# The meaning of an F3?



## paralegal (Jan 27, 2013)

I am trying to understand some of the terminology of speaker specs.
I am aware of what 'sensitivity' is but an F3 number of say, 31Hz or 20Hz escapes me. Does the lower number of Hz mean it will play lower or does it mean that the suspension of the speaker is looser and moves air easier with less power? I am trying to apply the numbers to choosing a speaker for a small 1.2 cu ft sealed box and a 10 or 12 inch driver.
I have attempted to use the formulas in the calculators but sometimes an F3 is given and another time it is not for a different speaker. Need some help.


----------



## ATOMICTECH62 (Jan 24, 2009)

F3 is the frequency where the output is 3 db lower.
If your Lp crossover is set at 80hz then it is 3db lower at 80hz.

If the box has an f3 of 30hz that is the point it starts dropping off.


----------



## Bayboy (Dec 29, 2010)

Also you should get familiar with cabin gain/transfer function, particularly the character your specific car produces since most of the specs you are wanting to know will be heavily affected by such. IE a sub's F3 almost means nothing once placed in the vehicle. The vehicle will change it and in some cases drastically. With that, it can become very dependent in designing a sub system.


----------



## BoostedOne (Nov 15, 2012)

F3 is also called the 3db down point... because thats the point in the roll off your output will be down 3db. Its not much of an indication of anything about the driver in particular but a result of how the driver and enclosure work together

Sent from my MB865 using Tapatalk 2


----------



## hpilot2004 (Dec 13, 2011)

Bayboy said:


> Also you should get familiar with cabin gain/transfer function, particularly the character your specific car produces since most of the specs you are wanting to know will be heavily affected by such. IE a sub's F3 almost means nothing once placed in the vehicle. The vehicle will change it and in some cases drastically. With that, it can become very dependent in designing a sub system.


So what you are saying, people should try to find the correct cabin gain frequency and try to find a subwoofer with an F3 that is close?


----------



## hpilot2004 (Dec 13, 2011)

Car Audio Cabin Gain Transfer Function


----------



## Bayboy (Dec 29, 2010)

hpilot2004 said:


> So what you are saying, people should try to find the correct cabin gain frequency and try to find a subwoofer with an F3 that is close?




Actually, that would work for most depending upon taste, but that is the general idea if one didn't have the means to EQ the subsequent natural rise. That is with sealed anyway. With ported it's sort of a horse of a different color since there are fatal penalties below tuning. 

The main thing is to become familiar with what your vehicle does to any sub you will install that way you can input that into the design consideration. Having a good EQ offsets pretty much all of that, but can make a difference if you are trying to create an efficient system by overshooting the response and creating headroom through EQ cuts.


----------



## paralegal (Jan 27, 2013)

I thought the F3 applied to speakers only, not the enclosure.
Now I am really confused


----------



## paralegal (Jan 27, 2013)

So, if I look at a 12" subwoofer that has an F3 of say 26hz and as sensitivity of 93 db at one watt at 26hz on axis, would that be the way to go if I am not interested in a high db output? (not sure if I have the terminology correct).
But a speaker in a proper enclsure that is down ony 3 db at 26Hz sounds like a great sub.
Please give me some input as most speakers don't even come close to the above.
I think there are two types of subwoofers:
- one for high output for db contests
- one for music and enjoyment
The latter appears to be far cheaper to buy as they don't need super ridiculous Xmax etc.
What bothers me is how do I avoid a speaker manufacturer that bends the specs in order to be all things to all people. Which manufacturer truthfully offer a Musical sub or a High db output sub?
All way to confusing for me so I will rely on the experienced contributors to this forum.
I have the money, I have the time, I have the skills to buy, install, build etc to get a HiFi sound reproduction system if that is possible. Thanks for reading my rant and I hope you can assist in this confusing market.


----------



## Bayboy (Dec 29, 2010)

paralegal said:


> I thought the F3 applied to speakers only, not the enclosure.
> Now I am really confused


If that confuses you, then you haven't learned the basics and going any further will probably lead to a stroke! Seriously.... I had a buddy that tried to jump stages in grasping general concepts & rules.... he woke up dead the next day & I wound up with all his gear! Get the gist of things and then all will make sense.


