40hz ratings/speaker response

Hi, as a neophyte to the technical end of this wonderful addiction, I am curious. If a speaker's frequency response capability is rated to say 40hz or above, what happens to that sound that was recorder that falls below that range? Say for instance the lower octaves on an accoustic piano, or a cello, electric bass etc? And again, what happens to a speaker, with the same rating, if the volume is "pushed" to hear and feel music that has a lower range?
Many would make a good argument that these speaker ratings are largely meaningless. But assuming they are at all meaningful, a rating will include a low end frequency and a tolerance. So it won't just say "40hz", but instead, it will say "40hz +/- 3dB". If you look at a frequency response curve of a speaker, it shows the output in decibels for the range of frequencies at a given signal strength. Ideally, a curve will be completely flat from 0 to infinity, meaning that all frequencies are equally represented. the 40hz +/- 3dB means that the curve is flat within 3db of the vertical center of the curve. In almost all cases, the curve deviates from flat at the low end and you can pretty much assume that that's where the greatest fall off is. So, for a given signal strength, you should hear the music pretty much as recorded, but as you approach the lower frequencies, frequencies of 40hz and less will be 3db or more "quieter" than they should be.

If you at all rely on this spec at all, remember that it is completely meaningless without the tolerance number. For instance, there are many speakers around for under $100 a pair that have a frequency response from 20hz to 30Khz!! (20hz at -18dB, that is!)
Hi, Joe: The frequency range quoted for a speaker is normally stated to some frequency at which point the response is down by 3db. Hence, the speaker has usuable output below that point, but it will be increasingly weak. If you looked at a graph of the frequency response, it would show how rapidly the frequency response drops -- if it is a severe drop, then the speaker's low frequency (or high frequency) response will very rapidly become almost too weak to hear.

If you have a speaker that is reasonably flat (+ or - 3db at 40 Hz), you will still get decent output for the lower frequencies of the acoustic bass and piano. The lowest note on an acoustic/string bass is about 32 Hz, and a Steinway Grand piano has a low note of about 28-29 Hz. Your speakers will probably reproduce the lowest notes of the bass and piano, but their volume will be diminished relative to the upper bass and lower midrange.

If the loss of full output at the lowest frequencies concerns you -- for example, if you want to reproduce the pedal tones of an organ -- then you will need to add a good subwoofer to your system. Subwoofers actually do more than just reproduce the bottom 1-2 octaves -- due to the crossover, they also relieve the woofer or mid-range of reproducing the deepest frequencies, which reduces their IM distortion levels. This often results in much cleaner, more transparent, and more dynamic sound reproduction by the main speaker.

There have quite a few threads lately on subwoofers, their pros and cons, and the better brands/models, so you may want to do some digging in the Audiogon archives for these threads.
A lower limit of 40 Hz is not that bad. The trouble is we only speak of fundamental tones and not the harmonics. A lot of instruments have second or third harmonic energy below 40 Hz. If it is a ported alignment, roll off below the 40 Hz FS will be 12 db per octave while a sealed alignment will be at 6 db. Trying to equalize the bass below the FS is tricky since it requires a great amount of power on the part of the amp and the ability to handle it on the part of the woofer. Only try moderate boost of about 4db. That will require over double the amp output than the non boost.
A speaker rated down to 40hz will play below the frequency, just rolled off. The amount of rolloff depends on the type of low freq. system. Bass reflex rolls off at twice rate of acoustic suspension below the low frequency resononce. But with room gain, a speaker rated down to 40hz ("faithfully" i.e. +/-2db etc.) would still reproduce down through the 30's and even some of the 20's depending on the room. Small rooms can offer 9db of gain at 20hz. You turn it up, and like with any driver, distortion will go up.
OK, time to get specific. Heres the crux of my problem.
the speaker in question is a B&W Nautilus804. the exact specs are: freq.range= -6db at 30hz and 30khz. and
-3db at 38hz and 22khz. the freq. response rating is:
45hz-20khz +/-2db. Now, to get more specific: last week I dug out an older Bonnie Raitt tape, for one song, just her voice, piano, and an occassional string/cello, lite guitar etc. Feeling somewhat nostalgic I turned it up pretty high(love that piano). Whereupon a woofer started to "rattle". I immediatley turned it down, inspected the speaker, seeing no damage, tried a different cd and the same results with some higher volume. My electronics are Classe CA300 amp, and Classe cp50 pre-amp. My BW dealer has agreed to replace the speaker no problem. But the speaker didn't tear, or pop, or freeze, it "rattled". Could that be something wrong with the electronics and not the speaker?
Wow it's so cool when everyone offers such great insight/advise. Keep in mind that the bass lift most rooms provide is not linear. It's probably your speaker that has failed you. If it's only one channel, reverse speakers to confirm the (1) speaker is the culprit. If not work your way back by reversing the the cable left to right and right to left, one by one from end to source. Eventually you will find the culprit. My guess it will be sooner rather than later. If it effects both channels you will need to find replacement gear and substitute end to source (try changing sources at the preamp first ) or have each piece bench checked. Good luck.
Speakers of various designs and tuning will respond differently when fed a signal below their natural resonance ( point of max output ). Well designed acoustic suspension ( sealed box ), infinite baffle ( designs that make use of huge volumes of air and a baffle to isolate the rear wave from the front wave ) and TL ( transmission line ) designs will respond relatively linearly but at reduced output.

