# Tuning a vented enclosure below Driver Fs....



## chad

Get some audio talk going here......

I have generally chosen drivers for vented enclosures that have an FS below the intended tuning freq. It's just a thing I have done since building a couple that sounded "not right" when tuning below driver Fs. A snappy search shows that in this config that below the driver FS distortion can and will go up.

Now why? it's a RESONANT feq, it should be usable above and below it just as normal right? but for some reason i prefer the sound of tuning above Fs.

Reason i asked is because of that HiVi 10" I was looking at, it has an Fs int he mid 30's but the "proper" vented enclosure calls for a 20 cycle tuning, and it looks GREAT on paper, be we all know that paper theory can lie.

What's your take?

Chad


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## Oliver

Read this Chad

http://hyperphysics.phy-astr.gsu.edu/hbase/sound/reson.html


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## chad

a$$hole said:


> Read this Chad
> 
> http://hyperphysics.phy-astr.gsu.edu/hbase/sound/reson.html


Yeah, i know what resonance is, the question remains, what happens BELOW driver resonance but ABOVE enclosure resonance. 

Say we build a bridge, we want the stuff on the bridge to NOT excite the bridge's resonant frequency. But the bridge is fully functional above and below the resonant freq... right?


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## Oliver

Galloping gertie  
http://en.wikipedia.org/wiki/Resonant_frequency

It is easy to make something vibrate at a given frequency [ sometimes the tradeoffs are not worth it, though ].

Some guys add weight to a cone to make it vibrate "slower", mass loading is the intended example.

It is easier to make it vibrate "faster" than it's natural frequency, but harder to make it vibrate "slower" than it usually does.


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## Oliver

Tis damping you are referring to  

http://en.wikipedia.org/wiki/Damping


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## Oliver

When something is unnatural it can be harder to do .

Try shortening your strides and limiting your arm swing when walking [ damp your self ], it can be done, just takes a lot of energy to move in an unnatural rhythym.


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## kappa546

i've usually tuned right around fs or slightly below. never ported anything with fs in the 30's.


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## chad

a$$hole said:


> When something is unnatural it can be harder to do .
> 
> Try shortening your strides and limiting your arm swing when walking [ damp your self ], it can be done, just takes a lot of energy to move in an unnatural rhythym.


Right but that's how it works, it plays fine ABOVE the freq, is it not equally hard to move BELOW that freq?


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## Oliver

There is a naturalness to moving faster[when you walk ] a hustle in your bustle { it is tiring but it feels good to just let everything swing "faster"}.

When you have to apply the brakes on your motion or swing "slower" than you normally do [ stop yourself each time, not the same thing as walking slower ]

Go fast, but physically reign in your step and arm swing [ ie move unnaturally ]


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## Oliver

You are in reality, starting the sub to move and before it gets to where it is going, [You STOP it, then START it, then STOP it, etc.., ]

Herky Jerky , baby  !

quote from damping link ]

damping is the quieting or abrupt silencing of the strings after they have been sounded, by pressing with the edge of the palm, or other parts of the hand such as the fingers on one or more strings near the bridge of the instrument. 

end quote ]


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## Tommythecat

chad said:


> It's just a thing I have done since building a couple that sounded "not right" when tuning below driver Fs.
> 
> ...but for some reason i prefer the sound of tuning below Fs.


What are you smoking? I can't really understand what you're trying to say and this is just one example.

Almost as bad as a$$hole...

So, I will suppose you meant: "my 'snappy' search says that playing below resonance increases distortion - why does it sound good when I tune below resonance though?"

So I'd ask you, what "snappy search" did you perform and what are you referring to?


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## chad

I should have said above, phone was ringing. I prefer tuning above the resonant freq of the driver.

Just one typo man. I edited it. You can calm down now.

Snappy serach, down and dirty google, did not go past the first page.


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## Abmolech

Driver resonance is a factor of suspension (compliance) and cone mass.
The question should be, does the enclosure change one of these factors, and if so, what resonant frequency have we now obtained.