----------



## paralegal (Jan 27, 2013)

I believe I have the drift of what I want and I understand the role that the vehicle interior plays in the equation but even on this forum the battle of what is the right setup rages on.
I have two subwoofers in my home system. I built them, they have Peerless drivers and passive rads in each cabinet they play flat to 20hz and the room is designed to keep the bass in the room with no standing waves. A car seems to suffer from too many ridiculous manufacturers claims as to amplifier power and even goes so far as to equate the power handling of a speaker as to how much sound they will play (as in loudness).
Way to confusing. I think the Peerless or Dayton 12" driver with an Onyx amp in a 1.2 cabinet or two 6 x 9 Tang Bands in the package tray is the way to go. Both appear to be quality manufacturers.


----------



## Bayboy (Dec 29, 2010)

That wasn't meant to discredit you... my apologies, but know that modeling can supersede anything a manufacturer suggests (box wise). If you're using something with excursion plots, then it can almost tell you how much power you can get away with as well. There's lots of tradeoffs when it comes to car audio so it really helps to know unless you don't mind making sawdust often. The latter isn't so bad though.... imagine back in the days before such knowledge & programs were widely available to most consumers.


----------



## paralegal (Jan 27, 2013)

Thank you, that helps.
So the Morel Primo 124 12 is one of those "jack of all trades" speakers?
I really like the look of this unit even though it has an F3 of 31Hz.


----------



## BoostedOne (Nov 15, 2012)

Wow. This thread has grown.

First there is Fs, which is limited to the driver. Thats the resonance. Simply put, its where the speaker won't want to play below.

F3... once you put it in a box, there will be an f3. Most of the formulas and calculators give you the anechoic response. What tjat means is if the enclosure was playing in a soundproof room. This isnt a bad thing. It helps compare apples to apples. 

Anyhow if you look at a sealed box it will play somewhat flat at higher notes and gradually roll off on the low notes. The flat area is 0db, for a reference. Its just a reference point, not literal db. The point where the 3db roll off hits is the f3. Changing box size on a sealed box will change the q which will alter the slope of the roll off....

On a ported box the port has some sort of response which gets superimposed over this curve. Depending on the box size, and how you tune the port, you can either extend the low end response or create a huge peak if you tune the port higher than the roll off.

But since a port has a narrow frequency range and is typically tuned at or below the f3, once you go below the f3 of the ported enclosure it doesnt play much at all.


A note on cabin gains and functions... to the guys who imply using anything more than an off the shelf flea market box is a waste unless you measure this stuff.... all that is dandy but are you also going to go thru the hassle to visit an audiologist and have the transfer function of your ears measured? 
Different people have different sensitivities to different sounds. With that in mind, why sweat it? You can't change the acoustics of your car. If you listen to a music with requirement of a certain frequency range ensure your box covers it easy. You don't need a box to play 25hz for Celine dion so who cares what the vehicle response is there and why tune your box to be "flat" if its only to accentuate what you dont need want or care about. I remember friends of mine gabbing about this 20 years ago...

Sent from my MB865 using Tapatalk 2


----------



## Oliver (Jun 25, 2007)

Does this help?

______________________________________________________________________
BuickGN wrote this !



> *Small sealed box= MORE cone control [BuickGN]*
> 
> Here are some links that support my argument of smaller box= less cone control and worse transients.
> 
> ...


----------



## paralegal (Jan 27, 2013)

Wow, I am impressed with the time you took with your reply.
I am now convinced that an ib sub is the way to go.
I can put one 8" in my package tray but my question is, which brand and model?
I see very few that are tagged as an ib speaker. What do I look for in the specs?
Or should I go with the Tang Band "race track" ovals with a dedicted amp?
These are definitely ib speakers.
I was leaning towards a 12" Dayton HF in a 1.2 cu ft sealed box.
You must have an opinion on either of these setups that you can share with me.
Thanks


----------



## paralegal (Jan 27, 2013)

cajunner,
The f3 figure is on the Morel website.
I thought that an F3 of 31hz would preclude any furhter extension of bass response no matter what enclosure it was placed in. I believe another member posted that the F3 was the minimum hertz for that speaker and it was down 3 db even at that.
So an F3 of 20Hz would be far better because I could tune the cabinet etc down to 20Hz -3db rather than the speaker that quotes an F3 of 31Hz.
Am I missing something?


