written by Mike Shea on 21 November 1999
One of the most popular subjects in home theater is the subwoofer. Even with large tower speakers, an added subwoofer can bring a whole new dimension to a system, giving it that extra "kick". Adding a subwoofer to a system allows your mains to be driven higher, instead of forcing them to perform at the lower frequencies which they generally aren't good at. Dolby Digital makes it even more important.
First a crash course in speaker sound. The common frequency range that is available on movie soundtracks is 20,000 hz (very high pitch) to 20 hz (very low pitch). Speakers are able to produce the high frequencies (20khz to about 80hz) without a problem, but frequencies below 80hz are much more difficult to produce. Since often a single amplifier and two drivers (tweeter and woofer) are asked to reproduce this sound, there is a lot of strain on both the amplifier and drivers. Even with a good powerful receiver, the lowest levels of sound force the receiver to put out more power than it has available, and thus neglect the higher tones which ironically, it would be much better at achieving. A subwoofer is a single cube-like cabinet that contains one or more large drivers (from 8" to 18") and a large dedicated amplifier (from 60 watts to 1400 watts). The larger the driver and amplifier, the lower and louder the sub.
It is important to know that the power and size of the sub are not the only thing that makes it good. Control is also very important. With such a large driver being moved by such a large amp, it is possible for the unit to misfire and cause a beat to skip or come early. It will vibrate or boom too much. This is the distortion of the subwoofer. It isn't so much a problem with movies (a good rumble is important for a meteor) but with music it can make Mozart sound like you want to put on your size 57 work pants and go cruise in your low rider for chicks. Many subwoofers have tricks to gain control over this problem. Velodyne has a device called an Active Servo Control that uses an extra magnetic field to control the subs behavior. M uses a second vented driver to make sure that the first doesn't lose control. For this reason, it is difficult to judge a sub by it's statistics alone. That is the purpose of the table at the bottom of this article. Name does matter a lot of times.
A subwoofer can be set up a number of different ways. It the most popular configuration it can handle all the base from all five channels, thus letting those channels only handle signals roughly 80 hz and above. This works best with bookshelf or satellite speakers which can't properly reproduce lower signals. With a system that has tower speakers, it can work in conjunction with the base from those speakers, or handle the base for the center and surrounds if they are still smaller speakers. With Dolby Digital and DTS, there is a dedicated low frequency effect (LFE) channel that contains the lowest level effects (explosions, meteors, harleys). With Dolby Digital, the specs call for a full 20hz to 20khz on every channel, and 20hz to 100hz on the LFE channel. This would require a separate subwoofer for every channel, plus the LFE. Without the use of active speakers (see below) this is pretty unrealistic. However, with a good single subwoofer and all channels set to small, all of the base will be properly reproduced by the subwoofer.
One of the newer debates within the home theater community is whether it is necessary to have two subwoofers. Articles in Home Theater Magazine and Steriophile's Guide to Home Theater point out that placement of a subwoofer is very difficult and by having two you are more likely to have one placed right for any position in the room. On the Video Essentials DVD it shows placement up front (even directly underneath the mains), placement to the sides of the audience, or even behind the audience. Two subwoofers can more accurately represent the lower signals than one, which is why many THX certified systems are only certified if they come with two subwoofers. The Atlantic Technology 350 and the discontinued Boston Acoustics THX systems both included two subwoofers. Now whether it is better to purchase two lower priced subwoofers over a single high powered subwoofer is a different question, and is one I have no answer to.
Active Speakers
One of the latest trends in speakers is the active speaker. Many high end companies such as Polk, Definitive Technologies, Boston Acoustics, and Energy. Definitive went so far as to release the first active center channel. What are active speakers? Basically they are a speaker containing its own internal amplifier which can power the woofer or subwoofers contained in the cabinet. The advantage of this design is both in ergonomics (no need to have a big old box) and in quality. Since a speaker is being built from the ground up by a single manufacturer, the amplifier, crossovers, drivers, and cabinet are all designed together creating a speaker with optimum performance for it's components. For instance, you don't have to worry about where your subwoofer crossover should be set to reduce stress on your midranges, it is all done for you in the speaker itself. All you have to do is set the gain of the subwoofer to your liking. Another advantage is to take the receiver or decoder out of the loop for speaker setup. You know that your main speaker can handle a full range signal and you can set it as such. You could also set the LFE (low frequency effect) track of a Dolby Digital or DTS soundtrack to go to your active main speakers. Many of the reviews of active speakers have been very positive. Both Home Theater Magazines and Stereophile's Guide to Home Theater gave the Definitive BP3000 and 2000 series active speakers good reviews, saying that the speakers performed very well with music and movies. Click for more info on the Definitive BP3000TL and C/L/R 3000 active center.
What are the disadvantages of active speakers? Mainly price right now. The powerful BP3000 Definitive Tech active bipolar tower speaker can set you back $4500 a pair. They contain a massive 18" woofer and 1000 watt amp and are flat from 20hz to 20khz (the full range audio spectrum). The more modestly priced (and powered) Definitive 2000 run about $1500 a pair with a 15" woofer and 300 watt amp. The other disadvantage is they will more likely than not still need a sub for a full home theater setup. The cabinets of the towers are just not large enough to outperform a large dedicated subwoofer. But when you do add in that extra LFE sub, the overall performance of your system would be astounding. A final disadvantage is location.
