Placement options – Impacts of location, orientation and treatments

[JonFo]

Since this thread is also becoming something of an acoustics course as a side effect, here is something way cool.

To really visualize what happens to waves in an enclosed area, please play around with the ripple tank applet linked here: http://www.falstad.com/ripple/

Select Dipole source, then chose to see the 3D view. Play with clearing waves and slowing the sim speed down to clearly see what happens to the sound after it leaves the speaker. Let it run for few seconds to see the kind of ‘ringing’ that can be induced by reflections.

Move the two source objects (using the mouse) into a typical corner placement and see what that does.

 

[JonFo]

The box mode applet is the one to use to see just how good (or bad) your room is. Set the relative dimensions of the box to match the relative ratios of your current room.

http://www.falstad.com/modebox/directions.html

Oh, don't cry to me when you see the results

 

[Rich]

Those are awesome simulations. Totally mesmerizing. Try adding three dipole sources to the ripple tank applet and and bring the frequency way down to see the effect of placing your descent in different locations in the same room with your summits.

With some good psychedelics, I could play with these applets for days.

 

[JonFo]

I got ten more boxes delivered today.
But long day at work, so no fun with those until the weekend.

Well the weekend is here, and I finally unboxed the rest of the new stuff.

I’ll play around and measure the new diffusers that came in this week.

But just in case anyone wonders what a ‘truckload’ of treatment boxes (and some of the packing material) looks like, here are the boxes before I flattened them and hauled them off the recycling center. It filled the bed of my pickup truck.

 

[JonFo]

Those are awesome simulations. Totally mesmerizing. Try adding three dipole sources to the ripple tank applet and and bring the frequency way down to see the effect of placing your descent in different locations in the same room with your summits.

With some good psychedelics, I could play with these applets for days.

Yep, they're totally cool, and quite educational as well.

I just wish there were a way of simulating the absorption and diffusion effects, instead of simple reflection.

I beleive CARACAD (which I own, but have not used in years) did some of that, I'll have to install Win98 in a VitualMachine instance to use it again.

 

[JonFo]

And here’s the first of some additional measurements I’ve made along with additional treatments deployed.

This one is the waterfall of the Center speaker at 6 meters with the 4x MiniTraps HF behind the screen and 2x MiniTraps HF behind the Monoliths along with 2x MiniTraps along side walls plus one Modo over the center, under the soffit. (no rear Mondo’s deployed yet in this one)

Note that there is still a lot of mid-frequency energy still left in the room. I’m thinking part of that is because of the screen causing reflections, but also because I’ve yet to treat the side walls between the screen and listening position. Also, some of it is reflected energy from the rear wall and it’s 4x skyline difusors.
(I just validated that by looking at a 5ms slice of time and sure enough most of those resonances are gone, which means they’ve built up in the room).

 

[JonFo]

This one is the waterfall of the Center speaker at 1 meter with the 4x MiniTraps HF behind the screen and 2x MiniTraps HF behind the Monoliths along with 2x MiniTraps along side walls plus one Modo over the center, under the soffit. (no rear Mondo’s deployed yet in this one)

Now we see that there is less room impact (being close to the speaker) and mid-range resonances are minimized. Still a big rise as head for the lower frequencies. But that will hopefully be tamed once we load down the room with traps. But the dialog intelligibility is vastly improved now, as is tonal balance.

 

[JonFo]

Now moving on to the Monolith measurements. These are more typical of everyone’s situation, as we have a dipole speaker, sitting three to four feet out in the room away from the wall behind it and some two or three feet away from the side wall next to it.

So here is the impulse response of the right Monolith with my old RPG Profoam tacked to the wall behind it and some foam on the side wall (blue trace). They reduce some of the reflectivity, but not totally.
As you can see in the red trace of the fully RealTraps treated surfaces, we have much better results, with the reflections pretty much tamed.

 

[JonFo]

This is the Waterfal plot for the right Monolith with the RealTraps in place behind it. Much improved mid-range and treble decays.

The rise in modes as it approaches 20ms indicates that the room modes are factoring back in. Again indicating additional side-wall treatments are needed.