Vented designs, such as ports, passive radiators, slot loaded, etc... will produce much lower output below that point with greater potential for distortion and even driver damage.

If you doubt this, try playing a highy warped record with a large speaker that is vented at high volume. The woofer will want to pop out of its' basket. This is one of the reasons why the "high pass filter" or "rumble filter" was invented.

While you would have similar results with a sealed box, the driver would not be nearly as "out of control". This is due to the damping that the "air spring" in the box supplies. Vented designs are "unloaded" or have no "damping" below the point of box tuning. The driver is therefore subject to greater excursion, which could result in damage. This damage could be immediate or accumulative over time.

With that in mind, most people with educated ears are able to discern the differences between vented and sealed designs simply by listening. One obviously sounds more natural and linear than the other. Sean
Thanks for the info folks. You have to be careful about jumping to conclusions based on that spec.

I would much rather have a speaker rated 40hz or so that handled that really well than most speakers sold today rated below that number. Northcreek is a good example.

Sean, I believe I understand you correctly when I assume you favor non-vented designs. I am not clear on some of the basic design concepts of transmission line and infinite baffle (are these vented or sealed box types) while I believe the acoustic suspension aspect of the sealed cabinet seems relatively straight forward. Forgive me, but could you elaborate?

Also, Clueless, do you mean that the NorthCreek ratings are conservative, and that their designs subjectively go lower than their rated output?

Thanks for the information gentlemen.
As Scott Campbell (and others) said in the first post your number was the frequency where your sound is down three decibals(-3db). This does not say much about the quality of any speaker despite the fact that it is used that way sometime. Lots of speakers with really low specs sound horrible. One the other hand, you look at a North Creek, I think their Rhythm has a rolloff/F3/-3db point (what ever you want to call it) that is not that deep by today's standards. Maybe 44hz. And it has a tuning frequency (Fb) of 39hz or so. Sean pointed out that vented designs progressively lose damping below that point.

However, the design of the speaker does a great job reproducing sound in the high 30hz and they sound very musical. The www.northcreekmusic.com site is worth a look. You can listen to this speaker in the right room without feeling you have lost the last octave of music. At least I can.

I remain,
Well, looks like I'm back in business. I had my electronics tested. The tech said there were no spikes, square waves etc. In fact, he said it had one of the "flatest" frequency response deviations he'd ever seen. so I can trust my Classe gear. BW has sent me a brand new replacement speaker so I'm back to music nirvana.
Thanks to those of you who shared your knowledge.
My problem is with the speakers rated at 25HZ, but i cannot hear much under 40Hz?! Except, when i turn volume up, up high, then i can hear window panes rattling? I own Wilson Watt/Puppy 3/2 and Conrad Johnson CAV 50 integrated with very low gain. Is my amp too weak? Thanks! Ursula
It's probably not your amp. Are you familiar with the Fletcher-Munson curve? Psycho acoustics play a big role. Our ears are more sensitive to certain frequencies than others. See www.allchurchsound.com/ACS/edart/fmelc.html or do a google search under "Fletcher-Munson." There are lots of sites that discuss this.

