John Sayers' Recording Studio Design Forum Archive

Well, I don't know what I must have done wrong.
Anyway!

Here is another measurement on a previous version 5.19!

Thanks, and I hope this one rolls,
Pablo

pabloandura wrote:Here is another measurement on a previous version 5.19

That one is fine! The file opens, the data is valid, and it looks about like what it should!

Just checking here: This test was taken BEFORE you put any treatment into the room, right? So now we also need the test AFTER you put the initial treatment in. That way we can compare the two, to find out if the treatment is doing what it is supposed to do...

The MDAT shows the modal response of the room quite clearly. There's modes (or other forms of resonance) at about 50.4 Hz, 55.7 Hz, 72, 82, 97, 107, 139, 173, 223, 242, 296, and 373. I'm assuming the Schroeder frequency for the room is somewhere around 300 Hz? I don't recall the dimensions of your room, but you can check how well those modes match the dimensions.

So you will need considerable bass trapping in there to deal with that. Hangers would be good, but the ones you are showing in the picture don't seem to be built right, so they won't be very effective. Why are the parallel to one wall? They are supposed to be angled into the room at about 30° to 60°, roughly. They don't seem very thick, either: What insulation did you use on there? Hangers also need to have insulation on the walls behind them, for maximum effectiveness. At least 4" (10cm).

I would start by reworking your hangers, then add additional insulation across the entire rear wall, between the hangers, as well as other bass traps in other parts of the room. But you'll have to be careful with that, so that you don't have too much absorption affecting the high end, or the room will end up too dead. You'll need to take the usual precautions for that.

But at least you have REW working now, and producing valid data!

- Stuart -

Hello Soundman!

Soundman2020 wrote:Just checking here: This test was taken BEFORE you put any treatment into the room, right? So now we also need the test AFTER you put the initial treatment in. That way we can compare the two, to find out if the treatment is doing what it is supposed to do...

I imagine that means it is not doing what it is supposed to! That is the file of the room as it was currently set the day I uploaded it! It's a fresh one.
I would expect an amazing result considering I had no knowledge of how the traps would affect the room, they are built out of drywall and they are covered in 5cm glass fiber. There is two big ones and three small ones in each corner. The big ones are 15kg each sized 240cm x 60cm x 1.25 cm. The small ones are 10 kg each sized 240 cm x 40 cm x 1.25 cm.

Soundman2020 wrote:The MDAT shows the modal response of the room quite clearly. There's modes (or other forms of resonance) at about 50.4 Hz, 55.7 Hz, 72, 82, 97, 107, 139, 173, 223, 242, 296, and 373. I'm assuming the Schroeder frequency for the room is somewhere around 300 Hz? I don't recall the dimensions of your room, but you can check how well those modes match the dimensions.

Thanks for confirming that my test was accurate! That is great news.

Soundman2020 wrote:So you will need considerable bass trapping in there to deal with that. Hangers would be good, but the ones you are showing in the picture don't seem to be built right, so they won't be very effective. Why are the parallel to one wall? They are supposed to be angled into the room at about 30° to 60°, roughly. They don't seem very thick, either: What insulation did you use on there? Hangers also need to have insulation on the walls behind them, for maximum effectiveness. At least 4" (10cm).

I will definitively be re-engineering those hangers to have the angle and the rock wool behind them.

Soundman2020 wrote:You'll need to take the usual precautions for that.

What do the usual precautions mean? I was considering superchunks to back up the corner hanging traps. And what is the value in REW I should pay attention to not deaden up my room? Would it be the RT60? I imagine that if a certain amount of absorption affects a frequency then it will also affect all the ones that are higher than it.

Soundman2020 wrote:I don't recall the dimensions of your room, but you can check how well those modes match the dimensions.

The room is 4m x 3.36m x 3m.
I checked the wavelenghts to 1/1 1/2 1/4 3/4 and so and I seem to find a match for the actual physical sizes so I'm super glad.

Since the solutions you throw at me seem to be dealing with absorption I imagine that diffusion is still not part of the picture or you may think we don't need it as much as absorption.
Should I just cover the area of the back wall at head level and see how that works?

Thanks for your insight!
Pablo

I imagine that means it is not doing what it is supposed to! That is the file of the room as it was currently set the day I uploaded it! It's a fresh one.

The purpose of the "baseline" test with REW is so that you have a clear picture of how the room was behaving all by itself, without any treatment. That allows you to design treatment for the specific issues that the room is actually producing. Here's a thread about how a control room is normally tuned: thread on building and tuning a corner control room. That gives you an idea of the process: start with the empty room, test it, look at the results, design treatment for the largest problems, install that, test again with REW to check that it is working, look for the next largest issue, design treatment for that, etc...