 

[JonFo]

RealTraps Diffusor test - behind Monolith

And this is for Rich, who asked to see what a diffuser would do behind the Monolith.

Here we can see that there is definitely much more energy retained and reflected with the diffuser. Note the longer ‘mountains’ and greater comb-filtering effects.

This alone would probably not be good.

If turned and tuned to angle the reflected energy away from the panel and onto the side walls, it might work, but I still have yet to try that.

In general, I’d say that strictly from a metrics standpoint, absorption behind the speaker is preferable.

 

[JonFo]

And the Diffuser stacked in front of a MiniTrap HF, along with a Minitrap on the side wall.

Here we can see that there is a little better spread of the energy retained reflected by the diffuser. The Minitrap probably helping to smooth some of it out, as well as the closer positioning of the Diffuser to the Monolith.


OK, but probably still too much energy being redirected back through the panel.

 

[JonFo]

And the before and after views of the Low Frequency impacts of the Minitraps.

Using a 200ms gate time, we can see the resonances affecting the bass region.

First, the view without the two additional RT diffusers in the corner behind the Monolith.

But note that the room already has: 4x Mondo’s in the rear + 4x Mini’s behind the screen and a Mondo over the center. So there’s already a good bit of benefit from all those traps.

What this and the next show is the delta between nothing in the corner and adding a Mini HF behind the speaker and a regular mini on the side wall behind the speaker.

 

[JonFo]

And post MiniTrap HF and MiniTrap. Nothing major, but it does reduce some of the resonances visible in the prior graph.
The overall decay is improved from 100 to 500. with more original energy and less reverberant energy.

 

[JonFo]

Finally, a waterfall metric taken with REW, showing the low frequencies, windowed to 300ms, of the right front Monolith taken from the main listening position at 6m.

This shows the room effect to the max. And here we can see that decay is much improved over the non-treated environment.
Still some work to do, which is why I still need to hang four corner TriTraps in the ceiling room corners and four Mondo traps along the side edges of ceiling and walls.

Also, must use some Sub EQ to dial out the resonances at <23Hz.

Overall, the improvement is great. Matter of fact, the EQ’s were so screwed up I had to turn most of them off after the trapping.

This means I still need to rebalance the entire gain structure and re-do all EQ’s once I’ve finished the trap placements.
So don’t take these graphs as the final word. It will hopefully get even better.

But it is illustrative of how bad a even a ‘good’ room can be before treatments.

 

[David Matz]

Mondo traps are amazing!

Thanks to JonFo, DTB, Rich, Ethan and everyone else contributing to this thread.

I placed my 2 Mondo traps in the corners of my room and out of incoherent muddy bass, I got nice 3-dimensional bass! Can't wait to get a couple more panels in the next few months for the other 2 corners to make it even more clear.

When I rotated the mondo traps 180 degrees moved them behind the speakers to absorb the rear wave, it sounded like my amp was broken - the music was dead and flat. I got much better results moving the speakers into the room by another foot. Does this make sense to anyone?

Thanks,
David

 

[DTB300]

Thanks to JonFo, DTB, Rich, Ethan and everyone else contributing to this thread.

I placed my 2 Mondo traps in the corners of my room and out of incoherent muddy bass, I got nice 3-dimensional bass! Can't wait to get a couple more panels in the next few months for the other 2 corners to make it even more clear.

When I rotated the mondo traps 180 degrees moved them behind the speakers to absorb the rear wave, it sounded like my amp was broken - the music was dead and flat. I got much better results moving the speakers into the room by another foot. Does this make sense to anyone?

Sure it makes sense as each room is different and each persons listening preferences and sound is different.

Placement in the corners is great for helping to tame the low end problems of the room as you found out.

Placement behind is a matter of if you like the results with absorption - some like diffusion - some like nothing. Results like Jon showed proves absorption is the best for "response", but it is your system and your likes that also have to be considered.

Great way to start with just a few panels as you can afford. More later on in the other corners will help some more. I was able to do my corners from floor to ceiling.