We know the motor has a limited capacity to overcome this phenomenon, however on either side of this range, it should present no more challenge to the performance (Xmax aside).

I like playing my subs up to Fs, rather than down to, just another way of skinning a cat?


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## chad

Abmolech said:


> Driver resonance is a factor of suspension (compliance) and cone mass.
> The question should be, does the enclosure change one of these factors, and if so, what resonant frequency have we now obtained.
> 
> We know the motor has a limited capacity to overcome this phenomenon, however on either side of this range, it should present no more challenge to the performance (Xmax aside).
> 
> I like playing my subs up to Fs, rather than down to, just another way of skinning a cat?


I remember you saying that AND in certain designs you play UP to the sealed resonance (electronically assisted), it certainly helps paint the picture.



Autiophile said:


> It makes sense to me that it should be useful above and below its resonant frequency.
> 
> Here is a quote of the only good discussion I have read on diyaudio on this topic.



That's one of the ones I read too


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## Abmolech

If we are evaluating reflex enclosures, we expect to use a highly compliant driver suspension system. This becomes "pear shaped", is for the desire of manufactures to provide a wide frequency response. The usual method is doping the cone (adding mass), with the "benefit" of a lower FS and smaller required enclosure volume. However we know the result loss in sensitivity can be substantial.
There are number of such manufactures that recommend the use of a larger cone (higher mass) over their smaller drivers because they have better sensitivity. (Always a clue to the doping artifact)

Point
We need to know the cone mass to truly evaluate the performance around Fs.


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## Robert_J

A lot of commercial subs tune below the driver's Fs. For example, the SVS 16-46 PC Plus used the TC Sounds db500 driver for years. The driver's Fs is 24hz. The SVS native tune is 16 hz and with port plugs can be changed to 12 or 8 hz. Also, the DIY home theater crowd has been doing this for a while as well. Steve Callas even coined the term LLT (Large, Low Tuned). Huge enclosures tuned to the single digits sometimes.

You can go back as far as the Avatar Audio (before they changed their name to Adire) Shiva. Dan's suggested enclosures included one tuned to 16hz.

-Robert


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## CBRworm

This could be totally false - but I had heard that if you tune the box below fs the driver would bottom very easily around the tuning frequency instead of well below it.


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## thylantyr

Tests
http://www.hometheatershack.com/for...s-lms-5400-18-2x18-page-ranking-200l-new.html

The tuning is less than driver Fs. It has PR's in the design
also that throw a wrench in the engine, but the distortion
does rise with SPL at low frequency. Nothing that worries
me, I'd rather tune low up to a certain point. But this is for
HT, not car audio.


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## demon2091tb

CBRworm said:


> This could be totally false - but I had heard that if you tune the box below fs the driver would bottom very easily around the tuning frequency instead of well below it.


Essentially unloading below driver FS & box tuning.


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## Eastcoast

I'm not an enclosure expert, but I don't think unloading has anything to do with the driver's fs. As you get closer to the ports tuned frequency the driver's excursion lessens, if you drop below that tuned freq, excursion will drastically increase, depending on volume, possibly to mechanical failure. The loading is a product of the enclosure, not the fs. Someone in the know correct me if I'm wrong.

As for tuning below FS, I've never had a problem doing it, though I've never preferred a vented enclosure anyway. But I always tuned low, like 23-25, as the dangerous unloading doesn't occur start for 2-3 hz below, so tuning that low, you were generally safe, and also avoided that obnoxious 40hz hump. 

Though its not as common nowadays with the power VC's are designed to take...back in the day, you could blow subs by tuning to 33 and wailing on the bass tracks, as excursion drops, so did cooling of the sub...creating that magic cooked smell.


