Question about frequency response specs

[James G]

Hi guys. I have been recently playing with test tones and it got me thinking about frequency response figures.

For example, my amp states response from 10Hz-100kHz and my speakers state 43Hz-40kHz, but I can send it even a 1Hz wave and can see the woofer slowly moving in and out. Of course I can't hear that but it shows that my system can recognize and react to that signal. Incidentally, I found I can't hear 18kHz or above. :( I can barely hear mosquito tone (17.4kHz) but anything beyond that is just silence. And I can hear 10Hz from my sub and that's rated at 28-200Hz (not just feel it, but recognize it as a tone).

Could somebody explain to me in simple terms how important these specs really are or what kind of role they play in a component? Thanks!

[Ali Tait]

I wouldn't worry about hearing to "only" 18k,there is very little if any music information at those frequencies,and in any case,18k is pretty good,even for a young person.I hear to about the same at 41,which is well above the average I think.As for the rest,don't worry about it.If your speakers sound good to you,then they are good.

[James G]

Nah, I'm not too worried about my hearing. It is what it is I guess. :lol:

I'm wondering why manufacturers post specs like 20Hz-20kHz. In my observations the stereo/speakers do react to signals outside of human hearing. So if there was some 1Hz interference going on in the background that I can't hear, I would imagine that it can still affect the performance of the speaker to produce the sounds I can hear.

I hear casual comments here and there on the internet like "it's not in the audible frequency range, so it shouldn't matter".

[Ali Tait]

Well I think the 20 to 20 thing came about because someone said a long time ago that this is the maximum human range of hearing,so speaker manufacurers latched on to this and decided that a speaker should have a good response within these frequencies,when in reality it really isn't necessary.For instance,take a full range driver like say Lowther.These sound beautifully coherent despite being found wanting by the 20-20 rule.Interestingly though,at a previous diy meet,supertweeters were tried on a full range horn and switched in and out.The difference was easily discernable,despite the tweeter response starting at about 25k.How is it that we could all hear something that we should be unable to hear? Harmonics perhaps?

[DSJR]

Just my jottings/typings here, but 10Hz shouldn't be heard, but it *should* be felt. A "tone" is almost certainly doubling or tripling of the fundamental, which many speakers do (and why a straining small bass unit can put double the frequency into the mix, seemingly giving more bass).

14Hz (easily reproduced by large transmission lines) gets the doors vibrating and 20Hz should give you a real push in the chest. Most bass on recordings is really between 40 and 80Hz to be honest.

As for high frequencies, most rooms will bring about a gentle rolloff above the upper mid (see the classic 1980's HiFi Choice book reviews). More importantly, the *dispersion* of the tweeters above and below should be more important - the BBC did loads of research on this forty years ago and the basic tenets still hold true and should be easier to achieve today as drive units are generally better behaved today.

"Frequency Response" is only one of many tests that should be carried out on speakers and most of the speaker rule book was written decades ago. I suspect that many cheaper models are deliberately crippled to make the upper ranges from the same maker appear to be so much better.

[Ali Tait]

Yes agreed I think that's rife with manufacturers-and not just speakers-where they will de-tune their cheaper kit so their better stuff will sell.

[Stratmangler]

I suspect that many cheaper models are deliberately crippled to make the upper ranges from the same maker appear to be so much better.

Surely not ?:eyebrows:

[DSJR]

Certainly in the crossover and the box reinforcement and filling departments, yes....

[James G]

Just my jottings/typings here, but 10Hz shouldn't be heard, but it *should* be felt. A "tone" is almost certainly doubling or tripling of the fundamental, which many speakers do (and why a straining small bass unit can put double the frequency into the mix, seemingly giving more bass).
.......

You have a good point. Maybe what I'm hearing is the "sympathetic ringing" of the box/thin plastic bass port tube? I had put polyester wool mat inside the sub enclosure, but perhaps I need to find a way to deaden the port tube too.

Oh, maybe put it up on spikes too! I have a few laying around here somewhere. The thought never even occurred to me until just now. I have it sitting right on the carpeting. The flooring is concrete.

[Themis]

For example, my amp states response from 10Hz-100kHz and my speakers state 43Hz-40kHz,
Frequency response is always stated between relative limits (+-3dB for amps or for instance -6dB for speakers) and for certain distortion limits (3% for speakers, for instance).

Which doesn't mean that 5Hz is not/cannot be reproduced ! It simply means that it may be reproduced at -20dB and at 10% of THD. ;)

[DSJR]

Remember the Linn Asak *DC 2 100 K*

[ahgotriddm]

Hi guys. I have been recently playing with test tones and it got me thinking about frequency response figures.

For example, my amp states response from 10Hz-100kHz and my speakers state 43Hz-40kHz, but I can send it even a 1Hz wave and can see the woofer slowly moving in and out. Of course I can't hear that but it shows that my system can recognize and react to that signal. Incidentally, I found I can't hear 18kHz or above. :( I can barely hear mosquito tone (17.4kHz) but anything beyond that is just silence. And I can hear 10Hz from my sub and that's rated at 28-200Hz (not just feel it, but recognize it as a tone).

Could somebody explain to me in simple terms how important these specs really are or what kind of role they play in a component? Thanks!
The reason that your speaker spec does not go down to 40 Hz and below is that the bass drive unit is not matched to the air below 43 Hz- it doesn't have a 'grip' on it, if you like. Modern amps go down flat to 10 Hz or lower because it is now easier to build amps that way, though it is doubtful whether many people hear any difference in practice in comparison to older amps that went down to 20 Hz. But you probably wouldn't want to buy a new amp that stopped at 20 Hz because you'd worry about how good the overall quality would be.

