1 subwoofer vs 2 subwoofers
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=102609
Printed Date: May 01, 2024 at 10:30 PM
Topic: 1 subwoofer vs 2 subwoofers
Posted By: frizkysquirrel
Subject: 1 subwoofer vs 2 subwoofers
Date Posted: February 27, 2008 at 5:57 PM
if i have two of the same 12" subs, is there a way to roughly calculate the output in decibels of two subs if i know the output in decibels of one of the sub by itself.
ill give an example if its unclear what im asking.
say i have one 12" 300 rms sub in a 1.5 cuft sealed box and i know it is 130 db at 40 hz.
i then put another of the exact same 12" sub powered the same rms as the other in the same box playing at the same tone of 40 hz.
is there a rough formula for getting the db of the two 12" side by side if i know the db of the one, or is there too many other factors of the sub design that would affect this?
thank :)
Replies:
Posted By: DYohn
Date Posted: February 27, 2008 at 6:20 PM
If one sub @ 300 watts = 130db, then 2 of the same subs @ 600 watts (300 apiece) = 136db. Roughly. ------------- Support the12volt.com
Posted By: haemphyst
Date Posted: February 27, 2008 at 6:23 PM
What I'm curious about is what woofer, only rated 300 watts, will do 130dB at 40Hz? That's freakin' LOUD! You'd have to be starting with somewhere around 100dB efficiency! (Minus cabin gain, of course.)
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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Posted By: frizkysquirrel
Date Posted: February 27, 2008 at 6:27 PM
its not real data, haha.
i just made up some random easy numbers because...
...i just wanted to know a relationship between one and two woofers and the decibel readings.
Posted By: DYohn
Date Posted: February 27, 2008 at 6:44 PM
Posted By: frizkysquirrel
Date Posted: February 27, 2008 at 6:53 PM
thanks :)
Posted By: i am an idiot
Date Posted: February 27, 2008 at 8:58 PM
In case you want to know the formula that was used to get the 136 Db estimate. Generally speaking, anytime you double the cone area of your subs you will see a 3 Db increase. Any time you double your power on the subs, this too will give you a 3 Db increase. You have done both. From 1 12 to 2 12s would give you 133 Db. Then you doubled the power, theoretically you should be at 136. Just in case you were asking yourself "is there a rough formula for getting the db of the two 12" side by side if i know the db of the one"
Posted By: stevdart
Date Posted: February 27, 2008 at 10:07 PM
Nice link, DYohn. I'm adding that to my favorites folder pronto! Notice on that linked calculator, friskysquirrel, that there are boxes to choose: "in phase" or "random phase". You'll see that 2 identical woofers that apply to the categegory "in phase" (sometimes said to be correlated) will theoretically give the extra 3 db due to the additional cone area. This cannot be said, though,if you are speaking of the front stereo soundstage or of subwoofers that are connected to the amp on separate channels. The theory here would be that the two channels are separate signals and, although some of the content may be correlated, the assumption has to be that the signals vary in stereo and thus considered "random phase" (to apply the calculator's intent). For your make believe scenario the subs would have to each receive exactly the same signal to calculate the additional 3 db for doubling cone area. Bridging channels, using a mono amp, or combining signals prior to input to a two-channel amp are common ways to correlate the output. ------------- Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: frizkysquirrel
Date Posted: March 07, 2008 at 9:53 AM
yea. sorry im just replying now. i was busy with classes and work.
but yes i know of the phase. this was covered in my physics 2 class.
if the subs are not in phase you will get dips in the amplitude where the out of phase sounds waves caused destructive interference. Likewise when you have the sound wave exactly in phase it will cause constructive interference causing an increase in amplitude.
As well as the sub woofers being out of phase cause destructive interference, since they play relatively few notes at a time, it will create resonant peaks and dips within the cabin.
oh how complicated sound gets.
Posted By: haemphyst
Date Posted: March 07, 2008 at 10:00 AM
frizkysquirrel wrote:
oh how complicated sound gets.
You have no idea yet, young padawan. 
Wait till you get into crossover slopes and alignments, including L-pads, Zobels, inductor interaction, proper capacitor selection... absolute phase, equalization, driver placement, time alignment... high frequency cabin interactions... Oh, man. THOSE are the fun times!  ------------- It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Posted By: frizkysquirrel
Date Posted: March 07, 2008 at 10:03 AM
yes, it does sounds like fun.
but actually it does.
learning is an addiction for me. especially if it helps me understand something i love better. i think i could sit here alllll day just reading the posts on this site.
Posted By: haemphyst
Date Posted: March 07, 2008 at 10:09 AM
It is fun... You have the benefit of computers to do it all for you now... Old dudes like me and DYohn had to learn it all by hand! (Not sayin' you're an "old dude", DYohn, really... Just sayin'... )
This is a fantastic site to learn from, I have learned TREMENDOUS amounts of very helpful information here in the last few years from many members on this board. I respect many of them quite highly! In fact, here's a "Thank you" to all of them! ------------- It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Posted By: DYohn
Date Posted: March 07, 2008 at 12:46 PM
haemphyst wrote:
It is fun... You have the benefit of computers to do it all for you now... Old dudes like me and DYohn had to learn it all by hand! (Not sayin' you're an "old dude", DYohn, really... Just sayin'... )
I *DO* resemble that comment... ------------- Support the12volt.com
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