I remain,

Maybe there isn't anything below 40HZ in the music to which you are listening!

Salut, Bob P.
Bob P. brings up a very valid point about lack of very low frequency content in most recordings. The other point that i would stress would be that your room or speaker placement may be limiting actual low frequency output. Most averaged sized rooms are "reasonably solid" down to the mid 30's or so in my experience. Sean
According to Stereophile test CD, it all stops at 40, at normal listening level.! Thanks.
Once again, I agree with Sean. While I don't think your amp is really the problem, more power wouldn't hurt.
Perhaps the size of the listening room has something to do with the limitation of sound frequency. Assume that sound travels at 1223km/hour at sea level. Then if my conversion table is correct, sound travels at 1,114 feet/second. The sound frequency that we are debating here is 40 cycles per second. The wavelength of sound at 40 cycles per second is about 28 feet. That means that it would take a 28 foot room to fully develop sound at 40 cycles per second. I think that this is size limitation of most listening rooms. Larger rooms will develop lower frequencies of sound. If you want to fully develop sound at 35 cycles per second, you will need a 32 foot room. If you want to fully develop sound at 30 cycles per second, you will need a 37 foot room. If you want to fully develop 25 cycles per second, you will need a 45 foot room, etc., etc. In conclusion, why are we torturing ourselves trying to get speakers of lower frequencies, when we should be considering getting LARGER ROOMS. Let's go for broke, if want to develop a one cycle per second sound wave, you will need a 1114 foot room!!!
Redwoodgarden, One only needs to have one dimension (could be cross diagnal, from opposite corners in a room) the size of ONE-HALF a wavelength, so divide all your calulations by 2 i.e. 40 hertz fits easily in a 14 ft room.

Bob P.
Thanks Bob(inpepinnovations) for the clarification. This old dog just learned a new trick.
Red, Keep in mind I am "technically challenged", but if your formula and theory is correct, what I really need to do is simply rearrange my listening room, a hassle, but doeable. As the one who started this thread, I have to ask Red, are you kidding? or is that really the way to maximize a deeper sound stage that will enhance bass?
I have recently read an article that stated that even if a certain low frequency fundamental tone is not reproduced by the speaker, if 2 or more higher harmonics of that fundamental are heard, the brain will psychoacoustically hear the fundamental tone. I have not actually verified this by testing, but it seems interesting. It may actually be the reason that some accurate mini-monitors seem to produce more bass than they should theoretically be capable of. It is common that mini speaker owners seem to be quite satisfied with the bass response of their speakers that are rated only down to 100Hz or even higher. Naturally, room loading and other factors may play into this. Anyone else heard about this phenomenon?
www.melhuish.org/audio/article3.htm if you haven't already seen it.
Clueless, thanks, that was where I read it. I just couldn't remember where it was. Also, I noticed he was pretty rough on quarter wave pipes in that article. But, if you really tear any design apart that far, then nothing will really hold up too well to that kind of scrutiny. I'm still thinking that I can get a "happy medium" of decent bass-boost, and limited notch-effects from comb-filtering, from the Voigt Pipes. He didn't even mention the "baffle-step" effect of the Voigt Pipes, where the narrow baffle reinforces the higher freq's and you get a drop-off where the baffle is no longer wide enough to reinforce the lower ones. I've got a couple of tricks up my sleeve to handle this, without resorting to a compensation circuit that destroys efficiency.
Joeb, the point that I was trying to make was that sound waves can't be heard if they don't have room to develop at least one full cycle. For simplicity sake, one cycle of sound meanders like the letter S. According to the laws of physics, one full cycle of sound at 40 cycles per second needs 28 feet to develop. That is why I thought 40 cps was the lower limit for a normal listening room. One would have to be rich to have a room large enough to hear deeper tones. However, Bob at inpepinnovations said that only one half of the space required for a full cycle is required in order to hear a low frequency. One half of a full cycle would look like the letter C instead of the letter S. Assuming that the revised theory is correct, 40 cycles per second (hertz) could be heard in a 14 foot room, not a 28 foot room as I first proposed. Also, sound at 25 hertz would only require a 23 foot room, not a 45 foot room. In short, my theory was shot down.

