40hz room mode RPG Modex Corner trap?

Hey guys,
Looking for some help with some room modes I am battling. Main offender is 40hz mode. (very typical with 8ft ceilings I suppose) I have several ASC tube traps that have helped a lot, but at this point the don't need much more broad bass damping just 40hz damping as the peak there is way above everything else.

So, two questions:

1. Has any one used the RPG Modex Corner trap?
Seems to be exactly what I need as they make a 40hz model. How effective are these? I think that to make a significant difference I may need so many that the cost will kill. Would 2-4 make a difference?

2. Any other ideas to kill the 40hz room mode short of an eq like the PARC?

If we could deal with 40 Hz effectively passively we would not have made the PARC. We have tried the Modex--and we love RPG products and use them all the time in our designs, but we have not gotten good results with the Modex. At 40 Hz, there's a lot of energy and a long wavelength. The only real passive option is a custom designed and built Helmhotz resonator. It can do the job--but it's not easy to build these properly, particularly if it's a high Q resonance and greater than 8 db.
I understand that the PARC might be a bit expensive. However, the Behringer DEQ2496 would do the job for you. See the several threads about this remarkable unit. By the way, Rives audio will tell you that LF room resonances, like 40 Hz, can't really be controlled by room treatments, and that is why they came up with the PARC.

Although they are more of a broadband solution, you might want to look into the Mondotraps made by Realtraps. They only absorb under about 100Hz or so (so your room doesn't become overdamped in the higher freq.). They are a lot cheaper than the RPG's........... Don't know if they are more/less effective, but certainly a higher Q.

I recently installed four of them alond with some of their other products in my listening room to great effect.

Thanks for the info. I have a lot of respect for the PARC from everything I've read, and actually I've got a huge amount of use from the rives test cd with the rat shack meter while doing speaker placement and adjusting my asc treatments. $3k is probably too much for me at the moment though, wish there was a cheaper version that did just one mode.

Rives, is your thought on the Modex what I was thinking that it would take so many that it would be better to just use a PARC? Also curious if you have an info on building a Helmhotz resonator? Not actually out of the question as I have access to shop and lab equipment and would be looking at a 5-8db cut if I use optimum speaker placement.

Mondotrap looks interesting, may work in a corner for me.

I'll check info on the DEQ2496, probably stupid not to try it for the price. Probably would shift my direction to using an out board dac or something since my current digital player is optimized for tube analog out and doing A/D/A would give me an aneurysm. ;-)

My experience is that a digital notch filter at 40Hz with a 6 Hz width worked fine for me....this kind of bass management adjustment is available on most DSP's because room resonance is such a common problem with subs that extend down to 20Hz.

Obviously this is not ideal but I think there is a limit to what can be achieved with room treatments. So your choice is either electronic tweaking using a DSP or the rather costly option of moving house and using a gymnasium size room for you system...

I am not sure if you can get an analog filter that would do the job adequately ( at least not cheaply as complex analog filters are very expensive )....digital filters are much easier to design and can still give great performance(in my mind).
Shadorne, can you recomend a unit that I look into? I guess it still puts me in the boat of going to a transport dac system, but I suppose I could try a TACT system or something.

I think most DSP's have digital notch filters.

I have an Anthem AVM 20 (second hand of course) which I feel is great value considering all the features and XLR outs. Good enough for me anyway. There are many other DSP's and some with more expensive DAC's than the AVM 20...so look around...maybe a Krell or Classe.

Myself I am not so worried about DAC quality and have not tested a lot of high end DAC's. I have never heard a TACT 2.2 for example - so I am not sure I can advise which DSP has the best. I am far from an expert on the various DAC's. It seems to be a whole area that I can't fathom....once distortion + noise figures get close to one hundredth of 1% then I feel well satisfied. (as my speakers put out 100 times that level of distortion.)

All I can say is that my AVM 20 helped clean up a nasty 40 Hz bump I had from room standing wave....no doubt other DSP's can do the job just as well....after all digital filters are just software programs. And I am almost certain that I could not achieve the same sharp notch with an analog EQ (at least not at a reasonable cost)
Nik--sorry been away from the gon for a while. The Modex has not been effective in our practical experience. It wasn't even an issue of how many. As to the Helmhotz--these are very tricky. Alton Everest does a nice write-up on them in Master Handbook of Acoustics. The issues become how rigid to make the box (determines Q factor) and how large (determines db drop).
I'm trying to learn about this stuff, too. So, my comments are those of a seeker, not an expert. I think the Behringer goes between pre-amp and amp, operates in the digital domain, and its output must be converted back to analog. So, it's not the best approach for someone using an analog (vinyl) front-end. The Rives PARC is all analog, which IMHO is a better hi-fi approach. The trade-off is that Behringer offers something like 32 bands, while PARC offers three. But I think three bands is enough, because this allows you to flatten the first three room peaks, and multiples thereof. And, whether with Behringer or PARC, you still need bass traps for the nulls. At any rate, I wouldn't use Behringer in my system. I'm saving my pennies for Rives PARC.
Jburidan...The PARC is by all accounts a fine piece of equipment, and if you can afford it and buy it I am sure you will see a big improvement in your system.

