how important is efficiency to look at

[spencer321 10+ year member]

debating on 4 12's or 2 15's

4 12's would be hifonics brutus 12's 86.5db@1w

2 15's would be audiowque sdc2.5 15's 90db@1w

now theory says that overall the 4 brutus would be 92.5db@1w due to theoretical gain and the 2 sdc2.5's would be 93db@1w due to theoretical gain but the 12's have more cone area...

my question is... what does all of that really mean as far as real world numbers are concerned? btw both setups would see ~1800w

Click to read more...

 

[JimJ 5,000+ posts]

In a car, I wouldn't worry too much about it. 12V power is cheap.

 

[spencer321 10+ year member]

ok then... i understand power is cheap but assuming your working with a set amount of power, say the limit of your electrical system before you start getting into big $$ for alts and batts, how does efficiency relate to cone area and SPL

if a 10" subwoofer has an efficiency of 93db@1w and an 18" subwoofer has 89db@1w under the same power the 10" should be louder? because that would completely contradict the cone area theory

 

[Electrodynamic 10+ year member]

It depends on your box size and how much room you're willing to sacrifice. Take a look at this short paper on efficiency. It should explain a lot.

 

[sundownz Pro Seller]

Those sensitivity numbers on SUB bass mean VERY little.

 

[spencer321 10+ year member]

It depends on your box size and how much room you're willing to sacrifice. Take a look at this short paper on efficiency. It should explain a lot.

love to, what paper?

 

[spencer321 10+ year member]

Those sensitivity numbers on SUB bass mean VERY little.

well i was reading the huge debate in the speaker section over pro-audio speakers vs regular speakers and how these with these 150+ systems the best way to get your front stage to keep up is horns and pro drivers because they are incredibly efficient (100db@1w+) and i was thinking why wouldn't the same apply to subs?

 

[spencer321 10+ year member]

bump

 

[T3mpest 10+ year member]

well i was reading the huge debate in the speaker section over pro-audio speakers vs regular speakers and how these with these 150+ systems the best way to get your front stage to keep up is horns and pro drivers because they are incredibly efficient (100db@1w+) and i was thinking why wouldn't the same apply to subs?

Becuase there is a difference between thermal and mechanical power handling... I'll explain.

SPL stands for sound pressure level. It's how loud something is and it literally is a measure of actual pressure. When a speaker is playing a tone, lets say 50hz, that literally does mean the cone will move 50times in one second to reproduce that tone. How loud it plays the tone depends how much pressure the cone can exert on the air. This is dependent on displacement. The bigger the cone is or the further it moves the better. Still with me? Good! Now is where it gets fun.

When a tweeter plays a 5k tone (5000hz) the cone literall gets to move 5000 times in one second. That's 500 times more than a sub gets to move when playing a 50hz tone. This is why subs must be bigger than a tweeter. To get similar SPL's the tweet is at an advantage, it moves super ****ing quick so there is no need to be of a large diameter NOR is there a reason for it to need to move very far. This is key. For a 1inch driver to reproduce a 5000hz tone at 120db's (think rock concert loud) the cone only has to move maybe 1/16 of an inch. However, if the driver is only 88db's effecient it also needs alot of power to get there. Over 2000 watts actually asuming no powe compression. Every doubling of power makes the cone move a little further and adds 3db's of output. As the coils get hot the relationship of power to excursion breaks down and we get even less than 3db's.

Now back to subs. Every dropping of one octave requires

4x the excursion to maintain air pressure (ie SPL, ie volume). If a sub is not capable of moving far enough to displace the air needed it simply won't be able to get that loud at that frequency. All drivers are limited by both thermal power handing and cone excursion. Which limit you hit first depends on the frequency you are asking it to play. If the frequency is low, usually below 200hz or so, displacement becomes the key factor. The cone is moving very few times per second so it has to move far. As we go up in frequency where no matter how much power we use, we won't run out of throw, then the actual effeciency of the driver and how much power it can handle becomes important.

Point is, we could make a sub that is 105db's effecient at 1000hz. If it only has .5" of xmax it won't hit 140db's at 35hz no matter how much power we put on it. 3db's for each doubling of power only works if the driver can move enough to hit the new distance required of a cone of that size at a given frequency. That's why effeciency on a sub is useless it's measured at 1000hz. All subs have enough excursion to produce decent SPL that high. Once we drop octaves four times (four octaves down from 1k is like 60hz) we need 256x whatever excursion it took for the sub to hit it's 1k reference tone SPL. Yeah we ware still using one watt of power but cone excursion went up alot comparitevely speaking. Once we start adding more power it's a pretty good bet that we simply run out of mechanical throw before we run out of cooling.

This phenomenon of cone excursion vs power applied is why ported SPL subs need to take so much power. When you put a sub in a ported box the cone moves VERY little around tuning. Mostly your exciting the air in the port to gain output. This essentially breaks the rule about cone excursion vs frequency. Since the cone barely moves we can dump lots of power onto the coils still and still not run out of exursion in a small range of frequencies (near tuning). This leads to the same situation we have with tweeters and midranges, thermal powerhandling is usually our limiting factor.

 

[Varinabassing 10+ year member]

T3mpest that was well said and i actually learned something ..... thanks for taking the time to type that out

 

[audioholic 5,000+ posts]

Nobody mentioned Hoffman's Iron Law? Im disappointed. Low frequency extension, small enclosure, high efficiency... chose two. So, if you want a subwoofer that plays in a small enclosure, but also want good low frequency extension... you will literally WANT a low efficiency setup. Excuse me, you will NEED one.

Also, consider that those advertised efficiency specs are for a raw speaker only, playing free-air with no enclosure. Once placed into an enclosure, the enclosure size/type/alignment plays a much bigger role in over all system efficiency than does the raw speaker itself. A low efficiency speaker in a high efficiency bandpass enclosure will still be a relatively high efficiency setup (for its given pass band of frequencies).

Now also consider that many manufacturers arrive at their efficiency specs using different testing methods. Sometimes for honest reasons, sometimes just to make their specs look better.

Now finally, consider that most (if not all?) efficiency specs are arrived at using a 1khz tone. How many of us even play our subs at 1khz? None.

So you tell me, how important is the advertised efficiency spec of the raw subwoofer (no enclosure) you are considering?

Lastly, it seems some people in this thread dont realize that cone area factors into the efficiency. For the record... it does.

Cheers.

 

[spencer321 10+ year member]

Good info T3mpest, but audioholic, i was curious when you were going to chime in. I was unaware that measurement was at 1k hz, so its pretty pointless

 

[audioholic 5,000+ posts]

I haven't been around as much lately. Im glad I was able to add to the thread.

 

[Electrodynamic 10+ year member]

love to, what paper?

This site doesn't underline the links apparently. Mouse over the sentence and you'll be able to click on it.

 

[sundownz Pro Seller]

Or - Click below :

http://stereointegrity.com/docs/Efficiency.pdf