Allow me to propose an anology to explain the limitation of the 40 hertz rated speaker. Imagine a soprano singer trying to sing bass. The vocal cords are too short to develop the lower frequencies, and thus distortion sets in. As you proposed, let's imagine that the soprano singer tries to sing bass even louder on the second try. The distortion would be louder and more pronounced, but the lower octave would never be reached. If the soprano singer continues these attempts, her vocal cords would be destroyed, just as a speaker would be destroyed in the same attempt.
Hi Twl:

Was just going through this site as I saw your post back here. You might enjoy??? ("God-awful" voigt pipe from the club of Norway", he says) it if you haven't already been there. I'm not sure what to make of it. I'm messing around with a few of the same Qs you are it seems.


Clueless, pipes are already made with a S0 of zero. Drivers are on the way, but not here yet. Everything is ready to just plug in the drivers. Apparently, Brines is really hot on the Mathcad program, but not too interested in using the right drivers for the Voigt pipes. He used everything but the Lowther, and these were designed to use the Lowther. So he takes these pipes, and plugs a much smaller driver into them and complains about the results. Now, I don't doubt for a minute that I will have issues with dips at the resonant points. But, whether the problems will be as bad as he says remains to be seen. If they are, then I'll try a few things, and may even shorten the pipe to open up the S0(narrow tip)area. But, I have read alot of testimonials that this pipe design sounds good. So we will have to just try it out and see.
Being a latecomer, I have the benefit of the earlier postings.
Sdcampbell, Gboren are right to the point with reading the specs and the importance of interpreting +/- 2 or 3dB. I understand that genuine spec ratings are recorded with some sort of standard reference equipment, sensor mounted 1m on axis infront of the speaker driven with some standard frequency sweep signals, in an anechoic chamber. So there is some standard measurement in the speaker manufacturing industry.
Red I love the climax of your soprano story! The room size resonance effect in our real listening area does distort the overall sound that we perceive, and resonance must be controlled with every practical means possible.
My own experience is that there is vast difference in bass reproduction between my M.Logan Aerius (45Hz +/-3dB) and my later acquired Dynaudio A72 (28 +/-3dB) despite what some of the above posts opined. With the exact same gear I had been using, the Dyns came out with so much ooomph(body)and deep sound staging, a big step closer to like "being there" feeling compared to the Aerius. All along I thought Aerius'45Hz is low enough for reproducing whatever in the CD; I was wrong!
I believe that when our ear response starts to roll off at some point, the guts (feeling) takes over down to even lower frequencies.
In a DARPA project during the 70s and 80s, a guy by the name of Patrick Flanagan was researching alternative communications techniques. He discovered and later patented a device called the "Flanagan Neurophone". The D.O.D. kept him from marketing it for 20 years. It is a device worn around the neck, kind of like a fat necklace. It receives sound and transduces it into the bone structure of the clavicles. It can make totally deaf people hear. Apparently, the bone structure can be vibrated in such a way as to simulate the activity of the ear, and is interpreted by the brain as sound. This leads me to agree with others that the "feel" of music in the body is important to the experience as well as hearing through the ears. I once tried headphones for primary listening, and found that the lack of "feel" was unsatisfactory for me. I gave up the headphones.
Twl, as the father of a deaf child I can't help wonder why the DOD would need to conspire to prevent deaf people from hearing? National Security? At any rate, a lot of deafness is neurological damage, not bone structure so your theory just doesn't fly. "Feelings" are often a 'Perceptual", and totally subjective state, however they are a "physical" reality, I am tempted to discuss the ancient "mind/body" dichotomy theories, but they probably don't need rehashing here.. There are theories that (more appropriately?) speak to the influences of "feelings" or better put, how we develop a capacity for a range of emotions. Suffice it to say that, one's life experiences have a lot to do with the range and depth of our emotions; hence different musical tastes. I am tempted to dive into a discussion of the reasons a person is attracted to "thrash" or say, ted (guts and glory, I AM America) Nugent, as opposed to say, Crosby Stills Nash and Young. but....
Joeb, it is not my theory. Just reporting the facts. From what I've heard about the Flanagan Neurophone, it doesn't rely on the ear at all, or the ear's neurology, but instead creates an entirely different path for the brain to interpret the sound. You may be able to find something about this on the web. The product is no longer squelched by the D.O.D. The man's name is Dr. Patrick Flanagan. I don't know if he is still alive or not. I heard the information on a radio show with Dr. Nick Begich, who was a friend and associate of Dr. Flanagan. Perhaps Dr. Begich has some info on how this device operates and how to get one.
Ursula66 wrote that her WATT/Puppy combo doesn't seem to have anything below 40 Hz. This is 100% true. Mr. Wilson's speakers have many things to commend them, bass isn't one of them. They do NOT have much output below 40 Hz, if they get there at all.

