subwoofer unloading

[playmysong 2]

I know that subwoofers unload under tuning frequencies in vented boxes and i was wondering what makes this happen. What's the physics behind it? I tried searching for the answer and everywhere it says the same thing, subs unload under the tuning frequency. I already know that, i want to know why it happens.

Thanks in advance for anyone that knows.

[aznboi3644 2]

The enclosure does not control the cone of the driver below tuning...the only thing controlling the subwoofer is the suspension

[djphilly 11]

I know that subwoofers unload under tuning frequencies in vented boxes and i was wondering what makes this happen. What's the physics behind it? I tried searching for the answer and everywhere it says the same thing, subs unload under the tuning frequency. I already know that, i want to know why it happens.

Thanks in advance for anyone that knows.

This is my Theory of what happens.

subs have a Fs which is the the free air resonant frequency of the speaker. if a sub has a Fs of 35 hz and you tune your box to 35 hz. the speaker will resonant at that frequency. tuning a box to far below that like 28hz, 25hz or something like that, I might not have the right kind of pressure to keep the speaker from hitting it's Xmech, which is the max mechanical excursion of the speaker. that's why you might hear stories of people say there 1500watt sub blew out on 900watts of power. because the speaker bottomed out and reach it's Xmech because of tuning below Fs.

[playmysong 2]

Well hey hey hey look what i found. Its some pretty good information on resonance if anyone else would like to take a look.

Here's the website: http://www.hometheaterhifi.com/volume_5_2/cmilleressayporting.html

Edited October 14, 2009 by takniteasy

[///M5 2,833]

Step 1 is to define whether you know what unloading means. After that perhaps determining why it happens would make sense.

[playmysong 2]

Well i don't know anything but ill try to define unloading to what i think it means.

Unloading is what subs do in vented enclosures when run below the tuning frequency of the port. When unloading, the sub has no back pressure from the enclosure and excurts uncontrollably acting as if it were in free air.

Am i somewhat right?

Edited October 14, 2009 by takniteasy

[djphilly 11]

Well i don't know anything but ill try to define unloading to what i think it means.

Unloading is what subs do in vented enclosures when run below the tuning frequency of the port. When unloading, the sub has no back pressure from the enclosure and excurts uncontrollably acting as if it were in free air.

Am i somewhat right?

the same as bottoming out. reaching its Xmech

[Impious 1,476]

the same as bottoming out. reaching its Xmech

That could be the result of a subwoofer in a ported enclosure unloading. But that's not "unloading".

OP: You definition of "unloading" seems to be reasonably accurate. I probably wouldn't call it's movement below tuning "uncontrollable", as the driver is still "controlled" by the motor and it's own suspension (and input signal). It's mechanical power handling is reduced, which makes it easier to overdrive the speaker. You could run a driver well under the tuning of an enclosure without issue as long as you kept power levels to low enough levels not overexcurt the driver.

Do you understand how a ported enclosure operates?

[djphilly 11]

the same as bottoming out. reaching its Xmech

That could be the result of a subwoofer in a ported enclosure unloading. But that's not "unloading".

OP: You definition of "unloading" seems to be reasonably accurate. I probably wouldn't call it's movement below tuning "uncontrollable", as the driver is still "controlled" by the motor and it's own suspension (and input signal). It's mechanical power handling is reduced, which makes it easier to overdrive the speaker. You could run a driver well under the tuning of an enclosure without issue as long as you kept power levels to low enough levels not overexcurt the driver.

Do you understand how a ported enclosure operates?

yes i understand how ported boxes work,

I also understand that keeping the power level low enough would not hurt the speaker while playing below tuning. the point i was making was doing that at higher levels.

[Impious 1,476]

the same as bottoming out. reaching its Xmech

That could be the result of a subwoofer in a ported enclosure unloading. But that's not "unloading".

OP: You definition of "unloading" seems to be reasonably accurate. I probably wouldn't call it's movement below tuning "uncontrollable", as the driver is still "controlled" by the motor and it's own suspension (and input signal). It's mechanical power handling is reduced, which makes it easier to overdrive the speaker. You could run a driver well under the tuning of an enclosure without issue as long as you kept power levels to low enough levels not overexcurt the driver.

