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7.1 system – 0, 2 or 4 bipoles for surrounds and rears?

childejc

Established Member
In this 7.1 layout
Plan-AVlayout.jpg

using in-ceiling speakers for my surrounds and rears, would I be better off with
  1. 4 monopoles
  2. 2 bipoles / dipoles and 2 monopoles
  3. 4 bipoles / dipoles

If you think I should have 2 of each, which 2 should be bipoles?

Should I consider tripoles?

Thanks
 
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childejc

Established Member
Thanks - I have heard that too, but it seems to me that if it is good to have a spread of sound from the side then the same would apply to the rears. But I have never heard anyone recommend 4 bipoles. Its always 2/2, with somtimes the rears being the bipoles. Hence my confusion...
 

Mark.Yudkin

Distinguished Member
Take a look at THX Home Theater 7.1 Speaker System Layout. It answers your question and explains why the rears should be direct radiating. The other reason has to do with the fact that your ears are (probably) on the side of your head (hence the desire to emulate a cinema's front to rear spread), rather than on the back of it.

A tripole is an attempt to overcome the "hole in the middle" effect of a dipole that some find very disconcerting. Bipolars do not have one side out of phase, and thus do not suffer from phase cancellation.

In the case of in-ceiling speakers - as per your question - I would have thought the whole question was academic, since such speakers are not on the wall aiming towards the listener, but are embedded in the ceiling. They are radiating down, not across.
 

Mark.Yudkin

Distinguished Member
If you review the descriptions of 7.1 on the THX web site (they're the source for home cinema) you'll see that the location of the rears is more complex than you describe it. You'll also see how 7.1 is used to handle 5.1 and 6.1 sources, how HD changes the recommendations and why, and how to handle the dichotomy.

There is a difference between in-ceiling - as you wrote - and where you have eseentially no control over directivity, and suspended from the ceiling - which would allow you to control the direction, and which is what I've done for for the rears and surrounds.

Bipolar rears are pointless (please study the THX web site), it's the surrounds (sides) where the question can be asked. If they have to be in the ceiing, then the discussion on bipolar etc really is moot - you can't spread the sound horizontally with a speaker that fires down. If you're hanging them off the ceiling them from the ceiling, that's a different matter.

As to whether you want bipolar / dipolar / tripolar, opinions vary and my standard advice is to arrange an in-situ try out. Listening in the dealer's room will be meaningless, as it's all about room interaction and personal taste. I'm using direct radiation all round BTW.
 

childejc

Established Member
Mark

I followed your link, but did not follow all the subsequent links, so I missed the bit about different THX modes and the way the rears are used in each case - very interesting. I also missed the link to Dolby TrueHD for a discrete 7.1 source - I see that they recommend putting the rears apart in that situation. Am I right to think that there are very few discrete 7.1 sources? That generally 7.1 is created from a 5.1 source? Is it therefore true that for most movie viewing, if I use THX modes, I would need the rears to be together?

Presumably as time goes by there will be more true 7.1 sources, so the ability to move the speakers depending on the source will be come more important. Any views on how much difference the different positioning actually makes? If it is significant maybe I should reconsider using floorstanders or stand mounted bookshelf speakers., which I can move as needed.

The in-ceilings I am considering are these - Bipolar In-Wall & In-Ceiling Speakers. Def Tech suggest these are actually suitable for use throughout a 7.1 system, including as front RCL. Given these are bi-polar, does that make any sense to you?

Out of interest, how far below the ceiling do your suspension mounts hold the speakers? And can you fit any decent bookshelf speakers in them?

Sorry to pester you with questions but there are so many options to consider and I want to make sure I get it as right as possible whilst my options are still open. Thanks again.
 

Mark.Yudkin

Distinguished Member
Discrete 7.1 is used on Bluray. DVD tops out at 6.1.

I did not see any indication that the bipolar speakers you're thinking of would be useful for front or centre. In-ceiling is always problematic, as you have no proper control over direction. In some ways, the term bipolar is not really accurate in the context of these speakers, and the site's description of what the speakers are trying to do provides a more accurate explanation than the buzzword.

The Fresco i's are designed to mount on walls and ceilings so they come complete with the mounting kit. They are not bookshelf speakers, although one can buy (short) stands so that they can function as such. Considering the price of the speakers you're thinking of, the Fresco i's price of £800 (each) may be a little above your (unstated) budget.

I separated the rears and used the relevant THX setting, as I expect to go Bluray some day and consider quality speakers to be a long-term investment (at the price, they have to be).
 

childejc

Established Member
Discrete 7.1 is used on Bluray. DVD tops out at 6.1.

I did not see any indication that the bipolar speakers you're thinking of would be useful for front or centre. In-ceiling is always problematic, as you have no proper control over direction. In some ways, the term bipolar is not really accurate in the context of these speakers, and the site's description of what the speakers are trying to do provides a more accurate explanation than the buzzword.

.


Mark - are you saying all bluray is 7.1, or just that 7.1 is only available via bluray, but is not necessarily always available?

