[Bumpy]

I have put a frequency sweep generator on my subwoofer to listen to its output.

The subs are specified at about 30 Hz minimum output. If I sweep downwards I can clearly hear 40 Hz and still some output at 30Hz below which it goes quiet.

All this is to be expected, but as I further turn the frequencies down the driver continues to respond (vibrate) even down to 10Hz where it pulses nicely.

My question "If the driver is still moving, where did the sound go?"

[JohnR]

First, the ear is less and less sensitive as frequency lowers.



Second, even tho the cone is moving it produces less acoustic output as frequency lowers.

With these factors combined there's a point below which you won't hear anything from the sub (except distortion products and motor/aerodynamic noise).

[Bumpy]

Thanks John

So just to complete the picture for me.

There are subs that get down to 10-15 Hz, so firstly, what have they done specifically to overcome these innate issues?   

And secondly if I use a microphone to measure the output, is it tuned to have the same shortcomings as the human ear and if not how is it ever possible to use measurement to optimise a speaker?

Thanks - Learning all the time

[JohnR]

There are subs that get down to 10-15 Hz, so firstly, what have they done specifically to overcome these innate issues?   

As you halve the frequency, the excursion of a given driver will increase by four times (*). So to get the same output level at a lower frequency, you need more excursion, larger drivers, or more of them (or all of the above). And more power to drive it.

(*) For a sealed box. A ported box increases output down to a point but below that rolls off faster. Also, there are a lot of factors like room gain and modes that confound apples-to-apples comparisons.

And secondly if I use a microphone to measure the output, is it tuned to have the same shortcomings as the human ear and if not how is it ever possible to use measurement to optimise a speaker?

No, a measurement microphone measures flat. Well, it has a calibration file that is used to correct the actual microphone response so that REW (or other software) gives you a result as though the mic were actually flat (down to the limit of the calibration).

The second part of your question is interesting, but I think it boils down to having a repeatable reference. You could EQ a speaker to make it sound more like you think it should sound at varying levels (the old "loudness" control) and there's the Harman room curve that has statistically determined that a bass boost sounds most natural to people on average (I don't know if I've ever seen any mention of the actual level though). But if the measurement itself tried to do that you would never know where you were at.

[Bumpy]

The second part of your question is interesting, but I think it boils down to having a repeatable reference. You could EQ a speaker to make it sound more like you think it should sound at varying levels (the old "loudness" control) and there's the Harman room curve that has statistically determined that a bass boost sounds most natural to people on average (I don't know if I've ever seen any mention of the actual level though). But if the measurement itself tried to do that you would never know where you were at.

#

Thanks again John

This bears out what I find, that measuring with REW is a good starting point but can always be improved by listening and further adjustment.

I flinch when I see measured traces in room where they have spend many hours and much cost getting it dead flat.

[Letitroll98]

Just to expand on JohnR's post, to get to that 10-20hz range at meaningful levels will require very large drivers, 15" minimum, very large boxes, and a few thousand watts of amplification.  And to what purpose.  For home theater there are sounds this low, I understand the opening tracks of Edge of Tomorrow has a 10hz digitally generated signal.  You can't hear this low, but you can feel it, and it will rattle dishes and pictures.  For music anything below 25hz is hyperbole unless you love pipe organ music and most music lovers are more interested in bass quality than quantity, or at least rank quality first.  My ideal system would be 10 refrigerator sized boxes with 18" drivers ran with 25,000 watts of amplification, but that's not happening until I win that Power Ball.  So it's really what your goals are, music, home theater, or a mixed use. 

[WGH]

For music anything below 25hz is hyperbole unless you love pipe organ music and most music lovers are more interested in bass quality than quantity, or at least rank quality first.

One feature of a real good sub that is rarely mentioned is the sense of space it brings to well recorded music. My speakers have a solid response to 34 Hz but I don't get the ambient room sound until I turn on the sub with the high-pass crossover set to 30 Hz. I don't have a sub for the rare organ and canon effects, I have a sub to transport me into the performance space.

To hear (or not hear) the room ambience is to listen to the Cowboy Junkies album "The Trinity Sessions". The first track "Mining for Gold" has Margo Timmins singing a cappella. The song has bass in the low 20's but without a sub most people will miss the huge ambience of the Church of the Holy Trinity in Toronto with its natural reverb.

The Sound of Silence by Paul McGowan of PS Audio
https://www.psaudio.com/pauls-posts/sound-silence/

Kevin Deal of Upscale Audio has an explanation of space
https://www.youtube.com/watch?v=pSHkpy2280Q

[Letitroll98]

I'd agree with all of that.   Bass done well it's a thing of beauty that helps create a greater degree of realism.  That being said, in small rooms low bass can be more problematic than helpful.  You really need a couple large floor to ceiling traps to do any good.  So in my den sized spare bedroom I'm experimenting with no sub with speakers cutting off before 50hz.  I'm really enjoying the intimacy, but I always go back to bass.

[JohnR]

I flinch when I see measured traces in room where they have spend many hours and much cost getting it dead flat.

Um... I'm afraid I'm not following. It's just a starting point.

[FullRangeMan]

All this is to be expected, but as I further turn the frequencies down the driver continues to respond (vibrate) even down to 10Hz where it pulses nicely.

My question "If the driver is still moving, where did the sound go?"

What are your age?
Seems your ears are working fine til down 40Hz or so.
Legend say a just born baby can hear til 20Hz.