New way for absorbing back wave?

[JonFo]

At 18", only bare and Profoam

Since the MiniTrapHF is about 4" thick and should be a few inches off the wall for low-freq effectiveness, it really does not fit behind an SL3 at 18".

So here are the other two materials, as we see, the bare wall is worst again.

Bottom line; treat the wall with something for improved results.

 

[JonFo]

Conclusions:

Looks like the ProFoam in the speaker is effective at losing the rear wave, but causes additional cavity and reflective resonances that are not beneficial.

Best option as several of us have been preaching lately is to treat the wall behind the speaker with a broadband absorber .

 

[SundayNiagara]

Really?! I seriously doubt the Yamaha room analyser software can handle a dipole speaker's radiation pattern. So why turn your stat into a box speaker just to satisfy the needs of your (rather limited) analyser software?

If you can't get the stats out at least 5 feet from the wall behind them, then you should think about another kind of speaker. Also, you will need a wall mounted flatscreen to avoid degrading the image with a large inert surface/object placed between the panels. Dipoles need breathing room because the backwave contributes to their overall SPL, but they also need good, bust-it-all-up diffusion (NOT absorption) of that backwave. This is necessary to minimize the diffraction effects that inevitably occur when the backwave (by now in a multitude of busted-up phase reflections we hope) finally meets the still-coherent frontwave.

Bingo!!!!!!!!!!!!!!!

 

[ted99]

Looks like the ProFoam in the speaker is effective at losing the rear wave, but causes additional cavity and reflective resonances that are not beneficial.

Best option as several of us have been preaching lately is to treat the wall behind the speaker with a broadband absorber .

There we have it. For those of us wanting to attenuate the back wave, the Minitrap HF behind the speaker is best. My WAF work-around of putting the foam in the speaker cavity absorbs the back wave, but introduces comb filtering because of near field reflections. Not good.

For my installation, I can put two layers of 12 in wide profoam behind the front curtains, which is about 30 in behind the panels. The centerpoint of the curved panel is aimed close to the center of where the foam will be at the angle giving the best response (using YPAO polarity errors as an indicator)The width is not as good as would be best ( If I had 24" available, I'd use the minitrap HF), but since it's invisible, it will pass the WAF test. According to the RPG graphs, it takes three layers of profoam to equal the above 300Hz attenuation of the minitrap HF. My two layers should give results closer to the minitrap HF results measured by JonFo with the single layer.

 

[benleeys]

Jon,
Am afraid my knowledge at interpreting response graphs is minimal at best. From the results of your tests, would you say that there is little difference in the distance one choose to position dipole speakers from the front wall beyond, say, 2ft with Mini HF traps as absorbant.

 

[JonFo]

Ben,

The positions further out measure better (that is 36” is better than 24” from the trap).

The improvements are primarily in the midbasss (but take that with a grain of salt, as it could be just better room interface at those frequencies in the new location and less the effect of the trap).
In the higher frequencies (>3K) it also measured better at 36”.

So I’d say, experiment with position to balance the mid-bass and bass, more than worry about the highs. The trap will help the highs pretty much equally at distances over 2 feet.

 

[benleeys]

Ben,

The positions further out measure better (that is 36” is better than 24” from the trap).

The improvements are primarily in the midbasss (but take that with a grain of salt, as it could be just better room interface at those frequencies in the new location and less the effect of the trap).
In the higher frequencies (>3K) it also measured better at 36”.

So I’d say, experiment with position to balance the mid-bass and bass, more than worry about the highs. The trap will help the highs pretty much equally at distances over 2 feet.

Many thanks for your advice, Jon. I presently have mine at 4.5ft from the wall and I like what I hear. Figure I'll leave them be, at least for the time being, till I lay my hands on the Anthem ARC-1.

 

[kach22i]

Bingo!!!!!!!!!!!!!!!

I agree, trust your ears not some machine.

 

[guido]

Back Wave and other set up elements

I just joined this site. Thanks for setting it up. It seems useful and informative. Regarding the "back wave," here is my experience.

At some point in the past I experimented with moving my ML SL3s to my empty and large finished basement on the assumption that having about 15 feet between speakers and front wall would delay (and possibly attenuate) the reflection from the front wall. The result was a clean but lifeless sound. So I moved everything back upstairs. The SL3s are now 54" from the back of the grill to a 14" deep bookcase which in turn stands against the front wall. There is an open door behind the right speaker that leads to a 4 feet wide hallway. There is a foam absorbing panel that normally hides a Toshiba back projection display that is embedded in the center of the bookcase. The speakers are 74" apart and slightly toed in. With this setup, I found that the critical element is the distance from speakers to listening chair. In my room, this turns out to be about 100". The chair sits on a rug that has a design of stripes parallel to the front wall. This helps me keep the chair exactly on the same spot. I've found that changes as small as 1/2" around the optimal location make a significant difference. I have two pairs of skyline diffusers midway on each side wall as well as two foam absorbers centered with the SL3s location (theoretically, there should be no appreciable reflections at this point, but in practice these panels do make a difference to the sound).

With this setup I got both the clarity, dynamics, detail, and transparency for which ML speakers are known, as well as great soundstaging and "bloom." Not content with this, I added a quasi Hafler Matrix set up using two old Spica Angelus I had in a prior system. (The "quasi" refers to deriving the input for the matrix not from the main amp, but from the preamp. The signal then goes through a home-made stepped resistors attenuator, which allows me to set the level of the back speakers with great precision, then to an old SAE MarkII amp, and then to the back L-R speakers). Sound from the back speakers is set so that it is barely audible when there is no signal going to the SL3s and the preamp volume is set at normal listening level. Contrary to my expectation, this setup does not yield the "Hafler ambiance" sound. It does, however, add a welcome realistic three-dimensionality to instruments and voices, which is quite addictive. It also contributes to the depth and quality of the bass, strangely enough, and does nothing to degrade the sound of the front speakers.

I'm very happy with the sound of this system. Next, I plan to add a subwoofer to try and further improve the handling of low frequencies.