Sorry for bad news...

And, yes there is lots of information below 40 Hz.

What happens when you put 20 Hz. into a speaker that rolls off at 40 Hz. is simply this: the cone moves a lot, there is some second, 4th, etc. harmonic reproduced, your amp works hard and may have reduced headroom if this coincides with a peak.

MOST speaker systems do NOT have significant output below 40 Hz. Period. In order to produce bass below 40 Hz. you need a few things that most speakers can not and do not have. That is in specific enough surface area & excursion to move the required air, which also requires a LARGE cabinet size.

It is true that you *can* make a small speaker that will have output that low, but it will NOT be able to have normal levels of sensitivity or output, or else it will have output below 40 Hz. that is WAY down from the midrange level. So, in practice, most speaker systems are not able to do much below 40 Hz. In practice, sorry to report, most have difficulty making it all the way to 40 Hz. 20 Hz is usually out of the question.

There are some exceptions in this regard, but they are rather few and far between. Many that advertise output in this region do not produce much usable bass unless they are set up in a particular manner or room postion/volume.

With the advent of the latest crop of high power handling/long linear excursion woofers we can expect to see much better bass response and lower F3 points in commercial speakers in the near future... but the price for this is the need for POWER on the amp end (and in the case of sealed cabinets, EQ AND POWER).

To a great extent, this reality is the basis for the existance of a market for what we call "subwoofers."

Bear, there is only one full range speaker that I know of that can effectively go down below 40hz...
K-horns. You don't need subwoofers when using K-horns. These full range speakers can easily handle organ notes down to 32hz. Around this point you no longer hear sound, you feel it in your chest. If speakers can handle frequencies below 40hz, you will be able to tell the difference in pitch between each frequency. This can not be done with speakers rated above 40hz.

Some have raved about LaScalas' deep base that can go down to 45hz. I have both pairs of the above speakers in my system. Trust me when I say that the K-horns can run rings around the LaScalas... even though they both use exactly the same 15 inch bass driver. What makes the difference is the folded horns inside the cabinets. You can not fight the laws of physics. Larger horns will create a deeper bass than smaller horns. It is possible to have two smaller 12 inch woofers develop bass notes down into the 20s with the proper horn cabinet (much below the range of the K-horn).
This is the principle of the soon to be released Klipsch Jubilee (home version).

Because of their high efficiency, K-horns only need 100 clean watts to produce 120db of earth shattering 32hz sound. Expensive high wattage amps are not needed to produce deep clean bass.
Well, that's not quite a true statement since the K horns are a three way system... so that can't be held to be different than any other speaker system.

K horns are capable of very good bass... but they are room dependent and they are a design that was conceived when there was only mono so they can be difficult in certain situations to set up for stereo...

Also, at that time there were virtually no "high power"
amps in the home. 35 watts was considered "high power" at
that time. 60 watts was MONSTER!!

Of the few really high power amps out there back then I can only think of the McIntosh MI 200 series, which was mostly for industrial and theatre applications, and unbelievably expensive for that time.

It is true that they are horns and so have a greater efficiency than do direct radiators by quite a bit.

Today there is a new generation of very linear, very long throw, high power woofers that changes everything for the better in terms of low bass. It is fairly simple now to get a small box to reproduce <20Hz, for real. High power amps for bass are pretty cheap now, and this makes the whole thing very practical whereas a few years ago it was very difficult to do.

For example if you check my website you can see my own personal subs with a new generation driver (not even the biggest and longest throw of them) retrofitted into an already really great subwoofer system... the result is there for you to see.

One can get the same output in a smaller sealed box too...
although you might need more drivers per side to equal the total max spl of my set up, its still more than you typically need in a home system. Compared to the K horn's volume, you'd likely still be under that for the same output today.

