# in-ceiling rear speaker placement?



## MikeL (Jun 18, 2006)

I've been looking for information regarding placement of rear in-ceiling speakers but can't seem to find any. Are there any formulas regarding how far back and at what angle (relative to the listening position) they should be placed?

In addition, am I losing anything with using in-ceilings for rears as apposed to standard speakers....will they sound too high (9 foot ceiling)? If I am losing something using in-ceilings would there be a case for going 7.1?

Thanks,
Mike


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## Chester (Feb 19, 2007)

The sound will be 'different' using in ceiling speakers, as a 'test' try looking down at the ground while listening to your speakers and then look up and notice how the sound changes... doing it right now, it sounds like 4-8kHz is a bit muffled: if you were to compare the hrtf (head related transfer function) graphs (assuming you ears are exactly like the model originally measured)... A while back I was going to figure out what you are talking about however I just never got around to it 

edit: i know there was a free program that allowed you to process audio so it sounded like it came from various directions using convolution (i think) I will try and find it again...


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## tonyvdb (Sep 5, 2007)

In ceiling speakers is a "last resort" option. For music you can get away with it but for Home Theater you will loose alot of the imaging and separation that you get with speakers placed behind/beside the listening position and up at about the 6' mark. 
You will need to pay at least twice if not three times as much to get in wall/ceiling speakers that will give you satisfactory results.


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## Chester (Feb 19, 2007)

http://www.holistiks.com/amphiotik/index.php
this site has the program I was thinking of, I know there is another one that is free (this gets you a demo) also there are some HRTF measurements done by the MIT media lab (in 1994 ) 
http://sound.media.mit.edu/resources/KEMAR.html
http://alumni.media.mit.edu/~kdm/hrtfdoc/hrtfdoc.html

It would make sense that using the difference between the hrtf response of where the speakers *are* relative to where you want them to sound like they are as a house curve would make it sound like the speaker is not in the ceiling... I will be investigating this  however help would be appreciated

The Holistiks program has all the MIT data in it (it appears) however there are also measurements done in Japan; this site appears to have them :http://www.sp.m.is.nagoya-u.ac.jp/HRTF/database.html


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## Chester (Feb 19, 2007)

I have made some progress  the best impulses to get (for figuring out differences between different directions) are the "Compact" ones, they have been pre-EQ'd so you have a 'pure' response.
http://sound.media.mit.edu/resources/KEMAR/compact.zip
There are stereo wav impulse responses in 10 degree elevation offsets, and 5 degree horizon offsets; using Ctrl+Shift+I in REW you can import the wav responses... should be able to make cal files (to find the differences between various measurements) too; been workin on that part now 

Addition: as it turns out (from my observations), a speaker directly overhead will have a *flatter* frequency response (to your ear) relative to a speaker placed directly on axis to the ear, which was a bit supprising


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## tonyvdb (Sep 5, 2007)

Chester said:


> Addition: as it turns out (from my observations), a speaker directly overhead will have a *flatter* frequency response (to your ear) relative to a speaker placed directly on axis to the ear, which was a bit supprising


Your findings are sound however you forget that anybody sitting outside of the "sweet spot" will not get much if any of the highs and that is why mounting them beside or behind gives much better coverage. Unless your the only one in the room and you sit just in the right spot (the listening position) you wont get very good results.


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## Chester (Feb 19, 2007)

True; my 'final correction' will probably be derived from looking at the trends of the responses; not necessarily a direct 1:1 mapping of the 90degree vertical to on axis to the ear. I am maybe 40% the way there so far  there is still a lot to figure out... Hopefully there is some sort of response that will yield decent results for all of the listeners in the room. Remember, there is no great way (that I know of) to setup a large "sweet spot" in a room to begin with, as you get more and more off axis of the tweeter/speaker the high frequency response will continue to decrease: I have had trouble pointing one tweeter in two directions myself  so there will always be compromises.

For our tv setup, we have two couches side by side, however I have configured them so that there is actually no one sitting in the sweet spot (the sweet spot is in the isle in the middle) however when setting the "toe in" I figured out what angle would make each tweeter have the greatest 'couch coverage' hitting both couches evenly and used that as the toe in which yields pretty good results; the front speakers are Klipsch Synergy F-1's and the rear speakers are MTX H825C (in ceiling speakers) however the ceiling speakers are in the wrong locations, basically right behind one of the couches (has been messed up since the house was built) so I do not actually use the rears at the moment  I need to cut some new holes...

