I read somewhere where you are not gonna get anything below 40Hz in a live performance, except maybe a movie. |
AFAIK, yes, the driver will continue to attempt to reproduce lower frequencies. Usually manufacturers measure their speakers with a -3db range. So it sounds as if your speakers are down 3 db at 40 hz. Depending on the slope of the crossover will depend of how much rolloff there will be at 20 hz. A 6 db per octave rolloff should be -9 db at 20 hz. A -12 db crossover design would be -15 at 20 hz, etc. |
a ported design may have a steeper rolloff than a sealed enclosure which may have less apparent bass but a more gradual slope. |
Your room will amplify bass frequency that corresponds to distance between front and back wall. If this distance is 18' then room will amplify 1150/18'/2=32Hz (where 1150 is speed of sound in ft/s and 2 is for travel forth and back to add). |
"I read somewhere where you are not gonna get anything below 40Hz in a live performance, except maybe a movie."
Possibly, if all piano performances don't use the lower 7 keys (27.5 - 38.9 Hz), and all the string basses don't use the 5th string (30.9 Hz), etc, etc. |
Lowest bass string E=41.2Hz With 5 or 6 string basses lowest frequency is still 41.2Hz because it is only for the ease of playing (music is typically written for 4 string bass). The issue here is not only extension but quality of the bass. My new Hyperions HPS-938 don't have extension of previous speakers but have better bass - more natural string attack and decay, better dynamics, less resonances etc. Tuning of the port, in addition to better woofers, plays role. With popular mass market speakers bass extension is what sells the speaker, no matter how distorted or poorly defined it is.
Yes piano goes lower, some special pianos even down to 16Hz but I don't know how often lowest A=27.5Hz is played. Perhaps not very often but in either case I can live without it. |
this is a neat frequency chart that shows instruments range
http://www.independentrecording.net/irn/resources/freqchart/main_display.htm |
It's an interesting question, and while I'm not an EE, here's my understandiing of how it works (for a dynamic/cone woofer):
The woofer is a system composed of 4 main parts; a cone, an electric motor attached to that cone, a box housing that cone, and a suspension connecting that cone to that box. The motor applies force that causes the cone to move and create sound. (I'll avoid the "push air" vs "pressurize" question because I don't think it's relevant to answering the question from the OP). The other 3 components in the system all constrain the movement of the cone to one degree or another.
Assume for a second that the motor system is large enough to move the cone an infinite distance if the motor has enough "fuel" (LF signal) from the amplifier. In this case, your question goes to the behavior of the cone. If the cone is sufficiently large and/or capable of moving infinitely far, it will (theoretically) have infinite low frequency capability. But it doesn't - the combination of cone/suspension/box always limits the max movement of the cone.
So, the size of the cone and it's maximum travel limit the entire bass system's low frequency capability. Once the cone reaches its maximum travel, further "push" from the motor will fail to move it further. As more LF signal is converted to force by the motor and the cone approaches its maximum excursion, the cone starts to resist and dynamics are compressed. Once maximum excursion is reached, excess signal is largely dissipated as heat.
Conceptually - at the extreme - one of 2 things eventually happens:
Overdriving the motor by sending it too much LF "fuel" will melt the voice coil element in the motor. If the motor is sufficiently robust that the voice coil survives the heat build-up, the cone would eventually deform/crush itself.
It's also possible that the LF capability will be limited by an undersized amp (not enough LF fuel).
That's my understanding, anyway (hope it's accurate, but I'm interested in hearing if some of the tech types here have a better answer.)
Marty |
Yes, they will go deeper. Sometimes I think the advertised frequency response of some speakers is just creative license. Saw an advertised rating of 40 Hz - 3dB for a sealed monitor with a 6.5" woofer. Don't think so. 60 or 70 maybe, but that doesn't sell speakers. Doesn't mean that speaker has poor bass, just a gradual roll-off and I would expect good transient response (tight bass). Some driver/box combinations have a steep roll-off and impedance curves going into the lowest frequencies. |
Yes, the woofer does try to play lower frequencies, unless there is a crossover cutting off those frequencies lower than a certain point, say 30Hz. Usually the bass driver is left to attempt to play those lower frequencies, but is less precise as the frequency drops.
If you look at the graph of a woofer's response you will see at the left side it will fall off, as though a steep hill to the left. This is the visual of the speaker's worsening in performance of the lower frequencies. It may perform at +/-3dB at 40Hz, but at 30Hz may by down to -6dB or so. The more veritcal the line as the curve turns down the worse the performance in terms of capacity to play the lower frequencies.
