Speakers too close to wall, what effect will this have?

[question]

I am having trouble in my (small) studio room at 105 Herz, about A flat.
There is an uncomfortable resonance and increase in volume around this pitch which makes it difficult to mix.
Due to the small size of the room, I am unable to get my Klein & Hummel 0300D Monitor speakers away from the wall.
I have had the room anylized and done some treatment; 4 corner bass traps, a cloud hanging over my mix position as well as carpet on the floor and absorbers on the wall behind me. A big improvement.
I write film music and mix at a fairly low volume level.
My question, could the proximity of the speakers to the wall cause such a specific frequency boost?
Can a room this size, (2 meter 75 X 4 meter 20) sound good?
Unfortunately, I am set up on the long wall. This means that the distance from the speakers to the back wall (with absorbers) is only about two and a half meters.
I tested the boxes in another room and this problem is eliminated, therfore it is surely the room. Any wisdom would be appreciated!

[drBill]

Originally Posted by question

My question, could the proximity of the speakers to the wall cause such a specific frequency boost?

I think you already answered your own question, but yes, it absolutely affects the sound when you place a speaker close to a wall. Accentuated bottom end. Getting a small box of a room to sound good is a challenge.

[el cochino]

Put some bass traps behind the monitors - stuff like RealTraps doesn't take up much room but works great. I have a very small room, too, and the Mini Traps made a big difference in how my mixes translate outside the studio.

[question]

Thanks for the reply El Cochino.
Do you mean directly "behind" the speakers? That is my problem, there is no "behind" due to the lack of width in the room. Or do you mean somewhere on the back wall not directly behind the speakers? If you have a solution, please explain how you solved this problem. I don't have 8 centemeters of space to spare.

[big country]

do you have room to fly your monitors?

my space is hella small def.not high end either

but In a small room flying the monitors seems like the only way

not sure this will solve your problem

[drBill]

Originally Posted by question

Thanks for the reply El Cochino.
Do you mean directly "behind" the speakers? That is my problem, there is no "behind" due to the lack of width in the room. Or do you mean somewhere on the back wall not directly behind the speakers? If you have a solution, please explain how you solved this problem. I don't have 8 centemeters of space to spare.

By behind, yes, he means behind. And still, there are coupling issues at play. Not the best situation to have your speakers up against a wall. some speakers have switches on the back for placement in a corner or up against a wall that rolls off bottom end. JBL's coome to mind...

[yarrick19]

From Genelec's website: (Genelec Inc. - Placing free-standing control room monitors)

Wall reflections interfere with the direct sound
A free standing speaker is usually surrounded by boundaries that generate reflections(walls, the ceiling and the floor). These boundaries act as acoustical mirrors to the speaker's radiation, enhancing or cancelling the direct sound, depending on the phase difference between the reflection and the direct sound at the listening position.

The problems of boundary refelections diminish as the frequency increases. This is because the directivity of a conventional loudspeaker increases with frequency. This is why the boundary reflections mostly cause problems at low frequencies.

The most common problem at low frequencies is the interference between the speaker's direct radiation and the reflection from the wall behind the speaker. At low frequencies this reflection is in phase with the direct sound. The phase of the reflected sound lags more as the frequency increases.




Figure 1. Wall behind the speaker induced low frequency cancellation.

Finally, at some frequency the reflection will be delayed so much as to be in opposite phase relative to the direct sound. Depending on the relative amplitudes of the direct and reflected sounds, a cancellation dip (typically 6...20 dB deep) will occur in the frequency response (figure 2).


Figure 2. The frequency response dips caused by a wall reflection.

To overcome this problem we can position the speakers far enough from the wall to move the first order interference dip below the lower cut-off frequency of the speaker. To move the dip down to 30 Hz, the distance needed is 2.8 meters.

Note that when you have a stereo pair, they must have exactly similar frequency responses to produce exact and accurate stereo imaging. The boundary reflections change the frequency responses of the speakers differently if they are at a different distance from the boundaries. You should take great care to place the loudspeaker pair to an exact symmetry in the listening room to maintain similar frequency responses for both speakers. This also implies that the listening room itself should be symmetrial along the axis between the speakers to fulfill this requirement. This is usually true for modern control room designs.