Clarification: when I say setup a large "sweet spot" I mean have a flat or corrected to be flat frequency response over more than one point... as you move from the point the response will become more and more colored

Another thought: I believe that the farther from the "large sweet spot" you can position the speaker, the more even a response you can get at the large listening location, granted; if you cannot direct the tweeters to be pointing somewhat at the listening location you may have very poor high frequency response because the more off axis you are the worse the highs will be...
-You can use a cheap flashlight to 'simulate' the initial response of a speaker quite well, typically a cheap flashlight will have a brighter spot in the center of the beam and tapers off the more off axis you get, just like a speaker does


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## tonyvdb (Sep 5, 2007)

Chester said:


> Hopefully there is some sort of response that will yield decent results for all of the listeners in the room. Remember, there is no great way (that I know of) to setup a large "sweet spot" in a room to begin with, as you get more and more off axis of the tweeter/speaker the high frequency response will continue to decrease: I have had trouble pointing one tweeter in two directions myself  so there will always be compromises.


Going 7.1 is a great way to improve coverage and even better is to use Dipoles and Bipoles for speakers as that dramatically improves coverage.


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## Chester (Feb 19, 2007)

True; you can always add more speakers  when I said "there is no great way (that I know of) to setup a large "sweet spot" in a room to begin with" I was considering a 2 channel system  or a 5 channel system with each channel driven independently.

As far as dipoles/bipoles, I do not have much experience with them (I had heard of them though) however I suspect they are a good solution to the problem; though I would like to see some polar response plots or something to get an idea about the directivity

EDIT: I meant a "2D directivity plot", however polar plots would also be good... an example being:








taken from:http://proaudio.com.es/equipos-pa/adamson-y10-line-array/


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## Rog111 (Jun 23, 2013)

This might be of interest to you I have kinda done this. So it caught my eye. Then and when I seen your post I wanted you to see it too. They are ceiling mount real speakers check it out. We are talking about JBL SYNTHESIS
system here I think there IT for just movie Home theater setup. Not many people will argue that point. 

The surround speaker polarity set up in this shows what I have always preached wire 2 speaker out of phase and you lose them in a room. Try it sometime. Now that is what surround speakers are suppose to do. 

When I dreamed of having real Di-pole speakers I had 4 Bose 501 hanging upside down by hooks in the bottom rear corners 2 side by side out of phase one pair to my left and one pair to my right, At the sweet spot seating position. Then to the front and rear of the side by side 501 I had 6 ceiling. With 3 in front in phase with the front firing Bose 501 Then 3 to the rear in phase with the rear firing Bose 501 So total 4 Bose 501s and 12 ceiling speakers. Now I have the real deal and to be honest the DIY Dipole out of phase array Sounded Better than My JBL S2A dipoles. I don't have a drop ceiling anymore or I just might go back, 
But for now I have my 2 JBL S2A to my sides and 2 Martinlogan Cinema hanging from the ceiling firing foward. I have a 7. 11 setup with martinLogan speakers all around most of my old jbl synthesis setup the processor to the 7.1 input on my DTC-9.8 Then 4 Jbl synthesis HT4V serve as Presence Speakers thanks to my old Yamaha DSP-1 By the way that 7.11 was not a typo but I'll save that for another day. the .11 = 10 peavey FH-2 folded horns and 1 JBL HTS 400


From the technical guide or the installation guide for JBL SYNTHESIS-DIGITAL. ACOUSTIC CALIBRATION ...

1. Side surround speakers are to be mounted with the top of the enclosure facing the center of
the room, as near to the adjacent wall as possible.
2. Rear surround speakers are to be mounted with the top of the enclosure facing the video
display screen, as near to the adjacent wall as possible.
3. If they are placed in a pre-fabricated hole or cutout in the ceiling, it must exceed the
speaker width by no less than 24".
3.1. Center the speaker in the opening.
3.2. Any open area behind the speaker must be filled to minimize acoustic resonances.
4. Do not allow anything to obstruct the drivers.
4.1. If decorative cloth is placed in front of the speakers, be sure the frame for the cloth
does not obstruct the drivers.


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