Broadband absorption behind monitors?

[DanDan]

You are welcome Rob. The REW ETC will display reflections. By their timing you could work out what distance they are etc. But if you play snooker, you can easily see them. Or use a mirror. You can also confirm which boundary is a particular reflection by moving the mic or speaker and observing what the reflection does in time.
When you have a good suspect in your sights, install treatment, or have a friend hold an absorber blocking a suspected location...... REW will show the reflection's absence now. At low frequencies, it is pretty easy to connect a reflection with say a null. Typically the Floor Reflection......
Higher up, it gets trickier and trickier. But the simple approach of moving and blocking remains totally valid. Better is better.
The minimal goal here is eliminating early reflections to the extent of -20dB for the first 20mS. You will probably do better than that.

[greenlounge]

DanDan. I have now positioned the panels and will redo the measurements. I have 2 more panels under construction to try and take the 1st reflections off one side wall.

Here is a picture of the front wall now.

[DanDan]

Wow that room is narrow. That places the traps almost in the corners. Where they would be remarkably effective. Much more so if you trap floor to ceiling.

Corner_RT424-vs-Gap-600.jpg

[greenlounge]

DanDan. The above photo probably gave you an unrealistic perspective of the room width.
Here is another photo further back in the room. On the left is a fireplace, which I think is actually doing good things to the room. It has a cast iron insert. Sorry about the mess in the room.

I have 2 more panels to be completed for 1st reflections on right hand side.

1 have 3 panels of 100mm FI48 left after this, each sheet being 2400x1200 and have a plan for this.

From this photo you can see the underlying asymmetry of the room.
I am thinking of having 2 absorbers one in front of the fireplace and the other that can be put across the front right hand side. These would be moveable, since the right one would block the door.
When not mixing the 2 absorber panels would be moved into a position for tracking, either for vocals or behind the drum kit. So I don’t know whether this would make them moveable absorber panels or Gobos.

I feel that this potentially requires another thread?

Thanks for all the assistance so far.

3B1BB3C3-542C-4EE6-83B4-0AB12E978628.jpeg

[greenlounge]

So I have completed 4 x 600 x 1200 mm panels, with FI48 100 mm panels, set in a 150mm deep frame..

These were placed in the following:
1. 1st reflection point on RHS - one. Obtained using the mirror trick.
2. Cloud over the mixing area. - one.
3. First reflection point over the fireplace. - two panels. Covers the 1st reflection point but wider.

The speakers are 80 mm from the front wall (back edge of the speaker to front wall) with NO treatment behind speakers.

Enclosed is the mdat file for this measurement, which contains only the L and R speaker measurements.

The waterfall shows very strange things at low frequencies, but my speaker specs (Eve SC208) say they go down to 36Hz (-3db), so I am not too sure whether what I see in the waterfall is actually valid or relevant?

Is it possible to get some feedback on these measurements to see what my next steps in treating this rooms should be?

Many thanks in advance.

dropbox link to mdat file is below:
https://www.dropbox.com/s/9dleie7jsr4nc ... .mdat?dl=0

[DanDan]

3D Chess. We are trying to optimise FR and Decay via locations of two speakers and a listener zone. Not easy. Quite often moving the speakers to the Front Wall will increase modal activity and overall LF level. It can be helpful to simply turn it down. Or block the ports if your speakers are reflex.

[greenlounge]

Yes.. it’s a bit like that DanDan. I have 3 sheets of F48 (2400x1200) left. It is in the plastic packaging it came in.. I straddled one across the front right hand side (temporarily) and did the measurement. The Right speaker measurement was better.

This room actually is very complex. I am not done yet.

One question.

What is the best REW reports to use for IR for low frequencies?

Waterfall shows it but not really accurate.
Spectrograph is the same.
I am now focusiing on RT60 using Topt as a measure. Thoughts?

Thanks again for your help.

[DanDan]

Hi Rob. To be honest I would often apply the certain treatments and then take the first baseline measurements.
Judge by clear improvements, rather than some big and unreadable differences or the unanswerable 'what is this response like, any good? '

There are different ways of assessing. BBC used to look a the Room Decay. Topt or T30 1/3 Octave in modern REW language.
Their wish was that no band should differ from it's next neighbours by more than 10%

You can also view the Waterfalls or Spectogram and so on. A smooth spectrum of FR and Decay, gracefully sloping down at HF........

You could try different speaker locations to drive the modes harder. On the floor, in a corner, has three boundaries boosting LF and all modes gather there. Mic in the opposite ceiling corner.

The speakers are 80 mm from the front wall (back edge of the speaker to front wall) with NO treatment behind speakers

.
Not clear, but can you try them 1mm from the Front Wall?
I skip around, different fora, threads, so you may have answered this already. Do you have a Cloud?

[greenlounge]

Thanks for the help DanDan. I will focus on the Topt and T30 reports.

Yes there is currently 1 1200x600 100mm thick cloud, suspended off the ceiling (ceiling height is 3 meters..
Regards Rob

[BackEastDon]

Another solution is flush mounting the speakers in soft and deep treatment wall, with the intention of absorbing some of the low frequencies before they have a chance to reflect back out into the room, delayed by however many ms to the direct signal. Of course, this requires very deep treatment in order to be effective all the way down the spectrum, if the loudspeakers go down to 40hz then the treatment would need to be around 2' thick in order to absorb down that low at 60% efficiency. Thicker than that and you quickly reach a point of diminishing returns with velocity based absorbers and membrane absorbers need to be deployed.

If your speakers are as close as you can get to the front wall already then any LF that goes behind will reflect off of the front wall with minimal delay, causing minimal audible problems. Ideally the front wall would be angled each side to follow the toe-in angle of your speakers, but even without that the issues will be minimised.

Paul

I was thinking about building a tapered wedge bass trap so the the slim taper just begins to fill the the gap edge of the monitor against the wall due to splaying. In reading this post, I'm wondering if there would be any benefit had to essentially build the treatment around the monitor, so that it is flush with the front baffle and still leaving the back of the monitor against the wall? It would be easy enough to use some 703 to frame out the pink fluffy around the monitor, even encasing the stand into the treatment. Essentially a faux soffit.

I am using passive monitors so cooling isn't an issue.

[gullfo]

you could mount the speakers on heavy stands (w/ appropriate speaker decoupling from the stand, including adding weight on top of the speaker if needed to ensure proper compression of the isolators if necessary). then have a framed set of absorption around it. for me, i'd still plan on adding a solid plate somewhere in that mix - e.g. the plywood/mdf plate sits on the back of the frame so the front is filled with insulation and covered with cloth.

example speaker stand in soft soffit 1.jpg

[BackEastDon]

Again, thanks Glenn

I'll download these when I'm on my Mac and will see if I can adapt this for the angled ceiling without shoving the speakers too far into the corner and keeping them at the right height. Also will have to come up with a plan to move a bunch of electrical as my quad outlets are all on the front wall.

[gullfo]

one option for the outlets would be to frame around them so you can access them through the front treatment and then run any necessary extenders (preferable with electrical filtering )

[greenlounge]

Glenn. Would not the soffit need to be rigid, for that to work? Is that why you are suggesting Madaf on the back?
Regards Rob

[BackEastDon]

one option for the outlets would be to frame around them so you can access them through the front treatment and then run any necessary extenders (preferable with electrical filtering )

Big fan of Tripp Lite Isobar's and if I really had any noise issues, I have access to a hospital grade transformer. Much more electronics oriented than acoustics.

I've temporarily surrounded myself in pink fluffy this evening and it is sounding great. I'm going to work on building the back framing and am still mulling this idea.