The second method is to push the speaker as close to the wall as possible to decrease the time delay of this reflection relative to the direct sound. This moves the interference problem to a higher frequency, where the speaker's own directivity decreases the rearward radiation and in this way the amplitude of the reflected sound attenuates effectively relative to the direct sound. Then, you should compensate the resulting boost of the bass frequencies by using the room response controls.

[big country]

you could fly your monitors and make a faring that goes around your monitors made of 703

I have something like that on my set up

definitely wont get rear reflections with a set up like that

[drBill]

Originally Posted by big country

you could fly your monitors and make a faring that goes around your monitors made of 703

I have something like that on my set up

definitely wont get rear reflections with a set up like that

It's not so much reflections as it is bass buildup. I'm not technical so I can't lay it out in engineering terms, but even with a soft surface behing the speaker, if it's againist the wall it's going to have a bottom end buildup.

[emptyman]

I solved my low-end monitor bump problems by doing the following:
1. make sure there are no "nulls" at mix position (if your monitors are close enough to the wall you should be fine)
2. use parametric EQ centered at trouble frequency then use your ears to reduce boom while maintaining musicality (I recommend using a calibration mic for this process as well)

you likely won't be able to flatten the low boost completely BUT the improvement should be enough for your ears to adjust and allow you to make consistent mixes, especially since you monitor at low volumes. Good luck :)

[question]

Thanks for the replies. Let me rephrase this point: I don't seem to have a general problem with the bass, actually the room doesn't sound too bad. It is a specific frequency (106 Hz) that is increasing in volume and causing problems. If I play a chromatic scale, the problem starts at about "G", gets worse at "Ab"(approx. 106 Hz), and starts to taper off at "A". The tones below and above this area are fine. I read on the Real Traps website about a room having three resonances; length, height and width, I suspect that my problem is somehow related to this fact. Can a small room like this sound good? Is such a problem solveable? The Klein & Hummel 0300D boxes do have EQ switches, but this frequency is so specific that it doesn't make sense to just cut the low mids.

[aussie_techie]

can you turn your room around? it should be better to face the short wall so you enough space behind you 4.2m is still a than ideal but you may find it is just long enough that the reflection off the back wall arnt so bad

have you tried adjusting the room matching circuitry of the monitor?

[big country]

maybe it has something to do with the three way or the crossover?

[Ethan Winer]

Originally Posted by question

I read on the Real Traps website about a room having three resonances; length, height and width, I suspect that my problem is somehow related to this fact.

Yes.

Can a small room like this sound good? Is such a problem solveable?

Yes! With bass traps.

I also suggest you measure your room using our low frequency test tones, or some other high resolution method. I'll bet you $100 that your bass problems are much worse than you think, and are at more frequencies than just 105 Hz.

--Ethan

[big country]

Originally Posted by Ethan Winer

Yes.


Yes! With bass traps.

I also suggest you measure your room using our low frequency test tones, or some other high resolution method. I'll bet you $100 that your bass problems are much worse than you think, and are at more frequencies than just 105 Hz.

--Ethan

in theory if 105hz is bad the fundamental of the multiples would be bad too just to a lesser degree as the higher the freq. less powerful

105hz
210hz
420hz
840hz
all of these frequency's carry the same path
its just an issue of whats shorter and whats longer and where they end

[big country]

Originally Posted by drBill

It's not so much reflections as it is bass buildup. I'm not technical so I can't lay it out in engineering terms, but even with a soft surface behing the speaker, if it's againist the wall it's going to have a bottom end buildup.

what I'm talking about is a makeshift soffet

[big country]

unless your hearing is perfectly flat on all frequencies
a perfectly tuned room wont do you much good

plus an RTA is mono

psychoacoustics play a big role in reality
think binaural

[big country]

or it could be what ever your seting your monitors on really likes 105hz

the more that I think about it sounds like your mids and your sub
are some how combining the fundamental freq in the room

[u b k]

Originally Posted by big country

what I'm talking about is a makeshift soffet

any chance you can elaborate on this? i've been experimenting with novel approaches to decoupling and i'd love to hear any other crazy ideas people are cooking up.

i'm working on creating a controlled-reflection zone; essentially a space within a large room that is neither totally isolated from the acoustics of the bigger space, nor completely dependent upon them.


gregoire
del
ubk
.

