ceiling speakers

[Lucid]

There is science in terms of speaker placement. The black art comes in the application of that science in relation to the compromises required for real world applications

If there's no need to consider furniture arrangements and seating positions then the rough rule of thumb is 1/3rds and 1/5ths. I'll explain....

Every room has a set of frequencies where the room resonates. Resonance is where the sound seems to boom. These frequencies are governed by the dimensions of the room; so there's on frequency for the length, one for the width and one for the height. We call these the fundamentals. The bigger the room then the lower those frequencies will be. The fundamentals for your room length and width (and based on a standard 2.4m ceiling height) are roughly 19Hz, 36.5Hz, and 72Hz. If you generate each of those tones and stand in the exact centre of the room then they'll sound incredibly loud, and as you move from the centre they'll die away to almost nothing at certain points. The result is that the sound changes a lot depending on where a person is sitting or standing for those frequencies.

Each frequency then has a series of harmonics. If you haven't come across harmonics before then the easiest way to think about them is to look at what happens when a guitar string is stopped at various points along the neck. The whole length of the string when plucked is the fundamental. Stop the string exactly half way along its length and pluck it then you hear the first harmonic. Do it at 1/4 and that's the second harmonic and so on. Rooms have harmonics too. Divide any room dimension in to even fractions (1/4, 1/8 and so on) then you'll be sat at one of the higher harmonics for that length.

So now you know the physics then here's how this applies to speaker and seating placement in rooms...

Even fractions are bad acoustically. Don't put your speakers in at 1/2 or 1/4 or 1/8th position of the length or width. All it will do is excite the room resonant modes and make certain frequencies boomy. Equally, don't arrange your seating so that listeners will end up sat with their heads at 1/2, 1/4, 1/8th etc of the length or width. What you should do instead is aim for speakers and listeners to be at the odd fractional lengths instead. So a 4.7m width means placing the centre of the speakers at 4.7/3 (1.56m) from the front or back walls. A 9m length means 3m from the side walls.

What you'll often find though is that there are joists or lighting in the way. In that case then go for the next nearest odd multiple (1/5th).

 

[bernardgreen]

Every room has a set of frequencies where the room resonates

True for the average domestic room. But not for a room with sound absorbent walls. Very disconcerting to stand in an anechoic chamber where all sound is absorbed when it reaches a surface.

But sound absorbing items in the room will affect the resonance of the room.

Stop the string exactly half way along its length and pluck it then you hear the first harmonic.

Stop it half way and damp it ( soft touch that does not fully stop the string ) at one quarter and the sound will be the same frequency but with over tones at twice the frequency.

A big soft sofa would damp the resonance, a solid piece of furnture would be like a stop on the string.

 

[Lucid]

Every room has a set of frequencies where the room resonates

True for the average domestic room. But not for a room with sound absorbent walls. Very disconcerting to stand in an anechoic chamber where all sound is absorbed when it reaches a surface.

But sound absorbing items in the room will affect the resonance of the room.

Stop the string exactly half way along its length and pluck it then you hear the first harmonic.

Stop it half way and damp it ( soft touch that does not fully stop the string ) at one quarter and the sound will be the same frequency but with over tones at twice the frequency.

A big soft sofa would damp the resonance, a solid piece of furnture would be like a stop on the string.

I'm not sure why you're being so nit-picky. We are talking about the speakers going in to a guy's living room and not anechoic chambers.

As for Hi-Fi enthusiasts (your word 'fanatics') having rooms lined with sound absorbing materials, only the really dumb ones would do this. A 'dead' sounding room is a sonic disaster for listening to music. We are used to having some reverberation, and so listening in a room without it or in a room that is overly damped just feels unnatural. Anyone interested in getting the most from their music or movie replay system would use a mixture of sound absorption and sound diffusion. Of the two it is sound diffusion that is the most useful.

 

[bernardgreen]

The anechoic chamber is the extreme of the absorbent room and is very good if one is listening to stereo and wants to have a near perfect re-creation of the sound image as recorded on location. Reflections from walls distort the sound image.