Do you understand how a ported enclosure operates?

yes i understand how ported boxes work,

I also understand that keeping the power level low enough would not hurt the speaker while playing below tuning. the point i was making was doing that at higher levels.

The rest of the post wasn't directed at you. Hence the reason it started with "OP:". It was directed towards the original poster.

[djphilly 11]

the same as bottoming out. reaching its Xmech

That could be the result of a subwoofer in a ported enclosure unloading. But that's not "unloading".

OP: You definition of "unloading" seems to be reasonably accurate. I probably wouldn't call it's movement below tuning "uncontrollable", as the driver is still "controlled" by the motor and it's own suspension (and input signal). It's mechanical power handling is reduced, which makes it easier to overdrive the speaker. You could run a driver well under the tuning of an enclosure without issue as long as you kept power levels to low enough levels not overexcurt the driver.

Do you understand how a ported enclosure operates?

yes i understand how ported boxes work,

I also understand that keeping the power level low enough would not hurt the speaker while playing below tuning. the point i was making was doing that at higher levels.

The rest of the post wasn't directed at you. Hence the reason it started with "OP:". It was directed towards the original poster.

Ok, sorry, my bad. I guess i wasn't paying attention

[playmysong 2]

It acts like another woofer according to dd so 2 subs in a sealed enclosure would be the same as 1 sub in a vented enclosure but that's not the case.

It works by the Helmholtz resonance, right? The air mass in the port resonates with the air in the box itself and the frequency it does it at is your Fb.

More mass in the port makes it slower to get going but has more inertia so it takes slower to get back so more mass or longer port is lower tuning and vice versa.

More air in the box makes the springiness of the box weaker so the spring or air doesn't fight back as hard or as fast so tuning is lower and vice versa.

I don't know if im making any sense. It's hard for me to explain stuff which is why im on this forum, to learn not to explain.

[Impious 1,476]

It sounds like you pretty much have the general jist of things.

From my understanding, the issue is that as you decrease further below tuning the port and driver begin increasingly moving out of phase...meaning as the driver is moving "in" the air in the port is moving "out" and vise versa. Thus it's no longer providing any active damping to the driver. The port is now basically acting like a hole in the box as far as the driver is concerned. This out-of-phase condition also explains the sharp roll-off in the frequency response of a ported enclosure as you decrease frequency below tuning.

Does that help?

[dbjunior 0]

if you are having this problem at or over tuning you are not unloading you are simply bottoming out the driver not good this means you have to much power going to the driver or to large a box. decrease one or both and the problem will go away. if you want to run the same amp you have now build a smaller box

[playmysong 2]

It sounds like you pretty much have the general jist of things.

From my understanding, the issue is that as you decrease further below tuning the port and driver begin increasingly moving out of phase...meaning as the driver is moving "in" the air in the port is moving "out" and vise versa. Thus it's no longer providing any active damping to the driver. The port is now basically acting like a hole in the box as far as the driver is concerned. This out-of-phase condition also explains the sharp roll-off in the frequency response of a ported enclosure as you decrease frequency below tuning.

Does that help?

Yes sir it does. It puts an easy picture to remember in my head. Thanks

[playmysong 2]

if you are having this problem at or over tuning you are not unloading you are simply bottoming out the driver not good this means you have to much power going to the driver or to large a box. decrease one or both and the problem will go away. if you want to run the same amp you have now build a smaller box

My box is only slightly bigger ( by .3 cu. ft.) than what my driver likes and it only needs a 1000 watts to power it. I don't have many problems with the saz 1000d. I have my ssf set somewhere around tuning which is 32 hz so im not in any risk of damaging it unless i turn up the gain but i can hear when its screaming from pain.

I only asked my question about unloading because i was interested in WHY subs unload under tuning frequencies, i know that it happens, its just a rule of vented enclosures.

[dbjunior 0]

if you are having this problem at or over tuning you are not unloading you are simply bottoming out the driver not good this means you have to much power going to the driver or to large a box. decrease one or both and the problem will go away. if you want to run the same amp you have now build a smaller box

My box is only slightly bigger ( by .3 cu. ft.) than what my driver likes and it only needs a 1000 watts to power it. I don't have many problems with the saz 1000d. I have my ssf set somewhere around tuning which is 32 hz so im not in any risk of damaging it unless i turn up the gain but i can hear when its screaming from pain.