[Ethan Winer]

Originally Posted by big country

in theory if 105hz is bad the fundamental of the multiples would be bad too just to a lesser degree

Maybe, maybe not. It depends on the wall construction, furnishings, and much more. In theory there will be resonances at those multiples (not really harmonics), but as you go higher in frequency common materials already in the room become more effective absorbers.

--Ethan

[SpiderM69]

Originally Posted by yarrick19

From Genelec's website: (Genelec Inc. - Placing free-standing control room monitors)

The second method is to push the speaker as close to the wall as possible to decrease the time delay of this reflection relative to the direct sound. This moves the interference problem to a higher frequency, where the speaker's own directivity decreases the rearward radiation and in this way the amplitude of the reflected sound attenuates effectively relative to the direct sound. Then, you should compensate the resulting boost of the bass frequencies by using the room response controls.

This is interesting for the situation you describe, and for the rest of us with small/smaller rooms.

Bass trapping, IMHO, does the trick even if monitors are too close to the wall. And maybe because of the statement above, is yet another reason why bass trapping is so important for smaller rooms.

I may get flamed for this beause it's unscientific, but I beleive the Auralex Mopads that I use make a difference, too. Even though close to the wall, the Mopads can angle your monitors down towards the listening position. This allows the rear of the monitor to not directly face the wall, but face it at an angle not only horizontally, but also vertically. I beleive that reduces rear reflections. It also reduces reflection on the wall directly behind you, although that's essentialy shifted downards, so dunno the effect of reflecting off the floor. Maybe Ethan can comment. What I do know if using them has helped solidify the image in my room.

The bottom picture on this page shows what I'm talking about re: the Mopads:
MoPAD Monitor Isolation Pads - Acoustic sound isolation products from Auralex Acoustics.

[question]

Thanks for the responses. My Klein & Hummel monitors are mounted from the sides in a "U" shaped bracket designed for these speakers, completely isolating them from the table etc. This is not the problem.

After reading on the Real Traps website, I am starting to believe that the 4 tall triangle shaped foam bass traps that I mounted in the rear corners are not absorbing the low frequencies adequately. I am not sure of the brand, I imported them from the US.

Does anyone have direct experience comparing the effectiveness of Ethan Winer's mini traps with this sort of foam type? I am sure that Ethan has measured the results, so if you are reading this, how do they compare?

[big country]

could be something else that resonates that freq

for example if my dog barks my 12 string guitar starts making noise

[Marineville]

Originally Posted by big country

if my dog barks my 12 string guitar starts making noise

If I play harmonica my dog starts making noise ...

[Ethan Winer]

Originally Posted by SpiderM69

TI beleive the Auralex Mopads that I use make a difference, too ... Maybe Ethan can comment.

Speaker decoupling is useful when the desk they rest on vibrates and resonates, but decoupling solves a very different problem than what bass traps do. Bass traps are always needed regardless. Even in well-proportioned rooms.

the Mopads can angle your monitors down towards the listening position.

This is usually frowned on. The speaker height should be such that the tweeters are at ear level when pointed straight ahead. Angling is a compromise that's best avoided.

--Ethan

[Marineville]

Originally Posted by Ethan Winer

The speaker height should be such that the tweeters are at ear level when pointed straight ahead. Angling is a compromise that's best avoided.

--Ethan

Interesting ... I found the best listening position for the Klein + Hummel 0300s I am auditioning is above the Mac screens and angled down towards me.

[Ethan Winer]

Originally Posted by Marineville

Interesting ... I found the best listening position for the Klein + Hummel 0300s I am auditioning is above the Mac screens and angled down towards me.

But how do you define "best?"

I probably should have clarified above, but the main issue is that the response at your ear changes with small head movements forward and back. Now, if you have an untreated or under-treated room, maybe some anomaly is reduced with positioning above your ears. Without seeing a photo of your setup it's difficult to judge. But in the grand scheme of things, having the tweeters level with your ears is the best arra