John Sayers' Recording Studio Design Forum Archive

there is a big boost at 50Hz after adding treatment. What the..!?

... It looks like you tripped over the cable and broke it!!
That is a pure, perfect 50 Hz tone that never dies away, nor even decreases slightly. It is constant level, forever.

You can see all the odd-order harmonics, crystal clear, at 150 Hz, 250 Hz, 350 Hz, 450 Hz... All doing the same thing: carrying on flat, forever....


You live in Australia, where the power mains is 50 Hz... Do the math ... 2+2 = Mains Hum! (And serious).


I'm surprised you didn't hear that! 50 Hz mains hum at 90 dB should be deafening!

The last tests were run at around 95dB...I just didn't do the calibrate thing.

Even allowing for the loud mains hum, your actual test levels are still only around 70 dB. I think your sound level meter is broken. Can you get hold of another one, one that is known to be accurate, and use that to calibrate REW? Are you SURE you are using it properly? Is it set to C and slow? Do you have it at the correct location, distance and angle when you take the readings?

So unfortunately, we still don't have usable baseline data! First you need to find the source of that mains hum and eliminate it, then re-calibrate REW and your system to produce 80 dB at each speaker individually, which means there will automatically be 86 dB with both speakers running.

- Stuart -

Soundman2020 wrote:

there is a big boost at 50Hz after adding treatment. What the..!?

... It looks like you tripped over the cable and broke it!!

Sigh. The mic was faulty. I didn't actually listen through the mic directly myself...but when I did ...there it was...50Hz all the way. So I'm waiting impatiently for a replacement at present.

Anyhoo...some progress pics.
I designed a wall panel frame that looks like this... And, when I found out the hanger I wanted to use cost $18 each...I designed an adaption of the design using off-cuts, that looks like this: So the frame hangs on it like this...I. am. a. genius! I've been working some ray tracing on grid paper and doing some pre-emptive placement of the panels...of course it all comes out for testing. AC goes in this week...

Question:
Is an angled hard backed cloud inevitable in this sized space (L:5300 W:4400 H:2300mm)...or do I wait and see what the tests reveal?

AC in...testing and treatment under way. Here's the REW data...v3.0 - New mic and I think I got the calibration thing right...

https://drive.google.com/a/aquinas.vic. ... sp=sharing

Next two panels will be an angled cloud over the desk/listening position as well as a cloud just in front of the couch at the rear wall.

I'm looking for input here: I have a 2400 x 1200 x 50mm panel of Bradford Ultratel fibreglass insulation that I was planning on fixing to a 16mm panel of MDF for a hard backed cloud. My thinking is to angle it about 20 degrees and have it be over the desk area...starting about 200mm from the front (facing) wall. Yes? No? Maybe? Or could it just be put flat to the ceiling??

The room is sounding pretty good so far - there is a small flutter echo that I think the clouds will deal with - I had the smaller one up in place just to listen and it seemed to deal really well with what I was hearing at the back of the room. Stuart, I'd be real curious to hear your analysis of the REW data.

I think this really is getting to the finish line...

Well it's getting pretty exciting here at studio build central.... Hardbacked cloud is in - 18mm MDF back with Bradford Ultratel 50mm fibreglass insulation on the front. I put 3.5 of the 70mm Soundscreen batts up on top as well. 2 of 5 I'm hoping to fit into the space. Mirrors the layout on the opposite wall A little sign I found at a 2nd hand shop.

So....whatdayathink? Looks alright? Not bad for a rank amateur IMO!

It sounds awesome so far. I had a listen to a range of different tracks yesterday, and the left right imaging as well as the sound stage are both really clear. The bass seems OK, but I still reckon there could be some improvement to be had in that area.

The MDAT file is here - it's got a load of tests in it - all Left / Right / L&R.
https://drive.google.com/a/aquinas.vic. ... sp=sharing

Question: I've got a couple of big dips that I'd love some advice about. How does one deal with such things? Are they significant enough to worry about?

I think I've dealt with all of the first point reflection for both the mix position and for the couch. Plus the test results seem to show a reasonably smooth response throughout...but I'm no expert (still working that learning curve)...Stuart...what say you?

You are getting quite a nice improvement there! The rear wall had a major effect on that, and it is coming along pretty well.

What are the final dimensions of your room (inner leaf hard surfaces? The modal response (empty room) doesn't seem to fit the original dimensions you gave...

Also, what are the final positions of your speakers and mix position? (in relation to the front wall, side walls, and height)?

