Film-Tech Forum ARCHIVE: Determining Proper Subwoofer for Home Theater Room

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Posted by Andy Bajew (Member # 5330) on 01-20-2010, 10:46 PM:

Simply put, is there an easy calculator or way to figure out the type of subwoofer that should be used for a home theater room? The room is 17 feet by 14 feet and 12 feet tall.

Also, this is for my roommates dad, he was given a 5000 dollar 'estimate' for a full set of Bowers and Wilkins speakers for the previously mentioned theater room and asked if I could find the best speakers for that price.

Posted by Joe Redifer (Member # 3) on 01-20-2010, 11:13 PM:

Velodyne has never done me any wrong. Don't go cheap! A 12-inch should do it, make sure it has at least 350 watts, preferably more. Hook it up via RCA, not speaker-level inputs. Keep it powered 24/7. Don't let it "sleep" when not in use (I'm not even sure that Velodynes have this option). Saving power is for hippies and I HATE HIPPIES!

Posted by Bobby Henderson (Member # 840) on 01-20-2010, 11:16 PM:

Ah, just do like Brad: stack about a dozen or so subwoofers under the screen (or TV set). If you don't have wind occurring in the room add more subs.
[evil]

If the sub bass in the room is done right it should be able to launch dishes off the kitchen table next door.

Posted by Joe Redifer (Member # 3) on 01-20-2010, 11:19 PM:

Agreed. If the neighbors aren't affected, you're doing it wrong. That is unless you insulate your walls with some of that sound blocking shit.

Posted by Bobby Henderson (Member # 840) on 01-20-2010, 11:22 PM:

Comment overheard by panicked neighbor in Rockwall, TX: "holy shit! It's an earthquake! It's late at night and I've woke up in Haiti!"

Posted by Brad Miller (Member # 2) on 01-20-2010, 11:40 PM:

Actually no it was never a problem in Rockwall due to the distance. Older setups have supposedly knocked dishes off of the counter in the house next door, although I never saw any broken dish evidence.

Andy, you need one of these sexy beasts!!! All other subwoofers are absolute crap compared to this monster. This can easily induce an instantaneous migraine if you like.

Posted by Joe Redifer (Member # 3) on 01-21-2010, 12:52 AM:

Ha! No, that wouldn't be very good in such a small room, such a beast needs more air to move. You'd get a migraine alright, but not very good LFE. Well, maybe if you went into another room while the movie was playing you'd hear some great bass but not in the room where the speaker is. You'll probably need a down-firing subwoofer.

Posted by Brad Miller (Member # 2) on 01-21-2010, 12:53 AM:

Nah, not at all.

Posted by Joe Redifer (Member # 3) on 01-21-2010, 01:00 AM:

OK I just checked my Velodyne sub and it is forward firing, but it also has some weird-ass thing on the bottom that when I push it, the forward-firing speaker moves outward. It feels kind of like a driver, but not really. The actual driver can't be more than 8 inches. It is really small, but you can feel the bass on your skin which is pretty rare at actual cinemas. Damn, I should have gone for the 10 or 12 inch. [evil]

Posted by Ian Parfrey (Member # 5122) on 01-21-2010, 02:18 AM:

These are subwoofers for girls. [sleep]

Etone Australia made a 24" driver that makes these things look like toys and could blow out candles...

....2 kilometers away. [thumbsup]

Posted by Joe Redifer (Member # 3) on 01-21-2010, 02:46 AM:

I thought Australia censored subwoofers along with everything else. [Smile]

Posted by Ian Parfrey (Member # 5122) on 01-21-2010, 02:50 AM:

We do. Thats why they don't make them anymore. [beer]

Posted by Steve Guttag (Member # 268) on 01-21-2010, 09:19 AM:

EV had the 30" subwoofer (30W). Big monstrosity. Didn't make it sound any better. But it could play deep with relatively little cone movement.

One issue with larger cones though is sag. I've seen cones go off-center...it takes a bit of time (years) and it affects larger cones with weaker compliances (surround/spider) more. Remember, the air gap in a typical driver does not allow for much of any sag. I would suggest a regular schedule of rotating the driver to keep it centered.

Steve

Posted by Sean Weitzel (Member # 244) on 01-21-2010, 10:56 AM:

Truth be told, watching a movie in Brad's Rockwall screening room was the first time I've ever experienced a movie explosion blow my hair around.

