My First Room Measurement

[Splinter2k]

Attached is my first room measurement. I attached 2-mdat files and the calibration file.

I'm still learning how to read things, but looks like I have a sizable dip around 100hz?

This is a studio mixing room. It is treated with panels, bass traps and diffusors on the back wall.

I would appreciate any feedback.

Thanks,

Keith

 

[Splinter2k]

Calibration file added to OP.

 

[dotnet]

Where were you during the “with me” measurment, assuming that the space normally occupied by your head would have been taken up by the microphone?

Is this two speakers playing simultaneously, or just one? Or two speakers and a sub?

What‘s interesting is that both the “with me” and “without me” measurements show a notch around 96Hz, so the first instinctive suspicion would be SBIR or some room interaction. But the excess group delay in the “with me” measurement is as smooth as a baby’s bottom (suggesting that the notch should be easy to EQ), whereas in the “without me” measurement it has a peak at 96Hz.

I don’t know what to make of that. Did you use a timing reference for the measurements?

 

[sm52]

Your mixing studio is well muted. Even a little too much. There is a difference with you and without you. This manifests itself 1 ms and further after the main pulse. Your presence adds 10-15 dB to the reflections without you. Were you approximately 35 cm away from the microphone when you measured with you?

 

[dotnet]

Were you approximately 35 cm away from the microphone when you measured with you?

You reckon that‘s what it is? I thought it’s perhaps reflections off the desk or something.

I also noticed the relatively high noise floor in the low frequencies. It shows well in the waterfall but doesn’t seem well correlated with the signal (i.e. doesn’t really look like reverb). Therefore I’m thinking external noise like cars, trains, building plant (like lifts or aircon), etc.

 

[Splinter2k]

Hello guys, thank you very much for your help with this!

1. The "With Me In" measure was done with me sitting in a chair directly behind the measurement microphone. I was trying to get as close to the listening position, but of course the microphone was in my way, so I had to sit a little further back.
2. The sound was playing out of both speakers and the mic was placed pointed straight up at ear level in the engineer position.
3. I did not use a timing reference and would appreciate some help on how to set that up. I have a Focusrite Clarett interface.
4. I'm not sure about the floor noise. There was family home and probably making noise outside the room. It's was treated for absorption and deflection, not isolation, so I am susceptible to outside noise. One thing I did notice, was that to get the input gain on the measurement microphone up to the recommended value, I had to turn the input up all the way on the front panel of the Focusrite.


A quick description regarding my room treatment (see pictures).

Room Size:
Its a smaller room 15' 6" x 11' 10". There is also a cutout cove in the middle of one wall.

Treatment:
There are isoThermal Bass Tubes (Acoustic Sciences Corp) in each corner. They can be rotated 180 degrees, on one side in addition to bass trapping, they add treble diffusion. On the other side they add treble absorption, instead of treble diffusion.

The panels around the room are 4" think panels from ATS Acoustics. The panels in the cove and doors are 2" thick.

The back wall has 3 rows of quadratic diffusors. They are constructed from MDF board.

The floor is bamboo flooring nailed and glued on top of Quiet Walk padding (non floating installation).

The drywall was removed from the ceiling and batt insulation was installed with the Kraft paper facing down in all areas except for the engineer listening area and the area above the rear coach. The fluffy part of the insulation is facing down in those areas. The ceiling is covered in Guildford of Main Whisper fabric on a track system.

Questions:

1. sm52, you mentioned the room being a little too muted. Would you recommend rotating the bass tubes to add more treble deflection vs absorption?
2. What do you guys think about the dip at 96hz? I'm assuming that is a comb filter from floor bounce? Should I try pushing the speakers closer to the wall. Since the room is smallish, I really would rather not pull the console further toward the center of the room.

 

[dotnet]

1. The "With Me In" measure was done with me sitting in a chair directly behind the measurement microphone. I was trying to get as close to the listening position, but of course the microphone was in my way, so I had to sit a little further back.

That would explain the early reflection at 1ms (ca. 33cm extra travel) – I was about to say, but then I noticed the same early reflection in the “without me” measurement. I‘m sticking to my desk reflection theory. EDIT: Apart from that the ETC looks super clean.

4. I'm not sure about the floor noise.

Not floor noise but noise floor. There seems to be something going on in the low frequencies that doesn’t look like reverb:

It looks constant and not decaying.

Overall I don’t find the room too dry from that waterfall plot. For a listening room I’d prefer something like 200-300ms, but for a studio 100-200 sounds about right.

