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Omnidirectional Speakers and Room Acoustics/Treatment

Bjorn

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I have a recommendation from an acoustician that I should use all diffusers and no absorbers due to the unique nature of omnidirectional speakers. I was also instructed not to use any treatment on the wall behind or in between the speakers.
Considering that diffusers need distance to avoid frequency lobing and comb filtering (less of problem than lobing) that's not a good recommendation that way I see it. I also very much disagree that one shouldn't use treatment on the wall behind the speakers.

Type of treatment will depend on proximity to surfaces in relation to speakers and the listening position, how much the treatment can build out, budget and design goal. But generally, diffusion alone in such a small room wouldn't work very well IMO. Diffusion requires more distance. A combination would be better. And avoid simple scattering units that will not diffuse the sound evenly.
 

Bjorn

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Omnidirectional speakers sound best with little to no treatment.
I disagree. No speaker sounds great with a lot of high gain early arriving reflections. Reflections need to be delayed in time to avoid being too detrimental, and that isn't possible in a small room with omnis or other speaker designs for that matter. You need more treatment with an omni speaker in a small room compared to a speaker with a narrow directivity.

There have been hifi shows where MBL satelite speakers were suppose to play in a small room and they ended up not playing at all but only showing the speakers because it sounded so bad.
 

nerdoldnerdith

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I disagree. No speaker sounds great with a lot of high gain early arriving reflections. Reflections need to be delayed in time to avoid being too detrimental, and that isn't possible in a small room with omnis or other speaker designs for that matter. You need more treatment with an omni speaker in a small room compared to a speaker with a narrow directivity.

There have been hifi shows where MBL satelite speakers were suppose to play in a small room and they ended up not playing at all but only showing the speakers because it sounded so bad.
Yeah, they sound best in a large, untreated room.

My Morrisons are currently set up in my living room, which has now been treated for my Genelecs. They definitely sounded better without the treatment.
 

Bjorn

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Yeah, they sound best in a large, untreated room.

My Morrisons are currently set up in my living room, which has now been treated for my Genelecs. They definitely sounded better without the treatment.
A more uneven frequency response, high gain specular reflections and flutter-echo doesn't give a better result. It's more likely the treatment wasn't good for the speaker.

In many cases it is because it can be too bandlimited, certain frequencies are over dampened, treatment are placed incorrectly in regards to the speakers directivity, the spectral content is changed, so called diffusers don't really diffuse, using 2D diffusers when it should have been 1D diffusers, perhaps the bass traps don't work much at lows at all and only absorps mids and highs which isn't preferably, or there's a need for another type of design criteria for the speaker or the listeners taste (i.e. more diffused energy).

No treatment migh be better than poor treatment but it's nothing like good treatment. Saying that no treatment is better is basically saying that one prefers an uneven frequency response, a more muddy and boomy bass with strong resonances, and frequencies that sticks out in the time domain.
 

Hipper

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There seems to be a lot of contradictory advice. I've no real knowledge of omni speakers. All I've read is that they throw out sound at all frequencies in all directions (compared to the typical box speaker which I use where the bass frequencies are omni-directional but the higher ones are more direct but still reflect off walls etc.).

I would guess people buy omnis because of their special characteristics.

Bass will be an issue whatever your speaker type because all speakers interact with the room in these frequencies. The only part of your room that matters when listening is your listening position (LP). However if you walk around your room listening to bass you will hear it sound different in different locations and that illustrates that moving your speakers and LP will affect the bass you hear, hence the need to carefully position them. I need bass traps for my box speakers and my guess is you would need them for your omnis. Correcting bass is the biggest challenge and can be done in four ways:

1. Careful positioning of your speakers and LP.
2. Bass traps.
3. One or more subwoofers.
4. DSP/EQ.

You can use any or all of these methods depending on your circumstances. I use positioning, bass traps and EQ.

