Myth or fact: ... Do subwoofers play below their FS

[vehementSPL 10+ year member]

Obviously they will play below their FS. But i guess I am more so asking it like this.... i have heard from many people that subs typically won't play very well below their fs (mainly just bad low end response). So if you get a sub with an fs of 45hz don't count on it playing lows even if tuned low. (Now i am not saying in any way shape or form this is correct) The reason i even question it is cause fs is taken free air correct? Can anybody shed some light on this for me please. Any help would be appreciated . Tonight i graphed a sub with fairly high fs. But it actually showing good low end response in my box. Not sure what to believe. I typically believe WinISD over things I hear online... give insight

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[Immacomputer 10+ year member]

It loses efficiency below the point of resonance that the system has. When you put a speaker in an enclosure, you increase the point of resonance because you're adding a mechanical resistance via air spring in the enclosure. This is, of course, if we're not talking about an IB installation where the system resonance will be at the free-air resonance of the speaker.

Here is a graph from two 8s with an Fs probably in the 40hz range in an enclosure tuned to 25hz.

Those were measurements and not theoretical. Below the probable system resonance, I get a loss of efficiency and the output rolls off. That doesn't mean there isn't a response down low but that it is slightly attenuated. This isn't true in all cases and it really depends on the setup. I should also specify that the measurements were taken about 3 feet from the enclosure in my room. Not a perfect anechoic environment but it's better than in a car. My room also naturally cuts everything around 70-75hz for some reason (maybe my mic?).

 

[ngsm13 5,000+ posts]

Yes, to your specific question...

nG

 

[vehementSPL 10+ year member]

It loses efficiency below the point of resonance that the system has. When you put a speaker in an enclosure, you increase the point of resonance because you're adding a mechanical resistance via air spring in the enclosure. This is, of course, if we're not talking about an IB installation where the system resonance will be at the free-air resonance of the speaker.
Here is a graph from two 8s with an Fs probably in the 40hz range in an enclosure tuned to 25hz.

Those were measurements and not theoretical. Below the probable system resonance, I get a loss of efficiency and the output rolls off. That doesn't mean there isn't a response down low but that it is slightly attenuated. This isn't true in all cases and it really depends on the setup. I should also specify that the measurements were taken about 3 feet from the enclosure in my room. Not a perfect anechoic environment but it's better than in a car. My room also naturally cuts everything around 70-75hz for some reason (maybe my mic?).

So depending on sub/enclosure it still may reproduce lower freq fine. So i should trust WINISD pro. I know there are other factors and if everything else was the same I would guess less efficient below those freq compared to a sub that had a lower fs if other things were the same (sorry extremely tired) prob will read this tomorrow and be like idiot. anyways. just give a response on if that sounds about correct. thanks

 

[Immacomputer 10+ year member]

So depending on sub/enclosure it still may reproduce lower freq fine. So i should trust WINISD pro. I know there are other factors and if everything else was the same I would guess less efficient below those freq compared to a sub that had a lower fs if other things were the same (sorry extremely tired) prob will read this tomorrow and be like idiot. anyways. just give a response on if that sounds about correct. thanks

Yes, it is very much enclosure dependent. Trust WinISD? Well you can but it's not going to be very accurate after a vehicle's transfer function or after parameter shifts. In a room with a predictable transfer function, sure but not so much a car.

The same thing applies to sealed enclosures. Model a few subs in sealed enclosures. Then check out in WinISD where is says Fsc under the Box tab. This is the new resonant frequency of the sub/enclosure system. Many subs model with Fsc in the 45-55hz range which would leave a theoretical loss of low frequencies if subs couldn't play below their Fs (Fsc or Fc is the same thing as the Fs of the driver).

 

[vehementSPL 10+ year member]

Yeah I guess I phrased that incorrectly. I know the vehicle is major part in the final sound. I typically do walls so what comes out of the box is what you feel (maybe not meter). It just was more should I trust it in a comparative relation to some of the lower fs subs I have used cause I got this sub to graph half way ok