FS of a Sub, and box Tuning>>>

[528hz 10+ year member]

So let's say my sub is at an FS of 33.9 hz. I understand that the FS is the point in which the sub "collectively performs."

What would happen if you tuned below the FS? What is the lowest frequency a sub with and FS of 33.9 produce?

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[Rashaddd 5,000+ posts]

I'm pretty sure FS is just the point at which its response starts to degrade, it will still play any frequency you throw at it, but fs is an indication of how well it will handle it

with an fs of 30, you'll play 20hz better than an fs of 40 will, but the box will affect this as well obviously

as far as tuning, I've never heard that you can't tune below fs, but i don't know exactly what wouldn't be good about doin so, if anything even is

 

[528hz 10+ year member]

I'm pretty sure FS is just the point at which its response starts to degrade, it will still play any frequency you throw at it, but fs is an indication of how well it will handle it
with an fs of 30, you'll play 20hz better than an fs of 40 will, but the box will affect this as well obviously

Hence the point at which the sub will "start" to respond with clarity?

I was just looking at the Fi BL and it's FS for the 12 is 38.7 hz. People claim they will get really low.......my whole point in bringing this question up, is that I was told that a sub with a high FS (I guess 33.9 is high?) will not get low.

 

[Rashaddd 5,000+ posts]

Idk who told you that, personally, i wouldn't think twice about doin what you're suggesting

I don't want to misinform you though so here's a bump for someone with more experience to chime in

 

[528hz 10+ year member]

Bump for some of these smart fvckers you hear about around here to chime in. Here's a thread that is very interesting as well:

http://www.diymobileaudio.com/forum/showthread.php?t=32911

 

[helotaxi 5,000+ posts]

The box is hugely important. Also you can't just look at Fs when trying to determine how low a sub will play. The whole collection of the sub's parameters will determine its frequency response.

The Fs of a driver is simply where the impedance curve of the driver peaks in a free-air environment. As soon as you put the driver in an enclosure its impedance curve changes. Where the resonant freq started will partially determine where it ends up but there is so much more to it.

Also look at who is saying that a sub is great on the lows and figure out what they consider "low." A lot of people think that there is low bass in rap music. That isn't low. The 83 hz resonance of that BTL is lower than the bass in 99% of the stuff out there in contemporary, mainstream music.

The ability to get low requires nothing more than the ability to move air. The lower you want to go at a given output level, the more air you have to move. Therefore given a large amount of cone area, a large amount of excursion or both, raw power can overcome natural resonance.

BTW the reason that the BTL has such a high Fs is that the suspension is REALLY stiff to aid in controlling the massive coil and cone assembly.

 

[bk12321 10+ year member]

As said above, there are tons and tons of factors that influence a speaker's frequency response.

As a standalone parameter, there isn't a whole lot you can tell from just knowing the Fs of a sub, but you can plug the Fs into a few formulas and get a rough approximation of how it might sound or what enclosure it might perform well in (notice MIGHT), and whether it's a more HT or mobile audio oriented speaker. Besides that, there are sooo many factors that come into play that you can't really tell a whole lot by just looking at the Fs.

I'm pretty sure FS is just the point at which its response starts to degrade, it will still play any frequency you throw at it, but fs is an indication of how well it will handle it
with an fs of 30, you'll play 20hz better than an fs of 40 will, but the box will affect this as well obviously

as far as tuning, I've never heard that you can't tune below fs, but i don't know exactly what wouldn't be good about doin so, if anything even is

Fs is the lowest frequency a subwoofer will play in free-air, i'm pretty sure. In an enclosure, it is the frequency of maximum impedance, and with a lot of speakers it is also where output begins to "roll-off".

Correct me if i'm wrong.

 

[dman4486 5,000+ posts]

THESE ARE NOT MY WORDS

Fs - Driver free air resonance, in Hz. This is the point at which driver impedance is maximum. "This parameter is the free-air resonant frequency of a speaker. Simply stated, it is the point at which the weight of the moving parts of the speaker becomes balanced with the force of the speaker suspension when in motion. If you've ever seen a piece of string start humming uncontrollably in the wind, you have seen the effect of reaching a resonant frequency. It is important to know this information so that you can prevent your enclosure from 'ringing'. With a loudspeaker, the mass of the moving parts, and the stiffness of the suspension (surround and spider) are the key elements that affect the resonant frequency. As a general rule of thumb, a lower Fs indicates a woofer that would be better for low-frequency reproduction than a woofer with a higher Fs. This is not always the case though, because other parameters affect the ultimate performance as well."

 

[Rashaddd 5,000+ posts]

Fs is the lowest frequency a subwoofer will play in free-air, i'm pretty sure. In an enclosure, it is the frequency of maximum impedance, and with a lot of speakers it is also where output begins to "roll-off".
Correct me if i'm wrong.

There's no such thing as 'the lowest a subwoofer will PLAY', as it will vibrate at whatever frequency input it has, free air or not. Fs is just an indicator of how it will handle different frequencies (how much/accurately it vibrates), but I'm pretty sure it has much more bearing in free air, and the box its in can change its response completely.

