $1050 USD. Each 27"x48"x8" unit is 137 pounds! Compare that to the report for the attached GIK T100 membrane trap ($190 USD, half the height and only 24 pounds). Looking at 100Hz, which is the T100's resonant frequency, you have:

• GIK T100: 6.98 Sabins per unit
• ACDA-10: 1.77 Sabins per unit

You may wonder if the comparison is fair given that the T100 report shows J mounting. J mounting indicates that something unusual or atypical was done. There is no associated standard, as there is for A mounting (flat on the ground) or E mounting (like A, but with brackets that hold up the tested unit, typically with 400mm spacing, and skirting around the resulting air gap to prevent absorption by the back of the tested unit). In the case of the T100, J mounting was described as wall mounted and no air gap. So all in all largely similar.

Acoustic Fields is likely going for low-level but linear absorption. As is, you'd have to cover the ceiling and every wall with these traps to make an appreciable difference. But even then the actual effectiveness is hard to guage since they don't post before/after acoustic results for their studio or listening room builds. The activated charcoal used for the trap interiors will also likely saturate over time with humidity.

It would be much cheaper, simpler and more effective to use targeted absorption with a number of different trap types.

Maybe My math is way off but at 40 and 50hz the acda-10 is far superior. Seems you chose the 100hz result. I believe we were talking specifically about less than 100hz no?

 

[pozz]

Maybe My math is way off but at 40 and 50hz the acda-10 is far superior. Seems you chose the 100hz result. I believe we were talking specifically about less than 100hz no?

No, you're right.

I chose 100Hz to compare the results with the T100. GIK haven't posted the RAL reports for the T70 or T40, which are tuned lower, so I couldn't make a fair comparison at those frequencies. The effective Q of these units is pretty narrow.

It terms of cost I could buy four T40s for every ACDA-10.

Again, sub-100Hz results are generally unreliable, and despite all the technical claims the full ACDA-10 report was never made available. Or even something simpler like in-room measurements. They have a dedicated listening room—they could easily post pics and REW results for that.

 

[Krunok]

No, you're right.

I chose 100Hz to compare the results with the T100. GIK haven't posted the RAL reports for the T70 or T40, which are tuned lower, so I couldn't make a fair comparison at those frequencies. The effective Q of these units is pretty narrow.

It terms of cost I could buy four T40s and for every ACDA-10.

Again, sub-100Hz results are generally unreliable, and despite all the technical claims the full ACDA-10 report was never made available. Or even something simpler like in-room measurements. They have a dedicated listening room—they could easily post pics and REW results for that.

I must admit I have yet to see a measurement in a non-professional environment where response below 100Hz was tamed only with passive absorbers without any room EQ.

 

[Kal Rubinson]

I'd like to know more about the RPG Modex series myself. Particularly if they work as advertised for low frequencies. I've only encountered a few other products designed this way. The GIK Acoustics T40, T70 and T100 and MSR Springtrap are the only ones I know of.

I've been using a pair of the MSR SpringTraps for years. My testing has not been rigorous or detailed but there was a visible (and audible) tightening of the acoustic decay at various problem areas in the <100Hz range. https://www.stereophile.com/content/music-round-56-page-2

 

[mitchco]

If I understand corretly Audiolense, like most other Room EQ solutions, requires multiple measurements from various points around the LP to be taken to calculate filters. Does it calculate filters based on the measurement taken from the central point of the LP while using other measurements only to analyze peaks and dips or it calculates some kind of average of all the measurements from which it then derives the filters?

In discussion with the developers of some of these DSP products and extensive testing on my end, not all Room EQ solutions are created equal. Dirac requires multiple measurements, as does many others and typically averages the measurements to calculate the filters Audiolense allows one to create a filter from either a single measurement or multiple measures. Acourate uses a single measurement to calculate the filter.

But Audiolense and Acourate comes with their own frequency dependent windowing (FDW) and psychoacoustic analysis algorithms. The result is both are unique in the sense that they do no try a full inversion of the measurement, but use their analysis algorithms to calculate how much dip to fill in depending on the dips bandwidth - very narrow, leave alone, somewhat narrow, only fill half way in, etc. It gets complicated fast.

In the case of Acourate, as documented in my book, based on a single analysis measurement, produces a filter that is very smooth in the low frequencies where I took 14 REW measurements across a 6' x 2' grid area at the LP which represents my couch. Audiolense was the same. I tried both a single analysis measurement and multiple measurements, and really there is not much difference.

I am not against bass traps, but having measured many rooms before and after, the traps have some effect both audible and measurable, but relatively speaking a (very) small contribution when compared to properly executed DSP room eq. When you factor in cost, there is no comparison.

