Added corner traps: results...

[Eric SVL]

Hey all,

I've been struggling with my response in the above-subwoofer-but-still-modal 100-300 Hz range, so I decided to try loading my front corners with bass traps. It wasn't the drop-in affair I expected. What follows are some pictures and measurements to document the experience.

Here is the system before the changes. Room is 16.9 L * 10.6 W * 8.0 H in feet.


Now, we start measuring and adding the GIK Tri-Traps.






Wait, what is going on here? I thought I was going to improve in that area, not make it worse. Let's zoom in on the 100-350 Hz region:



Clearly I am losing output in the very area I'm trying to fix. Maybe the absorption is changing where I need to place my speakers.

(3 hours and countless speaker and chair movements later)





This seems like the best I can do. Let's run Audyssey up to 400 Hz:



An improvement over the previous effort.

In the end, it is hard to determine just how much the corner traps did for this final measurement as they required me to move my speakers. All of the changes you see below 100 Hz are from moving the speakers, and a good portion of the changes above 100 Hz are, too. I think there is a synergistic effect though, as where the speakers ended up was not previously the best place for them. I would post waterfalls however they were corrupted by the noise from a wicked thunder storm as I was finishing up last night. Some other time.

I have not tried putting the Tri-Traps in the back of the room because there is no space. I thought it made the most sense to start at the front, but it's possible there is a greater benefit there.

Other notes: I am still getting used to the wide placement. I typically have them splashing the walls a bit so I get a big soundstage, as these were designed with their waveguide with great off-axis sound for small rooms (measurements here). With the wide placement, the toe-in is naturally greater and that has created some crazy center imaging. Vocalists may as well be standing in front of my TV they are so present. I am also getting less reflected and more direct sound, which is a bit brighter. I am used to these speakers being a little more laid back as most reviewers describe them. It goes to show how much placement can change what you hear. If you check the company's measurements against mine, you'll see how toe-in would lead to more treble energy, while more wall reflections (old placement) will lead to a greater contribution of off-axis sound which is down in level a bit, which leads to a more rolled-off in-room response.

However when discrete sounds hit the left or right speaker, they don't quite disappear as well in this configuration. I will probably play with this more at a later time. Full-range measurement:



If I can figure out my remaining modes I think I would be looking at a pretty great response for speakers-only. My nemesis right now is the big one at 90-100 Hz that I believe is a width mode down the center of the room. I think I could kill it once I get subs back in here (picture one under the TV), but that requires a higher crossover than I was planning on using. Any ideas?

P.S. – I'm also looking for ideas on stands/racks. Thanks!

 

[Todd Anderson]

Interesting. Have you considered pulling your mains a foot or so more forward?

Are your subs going in the front of the room?

 

[Eric SVL]

Moving the speakers forward creates more problems due to SBIR. As a bass source, they need to be near boundaries. Sub placement will be both front and rear.

 

[Conrad.]

Did the traps help with your waterfall at all?

 

[hemiutut]

Did the traps help with your T20,T30 at all?

I have used google translator
Regards

 

[DanDan]

Interesting, if a bit disappointing. Optimisiing speaker and listener positions is interactive, iterative. If you are lucky something might stabilise, e.g. Height or Width, but be prepared to tray every variation.
I find the RTA with Pink Noise, zoomed to LF, very useful for finding 'No Fly' zones. e.g. Narrow the speakers, move the mic about to see the best, narrow a bit more, check the listen position again....
If your speaker stands will oblige it could be worth trying your speakers upside down. Tweeter same position but the woofer radically shifted....
Treating Modes is often a 'given' but they may be not the major players at all, especially in a room with light walls. https://realtraps.com/art_modes.htm
But to be fair, your final response looks pretty decent. Have you tried taking two measurements at ear positions and averaging them?

 

[Sledge]

Optimyzing acoustic try/fail basis is a cost ineffective long run. The behaviour of the loudspeakers in the space is quite complex:
1) the radiation efficiency of the lowest frequencies is affected by the proximity of the boundaries - radiation in the free field is less effective than hals-space, qarter-space, 1/8space. This effect vary a little with the mic position (except the transition band behaviour)... increased wall absorbtion will decrease the measured SPL of this region. The transition frequency for this effect is determined by the distance from the boundary in relation to wavelength.
2) Modal activity of the room itself - placing a loudspeaker in the point of maximum SPL of standing wave of the room wil increase the excitation of this mode, so the measured SPL (valid for basic axial modes)
3) Interference of the direct/reflected energy - this has the strongest dependency on the position of the loudspeakers and mic
4) SPL gain caused by room reverberation - this is similar to points 2 and 3, but doesn't rely on specific geometry of loudspeakers and mic, e.g. decribes mainly room acoustics itself...

The effects of the "bass traps" is mainly visible on "room decay" where this treatment reduces reverberation time. This relation between treatment and result is much more straightforward than looking on the SPL. The SPL curve will show a summ of all the effects so it will not lead you to the goal directly. Increased aborbtion will decrease SPL where it was previously gained by improved radiation efficiency and/or constructive interferrence, but it will increase the SPL previously decreased by destructiove interferrence....

with the free standing loudspeakers it is usually the best to move them away from the walls, which minimizes the effect of 1-3, then increased absorbtion will not affect the direct sound. But in small room, if you may afford this, build a plaster-board (angled for optimal aiming) pre wall and flush the loudspeakers into the wall. In this case you will eliminate the problems of diffraction, SBIR and 1st reflection from the front wall and and you will signifficantly improve damping bellow 100 Hz. After that put strong damping (equivalent to 5-10 cm of rockwool, stronger to the front wall - timbre frame, fabric covering) to the ceiling and side walls between listening position and front wall.

