How to think about room correction settings like frequency range and gain?

[dominikz]

Before I followed your recommendation and when I did a RC measurement I placed my bookshelf speakers 5 cm from the back wall. But after the RC results I brought them back to the original position( 25 cm from the back wall). But although the sound result was great,if I read your post I think that was a a mistake, I had to keep my speakers 5cm from the wall. Right?

That is correct, you should keep your loudspeakers at the position where they were when you ran RC.
The resulting correction anyway only applies 100% to that placement. If you move your loudspeakers you should re-run RC as well.
There's no harm to experiment a bit with placement and run RC several times - it is actually a good way to see in practice how the dips move in frequency depending on loudspeaker distance from the various surfaces surrounding it (walls, floor, ceiling).

How would you measure the distance of a subwoofer from the wall? They tend to be deeper than main speakers and some are downward firing.

The rule of thumb is to measure from the center of the driver to the wall. Assuming most subwoofers are <60cm deep, if you place them against the wall even in worst case with the driver being about 60cm from the wall (i.e. sub with a front-facing driver) the first SBIR null/dip will be around 150Hz, so well above the typical crossover frequency of 80Hz.

So you do have some leeway with subwoofer placement, but with an 80Hz crossover the driver should definitely be less than ~1,1m from hard reflective surfaces (walls, floor, ceiling) to avoid SBIR.

If RC is used I will usually recommend corner placement for subs, because that results in very significant bass boost which provides IMHO very beneficial headroom, especially since the resonant peaks are easily knocked down by negative-gain PEQ.
Remember that it is easier to deal with peaks (we can do it with EQ) than it is to deal with dips/nulls (for this we need to optimize placement).

if the subject has already been pointed out in a much lighter way than your post...
the problem is your message will quickly get lost in limbo...
perhaps it would be good to create a section dedicated to these in-depth subjects, and rather synthetic...without necessarily dialogue etc...
but grouping this kind of message where everyone can browse and learn...


(there are in fact quite a few subjects covered by professional brands like Genelec Neumann etc...their sites often need to be dug for the literature, test signals that they offer)
;-)

Thanks! It is true, these kinds of post will quickly get buried in any kind of thread.

The usual issue is that, even if you make them a sticky / FAQ article, most people won't find them or be willing to read them carefully.
As you said yourself, a lot of this information is freely available around the net, but it is still unknown to most people. So many of us find ourselves writing posts with similar content many times over.

On the upside, I do believe that answering specific questions can help spread general knowledge more easily. So I don't really mind too much repeating the same information now and again.

 

[slartibartfast]

That is correct, you should keep your loudspeakers at the position where they were when you ran RC.
The resulting correction anyway only applies 100% to that placement. If you move your loudspeakers you should re-run RC as well.
There's no harm to experiment a bit with placement and run RC several times - it is actually a good way to see in practice how the dips move in frequency depending on loudspeaker distance from the various surfaces surrounding it (walls, floor, ceiling).


The rule of thumb is to measure from the center of the driver to the wall. Assuming most subwoofers are <60cm deep, if you place them against the wall even in worst case with the driver being about 60cm from the wall (i.e. sub with a front-facing driver) the first SBIR null/dip will be around 150Hz, so well above the typical crossover frequency of 80Hz.

So you do have some leeway with subwoofer placement, but with an 80Hz crossover the driver should definitely be less than ~1,1m from hard reflective surfaces (walls, floor, ceiling) to avoid SBIR.

If RC is used I will usually recommend corner placement for subs, because that results in very significant bass boost which provides IMHO very beneficial headroom, especially since the resonant peaks are easily knocked down by negative-gain PEQ.
Remember that it is easier to deal with peaks (we can do it with EQ) than it is to deal with dips/nulls (for this we need to optimize placement).


Thanks! It is true, these kinds of post will quickly get buried in any kind of thread.

The usual issue is that, even if you make them a sticky / FAQ article, most people won't find them or be willing to read them carefully.
As you said yourself, a lot of this information is freely available around the net, but it is still unknown to most people. So many of us find ourselves writing posts with similar content many times over.

On the upside, I do believe that answering specific questions can help spread general knowledge more easily. So I don't really mind too much repeating the same information now and again.

When I tried putting the sub in the corner it didn't make a noticeable difference. One of the walls was just plasterboard if that makes a difference.

 

[dominikz]

When I tried putting the sub in the corner it didn't make a noticeable difference. One of the walls was just plasterboard if that makes a difference.

