How To Calibrate a Multi Row Home Theater

[admin]

If you’ve got a multi row theater room, you’re probably wondering what the best method of calibration would be. Setting channel trims and delay settings properly are paramount to ensuring good sound quality, but at what seated position should they be set too? This article explores how to effectively ensure good calibration across the whole listening area and not just one sweet spot.


Discuss "How To Calibrate a Multi Row Home Theater" here. Read the article.

[shamus]

Thanks Gene.

If you’re on the fence about going direct radiator vs bi-pole for your side channels and you’ve got multiple rows of seating, I strongly encourage you to take the plunge for the bi-pole option.

What about using a pair of direct radiators for the sides?

[gene]

What about using a pair of direct radiators for the sides?

Nothing wrong with that, but as you can see in my article, you get better coverage with Bi-poles across multiple rows of seats.

[jostenmeat]

Interesting article. Since I've had two rows, I've actually worsened my surround envelopment (but it was awesome before, IMO).

I also have my center channel running hot. And it always seems like I am slowly, but surely, notching down the side surrounds. They are monopole bookshelves, but I now I am more strongly considering the bipole type. I am only somewhat hesitant, because I like my speakers, and the matching bipoles are not cheap by any means.

[shamus]

Nothing wrong with that, but as you can see in my article, you get better coverage with Bi-poles across multiple rows of seats.

Sorry Gene, I meant a pair on each side the way a bipole simulates.... like a theater (9 all together if you count the rears). Your Denon can use its A + B side speakers with separate delays, volume and even Audyssey.

Anybody try that?

[Savant]

Gene,

Great article, Gene. (As usual!!!)

If you don't mind, some thoughts, etc.:

1. For a slightly different approach, I have often found it useful to calibrate an HT at no fewer than 4 and as many as 10 different seating locations. An analyzer that allows a running average of the sound level to be taken is most useful for this since the measurement can be paused while the meter/mic is moved to the next location. This removes the guesswork involved in taking sound level readings at multiple points. If you can get the average response of all the different listening positions to come out like you want it, all the different compromises you talk about can get that much easier. Just be sure to choose as many left-side positions as right-side positions to average out the effects of proximity to side and rear channel loudspeakers.

2. Your article highlighted (for me anyway) the importance of size of room and subsequent treatment thereof. A larger room has less variation since the relative spacing of seating rows stays the same, but the distance to the sources increases. (Hence the reason a large movie theater is relatively simple to calibrate.) Moral: Build it as big as you can. A larger room is also relatively easier to treat. Since most listening positions are more firmly planted in the reverberant field, there will be fewer intracacies involved when treating with absorption or diffusion or both. In fact, the argument for diffusion gets better since overabsorbing could lead to highlighting echo problems. Of course, all this is moot unless you can get the distance between listener and side/rear source to be greater than about 8 feet. (And you have the appropriate ceiling height and front-to-seats spacing as shown in your diagram.)

3. The change in SPL vs. distance issue is noteworthy. What is also worth mentioning is the frequency dependence of this. It's related to the distance from the source. The 3 dB/halving you mentioned will only apply to frequencies whose wavelengths correspond to 1-2 times the distance from the source. In other words, you'll only observe the halving from your rear speakers - about 4 feet away - above about 300-500 Hz. Below that range, very little decrease versus distance. Highlighting once again the importance of good LF control. (It's also worth noting that a room treated primarily with diffusion in the rear sound field will experience almost no variation in sound level vs. distance over most of the frequency range.)

Some other minor things:

- IMO, microphone orientation doesn't matter if the mic is omnidirectional. (There's a good discussion of this topic here.) You could point it at the floor and get the same results. What you said about placing it above the back of the seats is very important though. In fact, be cognizant of diffraction effects over hard seatbacks if you're placing the microphone right behind a seat. The mid/high frequency sound levels could measure higher than when the mic is placed in front of the seat for sound coming from the front channels. (Or vice versa if the sound is coming from behind.)

- This is nitpicky, but - IMO - there's really not much point in reporting sound levels to the 1/10th of a decibel. Rounding to the nearest decibel is perfectly adequate since most people cannot hear changes of less than 1 dB. (I know that some would argue; research has certainly shown changes in 0.1 dB are detectable to some people. However, most of that research has involved the use of tones as the noise source. I know of very, very few people who can detect differences less than 1 dB when the source material is Batman Begins or Two Against Nature.)

[gene]

Gene,

Great article, Gene. (As usual!!!)

If you don't mind, some thoughts, etc.:

1. For a slightly different approach, I have often found it useful to calibrate an HT at no fewer than 4 and as many as 10 different seating locations. An analyzer that allows a running average of the sound level to be taken is most useful for this since the measurement can be paused while the meter/mic is moved to the next location. This removes the guesswork involved in taking sound level readings at multiple points. If you can get the average response of all the different listening positions to come out like you want it, all the different compromises you talk about can get that much easier. Just be sure to choose as many left-side positions as right-side positions to average out the effects of proximity to side and rear channel loudspeakers.

