Question Audio illusion, what creates it?

AJM1981

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Mar 26, 2021
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Something I wonder about with no background in loudspeaker design :)

Some loudspeakers have the illusion that some effects seem to come from the back within the speakers rather than from the front. Giving a pleasant depth to the experience.

What design features create this illusion?
 

nopiano

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If a speaker is accurate in phase and timing it should reproduce the depth (or closeness) that the microphones captured. Bear in mind that much of what passes for depth is manipulated by mixing, and a mid-range frequency dip can create an illusion of depth. So my comment applies to simply recorded acoustic instruments or voices.
 
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AJM1981

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If a speaker is accurate in phase and timing it should reproduce the depth (or closeness) that the microphones captured. Bear in mind that much of what passes for depth is manipulated by mixing, and a mid-range frequency dip can create an illusion of depth. So my comment applies to simply recorded acoustic instruments or voices.
Thanks, that is more to it. Adding to this it is probably a combination of better quality crossovers and cabinet design between an entry level loudspeaker and something a bit further up hill.

Do you know if things like for example the position of the bass reflex port and if it is single or double also has a minor effect?
 

manicm

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I don't think streaming will reproduce the effect, excuse my cynicism, but I have the CD of King Crimson's live B'Boom album.

The title track, on a reasonably good system, has an elliptical sound effect, or Frippertronics. A really good system will give the illusion that it moves around you.
 

nopiano

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Thanks, that is more to it. Adding to this it is probably a combination of better quality crossovers and cabinet design between an entry level loudspeaker and something a bit further up hill.

Do you know if things like for example the position of the bass reflex port and if it is single or double also has a minor effect?
My guess is that the bass region isn’t really relevant because low frequencies are omnidirectional. It’s in the midrange and treble that the ‘focus’ we hear as a solid sound stage - stereo - is created I believe.

A better cabinet will reduce colouration, and a better crossover will help the frequencies pass more evenly from one driver to the next.
 

AJM1981

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My guess is that the bass region isn’t really relevant because low frequencies are omnidirectional.
True, the turning point from bidirectional to omnidirectional is around 200hz. A side note is that it applies to random daily sounds as when there is any noise in life crossing those frequencies we are poorly to not able to locate it directly.

Altough it is a bit debatable as when it comes to music and loudspeakers that the same theory applies or just gets a bit different. Because when music plays we have a constant source and plenty of time to trace the bass source and when we know where the sub is there it will remain at that point for our ears and brain because we anchor it there. This should to some justify the use of a double sub in a stereo setup.

It’s in the midrange and treble that the ‘focus’ we hear as a solid sound stage - stereo - is created I believe.

A better cabinet will reduce colouration, and a better crossover will help the frequencies pass more evenly from one driver to the next.
Yes indeed.What is interesting is that the best loudspeaker designers most likely know a couple of things (understatement) about psychoacoustics as in perception of sound, the working of the ear and translation to our brain (which was not the answer to what created a certain illusion) . It is this engineering part which I consider interesting. Our ears and brain are not the source as some earlier answers would suggest but the receiver, and the philosophy behind a working mix to create certain emphasis and illusions is interesting in my opinion. Amar Bose was an engineer who studied this subject and applied certain elements and it is has for sure been a topic among good developers.

Some developers want their loudspeaker to emphasise the male or female voice for example, something which we can catch in a certain frequency range and can be used to get a good score in reviews. I often get the idea that reviewers mainly lay out why they like something but probably not have an idea what little set of adjustments in design are used to get that character or why type x is type x.

The developers might know how to tweak plenty of things to give one speaker a different character to another and "not" have the entry level model beat the one a few steps up the ladder and certainly not their current flag ship. :)
 
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AJM1981

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An interesting article about porting here.


Below the tuning frequency...

The key difference between a port and a PR is that at very low frequencies a port just acts a like a huge hole in the cab - basically it turns it into an open baffle design where the woofer back wave starts to cancel the front wave. A PR can obviously never act like a hole because it is a solid membrane - instead it acts like it is in free air itself and thus sucks energy out of the woofer at its free-air resonant frequency and produces out of phase output with the main woofer causing a distinct notch in response. When we see this plotted on a response graph this notch makes the roll-off of a PR appear steeper than with a port but it isn't really a change in transfer function so much as an additional function. Head lower in response and the port and PR response curve tend to converge and continue on the same slope together.
 

abacus

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The brain ear combination can use its learnt knowledge to guess what it should sound like providing cues are there. (Hence the only way to compare things is via a double blind test to remove external cues)
Think about it, you are hearing a sound stage in front of you that doesn’t exist, (Only sounds coming from 2 separate boxes exist) but the ear brain using its knowledge interprets it as a sound stage. (Even though as I said it doesn’t actually exist)

Bill
 

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