Axiom Home Page Forums General Discussion Technical Questions How do some subs go below 20Hz?

I've been researching subs lately and noted that some manufactures are able to get into 18, 16 or lower Hz for their subs, yet have the same size drivers as those who can only get to 25Hz or so. Is it mostly a factor of the size of the enclosure, or is it the digital processor and amplification? I'm sure its a combination of the above and more. Any technical help here?

Second question. Is there really a difference between 16Hz and 22Hz that one can discern? Or is it similar to high-end that once you reach a certain level, there really isn’t that much value perceived, as we simply can not hear such frequencies.

You may not be able to hear them, but you can feel them. They are indeed noticable.

TK, the somewhat over-simplified explanation is that to produce very low frequencies at an audible level a sub has to move a lot of air. The obvious way to do this is with a very big driver; a somewhat less obvious way is to use a smaller driver but to have it move farther out and in on each cycle, so that it moves as much or more air than the bigger driver. Designing drivers with long excursions is more difficult and they're more expensive. Also, a more powerful amp is needed to drive them with relatively low distortion at those frequencies(10% or so, compared to the 1% or so inaudible at higher frequencies).

As to whether we can actually hear all this, maybe not, but as Craig pointed out, if it's strong enough we can feel it. Human ears are relatively insensitive things, especially at very low and very high frequencies. The Fletcher-Munson(1930s investigators)curves show that enormously higher levels are required at low frequencies to be audible. Although Fletcher and Munson stopped at 30Hz(apparently they weren't real bass freaks)later investigators extended their work down to about 16Hz, although the required level to be heard at that frequency is so high that only recently have commercially available subs had much chance of supplying it. However, in our lust for ever-lower bass we should be aware of what Alan pointed out to us here .

EEEEEEEEEWWWWWWWW! I'd like to be the first to tell you that extremely loud and low bass isn't necessary to induce that particular reaction in a soldier. Just having several hundred people shooting real bullets at you can do the same thing.

Hi TK,

You're correct on the combination of DSP processing, long-excursion drivers and very large amplifiers (500 -600 watts in the new Axiom EP500/EP600 subwoofers). But you still have to make the enclosure larger (the EP600) if you want to keep the lowest frequencies linear to 16 Hz or lower. There are some sub manufacturers who claim subwoofer response to 17 Hz or lower. They may say, "our sub goes down to 17 Hz"; what they don't tell you is that the driver may move at 17 Hz, but its output may be -15 dB at that frequency, so there is no useful output.

Thanks to JohnK for his post on Fletcher-Munson. As to "hearing" those low frequencies, we feel/sense them more than hear them. For instance, if you look at the harmonic content of certain instruments--a pipe organ, for example--the 2nd harmonic of a 16-Hz pedal tone at 32 Hz has a greater intensity than the 16-Hz fundamental. We hear the 2nd harmonic at 32 Hz easily, but when you add a subwoofer capable of reproducing the fundamental at 16 Hz, it does add a sense of weight and power, the sort of thing that moves the pew under your butt in a big church when you hear a pipe organ played live.

Regards,

Alan-
What is the average lower-limit of actually hearing a note instead of feeling it? Is it different for men..i.e., can we justify EP500s and 600s to our spouses with a line like "I'm sorry honey; I can't help nature. When I listen to our system, I hear a huge hole between 18Hz and 24Hz"?

Mark,

In theory, it's 20 Hz, but I believe the line is blurred and varies somewhat from one person to the next. I have a friend (he does the Q&A column for Sound&Vision magazine) who absolutely claims to hear frequencies below 20 Hz. I believe him because he was a colleague and member of the listening panel for years of speaker tests at the NRC in Ottawa, and he's not into BS). The sub in my car has real output below 20 Hz but all I hear is the plastic door panels and other components rattling when the test frequencies go below 20 Hz. My friend actually "hears" them, he says. . .

