Tweeter frequency response

[ID.]

In looking at a number of speakers, I noticed top end frequency responses around 20-30khz to be common, but I also noticed a number of speakers I'm thinking of auditioning go up to 45 or even 55. I know our hearing is measured at a maximum of 20khz, so what is the theory behind going this high? what are the supposed benefits?

I'm aware of the science behind why it shouldn't make a difference because humans can't hear it, but would like to know why some people believe that it does/might, or your experiences with speakers that have frequency responses from 30khz+ or even experiences with super tweeters.

 

[007L2Thrill]

Well, all I know is what Tannoy say about there super tweeters and there wideband tweeters, here is a little bit what Tannoy say about there expensive Dimension speakers:

Modern programme material and sources (e.g. SACD / DVDA) have driven the requirement for loudspeakers with extended frequency bandwidth performance. Always at the forefront of audio evolution, Tannoy has been developing just such wide bandwidth loudspeaker technology over many years.

Music contains transient information and rich harmonics beyond the range of human hearing for pure tones. Even bass notes have leading edge transients reaching 30kHz. Operating between the roll-off point of the Dual ConcentricT high frequency unit and 54kHz, the Dimension SuperTweeterT will accurately reproduce the leading edge of individual notes allowing the listener to experience the entire bandwidth information of instruments.

In addition, by extending the frequency response by two octaves corrects time and phase response within the bandwidth of normal human hearing. Taking these acoustical phase anomalies beyond the range of human hearing adds realism to the soundstage by improving imaging and placement of instruments.

Musical instruments have energy up to and beyond 100kHz, but can we perceive it?
Researchers monitoring brainwave activity on subjects exposed to wide bandwidth material to 60kHz have conducted controlled experiments. By careful monitoring and noting subjective scores under blind conditions, it was discovered that the listeners were indeed responding to the ultrasonic components in the music.

Further experiments have deduced that profoundly deaf subjects rely on ultrasonic detection in their discrimination of speech and tones. These tests concluded the mechanism was through bone conduction, probably to a small organ in the inner ear called the saccule, which is effectively wired to the cochlea, the organ responsible for hearing as we know it.

The proof as always is in the listening; whatever the source - whether vinyl, compact disc or the latest SACD / DVDA technology. All of the technical features and attention to detail combine in the Dimension models to provide discerning audiophiles with incredible wide band detail for the ultimate musical experience.

Research continues into the actual mechanism of the perception of sound above 20kHz, but it can be clearly shown that the addition of a SuperTweeterT will better preserve the harmonic relationship between instruments.

To me they do add air, but I still like the old soft dome tweeter.

 

[ID.]

Interesting. I like air. I'd read that the add air, and I thought it might help add something with the few SACDs I have.

What about CDs which I believe cut off the hf around 20khz anyway?

 

[tyranniux42]

CD players have filters to cut off frequencies at 20khz or so due to Nyquist theory. the sampling rate of 44100hz allows CD's to perfectly (theoretically) produce the original source material up to 22050hz. (my nyquist theory is a little hazy as it was the first year of my degree but that much is correct i believe). The filtering is what allows the frequencies to be reproduced accurately. If no filter was implemented then the frequencies produced would not resemble the original waveform i dont think and would hence be useless...

Another reason however for a tweeter frequency response to go way above the limits of human hearing (aswell as the before mentioned harmonics etc. which help make up the lower frequencies accurately), even when using CD, is the breakup frequency. A tweeter with a response of 50Khz (usually to -6db unless its a super tweeter) will have a higher breakup frequency than one with a 30Khz response. The higher the breakup frequency the more closely the tweeter will follow the frequency response graph of the 'perfect' tweeter.

The best way to achieve this is to have a material that is both extremely stiff, and light. B&W try and achieve this with the use of diamond tweeters, and Focal use Beryllium. Both have different reasons, one is that Beryllium is one of the lightest materials and is very very stiff, Diamond however is the stiffest material know to man. Both sound good I'm sure, I've only heard the B&W tweeters myself.

Either of these will follow the plotted response if the ideal perfect tweeter very closely up until around 25 or 30Khz, which is above the limit of human hearing, thereby producing frequencies we can hear perfectly (or close to).

The ideal perfect tweeter by the way is one of infinite stiffness and infinitesimal mass if i remember correctly, which clearly doesnt exist in reality, but can be modelled easily enough....

anyway hope this wasnt too much of a ramble, if anyone is interested, B&W circulated a DVD a while ago describing this very well but im sure if you search breakup frequency on the web some interesting stuff will come up....

regards

Dan