It very well might, how much energy the wall absorbs/transmits/reflects at each frequency range will depend on its construction specifics. Drywall typically transmits low frequencies relatively efficiently (here's some examples), meaning that it won't reflect all of the low bass energy back in the room.

Theory says that by placing a sub in a corner will give you +18dB boost in the bass compared to free space (example), because the same amount of sound radiates into only 1/8 of the surface.
However that assumes that the surrounding surfaces are infinitely rigid and perfectly reflect the sound at any frequency. That is of course never the case in practice (though it is definitely close for thick concrete walls).

Another thing that happens if you place the sub in a corner is that it will maximally excite all of the strongest room modes.
That would be bad if you didn't use EQ, but is perfectly fine if you do because you gain headroom and you can easily knock down the resonance peaks with PEQ.

 

[canard]

a

That is correct, you should keep your loudspeakers at the position where they were when you ran RC.
The resulting correction anyway only applies 100% to that placement. If you move your loudspeakers you should re-run RC as well.
There's no harm to experiment a bit with placement and run RC several times - it is actually a good way to see in practice how the dips move in frequency depending on loudspeaker distance from the various surfaces surrounding it (walls, floor, ceiling).


The rule of thumb is to measure from the center of the driver to the wall. Assuming most subwoofers are <60cm deep, if you place them against the wall even in worst case with the driver being about 60cm from the wall (i.e. sub with a front-facing driver) the first SBIR null/dip will be around 150Hz, so well above the typical crossover frequency of 80Hz.

So you do have some leeway with subwoofer placement, but with an 80Hz crossover the driver should definitely be less than ~1,1m from hard reflective surfaces (walls, floor, ceiling) to avoid SBIR.

If RC is used I will usually recommend corner placement for subs, because that results in very significant bass boost which provides IMHO very beneficial headroom, especially since the resonant peaks are easily knocked down by negative-gain PEQ.
Remember that it is easier to deal with peaks (we can do it with EQ) than it is to deal with dips/nulls (for this we need to optimize placement).


Thanks! It is true, these kinds of post will quickly get buried in any kind of thread.

The usual issue is that, even if you make them a sticky / FAQ article, most people won't find them or be willing to read them carefully.
As you said yourself, a lot of this information is freely available around the net, but it is still unknown to most people. So many of us find ourselves writing posts with similar content many times over.

On the upside, I do believe that answering specific questions can help spread general knowledge more easily. So I don't really mind too much repeating the same information now and again.

;-)

 

[Musician]

While I agree with the main points of your post (i.e. close to wall placement has drawbacks and that treating the wall with absorption can be beneficial), I'm still quite convinced this type of placement is a very good option for most people.

Let me elaborate my position.

First, it is important to understand that the early reflection from the loudspeaker to the wall behind it will cause an interference pattern with the direct sound of the loudspeaker - this is a fact regardless of the distance between the loudspeaker and the wall - i.e. close to wall placement will not eliminate the interference.

What does change as we change the distance is:

• Delay between the direct sound and the early reflection,
• Frequency where the interference pattern starts, and
• How deep the nulls / how high the peaks are in the interference pattern.

We call this interference SBIR (Speaker Boundary Interference Response), and it applies to all boundaries (walls, ceiling, floor) around a loudspeaker, not just the wall behind it.

Here's an illustration from the Genelec article I linked to previously:

The main principle is that as we move the loudspeaker further from a wall the first dip in the response will move to a lower frequency and become deeper / more severe, and as we move it closer to a wall the first dip in the response will move to a higher frequency and become shallower / less severe.

Now, let's try to be pragmatic and calculate the first few SBIR null/peak frequencies for various distances from the wall:
View attachment 19606

The top row shows how close the front face of the loudspeaker needs to be to the wall to push the first SBIR null above 20kHz (i.e. the commonly accepted human hearing limit). As you can see, the distance to achieve this is only 4mm, meaning that the loudspeaker body would need to be in the wall.

Note that this is why soffit mounting of loudspeakers (i.e. installation where the loudspeaker front face is flush with the wall) is considered the ideal and is used widely in professional recording studios - when the loudspeaker front face is flush with the wall the SBIR frequencies will go to so high a frequency they will effectively be out of the human audible range.​

In other words, no box speaker can go that close to the wall behind it in most practical scenarios because the typical bookshelf speaker box depth is usually 30-50cm. Here I assume most people won't be willing to do construction work to place their speakers.
If we also assume additional ~5cm distance for back port to work properly, the realistic distance for many people will be 35-55cm from front face of the loudspeaker to the wall behind it. As you can see from the table will put the first SBIR null/dip between about 150-300Hz.