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## chad

Eastcoast said:


> I'm not an enclosure expert, but I don't think unloading has anything to do with the driver's fs. As you get closer to the ports tuned frequency the driver's excursion lessens, if you drop below that tuned freq, excursion will drastically increase, depending on volume, possibly to mechanical failure. The loading is a product of the enclosure, not the fs. Someone in the know correct me if I'm wrong.
> 
> As for tuning below FS, I've never had a problem doing it, though I've never preferred a vented enclosure anyway. But I always tuned low, like 23-25, as the dangerous unloading doesn't occur start for 2-3 hz below, so tuning that low, you were generally safe, and also avoided that obnoxious 40hz hump.
> 
> Though its not as common nowadays with the power VC's are designed to take...back in the day, you could blow subs by tuning to 33 and wailing on the bass tracks, as excursion drops, so did cooling of the sub...creating that magic cooked smell.



Totally agreed, right on track, I prefer proper vented, no bumps at all going for the lowest flat extension regardless of box size.


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## Oliver

If you were doing bench presses [exerise term = lying on your back while pushing weight ]unloading would be no weights.

if a subwoofer is pushing weight and then it unloads, the voice coil over excurts.

If you were pressing a weight and i removed the weight [ in the middle of your movement [ that would be unloading ]you would push the bar up really, really fast


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## 60ndown

how hard would it be to build a quick ported box tuned to 18hz?

i could whip 1 up in an hour / mystery.


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## 60ndown

a$$hole said:


> If you were doing bench presses [exerise term = lying on your back while pushing weight ]unloading would be no weights.
> 
> if a subwoofer is pushing weight and then it unloads, the voice coil over excurts.
> 
> If you were pressing a weight and i removed the weight [ in the middle of your movement [ that would be unloading ]you would push the bar up really, really fast


but it wouldnt unload until the frequency dropped below the tuning of teh box

(i think):blush:


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## Xander

If you tune below the FS then it will be playing a significant amount of material at the resonant frequency. That would produce audible distortion...no?


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## Oliver

http://en.wikipedia.org/wiki/Loudspeaker_enclosure

A loudspeaker enclosure is a cabinet designed to transmit sound to the listener via mounted loudspeaker drive units. The major role of the enclosure is to prevent the out of phase sound waves from the rear of the speaker from combining with the in-phase sound waves from the front of the speaker. Such mixing results in interference patterns and cancellation, causing the efficiency of the speaker to be reduced, particularly in the low frequencies where the wavelengths are large enough that interference will affect the entire listening area.

The plot thickens


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## Oliver

Ported -vs- sealed ?

http://diyaudiocorner.tripod.com/dilemma.htm


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## backwoods

I'm with you on this one. I really noticed it with low distortion PA drivers.


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## ErinH

Sure you already know this, but don't forget about harmonics. There are multiple resonant frequencies. The question is, how are these avoided as well?...


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## Luke352

From what I understand there is nothing wrong with playing above or below a drivers Fs, the problems exist when you try to play through it's Fs, I'm not sure of the term to use but the suspension basically loses it's control over the cone, so you are then relying on the loading or resistance that the enclosure provides on the cone. This may not be an issue too much with music or movies since the tones provided are constantly changeing and the microsecond of playing that freq the driver does probably won't be long enough to do any damage, but if you were to play that single note at the drivers Fs for any reasonably amount of time, and the drivers loss of control could end up in damage. 
The reason you see rises in distortion around Fs is probably because the cone is starting to self excite and move outside of the siganl being sent to it, or something like that.

Thats my take, but I'm probably wrong lol... hopefully we'll see some definite answers in this thread, as it's always something I've always wondered about aswell.


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## dejo

I have done it several times with great results. but always on a driver that was overmotored or heavily motored.


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## Oliver

I always find myself chasing butterflies in golden waves of grain  

Someday i'll catch one !
quote}
The low end was designed to reproduce full pipe organ fundamentals, including 32 foot pedal stops, and performs remarkably well in-room.
end quote}

This is from a horn enclosure thread.
http://personal.linkline.com/phorn/audio/hs_subwoofers.html


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