Noisebuster Responds

I raised some questions with Noisebuster about their units and how they worked.

My questions are in blue, their replies are in brown.




(a) Your headphones appear to be less sensitive than other sets of headphones - ie, they require more power to drive them at a given output level, no matter whether the switch was set for airline or audio device input, and no matter whether the noise reduction was on or off.

Yes, they are less sensitive than some and this is due to their impedance - it is 300R rather than 100R or 30R or even 8R seen in some headphones. This does not mean that they need more power, but they do need a higher voltage level than low impedance headphones for a given sound pressure level.

We chose 300R impedance to be compatible with the airlines and kept to this impedance for the EX so that LP did not have to produce two sets of headsets. Since the EX was introduced, the output of portable CD players has tended to drop in level.  This is due to growing awareness and concern at the hearing damage that high levels can induce and so there has been a move to restrict the volume levels that can be produced.

(b) Is there any reason at all why a person would ever have the noise reduction slider control set at other than maximum? Is this just a marketing gimmick or does it actually serve some useful purpose?

Some people experience a pressure effect when wearing the headphone in a quiet environment - the effect tends to disappear in a noisier situation. This is a psychological effect most likely caused by the imbalance in the perceived background noise spectrum caused by the action of the noise cancellation. The Variactive control allows the higher frequency noise cancellation to be reduced to counter this effect, while still working at lower frequencies to cancel such noises as the low frequency drone of an air conditioning system.

There is another aspect of the Variactive control however - it has an effect on the audio response. When cancellation is set to maximum, the audio response tends to be boosted a bit in the presence region. This boost partly counteracts the masking effect of the smaller amount of low frequency noise that remains after cancellation. In a quieter environment, reducing the Variactive control setting reduces this boost whilst still retaining some lower frequency noise cancellation. At its lowest setting, it produces a tonal balance that exhibits a brighter sound (more treble).

(c) The headphones seemed weak in the high frequency response.  This was most apparent by listening for the random amplifier noise ('hiss') between tracks on a CD. With all three sets of headphones I was testing adjusted to give similar sound levels, hiss was clearly apparent in the expensive headphones, slightly apparent in the cheap ones, and least apparent from your headphones (again at all settings). Any comment on this?

The frequency response of the NB-EX has been tested against various headsets of different types and ages. There has not been a particular standard for headphone responses until more recent times, and even now there is still little consistency regarding the balance between the low and high frequency regions.

To assess the relative audio responses of various headsets, they were measured on a dummy head. For reference, the dummy head was also placed into a listening room and a loudspeaker played sounds with a spectrum analyzer. The sound was then measured in the region of the dummy head to calibrate the measurements. The difficulty of measuring headphone sound fidelity is that the shape of the ear itself alters the response of the sound field it is immersed in and so a headset should be designed to produce a similarly altered response at the ear. This alteration occurs mainly above 1kHz, and consists of a broad boost in response centred on 3kHz with a gradual drop to a dip at around 10kHz before recovering at higher frequencies.

The NB-EX follows this trend reasonably closely, although it has a slightly stronger output around 1kHz because it is mainly intended for listening to music in a noisier environment.

A number of the headsets we measured tended to have a prominent peak around 10kHz instead of the dip that should occur. Sony headsets tended to exhibit this characteristic quite strongly (although to a varying degree amongst the different models). Lower cost headsets also had this characteristic but to a lesser degree. An earlier model of ours also has this 10kHz peak, but we corrected this for the current model. Compared to these headsets, the NB-EX would sound less bright and would not emphasize hiss to the same extent, so, although you are correct in your observation, we suggest that our headphones are giving the truer recreation of the sound - after all, it isn't as though you particularly want to hear hiss in any event, is it!

So in conclusion, the NB-EX might sound less bright than some headsets and would not emphasize hiss, but if a brighter balance is preferred in a quiet environment, the Variactive control can be adjusted to effect this. In the end, the choice of response for headsets is still very subjective given the different aural experience they provide, and there is still a very wide variation in responses between different manufacturers and models, far more so than with loudspeakers.

(d) I'm trying to remember how much I probably paid for one of your original model Noisebuster units from Sharper Image, at least five and perhaps more years ago. I'm guessing $150 - does that sound about right?

Yes, our first product came out at $149.  We are very proud that we have managed to consistently enhance the features on our units and, at the same time, drop their price, in the intervening years.

What do you think?. Send David an Email - [email protected]

Copyright 2001 by David M Rowell.