Is "room correction" such as Dirac, ARC, audyssey actually correcting for the room?

[vintologi]

From what i have learned the only proper way to actually correct the room is to change the actually change the room accoustics itself, you don't have to build a full anechoic chamber to get significant benefits there.

The main thing EQ is good for is correcting for flawed speakers and as we have seen often even very expensive speakers have inaccurate frequency response. Buyers are often in denial about this and it seems like the makers of "room correction" software play along by pretending the room was the only problem. People naturally do not want to hear how the speakers they spent 20000$ on aren't very good.

It's very rare for speakers to be within ±1 dB in terms of frequency response, it's very much achievable even without any EQ but then you have to use expensive drivers and audio companies rather spend that on marketing instead for the most part.

I can see very advanced software being beneficial if you have extra channels that is controlled by the software but that would require extra speakers which is more expensive than simply fixing the room (if the speakers are very high end).

 

[Apesbrain]

Designing and building a perfect room is ideal, but not a reality for most of us. All rooms have nodes where certain audio frequencies are reinforced or attenuated. "Room correction" can be used to even out those peaks and valleys.

This is true regardless of your choice of speakers, although some influence on this can be had in proper placement of speakers within the room.

 

[staticV3]

Yes, room correction like Dirac, Audyssey, etc is actually correcting for the room.

If you took a pair of perfect speakers and ran Dirac on them, then you would see a lot of correction being applied to smooth out room modes.

 

[voodooless]

Also, these tools are more that just EQ. They can also correct for time alignment issues, and can also help with reducing some reflections. This only works in within a limited sweet spot though where they can cancel out.

 

[Philbo King]

It corrects for room response in a very limited seating area.

 

[vintologi]

It corrects for room response in a very limited seating area.

Does it even fully correct it there?

I hear amir say that the brain actually differentiates between direct sound and reflections and if this is true "room correction" would actually mess up the direct on-axis response assuming the issue is with the room and not the speaker.

I guess it works better at low frequencies such as 10hz.

 

[Philbo King]

Does it even fully correct it there?

I hear amir say that the brain actually differentiates between direct sound and reflections and if this is true "room correction" would actually mess up the direct on-axis response assuming the issue is with the room and not the speaker.

I guess it works better at low frequencies such as 10hz.

Yeah, it's only useful below the Schroeder Freq.

 

[voodooless]

Does it even fully correct it there?

No. You cannot correct nulls for instance.

 

[Tim Link]

In any case where the direct sound and reflected sound merge soon enough the result is a single new impulse with a phase shift, and the ear/brain will not distinguish between the direct and reflected sound. I think you can see this on the spectrogram in REW. You can also see where late reflections appear as distinct new entities. The higher the frequency, the sooner a distinct, separate reflection can be seen.

Somebody feel free to correct me if needed.

At low frequencies the room and speaker kind of merge into a new device. At what frequency this happens depends on how soon early reflections arrive compared to the initial signal. The room correction experts I've been listening to do not try to change the speaker's output above a certain frequency, and then gradually bring in corrections as the frequency goes down, depending on the transition frequency of the room in question. Corrections for the whole room can probably only occur at the lowest frequencies. For a specific listening position it can be higher. Determining just what to correct and what not to is a bit of an art, with some scientific concepts as guidelines.

One area of significant percieved improvement at a specific listening position is stereo sound stage. This really only works best in the sweet spot so I think it's worth pursuing, making the left and right step response at the prime listening position as similar as possible. I like what I hear when I do that. My room causes a particularly bad early cancel in the left speaker, followed by a 20ms late arrival from a further reflection. FIR brute force can fix that by sending out a pre-signal and then delaying everything else by 20ms. This results in a slight pre-echo around the problem frequency, but the improvement is very much worth it to my ears. In other parts of the room it doesn't cause the sound to get any worse as far as I can tell. It's already imbalanced left to right anywhere off center so now it's just imbalanced differently.

Shooting for ultra flat response at the listening postion might be taking it too far. In my case, I can't seem to reliably get the same result day to day, and that's with positioning the mic. very carefully using a laser. Last night and this morning I see significant frequency response difference, which is baffling to me. I'm sure the mic is within 1/4" in any direction of where it was last night, still at 90 degrees, and still using the 90 degree calibration file. Sometimes I can get measuremetns to match very closely day to day. Other times I can't. I don't know why the green measurement this morning has extra energy at 35Hz and about 600Hz and up toward 20kHz. Temperature and humidity changes?

The phase correction still seems to be holding.

 

[Keith_W]

Shooting for ultra flat response at the listening postion might be taking it too far. In my case, I can't seem to reliably get the same result day to day, and that's with positioning the mic. very carefully using a laser. Last night and this morning I see significant frequency response difference, which is baffling to me. I'm sure the mic is within 1/4" in any direction of where it was last night, still at 90 degrees, and still using the 90 degree calibration file. Sometimes I can get measuremetns to match very closely day to day. Other times I can't. I don't know why the green measurement this morning has extra energy at 35Hz and about 600Hz and up toward 20kHz. Temperature and humidity changes?

In my experience, changes that occur between measurements may be due to:

- Measurement volume creating harmonic distortion. You usually see this in the upper frequencies depending on what is distorting - e.g. a heavily distorting woofer at 100Hz has 2nd and 3rd harmonics at 200Hz and 300Hz; a distorting tweeter at 5kHz has harmonics at 10kHz and 15kHz.
- Ambient noise. This usually causes a bass lift.
- Improper measurement technique. e.g. MMM's which are done too fast can pick up wind noise (again manifests as bass lift). You need to pay attention to the cable slapping on the mic stand. Poor microphone placement near reflecting surfaces, e.g. the mic stand itself can reflect high frequencies to an omni mic. If you measure with obstructions in the way, e.g. listening sofa, the distance of the mic from the sofa can affect the measurement.
- Sweep length. The noise rejection of the sweep can be improved by averaging several sweeps, or by increasing the power of the sweep. You can increase the power by increasing its height (volume) or width (longer sweep time). Increasing the volume of a sweep brings risk of harmonic distortion, loudspeaker or amplifier damage, etc. For this reason I prefer longer sweeps. A 45s sweep has up to 90dB of noise rejection.

We all know from personal experience that our systems sound different in the evening and in the day. The difference is due to ambient noise. I think many of us usually listen louder during the day and turn the volume down at night, and it's not just to avoid disturbing neighbours. It is because there is so little ambient noise that volume is not needed to hear soft detail. I used to do the same with measurements - turn up the volume to improve the SNR, but this may introduce distortion. Then we have both noise and distortion affecting the measurement. These days I only measure at night where I use a low volume to avoid distortion, and take a long sweep to reject ambient noise.

Temperature and humidity affect the speed of sound, but if you do the maths, it won't change the measurement by much. It will affect all measurements that are influenced by the speed of sound, e.g. time alignment, port tuning frequency, Schroder frequency, and so on. I have heard about some paper cone drivers being affected by ambient humidity but I have never seen and measurements that corroborate that claim.