This is, according to my experiences, the fastest and most straightforward way to controlled acoustics (and in smallest room often the only way)....and in the end also quite cheap, using common materials.... - e.g. material may cost like 600-1200 USD or so for the room in total....


EDIT: this is an example of treatment, as described, but in much large scale (designed by Philip Newell). Anyway, the treatment may be basically invisible, fully covered by fabric etc...

philipnewell.net/img/neptar.jpg

 

[DanDan]

Somewhere a bell is ringing... Are those Amphion Speakers with a rear facing Auxiliary Bass Radiator?

 

[Eric SVL]

The effects of the "bass traps" is mainly visible on "room decay" where this treatment reduces reverberation time. This relation between treatment and result is much more straightforward than looking on the SPL. The SPL curve will show a summ of all the effects so it will not lead you to the goal directly. Increased aborbtion will decrease SPL where it was previously gained by improved radiation efficiency and/or constructive interferrence, but it will increase the SPL previously decreased by destructiove interferrence....

I will post some waterfalls when I get around to that (need to pull the absorbers back out of the room again to do an A/B measurement, and the speakers have to be moved to reach them). Until then, this makes sense. Putting absorption in the corners is like moving a speaker further from the wall, or putting a speaker in an open space, so it makes sense that I would lose some reinforcement. However, I didn't see any areas where SPL increased.

with the free standing loudspeakers it is usually the best to move them away from the walls, which minimizes the effect of 1-3, then increased absorbtion will not affect the direct sound. But in small room, if you may afford this, build a plaster-board (angled for optimal aiming) pre wall and flush the loudspeakers into the wall. In this case you will eliminate the problems of diffraction, SBIR and 1st reflection from the front wall and and you will signifficantly improve damping bellow 100 Hz.

The reduction in SBIR was my goal, and putting the speakers closer to the walls has achieved that. I used to have big cancellations that disappeared using this method. I don't have the room to build a false wall, though. Maybe in a future home I can have flush-mounted speakers with perfect bass response.

 

[Eric SVL]

Somewhere a bell is ringing... Are those Amphion Speakers with a rear facing Auxiliary Bass Radiator?

https://www.buchardtaudio.com/shop/s400-black

 

[DanDan]

Tx Eric, quite similar to some Amphions I saw in another thread, in the sense that they both have a rear facing Auxiliary Bass Radiator. In that other thread the OP was disappointed that his commercial bass traps seemed to be doing nothing...... but, a whole different scenario, except for the speakers. Speaker tech is not really my area of expertise so I can only suggest that location is totally up for grabs. Try them everywhere feasible to see if you can get a better bass response. Remember that there will always be a dip due to floor bounce, and this might even gang up with Front Wall SBIR.
Also I think those speakers should work equally well upside down, which would place the woofer in quite a different spot. You might have to use temporary supports to get the height of the tweeter the same or right. In any case, location, location, location, up for grabs.

 

[Eric SVL]

Location has already been thoroughly explored, trust me. Many hours...days.

 

[Eric SVL]

Also I think those speakers should work equally well upside down, which would place the woofer in quite a different spot.

These speakers are slanted for time alignment since the tweeter is in a deep waveguide. Also, that would put the tweeter too high and mess up the response at my seat.

 

[DanDan]

Not if you changed the height of the stands. Woofer above or below optimum tweeter height is the same in terms of time.

 

[Eric SVL]

What would that accomplish? There is nothing wrong with the speakers' native orientation on its matching stands. Further, that would not help with bass issues.

 

[DanDan]

Changes of location of woofer can change LF response dramatically. Vertical is just as valid as any other dimension.

 

[Eric SVL]

Thanks, but I'm going to keep the tweeters at ear level.

 

[DanDan]

You are welcome, but I am wondering if you know what I am talking about. i.e. It is entirely possible to invert these speaker AND keep the tweeter at the same height if that turns out to be important ( which I do not think it is) The current orientation may be common, but 'native' no. Even the manufacturer states Can be placed directly up against a wall and upside down if necessary

 

[Eric SVL]

You can. That doesn't mean you should.

 

[DanDan]

OK

 

[peter08]

Changes of location of woofer can change LF response dramatically. Vertical is just as valid as any other dimension.

I didn't think of that, thanks for the suggestion; easy for a quick try-out since I won't need to move heavy speaker stands.

Just on a practical level, is it normally Ok to invert an active studio monitor which has a heavy transformer, amp/s and electronics built-in? Ventilation channels might be compromised, but then REW tests can be kept quite short.

 

[DanDan]

You are welcome. It is an unusual thought. But ADAM had a very popular Studio Monitor the S3A, designed for sitting flat on top of large consoles. Many of us benefitted from the better sound when it was turned vertical. Most studio monitors can be soffit mounted. But it depends entirely on the design I guess. If it has a cooling system which can't be inverted. Worth checking with the manufacturer. As you say an easy try out, and it is which a significant move of the LF source while keeping otherwise optimum locations.