Friday, May 8, 2015

Modex Modules

Modex modules from RPG are available tuned to 40, 50, 63, 80, 100, and 125 Hz.

Even Ethan Winer (designer of RealTraps) says they are good, but expensive for what you get, and he claims you'd need a lot of the low frequency units to actually do much good at low frequencies, just like his absorbers.  It's Surface Area, Surface Area, and Surface Area.  (As I was reading a blog about bass absorption which led me to the Modex, I noticed that Mr Winer has apparently been banned from WhatsBestForum.  I wonder what led to that and I still give him and the Forum considerable if not unlimited respect.)

But it seems to me that the Modex modules are fundamentally different from RealTraps.  RealTraps are broadband absorbers with reflectors that prevent higher frequencies from being absorbed.  Modex modules are tuned to specific frequency ranges (and therefore are as much like resonators as absorbers).  I would expect that tuned units like the 40 Hz Modex (exactly what I need) would be much more efficient at absorbing the lowest frequencies than the RealTraps (which have no special tuning).  And most things sold as "bass traps" now aren't really resonators (as the "trap" would suggest) but really broadband absorbers very much like RealTraps.  GIK, for example, makes similar absorbers, possibly better than RealTraps in some applications, but still only an absorber, not a tuned resonator.

UPDATE:  GIK actually now makes both untuned and tuned bass traps, and they are indeed an incredible bargain compared to RPG, even if RPG is better (which I'm not sure…and may not be).  In untuned traps, which GIK recommends as the starting point, GIK sells about 8 sq ft of bass trap for $139.  GIK's 40 Hz tuned trap comes in 24x24 for $239--compared with RPG's $684 for the same size.  GIK will even custom tune, and their stock lowest trap is 40 (I might need 45).  Neither GIK nor RPG are making true Helmhost resonators--at least in the models I am considering.  GIK looks like they know what they are doing, and are pressing forward too.  I think I will get some GIK traps soon.  I'll need to make more good measurements first.  Actually most if not all of the measurements I've posted here are with my existing equalizers in place.  What has to be done in designing room treatments is to measure the actual room response.  And I will do that in the prime listening spot and elsewhere, including the Bad Corner near the first bedroom.  That corner seems to concentrate the bass worse than any other location, and it leads to boomyness in bedrooms (though, when the sound absorbing doors are shut, all is attenuated a lot) which is highly undesirable also.  That's the corner where I intend to put the first bass traps.

UPDATE 2: Well, there isn't enough room in the Bad Corner.  I may have to use a Bag End eTrap there…and it might be more successful anyway.  Looking at GIK's before and after measurements with tuned traps…the tuned traps mainly suppress the decay, rather than the initial amplitude.  The untuned traps do go more after the initial amplitude.  Hmmn, along with the eTrap, I might need some damping, but it would have to be made to 15" sides, 15x30" would do.  That would be the top, and strap on the bottom.  A trap on the bottom would cover up the electrical outlet, while the eTrap would not.  eTrap was always my plan.  A GIK Scopus would also work, actually, since it can be hung flat against the wall.  One way or another, the combination of tuned and untuned traps in the Bad Corner would work.  But I could use a full size trap in the corner next to the kitchen door.  I need 3' of coverage on top, so I could get the standard two 24" trap package, and have one cut to 12".  It's basically the only wide open corner now.

Anyway, back to the original post...

Even Modex may not actually be Helmholtz Resonators…that terminology does not appear in anyones description.  But at least they are tuned and therefore resonator-like.

B&H Photo sells (special order) a pair of Modex 40Hz corner traps for $684.  Each has 4 sq ft front area (24x24), though relatively shallow for corner traps.  That's only a little more expensive (perhaps 1.5-2x) than traps made by GTK and RealTraps which are not tuned.

This is looking like a good option for the corner of the hallway adjacent to the living room.  The shallow depth is a blessing because there isn't much space.  The Modex might be no more objectionable than the Bag End eTrap I had been thinking of putting there.

Winer's charge about Modex being expensive would definitely apply to the Modex Metal Plate absorbers for $1944.  Those are claimed to have uniform absorption from 35-100 Hz.  They are thin but  have even more surface area: 60x40.  Strangely while B&H says they are 4" thick, there is a plot showing effectiveness vs depth.  The 4" depth has peak absorption just over 100 Hz, and almost nothing below 60Hz.  The 10" depth has peak absorption at 60 Hz.  So this doesn't match the description at all, and I'd be worried without doing more research.  But I won't be buying a $2000 absorber anyway.

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