Listening distance

Pierre The Bear

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I seem to remember an old rule that an equal triangle between your head and pair of speakers works well. Is this true?

 

SergeAuckland

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Yes, that's still the ideal. Whether the loudspeakers are aimed straight at the listener or their axes crossed in front of the listener depends on the loudspeakers, the room and the width of trhe listening area required.

Having the loudspeakers firing straight down the room with no toe-in will increase the side reflections and diffuse the stereo image. Increasing the distance between the listener and the loudspeakers (reducing the angle) will increase the room effect and diffuse the stereo image whereas shortening the distance (increasing the angle) will make the stereo image unstable and it will move sharply left or right with small head movements.

S

 

SergeAuckland

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The angle the speakers fire at you also affects tonal balance.
Indeed, for reasons both of room effect in terms of side-wall reflection/absorption and the direct sound off-axis response of the loudspeaker.

The loudspeaker's construction will also affect the off-axis response due to diffraction effects at the panel edges.

Complicated business, loudspeaker positioning!

S

 
M

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I don't quite understand this then because in my very small (9 x 7.5 ft) room, I sit in a pretty much 6 foot equilateral triangle arrangement with my speakers (Ditton 44's) 9" from the back wall and 18" from the side walls, firing straight down the line and the stereo image is very good, focussed and pretty stable.

As I start to toe-in the speakers, the imaging seems to become increasingly diffuse and not as well focussed, exactly the opposite to what I would expect.

Any ideas as to how / why ?

 

SergeAuckland

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I don't quite understand this then because in my very small (9 x 7.5 ft) room, I sit in a pretty much 6 foot equilateral triangle arrangement with my speakers (Ditton 44's) 9" from the back wall and 18" from the side walls, firing straight down the line and the stereo image is very good, focussed and pretty stable.As I start to toe-in the speakers, the imaging seems to become increasingly diffuse and not as well focussed, exactly the opposite to what I would expect.

Any ideas as to how / why ?
No, not really as like you, I would have expected the opposite. The only thought is that the back wall reflections are having an effect, whether there's anything between the loudspeakers like an equipment rack, a reflective surface like a coffee table. Room effects are probably the most difficult things to diagnose at long range.

S

 

SergeAuckland

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Is there anything to extending the distance to a little bit more than that equal to the space between ? E.G. 1.1 times the gap between. I've seen that recommended. That and some toe in.Can I ask someone, perhaps Serge, about the measurment of the space between : Should it be considered as space between the inside sides of the cabinets, or, the distance between centre points of the drivers ?

Since we're on the subject of positioning, may I also ask if there is something to avoiding having the same space behind and to the sides of the speakers. I have read that ideally you should seek to have a ratio of about 1.6 (exhangeable either way round ) , derived from that Golden Ratio theory stuff.
The difference between 1 and 1.1 is trivial and unlikely to make a large difference, although specific circumstances may dictate otherwise.

I don't know about Golden Ratios except in terms of the overall room dimensions, where they are considered a good way of spreading room modes, but having different distances to the side and behind, and not in a simple ratio makes sense. If the distance back and side are trhe same, then the loudspeaker is effectively in a corner, albeit some distance from the apex. There's also some suggestion that it's a Good Thing to have the distances behind and sides different on the left and right 'speakers, so trhat they're not symmetrical in the room. This may be difficult to accommodate domestically but may be worth trying.

Room acoustics do lend themselves to measurements, but in general, in a home setting, it's the one thing over anything else that I would try and see what works best subjectively, especially if the room has to work domestically too.

S

 

Tenson

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Do you trust a business that mainly sells cables and equipment isolators on the technical subject of acoustics? There is no such thing as a golden positioning ratio.

There are good room size ratios that spread the modes out evenly, but this is rather different to listener and speaker positioning. At any rate these 'good dimensions' expect flush boundary mounted speakers so they can predict how the modes will be excited.

You need to do far more complex calculation. Here is a nice web-app that can help with mode excitation - http://www.hunecke.de/en/calculators/loudspeakers.html

 

SergeAuckland

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Thanks Serge, for your reply.Could you also please answer what I asked about where to take "distance between" measurement i.e. between inside cabinet edges, or between centre points of drivers ? One method to another could mean a good foot of a difference. If meant to be say 7 or 8 feet apart, that's a big percentage difference especially.

Another room-speaker issue ..........

In my circumstances, a problem is short distance between head and wall behind. Very close maginifies certain bass. Cutting down from 1.1 to 1.0 listening distrance ratio would help a little to bring myself forward, but I'm still close, at maybe one and a half feet to two feet from wall behind. It's not going to change as I can't really re-arrange the room and listening position. The question then becomes, what panel would I need to place on the wall behind me ? I've been meaning to do that for a while.
Sorry, forgot about the distance between question:- Unless the 'speakers are very large, it isn't a critical measure, even the difference between 7 and 8 feet isn't that important, but I measure to the centre line of the drivers.

As to the listening position, a hard wall behind reflect all frequencies pretty much equally. It's not practical to do much about the bass as that requires large traps, but at low mid to high frequencies, an absorber like Rockwool works very well. I've covered the whole of one wall with 100mm rockwool behind a light curtain and it fixed flutter echoes and RT60 issues wonderfully. I would make a 1200x600x100 frame, fill it with 100mm Rockwool and then put a decorative fabric covering, tapestry, weaving, carpet or similar over it and hang it on the wall behind the listening seat. Rockwool is great stuff in that it works technically very well, but is also inert, so doesn't cause itching or respiratory issues unlike grass-fibre, and is fireproof. Rockwool is sold in bales, but many builders' merchants have the odd broken bale so you should be able to buy the one or two sheets you need. Even if you have to buy a whole bale, it's not expensive stuff and any surplus can just go in your loft as additional insulation.

