Single vs dual subs - Page 4 - AVS Forum
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post #91 of 110 Old 06-17-2010, 05:09 AM
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Exactly, I'm not using the extra 6db, but it did make the room sound more and more like it is "coasting" along (and it is). Which is always a good thing!

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post #92 of 110 Old 06-17-2010, 06:21 AM
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Quote:
Originally Posted by jaeelarr View Post

There is no boost in output even if you had 20 subs. More subs = less peaks and nulls, that's it.

Not true.

You will get a 3dB increase when you place subs together. 3dB for the first two, another 3dB when you add two more. Meaning 20 subs stacked together would give us around a +12dB gain.

Im not sure what the distance is before there isnt a 3dB increase but I think its maybe a meter.

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post #93 of 110 Old 06-17-2010, 06:23 AM
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Originally Posted by surap View Post

Just what I wanted to hear.

Thanks but I will comment. A null sometimes isnt missed in any listening test so is it worth the extra $$$ to just fix a null?? That is real question

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post #94 of 110 Old 06-17-2010, 06:25 AM
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Quote:
Originally Posted by craig john View Post

jaeelarr is correct in one respect: If you calibrate the *combined* output of the dual/multiple subs to the output of the speakers, there is no increase in level. Each sub would be turned down so that, when combined, they are playing at the same level the single sub would have been. There is only an increase in headroom, or "potential" output.

If this is what he meant, then he worded his comment very poorly to convey that message. OTOH, if he meant that adding additional subs does not increase system headroom, then he's just wrong.

Craig

Right, good post.

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post #95 of 110 Old 06-17-2010, 07:56 AM
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Why might it be that I am measuring a 6db increase (instead of the mentioned 3db) with my second sub? Is it the reaction of my room?

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post #96 of 110 Old 06-17-2010, 10:26 AM
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Quote:
Originally Posted by penngray View Post

Not true.

You will get a 3dB increase when you place subs together. 3dB for the first two, another 3dB when you add two more. Meaning 20 subs stacked together would give us around a +12dB gain.

Im not sure what the distance is before there isnt a 3dB increase but I think its maybe a meter.

Not true. It depends.

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Originally Posted by tony123 View Post

Why might it be that I am measuring a 6db increase (instead of the mentioned 3db) with my second sub? Is it the reaction of my room?

Because your subs are adding coherently at the measurement frequency.

If they're close enough together relative to wavelength, you're supposed to get 6dB per doubling of identical subs. At all distances.

If not, the answer varies. With uncorrelated signal, the average gain is 3dB per doubling.
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post #97 of 110 Old 06-17-2010, 10:39 AM
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OK so I have a single MFW-15 and since I have an older DENON without any auto processing I pretty much set levels on my own with the Radio Shack meter. If I were to add another identical sub (if that is possible) and level match them to the speakers at 85 db or so I will be doing nothing more than smoothing response and combating nulls.

However, if the max spl (just before amp clipping/distortion and the woofers physical limits) at my seated position with one MFW-15 was say 101db and I wanted to get to say 105 db would adding a second MFW and setting it up for max spl like the first would that not net me a 3db increase at the seating position and would be close to my goal of 105?

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post #98 of 110 Old 06-17-2010, 11:03 AM
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tlag, that's alot of big words...you'll have to slow down for this country boy. Am I understanding you to say that the fact that mine are positioned in close proximity to each other they act in a way to give 6db? And if I had positioned them say....one in front of room and one in the rear, they would be "uncorrelated" and thus only a 3db increase?

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post #99 of 110 Old 06-17-2010, 11:17 AM
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Quote:
Originally Posted by tony123 View Post

tlag, that's alot of big words...you'll have to slow down for this country boy. Am I understanding you to say that the fact that mine are positioned in close proximity to each other they act in a way to give 6db? And if I had positioned them say....one in front of room and one in the rear, they would be "uncorrelated" and thus only a 3db increase?

Sorry, just trying to be short and precise.

If you put the subs close together compared to the wavelength of interest, say, way less than 11ft for 100Hz, then you should measure a 6dB increase.

If you put them far apart relative to wavelength, actually, all bets are off. Depends more on the room and distances involved. This is one of the better room mode calculators I've found.

The uncorrelated 3dB thing was a red herring, I'm afraid, due to addressing the previous post. That's more from having two unrelated signals coming from two different points, which doesn't really apply to subs, but more to mains. Well, like I said, on average it may apply, but it's not really helpful. The room modes matter more...
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post #100 of 110 Old 06-17-2010, 11:20 AM
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Quote:
Originally Posted by ProblemHouston View Post

OK so I have a single MFW-15 and since I have an older DENON without any auto processing I pretty much set levels on my own with the Radio Shack meter. If I were to add another identical sub (if that is possible) and level match them to the speakers at 85 db or so I will be doing nothing more than smoothing response and combating nulls.

Correct.
Quote:


However, if the max spl (just before amp clipping/distortion and the woofers physical limits) at my seated position with one MFW-15 was say 101db and I wanted to get to say 105 db would adding a second MFW and setting it up for max spl like the first would that not net me a 3db increase at the seating position and would be close to my goal of 105?

Yes. Adding another identical sub at another position in the room, different distance, should get you to 104 dB max spl. If you added another sub and put it on top of the first, you would get to ~107dB max spl, but you wouldn't get any smoothing of response.
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post #101 of 110 Old 06-17-2010, 11:26 AM
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Quote:
Originally Posted by ProblemHouston View Post

OK so I have a single MFW-15 and since I have an older DENON without any auto processing I pretty much set levels on my own with the Radio Shack meter. If I were to add another identical sub (if that is possible) and level match them to the speakers at 85 db or so I will be doing nothing more than smoothing response and combating nulls.

