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Screen Height, Speaker Placment And Seating Loctions


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#1 MarkTecher

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Posted 01 July 2007 - 09:50 PM

Over the past few months, I have been asked to start a thread on Constant Image Height. Given that not everyone is into CIH, I thought this thread might be more useful if aimed at general HT front projection (but will include some CIH tips).

The points I would like to cover are –

A. Maximum screen size found by the height first.
B. Minimum and maximum seating distances.
C. A look at speaker placement given sound is still 50% of the experience.

A. Screen Height.

Whilst most people are probably thinking width or diagonal when they choose a screen, it is actually more important to address the screen height for a given room. Once you have the maximum screen height (remember you can always go smaller if it is too big), you simply multiply that by the chosen aspect ratio to find the screen width.

The diagram in THIS LINK is based on cinema viewing angles.

Given that the purpose of Home Theatre is to try and recreate the cinema experience in the home, it naturally makes sense to use these angles as a guide for your home theatre - especially if you’re using your projection system for viewing a movie that was originally filmed for cinema. There have been a few screen calculators that can be found on the Net with similar figures, however most were (are) limited to 16:9 screens. This one can be effectively adopted to any AR up to 2.39:1 simply by –

1. Taking the room’s length and dividing it by a number within the given values on the diagram (equal to or less then 5.18 and equal to or more than 3.68) and
2. Multiplying the found screen height by the chosen AR. The three common Aspect Ratios for video are 1,33:1, 1.78:1, and now 2.37:1.

The interesting part of this is that even if you do not want to go full CIH, your still getting the maximum 1.78:1 and 1.33:1 image for your room. Your only limitation is the width of the room.

B. Seating Distances.

The screen height is also best used to find your seating distance(s) for the locations for your seats.

Another reason I attached this diagram is that it gives an alternative to the screen width for calculating the seating distance by using the height. SMPTE [Society of Motion Pictures and Television Engineers] have a slightly broader range. They go so far to include a range from 2x to 4x the screen height. Note that the THX 36degree (3.68x) fits nicely within those guide lines. 2x is radically close, but some people find that provides the most immersive experience. Personally, I would not recommend less than 2.4x the screen height, even with a 1080 projector.

Avoid sitting on the back wall where possible. If your unable to move the seating forward, then you may need to consider reducing the image size.

C. Speaker Placements.

George Lucas was quoted as saying that Sound is 50% of the motion picture experience, and nothing could be more true for a good home theatre. As sound cues are designed to match the visuals, it makes sense to identify placement options that actually enhance the over all experience.

Lets start with the front stage – LCR or Left Centre Right. Traditionally for music only applications, wider is considered better. However it also being well noted that the optimum spacing is between 1800mm (6 feet) and 2400mm (8 feet). The centre channels is probably the most important speaker in the multi channel speaker layout, and can be responsible for up to 90% of a film soundtrack.

There basically three positions for the centre channel – Above, Behind (when using an AT screen) and Below. I strongly believe in the use of three identical speakers for the LCRs, and that the three speaker be placed at the same height. Naturally, I have to accept that this is not always possible in all cases.

The point to remember is that the centre speaker is not just an add on, so you need a speaker that actually matches (tonally) and its placement needs to be such that will enhance the L and R speakers in a multi-channel system.

A note for those into CIH.

Given that your able to project up to 3 different ARs, your need to exercise caution to the width of the Land R speakers. As mentioned above, generally wider is better, but given that your also trying to match sound with the picture, you need to consider the smaller Aspect Ratios of 1.78:1 and 1.33:1. My recommendation (if possible) is to place the speakers so that they line up with the 1.78:1 area of the screen. Listening tests have revealed some interesting results.
1. The sound cues do better match the smaller Aspect Ratios.
2. The speaker location actually provides a better (more natural) soundstage when watching a “Scope” film. This is because the placement of the speakers in both a cinema and dubbing stage are just inside the side masking of 1.85:1, so in essence we are replicating this in our homes.

Moving round to the surrounds. There are basically two types of speakers than can be used for the surrounds – diffuse and directional radiating speakers. Your choice will basically be dependent on the type of program you’re listening to. Having said that, you also need to consider two things –
1. the nature of surround (despite the very directional cues in today’s soundtracks) is mainly for ambience and
2. the fact that both film dubbing stages and cinemas use arrays of surrounds, so in order to create that, the diffuse radiator should be the preferred choice.

