JPO2005

Sound improvement for 0,00 Euro

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3 minutes ago, MartinC said:

Room mode patterns are independent of speaker placement but to what extent a particular mode is excited will be affected by speaker placement. Put a speaker at the null of a mode and it will be minimally excited for example, which is an approach sometimes exploited in systems with multiple subwoofers.

Thanks for this. I'm modeling it in my head and it makes sense that room modes would be independent of speaker position. It is a function of room geometry and wave lengths.

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1 minute ago, akamatsu said:

It is a function of room geometry and wavelengths.

Exactly.

There are other acoustic affects that relate to the positions of speakers, room boundaries and the listening position but these are distinct from room modes.

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Have a think about the tolerances builders use. 

If a builder manages to build a room to +/- 1cm on each of it's axis he'll be doing a decent job.

Then have a look at the flatness of the walls and ceiling - put a long flat edge on one of your walls and have a look  at the high and low points along the wall, it'll be greater than 1mm.

Next, get a laser level and check if all your walls are absolutely true vertically and your floor and ceiling are true horizontally, they won't be.

How about the symmetry of your room? Different furnishings around the room will lead to different refection and absorption patterns and these will have a far greater impact on what you hear than the positioning of the speakers.

Yes it's important to have your speakers properly placed, but it's just impossible to do it to the level you are suggesting and it having any effect on what you hear sitting in your chair.

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27 minutes ago, killie99 said:

Have a think about the tolerances builders use.

...not to mention the tolerances on the building of the speaker cabs themselves.

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Super Wammer
On 09/02/2020 at 07:26, Paulssurround said:

With Linn systems that are Exakted, the exact speaker placement in the room is critical to time alignment the calculations used in the algorithm that determines the timing of the treble, mids and tweeters, as it arrives at the listening position.

Unfortunately, its not.  The time alignment provided by Exakt is based on a nominal listening position.  Perhaps SPACE in an Exakt system does adjust this, but Exakt on its own doesn't.

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It is perhaps worth making a distinction between the time alignment between drivers in a loudspeaker (which I understand Exakt improves) and effects of speaker position. Moving an entire loudspeaker will change the relative time alignment of the signals from the drivers at a listening position far less than moving an individual driver by the same distance would.

Edited by MartinC

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18 hours ago, akamatsu said:

Thanks for this. I'm modeling it in my head and it makes sense that room modes would be independent of speaker position. It is a function of room geometry and wave lengths.

This may be of interest 

https://science-of-sound.net/2016/06/room-modes-speaker-placement/

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20 hours ago, MartinC said:

Exactly.

There are other acoustic affects that relate to the positions of speakers, room boundaries and the listening position but these are distinct from room modes.

The information below is from PeteLinn as stated in the thread on SO+v1 and virtual tunedem. It appears that room modes do depend on speaker locations.

SO optimises the loudspeaker-room interactions in three ways:

1. room mode optimisation; SO looks at the difference between the long-term response of your speakers in their practical locations in your room and in an anechoic environment, thus this optimisation depends only on your room, your speakers, and their practical locations

2. boundary (or placement) optimisation; SO looks at the difference between the short-term (or power) response of your speakers in their practical locations and ideal locations in your room, thus this optimisation depends only on your room (in truth, only really on the boundaries nearest your speakers), your speakers, and both their practical and ideal locations

3. time-of-flight optimisation; SO looks at the distances from your speakers to the listening location, thus this optimisation depends only on your room (at least in SOv2 were room environmental conditions are considered), your speakers, their practical locations, and your listening location.

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2 minutes ago, akamatsu said:

The information below is from PeteLinn as stated in the thread on SO+v1 and virtual tunedem. It appears that room modes do depend on speaker locations.

SO optimises the loudspeaker-room interactions in three ways:

1. room mode optimisation; SO looks at the difference between the long-term response of your speakers in their practical locations in your room and in an anechoic environment, thus this optimisation depends only on your room, your speakers, and their practical locations

2. boundary (or placement) optimisation; SO looks at the difference between the short-term (or power) response of your speakers in their practical locations and ideal locations in your room, thus this optimisation depends only on your room (in truth, only really on the boundaries nearest your speakers), your speakers, and both their practical and ideal locations

3. time-of-flight optimisation; SO looks at the distances from your speakers to the listening location, thus this optimisation depends only on your room (at least in SOv2 were room environmental conditions are considered), your speakers, their practical locations, and your listening location.

