Mysterious 50Hz cancellation by left and right

[QMuse]

The cancellation at 50 Hz is real. I can play sinusoidal tones. I can move myself toward the listening position. The sound disappears to my ears.

By the way this is the impuse on my REW.

View attachment 61620

When presented like this you can't see strange artifacts in impulse response measurement, but you can clearly see them the way I showed it.

 

[RayDunzl]

impulse response looks very weird

The speakers are Bose 901 VI.

Front side:

Back side:

 

[QMuse]

Front side:

View attachment 61621

Back side:

View attachment 61622

OMG.. That kind of explains it.

 

[QMuse]

The cancellation at 50 Hz is real. I can play sinusoidal tones. I can move myself toward the listening position. The sound disappears to my ears.

Yes, I can see that. Look here, wherever you see phase rolling-off you will see a problem with phase cancellation as red line (L+R response) isn't summed up correctly:

So at 49, 85 and 117Hz you can see that summed response is lower than individual response which implies cancellation.

 

[Lorenzo74]

The files.

it seems file you post are up to 400Hz. do you have full frequency sweep? 20-20k?
thanks

 

[QMuse]

Front side:

View attachment 61621

Back side:

View attachment 61622

Is that thing supposed to sit in corner?

 

[Pio2001]

Very asymmetrical living room.View attachment 61603

Hi Skyfly,
What are the walls that cause the 37 Hz resonance ?
If they are the side and front walls, that's ok, but if they are the left and right walls, then the AVAA should be more effective at cancelling it if it was on the other end of the room, of the left side of the diagram.
And if the walls that are causign this are floor and ceiling (that would mean 5 meters between them !), I think it should be a bit more effective if it was on the ceiling than on the floor.

The idea is to place the AVAA the closest to a wall that is involved (or in any place where the resonance is at its max), while being far from the speakers and far from the listener, so that it absorbs the most possible of unwanted acoustic energy while absorbing the least possible useful acoustic energy.
The device itself is just a sound eater. It is blind to good and evil. It absorbs everything that it sees. Good sound as well as bad sound.

 

[skyfly]

When presented like this you can't see strange artifacts in impulse response measurement, but you can clearly see them the way I showed it.

Sorry. I don't know how to display impulse response as you did.

 

[skyfly]

it seems file you post are up to 400Hz. do you have full frequency sweep? 20-20k?
thanks

I have, but L and R both played. I couldn't play sweep tones as many as I wanted, because it was not my house.

 

[skyfly]

Hi Skyfly,
What are the walls that cause the 37 Hz resonance ?
If they are the side and front walls, that's ok, but if they are the left and right walls, then the AVAA should be more effective at cancelling it if it was on the other end of the room, of the left side of the diagram.
And if the walls that are causign this are floor and ceiling (that would mean 5 meters between them !), I think it should be a bit more effective if it was on the ceiling than on the floor.

The idea is to place the AVAA the closest to a wall that is involved (or in any place where the resonance is at its max), while being far from the speakers and far from the listener, so that it absorbs the most possible of unwanted acoustic energy while absorbing the least possible useful acoustic energy.
The device itself is just a sound eater. It is blind to good and evil. It absorbs everything that it sees. Good sound as well as bad sound.

This was my rough guess about the unpleasant 37 Hz booming. The ceiling was low.

 

[RayDunzl]

Is that thing supposed to sit in corner?

No.

They are supposed to spew sound off the wall behind the speakers, and off the sidewall, but not be placed really "in a corner".

Bose called it "direct/reflecting"

https://assets.bose.com/content/dam...M195438_05_OG_901 Series VI Speaker_ENGvo.pdf

Oooh... A Review:

Bose 901 loudspeaker
J. Gordon Holt | Nov 7, 1995 | First Published: Nov 7, 1971

 

[Lorenzo74]

No.

They are supposed to spew sound off the wall behind the speakers, and off the sidewall, but not be placed really "in a corner".