I only asked my question about unloading because i was interested in WHY subs unload under tuning frequencies, i know that it happens, its just a rule of vented enclosures.

even the .3 cu might reduce the mechanical power handling to 800w and im sure the amp you have is capable of pushing 1200+ so its possible you are over powering it that or there may be a problem with the spiders being worn.

[playmysong 2]

Mike recommends 800 for ported boxes when they're regular sized so i probably reduced the mechanical power handling even more. I keep bass boost at 0 and have the gain at around 3/4. The pioneer deh p440 comes with a modest 2 volt preout. Although the box is a little big I have no problems with it. I watch the volume and so far i haven't heard any bottoming out or distortion since i fixed the settings on the headunit. Im going to build a new box to the right size so that should make my sub a little happier.

And by the way we're off topic. I got what i wanted to know and my sub has no problem in its current box.

Edited October 18, 2009 by takniteasy

[ChristianMcKay 1]

I know that subwoofers unload under tuning frequencies in vented boxes and i was wondering what makes this happen. What's the physics behind it? I tried searching for the answer and everywhere it says the same thing, subs unload under the tuning frequency. I already know that, i want to know why it happens.

Thanks in advance for anyone that knows.

This is my Theory of what happens.

subs have a Fs which is the the free air resonant frequency of the speaker. if a sub has a Fs of 35 hz and you tune your box to 35 hz. the speaker will resonant at that frequency. tuning a box to far below that like 28hz, 25hz or something like that, I might not have the right kind of pressure to keep the speaker from hitting it's Xmech, which is the max mechanical excursion of the speaker. that's why you might hear stories of people say there 1500watt sub blew out on 900watts of power. because the speaker bottomed out and reach it's Xmech because of tuning below Fs.

I like this explanation of this. I never knew that, which is another reason why my subs are all in sealed boxes.

[KU40 173]

I know that subwoofers unload under tuning frequencies in vented boxes and i was wondering what makes this happen. What's the physics behind it? I tried searching for the answer and everywhere it says the same thing, subs unload under the tuning frequency. I already know that, i want to know why it happens.

Thanks in advance for anyone that knows.

This is my Theory of what happens.

subs have a Fs which is the the free air resonant frequency of the speaker. if a sub has a Fs of 35 hz and you tune your box to 35 hz. the speaker will resonant at that frequency. tuning a box to far below that like 28hz, 25hz or something like that, I might not have the right kind of pressure to keep the speaker from hitting it's Xmech, which is the max mechanical excursion of the speaker. that's why you might hear stories of people say there 1500watt sub blew out on 900watts of power. because the speaker bottomed out and reach it's Xmech because of tuning below Fs.

The only issue is......why is tuning below Fs bad? In other words, why are frequencies below Fs bad but frequencies above it aren't? Your car has a resonating frequency, does it fall apart if you play a note below it?

If tuning below Fs is bad, what are we to do with the Sundown Nightshade, which has an Fs of 43 hz? The 12" FI BTL also has an Fs of 39 hz. Also, how about all of those home theater subwoofer enclosures that are tuned way low, like 12-15 hz? Those are definitely below 99% of all subs' Fs.

My point is that there isn't anything wrong with tuning below Fs. The problem with running into mechanical limits can occur at any frequency with the right amount of power. Even above tuning frequency and Fs.

[Boomboxx 1]

Just to point it out, (I think at least one of the above posters have it wrong) lowering the tuning frequency of the enclosure, will actually decrease the subwoofers excursion @ the same SPL levels compared to the sealed enclosure, making it take more power at those low frequencies (impedance will rise also, right).

Since we need 4 times the excursion to maintain the same SPL level at 20hz compared to 40hz (in a sealed/IB install), I don't see how tuning low isn't a good thing, it will not make the driver "unload" any easier, but it'll lower the treshold for where it will do so. Which is good, right?

If one is seeking a flat response from a capable driver, and stay linear while hitting high SPL numbers across the frequency band (sealed boxes don't do lows any good compared to a 20hz tuned ported enclosure), tuning low is a must in my opinion. Yes, it is unpractical with low tuning due to the long port(s) and big enclosure, and with some speakers it's just not a good idea due to their lack of low frequency capabilities in general, but: I've heard low tuned enclosures (with subwoofers that thrives in such boxes, like the SoundSplinter RL-p or JL W7's), allthough they're recommended for sealed also, honestly, the SQ is not lacking in any way, when putting them in a very low tuned enclosure. It just kills the sealed when it comes to output.

