I have never implemented this Linkwitz equivalent, being fully satisfied with the original natural crossfeed filter. I guess it sounds very similar to the Linkwitz filter, but is a little bit easier to realize. It easily can be tested between a CD-player and headphone amplifier (there is no insertion loss). I designed a modified version of the natural crossfeed filter that has a frequency response very similar to the Linkwitz filter. The delay times for the Linkwitz design (figure 2) are fairly natural, as the crossfeed signal has similar filter frequencies and thereby should have similar delay times as the natural crossover filter. However, more important is that a mono-signal at frequencies below 700 Hz is increased by up to 1.3 dB at a 60-Ohm load and up to 1.9 dB (!) at 50k Ohms. Responses were calculated for a 60 Ohm load (such as headphones) and for a very high output load (e.g., a headphone amplifier).Īs with the natural crossfeed filter, the direct signal with the Linkwitz filter shows a signal loss at lower frequencies, (-1.0 dB at 60 Ohms, -0.35 dB at 50k Ohms).
Figure 1 is a graph of the frequency response of both the direct-signal and of a mono-signal that is given on both signals simultaneously.
#Meier crossfeed simulator
The crossfeed design by Siegfried Linkwitz (see An Acoustic Simulator for Headphone Amplifiers by Chu Moy) includes a bass boost to compensate for low frequency cancellation. If there really is a psychoacoustic effect (a uni-directional bass is unnatural and I believe that, with headphones, this emphasizes its existence), then the effect has been (unconsciously) corrected for in the sonic design of the transducers. I believe that most bass-losses are due to psychoacoustic effects, but after thinking it over more carefully, enhancing the bass response of the natural crossfeed filter could be legitimate, because headphone sound is optimized without using crossfeed. To add bass or not to add bass….that is the question. A good speaker does not fatigue, and this exactly is the strength of the natural crossfeed filter. The rewards come while listening for longer periods of time. It’s like listening to loudspeakers – a balanced speaker does not jump at you at first hearing but is rather colourless/neutral/unobtrusive.
One should not expect a punchy bass, only a relaxation of the sound. I know, the crossfeed sound is nothing for a bass-freak. With the crossfeed activated, a weak cancellation will only be present at low frequencies, but at all frequencies, the sum of the sound pressures at both eardrums always equals the sum of the pressures in stereo mode!Īt first I also wondered about the apparent loss of bass, but actually, it is this unnatural, larger then life-size, uni-directional bass, that counts for most of the annoying effects of headphone listening. Listening in mono does introduce cancellation of low frequencies, but there is also cancellation higher frequencies (which is generally is even stronger since, with normal stereo recordings, low frequencies are more in phase). The effect is similar to that what is heard with a crossfeed filter, only much stronger. If you hear the same way I do, then you will notice that the bass suddenly seems to have weakened – it has become less pronounced. If you have an amplifier with a mono-switch, then here is a little experiment: listen to a stereo recording (by headphone) in stereo mode, and then press the mono-button and watch the bass.
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