Once the bass is dealt with it allows the rest of the frequencies to be clearer and that's where the real music is. If you have an echoey sound, that will be caused by reflections. These can be controlled by:

1. Absorption at specific locations.
2. Toe-in to some extent.

They cannot be really dealt with by DSP/EQ although you can use this to smooth the frequency response to some extent. The reason is that it is difficult for a microphone to distinguish between the direct sound from the speakers and sound reflected. It simply adds them up when they arrive at the mic.. Your ears/brain act differently - see psychoacoustics.

Diffusion, as has already been mentioned, needs a certain distance from the listener to work well.

I use absorbers to reduce reflections. My preference is for no reflections as I find this gives me sharp imaging - vocals strongly centred and the rest of the music spaced between the speakers with some but not much depth - all depending on the quality of the recording. I do not get an image outside of my speakers unless there's some recording peculiarity.

In your situation I would try and find a forum of your speaker owners and see what they suggest.
 

nerdoldnerdith

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Just going by personal experience, my omnidirectional speakers sounded best when there was no room treatment. They were calibrated to have a flat frequency response in the untreated room and they have been calibrated to have a flat frequency response in the treated room.

My speakers were designed to reproduce the sound of live music playing in a room, as if the instruments and musicians were actually in the room. They aren't designed to reproduce the space of the room. Real live, unamplified music doesn't require special acoustic treatment to sound good in a room. A real piano or a real guitar sounds best when played in a regular room where sound can bounce around and bring the music to life.
 

Hipper

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Just going by personal experience, my omnidirectional speakers sounded best when there was no room treatment. They were calibrated to have a flat frequency response in the untreated room and they have been calibrated to have a flat frequency response in the treated room.

My speakers were designed to reproduce the sound of live music playing in a room, as if the instruments and musicians were actually in the room. They aren't designed to reproduce the space of the room. Real live, unamplified music doesn't require special acoustic treatment to sound good in a room. A real piano or a real guitar sounds best when played in a regular room where sound can bounce around and bring the music to life.
I'm not sure about what you say about unamplified live music being played in untreated rooms applies all the time or even most of the time. Often venues are treated in some way and some sort of DSP/EQ may be used. If you listen to any recordings they will have been processed via a mic or mics (micing recordings seems to be an art in itself) and using some sort of DSP or other recording techniques. The producer/engineer will no doubt have some target audience.

In any case playing live music and playing recordings of live music is not the same thing for two reasons:

1. Our listening rooms are usually smaller, sometimes much smaller. Small room acoustics are different.
2. A live recording if done well will capture the music plus the room it's played in - for example a cathedral. When replaying this in a small room not only do you get the recording from the direct sound from the speakers but also any reflections developed in your room, such as side wall reflections.

For these reasons I'm convinced some sort of room treatment is needed to extract the best from the recordings after they leave your speaker (whatever your speaker type) and enter the room on the way to your ears. Sure the brain can do a lot of work to filter out stuff but if it doesn't have to do that work I feel we can get more into the music in a relaxed and enjoyable way.

All this is described in Floyd Toole's opus, 'Sound Reproduction' as part of the 'Circle of Confusion' that we listeners have to wade through.

However, your personal experience trumps all and if you enjoy what you hear in your circumstances, that is the main point of the exercise.
 

nerdoldnerdith

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I'm not sure about what you say about unamplified live music being played in untreated rooms applies all the time or even most of the time. Often venues are treated in some way and some sort of DSP/EQ may be used. If you listen to any recordings they will have been processed via a mic or mics (micing recordings seems to be an art in itself) and using some sort of DSP or other recording techniques. The producer/engineer will no doubt have some target audience.

In any case playing live music and playing recordings of live music is not the same thing for two reasons:

1. Our listening rooms are usually smaller, sometimes much smaller. Small room acoustics are different.
2. A live recording if done well will capture the music plus the room it's played in - for example a cathedral. When replaying this in a small room not only do you get the recording from the direct sound from the speakers but also any reflections developed in your room, such as side wall reflections.