2. Your article highlighted (for me anyway) the importance of size of room and subsequent treatment thereof. A larger room has less variation since the relative spacing of seating rows stays the same, but the distance to the sources increases. (Hence the reason a large movie theater is relatively simple to calibrate.) Moral: Build it as big as you can. A larger room is also relatively easier to treat. Since most listening positions are more firmly planted in the reverberant field, there will be fewer intracacies involved when treating with absorption or diffusion or both. In fact, the argument for diffusion gets better since overabsorbing could lead to highlighting echo problems. Of course, all this is moot unless you can get the distance between listener and side/rear source to be greater than about 8 feet. (And you have the appropriate ceiling height and front-to-seats spacing as shown in your diagram.)

3. The change in SPL vs. distance issue is noteworthy. What is also worth mentioning is the frequency dependence of this. It's related to the distance from the source. The 3 dB/halving you mentioned will only apply to frequencies whose wavelengths correspond to 1-2 times the distance from the source. In other words, you'll only observe the halving from your rear speakers - about 4 feet away - above about 300-500 Hz. Below that range, very little decrease versus distance. Highlighting once again the importance of good LF control. (It's also worth noting that a room treated primarily with diffusion in the rear sound field will experience almost no variation in sound level vs. distance over most of the frequency range.)

Some other minor things:

- IMO, microphone orientation doesn't matter if the mic is omnidirectional. (There's a good discussion of this topic here.) You could point it at the floor and get the same results. What you said about placing it above the back of the seats is very important though. In fact, be cognizant of diffraction effects over hard seatbacks if you're placing the microphone right behind a seat. The mid/high frequency sound levels could measure higher than when the mic is placed in front of the seat for sound coming from the front channels. (Or vice versa if the sound is coming from behind.)

- This is nitpicky, but - IMO - there's really not much point in reporting sound levels to the 1/10th of a decibel. Rounding to the nearest decibel is perfectly adequate since most people cannot hear changes of less than 1 dB. (I know that some would argue; research has certainly shown changes in 0.1 dB are detectable to some people. However, most of that research has involved the use of tones as the noise source. I know of very, very few people who can detect differences less than 1 dB when the source material is Batman Begins or Two Against Nature.)

Jeff great feedback!

I noticed in the past using Rat Shack SPL meters that supposidly have omni directional mics that simply placing them forward facing as opposed to up, wrecks havoc on calibration accuracy. I am pretty sure this didn't have to do with obstructions from furniture as much as the mic not being as omnidirectional as it should be. This is why I recommend pointing them up and away from surfaces of furniture.

I like your idea about averaging the SPL across all the seats but I also think the far left/right seats should be reserved for the casual listener and the mother-in-law that doesn't care about the fidelity as much. This is why I think the money seats should be dead center in each row with less emphasis placed on the others. This article was intended as a primer and simplified version. I didn't want to get too tech in it. But I invite you to write a version for advanced users using your methodology if your game

[Savant]

I have heard that about the RS meters, but have never experienced it. (I will have to look into it in more detail now, of course. Thanks! ) While I have absolutely nothing against the RS meters, I tend to implement 1/3- or 1/12-octave-band analyzers when calibrating, among other tools.

My averaging idea is admittedly more/most applicable to larger theaters, on the order of 2-3 rows of 4-5 or more seats per row. (It's especially difficult to justify calibrating to the center of a theater with an even number of seats across each row.) (It is equally challenging to explain to the owner of said theater the reasons why they should have considered an odd number of seats across each row. )

As for writing my own, it would be difficult to outdo you. You covered so much, my nitpicking aside, that audioholics en masse should be more than adequately armed to calibrate their rooms. I appreciate the invite, though, and will put the topic on The List. (When I ever get to The List is the significant variable!)

[jostenmeat]

Nothing wrong with that, but as you can see in my article, you get better coverage with Bi-poles across multiple rows of seats.

Gene, my local dealer has a good deal going on matching bipoles (blemished). What's cool is that I can trade stuff in as well. Questions before I might pull the trigger.

First the description about my setup:

- monopole side surrounds straddle two rows.
- When somewhat reclined in back row, the speakers are forward to the point of being about mid-calf or so.
- Above ear level of front row, at ear level of rear row when fully reclined. I guess 5 inches below ear level when fully upright.
- Each row has 4 seats. The listener on any extreme end of the opposite surround is about 11-12 ft depending on the side.
- The room is not an enclosed symmetrical rectangle, but with a large opening on one side.

Questions:
- Would a bipole's off-axis orientation be too extreme from 11-12 ft?
- Would a bipole'e effect in any way be compromised by being at or slightly below ear level? Or what I mean to ask is if a bipole might depend on higher mounting than a monopole would... I assume not, but safer to ask.
- Would a bipole's effectiveness greatly depend on either an enclosed or symmetrical room? I assume not, but safer to ask!

Bonus question free of charge:
- What do you think of changing out rear monopoles for bipoles? I have 7-8 ft behind rear row, but am really looking for anything that is easier to mount higher (wall mount) than my present PSB B25s.

Thank you, I appreciate any insight. I noted that the RBH speakers in your article have out-of-phase tweeters. The PSB S50s Im eyeing are bipole only, AFAIK. Thanks again!!!

[sbquart]

I want to add another set of side surrounds, I have an onkyo 805. What is the proper way to wire them up to the reciever and would each individual side speaker level match that of the other speakers or would you calibrate both speakers on say the right side at the same time to match the other speakers. I always feel the sound is to far forward when I am in my back row. I am running dipoles now from atlantic technology placed right between the rows.