However, if the max spl (just before amp clipping/distortion and the woofers physical limits) at my seated position with one MFW-15 was say 101db and I wanted to get to say 105 db would adding a second MFW and setting it up for max spl like the first would that not net me a 3db increase at the seating position and would be close to my goal of 105?

105dB at what frequency? In general, adding a second sub across the room from the first should smooth out response quite a bit. Better is to get hold of a measuring program like REW and figure out what the problem is before you try to fix "it." If there's a bad null at a higher frequency (above the LF cutoff), a smaller sub might work just as well.
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post #102 of 110 Old 06-17-2010, 11:41 AM
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Quote:
Originally Posted by fyzziks View Post

Correct.

Yes. Adding another identical sub at another position in the room, different distance, should get you to 104 dB max spl. If you added another sub and put it on top of the first, you would get to ~107dB max spl, but you wouldn't get any smoothing of response.

Sweet. Now to get a perceived twice as loud or double the volume I would need to increase SPL by 10db correct? So if 1 MFW-15 was 100db max SPL and I added two additional MFW's stacked I would have a perceived doubling in volume or it would appear to be twice as loud.

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post #103 of 110 Old 06-17-2010, 11:47 AM
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Originally Posted by ProblemHouston View Post

Sweet. Now to get a perceived twice as loud or double the volume I would need to increase SPL by 10db correct? So if 1 MFW-15 was 100db max SPL and I added two additional MFW's stacked I would have a perceived doubling in volume or it would appear to be twice as loud.

That rough rule applies in the midrange and higher. At low frequencies, it's much better than twice perceived loudness per 10dB. Look up the equal loudness curves.
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post #104 of 110 Old 06-17-2010, 11:49 AM
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Quote:
Originally Posted by tlag View Post

105dB at what frequency? In general, adding a second sub across the room from the first should smooth out response quite a bit. Better is to get hold of a measuring program like REW and figure out what the problem is before you try to fix "it." If there's a bad null at a higher frequency (above the LF cutoff), a smaller sub might work just as well.

I was just speaking in general terms. Not too big of a problem but when I had the sub in the corner it was great for movies at the seating position but for music was a bit boomy. I moved it more towards the center of the was and it smoothed out a bit. Actually I thing the boomyness just moved to the other end of the couch (about 45 degrees off axis). That end of the couch butts right up against the wall. I am trying to get another MFW-15 cause the pricing right now for a b-stock is really good and am just trying to figure out what to expect and how my placement will effect the sound.

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post #105 of 110 Old 06-17-2010, 11:59 PM
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Sure glad I posted my $.02, talk about a saddle burr in a tornado, no one even noticed

Spinning the rear tire at 150mph while at 3/4 lean angle will put wrinkles in your seat
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post #106 of 110 Old 06-18-2010, 09:11 AM
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Let's just simplify things folks without the jargon for a moment -

If you want a quake measuring 3.0 on the richter scale, go 1 sub.
If you want a quake measuring 8.0 on the richter scale, go 2 subs.

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post #107 of 110 Old 06-18-2010, 11:25 AM
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Originally Posted by Geoff4RFC View Post

Sure glad I posted my $.02, talk about a saddle burr in a tornado, no one even noticed

I read your post as I'm sure many other people did as well but you didn't really ask anything (other than "what do you think of my setup") or add anything to the discussion so I don't know what comments you were expecting. I can tell you that both of your subs are ported (that would be the large "port" hole you see on the front of your subs) and both subs are downfiring. The "firing" of the sub is just refering to which way the driver is facing. In your case, the drivers are mounted on the bottom of your subs and facing downwards.
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post #108 of 110 Old 06-18-2010, 11:48 AM
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Originally Posted by elerium View Post

I read your post as I'm sure many other people did as well but you didn't really ask anything (other than "what do you think of my setup") or add anything to the discussion so I don't know what comments you were expecting. I can tell you that both of your subs are ported (that would be the large "port" hole you see on the front of your subs) and both subs are downfiring. The "firing" of the sub is just refering to which way the driver is facing. In your case, the drivers are mounted on the bottom of your subs and facing downwards.

Right on, thanks for the reply. Yeah, the discussion was pretty much out of my league. I was hoping someone might notice I had my down firing subs mounted on plywood over carpet.

So I'll ask the direct question.......what is preferred? Down firing subs on carpet or wood?

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post #109 of 110 Old 06-18-2010, 12:02 PM
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Quote:
Originally Posted by Geoff4RFC View Post

Right on, thanks for the reply. Yeah, the discussion was pretty much out of my league. I was hoping someone might notice I had my down firing subs mounted on plywood over carpet.

So I'll ask the direct question.......what is preferred? Down firing subs on carpet or wood?

Doesn't matter. Carpet is not thick enough to have any impact on bass. The wavelength of an 80 Hz tone is over 14 ft. An inch of carpet is immaterial.

Craig

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post #110 of 110 Old 06-18-2010, 08:34 PM
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Originally Posted by craig john View Post

Doesn't matter. Carpet is not thick enough to have any impact on bass. The wavelength of an 80 Hz tone is over 14 ft. An inch of carpet is immaterial.

Craig

Thank you CJ. Knowledge is power and I've just gained some. I'm not as strong as I can be, but standing on the shoulders of members like you, I gain strength by the post.

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