For these reasons I'm convinced some sort of room treatment is needed to extract the best from the recordings after they leave your speaker (whatever your speaker type) and enter the room on the way to your ears. Sure the brain can do a lot of work to filter out stuff but if it doesn't have to do that work I feel we can get more into the music in a relaxed and enjoyable way.

All this is described in Floyd Toole's opus, 'Sound Reproduction' as part of the 'Circle of Confusion' that we listeners have to wade through.

However, your personal experience trumps all and if you enjoy what you hear in your circumstances, that is the main point of the exercise.
I have some of best monopole speakers and very good omnidirectional speakers. The way they reproduce sound in a room sounds totally different.

Most music has information about the acoustics of the room in which it was recorded and doesn't sound good on these omnidirectional speakers. The music that sounds best is dry recordings done in dead rooms with no added reverb or acoustic effects. When properly done the recording can sound like an actual piano or an actual drumset is playing in my room.

These speakers are not good for giving you a window into a different venue. Their purpose is to interact with your room the way real instruments would, which conventional monopole speakers don't do.

As a pianist myself, a piano sounds best in big open rooms with a decent amount of reverberation. Pianos don't sound very good when you play them in recording studios with good acoustics for reproducing sound. As a matter of fact, most piano music is recorded in rooms like this and has a lot of reverb.

Omnidirectional speakers are good for reproducing the sound of live, unamplified sound. It's a kind of music that most people today unfortunately don't have the privilege of ever hearing with the prevalence of PA systems. The only people who get to listen to it are those who play live music and those who attend concerts at good symphony halls or jazz venues.
 
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Denosaur22

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Considering that diffusers need distance to avoid frequency lobing and comb filtering (less of problem than lobing) that's not a good recommendation that way I see it. I also very much disagree that one shouldn't use treatment on the wall behind the speakers.

Type of treatment will depend on proximity to surfaces in relation to speakers and the listening position, how much the treatment can build out, budget and design goal. But generally, diffusion alone in such a small room wouldn't work very well IMO. Diffusion requires more distance. A combination would be better. And avoid simple scattering units that will not diffuse the sound evenly.
Combination as in products that both simultaneously diffuse and absorb?
 

Bjorn

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As a pianist myself, a piano sounds best in big open rooms with a decent amount of reverberation. Pianos don't sound very good when you play them in recording studios with good acoustics for reproducing sound. As a matter of fact, most piano music is recorded in rooms like this and has a lot of reverb.
Perhaps you have in mind a very dampened room when you say "good recording acoustics for reproducing sound". But much use of absorption isn't really good acoustics for recordrings. Typically such rooms are often not treated broadband either, changing the spectral content besides being overly dry and dead.

The use of diffusion, something like below is generally prefered for recordings, but requires more space and often adds to the cost.
1.jpg


DIFR2_MAIN (Custom).jpg


I think a challenge discussing this is that we have different opinions and experiences of what good acoustics is. Not many have heard a room that's treated with really high quality products and knowledge. That's actually very rare. A lot of acoustic products in the market today are also generally poor or outdated. The whole thing is a bit of a mess, not unlike how the market is for speakers and lack of understanding measurements and how speaker intereact in the rooms.
 

Bjorn

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Combination as in products that both simultaneously diffuse and absorb?
Not necessarily but could be that too. However, products that do both don't necessarily offer a high diffuse coefficiency. They will normally offer "somewhat" diffusion and absorb a lot more than a "pure" diffuser.
 
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Denosaur22

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Perhaps you have in mind a very dampened room when you say "good recording acoustics for reproducing sound". But much use of absorption isn't really good acoustics for recordrings. Typically such rooms are often not treated broadband either, changing the spectral content besides being overly dry and dead.