As for the 96k dip, that beats me. Extinction through boundary interference would suggest a boundary at about 89cm away. Is that the distance from the woofers to the side walls perhaps? I still don’t understand why the excess group delay (expected for SBIR) only shows with you in the room but not without you. Your presence should make no difference, unless you stand between the speaker and the wall.

BTW, I’d avoid getting close to the microphone during measurements, best to sit on the couch at the back.

 

[Splinter2k]

doNet,

Yeah, the noise floor is strange! Just so I understand, since it doesn't look like reverb, does it look more like some type of artifact in the measurement versus an actual frequency issue in the room?

I did measure from the woofers to the walls and yes, they are just about 89cms. I'm going to try moving the bass tube forward to be between the speakers and the walls, just to see how that changes the measurement.

Just out of curiosity, I put the speakers directly in front of the panels on my front wall and re-measured (graph screenshot attached). It moved the dip down around 65hz and decreased it around 6db. This probably makes perfect sense to you acoustic gurus. My thinking was that maybe I need to spread my front wall panels out, so they are directly behind the speakers? Maybe add another narrow panel in the middle of the two then.

I also, put the speakers on their sides, closer to the wall with the tweeters facing inward. I'm just learning to read these graphs, but it looks like it really smoothed out the curves from 200hz up.

I figured out how to do the timing reference on my second input/output pair. I'm going to redo my measurements and experiment with the bass tubes and speaker placement more.

Thanks again for your help!

 

[sm52]

sm52, you mentioned the room being a little too muted. Would you recommend rotating the bass tubes to add more treble deflection vs absorption?

I don't know much about what's best for a mixing studio, but 120ms to full decay seems way too short for me. 200ms is fine. Rotate the bass traps 180 degrees and measure.
About 96 Hertz. I think you can try moving the entire mixer table to the left and measure, then to the right and measure. Maybe you can choose a good position. That is, the reason for the hole at this frequency is in the room itself.
The noise that dotnet pointed out in the screenshot has nothing to do with the sound from the speakers or the interaction with the room. The source of this noise is most likely external. It penetrates through the floor or ceiling or whatever.
There is a reflection after 0.2 ms, this is most likely from the mixing table.
Rattling at high frequencies due to the fact that two speakers are measured at the same time. To prevent this from happening, the microphone should be exactly in the middle between the speakers.

 

[Splinter2k]

I don't know much about what's best for a mixing studio, but 120ms to full decay seems way too short for me. 200ms is fine. Rotate the bass traps 180 degrees and measure.
About 96 Hertz. I think you can try moving the entire mixer table to the left and measure, then to the right and measure. Maybe you can choose a good position. That is, the reason for the hole at this frequency is in the room itself.
The noise that dotnet pointed out in the screenshot has nothing to do with the sound from the speakers or the interaction with the room. The source of this noise is most likely external. It penetrates through the floor or ceiling or whatever.
There is a reflection after 0.2 ms, this is most likely from the mixing table.
Rattling at high frequencies due to the fact that two speakers are measured at the same time. To prevent this from happening, the microphone should be exactly in the middle between the speakers.

Thank you sm52, I will rotate the tubes and re-measure. I added another chart to my post above, with measurements with the speakers on their sides. I have the smoothing set to 1/3 octave.

With regard to the noise, there is a basement underneath me, but I made sure the furnace wasn't running. The only other thing I have sitting right on the floor is an APC battery backup, it has a fan but in my amateur mind, it doesn't seem like it would be outputting in that frequency range.

 

[Splinter2k]

Here is a new measurement without me in the room. I played around with speaker placement and also place two extra panels I had behind the speakers on the front wall. It seems to have made a big difference in the 96Hz dip. It's still there but much less. I did pick up a little spike in the high end between 4-7K.

The noise floor on the low end seems to still be there, but better.

Any thoughts on the new measurements?

Thank you!

 

[sam_adams]

@Splinter2k, in order to better evaluate the measurements you are making, don't post average measurements. Make a measurement of the left and the right speakers separately. You can make measurements with the mic placed horizontally pointing at the speakers for evaluation of the direct sound and with the mic pointing vertically towards the ceiling to better evaluate the room acoustics.

 

[sm52]

Here is a new measurement

Nothing can be said about this measurement. Since you got it by averaging. In this case, the phase is lost. So it's just one line. Do not average or smooth measurements when posting for discussion.

 

[Splinter2k]

Nothing can be said about this measurement. Since you got it by averaging. In this case, the phase is lost. So it's just one line. Do not average or smooth measurements when posting for discussion.

I will repost without the averaging. Thanks

 

[DanDan]

Small traps behind the speakers often make the Front Wall BIR worse.