At the top end, the higher the figure, the better. Some older people may not be able to hear much above 10 kHz, but they can hear differences in top end responses, because wave form is affected. The front of a wave form very largely allows the ear to identify different instruments and voices, and an accurate shape of that front edge requires the highest harmonic frequencies. So one might not hear 'higher' with a better top end spec, but one will hear more acoustic clues, better definition and localisation of instruments, less smearing, with less trying to work out what is going on in busy passages.

So, while there is much more to specs than frequency responses, one should generally go for as wide a response as possible.

[Barry]

Hello James,

Frequency response is exactly that – it is the frequency range over which the item in question will respond. No more no less. As Dimitri has correctly stated, a frequency response quoted without limits is meaningless. If for example you are driving your speakers with a direct-coupled amplifier, you will indeed see the cone of your driver moving at 10Hz, though you will neither ‘hear’ this tone nor ‘feel’ it, as the driver will be unable to move enough air. In other words the fact that your system can respond to frequencies beyond the range 20Hz – 20kHz, doesn’t mean much.

What is much more important is how flat, or uniform, the system response is within the 20Hz to 20kHz range. That is why the amplitude tolerance band is important: usually quoted for amplifiers and electronics as +/- 0.1dB, for pick up cartridges as +/- 1dB and for speakers, +/- 3dB. Of course, the room within which you listen will alter all of this. You will be doing well to arrange things so that the overall response at your listening position is flat to within +/- 5dB.

So why quote a frequency range of 20 – 20,000 Hz? Well this is the frequency range within which we can hear ‘pure’ tones. Below 20Hz, you no longer hear the tone - rather you feel it. Anyway outside of electronic music, the only instruments that can produce a note below 20Hz are some pipe organs with a 16Hz pipe; four octaves below middle C. Some versions of Strauss’s ‘Also Sprach Zarathustra’ (the opening theme music for the film ‘2001, A Space Odyssey’) start with this note, but you will never hear it, rather you will hear your speakers ‘doubling’ and producing a tone of 32Hz (in other words distorting at something like 80%). Similarly, for those frequencies higher than 20kHz. Again you no longer hear them but sense them; they define the timbre of instruments like the piccolo, oboe, viola, violin and the already mentioned pipe organ. These high frequency components also define the sound of non-pitched instruments such as snare drums, cymbals and the triangle.

Now as I say, you will not be able to hear these harmonics as pure tones; the human hearing does not go up that high (though some asthmatic children can hear pure tones above 20kHz) and anyway the upper limit falls off with age. For example, my hearing is quite uneven above 10kHz: I can’t hear anything above 12kHz, can perceive a 16kHz note then nothing after that. This however is not to say that one cannot perceive these components as harmonics. To give you an example, there is a demonstration record, made in 1973, by J B Lansing to promote their loudspeakers. The record is called ‘Sessions’, it doesn’t have a recording number and I suspect that it is now long out of print. On it is a short violin piece, first recorded full range. It is then repeated with all the harmonics above 15kHz filtered out. Then again with all harmonics above 14kHz filtered out and so on, in 1kHz steps down to 10kHz. As I said my hearing is erratic above 10kHz, and I would be lying if I said I could definitely hear pure tones above this frequency, yet the effect of harmonic filtration above 15kHz is immediately obvious and plain to hear. I suspect this is why some people have commented that the use of super-tweeters operating above 22kHz can make a difference.

Trust this of interest.

Regards

[Ali Tait]

I don't pretend to know much about the subject Barry,but I guess my supposition that the clear difference between supertweeter and no supertweeter being down to harmonics is largely correct then?

[Marco]

The reason that your speaker spec does not go down to 40 Hz and below is that the bass drive unit is not matched to the air below 43 Hz- it doesn't have a 'grip' on it, if you like. Modern amps go down flat to 10 Hz or lower because it is now easier to build amps that way, though it is doubtful whether many people hear any difference in practice in comparison to older amps that went down to 20 Hz. But you probably wouldn't want to buy a new amp that stopped at 20 Hz because you'd worry about how good the overall quality would be.

At the top end, the higher the figure, the better. Some older people may not be able to hear much above 10 kHz, but they can hear differences in top end responses, because wave form is affected. The front of a wave form very largely allows the ear to identify different instruments and voices, and an accurate shape of that front edge requires the highest harmonic frequencies. So one might not hear 'higher' with a better top end spec, but one will hear more acoustic clues, better definition and localisation of instruments, less smearing, with less trying to work out what is going on in busy passages.

So, while there is much more to specs than frequency responses, one should generally go for as wide a response as possible.

Hi "ahgotriddm",

Welcome to AOS :)

Please pop into the Welcome area of the forum at your first opportunity and introduce yourself to our membership by giving your real first name, basic location, system details and taste of music, as this is the required procedure when joining our community.

Thanks! :cool:

Marco.

[Barry]

I don't pretend to know much about the subject Barry,but I guess my supposition that the clear difference between supertweeter and no supertweeter being down to harmonics is largely correct then?

Hi Ali,

Yes, I think that's what is going on here. My high frequency hearing is not that clever, though commensurate for my age. I was really surprised by the demo tracks on the LP I cited - I could definitely hear the effect of harmonic filtration above 15kHz, yet would not be able to reliably hear a pure tone of the same frequency.

Regards

[James G]

Thanks Dimitri, Barry and "riddm". Great posts. I just learned quite a bit I think about those specs!