Yes I am a bit ni picking. But it comes from having seen and heard some horrendously un-sucessful audio installations

As for Hi-Fi enthusiasts (your word 'fanatics')

Enthusiasts enjoy the music,
Fanatics keep Russ Andrews in business,, fanatics enjoy the ( perceived by them ) perfection of the reproduction process. . ( sound reproduction. they may not be aware of any other process )

 

[Lucid]

The anechoic chamber is the extreme of the absorbent room and is very good if one is listening to stereo and wants to have a near perfect re-creation of the sound image as recorded on location. Reflections from walls distort the sound image.

I am well aware of what an anechoic chamber is and its advantages having used one in the past. However, it's not a pleasant listening environment for lots of other reasons. It's neither practical nor is it desirable to replicate that effect in a domestic listening room. Orchestras, bands, choirs etc do not perform live in echo-less environments, quite the opposite in fact. We are used to hearing the environment as well as the sound source, and the same goes for music reproduced at home.

Yes I am a bit ni picking. But it comes from having seen and heard some horrendously un-sucessful audio installations

Thank you for the acknowledgement.

I don't doubt that you have heard some bad installations. So have I. However, in the context of this forum all we are trying to do is to help people avoid the major pitfalls when they're trying to get some use from their audio visual equipment. I suspect we could both go to extreme lengths planning an installation, but along the way we'd lose the attention of the enquirer who often is just looking for some simple answers.

Enthusiasts enjoy the music,
Fanatics keep Russ Andrews in business,, fanatics enjoy the ( perceived by them ) perfection of the reproduction process. . ( sound reproduction. they may not be aware of any other process )

Well, I know enough enthusiasts who use fancy- mains leads, equipment racks and the like but who would baulk at the idea of being called a fanatic.

Your original point was that fanatics would attempt to produce and echo-less room by lining it in sound absorbing materials. My view is that fanatics obsess over detail, and anyone making an obsessive study of acoustics would know that a mixture of absorption and diffusion are required. Hence 'fanatics' in the plural sense would be unlikely to do what you originally suggested.

 

[Jupiter01]

Thanks guys. I've ordered the cable, let's start there
On the placement of speakers I've now read your guidance twice but I'm stil struggling with the locations you are suggesting. The preamble makes sense and I found the theory very interesting. I thought it would help if I send you a map of my house along with an indication on where "stuff" is and is going:

The red rectangles are sofas and there will be a dining table below the roof lantern. The roof lantern is around 3m by 3m.
For completeness, the amp, etc. is going under the TV and I want speakers throughout the ground floor. This includes the front lounge and dinning area along with kitchen and hallway. I'm also going to be stuffing acoustic insulation between the floor joists.

I thought If I can understand the rationale used for the lounge at the back, I can then extrapolate this out for the rest of the house. Thanks again.

 

[Lucid]

You say you follow the preamble and (my guess) some of the theory. So what exactly is it you're struggling with specifically?

 

[Jupiter01]

Hi @Lucid, I'm struggling with the placement and this part of your post:

Even fractions are bad acoustically. Don't put your speakers in at 1/2 or 1/4 or 1/8th position of the length or width. All it will do is excite the room resonant modes and make certain frequencies boomy. Equally, don't arrange your seating so that listeners will end up sat with their heads at 1/2, 1/4, 1/8th etc of the length or width. What you should do instead is aim for speakers and listeners to be at the odd fractional lengths instead. So a 4.7m width means placing the centre of the speakers at 4.7/3 (1.56m) from the front or back walls. A 9m length means 3m from the side walls.

Where is the 1.56m point for instance? How many speakers are reccommended in this space? How much distance do I need to have between each speaker? That's the part I am unclear on.
There was also a focus on the configuration of the room so I thought it would be helpfulto draw this up for your comment.

Instinctively, I felt that I would need 4 speakers in this space but I would struggle to substantiate this...