The bass seems OK, but I still reckon there could be some improvement to be had in that area.

Yup. True. It can be better.

Some of what you are seeing seems to be SBIR, so it might be a good time to do some tweaking of your listening position and speaker positions.

First, try moving your mix position a bit, forwards and backwards, to see if there is a better (smoother bass response) location in the general vicinity of where you have it now. Then try moving the speakers a bit further apart / closer together, while making to corresponding adjustments in the angles. You should be able to get a bit of improvement there.

However, it also looks like you have issues with the side walls: you might need more bass trapping on those. I would use the wall/ceiling corner for that.

Your cloud could also be angled a bit less, and moved a bit closer to the mix position (a bit further away from the front wall). For example, try it with an angle of about 15°, and maybe 25cm from the front wall, then again at 50cm from the front wall.

Tweaks like that can often get you unexpected results.

Also, what speakers are those? How do you have the rear panel controls set right now?

There's one more piece of magic that we can do when you have finished with everything else... PM me about that...


- Stuart -

Right...
I moved speakers around and listening position....then I moved the cloud forward...and I'm getting a much better room response..I think.
Room Dimensions (hard surfaces) W:4435mm L:536mm H:2290mm (height varies a lot across the room...this an approx average)

The speakers are currently 1200mm from the side walls and 700 mm from the front wall, with the mix position about 1700mm from the front wall.

Question: My speakers are further apart than I am from them...I think I've read that this is bad? I'm around 1450mm from each speaker while they are around 1850mm apart. When I moved them closer together, the bass response got way bumpier than at this distance. When I listen to music the separation seems reeeeally good, vocals are dead centre and the sound stage is excellent. In fact, I think it's really showing me the limitations of these speakers - Mackie MR5's.

Speaking of which...here's the settings on the back of the Mackies I put an LED strip on the back of the cloud to show off my feature wall. Here are some pics of the side treatment... I think I'm about done. Just gotta finish the guitar gallery and a couple bits of trim. Then it's time to rock \m/,

I've added some REW measurements for the geeks out there... ...I know..it takes one to know one...
https://drive.google.com/open?id=0B1XmY ... 2lOUDcybGM

Regarding Speaer distance - Mike Stavrou summed it up best for me.

He (RE: "Mixing with your mind") spoke about the sound "Ribbon"

Imagine a long plank that you can put your speakers on. You sit in your listening position and have two people push and pull the speakers in and out to find the best spot.

If they are too close then the sound "bulges" in the centre, if they are too far apart, then the middle sounds weak and the stereo effect is too pronounced.

I've seen the "Equilateral triangle" diagrams as well, but the "sound ribbon" makes sense to me and can be proven by actually doing it.

If you can't move the speaker positions, you may find moving the chair back and forth may create the same effect. I would suggest experimenting and then marking out the "best" chair position.

Hope this is of some help

Imagine a long plank that you can put your speakers on. You sit in your listening position and have two people push and pull the speakers in and out to find the best spot.

Then again, you could just calculate the best position, based on room dimensions, speaker Q, treatment, and SBIR... Which was done way back, several pages ago ...

If they are too close then the sound "bulges" in the centre, if they are too far apart, then the middle sounds weak and the stereo effect is too pronounced

Not if you calculate correctly, and toe them in correctly to keep the acoustic axis intercept in the right location. Contrary to popular belief, there is not just one fixed position that works, nor one fixed angle. There's a fairly broad range of distances and angles that are usable. They key is to minimize SBIR by setting up the speakers in the best relationship to the front and rear walls, with correct treatment, locate the mix position correctly, then test with REW and tweak as needed, according to the actual acoustic response of the room, rather than based on internet myths and old wives' tales...

I've seen the "Equilateral triangle" diagrams as well,

The concept of that triangle is basically correct, but the way they are drawn in most texts (and copied all over the internet, out of ignorance) is usually wrong. It's fine for people who have had their ears surgically relocated into their eyeballs, but for the rest of us with our ears still located in the same position where the good Lord put them originally, the typical "equilateral triangle" is wrong.

you may find moving the chair back and forth may create the same effect.

That would not be a good idea if you do it more than a couple of inches, since the mix position location is fixed initially based on the minimal modal response position in the room, in most cases. And since the majority of home studios are built inside small rooms, moving your chair back is going to put your ears in the central null of the room, as well as reducing the round-trip distance to the rear wall, likely putting the reverberant field timing inside the Haas time, thus messing up your psycho-acoustic ability to determine directionality even more.

- Stuart -