Axiom Home Page Forums General Discussion Advice from Axiom Owners Subwoofer Prewiring?

I'm trying to determine the locations for prewiring a dedicated media room for a 7.1 setup. I've read through a lot of the posts on this forum (lots of great info and friendly people, by the way!) and have more-or-less figured out the placements for the 7 speakers. However, I don't know where I should prewire the cable for the subwoofer. I don't have a Web server to post a diagram of the room on, so let me try to describe it: the room is 20 ft east-west, 15 ft north-south, and 10 ft tall. The door into the room is in the northwest corner of the north wall, and there are 2 windows along the south wall. The front speakers and projection screen will be along the east wall, 1 side surround speaker will be on the north wall, another side surround speaker will be on the south wall, and the 2 rear surround speakers will be on the west wall. I hope that description is helpful.

Anyways, I realize that exact subwoofer placement is dependent on the particular acoustics of the room and to some extent on personal preferences. However, where should I likely anticipate putting the subwoofer? Or in other words, where do Axiom owners end up putting the subwoofer in relation to the other speakers? Ii realize that it'd be difficult to give exact advice without listening to the system in the room, so I just need advice on an approximate location in the room so I know where to specify the prewiring.

Also, would it be prudent to prewire for 2 subwoofers? If so, should the prewiring locations be on opposite sides/corners of the room from each other? Though it's more expensive, would 2 EP350s be a better or more flexible option than 1 EP500? I'm considering 2 M60s, 1 VP150, and 4 QS8s as the other speakers currently. Any advice would be appreciated. Thanks.

Dennis welcome! Whenever you say prewire, is your room existing or under construction?

Whenever I pre-wired my 25'x14' room for the sub(s) I routed the RG6 coax to four locations ... 1-Left mid sidewall, 2-left front corner, 3-right front corner and 4-right mid sidewall and hindsight being 20-20 I should have pre-wired both rear corners as well, just for good measure.

*If* I were you and it was up to *me*, I'd pre-wire all four corners and both mid sidewalls.

Two 350s will not be better or equal one 500 due to the output level of the 500 and how low it can go but 2 350s will fill your room better than one 350 but then again if I were *you* I'd most certainly opt for the 500. You can always add another at a later point in time because the room is already pre-wired for it.

Does the room look something like this ?



If so, and if the dimensions are accurate, your biggest challenge is going to be a response peak around 56 Hz, caused by the fact that the height (10 feet) is exactly twice the length (20 feet). In order to tame that 56 Hz peak, you will want the sub ~5 feet from one of the side walls, and ideally from two side walls.

I marked a few possible locations. #3 only works if you have a couch or seat in approximately that location and can put the sub behind the seating. If I were you I would start by prewiring for at least #1 and #2, since with a reasonably long cable you can also cover #4 and #5. If the seating fits, #3 might be best of all if the response peak turns out to be really annoying and if you're not into buying equalizers.

Does anyone know if a Denon receiver manual EQ has a control arount 60 Hz ?

EDIT -- first thing I should mention is that placing the sub to correct for room peaks normally works, but doesn't seem to be working for Randy (sirquack). We don't know why yet, so don't be holding your breath for perfect response the first time you fire up the system

re: 2x EP350 vs. 1x EP500 -- I don't *think* this is going to be the kind of "problem room" where multiple subs are going to be required, since one of your offending dimensions is vertical and the other horizontal. Some bass trapping will probably be more effective than multiple less expensive subs. Given that, I would definitely argue for a 500 over 2x 350.

BTW, before you ask -- yes hanging the sub 5 feet off the ground would probably help smooth out your room responses

I believe my 2805 has manual eq at the following positions and can be adjusted in .5dB increments from -6dB to +6dB.

63hz
125hz
250hz
500hz
1khz
2khz
4khz
8khz

Bridgman, you rock! Thanks for taking the time to even draw out the room! Some additional details about the room.

1) The 20'x15' dimensions of the room are approximate, based on the floorplan that the builder hands out when visitors look at their community. It's likely that the exact dimensions might be something like 20'3" x 15'7", or whatever. We're still in the process of finalizing the design for our house, so I don't have exact dimensions from the blueprint. Which leads to...

2) The 15' dimension of the room is negotiable. On the other side of the north wall is a 19'x20' gameroom, which my wife is willing to let me "borrow" a couple of feet (along the 19' dimension) from for the media room. Would this help prevent of the problems with certain frequencies?

3) The ceiling is actually about 9' high on the east, west and south walls, and slopes to 10' high a couple of feet into the room along each of these walls. It's not quite a tray ceiling, though I don't know the exact term for it. Will this affect things any?

4) The back (western) 8'x15' of the room will be raised 1' above the front (eastern) 12'x15' of the room. I assume I'll need to have insulation placed in the 1' riser so that it doesn't cause unintended echoing. Or can I somehow manipulate it to some advantage?

5) For the speaker wires, I had to ask specifically for 12 AWG wire, or the builder was going to put in 16 AWG wires. Are there different type of RG6 cables, or is that already as specific as it needs to be?

Thanks for everyone's input so far!

>>2) The 15' dimension of the room is negotiable. On the other side of the north wall is a 19'x20' gameroom, which my wife is willing to let me "borrow" a couple of feet (along the 19' dimension) from for the media room. Would this help prevent of the problems with certain frequencies?

My first thought would be to stay with something like 15 feet -- that's a nice size for an HT and you want to keep the dimensions "unrelated" as much as possible. It's the length being twice the height which poses the challenge.

>>3) The ceiling is actually about 9' high on the east, west and south walls, and slopes to 10' high a couple of feet into the room along each of these walls.