 

[Lucid]

Okay. I presume you understand the concept of fractions well enough that if I said divide the length of your room in to 1/3rds and mark each division then you'd take 9m, divide it by 3 and end up with 1/3rd = 3m, right? Then taking the TV wall as the start point, you put a mark at 3m to signify the point that is 1/3rd of the room's length, and one at 6m to signify the point at 2/3rds of the rooms length.

Now if I said "Please divide the room's width in to thirds" then you'd follow the same method, correct? So 4.7m/3 = 1.56m = 1/3rd. Therefore 2/3rds = 2x 1.56m = 3.12m

Then if I said "Find the point on the ceiling of your room that is 1/3rd the length back from the TV wall, and 1/3rd the width of the room from the wall with the bi-fold doors", would you be able to do that? That's all this is. It's dividing the room up along its length and then its width, and then seeing where those lines of division intersect.

Speaker Locations In Thirds

• Lucid
• 7 Mar 2016
• 1

Clearly the right-most speakers can't go at a 1/3rd multiple of the room's length because the roof lantern is there. So the next thing to do is divide the room's length in to 1/5ths and see if the result is any better. (see below)

Speaker Locations In Thirds And Fifths

• Lucid
• 7 Mar 2016

Of course there's nothing to stop you mixing 1/3rd positions and 1/5th positions. The diagram below shows the speakers nearest the TV at 1/3rd of the room length and those nearest the roof lantern at a multiple of 1/5th.

Speaker Locations In Thirds And Fifths_simplified

• Lucid
• 7 Mar 2016

The point of the exercise is to take some control of the speaker placement based on solid acoustic principles rather than accepting some arbitrary positions because "It looks nice" or "That's where the electrician put them". Both those result in the"horrendously unsucessful audio installations" to which bernardgreen alluded. Electricians tend to go with what's easiest and most convenient for them; by-and-large they are not audio and video installation engineers.

 

[bernardgreen]

It's neither practical nor is it desirable to replicate that effect in a domestic listening room. Orchestras, bands, choirs etc do not perform live in echo-less environments, quite the opposite in fact

A stereo recording of a band playing in an open air environment will only be able to create anything like the same sound image ( the placement of the various instruments relative each other ) if the room has the similar echo characteristics to those of the location where the recording was made and the loudspeaker positions relate to the position of the microphones.

I still maintain it is a black art and cannot be predicted. Trial and error with speakers on temporary mountings being tried in different locations until the best results are obtained.

That said with a lot of modern "music" the need for accurate reproduction is not so essential

 

[Lucid]

A stereo recording of a band playing in an open air environment will only be able to create anything like the same sound image ( the placement of the various instruments relative each other ) if the room has the similar echo characteristics to those of the location where the recording was made and the loudspeaker positions relate to the position of the microphones.

Here's where you and I diverge. My view is that depending on the recording technique a live single-pass recording will contain some element of the ambient signature of the room to a greater or lesser degree. No amount of speaker placement experiments or room treatment is ever going to reproduce that sound, nor should it. If it's a living room then the room should be comfortable for normal conversation. Any room treatment should focus on dealing with the worst room modes and absorbing first reflections. After that the aim should be to dissipate the energy within the room to reduce the RT60 time by using diffusers.

Recording is itself a compromised process, as is the process of reproduction. Very few of us have the space or funds for the sort of size of speakers and power of system to faithfully reproduce a single double bass or a concert piano let alone a full orchestra or band; so why chase unrealistic goals.

I still maintain it is a black art and cannot be predicted. Trial and error with speakers on temporary mountings being tried in different locations until the best results are obtained.

There will be elements of fine tuning. But IMO most of the elements of "black art" is because the practitioner might not have the right tools to understand the room acoustics or the products being installed. Once an installer starts to plot the room acoustics from the main listening positions with a calibrated mic and test tone sweeps then things become far clearer. However, once one starts to cut holes in a ceiling it's somewhat more difficult in a practical sense to say "Let's try that speaker 20cm further in this direction". Given too that with ceiling speakers the backbox is the ceiling void then how do you possibly hope to recreate that with a temporary install?