It is known that the more subwoofers one has, the better. For one example of a true system able to fully recreate the sound required to mimic the sound of a theater, take a look at the high end theater recommendation. It is widly accepted that adding a subwoofer to a home theater system is one of the largest bangs for the buck.
From: slim ( jsader555@yahoo.com ) on 21 June 2004
Subject: my sub
my sub is leaking air through two holes. i think the holes are for two tweaters should i seal the holes up and or add two new tweaters or leave it as it is email e with you advise.!!!
From: slim ( jsadler555@yahoo.com ) on 21 June 2004
Subject: subs
ive just started doing a home system for my room i allready have a sub though its quite small and i want at least two more (cos i love bass) can someone please advise me on this. i plan to have 2 subs under my bed two normal towers sets on my back wall and twoo tower sets on my front wall and a sub on the front and a sub at the back what do you think please email me with your help someone plz help me plz !!!!1!
From: Glenn ( zythriss@hotmail.com ) on 17 February 2003
Subject: Apartments and subwoofers don't mix
For my two cents, apartments and subwoofers don't mix. I live beneath a fellow that has an entertainment center with subwoofers, and 5 times I've had to go up and ask him to turn it down. I've tried encouraging him to raise the speakers off of the floor, and away from the wall where the air ducts run, but so far he just doesn't get the point. It sounds like I'm living under an airport runway. The landlord is getting involved in this this week, and the police are the next step if he doesn't clean up his act. People.. be considerate if your neighbors if you live in an apartment.. keep the subwoofers down or off. Move to a house in the country if you can't be without your precious bass. Landlords, I encourage you to consider adding clauses to leases banning the use of large entertainment centers and specifically subwoofers.
From: brian ( venpick@yahoo.com ) on 22 December 2002
Subject: amps for subs
Hey i was reading these post and realize im only 2 years late but, I have had good results powering my sub with a seperate old old old school reciever. You know the kind that we all had as kids. the kind you can find at salvation army for nickels. The pre out from my high dollar main reciever into the aux input of the cheap amp (complete with treble and bass adjustments) to the one and only sub speaker. it works great and no expensive amplifed sub speakers to buy. just hide it behind the rest of the system so people dont fiddle with the volume or try to listen to the radio or other features of the amp and there you go. hope this helps.
From: Mike ( mshea@liquidtheater.com ) on 13 November 2002
Subject: HSU VT-2 Subwoofer highly rated $500 sub
There are a lot of good reviews on the HSU VT-2 Subwoofer. It runs $500 delivered and can be ordered over the net. A lot of non-glossy audio mags (the good people) rate it very highly. If you are looking for a good sub, this may be the one.
From: Joe Gannon ( JosephGannon@NetZero.Net ) on 14 March 2002
Subject: Bose Sucks...
Great job! Very informative.
FYI...
I have 5 jbl hls610s, and a two home built bose acoustic cannons (20' long 14" w/ jbl le14a woofers 1/4 way in) under my bed. Denon receiver, pioneer dvd, Carver amp drives subs 20hz - 80hz.
This is a low end system. It sounds open and airy and DEEP. Got everything at web auctions.
Regards
Joe Gannon
From: Mike ( mshea@liquidtheater.com ) on 7 August 2000
Subject: SVS Subwoofers
There has been a lot of excitment about a sub that has been catering to the users of Home Theater Forum. The SVS Subwoofers look a lot like the Hsu Subwoofers but with a bit of a lower pricetag and a huge thumbs up by the HTF crowd. Give them a look before picking up something else.
From: LaserBoy ( garlanrd@purdue.edu ) on 20 April 2000
Subject: I MUST WANNA GO DEAF!
Yea, I said that I had dual 10'' subs right, but I'm in the process of hooking up 15'' subs. Yea, I really want to feel pounding in my head for hours after listening. I think that I've spent a little too much time in dance clubs and loud parties. I know that it could damage my hearing. Maybe I should get a decibel meter thingy?
Third message in a row...ok, I'll stop for now.
From: LaserBoy ( garlanrd@purdue.edu ) on 20 April 2000
Subject: College Student
Did I forget to mention that I'm in college? This means that I'm determined to get the most use out of the stuff I have. I mean of course it would make more sense to have a dedicated home system and a dedicated car system. But my wants exceed my cash flow.
From: LaserBoy ( garlanrd@purdue.edu ) on 20 April 2000
Subject: Bicycle Home theater!!! LOL! I'm a nut!
