Looking for a Rule of Thumb for Subs - AVS Forum
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post #1 of 15 Old 02-10-2014, 05:19 PM - Thread Starter
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So is there a simple rule of thumb or an easy to use formula to help you determine what size sub-woofer you need for a given sized room? I find the bigger is always better argument is kind of weak (token: That's not what she said!). cool.gif

After reading quite a few sticky links I came across this website for speakers and the amount of amplification needed: http://www.crownaudio.com/elect-pwr-req.htm Is there one like this for subs? Or do I just use the same formula for a sub and spread it across one speaker? I don't need an in-depth PHD level physics discussion, I just want to roughly gauge what I will need for a decent home theater experience.
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post #2 of 15 Old 02-10-2014, 05:52 PM
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How about this: "1 sub for 1 seat, multiple subs if multiple seats", is that easy enough?

Besides that, there are a gazillion references on how much air you need to move in a give size room to reach spl levels, why multi-subs, etc.
What does your search skills reveal when you put them to use?

Have you even looked in the sticky that is in this forum you posted before posting, or not?
http://www.avsforum.com/t/824554/setting-up-your-home-theater-101

sorry to sound like I'm ragging on you, but lately seems many people ask q's w/o reading the great stickies that are here just for that purpose.
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post #3 of 15 Old 02-10-2014, 06:04 PM - Thread Starter
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Quote:
Originally Posted by mtbdudex View Post

How about this: "1 sub for 1 seat, multiple subs if multiple seats", is that easy enough?

Besides that, there are a gazillion references on how much air you need to move in a give size room to reach spl levels, why multi-subs, etc.
What does your search skills reveal when you put them to use?

Have you even looked in the sticky that is in this forum you posted before posting, or not?
http://www.avsforum.com/t/824554/setting-up-your-home-theater-101

sorry to sound like I'm ragging on you, but lately seems many people ask q's w/o reading the great stickies that are here just for that purpose.

Couple of points - Yes, I've read the sticky which is how I found how the link above speaker amplification. I did review the sticky in advance (over multiple days) and no, I could not find a link that answers the question I have. If you would enlighten me I would appreciate it.

PS - The sticky is outdated with a sizable percentage of broken links.
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post #4 of 15 Old 02-10-2014, 06:08 PM
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Quote:
Originally Posted by Turlen View Post


PS - The sticky is outdated with a sizable percentage of broken links.

honestly I'm going to watch some HDTV, and I'm sure then others will help you.
But, you are right so many of those stickies are old/outdated/broken, yet AVS seems to not care nor police the stickies....wonder why.....

[edit]
spend a few hours reading this forum, you will learn most you need to know
http://www.data-bass.com/home
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post #5 of 15 Old 02-11-2014, 03:33 AM
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Quote:
Originally Posted by Turlen View Post

So is there a simple rule of thumb or an easy to use formula to help you determine what size sub-woofer you need for a given sized room?
What you need to determine is how loud you want it to play at what f3 and the distance to the sub, then calculate back to determine the amount of air that needs to be displaced. Then work out how to achieve that.
But for most people the ROT is: you probably don't have enough subs in terms of number or capacity.
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post #6 of 15 Old 02-11-2014, 04:57 AM
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Quote:
Originally Posted by Turlen View Post

So is there a simple rule of thumb or an easy to use formula to help you determine what size sub-woofer you need for a given sized room? I find the bigger is always better argument is kind of weak (token: That's not what she said!). cool.gif

After reading quite a few sticky links I came across this website for speakers and the amount of amplification needed: http://www.crownaudio.com/elect-pwr-req.htm Is there one like this for subs? Or do I just use the same formula for a sub and spread it across one speaker? I don't need an in-depth PHD level physics discussion, I just want to roughly gauge what I will need for a decent home theater experience.

This post is missing several parameters that relate very strongly to the choice of a subwoofer:

(1) Desired Bass Extension.

(2) Desired SPL

I would break Desired bass Extension down into 3 ranges:

(a) Just want to amplify conventional music - clean response down to 32 Hz is a pretty good solution. Note there are few if any conventional full range speakers that can do this cleanly. A sub is not an option, it is a de facto requirement.

(b) Basically want great sound from both music and drama - clean response down to 20 Hz is "good enough". Note that obtaining sufficient SPL at 20 Hz with 10% or less THD probably exceeds the capabilities of most commerically-available subwoofers.

(3) Wish to create the impression of the earth shifting in its orbit - the sky is the limit - pick a number 10, 6, 3 Hz.

For SPL's you want to be able to go 60 dB or more above the threshold of hearing or ambient noise level in your room at the chosen bass extension frequency. The Fletcher Munsen curve is your friend.

Strictly speaking listening distance not room size dictates the required SPL output of your upper range speakers - LCR and surround.

