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SO and Practical Position
2017-06-24, 16:34
Post: #1
SO and Practical Position
If like me you've been intrigued by the mysterious 'Practical Speaker Positioning' in SO/SO+, I think this is what it looks like in reality...

[Image: attachment.php?aid=10875]


There's a separate filter for each speaker with a very wide bandwidth and not very deep. Frequency in this case is 64.8 Hz, depth is 3.7 dB and bandwidth 1.32 Octaves.

I had visions of massively complex troughs and ridges made up of multiple filters!

If you go 'the other way' and tell it that your speakers' practical positions are farther out into the room and the ideal positions are closer to the walls, it does boost rather than cut those frequencies.

Tell it that the practical and ideal positions are identical and it simply doesn't create a filter - as you'd expect.

Maybe not the most useful information ever, but I think it's good to know what's actually happening when you switch these things on.


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2017-06-24, 17:26
Post: #2
RE: SO and Practical Position
I've never understood. Who tells me what is the ideal position for my space.

Greetings Jörn (sorry for my awful english)
Hörland - Over 40 years LINN
Open Source Seite: http://www.jpo-aktuell.de/OpenSource.php

New LP12, Radikal, Urika, Kore, Ekos SE, Kristal / QNAP 569 Pro / RME UCX
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2017-06-24, 17:54 (This post was last modified: 2017-06-24 18:08 by Briain.)
Post: #3
RE: SO and Practical Position
(2017-06-24 17:26)JPO2005 Wrote:  I've never understood. Who tells me what is the ideal position for my space.

The concept is to try your speakers in many positions until you find which sounds most musical (and as you likely already know, it can make a massive difference, where even the greatest speakers can sound utterly dreadful when positioned badly). Then, if you really must move them, perhaps due to room aesthetics (or if you are told to move them by your partner) or perhaps one of them ends up being in a position where it blocks the natural walking route across or into the room, then you move them to where you have to move them to and also enter that information, then Konfig will do its best to compensate via a combination of the SO dips and also apply a (wider and shallower) correction in an attempt to compensate for what the change to the room boundary dimension (with respect to what was the ideal position) does to the bass levels.

Of course, if you have no such restrictions, you simply position them to where they sound best and Konfig will only apply the SO dips. Whilst I do use the SO feature (and the difference it makes to my system is massive) I spent ages finding the best sonic position for the speakers and fortunately for me, they landed in a position where it was practical to keep them, so I have never tried the ideal vs practical feature set of SO and thus I cannot comment on its effectiveness.

Bri

KDS/1 (music) + ADSM (AV) -> KK/1 -> 350A + miniDSP time & phase aligned 345 rear sub
KDS Renew -> Homebrew fixed attenuator -> 2250/D -> 212 and Sizmik front sub (bedroom)
MDSI -> 104C (awaiting installation in my kitchen)
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2017-06-24, 17:57
Post: #4
RE: SO and Practical Position
(2017-06-24 17:26)JPO2005 Wrote:  I've never understood. Who tells me what is the ideal position for my space.

Nobody is the simple answer Smile Your ears tell you where in the room your speakers sound at their best... Then you get told where you're allowed to have them!
SO attempts to make your speakers sound as good in the practical position as they did in the ideal position. Opinions vary as to whether or not it works.

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2017-06-24, 18:08
Post: #5
RE: SO and Practical Position
Hmmh, finding the best position is practically impossible. We would have the parameters:
1. Distance to rear wall
2. Distance to the side walls
3. How many angles
4. Spikes as low as possible in the stand without losing the same height

The loudspeaker must be firmly fixed at the tested position and the same height.
Since we know that for example at the distance to the back wall a cm make a large sound difference or the angle a few tenth degrees, I am not clear how one should realize this.