All I need is a dual channel amplifer that will deliever 150 to 200 rms watts into two channels or a single channel amplifer that will deliver around 300 rms watts. I mean, my god, all I want is a little music. I doubt that an amplifer that is able to deliver this could cost too much as my car speakers are 4 ohm and most home audio amplifers are made to work with 8 ohm speakers. Meaning that I can get twice the power out of a home amplifer in rms watts than the rated rms output. Granted the home amplifer will have to be able to handle the larger power output. This is sorta a gamble, because while High-end amps like the OUTLAW do handle lower resistance loads; I doubt that all amps would be of this quality. But if an amp can't handle the greater power output, then That means Its time to "overclock" the amp!!! Can't really overclock it, but add additionally cooling and there you have it "Free" power! A friend who is going to college in California (he is coming to Chicago for the summer) apparently got a home amp for christmas and is currently powering a couple of subs (not sure whether they are home subs or car subs, I don't see how this would matter). Anyway, I hope it outputs sufficient power so I can get some decent excursion out of my subs. I'll tell you guys how it goes at the end of May.
From: Bonez ( bsfrank@bu.edu ) on 20 April 2000
Subject: home theater = bicycle
So... I was thinking about moving my whole home theater system to my bicycle (since I don't have a car.) My system will have to run on the power generated by my legs pumping the pedals. I will have to keep the volume pretty low so I don't exceed my power inputs. I will just strap the fronts to my handlbars, the center to my front bumper, and the surrounds to my shoulders. I figured that I could sit on top of the sub for realism.
From: Mike ( mshea@liquidtheater.com ) on 19 April 2000
Subject: Car != home theater
Sorry stud. Trying to use a car subwoofer for home theater isn't probably the best idea. Dedicated home theater subwoofers are designed in for a much different environment. Sure it is $$ but getting a dedicated sub will only cost about $300. I bet it will sound better than some crazy setup with a car woofer. You get what you pay for.
From: Laser Boy ( garlanrd@purdue.edu ) on 19 April 2000
Subject: Home Amplifiers = Big $$$
Yea, I'm looking for an amp to just drive the subwoofers. I checked out the Outlaw and saw the $1,000 price tag. I don't need 5 channels of power. I only need the amp to be able to power the subs for music purposes...so my roommate and I can get evicted this summer! (well hopefully not)
I'm starting to wonder how difficult it would be to power one of my car amplifers from an outlet, couldn't be too easy with AC current coming from the wall and my Amp only capable of recieving DC current at 12V.
From: Mike ( mshea@liquidtheater.com ) on 18 April 2000
Subject: Amps
One thing you will find, Ryan, is that amplifiers in home theater and amplifiers in car audio are really different things. Frankly, I wouldn't run anything bigger than a 6" woofer without a dedicated amplifier for it. I am a big believer in satelite systems that use smaller main speakers with smaller amplifiers and then dedicated subwoofers with their own high power amps. You can buy a dedicated amplifier for your speakers anyway like the very nice Outlaw Amplifier but I still think for the money you are better off buying smaller bookshelf speakers and dedicated amplifiers or large tower speakers with built in powered woofers like the awesome Definitive BP3000TL speakers. With dedicated amplification used for each driver you get the best sound with the least distortion.
From: Mike ( mshea@liquidtheater.com ) on 18 April 2000
Subject: Subs in Apartment
I have to say after five years of apartment life that I really want a house when it comes to home theater. Large subs really aren't for apartment life and without them you are not really getting the full home theater effect. That is why I chose the modest Energy Exl-S8 sub for my home theater. It gives me a good punch but doesn't get me evicted. Only twice did my upstairs neighbor complain. Still, I really want the cool four subwoofer setup of my high end dream system
From: Laserboy ( garlanrd@purdue.edu ) on 18 April 2000
Subject: Update
After reading through some of the home theater pages, I would like to state that if you live in an apartment huge subwoofers probably aren't a great idea. Ah, maybe the neighbors wouldn't mind too much?
From: Laserboy ( garlanrd@purdue.edu ) on 18 April 2000
Subject: Subwoofers
As car audio enthusiast, I'd say you'd want giant subs (at least 18''; that way they can play deep) and as many as possible (the more surface area the better) that way you can really get the pounding audio experience free of distortion or muddy bass. I mean in my car dual 10'' subs boom, but 15's pound but thats in the small volume of a car, in a big room you need lots of Surface area and lots of power.
Mike, Where do you buy amplifiers? All of the amplifiers I've seen are labeled as recievers and only output say 100 watts rms to 5 channels. I don't care to have a reciever. I just want a home audio amp that can pound out the watts to one channel...So if I want to bring my car subwoofers inside, then I can.
From: Mike ( mshea@liquidtheater.com ) on 2 December 1999
I would definitly go for the Definitive PF15TL. For $600 you get a 15" driver, a 325 watt amp and some excellent features. Both the publications and user comments have been excellent. Check out this Home Theater Magazine Review (PDF) and these user comments from Audio Advisor.
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From: kspv ( kspvpk@vsnl.net ) on 29 June 2004
Subject: Reply to Slim
Dear Slim,
The two holes on the sub through which air is leaking are most probably tuned ports of the vented (bass-reflex) design. They are not meant for fixing tweeters (who would think of fixing tweeters on a subwoofer?). So don't mess with them.
As far as the number of subwoofers for your home-theatre system is concerned, a single, accurate and powerful high-end sub will do unless you sleep in an air-port lounge or something. Concentrate more on fidelity rather than volume. You would be far better off!