There position in the room should be so as to provide a sense of envelopment. The ITU-R was created to provide 5.1 content creators a uniform layout for the 5.1 speakers. The surround placement is flexible offering placement options centered on +/-110degrees with +/-10degree from that position. 110 degrees was chosen as it represents the best compromise between what best for envelopment (+/-90degrees) and what is best for rear imaging (+/-135degrees).

For home theatre, the surrounds should be located at +/-90degrees to the seating position. If you have multiple rows, then you need to decide what is going to work best. In some situations (big rooms) you may actually have to employ additional surround speakers.

Extended surrounds.

With the introduction of Dolby Digital EX and DTS ES came the back Surround channel. Whilst both have a matrixed version, DTS also offers a discrete version. Both EX and ES are 6.1 but are best played over a 7.1 speaker system so that the Back Surround information does not suffer “pulling” if seated off axis like you hear from a 6.1 speaker layout. The real beauty of extended surround systems is that they allow a deeper seating area. With 5.1, if your seated behind the LS and RS, your technically out of the sound field, yet with 7.1 speaker system, your still in that field even if seated behind the LS and RS so single speakers at the sides can still work for multiple rows of seats.

Sub-woofers.

There are many tried and proven methods for sub-woofer placement. The best location is the one that delivers the flattest response in your room.

I hope the information is useful…

Mark

#2 Mannah

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Posted 01 July 2007 - 10:52 PM

First.

Also, good write up. I will have a good read of this tomorrow at work :D Thanks Mark

#3 AndrewW

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Posted 01 July 2007 - 10:55 PM

First.


Please god no.

This is not whirlpool or the WoW forums.

Caniffe, can we have a shoot on sight order for people who do this please ?

#4 JoshH

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Posted 01 July 2007 - 11:45 PM

Please god no.

This is not whirlpool or the WoW forums.

Caniffe, can we have a shoot on sight order for people who do this please ?

Agreed - totally uncool.

Either write a response - or dont. Placeholders are just inappropriate.

#5 The_Preacher1973

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Posted 02 July 2007 - 12:23 PM

C. Speaker Placements.

Lets start with the front stage – LCR or Left Centre Right. Traditionally for music only applications, wider is considered better. However it also being well noted that the optimum spacing is between 1800mm (6 feet) and 2400mm (8 feet). The centre channels is probably the most important speaker in the multi channel speaker layout, and can be responsible for up to 90% of a film soundtrack.


Mark,

Could you explain this a bit more please? Does this spacing change with screen size and aspect ratio?

I’m looking to use a 3.8m wide AT 2.37 screen. It’s most likely that my masking system won’t be AT. Therefore I have two choices with speaker location for the fronts. Either I place them beside and slightly in front of the 2.37 screen or behind the screen within the 16:9 area (2.84m apart). I’m concerned that by placing them this close the soundstage won’t be large enough.

#6 MarkTecher

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Posted 02 July 2007 - 06:24 PM

Mark,

Could you explain this a bit more please? Does this spacing change with screen size and aspect ratio?

I’m looking to use a 3.8m wide AT 2.37 screen. It’s most likely that my masking system won’t be AT. Therefore I have two choices with speaker location for the fronts. Either I place them beside and slightly in front of the 2.37 screen or behind the screen within the 16:9 area (2.84m apart). I’m concerned that by placing them this close the soundstage won’t be large enough.


Hi Preach.

2.84m is very wide.

Basically with 2CH music only sources, a subtended equal-lateral triangle from speakers to listening position is said to be the best for separation and imaging and the ITU-R recommends the same for 5.1 layouts and MC programming.

Whilst this is great for audio only, I feel that things need to change when sound accompanies a picture. In film sound, the sound cues are supposed to describe the visuals, so close matching of sound and picture are needed. Projectors certainly allow for a wider spacing because of the large image size they can produce opposed to the smaller screen of direct view sets and even Dolby labs has published a narrower angle of 45 degrees (+/-22.5 off the centre).

What I am seeing more and more of is that people are still placing their speakers at the sides of the screen, possibly carried over from their direct view days. This is fine for 1.33:1 screen as it is constant width and works for 1.78:1 as it is both constant height and constant width, but as we increase the aspect ratio out to 2.37:1 for true constant hight systems, our 1.78:1 and our 1.33:1 image/sound cues become some what detached - especially the 1.33:1 image if our speakers are at the edges.

With my first "scope" set up, I did place the speakers all under the screen with the L and R at the far edges of the screen. What I found was that (and this is well documented) that I was seeing objects in one location and hearing the sound cues in another. This happens because we are more sensitive to horizontal mis-alignment than we are to vertical in sound (the opposite for image), so whilst we can tolerate hearing the speakers under the image, it is the width that becomes troublesome.

