# Eureka or bust... Stereo experiments.

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#### Robbintip

My experimental statement is: if we are to recreate the recorded experience of the microphone, we need recreate the flow of waves in our listening position as if we are the microphone in the recording position.

It is part thought and part practical experiment to participate in if you like. It takes almost no effort to try out a little practical and therefore would be appreciated if you did, before roasting me to hell and back.

The story:
Stereo microphones are two figure of eight aka dipole mics, coincidently placed above eachother, with 90 degree rotation. The Blumlein array as you might know. Thanks for reminding me Ben.

In order to recreate a recording as if we are the microphone, we need all four poles to be present for this experiment.
Two speakers should suffice, because a speaker can move both ways, and take care of the positive, and negative pressure flowing through the recording microphone, right?

Maybe not..
My closed box speakers are monopoles. The negative part of a sinus, inward movement of the cone, produces an inward wave that should be absorbed by the box. These inward movements, are difficult to hear because they can't produce an outward radiating negative sound pressure wave. That's just physics of sound propagation through gases like air.
However they are present in the recording and as such, should be reproduced.

I could build dipole speakers. But it would require the reflections of the room to carry the sound radiating of the back of those speakers towards my ears, because any direct-radiating negative wave would cancel out inherent to their design. These reflections are delayed, so non-coincident in contrary to the microphone signal. Skipping dipole, and difficult room accoustic maths...

I tried thinking up a speaker that bends the sound coming from the other pole around, delaying it enough to not cancel out. But all contained in a box design. What I came up with reminded me of something, I basically re-invented the Karlsson resonator, lol.
This wasn't going to work as coincident design unfortunately. If I really invented this design with this pupose in mind, I would bury the design philosophy under a thick layer of marketing and capitalize on the side effects. Next..

Looking at the double figure of eight microphone polar pattern again, I got an idea.
If my speakers have to abide laws of physics, don't introduce room reflections and sound signatures as part of their design and have to be coincidentally expressing both in and out of phase sound, the only thing they could be are monopoles, just plain old box speakers. I'm just going to need another pair of monopoles to add up to the total amount of the 4 poles of the stereo microphone. Out with dual mono, in with stereo.

Spacing of the speakers in accordance with microphone will be 90 degrees apart. Obviously speaker phases should also match the pattern of the microphone. And looking at the microphone pattern, you can see that the left front speaker would face head on to the speaker located rear right. They would need to be fed the same signal, but out of phase to properly mirror (or superimpose). Same goes for the right front, it's signal is the same, but inverted compared to left rear, just like the microphone.

At the bottom of almost every page of Linkwitz' website, he says:
What you hear is not the air pressure variation in itself
but what has drawn your attention
in the streams of superimposed air pressure variations
I hope this experiment succeeds in recreating that experience.

Things to consider...
Is this a well-known practice? How is it called?
Does it sound rubbish?

Circumference of the circle of speakers I would guess would be open to experiment:
-How close can you place them against a wall without accoustic of the room taking over?
-Can you convert them to omnipoles with positive effect?
What about pinna cues to insert with the rears, or is it enough to have cues from our actual ears?

Another question that might get answered: Can boxed speakers now finally dampened to the point they sound 'dead', to sound better in the system?

Eureka or bust. I'm going to try it tomorrow.

I will try this Paul McCartney song first because of the wording:
Figure of Eight said:
Well you've got me dancing in a figure of eight,
Don't know if I'm coming or going, I'm early or late.
Round and round the ring I go,
I want to know, I want to know,
Why can't we travel a continuous line?
Make love reliable covenant all the time.
Up and down the hills I go, I got to know, I got to know.
Is is better to love another
Than to go go for a walk in the dark?
Is it better to love than to give in to hate?
Yeah we'd better take good care of each other
Avoid slipping back off the straight and narrow,
It's better by far than getting stuck in a figure of eight.
Well figure it out for yourself little girl,
It don't go nowhere at all,
It's nothing more than a tape loop in a big dance hall.
You've got me running
You've got me running

An acoustic event has dimensions of Time, Tone, Loudness and Space
Have they been recorded and rendered sensibly?