I'm currently experimenting with the Axiom EP500 sub in my living room, and it's scary at times what I "hear" from it. With pipe organ and orchestral bass drum, there is a powerful reverberance that I really miss when I switch to the old sub (a decent Mirage with two drivers). The old Mirage simply has no output below 27 Hz.

Once you hear/feel genuine output in the sub-20-Hz range, you don't want to do without it. . . You'll also hear weird low-frequency garbage on some live network HD sports broadcasts that have Dolby Digital 5.1. The audio engineers don't realize it's there because the monitors they use simply don't reproduce it. I sometimes reduce the sub level or turn it off when that stuff comes through.

Regards,

Mark,

And yes, I think the low-frequency limit is different for men and women, although I have no scientific data to support that statement. It seems that many women don't seem to like the low-frequency stuff that lots of men like. I don't know what it is.

A reckless generalization, I know, but over the years (and I've lived a long time--ha, ha) I've actually met women who baldly state: "I don't like bass. . ." Perhaps more research is needed, and why don't you do some, Mark?

Regards,

In reply to:

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You'll also hear weird low-frequency garbage on some live network HD sports broadcasts that have Dolby Digital 5.1.

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I was watching "Boston Legal" last night (tivo'd) and during a simple scene in the office the sub started going quite wonky. Not sure how low the effect was, but it was certainly odd.

In reply to:

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Perhaps more research is needed, and why don't you do some, Mark?

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Cool! Send a 500 my way and I'll long-term test it more thoroughly than any test report I've ever read!

Send me a 600 and Mark and I will compare notes.

See? I showed restraint.

Alan and Johnk: Thank you very much for your replys. I love the science behind most everything—and I’m discovering more and more of it each day in the world of audio. It’s like being in High school AP Chemistry all over again. Loving it!!

Now I want to take this discussion to a more personal application level. As has been seen on my other posts lately, I have a family room that is open to a kitchen. They are roughly 16X24X9 (kitchen adding another 16X20X9).

I’m seriously looking at the following three subs:
Axiom EP350 12 inch driver, 200 Watts, Freq Resp +/- 3db (Hz) 25 ($650)
HSU STF-3, 12 inch driver, 300 Watts, Bass extension +/- 2 dB: 25Hz ($600)
SVS PB12-ISD 12 inch driver, 320 Watts, 22 Hz ($599)

Price is all comparable; frequency is all comparable, unless 3 Hz is a big difference in the low end. I honestly wouldn’t know.

Since sitting in a room and listening to each one individually is not really an option, how can the numbers game be worked to make a logical comparison? Now some would say that asking Alan that would only give me a biased opinion, since his check comes from Axiom; however, I somewhat disagree. I’ve seen your posts, Alan, over the past month or so and haven’t felt that you directly push people toward Axiom. You state the facts of science and encourage personal preference take presidence in listening—whenever possible. So, Alan, any assistance with how a person should look at subs to make a decision would be well received.

Thanks.

I think you are putting him in quite the position. Don't be surprised if he doesn't respond.

I don't agree. I'm not asking which one to choose, rather what should someone should look for when selecting a sub.

Look at it like a new car...the more you spend the more extras/options come with it, like adjustments on the back...hook-ups/gain/phase/crossover etc.etc.

Mark, I know that you were looking for a specific answer to the question of how low that we can actually hear, but as Alan implied, unfortunately you ain't gonna get it. You should look at these equal loudness graphs which don't appear to be Fletcher-Munson(the term is often applied to them generically)but rather from the work that Robinson and Dadson did in the 1950s. Note for example that to get the same subjective loudness as say 80 phons(80dB at 1,000Hz, a comfortably loud level)would require about 112dB at 20Hz. Even more recent investigations indicate that the previous results at very low frequencies may be optimistic. For example, the paper by Suzuki and Takashima summarizes much of this. Note in fig.1 on p. 919 that the latest results indicate even higher levels are needed at very low frequencies for audibility. I suppose that the bottom line may be that your walls will collapse before you'd actually hear below 20Hz.