What I am suggesting (and 3 CIH'ers on this forum now do this) is to move the L and R speakers to be in line (vertically) with the 1.78:1 mark. Careful listening tests revealed the benefits for sound/picture integration for all three major aspect ratios and actually really beneficial to the "scope" image. In a real cinema and in the large dubbing stages where film soundtracks are mixed, the L and R speakers are just inside the side masking, so when the sound cue are mixed, they are mixed for those locations.

I feel that doing the same at home only heightens the experience to better match what was intended at the mixing session. Sound only sources (2CH stereo) may suffer as a result, so some compromise is needed if you watch more than just listen, but in your case, 2.84m is still very wide.

This is of course assuming that you have the height to place the speakers under the screen. The other option is to go AT, but unless your prepared to make some serious mods to the HT room, I would caution any one thinking it is as as simple as placing the screen in front of the speakers. Trust me, there is a lot more to it than that...

Mark

#7 The_Preacher1973

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Posted 02 July 2007 - 08:22 PM

This is of course assuming that you have the height to place the speakers under the screen. The other option is to go AT, but unless your prepared to make some serious mods to the HT room, I would caution any one thinking it is as as simple as placing the screen in front of the speakers. Trust me, there is a lot more to it than that...

Mark


Thanks for the detailed explanation. I'm hoping to have a dedicated theatre room when I get back and the room will be built from scratch as part of rennovations so I should be able to do it right. I presume when you say there is much more to it than that you're referring to treating the front wall?

I intend to get the builders to leave the room incomplete with no interior trim on either walls or ceiling. This will give me the opportunity plan the room properly. I feel that investing in getting the room right will be my best use of funds at that stage. I can always upgrade my gear later. A room is forever (or very expensive to change later).

Anyway, still no firm date as to when I'm returning to Brisbane so this is all a pipe dream. B)

#8 MarkTecher

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Posted 02 July 2007 - 08:56 PM

Thanks for the detailed explanation. I'm hoping to have a dedicated theatre room when I get back and the room will be built from scratch as part of rennovations so I should be able to do it right. I presume when you say there is much more to it than that you're referring to treating the front wall?


Your welcome :) Yes treating the front wall including baffling the speakers...

A room is forever (or very expensive to change later).


Ain't that the truth...

Anyway, still no firm date as to when I'm returning to Brisbane so this is all a pipe dream. B)


It's good to have dreams...

Mark

#9 Taki

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Posted 02 July 2007 - 10:40 PM

I agree with having the speakers inside the 16x9 frame.

I used to have them just inside the 2.35 edges but found it too wide.

As Mark said, it actually sounds better even for scope films having the speakers inside the 16x9 frame.

The added advantage of doing this for those with AT screens is that you don't need AT side masking for 2.35-16x9.

#10 MarkTecher

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Posted 03 July 2007 - 01:39 AM

I agree with having the speakers inside the 16x9 frame.


and 3 CIH'ers on this forum now do this


And you were one of the three I had in mind :)

Mark

#11 MarkTecher

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Posted 24 July 2007 - 10:28 AM

I have compiled the official CIH list (as requested) but realized that if I post it here, it can only be editied (for updates) by the mods...

Mark :mellow:

#12 Prior

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Posted 24 July 2007 - 11:00 AM

I have a question for you Mark.

I am considering Floor standers for my rear speakers (Krix Apex) in a 5.1 setup, as I will be able to better place them. Currently, my surround speakers are mounted high, and above a cabinet on one side, and a bookcase on the other. By using floor standers, I can get the speakers down to what I understand is a "prefered" position.

Now, the question is, if I later decided to expand to a 7.1 system, is it better to run the 4 surround speakers at the same height? or won't it matter if one of the pairs is mounted high?

Cheers,

Chris

#13 Stets

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Posted 24 July 2007 - 01:04 PM

Thanks Mark

Very informative and timely write up as I've just finished designing my DVD rack for the new home theatre DVD Rack which at 2.6metres long would place my floor standing fronts beyond the 1.78:1 mask

If the speakers are positioned at the extremities of the 2.37:1 screen will toeing them in help with the sound location

#14 yamapro

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Posted 24 July 2007 - 07:12 PM

Great write up and very usefull information Mark.