Greetings Jörn (sorry for my awful english)
Hörland - Over 40 years LINN
Open Source Seite: http://www.jpo-aktuell.de/OpenSource.php

New LP12, Radikal, Urika, Kore, Ekos SE, Kristal / QNAP 569 Pro / RME UCX
Akurate Exakt DSM2 / Kinsky (Minim) - Sneaky
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2017-06-24, 18:42
Post: #6
RE: SO and Practical Position
(2017-06-24 18:08)JPO2005 Wrote:  Hmmh, finding the best position is practically impossible. We would have the parameters:
1. Distance to rear wall
2. Distance to the side walls
3. How many angles
4. Spikes as low as possible in the stand without losing the same height

The loudspeaker must be firmly fixed at the tested position and the same height.
Since we know that for example at the distance to the back wall a cm make a large sound difference or the angle a few tenth degrees, I am not clear how one should realize this.

There is a method to achieve the correct position. Might take a bit of practice but it is worth the effort.
https://www.linn.co.uk/tunedem

Gary

LP12/Cirkus/Radikal/Kore/Ekos1/Tkable balanced/Uphorik/Krystal/ADSM/1/aktiv Akubariks
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2017-06-24, 19:02
Post: #7
RE: SO and Practical Position
(2017-06-24 18:42)bettermusic Wrote:  
(2017-06-24 18:08)JPO2005 Wrote:  Hmmh, finding the best position is practically impossible. We would have the parameters:
1. Distance to rear wall
2. Distance to the side walls
3. How many angles
4. Spikes as low as possible in the stand without losing the same height

The loudspeaker must be firmly fixed at the tested position and the same height.
Since we know that for example at the distance to the back wall a cm make a large sound difference or the angle a few tenth degrees, I am not clear how one should realize this.

There is a method to achieve the correct position. Might take a bit of practice but it is worth the effort.
https://www.linn.co.uk/tunedem

...but assuming you find it, you're stuffed if it's not practical. SO can go some way to mitigating the difference but it will never come close to having the speakers in their ideal locations - and now you know how good they could sound, which will niggle.
Besides, I think Jörn was referring to the practicalities of moving the speakers and ensuring each location you try is as optimal as possible from the speaker point-of-view - levelling etc can make a large difference. By the time you have all that sorted you've forgotten what the previous location sounded like. Probably best to just remove the spikes and put up with the levelling?

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2017-06-24, 19:24 (This post was last modified: 2017-06-24 19:33 by Briain.)
Post: #8
RE: SO and Practical Position
(2017-06-24 18:08)JPO2005 Wrote:  Hmmh, finding the best position is practically impossible. We would have the parameters:
1. Distance to rear wall
2. Distance to the side walls
3. How many angles
4. Spikes as low as possible in the stand without losing the same height

The loudspeaker must be firmly fixed at the tested position and the same height.
Since we know that for example at the distance to the back wall a cm make a large sound difference or the angle a few tenth degrees, I am not clear how one should realize this.

For the distance to the side wall, Linn chose to use the edge of the cabinet as the measurement reference point, and within Konfig, it will - behind the scenes - first change that figure to instead being the dimension to the middle of the bass unit (in other words, it will add half of the cabinet's width to your measured length) then that re-calculated dimension will be pumped into the algorithm that calculates modes (and if using the ideal vs practical feature, also for the boundary calculations). I haven't seen the results of the boundary correction, but I expect that if you push the speakers further towards the front wall, it will be a shallow and very wide bell shaped dip, but given the wavelengths involved, small errors in dimensions (e.g. from toe-in) will probably be insignificant, but based on the above, you could easily figure out corrected dimensions and instead enter them.

When I added my rear sub (which sits near a corner and points towards the middle of the room) I chose the distance to the front wall as being the median (as in between left and right distances to the cabinet face) and for the side dimension, I had to adjust the length to the side wall to compensate for the error of it now being at 45 degrees (such that Konfig would then correctly calculate the position of the centre of the unit, then feed that into the SO algorithms). That made a noticeable difference to the calculated results as the difference was quite a few centimetres.

My 350As are also slightly toed in, but the change in bass unit position is actually pretty tiny (particularly so given the size of wavelengths involved). Of course, I was only generating mode dips as I didn't need to move the speakers from the ideal positions, so at the end of the day, I adjusted all these dips by using a mixture of very rapid repeating sweeps (e.g. 20 -> 50 Hz over 1 second and once finished with that, 50 -> 80 Hz over 1 second) to get a rough idea what was going on, then adjusting them for best musicality (so the foot tapping test) so dimensional errors were unimportant as the dips were going to be changed, anyway.

