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are 3db important?


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t-roy81 
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Posted: March 04, 2006 at 9:15 AM / IP Logged  

what is the point where yours ears pop?, ive heard of it, and my car seems to come close but i was just wondering. is there one?

Oh Man Theres Troy
DYohn 
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Posted: March 04, 2006 at 9:57 AM / IP Logged  

t-roy81 wrote:
what is the point where yours ears pop?, ive heard of it, and my car seems to come close but i was just wondering. is there one?

Huh?

Thanks for reposting those bits of info, stevedart.

gbear14275 if you hit 134.4 with 450 watts, that simply means your subwofer system coupled with the cabin gain in your car is about 107.4 db/watt-meter efficient.  Nothing magical or non-conforming about that.  It's pretty high, though.

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DYohn 
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Posted: March 04, 2006 at 10:05 AM / IP Logged  

t-roy, if you are talking about "popping your ears" due to sound pressure levels, that is a myth.  However, if you are talking about hearing damage, OSHA has set the following limits as the point where irreversable hearing loss occurs.  Note that it is a volume level in dbA (which is simply a method of measuring decibels) and the time you must be exposed to that level before you begin losing your hearing.  Also note that it has nothing to do with the frequency of the sound, it is just gross SPL measurements.  Many doctors think the limits are too high and the times too long:

90 dbA8 hrs
92 dbA6 hrs
95 dbA4 hrs
97 dbA3 hrs
100 dbA2 hrs
102 dbA1.5 hrs
105 dbA1 hr
110 dbA0.5 hr
115 dbA0.25 hr or less

Any exposure to levels higher than that will cause hearing loss, and exposure to sharp momentary impacts less than 1/10 of one second of 140 db or greater will permanently damage your hearing.

The answer?  Turn it down or wear hearing protection.

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stevdart 
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Posted: March 04, 2006 at 11:34 AM / IP Logged  
DYohn wrote:

t-roy, if one speaker @ 400 watts can generate 116 db, then 2 speakers @ 400 watts each with all else being equal should generate 119 db.

I'm not so sure I understand this after all.  I would have guessed 119 db just with the doubling of cone area alone...which means the same 400 watts is being shared with both subs.  Doubling the power, too, should give us an additional +3db, making it 122 db.  Otherwise, why do we make a point of the doubling of cone area if we're achieving the only gain by doubling power?

Typo?  Or do I not get it?

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
DYohn 
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Posted: March 04, 2006 at 12:14 PM / IP Logged  

No, it's not a typo.  Adding two EQUAL sources together (assuming no cancellation or other ineractive effects, and assuming the measurement is taken from the same distance) results in approximately a +3db SPL increase.

If you simply increase the cone area and keep the gross power the same, you realize no net increase.  For example, take a single sub with 400 watts going to it and let's say it produces 100 db SPL.  Add a second sub (doubling the surface area) but keep the same 400 watts, and now the power for each sub is reduced to 200 watts.  The first sub's output will be dropped by -3db (power cut in half) to 97 db SPL, and the second sub at 200 watts will add +3db due to doubling the surface area, resulting in a net 100 db SPL.  Exactly where you started.  Now if the power to both subs is maintained at 400 watts, the 100 db SPL output from the first remains, and the second sub adds +3db for a net 103 db SPL.  Adding two equal sources is the same as doubling the power to one source.

Make sense?

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stevdart 
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Posted: March 04, 2006 at 1:05 PM / IP Logged  

Yeah, thanks for clearing that up for me.  I think that for about 2 years I've been figuring this "cone area" increase wrong and posting wrong numbers on this forum.  It must be something I read one time and it just became embedded in my mind.

Then the only reason for adding sub cone area is to handle the extra power that you're applying to increase the db level.  So  "double the cone area for +3 db", if it's said at all and is not just a figment of my imagination, is a myth.  Without the power being doubled, regardless of number of subs, the +3 db doesn't happen.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
DYohn 
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Posted: March 04, 2006 at 1:16 PM / IP Logged  
That's correct, unless we're talking about increasing the cone area of a single sub.  For example, a 15" speaker generally has a little over twice the cone area of a 10" speaker, so with the same power going to both (and all else being equal) the 15" will have approx. +3db SPL increase over the 10" due to "doubling the cone area" with no change in the electrical power being utilized.   Also realize that many times in car audio especially, when we add a speaker we are also cutting the net impedance in half which (assuming the amplifier can handle it) also doubles the power output from the amp.  So adding a second driver cuts the total load from, say, 4-ohms to 2-ohms, and doubles the amplifier power output.  This then delivers the same power to each speaker as was originally being delivered to one, netting a +3db increase.
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stevdart 
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Posted: March 04, 2006 at 2:04 PM / IP Logged  

Anybody who has gotten through this thread this far should know that my lengthy response on the first page was only partly correct.

extrmndor3 wrote:
so i read everytime you add a sub you add 3 db...if i add another sub it will add 3db...if i double the power another 3 db 

I responded, "Not everytime you add a sub...it's everytime you double the number of subs increases 3 db's."  That is wrong, because neither is true.

