Sensitivity on subwoofers

[kirill007]

How important is the sensitivity on subwoofers? (because i thought it was measured at 1khz.)

(only correct answers please, if u don't know for sure then don't answer.)

[kirill007]

So guys what's you're look on sensitivity?

[hdorre]

What is sensitivity? The sensitivity of a driver is typically defined as the sound pressure level of the loudspeaker given 1 watt of power input, measured at a distance of 1 meter, measured on-axis with the loudspeaker and measured in infinite space with the loudspeaker mounted to an infinite baffle. While the later part is typically assumed but not stated, the former part is the reason you generally see "1w/1m" or "2.83V/1m" stated along with the sensitivity specification.

But wait, is 1w/1m equal to 2.83V/1m? The answer is only for an 8ohm impedance driver. We know this because of ohms law, where Power = Voltage^2/Resistance. If the load is anything other than 8ohm then the resulting sensitivity rating will not be a 1w measurement! If the driver is 4ohm and the measurement is a 2.83V measurement, we can find the amount of power input with the formula 2.83^2/4 = 2w. This means that sensitivity will be overstated by 3db compared to a true 1w measurement. I have seen many unscrupulous companies take a dual 2ohm/coil subwoofer, wire the coils in parallel and then rate sensitivity at 2.83V, overstating sensitivity by 9db!

Due to these and other variations in rating methods and some manufacturers not even stating a method, it can often be difficult to directly compare one subwoofer's sensitivity to another's. However, if you are able to obtain the Thiele-Small parameters for the subwoofer there is one surefire way to calculate an accurate sensitivity measurement for a driver. And that is with the following formulas;

Efficiency (N₀) = 9.64 * 10^(-10) * Fs^3 * Vas / Qes

*To express as a percent, multiply by 100

*Vas in liters

Sensitivity (SPL) = 112 + 10*Log(N₀)

The Efficiency (N₀) calculation expresses, typically as a percentage, the amount of power input that is converted to acoustic power. With the sensitivity calculation we can convert the efficiency of the driver to a 1w/1m sensitivity rating. As long as the T/S parameters are accurate, utilizing this formula will put any two drivers on a level playing field and allow you to directly and accurately compare sensitivity (or efficiency) between drivers.

Okay, but higher is still better because higher means it's louder, right? Not necessarily the case. There are a few issues here that need to be discussed to better understand why.

From a driver design perspective, we can see from the above formulas that there are two ways in which to increase sensitivity for a given driver diameter; increasing Fs or decreasing Qes (or both). Adjusting either of these two parameters, however, is ultimately going to affect how the driver responds in a given enclosure. And this relationship, as it relates to enclosure size, sensitivity and low frequency extension, has been defined through a rule known as Hoffman's Iron Law. As you can see from the link (which I highly suggest you read), it's already been covered in relative detail elsewhere on the site. But it's important to us here, so it's worth touching on again.

In short, Hoffmans Iron Law states that we can only have two of the following three;

• Low frequency extension
• Small enclosure
• High sensitivity

What's important to take away from this is that if you want high sensitivity and a small enclosure, you will necessarily sacrifice low frequency extension. Or, conversely, if you desire extended low frequency output from a small enclosure, you must necessarily sacrifice sensitivity. While a given driver may have a higher rated sensitivity, that driver may actually have less output in the subbass region once the effects of the enclosure are taken into consideration since it may begin it's rolloff at a higher frequency. And given in car audio we typically require reasonable enclosure volumes, having a high sensitivity can actually be disadvantageous.

The second factor we need to consider is how output is achieved. Sensitivity isn't what determines maximum output. Output is a function of air displacement. The maximum amount of linear displacement (Vd) you can achieve is limited by your cone area (Sd) and linear excursion (Xmax). As you increase the amount of displacement at your disposal, you increase the potential linear output you can achieve. Even though a driver may have a higher sensitivity, if it's maximum linear displacement (Vd) is less than that of a driver with a lower sensitivity, the lower sensitivity driver will have the potential for higher levels of output.

We also have to consider the effects of Power Compression (and I again urge you to read the link). Consider the effects of power compression applied to our scenario. A higher sensitivity driver may, for example, begin to experience more power compression at a lower output level than a lower sensitivity driver. If this is the case, then as output is increased beyond that level the higher sensitivity driver would gain less output for each increase in power and experience more parameter shift.

[kirill007]

More people who have anything to say about it?

HOw important is it?

(although the quote hdorre uses sums it quite up)

[Ford302Redneck]

More people who have anything to say about it?

HOw important is it?

(although the quote hdorre uses sums it quite up)

He finally posts useful information.

I'm proud.

[Alex K]

very nice copy paste hunter. hehe

[BanginOnABudget]

ford god damn, just shut the fuck up dude, you're always talking shit on people, i give it a month at most and you'll be banned.

and sensitivity isnt really that big of a deal unless its below 85db/spl, in my personal opinion the sensitivity isnt that important unless you want to go for an spl oriented setup, the the higher the sensitivity the better.

[skittlesRgood]

hdorre, might want to say where you got that from.

with mid-bass i have noticed that drivers with somewhat lower sensitivity do better/have more mid-bass. higher sensitivity means they do better as a mid-range.

everything else is in hdorre's quote.

[kirill007]

hdorre, might want to say where you got that from.

with mid-bass i have noticed that drivers with somewhat lower sensitivity do better/have more mid-bass. higher sensitivity means they do better as a mid-range.

everything else is in hdorre's quote.

He got it from the stickied thread from SSA i think. (yes ford302 i also think xD)

good info

That's because sensitivity is measured at 1000hz, so if it's lower it sometimes means it will play louder down low.(higher is the opposite like you have mentioned )

Edited February 7, 2011 by kirill007

[Ford302Redneck]

ford god damn, just shut the fuck up dude, you're always talking shit on people, i give it a month at most and you'll be banned.

and sensitivity isnt really that big of a deal unless its below 85db/spl, in my personal opinion the sensitivity isnt that important unless you want to go for an spl oriented setup, the the higher the sensitivity the better.

Actually wasn't talking shit this time.

So you need to calm your ass down. Your the one that needs to be banned for all those cuss words you just posted. As all none of that was called for.

Also, if this forum bans everybody that calls out people, I'm sure there won't be many people left. But idiots who don't know the real answers.