However, Bass is non directional and te3nds to fill the entire room, so room size matters more.
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post #7 of 15 Old 02-11-2014, 09:33 AM
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arny and A9X-308;
concur with your posts.
Reason I pointed the OP, Turlen, to data-bass.com is there one can visually see in a nice comparison table the various freq and spl many commercial and DIY subwoofers will obtain, a site by fellow AVS member.
screen snapshot example - many more on the swite:
data-bass%2520websiteImage.JPG

Of all the sub-woofer threads I've seen on various forums, these 2 on blu-ray.com do a decent job of summarizing many-many discrete info sources.
http://forum.blu-ray.com/showthread.php?t=43669
and
http://forum.blu-ray.com/showthread.php?t=48286

Now;
Back to the OP's Q:
Looking for a Rule of Thumb for Subs.....

Has there been correlation of :
room size (volume) to subwoofer displacement volume to spl

that either of you are aware of?
Google search....https://www.google.com/search?q=rule+of+thumb+sizing+subwoofer&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

How about this one?
http://www.audioholics.com/loudspeaker-design/subwoofer-room-size
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post #8 of 15 Old 02-11-2014, 09:56 AM
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Quote:
Originally Posted by mtbdudex View Post

arny and A9X-308;

Reason I pointed the OP, Turlen, to data-bass.com is there one can visually see in a nice comparison table the various freq and spl many commercial and DIY subwoofers will obtain
You've still got to know how to interpret the data.
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post #9 of 15 Old 02-11-2014, 11:15 AM
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Quote:
Originally Posted by A9X-308 View Post

Quote:
Originally Posted by mtbdudex View Post

arny and A9X-308;

Reason I pointed the OP, Turlen, to data-bass.com is there one can visually see in a nice comparison table the various freq and spl many commercial and DIY subwoofers will obtain
You've still got to know how to interpret the data.

+1

However, some people seem to want definitive answers even if they can't quantify what they want. And, no serious technical questions or discussion please! ;-)
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post #10 of 15 Old 02-11-2014, 03:00 PM - Thread Starter
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I thank everybody who replied for their time and assistance. I'll do some more research.
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post #11 of 15 Old 02-11-2014, 03:43 PM
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turlen, you've been an avs member 6 years now, same as me.
I can remember me first getting into the forums and people getting all over me for not doing some basic research before asking a Q.
Transparently, I backed off asking Q's for quite a while.

good luck in your pursuits.
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post #12 of 15 Old 02-11-2014, 10:30 PM
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Originally Posted by Turlen View Post

I thank everybody who replied for their time and assistance. I'll do some more research.
I'm more answering the post before you edited it. You asked a very complex question and seemed to expect a "Just Buy This" answer where there really is none. Without knowing you none of us have any idea what is good or 'enough' or what any other adjective descriptor means to you and all you'll otherwise get is "I have a Brand X and it beats the snot out of all subs under $X". There is no rule of thumb - to get really good bass and sub bass is quite a bit of engineering. If you want to learn, ask, but you'll get asked a lot of questions to help narrow down a result for what is really an engineering problem.
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post #13 of 15 Old 02-12-2014, 12:50 AM
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Originally Posted by arnyk View Post

For SPL's you want to be able to go 60 dB or more above the threshold of hearing or ambient noise level in your room at the chosen bass extension frequency. The Fletcher Munsen curve is your friend.

 

Am I misunderstanding something here or does this recommendation mean that if, say, one wishes to aim for a clear response down to 20 Hz one would want the subwoofer (or rather subwoofers, perhaps) to be able to play that 20Hz cleanly at ca 130db? Isn't that a heck of a lot?

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post #14 of 15 Old 02-12-2014, 01:02 AM
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Originally Posted by dagdrivaren View Post

Am I misunderstanding something here or does this recommendation mean that if, say, one wishes to aim for a clear response down to 20 Hz one would want the subwoofer (or rather subwoofers, perhaps) to be able to play that 20Hz cleanly at ca 130db? Isn't that a heck of a lot?
Depends if you want the LFE below 20Hz at reasonable levels. 20Hz is the entrance foyer to LFE.
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post #15 of 15 Old 02-12-2014, 03:38 AM
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Quote:
Originally Posted by dagdrivaren View Post

Quote:
Originally Posted by arnyk View Post

For SPL's you want to be able to go 60 dB or more above the threshold of hearing or ambient noise level in your room at the chosen bass extension frequency. The Fletcher Munsen curve is your friend.

Am I misunderstanding something here or does this recommendation mean that if, say, one wishes to aim for a clear response down to 20 Hz one would want the subwoofer (or rather subwoofers, perhaps) to be able to play that 20Hz cleanly at ca 130db? Isn't that a heck of a lot?

The threshold of hearing at 20 Hz is 75 dB SPL, so 60 dB above that is 135 dB.

The background noise in a listening room at 20 Hz is off of most Noise Contour charts which typically go down to only 64 Hz, but probably in the same range or louder.

I picked the 60 dB margin based on psychoacoustic criteria, and it does seem to be just about mission impossible at low frequencies.

It is all a bit humbling, because many pretty good real world subs can only put out 95 dB SPL at 20 Hz @ 10% THD, and that is only 20 dB above the threshold of hearing. I guess this needs to be reviewed some more. Based on my own listening, > 100 dB @ 20 Hz is where things start getting impressive.
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