To the OP, I think in terms of this its a matter of trying, go for what you want, and if it really doesn't work out, adjust from there. Or, if its not worth the hassle, just go with tried and tested methods that we all know work well 99% of the time.

 

[528hz 10+ year member]

Ah, there are some of you....

Yeah, I forgot to take into thought that FS is a free-air calculation. I also maybe put my question in the wrong context to begin with......my concern is what would happen if you ran a 20-30hz tone through the sub.....would it produce sound? Would it distort? The actual tuning of the box only really plays it's biggest role depending on what frequecy is being pushed through the sub an a any given time, right? Granted, the lower a box is tuned, the greater the ability for it produce lower notes depending on sub. In this case, the sub is an FS of 33.9 hz.

But let's say we have a 30hz tuned box and 35hz tuned box. Both the same slot port design, same power, same speaker, same everything except tuning. Will there be any impact/difference from each of the two producing a 45hz bass frequency? Will one be louder than the other for frequencies (10-15 hz ABOVE) tuning?

My philisophical thinking has always been that the lower you tune, the tighter the output throughout everything above the tuning frequency. I do understand that many other factors come into play with the box design, but I'm talking about everything being equal, just box tuning.

Do I make sense, or am wrong in my thinking?

 

[Rashaddd 5,000+ posts]

I think you're overthinking it, lower tuning means extended response in the lower range, while it also means you start to lose response earlier. If for example your output started to drop a little around 50 hz when you were tuned at 30hz, then by tuning to 20 hz you might start to drop a little at 40-45 hz. I don't think the fs has much to do with this, other than: the lower the fs, the better extended lower output would be.

Sorry if I'm not helping, just doin what I can

 

[dman4486 5,000+ posts]

I think you're overthinking it, lower tuning means extended response in the lower range, while it also means you start to lose response earlier. If for example your output started to drop a little around 50 hz when you were tuned at 30hz, then by tuning to 20 hz you might start to drop a little at 40-45 hz. I don't think the fs has much to do with this, other than: the lower the fs, the better extended lower output would be.
Sorry if I'm not helping, just doin what I can

I do not agree...I have very good response all the way up into the 80hz range where my lpf is.

edit: in a bandpass yes....

 

[helotaxi 5,000+ posts]

But let's say we have a 30hz tuned box and 35hz tuned box. Both the same slot port design, same power, same speaker, same everything except tuning. Will there be any impact/difference from each of the two producing a 45hz bass frequency? Will one be louder than the other for frequencies (10-15 hz ABOVE) tuning?

Impossible to answer without knowing all the parameters of both the sub and box. Will one be louder? Probably. Which one? Impossible to say without knowing more.

 

[Rashaddd 5,000+ posts]

I do not agree...I have very good response all the way up into the 80hz range where my lpf is.

edit: in a bandpass yes....

I didn't say response completely drops off or even very noticeably, but it will affect your numbers. Why do you think people would ever tune high if this wasn't the case? Why not be able to hit the lows hard while hitting the higher bass at full capacity? Because you can't have both. Again, its not to say that all of a sudden you'll be like wtf where's my bass, but you will lose dB's (or fractions of them)

 

[dman4486 5,000+ posts]

I didn't say response completely drops off or even very noticeably, but it will affect your numbers. Why do you think people would ever tune high if this wasn't the case? Why not be able to hit the lows hard while hitting the higher bass at full capacity? Because you can't have both. Again, its not to say that all of a sudden you'll be like wtf where's my bass, but you will lose dB's (or fractions of them)

this is a plot of my enclosure, and there is no audible response change over the range. So where is the drop in upper frequencies?

they tune high because it induces a peak above the rest of the range such as this curve (different driver, but the curves work the same for all drivers I have ever plotted)

 

[528hz 10+ year member]

Hey dman, you want to design me a box?

 

[Rashaddd 5,000+ posts]

this is a plot of my enclosure, and there is no audible response change over the range. So where is the drop in upper frequencies?

they tune high because it induces a peak above the rest of the range such as this curve (different driver, but the curves work the same for all drivers I have ever plotted)

Huh, well I guess you're probably right, but for some reason every box output calc i've ever used has shown a slight decrease in upper response and a more linear bottom end from tuning lower, using the same driver specs.

 

[dman4486 5,000+ posts]

Hey dman, you want to design me a box?

let me know what you would like from the enclosure, and pm me some theile for whatever driver

 

[Frank1009]

this is a plot of my enclosure, and there is no audible response change over the range. So where is the drop in upper frequencies?

they tune high because it induces a peak above the rest of the range such as this curve (different driver, but the curves work the same for all drivers I have ever plotted)

 

[Frank1009]

this is a plot of my enclosure, and there is no audible response change over the range. So where is the drop in upper frequencies?

they tune high because it induces a peak above the rest of the range such as this curve (different driver, but the curves work the same for all drivers I have ever plotted)

You're literally tuned just under your FS spec as the pic shows, you will absolutely not have the same output all the way up to 80hz with a 24hz tune, that's not how ported boxes work. You probably have a significant roll off around 50-60hz, it's simple math and common sense you won't ever get same output on that wide of a range.