Oh good. That means the 10' dimension is to the drywall, not to the floor above, so you're really talking closer to 11 feet. Actually -- what do you have above, another floor or attic ?

Assuming your ceiling is drywalled, I would be thinking real hard about asking the builder to leave some openings, stuff 'em full of insulation, then cover with either a wood grill or burlap / speaker cloth.

If the room above is a cold attic and the builder is planning on blowing insulation on top of your drywall ceiling then this would need to be a bit more complicated, of course

>>It's not quite a tray ceiling, though I don't know the exact term for it. Will this affect things any?

Is that what they call a "coffered" ceiling, or would it be more correct to say "there is a soffit all around the room" ? If you want to be overwhelmed with ideas and annoy your family, go to the RealTraps site and look at "soffit traps"

>>4) The back (western) 8'x15' of the room will be raised 1' above the front (eastern) 12'x15' of the room. I assume I'll need to have insulation placed in the 1' riser so that it doesn't cause unintended echoing. Or can I somehow manipulate it to some advantage?

I don't know the answer to this one but it's a very good question. If the raised section is big like this, it can also help by reducing the effective height of the room from 10 feet to 9 feet, IF the construction is solid enough eg. double thickness of heavy plywood and lots of bracing.

>>5) For the speaker wires, I had to ask specifically for 12 AWG wire, or the builder was going to put in 16 AWG wires. Are there different type of RG6 cables, or is that already as specific as it needs to be?

There are different kinds of RG6 but I don't think it matters in this application -- the differences are just related to flexibility vs. signal loss at RF frequencies over long distances.

Builders sure love their 16 ga speaker wire, don't they ? In my house we specified 12 ga, everyone signed off 12 ga, and they STILL ran 16. Fortunately I put all the boxes in the wrong places anyways and am not using the pre-wiring

I should just mention something before we go too far with this... if you just switch off the computer and never come back your HT dimensions and room acoustics will be as good as or better than the rooms of most of the board members, probably including my own.

Just try to keep the dimensions from being exact multiples of each other, and remember that no matter how bad your dimensions are bass trapping will reduce the effect of the offending room resonances.

Everything we talk about here is to give you an idea of things which *could* be considered during construction which will give you a head start on the inevitable tweaking, treatment and re-arranging you will probably be doing for the next few years

Bridgman, thanks for updating the pic! Also, thanks for all your recs. Since builders tend to charge an arm and a leg for upgrades to the house, I'm trying to just pay for the modificiations that'd be more expensive down the road than now. Hence, trying to get the prewiring right. Admittedly, some of the ceiling stuff and "soffit traps" you mentioned may be a little more involved than I was thinking. Would they make that much of a difference? I'd hardly consider myself an audiophile, so subtle differences would probably be lost on me. I've never had more than a 2.1 inexpensive setup before, so just moving up to a 7.1 setup with a >$400 receiver will "wow" me, and I'd be none the wiser.

BrotherBob, thanks for your input also. Let me ask you (and the other forum members) this: would going with 2 EP-350's be a mistake? Costwise, it's only $140 more for the EP-350's, and they could give me flexibility for placement to deal with room acoustics problems, plus I can start with one, then add another later as finances allow. I'm not that much of a bass person, so I don't anticipate needing more than 1 EP-500 or 2 EP-350. That's my rationale for leaning toward 2 EP-350's, but if you think I'm making a mistake, please tell me so. Now that I think about it, though, are there many receivers below $1500 that have multiple sub outputs? Or will going with 1 sub be my only choice at that price point anyways?

Again, thanks for all the input so far!

Dennis Imo, you would be better off saving some money and just getting the EP500 if the finances allow, as far as the receiver goes you don't need multiple sub outlets to hook up 2 subs if you decide to go that route.

Another vote for the 500. Dennis, the two 350s will give you some flexibility in dealing with horrible room problems, but the single 500 will give you the same output AND will do a much better job of handling the very low notes. I don't think you are going to have enough room problems to need dual subs for that reason, and IMO a single 500 will be more satisfying than 2 350s.

Regarding the rest of the treatments, everything we are talking about here is fancier than your typical good home theater, ie none if this is "stuff you have to do". As long as you avoid horrid dimensions all of the other important things are easy to do at any time afterwards, eg put down a nice rug or a couple of wall hangings if the room is too live. You are asking all the right questions -- get the wiring worked out in advance (don't forget the projector), figure out where your equipment is going to go. Put a bit of effort into the lighting -- a few $$ and planning here can really make the room look spiffy -- and make sure the room can be REALLY dark when watching a movie.

If you are trying to build the ultimate home theater you really do need to be thinking about all this stuff at construction time, but very few of us have those kind of rooms. If you want to see some really cool rooms, though, go to the Rives Audio site at www.rivesaudio.com.

EDIT -- the one place where planning ahead can help is making the treatments "invisible" if your family might have problems with the appearance of some of the bigger treatments like bass traps. At the very least it might be good to identify a few spots on the back and side walls (near corners) and ceiling (between screen and first listening position) where you *could* cut away drywall in the future and stuff the space between the studs/joists full of insulation.

If you are going to have a drywall ceiling try to keep an area duct-free that you can chop into later. Try to walk through occasionally with a video camera during construction if you can -- still pics are good but you never seem to have a picture of the wall you are interested in a year later ;(

If you can keep wiring and HVAC out of the first pair of studs in the corners that will let you hide bass traps in the future. Randy just finished building a pair of big bass traps -- he can probably comment on how "WAF-friendly" the results were.