 

[Bounce44.1]

A bit odd if one considers who posted the test results in the first place. It seems that this entire site is based on test results over everything else, no?

For sure I have no answer to the <100hz problem most rooms have. Nor do I have any preference for the solution. I try not to belittle anyone with simply a different idea.

 

[Krunok]

In the case of Acourate, as documented in my book, based on a single analysis measurement, produces a filter that is very smooth in the low frequencies where I took 14 REW measurements across a 6' x 2' grid area at the LP which represents my couch. Audiolense was the same. I tried both a single analysis measurement and multiple measurements, and really there is not much difference.

My case is quite different: I made 10 sweep measurements and 70+ RTA samples using moving mic method over the area of 1m wide and 0.5m deep. Both came identical and showed that there was significant differences (+/- 5dB) in response between measurement points. My guess is that is happening as a result of top firing secondary woofer which causes a lot of reflections in my room. That situation complicated manual design of filters quite a lot, hence my question how Audiolense is doing it.

For the same reason phase and GD graphs look like a nightmare when measured at LP. I had to take nearfield measurement from app 30cm to properly correct phase. When I tried automatic correction with DRC (which also relies on the single sweep) it was not able to correct phase properly which resulted in a non-linear LF response when measuring both speakers response, although each speaker measured pretty well when played separately.

I am not against bass traps, but having measured many rooms before and after, the traps have some effect both audible and measurable, but relatively speaking a (very) small contribution when compared to properly executed DSP room eq. When you factor in cost, there is no comparison.

I absolutely agree. Traps may help with decay to some point but if you want linear LF response room EQ is the only way.

 

[Kal Rubinson]

I am not against bass traps, but having measured many rooms before and after, the traps have some effect both audible and measurable, but relatively speaking a (very) small contribution when compared to properly executed DSP room eq. When you factor in cost, there is no comparison.

I agree. I kept the MSR traps because they made a subjective effect as well as a measurable one and, at the time, I did not have access to any of the more modern DSP tools we have now. Also, due to an honest misunderstanding with the manufacturer, I felt obligated to buy them. Since they sit neatly in the corner and, afaik, do no harm, they remain even though I rely more on DSP these days.

 

[Krunok]

It seems that this entire site is based on test results over everything else, no?

Which shouldn't really come as a surprise considering the site is named "Audiosciencereview", no?

 

[Bounce44.1]

No worries.

 

[Hipper]

I must admit I have yet to see a measurement in a non-professional environment where response below 100Hz was tamed only with passive absorbers without any room EQ.

Not tamed but improved!

One GIK Soffit Trap in each front corner.

Adding bass traps: one in each front corner, two in each front corner, front wall-ceiling, rear wall-ceiling, side wall-ceiling, finally rear wall-wall corners.

No smoothing, really!

So a lot of bass traps does do something below 100Hz but certainly does not solve the issues, in particular the big dip around 50Hz (I tried everything to solve this - moving speakers and chair, checking everything including the equaliser was working properly, and searching for peaks all around the room. I've still no idea what causes it but surprisingly adding 10dB with an equaliser was able to fill it in - to hell with the rules!).

Of course not only is the frequency response improved - much smoother, but the delay times have radically changed for the better. Indeed this is probably the biggest achievement of the room treatment (the ringing at 40Hz is mostly external traffic noise. It's clearer on a spectogram).

 

[Krunok]

Not tamed but improved!



View attachment 32484

So a lot of bass traps does do something below 100Hz but certainly does nor solve the issues, in particular the big dip around 50Hz (I tried everything to solve this - moving speakers and chair, checking everything including the equaliser was working properly, and searching for peaks all around the room. I've still no idea what causes it but surprisingly adding 10dB with an equaliser was able to fill it in - to hell with the rules!).

Of course not only is the frequency response improved - much smoother, but the delay times have radically changed for the better. Indeed this is probably the biggest achievement of the room treatment.

Well, don't get me wrong, but here are my 2 cents: you spent hell lot of money on those bass traps and, while it is true that decay improved significantly, your frequency response in the 30Hz-300Hz region still lies between 45dB and 72dB, and that cannot be called satisfactory.

Here is response of my speakers in the same region after correction, 1/12 smoothing. It costed me 50 GBP for a fanless used Dell PC on which I installed Volumio, BruteFIR convolver and fitlers I created manuualy with rePhase based on measurements made with REW.

 

[pozz]

@Krunok the main thing that EQ software cannot provide is control of reverb time. It's a physical characteristic which has to be altered using physical means.

 

[Krunok]

@Krunok the main thing that EQ software cannot provide is control of reverb time. It's a physical characteristic which has to be altered using physical means.

True. And while decay is important it is still far less important than linear frequency response.