S.

Adding just one panel as described will stop the reflections from behind, but there isn't enough extra absorbtion to affect the "feel" of the room, it will make it slightly less bright, but not much so.

 

Tenson

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Measure from driver centres. For room modes consider bass driver.

You need an absorptive panel behind you. Hang a duvet over a couple of broom handles behind your head, see what it does to the sound.

A couple of GIK 244 bradband bass traps should work nicely (full range option, not range limiter).

 

brystonian

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I have the same problem of sitting with my head about a foot off the back wall. I've got a pair of GIK 244's directly behind my head and it definitely helps. I do have one straddling each corner too. Seems to have flattened the response nicely. But there is still a bit of flutter and the decay time is a little long. So more will be going in soon.

 

SergeAuckland

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Measure from driver centres. For room modes consider bass driver.You need an absorptive panel behind you. Hang a duvet over a couple of broom handles behind your head, see what it does to the sound.

A couple of GIK 244 bradband bass traps should work nicely (full range option, not range limiter).
Those GIK panels do look pretty useful. Still won't do a lot at LF, but then very little will. For the application required, they should work well, and are likely to be more acceptable domestically than a 100mm Rockwool panel.

S

 

Tenson

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This could help with LF. http://www.rpginc.com/product_Modex_Plate.cfm

It can be an issue, as well as higher frequency interference. I visited a room recently that was getting a 45Hz null from the rear wall reflection cancelling with the direct sound. Move closer and the frequency went up, move away and it went down, but it was always there. In the absense of funds I sugested some DIY 'hangers' ala John Sayers.

 

awkwardbydesign

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I have treated my walls (a lot!) and still get some flutter echo. It's the floor and ceiling! Solid floor with 8'x6' rug, and it still echoes. I intend to treat the ceiling, but at 2.3m high there is very little room to play with. We can't even have pendant lights as I whack them putting on my crash helmet.

I'm working on something shallow enough to get it past quality control (my wife) but still be effective. Tricky.

 

Tenson

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Flutter echo when clapping hands etc.. is not always a problem. Get someone to clap their hands standing where the speakers are and you sit at the listening position. Do you hear flutter?

 

awkwardbydesign

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I definitely hear clapping!

Actually there is a peak at around the same frequency which affects my wife more than me. Mainly in one ear. Not the deaf one she aims at me.

 

GR1

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It's very important to not get too hung up about hearing a bit of reverb and trying to make a room too dead. Your brain knows roughly what contribution a room should make to the sound as soon as you walk into it and compensates for it. My first job was in a film dubbing studio and when I went into the voice over booth it was so acoustically dead that I literally couldn't hear myself speak which is ideal for a recording studio but crap for a listening environment. Similarly when I was working on the fit up of a West End musical the Production Sound Engineer sent a lad into the orchestra pit to dress the drum booth and he covered every surface to such a degree that the drummer was over playing the kit - literally beating the crap out of it - because he couldn't hear himself play, thus destroying any subtlety in his playing [such as there might be with a drummer !]. A bit of room treatment can help but if you do too much it will sound very unnatural.

 

SergeAuckland

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It's very important to not get too hung up about hearing a bit of reverb and trying to make a room too dead. Your brain knows roughly what contribution a room should make to the sound as soon as you walk into it and compensates for it. My first job was in a film dubbing studio and when I went into the voice over booth it was so acoustically dead that I literally couldn't hear myself speak which is ideal for a recording studio but crap for a listening environment. Similarly when I was working on the fit up of a West End musical the Production Sound Engineer sent a lad into the orchestra pit to dress the drum booth and he covered every surface to such a degree that the drummer was over playing the kit - literally beating the crap out of it - because he couldn't hear himself play, thus destroying any subtlety in his playing [such as there might be with a drummer !]. A bit of room treatment can help but if you do too much it will sound very unnatural.
Totally agree. Anyone who's been inside an anechoic chamber knows how oppressive that can be. There are ideal RT60 times for performing music, which differ according to the type and scale of the music...which is why chamber music is performed in smallish rooms and symphonies are performed in larger rooms and organ music is performed in spaces with long RT60 times. These times all tend to be longer than the ideal RT60 time for reproducing music, 300ms to 500mS is a good range to aim for. 200mS will give more intelligible speech, 800mS will give a greater sense of scale, but for home use, somewhere around the 300-500mS decay time is good. However, as important as the RT60 time is, it should be reasonably smooth from LF to HF. If it's long at LF and falls like a stone at HF, the room will be unpleasantly bass heavy, the ideal is a smooth shortening of RT60 times as frequency rises, but staying somewhere around the 300-500mS mark.

RT60 times can be measured reasonably easily at home using a white noise burst of say, 1 second long, record the noise burst on Audacity, Cool Edit, Audition or similar, then see how long the tail of the decaying noise is before it reaches 60dB below the level of the noise. It might be difficult at home depending on the location for the noise ever to get down to -60dB as that requires a very quiet room..depending of course on how loud it was before the deacy started, but at say 90dB SPL of noise, getting to -60dB requires a room with no more than 30dB SPL of background noise. If that's the case, then measure how long the first 10dB takes, the second 10dB, the third 10dB, check that it's reasonably linear then extrapolate for 60dB.

I did it for my listening room, and I can't remember the exact figures, but somewhere under 500mS, so quite happy. Before the Rockwool and rugs, however, it was around 2 seconds with a nasty clangy flutter echo.

S.

 

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