HT017 – Subwoofer Placement in your Home Theater

Episode #017
Host:  Mike Deckys
Guest: James Lindenschmidt – General Manager – RealTraps
Topic:  Subwoofer Placement in your Home Theater

Download Full Transcript here

On this episode of the Smarter Home Theater Show from Real Traps we welcome back James JWL Lindenschmidt who is the General Manager and Acoustic Expert of this high performance acoustics treatment manufacturer.  So, James, thank you so much for your time and coming back to talk to us.

James:  Thanks a lot.  Glad to be back.

Mike:  Thanks James.  Now on this episode let’s focus in on subwoofers and more specifically subwoofer placement.  You know it has been said and we have said before that bass trapping is the first, best and easiest way to improve sound quality.  So explain to us why that is.

James:  Well, because it gives the subwoofer an accurate environment within which to work.  We talked a lot about bass trapping and the need for it in the past several episodes that I have been on.  Without bass trapping most rooms have a very uneven and not accurate frequency response.  So even if you put the best subwoofer in the world into your room that is poor acoustically you are only going to get so far with it.  You have a great subwoofer but the room that it is operating in is dramatically coloring the sound that it is capable of producing.  So the idea with bass trapping is to reduce the amount that the room influences the way the subwoofer sounds.

Mike: Ok, now is having a single high quality subwoofer better than having multiple subwoofers?

James:  That is a great question and there is a lot of debate on this particular issue.   The argument for having multiple subwoofers is that you can sort of control how the bass behaves in different spots in the room.  In other words if you just have one subwoofer just because of the nature of the way low frequency energy works in a small room, which we are dealing with in home theaters,  there is going to be some spots in the room where the subs is much louder than other spots in the room.  And where it gets loud and where it gets soft is going to vary according to frequency as well in the room.  So you are going to get completely different room response curves.  You know, based on where the subwoofers are placed.  So the idea of multiple subwoofers is you can place the subs in different spots to generally even out the response pretty much over all of the room.  If that makes sense.  So that if subwoofer A produces a null at 40 hertz at the listening position, whatever I am just throwing out examples, then what you want to do is place subwoofer B in a position where it might have a peak at 40 hertz.  So the peaks from one subwoofer sort of helps supplement the null from the other subwoofer.  If that makes sense.

Mike:  Yes

James:  And you are left with a more average response. I am oversimplifying of course but you get the idea.  So whether multiples are better, maybe so maybe not.  If it is well implemented and you are in a treated room and you have done some careful placement and sort of testing, I would say that in my experience the best rooms come from having multiple subwoofers.  But, again, the fact that it is multiple is probably not necessarily the most important thing.  I think it is better to have one decent subwoofer and treatment than it is to have two of the best subs in the world with no treatment.  If that makes sense?

Mike:  Okay.

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James:   It also depends on the system and the type of sound that you like as you are listening.  There are so many variable and so many opinions. But that is my take. Multiple subs can be very useful in situations and give better results, again, provided that a lot of other pieces of the puzzle are also in place.

Mike:   Are receivers set up to have multiple subs or do you split the line out to get multiple subs?

James:  Generally you just split the line out.  You want all the subs playing the same thing pretty much.  The benefits that you get just sort of happens with placement.

Mike:  Now as far as types of subwoofers, you have active, you have passive, you have ported.  Can you explain briefly the different types there are and any benefits that each one has?

James:  Yes, sure.  Active and passive –active just means that the sub has its own amplifier.  You don’t have to use the receivers, amplifier or whatever you have.  Integrated amplifiers or whatever it is.   So the sub has its own power.  Generally that is what I prefer, is active subs for a couple of reasons.  One is bass needs a lot of power to sound as loud and as clean as higher frequencies.  Generally from 100 hertz on down you probably need about 10 times the power to move that air at those low frequencies of big wavelength sounds.  You need a lot more power to get those to sound loud and clean.

Mike: Wow!  About ten times the power?

James:  Generally, yes, generally.  That might be an exaggeration but…

Mike:  It’s a lot.

James:  Yes, it’s a lot.  If you look at all the different places subwoofers are used, from a home theaters to commercial movie theaters to concert halls when they are playing at the big stadiums.   The vast majority of the power being used for those applications is going to the subwoofers.  And again, it is just because to move that much air for those low frequencies just takes a lot of power, you have to move a lot of air.  So that is one reason that I prefer active subs is because you are not taxing you receiver by putting this huge power demand on it.  You can let the power built into the receiver take care of the high frequencies and the low frequencies has its own amplifier.  And there is a second reason I prefer actives generally, and again this is well designed subwoofer, there is a phenomenon between the speaker itself and the amplifier.  There is a technique that they can use, and I believe that the technique is called feedback of some sort.  I forget the technical term for it.   But basically it is a way to dramatically reduce distortion.  Because the amplifier, since I don’t have to make the sub work with a wide verity of amplifiers (in other words the sub is only working with its own amplifier built into it)they can really sort of tweek the circuit amplifier to work really well with that particular speaker.  As opposed to it being a sort of general sort of as long as it is a 4 Ohm speaker it is okay. They can really sort of tweek it out.  There is a way to sort of feedback some of what the speaker is doing back into the amplifier so it can compensate.  The result of that is it dramatically lowers the distortion and I am not enough of an engineer to talk more specifically about it and I might even have the name wrong.  I think it is negative feedback or something like that.  But I do know of this technique, but that is only possible with active subwoofers because the amplifier circuit and the speaker have to be known quantities and specifically be working together in that way.  And that is just not possible with passive systems.  So for both of those reasons I think people are generally better off with active subs.

