Equired to BK about XXLS-400, they advised front firing.. - AVS Forum
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post #1 of 11 Old 04-09-2013, 02:58 PM - Thread Starter
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Hi,
I'm trying to decide whether to get a front firing or down firing XXLS-400 sub woofer. I emailed BK and the response was (I hope Tom doesn't mind me quoting) "If your wooden floors are on concrete the the downward firing and if they are on joists then the forward firing".

I have joists, floorboards, carpet. Room is about 13 to 15 ft long, 9 or 10 ft wide, ceiling about 8ft.

I was surprised because when I search the forums, the general consensus seems to be that it doesn't make any difference.

Part of the decision is based around placement and aesthetics (though sound is the ultimate decider). If I get a forward firing, it feels like I should put it facing people on the opposite side of the room. I have a computer desk in the corner it could go under too, so it perhaps doesn't matter what colour I get in that case, and one side will be black anyway with the speaker grill.

If on the other hand I get a down firing, I keep thinking about putting it next to the sofa where a small table currently is, in which case I'd likely get a light oak finish. The annoying thing about that is I'd have to wait about 2 weeks for it ;-) Whereas there's a few plain black ones available from BK right now and I've got a film night coming up on Saturday with some friends round.. but that's a bad excuse to rush I guess!

Truth be told though, I'd probably prefer a light oak one anyway, decisions decisions..

Any advice would be appreciated.

Thanks!
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post #2 of 11 Old 04-09-2013, 03:00 PM
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It doesn't make a difference in this case.
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post #3 of 11 Old 04-09-2013, 03:18 PM
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Originally Posted by leninGHOLA View Post

It doesn't make a difference in this case.
From a dispersion standpoint within the subwoofer bandwidth it never makes a difference, the low frequencies from a sub radiate equally in all directions. Downward tend to sound a bit cleaner, as above bandwidth directional harmonics are acoustically filtered by down, or rear, firing. I can't imagine why anyone would make a recommendation based on the floor type.

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post #4 of 11 Old 04-09-2013, 04:18 PM - Thread Starter
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How confusing! :-(

If it makes any difference, my fronts and rears are all old mordaunt short speakers, MS 902's, with the 905C center. I wasn't sure if I should be pushing the subs up to 100hz or even 120hz since they are fairly small speakers, therefore making the subs a little more directional and needing a cleaner sound (which seemed like front facing would, but could be wrong).

I'd like to use it for both music and home theater, though the latter a fair bit more.

My guess about the concrete floor would be that downward facing could bounce off of it, whereas with joists a lot of it might go *through* the floor and into the space below.

But I'm only guessing and trying to see the wood through the trees.
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post #5 of 11 Old 04-09-2013, 04:37 PM
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Originally Posted by Mark_Sim View Post


My guess about the concrete floor would be that downward facing could bounce off of it, whereas with joists a lot of it might go *through* the floor and into the space below.
Logical, but logic and acoustics seldom coincide. Low frequencies being radiated omni-directionally the result with a down, rear, top or front firing sub will be the same in the lows.
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I wasn't sure if I should be pushing the subs up to 100hz or even 120hz since they are fairly small speakers, therefore making the subs a little more directional and needing a cleaner sound (which seemed like front facing would, but could be wrong).
You've got it backwards. The higher you run the subs the more directional content there will be, both within and above the sub bandwidth. You want to minimize directional content. Down firing and rear firing are best for that, especially down firing into a carpet.
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post #6 of 11 Old 04-09-2013, 05:12 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Logical, but logic and acoustics seldom coincide. Low frequencies being radiated omni-directionally the result with a down, rear, top or front firing sub will be the same in the lows.
You've got it backwards. The higher you run the subs the more directional content there will be, both within and above the sub bandwidth. You want to minimize directional content. Down firing and rear firing are best for that, especially down firing into a carpet.

Bill is right...i had a problem with air pressure hitting me HARD right at my ears..turned my HSU VTF-15 into a down firing position and it tamed the pressure big time and since the waves pound my wood floor instead the sub has even MORE feel! In my room for some reason it favors down firing subs vs front facing.

The other advantage is if there is any center channel leakage to your sub of any kind with your AVR you will not hear it as much with the driver facing the floor instead of facing you. No need for a second center channel...heh heh...

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post #7 of 11 Old 04-10-2013, 12:41 AM - Thread Starter
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Thanks everyone. I just wish I knew why Tom would advise what he did. It can't be for commercial reasons as either way he is getting a sale. Perhaps I should just ask him.

I wish I could try both, but unfortunately these aren't just pick up and take home to try - they have to be made for you, so at the moment it feels like a bit of a gamble.
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post #8 of 11 Old 04-10-2013, 08:08 AM
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Originally Posted by Mark_Sim View Post

Thanks everyone. I just wish I knew why Tom would advise what he did.
My guess is that he's a customer service rep, not an acoustical engineer. From a technical standpoint there's no reason to offer both down and forward firing, but there is a marketing reason. Most users think that if you can't see the cone you won't hear the sound that it makes. With tweeters that's true. With subs, it isn't.
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post #9 of 11 Old 10-04-2013, 02:39 AM
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The reason Tom would have stated FF is due to your floor type. As the floor in not solid i.e. stone or concrete it will resonate which in turn may cause boom and colouration (yes stone does also resonate too). It will be dependant on the joists/floorboards flex and also if they are air tight.  If the floor is not sealed (airtight) the sound will travel through the floorboard and into the void below which again may cause boom. You can help counter act this buy standing the sub on an isolator such as a granite plinth or use DSP to remove any harmonics and peaks this will help with FF and DF subs.

 

You may still get boom with a FF sub as every room acoustics are different but FF can be more tolerant to positioning than DF due to the boundary loading differences. 

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post #10 of 11 Old 10-04-2013, 05:37 AM
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Originally Posted by tris101 View Post

The reason Tom would have stated FF is due to your floor type.
The floor type is moot. No matter what direction the driver faces the sound radiation pattern from a subwoofer is omni-directional, ie., in every direction with equal intensity.

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post #11 of 11 Old 10-04-2013, 06:19 AM
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The floor construction does have bearing on the sound as does the wall location in relation to the speaker position. Yes a subwoofer sound is omni-directional but the proximity and type of structure have an affect. Stick a sub in the corner of the room what happens? bass boost and peak, put it in a free space and you will reduce the spikes. What happens if you put a large piece of granite under to DF sub when is on floor boards? it gets tighter and boom is reduced. Get a DF sub and mount it on its side and see if it sounds and eqs the same I would say there is a difference.

 

Yes all room acoustics are different and there are no hard and fast rule as there are too many variables.

 

But I'm sure you know more than me on this subject given your background.. I'm talking from personal trials and experimentation, so feel free to disregard my comments.

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