----------



## SPLEclipse (Aug 17, 2012)

I can't find the f3 you're talking about on Morels's site, but that's beyond the point. The f3 point isn't a brickwall below which no sound will be produced. It's the point where the speaker will begin to play less and less loudly the lower in frequency you go. If you have two sealed boxes, one with an f3 of 30hz and one with an f3 of 50hz, the 30hz one will play lower, louder. The thing is, both of those systems might use the same woofer, but have different boxes. That's why the f3 is dependent on the enclosure as well as the woofer. Another thing to consider is that the box with an f3 of 30hz might be louder at, say, 25hz, but the box with an f3 of 50hz might be louder at 55hz, so you have to tailor the output to match both your preferred tastes and the environment the system will be playing in. In a home, the choice is easy, you would pick the one with a lower f3, right? In a car, there's a natural gain at lower frequencies, so if you take that into account (this is "transfer function"), the system with an f3 of 50hz might actually sound flatter than the one with an f3 of 30hz, AND get louder over a vast majority of the frequencies you will be listening to! If you choose a system with an f3 of 20hz, it will absolutely rock out at lower frequencies (probably to the point where you would have to use an eq to tame it), but will be quieter over a vast majority of the audible spectrum.


----------



## 14642 (May 19, 2008)

F3 applies to any frequency response measurement that includes a high- or low-pass filter, whether that filter is inherent in the design of the product (like a speaker) or in an amplifier or signal processor. F3 is the point at which the output is 3dB lower than in the passband (the range of frequencies over which the product is intended to be used or the range of frequencies where the response is flat). For electronics, the F3 is also called the "half power point" because half the power is equal to a 3dB reduction in output. 

For electronics, F3 is often intended to indicate the end of flat response. An amplifier that has a frequency response from 20Hz-20kHz will have half power points at 20Hz and 20kHz. 

The same scale isoften applies to speakers in stating their frequency response, but it's less useful with speakers, especially subwoofers. We ALWAYS use subs below their F3, unless, as one poster suggested, we can find a sub in a box that has a really low F3 for use at home. In little boxes (especially sealed ones) in cars, the measured F3 of the sub and box combination (without considering transfer function) is often 60 or 70Hz. 

Looking under every rock in the yard for a subwoofer that has an F3 to match your car's transfer function is a ridiculous waste of time. If you can afford an RTA to make these measurements and have the extra time to do it and to search and search for just the right woofer, use your time more productively and mow a couple of lawns and buy yourself an EQ with a single parametric band. Then, choose a woofer you like that will play down to 70Hz in a sealed box that will fit nicely in your trunk and EQ the sound you like. If you like more bass than that and can spare the extra space for a vented box, then do that.

Tuning a vented box isn't a matter of matching the box's tuning frequency with your car, it's a matter of matching the box's tuning frequency with the paraneters of your woofer and the box size. Choose the tuning frequency of the box for optimum performance irrespective of the car and then EQ the shape of the bass so that you like it.


----------



## goodstuff (Jan 9, 2008)

sub'd.


----------



## minbari (Mar 3, 2011)

paralegal said:


> cajunner,
> The f3 figure is on the Morel website.
> I thought that an F3 of 31hz would preclude any furhter extension of bass response no matter what enclosure it was placed in. I believe another member posted that the F3 was the minimum hertz for that speaker and it was down 3 db even at that.
> So an F3 of 20Hz would be far better because I could tune the cabinet etc down to 20Hz -3db rather than the speaker that quotes an F3 of 31Hz.
> Am I missing something?


I will add one more thing to canjaners response. model out a sealed box with a 20hz F3, 30hz F3, then 60hz F3. the only way to lower the F3 of a sealed box is to make it bigger. in the case of a 20hz F3 ALOT bigger.

the side effects of a bigger sealed enclosure are not always good either.


----------



## Bluenote (Aug 29, 2008)

hpilot2004 said:


> Car Audio Cabin Gain Transfer Function


^ Great note! Thx


----------



## Oliver (Jun 25, 2007)

Andy Wehmeyer said:


> *Looking under every rock in the yard for a subwoofer that has an F3 to match your car's transfer function is a ridiculous waste of time.* If you can afford an RTA to make these measurements and have the extra time to do it and to search and search for just the right woofer,* use your time more productively and mow a couple of lawns and buy yourself an EQ* with a single parametric band.





goodstuff said:


> sub'd.


*Thank You, Andy !*

:snacks:


----------