None of that contradicts what I've posted above?

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5 minutes ago, MartinC said:

None of that contradicts what I've posted above?

I'm not sure. I'm just trying to understand how speaker position relates to room modes. According to PeteLinn, speaker position does factor in.

Edited by akamatsu

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1 minute ago, akamatsu said:

I'm not sure. I'm just trying to understand how speaker position relates to room modes. According to PeteLinn, speaker position does factor in.

Not really. I'll post a proper response later...

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3 minutes ago, MartinC said:

Not really. I'll post a proper response later...

Thank you. I look forward to your response. I'll stop scratching my head.

Edited by akamatsu

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First up, the shape of a room, where the speakers are in it and where the listening position is will all absolutely affect the sound that someone hears. What SO does is to attempt to simulate and compensate for the effects of this complex interaction. Where I think there is some confusion is the contribution that room modes make to this.

Room modes are the resonant frequencies of a room, which to some extent you can think of like the resonant frequencies of say a bell. The frequencies of both are determined by their construction/geometry, not where a speaker is in a room or where you hit a bell. Where a speaker is in the room will though affect how much a particular mode is excited, and where the listener sits will also affect how loud that particular frequency sounds. 

An entirely different but important way that speaker placement affects sound is the way that this changes how sound coming to your ears directly from the speaker interacts with that reflected on the walls, floor and ceiling. This link gives a little more detail without getting too technical I think:

https://www.gikacoustics.com/speaker-boundary-interference-response-sbir/

There are other ways that speaker position affects sound but these are the main ones at low frequencies.

Edited by MartinC
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^^ Yes, exactly this. Room modal patterns exist for reflecting soundwaves in an enclosed volume, across the entire frequency spectrum. It is akin to a unique fingerprint, peculiar to the precise geometry of the enclosed space. Modal frequencies above 120 Hz or so are numerous and evenly distributed and do not generally adversely affect perceived sound quality. Conversely, lower frequency room modes are less evenly spaced and are readily discerned by ear, recognised as reinforcement and cancellation distortions which correspond to measurable peaks and troughs in frequency response.

The excitation of this underlying pattern of LF room modes is what we actually perceive and every individual “point” in space has a unique perspective on this. This in turn is dependent on a) the position of the source of the LF excitation (primarily the bass drivers) and b) the amount of LF energy available to excite the underlying modal pattern. The latter is hence dependent not only on the output of the LF source, but also on the LF transmission/absorption properties of the structural boundaries of the enclosed space.

So, dimensions, shape and structure of the room, combined with listening position, loudspeaker position and bass output, all affect undesirable LF modal anomalies.

Edited by fredbatch
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On ‎09‎/‎02‎/‎2020 at 20:11, Monkey Wrench said:

“The placement of the speakers....also effects the creation of room modes, which strongly influences sound quality”.

Not really. Room modes are determined by the room’s dimensions. They exist whether there is a loudspeaker in the room, or not.

“I’m afraid I'm firmly on the side of a 5 mm shift in speaker position being too small to make an obvious audible difference”.

Nope. Moving a speaker backwards or forwards by the thickness of a sheet of A4 will change the phase alignment of the signal and hence a better or worse musical performance.

It is impossible to physically control such movement when positioning a loudspeaker for optimum performance, though spikes on a hard floor will allow you to get at or near one millimetre. Beyond that Space Op used correctly will allow you to virtually move the loudspeaker very small, and clearly audible, distances. 

One caveat...you only fully benefit if you both understand and use the Tune Dem

Quite so .

Since long  before SO this fine adjustment of speaker placement with  respect to the rear wall has been an integral part of the "tune dem"  centred set up process.

The method essentially being to move the speakers a certain distance backwards or forwards ..then half that distance , then half   again , until we're satisfied we've hit the sweet spot.  Within the constraints of practicality  [and domestic harmony :D] it works very well.

Edited by Smokestack

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