Mike:  Okay, now once you have your sub and you are trying to figure out where to put it are there any shortcuts to figuring out where to put it besides getting the equipment that we talked about on previous episodes?

James:   Well a lot of people will have their sort of favorite tricks that they have picked up over the years.  And one of them is corner placement.  Generally for the same reason the bass traps work so well in corners, is there is usually a bass filled up in the corner.  So if you put your subwoofer in the spot where the bass build up is it is really going to crank out the low end.  And a lot of people find that sort of exciting to listen to, especially for movies when you have explosions and things like that.  If you put a sub in the corner that whole room is going to resonate and those things and it is just going to be exciting.  So a lot of people prefer to do that.  And audio file may not like that as much because it is probably less accurate even though it is exciting sounding.  It really depends on your preference.   The only way to go from my point of view really is to experiment.  And that is sort of a cop out of an answer, but it is really true.  Acoustics is so complex that – not to mention partly from one subwoofer to the next, there is a lot of variables there.  The only way to be sure is to experiment.  I have a few techniques that I like to use.  It is sort of strange actually but the first one that I like to do is if I just bring in a subwoofer into the room what I generally like to do is put the subwoofer right in the listening position.  In other words, where you normally sit when you are watching a movie to whatever.  And if possible get it up off the ground so that the actual subwoofer itself, the part that is moving, is right at your ear level when you are sitting there.  So, of course, that might be a deal breaker in some rooms being able to get the subwoofer 4 feet off the ground, or whatever.  If possible that is what you should do.  Get something with a lot of bass in it playing pretty good.  Something you are familiar with and at that point literally what I will do is get on the ground and crawl around the floor and listen for good placement where the sound that I am hearing is the bass that I know from that song that I know so well.  And it sound really good.  And then I will take a piece of masking tape, or something, and put an X on the ground when I find a few spots that I like.  I will go huntin for a handful of those spots.  At least 3, more than 6 isn’t that useful, somewhere in there.  3 or 4 or 5 or whatever spots that you think sounds pretty good when you are crawling on the floor.  Then what I’ll do, once I find those spots, is that is sort of my starting points.   Those are the places that I want to investigate and check out in a little more detail. So what I will do then is I will take the sub down from the listening position at your level and I will just lay it on that masking tape X that I put down.  You know those 3 or 4 spots.  And some of those will pretty obviously sound better than others.  Hopefully the idea is to eliminate the ones that don’t sound as good.  Generally I try to narrow it down to the two  best sounding of the spots.  Maybe 3 if there are a couple that are close and I can’t quite make up my mind.  Let’s say that you narrow it down to 2 spots that sound good from there.  At that point that is when I get out the testing set up and I use the room testing of software that we talked about in the last episode.  And I will shoot the room with the sub in both places.  And it is important to make sure that you don’t move the microphone for those tests.  In other words keep the microphone in exactly the same spot.  Run the test with the sub in one location and then without doing anything at all to the microphone just simply move the sub to the other location and run the test again.  And at that point you can see, if you are not quite sure and they both sound good to you, there is not a huge difference, then this will definitely show you.   This will go wow with this one, they are pretty close but this frequency response is a little bit flatter than the other one.  So that is generally the one I go with.  If I found a few spots and they both sound good to my ear and I can’t quite decide, that is where testing is really useful.  Because you can make sure that you’ve got a spot that not only tests well but sounds good to your ear.

Mike: Alright, well cool.  That sound like a pretty easy option.  Even if you stop with one of the best two you can even just pick the one you like best and you don’t have to do anymore testing.  And it’s kind of an inexpensive quick tip to figure it out.

James:  Absolutely. It just takes some time and its – with all the steps I would expect it to take roughly about an hour, experimenting a little bit and a little bit of groundwork.  You have to move stuff around and crawl around on the floor a little bit.  But it goes well and it is definitely time well spent.  Because when you are done with that it is a great investment of time because it is will just make your system sound better.

Mike: Right.  It is all about the experience.  Right?

James:  Absolutely.

Mike: Alright.  And of course if anybody wants more information they can just go to the Real Traps website.   And I know if they click on the Acoustics Info tab across the top.  You have a bunch of articles and videos and downloads and all kinds of neat stuff to learn more.  So anything else you would like to add?

James:  Yes, that is pretty much it.  There is a ton of info on the site.

Mike:  Well, it doesn’t sound all that tough to do and you can make a big improvement in your system with a couple easy steps.  So please, don’t forget to support The Smarter Home Theater Show by supporting our sponsor.  Your support of them helps to support us.  Just go to SmarterHomeTheater.com and click on Support the Show to learn how to help us out.  And don’t forget to subscribe to our email newsletter for insider tips, cool contests, and more.  Just go to SmarterHomeTheater.com to learn more.  And if anyone has a specific question feel free to contact me using the contact form on The Smarter Home Theater website. And James, if somebody has a specific question about acoustics are you available?

James:  You know obviously if people have questions about treating the room or anything like that feel free to contact me as well.  And I would be glad to help them out.

Mike: Okay.  Thanks much James.  We appreciate your time.

James:  Very good.  Thanks for the call.