In my opinion, a 10W7 in a 4 cu.ft. @ 22hz enclosure, sounds BETTER (the low notes sound more effortless) and has the capability of getting much louder, than a 10W7 in 1.5 cu.ft. sealed. 3dB more @ 40hz, and 6dB more @ 30hz, 10dB more @ 20hz - that says a lot. With enough power, I do think you'll bottom the sub out in the sealed enclosure @ 25hz, while the one in the ported enclosure laughs at the same SPL.

Not saying ported is always better, it obviously depends on the sub, but if the sub thrives in a ported box, and I have the room for a <30hz tuned enclosure, that's what I'll build.

[mjmarovi 8]

The only issue is......why is tuning below Fs bad? In other words, why are frequencies below Fs bad but frequencies above it aren't? Your car has a resonating frequency, does it fall apart if you play a note below it?

If tuning below Fs is bad, what are we to do with the Sundown Nightshade, which has an Fs of 43 hz? The 12" FI BTL also has an Fs of 39 hz. Also, how about all of those home theater subwoofer enclosures that are tuned way low, like 12-15 hz? Those are definitely below 99% of all subs' Fs.

My point is that there isn't anything wrong with tuning below Fs. The problem with running into mechanical limits can occur at any frequency with the right amount of power. Even above tuning frequency and Fs.

absolutely! I had explained this in another thread where someone was asking for woofers with lower Fs because they wanted to hit the lows. I had to explain to them how they were looking for the wrong thing.

As for the "unloading" yeh quite simply as far as my understanding is, the woofer not even necessarily 1-3 frequencies below tuning, but at a certain point below tuning will be to far out of phase with the enclosure, and when the woofer attempts to retract after pushing out to play the note, air is then trying to get back into the box as opposed to vice versa as it should, which causes the woofer to actually unload. Now I believe someone already touched it on, but unloading doesn't always happen below tuning, only when pushing the driver hard enough below tuning.

For example, I know some guys in SQ setups that have higher tunes and play woofers almost exclusively below tuning, but at low levels which results in very accurate suttle bass which is ideal for true SQ comps.

[djphilly 11]

I know that subwoofers unload under tuning frequencies in vented boxes and i was wondering what makes this happen. What's the physics behind it? I tried searching for the answer and everywhere it says the same thing, subs unload under the tuning frequency. I already know that, i want to know why it happens.

Thanks in advance for anyone that knows.

This is my Theory of what happens.

subs have a Fs which is the the free air resonant frequency of the speaker. if a sub has a Fs of 35 hz and you tune your box to 35 hz. the speaker will resonant at that frequency. tuning a box to far below that like 28hz, 25hz or something like that, I might not have the right kind of pressure to keep the speaker from hitting it's Xmech, which is the max mechanical excursion of the speaker. that's why you might hear stories of people say there 1500watt sub blew out on 900watts of power. because the speaker bottomed out and reach it's Xmech because of tuning below Fs.

The only issue is......why is tuning below Fs bad? In other words, why are frequencies below Fs bad but frequencies above it aren't? Your car has a resonating frequency, does it fall apart if you play a note below it?

If tuning below Fs is bad, what are we to do with the Sundown Nightshade, which has an Fs of 43 hz? The 12" FI BTL also has an Fs of 39 hz. Also, how about all of those home theater subwoofer enclosures that are tuned way low, like 12-15 hz? Those are definitely below 99% of all subs' Fs.

My point is that there isn't anything wrong with tuning below Fs. The problem with running into mechanical limits can occur at any frequency with the right amount of power. Even above tuning frequency and Fs.

your totally right with the right power, you can go all day tuning below Fs. I have some MTX subs i'm using for home theatre and play as low as 15 hz or lower tones sometimes in movies. with no problem. but you have to get the power right.

[tequila 2]

so what about subwoofers that like high tuning?

like the hdc3, its preferred tuning freq is 36hz+ (orsomething around).

you shouldnt play these loud below tuning? there must be more involved right?

[KU40 173]

No, there's nothing more involved. You shouldn't put full power to any sub under tuning, regardless of sub or recommended tuning frequency.