Please keep in mind that I am not anti-horn by any stretch of the imagination, as I own several horns of rather large size.
Bear, your excellent posts beg for your website address. I'm sure others here will note that you have not used this site to further your business. So by request, pray tell.
There are several ways to achieve low frequency extension. The most commonly used methods are:

A) using some type of vent i.e. port, passive radiator, tuned slot, aperiodic ( vario-vent ) etc.. This combines the backwave of the woofer with the front wave of the woofer. The vent is tuned lower than the resonance point of the woofer in the box. This approach typically extends bass response appr 1 octave lower ( strictly a ballpark figure ), reduces cone excursion for a given power level, increases sensitivity and spl capability, etc...

The drawbacks to this approach are that the woofers become far more susceptible to bottoming out when fed a high level signal below the frequency that the vent is tuned at. This is one of the reasons that "rumble filters" were invented, as record warps play MAJOR havoc on larger vented speakers.

In a direct comparison with a properly designed sealed box of reasonable Q, the transient response of a vented box will always be slower, sloppier and suffer from more ringing. In effect, we've picked up low frequency extension and spl capability at the expense of definition and attack / decay characteristics. Sealed vs vented designs would be a perfect example of the old "quantity vs quality" dilemma.

B) active equalization is applied to the driver. The rate of boost and frequencies that are effected are based on the specific speaker and box being used. While this approach has merit, the most common problem is an increase in driver doubling ( distortion ) and a massive increase in power requirements. This approach is most succesful with sealed designs due to their shallower roll-off rate as compared to a vented design. Since most sealed designs already require higher power amps to get the woofer "strokin", adding a few hundred more watts is not really a big deal : )

For the record, this is the approach that Bag End took with their electronically equalized subs. Bobby P's "Merlin" speakers also use this approach when using his "BAM" system. Keep in mind that this approach WILL sacrifice ultimate SPL capabilities and potentially increase distortion. It can also damage the driver due to "force feeding it" increased power within a frequency range that it would not normally handle in the same non-equalized situation.

C) speaker placement is designed to take advantage of room reinforcement and room nodes. While the Klipschorn uses this method to some extent, i am primarily talking about smaller boxes that need to be corner loaded to achieve the results that they do. In most of these designs, quality of sound typically plays second fiddle to quantity.

In this case, i am primarily speaking of the drastic differences of arrival times of the soundwaves generated by the various drivers being used within the system at the listening point. This results in a "mish-mash" of sound with a lack of coherency or unified presentation. While there is nothing wrong with taking advantage of room acoustics and "room gain", most designs lack the amount of research and knowledge to fully accomplish such a feat.

While i did somewhat exclude K-horns in the placement category, i would include them in the "time delay" category. This is due to the various lengths of horns used within the different frequency ranges and the paths traveled before the sound makes it to our ears*.

D) use drivers with a large radiating surface, long excursion capabilities and a large box. Obviously, this is not an approach that most folks are willing to live with. However, it is about the only approach that works well with the least amount of electro-acoustic drawbacks. The only real drawbacks in such a design is that of physical size and the associated placement issues and the potential for larger than average amounts of power.

Most any other design other than the "King Kong" approach becomes a juggling act. The designer has to choose which of the "necessary evils" he is willing to accept in order to achieve the goals he has set forth within the constraints he has to work with.

Given all of the above info, we are currently stretching many speaker designs ( especially small two ways ) to a point that was unimaginable 25 - 30 years ago. Most of this has to do with the advances in driver design, materials used, increases in technology and research and computer optimization. This is not to say that all newer designs are better than all of the older designs. As a general rule though, i would say that it is not far from that point. As usual, there are always exceptions to every rule or generalization and i'm sure that someone will bring up a few of them : ) Sean

* As Bear stated, i am not "against" horn designs. I have owned many pairs of horn based speakers and still do. However, "facts is facts" and one should not present information without presenting both sides of the coin. As such, a bass horn would have to be HUGE to actually go down to what most of us would consider "sub" territory.
Once again, well done Sean. Thanks.
Unsound, you should be able to click on my name and get to my info page, where I am listed as a manufacturer, and somewhere on this site get to my web address...

but since you asked, and that makes it "legal" :- )