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Comment by patrakov | Hacker News Reader

Well, the author could do more research.

There are HiFi speakers that are designed to provide the correct frequency response when placed near a wall and sound wrong otherwise. "Klipschorn" would be an extreme example of this category.

There are other speakers (actually the majority) that are not designed to be placed against a wall, but, if you use digital room correction features in your HiFi receiver, they still have to be placed against the wall, so that there is less work for the DSP to do.

There are also so-called "electrostatic speakers" (e.g. "Quad ESL 2912") which absolutely must not be placed near the wall, because the rear wave is in counter-phase (unlike the traditional speakers), and will cancel the front wave exactly.

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There are some problems that cannot be corrected through room correction EQ, namely the Speaker Boundary Interference Effect, which happens when the reflection from a wall is out-of-phase with the signal that you want to hear, and produces a deep valley in the frequency response.

You could try boosting at the frequency that the valley is at, but that makes both the signal _and the reflection_ equally as loud. Therefore, they cancel out in almost the same manner for basically no net gain.

Bingo, they are called room modes:

https://en.wikipedia.org/wiki/Room_modes?wprov=sfla1

Their influence can be be diminshed with absorbers, construction of a room without parallel walls or so big that they can't be heard (eg Concert halls)

>There are HiFi speakers that are designed to provide the correct frequency response when placed near a wall

Another example may be the Ohm Walsh line of loudspeakers. I've only ever heard positive things about how close-to-life it sounds, and that's accomplished with the unique upward-facing driver and using walls and corners to an advantage.

I know zero about this topic. Are there dynamic audio sensors that could provide real time adaptions to the room audio profile? Something like a light meter in photography?

That's exactly what the digital room correction is that the comment you replied to mentioned, except it's not real-time, since the profile doesn't change rapidly. You push a button to run it every time you make major room changes like moving the speakers.

Ah gotcha. Thanks!

Only for the trivial cases. You could tell if the speaker is placed in a drastically bad place, ie it sounds bad everywhere, but you wouldn't be able to tell if the speaker sounds good where the listener is. For that you need to put a microphone (which itself would need to be of relatively good quality) where the listeners ears are.

Even with measurements like that, it's pretty nontrivial to compensate for it. It's technically a proven problem[1] (solvable for some convex shapes) but its a little more complex than just adjusting the volume or phase of a given frequency. A room -and by extension all the little nooks and crannies of a room- acts as a resonator, and will gather and sustain notes. You need to counter that sustain ahead of time.

1: https://en.wikipedia.org/wiki/Hearing_the_shape_of_a_drum

oh absolutely. http://accueq.onkyousa.com/

I wonder why this is not more common.

It should take a (cheap) microphone with a known response curve and a sine wave generator to calibrate any number of speakers in a room.

Most midrange A/V receivers come with mics these days to do this sort of calibration. For example, Denon's version of this is called Audyssey http://manuals.denon.com/avrx4100w/NA/EN/GFNFSYnuokgukf.php

It's quite common, actually. Yamaha, Onkyo, Denon, Marantz all have versions of it on nearly all their home-theater receivers.

I believe apple homepods do this - “ Direct and ambient audio beamforming Computational audio for real-time tuning”[1]

[1] https://www.apple.com/homepod-2018/specs/

Beamforming is a way of taking an array of drivers and manipulating their phase and frequency response to direct the sound in a calculated direction. IE, you can have seven drivers in a ring, and you can direct the sound in ONE direction instead of ALL directions.

Amazon Alexa does the same thing, except with an array of microphones.

Ah, I figured that would help with this issue as well but I can see it’s a different thing now, thank you.

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