 

[bernardgreen]

few of us have the space or funds for the sort of size of speakers

My lasting memory of sound was a chap who in the 60's recorded organ music as part of his fascination with pipe and barrel organs. He had developed a microphone and recording technique that had a virtually flat response down to 5 Hz ( or maybe lower ). His bass speaker was in the party wall between his house and the empty house next door. You felt the bass notes vibtrating your body. The only other place I have felt that was when standing in the pipe gallery of a german cathedral between two bass pipes.

 

[Jupiter01]

@Lucid I really appreciate the effort you have gone to. Thiss is very helpful and I am now very clear on what needs to be done. One further question if I may please, what detrmines whether I should have 4 or 10 speakers in this space? Is this an arbitrary decision or is there some sizing that goes into this?

If I did want two speakers in this area, presumably I would then divide the width into two to find teh central point and then carve the length into 1/3 or 1/5 and put the speakers at the intersections? I ask this question, both to understand the prinicple above but I may have this situation in the kitchen, hallway, etc.

Thanks again.

 

[Lucid]

What type, how many, and the configuration of speakers is driven by the volume of space, and the background noise to be dealt with (homes are generally fairly quiet compared to say factories or shops, so this is less of an issue), and whether the client wants sound focussed over a certain area (seating zone) or spread out evenly throughout the space. Then there's budget of course.

Unless the budget is unlimited then hallways and utility areas generally don't generally require the sort of quality that you'd have in the main listening areas. For this reason I tend to use smaller 'contractor quality' speakers or the base-models of the better ranges. These are speakers with a 4"~5" woofer and a basic Mylar (plastic) tweeter. They generally tip in at around £50-£80 each. These don't have a lot of bass but they're only used for background sound levels.

For small areas that justify better quality then a single-point stereo speaker is ideal. This looks like a single 6"-8" speaker but it works a bit like a sub-sat speaker system that you might use with a PC; there's a single bass driver which is mono, but two tweeters, one for the left and one for right treble frequencies. It is fed by two speaker wires (Left and Right) just like you would wire stereo speakers. The speaker itself has two sets of connection (left & right) and a circuit called a crossover does the bass / treble and left / right split. The result is that stereo sound comes out of a single point in the ceiling. Single-point stereo speakers are good for bathrooms, dressing rooms, en-suites, small kitchens etc. I tend to use them in spaces up to 3x3m. Good quality ones generally start at around the £150-£200 price mark. These have enough bass and high-enough audio fidelity to be comparable with- or superior to- a typical £200+ mini or micro Hi-Fi.

For larger areas such as your lounge-cum-dining area then small contract speakers and single-point stereo speakers aren't suitable. Here's where you need more bass (so a bigger bass driver at 6"~8") and a Hi-Fi grade tweeter (soft dome or titanium metal). Other useful features are a tilting tweeter so that the sound can be directed somewhat; maybe some bass and treble adjustment;and possibly the ability to link speakers in a daisy-chain so that 4 speakers only take up the same number of outputs as a basic stereo pair. This last feature is called "4/8 Ohm Switching" and it doesn't appear on too many speakers but it saves a fortune in amplification costs. The bass is equivalent to a typical £300~£500 mini or micro Hi-Fi. These ceiling speakers start at around £250~£300 per pair.

If you are concentrating the sound around (over) a central listening area then four speakers should be sufficient. On the other hand, if you want sound everywhere and for it to be at an even volume throughout a large room then you will meed more speakers. As a rough guide then speakers of this quality will be required at a coverage rate of approximately 1 per 4~6 square meters. This would equate to 8~10 speakers in your room. However, you have a ceiling lantern so some of the ceiling area is missing, and it's also going to have an effect on the sound beneath it, so I would avoid putting speakers too close to it. Unless there's a compelling reason to do otherwise, then the most I would go is six speakers in that room at the 1st, 2nd and 3rd 1/5th points back from the screen.

 

[winston1]

Right so you have 4 speakers in that room. Which ones go to the left channel and which to the right?