Posted by Ian Parfrey (Member # 5122) on 01-21-2010, 11:18 AM:

Steve.

That may well be the reason Etone discontinued the 24" beast some years ago, but I'm unsure of the actual reason for doing so.

But if cone sag is the reason, couldn't the manufacturer beef up the spider assembly to cater for the increase in cone mass or would that make the whole thing less responsive and unworkable?

Posted by Steve Guttag (Member # 268) on 01-21-2010, 11:59 AM:

One reason for using the larger cone is to move the air with less motion and presumably get a deeper (lower) response. With that one really would want to go to a weaker compliance (say foam or better yet, rubber since foam rots too fast)...this will lower the response of the whole system. Stiffening the spider and compliance would work against that.

Steve

Posted by Scott Norwood (Member # 30) on 01-21-2010, 01:26 PM:

With respect to the original question, the subwoofer needs to be able to produce 115 dBC SPL at the "average" seating location. You will need to know the location of the subwoofer and its efficiency, as well as the location of the "average" seat. From this, you can determine what size amplifier you need to drive it, and ensure that the number of watts required does not exceed the maximum "program" power capacity of the subwoofer. You may end up needing multiple subwoofers, and you will want a safety margin to ensure that the amp does not clip and damage the speaker.

The frequency response plot for both the subwoofer and stage speakers is also important, to ensure that there is a reasonable crossover point with sufficent overlap for both the sub and main speakers. Once everything is installed, you can set the exact crossover point and sub level with an RTA.

This much is easy enough. What is not clear to me is how room acoustics affect the math. Efficiency measures are supposed to be done in an anechoic chamber. But what happens when you put the speaker behind a screen? What if the room is super-reflective? What about rooms with dead spots? And how is this affected by being a small room and not a theatre-size room?

Posted by Louis Bornwasser (Member # 3063) on 01-21-2010, 06:19 PM:

Just make it downward firing or . . . . better yet, put a clockwork motor in to rotate it slowly like a rotisserie chicken. Louis

Posted by Mark Gulbrandsen (Member # 72) on 01-21-2010, 06:51 PM:

Joe,

The other "thingy" is called a passive radiator... it's actually a "thingy" that causes higher harmonic distortion because it's movement is slightly delayed from the main driver. You may think it sounds good but the reproduction from that type of subwoofer system is not usually as "fast" as from a plain ole subwoofer.

Steve,

A late friend of mine that was a retired Radio Engineer had a stereo with a pair of cabinets with the 30" E-V drivers in them. As I remember they were fairly impressive... but I was probably about 16 years old when I first heard them and anything back then that large was bound to be impressive. I'm sure that any speaker that large would suffer form alot of cone breakup since it was just a paper cone. Cone materials have come a very long way since those days.

Mark

Posted by Joe Redifer (Member # 3) on 01-21-2010, 11:36 PM:

All subwoofers are inherently slow simply based on what frequencies they reproduce. But I know what you mean, the difference is negligible.

quote: Mark Gulbrandsen
You may think it sounds good but...

But I would be wrong in thinking that? Is that what you are saying? I wouldn't recommend it for a real theater, but for the home it kicks tons of ass in a small space. I have mine set up in discrete mode only. I don't do any high-pass filtering of any of the other channels.

Posted by Ron Lacheur (Member # 1126) on 01-22-2010, 11:54 AM:

You could go with the QSC 21" subwoofer, or you could pull out all the stops and go with this.

Posted by Brad Miller (Member # 2) on 01-22-2010, 12:07 PM:

Andy, come visit me and I will implode your skull with the QSC. You might look funny after that, but you will agree it is phenomenal. [Big Grin]

Posted by Ron Lacheur (Member # 1126) on 01-22-2010, 01:49 PM:

Did you replace your subs in the screening room with the QSCs? Or are you using these in new installs?

Posted by Sam Graham (Member # 2889) on 01-22-2010, 07:59 PM:

This is what I'm using (in a much smaller space) and am quite happy with it. But for the space you're talking about, I'd suggest this. Or maybe a pair of them.

Posted by Brad Miller (Member # 2) on 01-22-2010, 08:38 PM:

Yes and yes.

Posted by Ron Lacheur (Member # 1126) on 01-22-2010, 09:19 PM:

Interesting. Just for curiousity, how many of the 21" did you use to replace to EVs?