When we later got the stereo SO, I again used my rapid sweeps and this time they indicated SO was doing a very good job with the calculated settings, so I pretty much left it as set and intended later tweaking them by using real music, but it all sounds pretty reasonable as it is, so I never actually got round to doing that last part (one day I'll find time to do so).

The only odd anomaly is that with the new stereo calculations version of SO, there's now a width mode dip at 30 Hz and despite there being a dip set, when I rapidly sweep past it I can still hear the mode doing its stuff (sounds like a ripped speaker cone) but all the other frequencies (including twice the width mode frequency) now sound pretty good (it sounds even and there are no other distortion anomalies). With SO switched off, you can clearly hear various distorted frequencies when you rapidly sweep the system through the room modes; it does actually sound like you have faulty bass units, but when you stand in front of them, there is no distortion coming from the unit, itself.

I think the best sonic solution for that 30 Hz W1 mode would be to knock down the side walls and replace them with two rows of Acrow props, but living in Scotland (and at 150 m above sea level) I suspect that it would get a bit draughty in winter.

Bri

KDS/1 (music) + ADSM (AV) -> KK/1 -> 350A + miniDSP time & phase aligned 345 rear sub
KDS Renew -> Homebrew fixed attenuator -> 2250/D -> 212 and Sizmik front sub (bedroom)
MDSI -> 104C (awaiting installation in my kitchen)
MDSI -> Shahinian Arc (installed at my mum's house)
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2017-06-24, 19:30
Post: #9
RE: SO and Practical Position
(2017-06-24 16:34)phino Wrote:  If like me you've been intrigued by the mysterious 'Practical Speaker Positioning' in SO/SO+, I think this is what it looks like in reality...

[Image: attachment.php?aid=10875]


There's a separate filter for each speaker with a very wide bandwidth and not very deep. Frequency in this case is 64.8 Hz, depth is 3.7 dB and bandwidth 1.32 Octaves.

I had visions of massively complex troughs and ridges made up of multiple filters!

If you go 'the other way' and tell it that your speakers' practical positions are farther out into the room and the ideal positions are closer to the walls, it does boost rather than cut those frequencies.

Tell it that the practical and ideal positions are identical and it simply doesn't create a filter - as you'd expect.

Maybe not the most useful information ever, but I think it's good to know what's actually happening when you switch these things on.

Hi Phino,

I am not sure that the frequency at 64.8 Hz is generated for the practical position only.

SPACE optimization seems to generate these very wide bandwidth room modes under a few situations.

For example, I usually see these type of generated room modes if I create a new custom filter at a specific frequency , and then SPACE will automatically populate the bandwidth as having a very wide octave width.

I don't know why it does that, but I usually reduce the bandwidth significantly, otherwise the mids and highs can be quite muddy.

I usually have the ideal and practical position the same in my system.

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Room Acoustics: SPACE, SubDude HT's, Acoustic Panels
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2017-06-24, 19:35
Post: #10
RE: SO and Practical Position
(2017-06-24 19:24)Briain Wrote:  Linn chose to use the edge of the cabinet, and within Konfig, it will - behind the scenes - change that edge dimension to a dimension to the middle of the bass unit, then that new dimension will be pumped into the algorithm that calculates modes (and if using the ideal vs practical feature, also for the boundary calculations). I haven't seen the results of the boundary correction, but I expect that if you push the speakers further towards the front wall, it will be a shallow and very wide bell shaped dip, but given the wavelengths involved, small errors in dimensions (e.g. from toe-in) will probably be insignificant, but you could calculate corrected dimensions and instead enter them.

Yup - that's the picture I put in the original post. In the SO file you'll see a BoundaryOptimisation element for each speaker with the filter details. I transferred these values into one of the custom filters to see what it looked like in the context of the visible SO filters. So yes, very wide and shallow.

Maybe you could get some of that acoustically transparent cinema screen stuff to replace your side walls Smile

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