Dan

 

[Rich]

When I rotated the mondo traps 180 degrees moved them behind the speakers to absorb the rear wave, it sounded like my amp was broken - the music was dead and flat. I got much better results moving the speakers into the room by another foot. Does this make sense to anyone?

Well obviously it is because you didn't give them sufficient time to burn in. (just kidding)

Absorption behind the panels can take a little bit of getting used to because it lowers the overall sound levels. You may need to turn your preamp up higher to get the same sound levels you were used to before. At first it may sound less lively, but I would say that what you are perceiving as liveliness is really just the excess energy of reflected sound and comb filtering that is ultimately damaging your imaging and soundstaging. There is no reason the sound coming out of the front of the speakers should be any less lively or have less frequency response simply because it is not being augmented by the reflections from the rear wave of the speaker. Otherwise, how could box speakers be considered so dynamic and lively.

If anything, your sound should be much clearer. You should get much more clarity and better imaging and soundstaging with absorption behind your panels vs. a flat wall and the inherent first order reflections. I would recommend giving it another try for a longer period and don't be afraid to turn the volume up. Put on some great vocal recordings or something that really shows off your system's imaging and see if you don't think there is a vast improvement.

If you don't, that's alright. You will have proven that you prefer the sound of diffusion or a flat wall behind your speakers, in your room, with your system. Nothing wrong with that, and at least you will know for sure that you have it set up the best it can be for your preferences. As Dan says above and like many things in this hobby, it is very subjective and some people will just prefer one over the other. I know that after extensive testing of different methods, I couldn't go back to flat wall or diffusion behind my MLs. Absorption gives me the highest fidelity in my room and with my system.

 

[Craig]

When I rotated the mondo traps 180 degrees moved them behind the speakers to absorb the rear wave, it sounded like my amp was broken - the music was dead and flat. I got much better results moving the speakers into the room by another foot. Does this make sense to anyone?

My answer is based on theory from articles from variuos sources and not from any formal testing of my own. However, My own experiences seem to confirm these theorys for my room interaction and speakers setup.

It shouldn't be surprising to hear better results from moving the speakers more into the room and away from the front wall. It changes the timing of when you hear the backwave after it reflects off the front wall in relation to the timing of the wave you hear from the front of the speaker panel. When you get this timing right it should help imaging, soundstage, tonal balance and seem more transparent. 4-5 feet work well. In this position you don't need as much absorption on the front wall but some does help. Especially bass traps in the corners of the walls and where the floors and walls meet. I would suspect the sound from the backwave needs to managed with speaker positioning in regards to timing rather than trying to absorb it to the point that the speakers become monopole speakers.

 

[Ethan Winer]

Sure it makes sense as each room is different and each persons listening preferences and sound is different.

Absorption behind the panels can take a little bit of getting used to

I agree with both of these comments. A well-treated room can be almost an acquired taste, especially for people who are used to excess ambience. Without the echoes you're used to hearing, music is sometimes reported as sounding "flat and lifeless." I happen to prefer rooms on the dead side, because in my experience you actually get more ambience and reverb. Well, more of what's in the recording, since it's no longer masked by the small-room reverb and ambience created by your room.

Maybe leave the panels there for a few days and see if you grow to prefer the sound. If not, you can always turn 'em back around and put them where you think they sound best.

--Ethan

 

[Rich]

I happen to prefer rooms on the dead side, because in my experience you actually get more ambience and reverb. Well, more of what's in the recording, since it's no longer masked by the small-room reverb and ambience created by your room.

This has been my experience as well. I hear much deeper into the acoustical space that the songs were recorded in now that I don't have the excess ambiance generated by wall reflections.

My father-in-law heard my system for the first time the other day. As soon as he walked into the room he noticed the difference in acoustics. The rest of my house is very live sounding and when you walk into the listening room it is a noticeable change -- much more quiet. Then I turned on the system and he was blown away by the realism of Rebecca Pidgeon's voice singing "Spanish Harlem" on the Audiophile Voices SACD. That track is absolutely stunning when your acoustics are right.