Bose called it "direct/reflecting"

View attachment 61736

https://assets.bose.com/content/dam/Bose_DAM/Web/consumer_electronics/global/products/speakers/901_directreflecting_speaker_system/pdf/AM195438_05_OG_901 Series VI Speaker_ENGvo.pdf

Oooh... A Review:

Bose 901 loudspeaker
J. Gordon Holt | Nov 7, 1995 | First Published: Nov 7, 1971

View attachment 61741

i was tempted by latest version after a casual audition many years ago in my audiophile 1.0 life.
Here one interesting review
https://www.tonepublications.com/review/we-review-the-bose-901/
Any of you manage to retrieve the raved review from Julian Hirsch on Stereo Review?
I couldn’t.

pls. don’t forget that one of the nine 901 full range driver embodies more Engineering hours than any other speaker ever designed.
manufacturing tolerances are by far lowest among other companies in that period.


we might like it or dislike but it was a masterpiece of engineering as the outcome of best MIT talents of the ‘70s & ‘80s. A real speaker for (virtual vintage) Audiosciencereview website.
Would be interesting to know why it captureD the preferences of so many music lovers in so many decades...
Any ideas?
My Best
Lorenzo

 

[skyfly]

No.

They are supposed to spew sound off the wall behind the speakers, and off the sidewall, but not be placed really "in a corner".

Bose called it "direct/reflecting"

View attachment 61736

https://assets.bose.com/content/dam/Bose_DAM/Web/consumer_electronics/global/products/speakers/901_directreflecting_speaker_system/pdf/AM195438_05_OG_901 Series VI Speaker_ENGvo.pdf

Oooh... A Review:

Bose 901 loudspeaker
J. Gordon Holt | Nov 7, 1995 | First Published: Nov 7, 1971

View attachment 61741

This is the reason for low wife acceptance factor of Bose 901. The speaker's width is 55 cm and the minimum recommended almost-empty space on each side is 45 cm: total width is about 145 cm.

I wish Bose releases 901.2 with inverted-V-shaped rear, one side slightly pointing up and the other slightly pointing down to combat repeated reflection between the speaker and the wall.

 

[A800]

Isn't this "Direct/Reflecting" stuff total BS?
The microphone(s) for example recorded all the direct and reflected "sound" as it should be already?

 

[skyfly]

Isn't this "Direct/Reflecting" stuff total BS?
The microphone(s) for example recorded all the direct and reflected "sound" as it should be already?

An engineer at Dolby said, he expects consumers to hear both direct sound from speaker and reflected sound from walls in the listening room. He added that he wants more high frequency reflection than today's standard: 180 degrees uniform radiation, but not as much as 360 degrees uniform radiation as In MBL (yes, he mentioned the high-end brand MBL in the talk).

 

[A800]

An engineer at Dolby said, he expects consumers to hear both direct sound from speaker and reflected sound from walls in the listening room. He added that he wants more high frequency reflection than today's standard: 180 degrees uniform radiation, but not as much as 360 degrees uniform radiation as In MBL (yes, he mentioned the high-end brand MBL in the talk).

But where is your reflected sound when you use headphones for example?

 

[skyfly]

But where is your reflected sound when you use headphones for example?

Headphones are tuned with a bump at lower high frequency, perhaps for "average" ear.

I like the idea of getting sound from various directions, instead of getting dominant sound from a single direction. You can understand why by playing pink noise on a speaker and rotate your head. You will feel quite mush variation in the sound.

 

[skyfly]

I moved PSI AVAA to the corner on the listener's wall. I also moved left speaker to the right by 2cm, and the right speaker to the right by 25cm. The cancellation at 50Hz is a little less severe. I could not experiment as much as I would on my own system.

P.S.: the mic graph is not from measurement of the particular mic. It is the graph on the catalog made by the manufacturer. The brand's specialty is PC speakers, and mics (lower price than the price of entry models of famous brands).