Big rooms and surround systems

[mustang guy]

For those of us who have very large rooms I wanted to share what I have found. You can have more than two side surround and more than two rear surround. If you have a long room, you might want to have two side surrounds on each side wall. In the Dolby Digital 7.1 spec, the side surrounds are mounted starting 1/3 of the way back, and are repeated every 2 to 3 meters. That means if you have a theater which is 60' long like me, the surrounds would be at 20', and another about every 10' to the back wall. That means left side (LS) 20', LS 30', LS 40', and LS 50'. Personally, I don't think a corner is a good place for a side surround because of wall reflections. Than means in a 60' theater, there will be a minimum of 8 side surrounds. My theater is 50' wide, so I would have a rears that at 10', 20', 30', and 40', again avoiding the corners. That is a total of 4 rear surrounds. Obviously one would need a preamp and use amplifiers to distribute the single signal into multiple signals. For instance, my back side left (BSL) surround signal would go into an amp and come out to the speakers at 10' and 20'. My left side (LS) surround signal would go into an amp and come out to the four side speakers at LS 20' - LS 40'.

What this means in my case is that with my 50' wide and 60' deep theater, I will have a total of 12 surround speakers to provide the 4 discreet channels. As far as the front 3 left/center/right (L/C/R) and the low frequency effects (LFE or subwoofer), the additional speakers are only for the left and the right if the screen is VERY wide. This does not apply in my case. Placement of the subwoofer(s) is interesting. Here is what it says: "The subwoofer cluster should be placed asymmetrically with respect to the center of the room to minimize stimulation of standing waves (room modes)." By their diagram, this seems to mean that you should never center a sub on a wall facing another. They simply offset the subs slightly to one side or the other of the centerline. Furthermore, they recommend clustering the subs rather than spreading them out all over the room.

Most of you know that my large theater isn't really a theater at all, it is a shop. There are not seats filling the space, there are tools and cars, etc. I have a couple sofas and several chairs that can be moved around. It is likely that I will take some of the above advice, but definitely not all. I just found it fascinating that we don't have to be STUCK with one surround per channel. There is absolutely nothing bad about having a surround every 2 meters! Bi-pole surrounds do a good job of acting like several surround speakers, but they do not exactly follow the Dolby standard used in theaters. Those surrounds should be placed every 2-3 meters.

As usual, when I figure something out suddenly, I share it here. If the information were obvious, it wouldn't have taken me this long to have the epiphany. Nobody here ever talks about more than one speaker per surround channel. I think it's high time we did in large theaters.

[Youthman]

Your conclusion makes good sense because that's what they do in movie theaters. My guess is the reason we don't talk about it much is because most of us don't have a 50 foot theater lol

Definitely some great information though for those that do

[mustang guy]

Your conclusion makes good sense because that's what they do in movie theaters. My guess is the reason we don't talk about it much is because most of us don't have a 50 foot theater lol

Definitely some great information though for those that do

A home theater with a length of 21' or more could use multiple side surrounds. For example: If you have a 21' deep theater, your first side would be at 1/3 of the way, or 7', and the next one would be between 13' 7" and 16' 11".

[Youthman]

For example: If you have a 21' deep theater, your first side would be at 1/3 of the way, or 7', and the next one would be between 13' 7" and 16' 11".

That would place a surround in front of your listening position. Is that good?

[mustang guy]

For example: If you have a 21' deep theater, your first side would be at 1/3 of the way, or 7', and the next one would be between 13' 7" and 16' 11".

That would place a surround in front of your listening position. Is that good?

Good question. I am not sure of the answer. In a theater, unless you are sitting in the very front 1/3 of the theater, you are going to have sides in front of your listening position. I would consider using an amp that has gain knobs for the sides, so the rearmost side surround had a bit more gain than the front. It seems to depend on what sounds are being sent to the side surrounds in the movie you are watching. It definitely deserves testing!

[steve sells]

I have been thinking about this myself, having a long narrow room, I wanted the RS-62 for a pair of sides, but looking at the physics, in a theater, we do have some in fornt of us, and some way back. But mostly I hear the ones closest to my seating position.

IF the sides are all the same speaker, then it makes sence we would get most our direct sound from the near speakers, and reflected sounds would be enhanced from the others further away. but I dont have room for 4 rs-62, mainly due to weight, and because of door ways and windows in my living room. But I could manage 4 of the rs-52, so have not done anything yet. I currectly am using the rs-41's as my sides, and some older KLH for the rears until I decide then I will move the rs-41's to the back position.

[mustang guy]

One thing that is very different about movie theaters is the ceiling height. The surrounds in movie theaters is typically high up. Being high, they are off angle from people directly under them, and therefor less loud. In a typical home theater, the speaker is practically at ear level. That would seem like a good reason to have bipoles! Still, having them high and angled properly, would be the best, because the people farthest away would be listening to a speaker pointing directly at them, and the people closest would be vertically off angle.

[derrickdj1]

I like the concept of using more surrounds. Side and rear surrounds are very doable. They may provide more impact than FH/FW speakers in a long room. I have never liked the surrounds near ear level and mount mine high up and slighly benind the main LP's.

[Scrappydue]

wouldn't this require a special processor of some sort with all kinds of special delays and what not? i would think if not researched and done VERY carefully multiple surrounds on a single channel would do more harm than good.

[ZombieWoof]

IIRC theaters have processors for this

[mustang guy]

wouldn't this require a special processor of some sort with all kinds of special delays and what not? i would think if not researched and done VERY carefully multiple surrounds on a single channel would do more harm than good.

Good point! I'm gonna have to do a bit of research before I pull the trigger on my setup. I was planning to use 8 KPT-200's as my surrounds to KPT-684 and KPT-942's for the front, and the THT's for the rear... For now, I still have the 6 LaScalas, and am using the KPT-684's as subs.

[garyrc]

For what it's worth, the earliest movie surround (excepting Fantasia's Fantasound) had approximately 1 surround on each side in front of about row 10, then they were more or less evenly spaced up the sides and around the back. This included Cinerama at the Orpheum in San Francisco (where the first surounds were -- maybe -- 12 feet off of the main floor, then were spaced back both on the first floor and in the balcony), 70 mm Todd-AO at the Coronet in S.F., where the surrounds were actually in the ceiling (talk about high!), toward each side, but the surround sound seemed to come from the sides anyway, except when the big ship flew over in Star Wars 22 years after the Coronet was equipped for 70mm .... then, that ship was definitely above, since that made sense. I was in touch with a projectionist who worked in the late '50s and '60s who confirms that Todd-AO's single surround channel was switchable to either left, right, or both. Surrounds for for road show theaters in those days were not the itsy bitsy things we see in some theaters today (although some surrounds in 35 mm CinemaScope theaters were 15" direct radiators in little boxes). The Orpheum had Altecs about 4.5 feet high and about 2 feet wide. The Coronet's ceiling speakers were in even larger enclosures which, due to their size, shape, and 2" edge trim looked like JBL's "scoop" horns, but the grille cloth kept me from confirming that (Todd-AO contracted with Ampex for their theater sound, and Ampex brought in JBL).

I assume that cinema mixers expect at least 1 surround on each side to be in front of most of the audience, but I don't know if those who re-mix for Blu-ray/DVD expect that in home theaters.