As always, very much appreciated :D

It's great to see the level of sophistication many of us are now incorporating into our 'entertainment zones' at home and a lot of it is largely thanks to a few very good people like yourself ;)

Also Fwiw and to anyone interested, we're trying to get ourselves a house built soon and it gives me a blank canvass to design a dedicated theatre from the room layout stage! Sooooo exciting... (especially as i will be able to incorporate CIH along with AT screens, electronic controlled side masking and true uncompressed 7.1ch surround) - for a reasonable budget many of us can now have theatres in our homes with top notch equipment and set up to rival, if not slay the local multiplexes :D :D :D

#15 MarkTecher

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Posted 24 July 2007 - 08:15 PM

I have a question for you Mark.

I am considering Floor standers for my rear speakers (Krix Apex) in a 5.1 setup, as I will be able to better place them. Currently, my surround speakers are mounted high, and above a cabinet on one side, and a bookcase on the other. By using floor standers, I can get the speakers down to what I understand is a "prefered" position.

Now, the question is, if I later decided to expand to a 7.1 system, is it better to run the 4 surround speakers at the same height? or won't it matter if one of the pairs is mounted high?

Cheers,

Chris


Where possible you should have the four surrounds at the same height. Back Surrounds essentially do for the surrounds what front centre does for the front stage. The best results will depend on how well your speakers are tonally matched as well as their placement. Unlike the front LCR speakers, surrounds can be elevated to as high as 30 degrees above seated ear height...

If the speakers are positioned at the extremities of the 2.37:1 screen will toeing them in help with the sound location


It helps for 2.37:1, but may still leave you hearing sounds too wide for the smaller ARs of 1.78:1 and 1.33:1. Human hearing is more sensitive to horizontal mis-aligmnent than vertical. I do hear the difference, but most that visit my system would not notice if the speakers were placed wide...

Great write up and very usefull information Mark.

As always, very much appreciated biggrin.gif

It's great to see the level of sophistication many of us are now incorporating into our 'entertainment zones' at home and a lot of it is largely thanks to a few very good people like yourself wink.gif

Also Fwiw and to anyone interested, we're trying to get ourselves a house built soon and it gives me a blank canvass to design a dedicated theatre from the room layout stage! Sooooo exciting... (especially as i will be able to incorporate CIH along with AT screens, electronic controlled side masking and true uncompressed 7.1ch surround) - for a reasonable budget many of us can now have theatres in our homes with top notch equipment and set up to rival, if not slay the local multiplexes biggrin.gif biggrin.gif biggrin.gif


Maybe something like THIS :)

Mark

#16 yamapro

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Posted 25 July 2007 - 05:43 PM

Maybe something quite similar...although slightly bigger perhaps :D

#17 MarkTecher

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Posted 25 July 2007 - 06:30 PM

Maybe something quite similar...although slightly bigger perhaps :D

Well it is easy to scale up if need be...

Mark

#18 Coops22

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Posted 03 August 2008 - 12:19 AM

I was just doing a search on CIH and seeing as though this has such great info I thought I'd give it a bump. I already have a diy scope screen but I want to go curved next and a bit bigger. Anyway thanks Mark for the great read.

#19 MarkTecher

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Posted 03 August 2008 - 06:08 PM

I was just doing a search on CIH and seeing as though this has such great info I thought I'd give it a bump. I already have a diy scope screen but I want to go curved next and a bit bigger. Anyway thanks Mark for the great read.


Hey cool Coops, thanks :)

Mark

#20 weff

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Posted 11 November 2009 - 03:21 PM

The original article references the following (now locked) link http://home1.gte.net...39/thxscope.gif

Accordingly, it is somewhat difficult to interpret to get screen height/viewing distance figures!

Does anyone have a copy of the target file http://home1.gte.net...39/thxscope.gif that they could display here ?

#21 50MXE20

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Posted 11 November 2009 - 06:19 PM

The THX site seems to have removed the diagrams with angles but the Dolby site still has a few

http://www.dolby.com...uide/index.html
They talk about 22 to 26 degrees

#22 MarkTecher

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Posted 12 November 2009 - 11:56 AM

It seems THX is working around a fixed screen or large flat panel where the viewing angle is 40 degrees and with the L and R speaker outside of that. It might be safe to assume that they are recommending 60 degrees for thier L and R placement on the diagram in THIS LINK.

#23 50MXE20

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Posted 12 November 2009 - 02:49 PM

30 degrees each?

#24 MarkTecher

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Posted 12 November 2009 - 03:34 PM

30 degrees each?


I would say so. It seems that they have based their front layout on the ITU-R.

#25 EasterBunny

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Posted 13 November 2009 - 08:57 AM

I would say so. It seems that they have based their front layout on the ITU-R.


Isn't it 45 degrees between them

http://www.thx.com/h...kers/front.html

much the same as Dolby but DTS seem to favor the slightly wider 60 degrees.