However, for other readers, if not you, I do want to correct several comments and misconceptions about the Behringer.
1..Unlike the PARC it can boost as well as cut. (Word on the street is that a future version of PARC will do this also).
2..It includes a 61 band specteum analyser (or Real Time Analyser, RTA) so you can easily see what is wrong and how it gets fixed.
3...It has a completely automatic equalization process that eliminates a lot of guesswork. (And is fun to watch).
4...As you say, it has many (31) bands, with bandwidths adjustable from 1/3 octave and up. But it also has several bands of parametric equalization, and several notch filters (cut only like PARC) with bandwidth as small (sharp) as 1/60 octave. There are a bunch more things it can do, but with the possible exception of delay (to compensate for speaker locations) you probably would not use them in the home audio application.
5...It is digital. IMHO, to reject it simply for this reason, without ever actually listening to it is stupid. The A/D and D/A are modern 24 bit modules run at 96KHz. FWIW, 24 bits gives resolution 256 times better than a CD, and the bandwidth is more than double. The actual digital processing is done by a 32 bit Floating Point processor, so there is no issue of resolution for this function. Of course these are all words, and one should not accept them as a garantee of good sound any more than one should accept your suggestion that the sound must be bad. Please reserve judgement on how the Behringer sounds until you hear one.
6...Finally, it costs about 1/10 of a PARC. This is a good deal for a spectrum analyer (to help with your PARC setup) even if you are never curious enough to put the Behringer in your signal path.
Probably should pick up a copy of the Master Handbook of Acoustics to learn a bit more about the basics.

The basic school of thought that I have got off several forums is that Broadband bass trapping is the simplest acoustical method of dealing with room modes with my situation. I guess what people are telling me is that with increased broadband bass trapping I can bring up the nulls around 40hz and cut a bit on the 40hz hump. I think that the idea is that while I may not get a huge cut at 40hz if things are over all smoother my ears will fixate less on the problem area. I'm going to give this a try and then may explore other options.

As to the Behringer, it really seems to be a smoking deal in terms of features/price and as noted the spectrum analyzer function alone could be very useful. I think that many people are suspicious of adding another set of A to D to A to their system. I guess it is simple to try it with all settings flat and see what it does to the analog input. If it doesn't adversely effect inputs from vinyl or SACD then a suppose then hey there you go. I actually have few doubts about the digital side of the Behringer, but would be shocked if the analog output circuity cost more than a $1 ... it may sound pretty good but no matter how good your source you are now limited by the Behringer's output quality. For myself if I was running a transport / DAC set up like I was a couple years ago I would jump on trying it between the two. In that situation I would have all the benefits and still have my DAC's analog stage in line with the preamp.

Eldartford, in your system is the Behringer transparent with everything flat and using an analog input signal?

Nikturner920...To my ears, with Channel Islands D-200 amps driving Magneplanar MG1.6 through 4 foot Goertz cables...YES.

However, if you determine audio quality by how much it costs, check out the Reference Audio Mods changes, available for the DEQ2496 and costing about $1500, including $600 output transformers said to reach the audiophile heights.

Again I repeat my mantra...Buy it for the RTA. The EQ will sell itself if you try it.
Interesting, just found your review post. What are you using for a source if I may ask? Seemed from you other post you go from the 2496 straight to the amps?

Nikturner920...Although I do have LP, my best source (IMHO) is a Denon 2900 with Underwood mod, via unprocessed pass through of Rotel 1066.

My three DEQ2496s are between the preamp and the power amps. It would be better to use a TAPE loop (unaffected by volume control) but that is not available for multichannel. I could put the DEQ2496s between the Denon and the Rotel, but then I could only use them for disc player programs.

For 2-channel you could run digital from a cheap player into the Behringer, which would be an equalizer and DAC rolled into one, and then out through a passive attenuator to the power amp. Lots of Bang for the Buck.