67 Hz notch with KH 120 II

[Flaesh]

the 67Hz dip?

Does the frequency of the drop-out change when the microphone is moved back and forth? Both in reality and in the simulation.
ps: highlighted the direction in bold font

 

[Curvature]

~67Hz is a common mode seen in a lot of home settings. It's to do with standard ceiling heights of 2.4m or 8ft high. https://www.hunecke.de/en/calculators/room-eigenmodes.html The difference in frequency from the simulation and the shape of the dip are to do with the flexure of the walls, altering the phase of reflected sound.

Panel absorbers (not foam or fibreglass), electronic absorbers (Psi Audio), multiple subs and EQ (with FIR filters) will help.

Easiest is to buy some subs if your budget and room allow. The KH750 is expensive and kind of small, but that and the MA1 will have good results through Neumann's autoEQ program, which uses FIR filters for phase compensation.

 

[lsanbourne]

Thanks a lot. I have gotten Floyd Toole's book and learned a lot. I'm a bit stuck at the moment because I am wondering if a non-DSP monitor speaker would be better (to avoid multiple DAC -> ADC -> DAC and keep sample rate at original (KH 120 II downsamples)). However, MA-1 is easy, and if I switched to speakers like Genelec that are better loved by the Bob Katzes of the world* and not constrained in sample rate, I'd have to sell speakers and MA-1 mic, and invest wholly in Genelec...which I'm reluctant to do without hearing the difference.

The only real point of comparison is that before I had these Neumanns I had Geithains (https://www.me-geithain.de/en/rl-944k.html), which I thought sounded much better (subjectively) but had this 60Hz hum that the mfr said was inevitable when running them in North America.

By the way when you say panels (not foam/fibreglass), can you give an example of such a product? I was looking at hanging 60Hz GIK bass trap panels above me.

* Bob Katz writes that nearfield monitoring is basically like big headphones and therefore unwise for mastering/mixing — but that Genelecs nearfields are decent for the task. My room is small but I'd be up for putting the speakers a bit farther away ... and perhaps above facing down, to avoid comb reflections from the desk?? https://www.digido.com/ufaqs/nearfield-monitors-for-mastering/

 

[Curvature]

I'm a bit stuck at the moment because I am wondering if a non-DSP monitor speaker would be better (to avoid multiple DAC -> ADC -> DAC and keep sample rate at original (KH 120 II downsamples))

The conversion is transparent and has no audible impact. There's no worthwhile reason to use high sample rates beyond 44.1 or 48kHz, either.

The only real point of comparison is that before I had these Neumanns I had Geithains (https://www.me-geithain.de/en/rl-944k.html), which I thought sounded much better (subjectively) but had this 60Hz hum that the mfr said was inevitable when running them in North America.

The Geithains are cardioid, so the radiation pattern is controlled to a lower frequency (~250Hx) than the Neumann speakers (1kHz, using the -6dB trace in the link below. Unfortunately we don't have any detailed measurements of Geithain speakers to make a worthwhile comparison.

Graphs and Measurements for Neumann KH 120 II

www.spinorama.org

I don't understand why there would be a hum with Geithains in NA that can't be fixed. Audible hum indicates a ground loop. The speaker has regulated power, too, so there should be no inherent issues. Just a strange thing to say by the manufacturer.

By the way when you say panels (not foam/fibreglass), can you give an example of such a product? I was looking at hanging 60Hz GIK bass trap panels above me.

https://www.gikacoustics.com/products/flexrange-bass-trap-panel Anything with a "range limiter" uses a tuned membrane or panel to absorb lower frequencies. That said, you would need a lot of these to make a significant difference below 100Hz.

My favorite product is the RPG Modex Plate: https://www.rpgacoustic.com/product/modex-plate-2-0/ Another very strong product is the Artnovion Subtrap: https://artnovion.com/product-categories/9-bass-trap/products/320-sub-trap-range But these are both heavy, large and expense. Two of the Modex Plates will produce good results.