And I said, "Look at the case above where we increased the number of subs from 1 to 8 to achieve a 9 db gain....we just about doubled the loudness."  That is wrong, because of the same reasons.  I wasn't considering a change in power, only an increase in number of subs.

This is a question where we first have to find out some pertinent details before we can respond. 

  • Are you keeping the same size sub or are you switching to a larger or smaller size?
  • Will you switch the subwoofers to a different coil configuration so that the impedance load on the amp remains the same as it was when you were using one sub?
  • If you're adding a sub identical to the one you already have, what will the amplifier output at this different impedance load?  How does it compare to the output into the single sub?

This can only be a "theory" response unless we know these details.  It becomes a complicated calculation and can be different with each situation.  And we still have that shadowy gray area to consider:  the increase in cabin gain that happens when you increase the decibels.

Like I hear the pros say it, "Build it and read it with a meter."

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
jeffchilcott 
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Posted: March 04, 2006 at 3:55 PM / IP Logged  
Alright I believe I have been summoned to the post for a reason.
There are many many factors besides the doubling of cone space and power, many of which have nothing to do with the amp, or sub.
I will start from the beging and work through the design of a full tilt SPL system
Electrical is the most important, while you might have an amp that is capable of producing 2400 watts at (X) ohm this is a measurment normally taken at 14.1-14.8volts constant! no power drop what so ever.   In a real world application this is 99% impossible
So if you 2400 watt amp, say in example like we have been using a memphis 2000d was rated at 15.1 volts...(very high voltage for published ratings)   then if you experience a voltage drop to 12.0 volts your 2400 watt rating becomes 1907watts
So your first Issue is to address voltage drop so you dont lose valuble power, next find the breaking point of your amp
(DO NOT ATTEMP THIS UNLESS YOU HAVE MONEY TO REPLACE YOUR EQUIPMENT OFTEN!!!!!)
The amp we are currently using is rated to have a minimun impedance of 2 ohm. At the last show we were running at .76 nominal impedance with 1.05 ohm impedance after box rise (a whole diffrent ball game altoghter!)
Amps will become very unstable and unefficent at these points, and generate alot of heat. But for 3-5 second burps alot of amps will hold up with non flucuating voltage
Movement of airflow.
This will start with the inside of your box, angling walls, rounding edges, large diameter ports ect ect
Basically doing anything you can to help the air flow out of the box and into the cab of the vehicle.
I have actually seen vehicles quiter due to placement of amps and battery because they restricted the aiflow coming out of the ports or moving into the front of the vehicle.
To see how close the calculations will come I am sure many of you have seen the video of our vehicle doing 150.6db so I will plug the #'s in and see what we come to
12" kicker L7 Efficency 87.4db @ 1 watt @ 1 meter
Our amp produced 3260watts during a full burp, this measurment was via a clamp meter and DMM..AC voltage X AC current
3260/2=1630watts per sub
87db+3db(for second sub)=90db at 1watt at 1 meter
90db+3=93@2watt
93+3=96@4
96+3=99@8
99+3=102@16
105@32
108@64
111@128
114@256
117@512
120@1024
123DB@2048watts@1 meter
Now where did our extra 27 decibles come from?
There is also another factor we have came across in the last year.   Humidity, heat, rain
Based on the heat and humidity we have seen loses of up to 1db from show to show with an untouched setup
There are soo many factors that can can change the actual DB level a given setup or vehilce can achive, is 3db a big diffrence....when your above 150db YES it is...but for a common consumer a 3 db increase might leave you lacking what you really expected.
But due to the given varibles and I have tested this before...in a ported enclosure you can see gains of up to 5-6 db from adding a sub with the same amount of power as the previous. In a sealed encloused you can still see 3-5 db increases!
Now a shamless plug of our video so more people can see it, haha
http://realmofexcursion.com/videos/Competitions/kickercomp.2.wmv
2009 0-1000 Trunk WR 154.0DB 2009 1001+ Trunk WR
2007 USACI World Champion
2007 World Record
2006 USACI Finals 2nd Place
DYohn 
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Posted: March 04, 2006 at 4:47 PM / IP Logged  
Great posts.  The things Jeff and Steve are discussing is why I always use words and phrases like "approximately" and "all else being equal" and "assuming no cancellation of interaction effects" and "ignoring" or "including cabin gain."  SPL is almost impossible to calculate on paper and be certain of your results.  are 3db  important? - Page 2 -- posted image.
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