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Understanding Fs and Qts


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I hope I don't catch too much heat for this, but I was wondering if someone could explain the Resonance Frequency(Fs) of a speaker, as well as the Total Q-Factor(Qts). :noob: < Me

I always just assumed that the Fs was the lowest tuning frequency, and Qts I honestly have no idea. But I'd really like to know, and yes I know Google is free, but I'd like to get an explanation from someone on here that will be easily understood. Thanks for your help and patients! :drinks:


Kickin' Cruiser

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Stage 3
Dash, Door Panels,
4th Order wall 4 - 15's
on a DC 5.0K 2 DC 5.0K's


Solo X 15 (v.2) Sub Build

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Fs is simply the resonance of the parts in a free air environment, in all honesty it is pretty much a worthless parameter.

It does not indicate the frequency response of a sub (lower Fs is not going to automatically "hit lower" contrary to popular belief) and Higher Fs does not mean that a sub will not "hit the low notes". A speaker simply does what you tell it to do in the environment that you put it in. Putting a High Fs subwoofer in a box tuned to 33Hz does not mean it is not going to play the frequency range from the Fs to tuning..and totally miss it. That is not how it works and is totally urban myth. It will do whatever you tell it to do, including destroy itself. Simply because it does not know any better.

Qts is the "overall Q" of the speaker, and is something that dictates motor force and what kind of enclosure a speaker should be in.

Low Qts woofers (say .35 and down) should be in a ported alignment only.

Mid Qts woofers (say .36 to . 45 or so) works well in a sealed or ported alignment.

High Qts woofers (say .46 and higher arbitrarily) works best in a sealed alignment. Again, these figures are arbitrary and what I feel/think is 'optimal' for a musical scenario and daily driving. This is not a law, it is simply what I think and is my opinion.

However, you can stick a high qts woofer in a ported enclosure..and get one heck of a peak out of it...and make it work great for SPL :).

Qts is indicative of motor force as well. (Bl)

Lower Qts will allow more motor force, Higher QTS will not allow it.

Hope this helps.

Edited by NDMstang65

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Okay, thanks for the reply. But I think I may be a little more confused now. I think I'm gonna do some more reading, thanks again for taking the time to try to explain it to me! I did catch most of it! :drinks:


Kickin' Cruiser

Seller Feedback


Stage 3
Dash, Door Panels,
4th Order wall 4 - 15's
on a DC 5.0K 2 DC 5.0K's


Solo X 15 (v.2) Sub Build

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I couldnt have said it any better.

Although fs is still a valid spec for me....kind of.

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2008 California state record holder 157.2 Bassrace2009 California state record holder 157.0 BassraceRollin 50's 158.7db2009 King of Cali Bassrace2009 USACi score 160.5 @ 42hz
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good info here... :good:

Pioneer Premier P880PRS ll Front Stage: US Acoustics 4060 - Random speakers currently ll Sub Stage: Crescendo BC3500D - 15" Xcon sealed @ 3.28 cubes ll Electrical: - Kinetik HC1800(front) NEW***DieHard P-2(rear)

beaker- I know this sounds like a lot of anime bullshit, but it is true.

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nice explanation stang, you said it perfectly!! i do have some opinions about FS of a sub though, in colloquial words so OP can understand it, i think about FS as this, a sub with a low FS makes it easier to play strong on the lows and viceversa, maybe i´m wrong but this what my testings have showed me in the past, once again, i only used the term EASIER, of course a high FS sub can play strong on lows , as stang said, "It will do whatever you tell it to do"!!!

About QTS, well, my boy explained you this thing perfectly, specially the SPL part, i´ve gotten GREAT results with cheap ass subs that has a high QTS value using tiny boxes :)

I´m the SPL Gains topic creator!! wanna get louder?? check this: SPL Gains. Panamenian 2009 & 2010 & 2014 Bass Race 149.9 Champion!

2 15" subs and a 2K wired at 1 ohm, http://www.stevemeadedesigns.com/board/topic/167788-fecupe2001-2-15s-on-a-2k-video-on-page-3/

8 Massive 15" subs and small power, http://www.stevemeadedesigns.com/board/topic/179296-fecupe2001s-8-15s-4th-order-bandpass-wall/

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