When will Jabra offer something similar? Is there a reason no one else offers such headsets?

Hi Jacob,

Thank you for your interest in our products! However, it seems like you have misinterpreted the design principles in feed-forward and feedback controls incorporating acoustic components and the inevitable design considerations that are required. As the lead design engineer for ANC solutions here at Jabra, let me try to elaborate on this.

For the feed-forward solution, in your second sentence you state that there are two microphones inside the earcup, hence you state that the feedforward microphone is also placed inside the earcup. This is not correct, neither in our products nor any other ANC product on the market utilizing feed-forward ANC. The feed–forward microphone is placed outside the earcup, the feedback microphone inside the earcup. See the pictures in this blog.

Also, your statement: “In feedforward control, this signal is used to adapt the controller and minimize the noise at the error sensor” is not compliant with the basic principles of feed-forward operation, as feed-forward is a so-called open-loop circuit, hence it has no error-correction nor any adaption to the error that occurs (i.e. the noise). It uses a reference sensor instead, in this case the feed-forward microphone.

Feed-forward is based on predicting the error, in this case the noise. The main advantage in an ANC headset is that the error (noise) is picked up before it reaches the ear; hence it has a phase (time) advantage that is beneficial towards higher frequencies. The noise outside the earcup is different from the noise experienced by the user wearing the headset, as the earcup has an impact on the noise reaching the ears. The feed-forward controller simply acts as a transfer function block that mimics this difference. You can say that the feed-forward is a ballistic solution, as the system never checks whether it actually hits the target – this is solely a matter of how well the controller’s designed transfer function matches the actual transfer function between the outside and inside of the earcup.

As the feed-forward transfer block by definition is not adaptive, only one specific transfer function is implemented. However, a large number of variations exist in the acoustics of an earcup. To name a few:

– No two set of ears are identical, hence no set of ears has the same transfer function relative to the feed-forward microphone.

– Noise coming from different angles gives different transfer functions between the feed-forward microphone and the ear, due to the inevitable fact the eardrum and the feed-forward microphone are not placed in the same physical position. The higher the frequency, the larger the resulting variation.

– The natural leaks between the earcushion and the user’s head causes varying low-frequency amplitude and phase response of the speaker.

These variances need to be taken into consideration when designing the feed-forward controller, as one single transfer function has to cope with all the expected variances. If these variations are not taken into consideration, you could end up having users that would experience that the feed-forward system actually amplifies the noise at some frequencies instead of reducing it. This compromise reduces the effective frequency bandwidth of the feed-forward controller, as the frequency span that has satisfactory low amplitude and phase variations throughout different users and different noise angle is limited.

For wind noise, feed-forward is really a mediocre performer. This is due to the fact that wind noise contains low frequencies and that noise artifact caused by the wind vortexes around the mechanics close to the feed-forward microphone in windy environments also contributes heavily to this. This means that the feed-forward microphone picks up wind noise that is not present at the ear – but it is fed though the controller and hence reproduces phase-inverted noise to the speaker of the earcup, even though it is not required. Feed-forward actually introduces and amplifies wind noise to the ear!

The conclusion for feed-forward is still that:

– The feed-forward solution has the advantage that it can act on higher frequencies than the feedback solution.

– As is has no native error and variation correction, the performance is limited to a narrow frequency range (=small bandwidth).

– Wind noise handling is mediocre.

I do not agree with your statement that “Feedback control is the same set-up as feedforward“. The feedback ANC is fundamentally different from the feed-forward type, as it is based on correcting the error that has already occurred, without being able to predict the error in advance. Hence, it has an error sensor and no reference sensor, and it is a closed loop design. This makes it the exact opposite of the feed-forward design.

As the feedback reacts on the “trailing edge” of the noise, it is very dependent on initiating the anti-noise to the speaker without introducing further delay. The noise is real-time, meaning that there is no time to process the counteracting anti-nose signal. Already taking the physical distance between the feedback microphone and the speaker diaphragm into account, this introduces a phase (time) delay. Along with the natural phase delay of a speaker towards higher frequencies, it limits the performance towards upper frequencies due to the decreasing phase and gain margins in the feedback loop. However as the feedback loop is constantly monitoring the residual noise and adjusting the performance, it is more capable to counteract the earlier mentioned variations; hence its frequency bandwidth of operation is larger/wider than compared to the feed-forward.

For wind noise, the feedback microphone is very efficient in reducing the wind noise due to its low frequency capabilities. On top of this it does not pick up any “false” noise as the feed-forward microphone does.
This means that not only is the feedback solution superior in wind noise suppression, in a hybrid system it can actually also counteract the wind noise errors introduced by the feed-forward solution.

This brings me to the conclusions for feedback that still is:

– The feedback solution has the disadvantage that it cannot act on higher frequencies compared to the feed-forward solution.
– As the feedback loop essentially acts as an error and variance corrector, it can act on a wide range of frequencies (=large bandwidth).
– Wind noise handling is good, and it can even counteract the wind noise introduced by the feed-forward solution in a hybrid system.

I hope that this clarifies the advantages and differences between the feed-forward and the feedback solutions – and also why we have chosen to implement both in our current ANC solutions, as they complement each other very well!

In both Biz 2300 and 2400, the speakers only have passive noise cancellation. The microphones have varying degrees of noise cancellation, ranging from medium to high depending on which variant you’re looking for. The Biz 2400 has some variants with so-called Ultra Noise Cancelling microphones, which offers the best performance in very noisy environments like call center (http://jabrablog.wpengine.com/business/contact-center-headsets/jabra-biz-2400ii)

If you’re looking for ANC in the speakers, Evolve 80 (http://jabrablog.wpengine.com/business/office-headsets/jabra-evolve/jabra-evolve-80) is the way to go.

Do BIZ 2300 and 2400 include any of ANC types?
If not, is there any other noise cancellation feature for speakers included or just for microphones in those models?

Best regards,
Greg