The table above should also illustrate that by pushing the loudspeaker away from the wall we push the SBIR interference to a lower frequency and spread it over a wider frequency range.

As you can see, having the loudspeaker more than about 0,6m from the wall behind it will put the first/main SBIR null/dip right in the upper bass (80-150Hz), where a lot of the energy is in many mixes. This dip will also be more severe (i.e. deeper) than the one caused by closer to wall placement.

This is why placing loudspeakers such that their front face is >0,6m from the wall behind is usually not recommended. This is also why for full-range loudspeakers (i.e. loudspeakers used without subwoofers) it is recommended to place them close to the wall behind them.

Now notice that for speaker placement >1,1m from the wall the first SBIR dip gets below ~80Hz.
If you have your loudspeakers high-passed at 80Hz (e.g. because you have a subwoofer with 80Hz crossover) then in this case the first SBIR dip goes out of the operating range of the loudspeaker - which is great! While this doesn't solve the subsequent SBIR peaks and dips, the 1st dip is the deepest and the most audibly offending.

This is why speaker placement >1,1m from the wall is recommended for systems crossed to a sub at 80Hz. In this case the sub is recommended to be placed as close as possible to a wall to keep the subwoover SBIR null/dip above 80Hz. In this way the main SBIR nulls of both the loudspeakers and the subwoofer are outside of their operating ranges - making this the second-best placement option (i.e. behind soffit mounting loudspeakers).

However, the problem with this is that having loudspeakers >1,1m into the room is quite intrusive and not really an option for most people for practical reasons.
Note that pushing the loudspeakers close to the wall behind is still an acceptable (but slightly worse) alternative, for the same reasons as explained above. It may be an acceptable compromise to many for practical reasons.

As we can see, neither placement option 1 (soffit mounting loudspeakers) nor option 2 (loudspeakers >1,1m into the room + a well integrated subwoofer) may be practical for most people.
On the other hand, placement close to the wall behind is a reasonable compromise that works similarly well with and without subwoofers, and is not physically intrusive.

Now let me come back to your suggestion to add acoustic treatment to the back wall. The intention here would to absorb the early reflection from the back of the loudspeaker and thereby avoid the SBIR interference altogether.

First, let's see how the back reflection spectrum actually looks like compared to the direct sound for two different box-type front-firing loudspeakers (blue is the direct sound, green is the back reflection, solid lines belong to speaker 1, and dashed lines belong to speaker 2; source):
View attachment 19607
Since most commercial loudspeaker designs are not omnidirectional, the spectrum of the back reflection will be decreasing with frequency - which is what we see in this plot too for both speakers. The slope of this decrease depends on loudspeaker directivity - wide directivity designs (speaker 1) will decrease slower, while narrow directivity designs (speaker 2) will decrease faster with frequency.

We can see that in both speakers by about 1000Hz the back reflection is already attenuated by about -10dB compared to the direct sound. This explains why we see that SBIR interference becomes less severe as it is pushed up in frequency - the back reflection has less energy and therefore less influence on the total sound heard at the main listening position.

This also means that if we are to try and absorb the back reflection we need absorbers that have high absorption below 1000Hz, and especially high absorption at the frequency of the first / main SBIR null.

On the other hand, typical porous absorbers work well at high frequencies but poorly at low frequencies. So if we wish to have any theoretical chance of minimizing the SBIR dip via acoustic treatment we need to push the loudspeaker close to the wall behind so that the SBIR null goes as high as possible in frequency.

Now let's looks at the sound absorption coefficient of some commonly used acoustic panels (source):

As you can see, even 10cm thick acoustic foam is not very efficient <300Hz, and such thickness won't even fit behind the loudspeaker if we pushed it close enough to the wall to put the SBIR dip >200Hz.
Mineral/glass wool panels are much more efficient at these frequencies, but again the thickness required to be efficient <300Hz make them difficult to place behind a loudspeaker when placed close to the wall behind.

If you push the loudspeaker further from the wall you will be able to place thicker absorption panels, but then the SBIR dip will move lower in frequency and unfortunately it will again end up below the panel operating range.
While perhaps not impossible, this should illustrate that absorbing the back reflection will be challenging at the very least.

Not to mention that most people probably don't want to have 10cm thick acoustic panels in their living rooms...

Having all of the above in mind, I stand behind my recommendation to place loudspeakers close to the wall behind them. It is IMHO a reasonable compromise that sounds quite good (even if not the best), while not being very intrusive in residential spaces.

