Thought Experiment: Listener Boundary

[-Matt-]

Consider a baffle wall. The speaker baffles are flush with the wall and so SBIR is eliminated.

Now for a slightly odd idea...

What if an indentation is made in the listener wall, which you can rest your head back into, so that your ears are flush with the wall.

Would this also eliminate LBIR?

Might you expect any other effects in this arrangement? (Audio ones, not neck ache)!

Would it sound good or awful?

 

[JPA]

I general you don't want to sit against the back wall because room modes (bass standing waves) are at a peak there. You'd hear boomy, uneven bass. That would probably be worse than any LBIR effects you manage to eliminate.

 

[anotherhobby]

I'm trying to picture this. Do you have a diagram?

 

[alex-z]

SBIR is bad because the short distance causes a relatively strong reflection, which your brain has trouble filtering due to the time differential being so small. You can take a recording of the same speaker, moving it away from a wall in 1ft intervals, and untrained listeners can notice the difference in tonality.

The rear wall reflection is substantially less problematic because the strength of the reflection is lower, and the time arrival is late enough to be processed and largely ignored by our ears. Placing your head against the rear wall would be purely detrimental. Not only would you experience bass boom due to the high pressure near boundary surfaces, but the ratio of direct vs reflected energy would fall. Easily verifiable with the C50/C80 values. The optimal seating position in many rooms is 38 or 62% of the length.

 

[-Matt-]

I'm trying to picture this. Do you have a diagram?

Sorry for my artistic skills! This is supposed to be a plan view:

I general you don't want to sit against the back wall because room modes (bass standing waves) are at a peak there. You'd hear boomy, uneven bass. That would probably be worse than any LBIR effects you manage to eliminate.

In theory your ears would be at a node for ALL frequencies and so you might expect not to hear any standing waves at all?

The rear wall reflection is substantially less problematic because the strength of the reflection is lower, and the time arrival is late enough to be processed and largely ignored by our ears.

Surely that depends upon how close you are to the rear wall. If you sit say 30cm from the rear wall but your speakers are 5m from the front wall then LBIR could be far more significant than SBIR. (Or, indeed, if you have a baffle wall for the speakers).

Placing your head against the rear wall would be purely detrimental. Not only would you experience bass boom due to the high pressure near boundary surfaces, but the ratio of direct vs reflected energy would fall. Easily verifiable with the C50/C80 values.

I would agree if you were talking about being NEAR to the rear wall. But are you sure that this still holds if your ears are effectively AT and PART OF the boundary?

The optimal seating position in many rooms is 38 or 62% of the length.

No argument on that, but it is not the (strange) case under consideration here.

 

[Dal1as]

You can test this yourself by either grabbing the rear of each ear and pulling them forward like Dumbo ears. Or just cupping your hands behind each and facing them forward.

Or maybe tape giant cardboard boxes to your head.

Take pics of course.

As for the answer well it depends but it would obviously change the frequency response and amplitude of the signal source.

 

[Astoneroad]

Or maybe tape giant cardboard boxes to your head.
Take pics of course.

Ok... now what?

 

[-Matt-]

This is why I posed it as a thought experiment!

Of course I don't plan to actually try burying my head in the wall (even if some comments here may make me want to)!

I'm interested to discuss if the well known benefits of a baffle wall arrangement at the speaker boundary could somehow be extended to the listener boundary.

 

[-Matt-]

You can test this yourself by either grabbing the rear of each ear and pulling them forward like Dumbo ears. Or just cupping your hands behind each and facing them forward.

In fact, this can sometimes make a significant improvement.

I once attended a stadium concert and was seated high up, a few meters from the concrete outer wall and beneath an awning. The bass boom was so powerful that it sounded awful. Cupping my ears did make a large improvement - although probably made me look a bit funny.

 

[Dal1as]

In fact, this can sometimes make a significant improvement.

I once attended a stadium concert and was seated high up, a few meters from the concrete outer wall and beneath an awning. The bass boom was so powerful that it sounded awful. Cupping my ears did make a large improvement - although probably made me look a bit funny.

I recently went to a Maiden concert with the wife and my 17 year old musician son. We used these nice musician earplugs which helped a lot and the production was done really well. My son had a blast but had to critique and talk about changes in speed, beats, and a bunch of other musical bliss. He was in heaven so I obliged him and In order to hear what he was saying I would cup my ears with my hands when facing him. We held conversations all through the concert no problem.

 

[-Matt-]

The problem I described was not so much the overall level (although it was very loud). It was the balance between bass and higher frequencies. (Not sure if plugs help with that)?

I seemed to be sitting at just the wrong distance from the rear wall so that there was a huge boost in the bass that overpowered everything else. Cupping the ears seemed to allow me to get proportionally more of the direct sound at higher frequencies and less of the bass reinforcement from behind. (Just slightly, but it was enough to make quite a noticable improvement to the balance).

Lesson learned - If I ever go to another concert there, I'll try to get standing tickets.

Anyway, the experience emphasised the importance of LBIR to me, which probably has something to do with why I'm pondering the thought experiment above.