The room is 4m x 3.36m x 3m.
I checked the wavelenghts to 1/1 1/2 1/4 3/4 and so and I seem to find a match for the actual physical sizes so I'm super glad.

The strange things is that the modal activity in your room is rather clear, yet it does not match those dimensions! I plugged in your dimensions to one of the best mode calculators on the Internet ( http://www.bobgolds.com/Mode/RoomModes.htm ), and almost nothing matches! There are a few that are close (p5,7, your 2.0.0 axial seems to be right for the 97 Hz mode visible in your data), but most are not close enough. The only that hits spot-on, is 172 Hz, where you have a firestorm of FOUR modal issues, right on top of each other:

172.2 hz (0,0,3 Axial)
172.2 hz (4,0,0 Axial)
172.5 hz (2,2,2 Oblique)
172.8 hz (3,0,2 Tangential)

Two axial, on oblique AND a tangential! All on practically the exact same frequency. That's interesting.... But the other modes do not match your dimensions, which tells me that either you measured the dimensions wrong (they are not accurate to the nearest cm), or that the walls are very thin, with another thicker, heavier wall behind, or that you left a door or window open, or that you were inside the room when the test ran, or several other possibilities...

I will definitively be re-engineering those hangers to have the angle and the rock wool behind them.

Also, make them thicker (at least 25mm insulation, 50 mm would be better), and use semi-rigid insulation.

What do the usual precautions mean?

Covering the front of your bass traps and/or other treatment devices with something like plastic, or perhaps even thin wood, or maybe slats, to reflect the higher frequencies back into the room while only allowing the lower frequencies to be trapped.

I was considering superchunks to back up the corner hanging traps.

If you have hangers in your vertical corners, then there is no space for superchunks. The go in the same location, so you can't have both: one or the other. But you could add horizontal superchunks, in the wall/ceiling corners.

And what is the value in REW I should pay attention to not deaden up my room? Would it be the RT60?

Mostly, yes, but the waterfall and spectrogram are also useful. For RT60, first calculate the overall decay time that your room should have, then compare the results you are getting for each 1/3 octave frequency band. If the decay time for any frequency band is considerably higher than the target decay time, then you need more absorption aimed at that specific frequency range. If the time is considerably LOWER than the target decay time, then you need to add reflection or non.numeric diffusion for that frequency, in order to bring the decay time up again. The final goal (which is very hard to achieve!) is to get all of the decay times for all of the frequency bands to the exact same level. It is allowable to have slightly longer decay times in the very low end of the spectrum, and slightly shorter in the very high end, but for the middle the goal is to have no more than 0.05seconds (50ms) difference in decay times, between adjacent bands. As I say, that is very hard to do, especially in a small room, and it's unlikely you will actually be able to get that perfectly, but that's the general idea.

I imagine that if a certain amount of absorption affects a frequency then it will also affect all the ones that are higher than it.

That's usually the case, yes, but there are exceptions. It has to do the the gas flow resistivity of the absorption (which is also called "acoustic impedance") as well as the angle of incidence, and other factors. But mostly, yes, if an absorption panel affects one frequency then it very probably does affect all higher frequencies to an increasingly larger extent. Which is why you need some type of reflective surface in front of it, to prevent it from seeing those higher frequencies. Thin plastic works for very high frequencies, thicker plastic for highs, thin laminates for high mids, and thicker wood for low mids. There's also the issue of wavelength vs. object size: in general, any object will only affect sounds whose wavelength is similar in size to the dimensions of the object, or smaller. So you can use that effect as well, in addition to thickness, to tune your reflective surfaces.

Since the solutions you throw at me seem to be dealing with absorption I imagine that diffusion is still not part of the picture or you may think we don't need it as much as absorption.

Your room is tool small to be able to use numeric-based diffusers (such as 2D and 3D Schroeder diffusers, BAD panels, etc.), so those are not options. You could probably use poly-cylindrical diffusers if it turns out that you need something, but it's too soon to say.

Should I just cover the area of the back wall at head level and see how that works?

Cover the entire rear wall with at least 4" (10cm) of absorption, similar to OC-703 or OC-701, and 6" (15cm) would be better. Then re-build your hangers in front of that. If that is sucking out too much of the high end, use plastic / foil / thin laminate in front of it, to return some of the highs.

Test with REW all the time as you proceed, to check that your devices are doing what they are supposed to do, then plan the next step based on the results after the previous step.


- Stuart -