Do not expect a speaker with specs like 40Hz +/- 3dB to do well at 25 or 20Hz. It will not. You will not get the lowest, deepest bass in abundance from such a speaker, no matter what anyone tells you in selling it. If you want lower bass, bass you can feel, etc. you simply have to find a speaker with the proper drivers/specs. At this time, while I can still move around big speakers, I choose not to use a speaker with specs like 40Hz for my reference. There are many speakers with just as good sound quality and far better lower end, say 16-20Hz performance, though you will usually pay a lot more for it. It is relatively easy to find competent speakers with bass specs such as 25-28Hz +/-3dB, and that would give you a lot of low end. Again, if someone is showing you a smaller tower speaker, or a bookshelf speaker with smaller drivers and a rating of 40-45Hz without any tight specification like "+/- 3dB" avoid it if you want powerful bass; it will never give it to you. It will perform more poorly if the number is higher, such as +/- 5dB, or even worse +/- 10dB. A very tight measurement is +/-2dB.
Having said all that, this doesn't tell you what the tonal character of the speaker is, which is why you do not typically want to buy a speaker unheard. The type of cabinet used, and whether it is ported or a sealed enclosure design of a box speaker, and the crossover network also vastly influence the sound the bass makes. So, you will want to hear a speaker you are considering purchasing if possible.
If you go the small speaker route with less bass you can always do a sub.
But, yes, any bass driver attempts to go lower along with the frequencies of the media unless cut off by a crossover. It would also attempt to go higher as well, but the crossovers limit it. Regarding a driver reaching "infinity", it will distort badly as it is pushed harder and attempts to play frequencies increasingly outside of it's optimum range of operation. |
Thanks for all the great answers. I have another question. Since the driver continues to try to reproduce these lower frequences, does it do any harm to the driver sonically or physically? |
Frequency respone specifications are often so generalized that they have very limited value.
Some mags like stereophile will do more comprehensive actual measurements of fr and others. Those are more useful in terms of measuring actual performance.
For the average joe, a reference test cd or record to generate test tones at various frequencies and your ears as the measuring device can be insightful. Or a spl level meter device can be used.
Of course music is a much more complex signal to reproduce than any test tone, but a suite of variable test tones can gjve at least some degree of quantifiable measurement of how you system and your ears perform. |
Yes there is harm done. It uses a lot of the amps power to reproduce
what it can at the lower frequency which can negatively affect the rest of
the music and leads to clipping distortions at lower volume than
otherwise. |
Does anybody produce a QUALITY high pass filter that can be inserted between the pre and the amp without compromising signal quality? Don't trust the networks installed in subwoffers. To many external influences on original signal. |
62bakes - One way they increase extension of the speaker is to put second woofer for the lowest bass only (higher frequencies filtered out by xover). For two way speakers it is called 2 1/2 way speaker (pretty much like adding subwoofer). I suspect that small drivers, being point source, will have more interaction with the room than large woofers where bigger percentage of the sound goes direct.
Distortion might be caused by by nonlinearity of the motor especially at max extension of the membrane. Most of drivers are designed as overhanged type where magnetic gap is narrow but coil is long extending outside of the gap. Some drivers (like in Acoustic Zen Adagio) have underhung motor meaning that gap is very wide and the whole (narrow) coil is inside of the gap. This scheme is more linear but requires drivers with very large magnets - more expensive. Some tweeters are made that way as well (to lower distortion at max power) including Morel Supreme. |
Kijanki - the speed of sound in dry air is 343.2 M / Sec = 1126 ft/Sec |
Pbnaudio, We don't have exactly dry air here (Chicago) but I will settle for 1135ft/s which is speed of sound in dry air at 75degF - and this is my last offer.
Same example with new numbers: 1135/18/2=31.5Hz |
62bakes: You can use just the high pass section of an active crossover, like a Marchand. Doing something similar with a NHT X2, which has a relatively simple choice of 3 fixed 12 dB/octave filters. Except for the Pass XVR-1, most active xovers use opamps which are not always totally transparent. 24 dB/octave filters are usually cascaded (series) but have their advantages. Then, there's digital xovers which require another ADC/DAC conversion but can offer incredible versatility. |
A 5 string bass with a low B string creates, at least at the fundamental tone, a 31hz signal...using test tones I've found that my system (including a sub) easily reproduces that frequency, and a nice test is the bass note at the beginning of Donald Fagan's "Morph the Cat"...a solid B. I do use a phono preamp with a rumble filter (20hz), and before that (when I had a preamp with a phono stage) I found an older pair of Nakamichi line filters that worked really well to tame woofer rumble floppage. I think in live music there's a lot of stuff going on under 40hz, like kick drum overtones (undertones?) subway tunnels under the floor, or heavy footed waiters bringing my bar tab check. |
In general, clipping due to low frequency noise being generated is fairly common with vinyl rigs. With digital, it is practically not really a concern. If speakers are producing poor or unneeded output of actual music signal at lower frequencies,then filtering is a good option to use power available more constructively. |