#### Attachments

• superimposed monopoles.png
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#### picowallspeaker

My closed box speakers are monopoles. The negative part of a sinus, inward movement of the cone, produces an inward wave that should be absorbed by the box. These inward movements, are difficult to hear because they can't produce an outward radiating negative sound pressure wave. That's just physics of sound propagation through gases like air.
However they are present in the recording and as such, should be reproduced.
Well, as you said, this is re-production ( of an event) through electronic and mechanical devices. When it comes to transduction from electrical to mechanical, you have the useful output which is the front wave from the speaker's membrane AND the error output, 100% error because it's in anti-phase- the negation of the front one, from the rear of the membrane.
The problem consists in eliminating the back wave
Another question that might get answered: Can boxed speakers now finally dampened to the point they sound 'dead', to sound better in the system?

Big problem! The box boundaries are usually made with wood, which is not a good sound-proofing material. The membrane itself is thin and good ol' paper is not sufficient to block the inner pressure without deforming.
Nowadays we have better materials but still the very low frequencies see no boundaries. The optimum would be to let the backwave expand in another room or outside but this is in contradiction with the placing of the two sources ( speakers) in the room adeguately distant from the walls; this brings to the so-called room treatment and so on...

#### TNT

Paid Member
What you hear is not the air pressure variation in itself
but what has drawn your attention
in the streams of superimposed air pressure variations

I don't get the difference... help!

//

#### TNT

Paid Member
I think it is worthwhile to think about the whole record/replay chain including both locations. Like you do here. It's the way to progress the SOTA. One aspect is to fix the incoming direct sound wave angels which is only 2 for stereo but many in reality.

//

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#### scottjoplin

Reminds me a little of a Double Bass Array. Shouldn't the phase inverted speakers be delayed in order to emulate the microphone since they are a distance apart? Microphone - Wikipedia

#### picowallspeaker

What you hear is not the air pressure variation in itself
but what has drawn your attention
in the streams of superimposed air pressure variations

I don't get the difference... help!

//

After the ears there's the brain < emotions, stress, environment etc.>
The brain decides which is the useful information to pick, and that it's called attention. But you're unaware of it

#### billshurv

Paid Member
But surely the figure of 8 is only ONE mic technique. As the liner notes rarely tell you what mikes were used you are a little stuffed.

#### TNT

Paid Member
After the ears there's the brain < emotions, stress, environment etc.>
The brain decides which is the useful information to pick, and that it's called attention. But you're unaware of it

I see your smiley. To me it says that you don't agree on my statement or think you found something that breaks my reasoning. I think I understand what you say but it definitely doesn't change my view. If you can recreate the sound wave exactly how it was in the original location, how the "earbrain" works is irrelevant as I see it.

//

#### picowallspeaker

I see your smiley. To me it says that you don't agree on my statement or think you found something that breaks my reasoning. I think I understand what you say but it definitely doesn't change my view. If you can recreate the sound wave exactly how it was in the original location, how the "earbrain" works is irrelevant as I see it.

//

To recreate the original event you should have
Perfect source
Perfect amplifier
Perfect cables
Perfect eeh uhm speakers
Perfect room

And still there might be something that is going on that is not perfect
Who is it?
Ah, the listener !

Or.. may it be the production?

Aaand...now I'm gonna post in What Are The FUll Albums that you listened to...

#### DF96

Robbintip said:
My experimental statement is: if we are to recreate the recorded experience of the microphone, we need recreate the flow of waves in our listening position as if we are the microphone in the recording position.
Why would you want to recreate the "experience" of the microphone? Would it not be better to recreate the experience of an audience member?

Robbintip said:
Stereo microphones are two figure of eight aka dipole mics, coincidently placed above eachother, with 90 degree rotation. The Blumlein array as you might know.
No, that is merely one possible stereo mike configuration - and in my opinion not the best one. Better arrangements use some spacing too.

Be aware that most 'stereo' recordings do not use a stereo mike at all. They merely panpot lots of mono sources, with or without some phase adjustment.

By starting with a number of false premises you are not likely to end up anywhere useful.

#### TNT

Paid Member
To recreate the original event you should have
Perfect source
Perfect amplifier
Perfect cables
Perfect eeh uhm speakers
Perfect room

And still there might be something that is going on that is not perfect
Who is it?
Ah, the listener !

Or.. may it be the production?

Aaand...now I'm gonna post in What Are The FUll Albums that you listened to...

Sorry, but not even close. Those are the simple parts.