On the other point the mention of using the Def Tech UIW BPZ/A (or presumably the BP/A) for all 7 speakers comes from the pdf brochure here http://www.definitivetech.com/literaturereq/prod_lit/UIWBrochure_Complete_0208.pdf. The relevant paragraph, on the first page, is this:

"Choose Our Ultimate Performance Architectural Speakers for a Spectacular Built-in Home Theater System
In addition to bringing music into every room in your house, Definitive UIW speakers are perfect for a spectacular-sounding, high-performance home theater system. Choosing the perfect system is easy because all Definitive speakers are engineered to have the same timbral balance and sonic signature; so they can all be used together in any combination with excellent results. The top-of-the-line signature Definitive UIW home theater system would use three matching UIW BPZ/As or UIW 75s across the front and UIW BPZ/As as rear and/or side surround speakers.
This system will sound great and deliver excellent bass without a separate subwoofer.
However, you can add any of Definitive’s superb powered subwoofers for even higher performance. Remember: any combination of UIWs will work well together and deliver superior performance; so pick the ones that best suit your budget as well as your specific size, design, mounting and listening requirements."

I'm reviewing my design to see if I can in fact put my left and right surrounds onto the wall. For this to work they would have to be above the window height, at about 2.25m. With my ears being at 1.0m when seated, is this too high? Alternatively I could suspend them from the ceiling (which is 2.45m), but I think this would be a similar height. Finally, I could put the speakers on moveable mounts. This is in a way the most appealing as it means I have some flexibility, but I'm not sure how I would get them to the recommended minimum 1.8m (ie minimum 2' above listening position). Of these 2 options do you have a preference?

Thanks
 

Mark.Yudkin

Distinguished Member
Bluray may be anything from mono to 7.1. DVD tops out at 6.1.

I think I see where the misunderstanding has arisen, but it may take a longer explanation. My front speakers are full range electrostatic dipoles - the word dipole being used in its original and technically correct sense of a speaker which radiates an out of phase image in the opposite direction (that is 180°). That is the speaker radiates equally out of the front and the rear (and hence is hard to place). Since phase cancellation can be an issue with the low frequencies in such an arrangement, an alternative is to have the front and rear in phase. This is what Definitive's free-standing bipolar speakers do, as is explained in the section "The Sonic Benefits of our Extraordinary Bipolar UIW Speakers" on p2 of the PDF.

With the introduction of sourround sound speakers, the problem was how to emulate the cinema's line-up of side speakers in a domestic environment, using only two speakers. The idea was to have a speaker with drivers facing in different directions (typically less than 90°) and the terminology (bipole / dipole) was abused for this purpose, with scant regard to mathemetics and precision. The term has become so common in its wrong meaning, that many people no longer know the real meaning.

Definitive's aim is to reproduce this (truly bipolar) soundstage somehow with in-ceiling and in-wall speakers. However, it is important that you realize that bipolar in this context is not the common usage, any more than my ESL-63s have the dipolar arrangement of a "dipolar surround speaker" (whose sound makes me cringe - but YMMV).

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In-wall speakers are always difficult to deal with, as you don't get a chance to audition in-situ, and you don't really get much chance to tune the positioning if you get it wrong at installation. The best advice I can offer is to go to a home automation specialist as they'll have experience. On-wall / on-ceiling speakers are simpler to deal with.

Like you, I had no means of positioning surround speakers at the recommended height, nor any means of placing free standing speakers. Even more annoying was that the speaker height limit meant no electrostats (Script i). One side speaker is above a door, the rear speakers above the dining table. The compromise was to aim then down suitably.
 

childejc

Established Member
Mark

Thanks for the further clarification, which was helpful. I had not appreciated the distinction between di / bi pole speakers or that the term was misused in the way you describe.

Nevertheless it still seems a little odd to use a bi-polar (in either sense) for a centre speech speaker, as they suggest, as speech is the one thing that you do want to be directional. However, this is academic as I will not be using one of their bipolars for my centre. Incidentally, I notice you do not even have a centre. How directional is the voice sound from your dipole system?

I have 3 follow up questions if you don't mind me asking.
1. Do you believe speakers suspended from either the wall or ceiling are better than in-wall/ceiling, assuming I have that option?
2. I think you feel it is better to put speakers in or on the side and rear walls rather than the ceiling - is that correct?
2. This question is only relevant if answer yes to question 2. I have the option of putting my 2 rears either on/in the ceiling or the rear wall. Given my 2 side surrounds will almost certainly have to be on/in the ceiling, does this mean the 2 rears should also be on/in the ceiling, or would it be good to put them on/in the rear wall, even though the sides are on/in the ceiling?

Thanks again
 

Mark.Yudkin

Distinguished Member
1. Do you believe speakers suspended from either the wall or ceiling are better than in-wall/ceiling, assuming I have that option?
They are easier to set up and replace.
2. I think you feel it is better to put speakers in or on the side and rear walls rather than the ceiling - is that correct?
Better yes, but many of us don't really have the choice. It's all about compromise.
2. This question is only relevant if answer yes to question 2. I have the option of putting my 2 rears either on/in the ceiling or the rear wall. Given my 2 side surrounds will almost certainly have to be on/in the ceiling, does this mean the 2 rears should also be on/in the ceiling, or would it be good to put them on/in the rear wall, even though the sides are on/in the ceiling?
It make aesthetic sense for you to be consistent, as you have to live in the room. Ask your wife what she prefers.

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Quad ESLs have excellent audio characteristics and produce a very accurate and stable image. You need room for such speakers (at least 1m behind the speaker), a wife who doesn't complain about a speaker that's 1m tall and 70cm wide and an adequate budget (the smaller ESL-2805 retails for £4500 a pair).
 

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