Posted by Victor Liorentas (Member # 5272) on 01-22-2010, 09:23 PM:

I am very impressed with Rel t2 subs,i have a t2 but they also make a t1 and t3!
High end home stuff that produces a quality of bass i love!

Posted by Jake Spell (Member # 5294) on 01-22-2010, 11:20 PM:

personally, I prefer more smaller woffers, to one bigger one

Posted by Michael Voiland (Member # 5386) on 01-23-2010, 02:29 AM:

Brad this one wins Big Sub [Wink]

Posted by Steve Guttag (Member # 268) on 01-23-2010, 06:54 AM:

In what way does it "win?" It doesn't play very deep. JBL has numerous superior subs in the ASB line (will play as loud/louder, deeper, flatter).

But for conventional theatre use, ˆ wouldn't use them either. I would stick to cinema subwoofers (JBL 4645C, 4642 or the QSC varients). They are going to perform better and cost less/watt and frequency response than a rental/staging speaker that is built for hanging and road trips.

Steve

Posted by David Stambaugh (Member # 1102) on 01-23-2010, 10:34 AM:

Sam, I have a lowly Hsu STF-2 and am *very* happy with it.

Posted by Steve Guttag (Member # 268) on 01-23-2010, 11:09 AM:

I use the JBL B460

Steve

Posted by Ian Parfrey (Member # 5122) on 01-23-2010, 01:39 PM:

I hope the magnetic shielding is good on that enclosure Steve. How would those analogue tapes fare sitting that close to the driver or is that a feature of that system?

Posted by Steve Guttag (Member # 268) on 01-23-2010, 03:20 PM:

That was a link to the Lansing Heritage site...my B460 has DVDs on top of it...so far, no problems. The driver is the JBL 2245H...it has no magnetic shielding so it was probably unwise to set the tapes on it...then again, it was probably at enough distance to not matter.

Steve

Posted by Mike Schindler (Member # 1309) on 01-23-2010, 07:52 PM:

I have a related question. I have a Dayton "Tiny Mighty," which I think is a 12-inch down-firing sub. My problem is that I now live in an apartment, and I'm worried about disturbing the neighbors.

The only people I really have to worry about are the ones below me. The apartment has hardwood floors, although there is carpeting, drapes and a bunch of cushiony chairs. I've considered investing in a "Subdude," which is supposed to limit room vibrations, but I'm still worried about the soundwaves themselves traveling into the apartment below.

Is there anything I can do to contain the sound in the apartment, or am I pretty much screwed?

Posted by Joe Redifer (Member # 3) on 01-23-2010, 10:05 PM:

Wear headphones.

Also, be careful. Apartments have a tendency to catch on fire when one of the meth kitchens in the complex blow up.

Posted by Jarret Chessell (Member # 5077) on 01-23-2010, 11:54 PM:

I have a small room with hardwood floors. I own half of an old semi, I'm sure the neighbours feel when I'm using my home theatre. I have an entry level yamaha sub (probably 6"??) that I haven't bothered replacing because it carries across the floor too easily, and metering it to 115db isn't an option (plus the microphone on my iPhone rta starts clipping at 85db [Big Grin]

). I think I only have it set to around 6Xdb, it does the trick for most movies and xbox games. I'll get something better after I move somewhere with no one around me.

oh, Joe, why aren't we letting our subs go into sleep mode??

Posted by Joe Redifer (Member # 3) on 01-24-2010, 02:21 AM:

Why would you want them to sleep? Do you think they can wake up fast enough when a sudden sound is sent its way? Turn them off along with the rest of your sound system if you must, but sleep mode is useless and can cause clipped content. I've heard it before and it was very annoying.

I always leave mine on, though. Just like my computer, never sleeps or powers off (hard drives don't even spin down). Monitor shuts off after half an hour, but that's it.

Posted by Bobby Henderson (Member # 840) on 01-24-2010, 10:04 AM:

Those neighbors are wusses. What's a little subwoofer activity compared to artillery explosions? I should able to call up the folks at Fort Sill and cry about their bang bangs rattling my windows or waking me up from time to time. Usually I sleep right through it. I just pray I don't sleep through a tornado warning!

Posted by Frank Angel (Member # 248) on 01-26-2010, 07:37 AM:

My memory fails me, but at one point I recall there was a unique subbass system that used a motor to drive a diaphram. The advantage was that it could produce a much louder output in a much smaller space than a conventional system. Anyone know what this thing was?