At this point it is perhaps worth to mention cardioid bass loudspeakers. These are designed to minimize the level of the back reflection in the 100-300Hz range (example), and thereby decrease SBIR null/dip severity for close to wall placement. They are an amazing solution to these issues for residential spaces, but are unfortunately still quite expensive.

So to summarize, my placement recommendations are as follows:

• The generic recommendation is to put loudspeakers close to the wall behind.
  • It is simple, sounds good and is non-physical-intrusive, but also not ideal.
• For those that don't want compromises the following "better" options exists (from "best" to "worst"):
  1. Soffit mounting loudspeakers
  2. Cardioid bass loudspeaker placed close to a wall
  3. Front-firing loudspeakers <1,1m away from walls and integrated to subwoofer(s) crossed at 80Hz
  4. Front-firing loudspeakers close to the wall behind and try to absorb the SBIR dip

Hope this is useful!


Again I can agree only partially.
DSP will not solve everything, this I agree with completely, and I also agree that people shouldn't expect that using DSP/RC will magically solve all acoustic problems - regardless of how it is sometimes marketed.

But even in case of less-than-ideal placement DSP can solve some very audible issues and thereby improve the sound significantly. Note that we're much more sensitive to peaks than dips, so addressing peaks has huge value and DSP is pretty well-suited for that task. I disagree that this is a waste of time.

However a big issue with automated room correction / DSP is that it can also try to correct issues that simply aren't there and thereby can also make the sound significantly worse. Unfortunately we're still at a point where significant competence is needed from the end-user to tune the settings to make it work well. This is definitely why it can feel like a waste of time.

Finally, I fully agree that optimizing placement/layout and then carefully applying DSP is the optimal solution. This is perhaps great news for us audio enthusiasts, but I'm sure it is really discouraging for casual users who probably just want audio systems that are easy to setup and use and just sound good.

That was good teaching, thank you !
By the way, Im an enthusiast who always listen at sweet spot, and I like the colorations with loudspeakers placed a bit out from the frontwall, getting some SBIR and this might help filling out some of the quirks from the very flawed stereo system. Theres no perfection to be had with only two loudspeakers with stereo material ( as you know ). My reference is also not the monitor sound used in the studio, but real acoustical instruments in the concert hall. My listening philosophy is not an ”open window” to the recording, its more like a ” live sound illusion”.

When I constructed my threeway diy loudspeaker with dsp crossovers, I did a lot of measurements , did a lot of reading and learned a lot by doing all the mistakes a beginner could ever make. The conclusion I made after that adventure ( and having expensive SAM monitors for two years ) was that a perfect measuring mono loudspeaker didnt sound quite as good in a stereo setup.

 

[dominikz]

That was good teaching, thank you !
By the way, Im an enthusiast who always listen at sweet spot, and I like the colorations with loudspeakers placed a bit out from the frontwall, getting some SBIR and this might help filling out some of the quirks from the very flawed stereo system. Theres no perfection to be had with only two loudspeakers with stereo material ( as you know ). My reference is also not the monitor sound used in the studio, but real acoustical instruments in the concert hall. My listening philosophy is not an ”open window” to the recording, its more like a ” live sound illusion”.

When I constructed my threeway diy loudspeaker with dsp crossovers, I did a lot of measurements , did a lot of reading and learned a lot by doing all the mistakes a beginner could ever make. The conclusion I made after that adventure ( and having expensive SAM monitors for two years ) was that a perfect measuring mono loudspeaker didnt sound quite as good in a stereo setup.

It is great that you found a solution which works for you and helps you enjoy the music you like!

My own experience with loudspeakers that measure well in mono was always positive in stereo as well.

 

[Adam205]

Cieľová krivka: B&K

 

[Adam205]

How does my curve look? Is it okay?

 

[Wiimer]

Ako vyzerá moja krivka? je to v poriadku?

Could you please post it in English?
Thanks.

 

[onek00lj4y]

This is the best for learning about room correction god I love my wiim Pro thanks guys this info is fantastic for a newbie to me, way better than trying to understand youtube vids this wiim forum is the best.

 

[dominikz]

How does my curve look? Is it okay?

It looks OK, though I'd suggest to use the "Individual Channel Room Correction" when the option is presented. That will give you a bit more bass.

Judging from the massive peak at 8kHz I assume you used the smartphone built-in mic to measure, right?
You would get a more reliable measurement and correction with an external calibrated measurement microphone; however the practical difference might or might not be significant. No way to know.

Most importantly, if you are happy with the result, it is good.