The use of diffusion, something like below is generally prefered for recordings, but requires more space and often adds to the cost.
View attachment 199777

View attachment 199778

I think a challenge discussing this is that we have different opinions and experiences of what good acoustics is. Not many have heard a room that's treated with really high quality products and knowledge. That's actually very rare. A lot of acoustic products in the market today are also generally poor or outdated. The whole thing is a bit of a mess, not unlike how the market is for speakers and lack of understanding measurements and how speaker intereact in the rooms.
Well said. That's exactly why I'm here posting on the forum. I'm not ashamed to admit I know even less! It is all a bit confusing. It's a financial investment, for sure. I'd like to make a smart, informed decision if possible. Would DSP /calibration be a better initial investment?
 

Bjorn

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DSP is nice for especially:
1. Improving the on-axis response of passive speakers.

2. Integrate subwoofer(s)

3. Reduce some low frequency peaks where treatment.may not be an option.

4. Tailor the overall response with shelving.

All of this requires knowledge to do and one cannot rely on auto correction, which will almost always contribute negatively on several areas.

While DSP is great it doesn't replace treatment. Acoustic treatment is always where one should start. It's basically the road for the vehicle. It lays the foundation and EQ will also work better when a room is treated.
 

MattHooper

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My room is 13' by 15' with various types of room treatment built in and the ability to somewhat modulate the reflectivity of the room (e.g. pulling thick velvet curtains to any point on any wall).

When I owned the MBL 121 omnis I found that an "in between" mix of reflectivity sounded best. Sorry, no room measurements, but I'd describe it as slightly leaning toward over damped. They would indeed sound even more "live" with more room reflections - same with most speakers I've owned. But it would come at the cost of some increasing blanching/homogenizing of instrumental timbre and less emphasis of the recorded acoustic. In fact just about the most realistic sound I've ever heard came from MBL 101s at a reviewers place, in a notoriously teeny little room, reminded me more of sitting in a closet. But it was heavily treated and...my goodness the spooky dimensionality and realism was out of this world.
 

Bjorn

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(e.g. pulling thick velvet curtains to any point on any wall).
Curtains are a very bandlimited treatment, only absorbing some in the highs, and changing the spectral content greatly. It's not considered as serious acoustic treatment. A correct and good result requires broadband treatment and the treatment of the specular energy needs to placed with accuracy at correct and certain places to avoid removing energy and ambience that is important to maintain.
 

MattHooper

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Curtains are a very bandlimited treatment, only absorbing some in the highs, and changing the spectral content greatly. It's not considered as serious acoustic treatment. A correct and good result requires broadband treatment and the treatment of the specular energy needs to placed with accuracy at correct and certain places to avoid removing energy and ambience that is important to maintain.

Oh, yes I realize that. (And my room has other treatments - it was designed with the input of an acoustical).

But there is theory and there is practice.

But in practice, I've found curtains have been excellent for manipulating the sound to my taste.

(It reminds me of when I was turning my room in to a home theater. The room is on the main floor, with a large opening to the main hallway.
I was concerned about too much sound escaping from the room to bother others if I were watching a movie. The theory about containing sound
from all the home theater builders was in how you can't 1/2 ass it if you want sound isolation, sound, like water, will escape wherever it can, it has to be a perfect seal for the room, all sorts of calculations on the thickness/design of the barrier etc. Yet for me thick velvet curtains pulled across the opening did all I needed. Doesn't fully stop the sound getting out, but reduces it so significantly as to get the job done for my situation).
 
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Denosaur22

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Well... The best method is to use a PC as a head unit and install free software for PEQ control. The other option is to get hardware DSP PEQ. That could be done with a miniDSP 2x4 or a miniDSP 2x4 HD (Has a faster computer processor inside.) and also buy a UMIK-1 calibrated microphone so you can use REW a free software to set up your DSP PEQ. The miniDSP unit would go between the receiver and the amp and so all sources could be PEQ'd.
I'm taking your advice.
What are your thoughts about the 2x4HD vs DDRC-24 vs Flex?

I assume with the 2x4 HD you connect it to a computer, do the calibration/EQ, set it and then forget it?
 
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