* Bob Katz writes that nearfield monitoring is basically like big headphones and therefore unwise for mastering/mixing — but that Genelecs nearfields are decent for the task. My room is small but I'd be up for putting the speakers a bit farther away ... and perhaps above facing down, to avoid comb reflections from the desk?? https://www.digido.com/ufaqs/nearfield-monitors-for-mastering/

Bob Katz doesn't have the best technical knowledge. It's no problem to mix on small speakers in a small room that don't sit far away. Check your mixes on headphones and other soundsystems.

The specific issue that all rooms have, difficult to address, is SBIR, caused by nonminimum phase cancelations where the direct sound is affected by the reflected sound, around 100-400Hz. Desk reflections are part of that.

EQ will help, particularly with the MA1, as will treatment.

 

[lsanbourne]

The conversion is transparent and has no audible impact. There's no worthwhile reason to use high sample rates beyond 44.1 or 48kHz, either.

Got it. I will do some blind tests to see if I can reliably hear higher sample rates.

The Geithains are cardioid, so the radiation pattern is controlled to a lower frequency (~250Hx) than the Neumann speakers (1kHz, using the -6dB trace in the link below. Unfortunately we don't have any detailed measurements of Geithain speakers to make a worthwhile comparison.

Graphs and Measurements for Neumann KH 120 II

www.spinorama.org

I don't understand why there would be a hum with Geithains in NA that can't be fixed. Audible hum indicates a ground loop. The speaker has regulated power, too, so there should be no inherent issues. Just a strange thing to say by the manufacturer.

This was their reply:

All active speakers produce a small amount of noise if you listen from a very close distance.
This noise could contain also small amounts of hum. Due to competent tolerance this may vary from unit to unit.
The 906 are intended to be used from 1.0m to 2.6m. Therefore we also state a guaranteed maximum noise level of 7dBA.
It is a parameter measured within the series production. In this time we checked and
we had a noise level 2dBA and on some unit even 0.5 dB lower and on the final listening test.

Only we could not check at 60Hz, and that might worsen the hum a bit. That means
the noise should not be audible in the desired listening distance of 1m or more (lower as 7 dBA ). The noise should be within our tolerances.

https://www.gikacoustics.com/products/flexrange-bass-trap-panel Anything with a "range limiter" uses a tuned membrane or panel to absorb lower frequencies. That said, you would need a lot of these to make a significant difference below 100Hz.

My favorite product is the RPG Modex Plate: https://www.rpgacoustic.com/product/modex-plate-2-0/ Another very strong product is the Artnovion Subtrap: https://artnovion.com/product-categories/9-bass-trap/products/320-sub-trap-range But these are both heavy, large and expense. Two of the Modex Plates will produce good results.

Thanks for the tips. I rent my place and don't know if I can hang something large and heavy, unfortunately.

Bob Katz doesn't have the best technical knowledge.

What are some examples of his subpar technical knowledge?

It's no problem to mix on small speakers in a small room that don't sit far away. Check your mixes on headphones and other soundsystems.

His point is that nearfield monitors are too similar to headphones and not a great simulation of larger loudspeakers. Would I be able to use KH 120 II a bit farther away as a midfield monitor? I'm curious why he suggests the Genelecs at the end of that article rather than Neumann.

The specific issue that all rooms have, difficult to address, is SBIR, caused by nonminimum phase cancelations where the direct sound is affected by the reflected sound, around 100-400Hz. Desk reflections are part of that.

EQ will help, particularly with the MA1, as will treatment.

Yes, MA1 EQ has already helped a great detail, but the bass dip still happens (without subs/treatment).

 

[unmutual]

The miserable little room:
3.3m wide
3.8m long
2.4m tall

I entered your room's dimensions into amroc (room mode calculator).

amroc - THE Room Mode Calculator

HTML5 room mode calculator. Read and hear the tune of axial, tangential and oblique modes. Scientific sources included.

amcoustics.com

Look at the room mode values and the visualizations. The 68-69 Hz region (remember, this is a prediction, actual values could be slightly different, for instance 67 Hz) is strong in the corners, and therefore weak in the rest if the room.

This is not a problem to solve with EQ. I would instead add a subwoofer and try various placements.

 

[Flaesh]

Don't attach too much importance to this picture:

And to this also:

Ref is similar to the previous one, absorption added only in the longitudinal direction.