//

#### Robbintip

But surely the figure of 8 is only ONE mic technique. As the liner notes rarely tell you what mikes were used you are a little stuffed.
Thanks for noting. I am now looking for records made exclusively with this type of microphone.
My testing for this experiment will be limited to these recordings to begin with, but might move on to other types.

Why would you want to recreate the "experience" of the microphone? Would it not be better to recreate the experience of an audience member?
Because audience members don't have microphone outputs, it's not easy to recreate that.
But you are right, that it might be a target. It will be interesting to hear what kind of experience this set-up gives. If sounds seem to originate from inside the head like headphones can provoke, or can be heard as if originating from elsewhere and maybe even both.

If it does not sound 'right', I might take a look at delay and/or HRTF possibly.
For now I'm just keeping it simple, plugging in an extra pair of superimposed speakers.

#### Robbintip

For incorporating as much room accoustics while listening to a record that has none, like a non reverberant studio recording, I thought of another type of speaker: The quadpole.
It essentially is two dipole speakers, placed coincidentally, like the Blumlein array.
If my thinking is correct, this speaker, with the right recording, will produce a sound that resembles the artist standing at the speaker location, singing through the speaker like it was a microphone. Being a stereo recording, sounds are spread out into the room in a natural way.

This might be a secondary project to tinker with later.

#### Robbintip

Tested.
Can't believe the manifestation. Going to listen some more.

#### Robbintip

Reminds me a little of a Double Bass Array. Shouldn't the phase inverted speakers be delayed in order to emulate the microphone since they are a distance apart? Microphone - Wikipedia

I would just place them on the opposite side of the listener. Delay should be minimal, if at all with this approach, and don't cancel each other out on their way to the subject. Both phases should be trnasduced into air motion this way.

#### wiseoldtech

Chasing rainbows in home reproduction of audio is futile.
But have fun.

#### scottjoplin

I would just place them on the opposite side of the listener. Delay should be minimal, if at all with this approach, and don't cancel each other out on their way to the subject. Both phases should be trnasduced into air motion this way.
You could be right, I'm trying to get what's happening at the listening position, one speaker's blowing whilst the other is sucking not sure how different the end result would be. How would you describe your listening impressions of the difference?

From elsewhere: https://www.diyaudio.com/forums/multi-way/344709-crossover-design-depth-field-6.html#post5966046

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#### Robbintip

To be honoust I don't know about subwoofers yet.
I would visualize two people in a hot tub, each one jumping up and down at the same frequency, but exactly out of phase. I gues it would make the waves more uniform.
Air doesn't move very different than this I would guess..

Here's how to freak somebody out when you are driving a car: hold up a lighter. Take a corner. The flame will move the opposite direction
That's why I find it difficult to believe that sound will 'pressurize' a room in a uniform manner under a certain frequency. I might make a video showing what movement my room door makes at 8hz, it doesn't resemble a sinus IMO. There is a noticable peak, then a 'long' silence, then a peak again. You can feel the 'pressure' but it hitting your chest more reminds me of ocean waves hitting me at the beach than the sinus I see on the screen.

It is so easy to try for yourself. Grab a couple of speakers, preferibly the same models, an amplifier.
Put the 4 speakers in a circle, at 12, 3, 6 and 9 o' clock around you, at the same distances. Aim them exactly across the middle.
Wire the fronts up like you are used to.
Wire your left rear in parallel with front right. Reverse polarity on the rear.
Wire your right rear in parallel with front left. Reverse polarity on the rear.
Done.
Have fun. Let me know what you think.

#### scottjoplin

The DBA works by effectively absorbing/cancelling the wave at the rear wall. Something similar my be happening in your set up, that's why using a delay may be interesting

#### Robbintip

This morning I woke up after a good nights sleep, ready for a reality check.
Disconnected the rear speakers and listened to some music for a couple of hours until I was used to the sound again.

Grabbed a snack, connected the rears again. Attenuated the rear speakers a bit, dialed in a little less delay as I was now sitting on my back all over the couch in full comfort mode.
There it was again...

Albums on repeat right now:
Dire Straits - Brothers in Arms
Pink Floyd - Dark Side of the Moon

Surprisingly, some modern studio music productions have amazing depth as well. The Weeknd - High For This has some sound that is clearly projected from behind.

Funny: Dire Straits' Walk of life scared me shitless when somebody apparently closes the studio door at 2:31. Not related to this particular experiment though.

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