Posted by Tom Mundell (Member # 4555) on 01-26-2010, 10:03 AM:

quote: Mike Schindler
Is there anything I can do to contain the sound in the apartment, or am I pretty much screwed?

I haven't found any way to completely isolate the sound yet; I've been using these (similar to the SubDude I think) with my left/right speakers and it seems to help a lot; I'm in an apartment with hardwood floors and no carpet. They really do cut down on a lot of vibrations going into the floor which could be heard in adjacent rooms. It's not perfect, you'll still hear some sound in other rooms, but it seems the idea more or less works. I'm not sure about this "purity of tone that has to be heard to be believed!", I couldn't hear any difference in my setup.

Posted by John Hawkinson (Member # 1135) on 01-26-2010, 12:31 PM:

Well, of course you don't believe it, you can't hear the difference! It's only the people who "hear the difference" who "believe it."

[Big Grin]

--jhawk

Posted by Ron Lacheur (Member # 1126) on 01-26-2010, 01:52 PM:

quote: Frank Angel
My memory fails me, but at one point I recall there was a unique subbass system that used a motor to drive a diaphram. The advantage was that it could produce a much louder output in a much smaller space than a conventional system. Anyone know what this thing was?

That's most likely the Servodrive.

Posted by Andy Bajew (Member # 5330) on 01-26-2010, 06:28 PM:

quote:
Andy, come visit me and I will implode your skull with the QSC. [Big Grin]

This sounds like an interesting offer. Almost too tempting to refuse.

Posted by Jake Spell (Member # 5294) on 01-26-2010, 09:50 PM:

As far as sleep mode, just send some sound to them beofr you start the movie, like sat direct tv, or some trailers

Posted by Andy Bajew (Member # 5330) on 01-27-2010, 09:24 PM:

quote: Joe Redifer
Also, be careful. Apartments have a tendency to catch on fire when one of the meth kitchens in the complex blow up.

Hahahaha! Joe..this may be one of the funniest things I have heard in a while.

Just to inform what I went with for my speaker system, I got the Bowers & Wilkins 683 Theatre Set and am still searching for the sub.

Posted by Frank Angel (Member # 248) on 01-28-2010, 07:02 AM:

Andy, it's real simple. You just keep buying them and stacking them in the corner of the room, trying as hard as you can to orient them so the drivers couple, and then test them: Play EARTHQUAKE. If you can't get them to vibrate your gonades to orgasm during the big earthquake scenes, you don't have enough. Buy more, stake them, then repeat the test. [beer]

It should be noted that, without telling her, you should use your girlfriend as the test subject after yourself, as women tend to be more difficult to reach "O-Level" of excitation (make sure the fader is set at 7.) Thing is, she probably won't actually tell you when she's reached that pivotal O-Level, but if she keeps saying, "Honey, let's watch EARTHQUAKE!" every time she comes over, you know your system is functioning properly; the word "tweaked" will have a whole new meaning for you. Of course with a well tweaked system, you can play EARTHQUAKE as offen as you like when she's not around. [beer]

Posted by Paul Trimboli (Member # 1509) on 01-30-2010, 11:55 PM:

Really what you want to is to place multiple subs around the room 2 is good 4 is better. The reason for doing this is that reproducing bass in a small room (small acoustically- a 20hz wave for example is 17 meters long) is that the in the bass range the sound will be dominated by the room modes (the resonances of the room). You end up with peaks and dips as at various frequencies as the sub excites the various room modes and as the sound wave strikes the walls and then starts traveling back in the opposite direction. The wavefront is now out of phase so it cancels the first wavefront out causing a dip in the response (or a peak if the first wavefront and reflected wavefront are in phase with each other). By using multiple subs placed around the room you can smooth out the room response through what is really brute force. The other advantage is that the work is now spread over multiple speakers so the distortion will be lower as their excursion will be less. Here is a link to a paper put out by harman on the topic- Sub Bass Optimization using Multiple Subs

Posted by John Wilson (Member # 269) on 01-31-2010, 03:14 AM:

Paul! Where have you been?

Posted by Paul Trimboli (Member # 1509) on 01-31-2010, 03:35 AM:

Still around John and still working part time in the industry at an outdoor cinema here in Perth a couple of nights a week.