After soaking in the explanation of head end ringing in our last issue, you should appreciate this follow up which tells us how exactly it negatively affects your listening experience. You are, after all, among the finest listeners in the world. Demanding only the finest in musical reproduction, you deserve to know how to extract the ultimate enjoyment from your system. Enjoy!

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Sound Masking

The best sound masking sound is a sound that sounds just like the sound that it is supposed to mask, except that the masking sound is a time and phase scrambled version of the original sound. The worst masking sound sounds nothing like the sound that is supposed to be masked. How loud would a hiss sound have to be to mask the staccato tonal presence of a rapidly plucked bass guitar? Probably 40 dB louder than the guitar. If the guitar is being played at 50 dB,A and a steam pipe hiss is kicked on at about 90 dB,A, maybe, just maybe most of the guitar sound would be drowned out. But if the reverberant sound of the guitar itself was used along with a wild set of time delayed attack transients mixed back in, we could mask out the guitar with a sound masking sound level that equals the guitar level alone. Post masking is the psychoacoustic process of listening to a direct sound which is quickly followed by a sound masking type of sound. In this case the head end ringing is post masking the direct signal.

Let’s look at the statistical version of music. There are 8 separate sound bursts per second, which means each burst lasts 1/16 second and it is followed by 1/16 second of silence, in a perfect world. The head end ringing energy from the leading edge of the former attack transient begins arriving at the listener’s position 1/12th second after the leading edge is heard, which is slightly after the tone burst turns off.

Secondly, that same head end ringing is arriving at the listener at just about the same time that the next attack transient begins to arrive. The scrambled version of the leading edge of the first attack transient begins to arrive after 1/12 second after the beginning of the direct signal 1/16th second tone burst. That means the scrambled part of that tone burst begins to arrive just after the end of the direct tone burst, and it proceeds to fill in this subsequent silent 1/16th second time period in the tone burst sequence.

There is another aspect of attack transients we need to take a look at. It’s about listening to music and understanding what we are hearing. Each sound of music can be outlined by the ARSD pattern. When people in general listen to music they listen to the sequence of sustains. But when audiophiles and recording engineers listen, people heavily vested into the sound of the sound they are hearing, they naturally or through training learn to focus on and hear the sound of the attack transient. The truth of the sound is in the sound of the attack transient part of the sound, not in the sustain.

This is born out through psychoacoustic testing. The fundamentals and upper partials of an attack transient define the coloration of the tone of an instrument. Yet, some instruments can have exactly the same set of overtones and sound the same during the sustain but still sound different when their sound includes the attack transient. Tests have been done where the upper partials of an instrument are electronically time delayed, changing the relative phase of the fundamental to the upper partials. There is but only a slight recognition of the changes being made. However if the changes are made before each sound is struck, which includes the attack transient, the relative shifts if upper partial waveform timing are readily noticed. It was only when the phase alignment of the upper partials were included in the attack transient that synthesized musical notes began to sound real.

If we are listening to a rapid sequence of tone bursts, we want to hear the fine structure of the leading edge of the attack transient. This is where the accuracy or irregularity of the upper partial harmonic structure of the musical tone is best perceived. The musicality revealing fine structure of the attack transient can be masked, obscured by excessive early reverberation, head end ringing. We might electronically be revealing the top 15 dB of the attack transient, as it rises up out of the background din of ongoing sounds that are part of the music. However, due to head end ringing, we might only be able to sonically reveal just the top 4 dB of the attack transient.

The real program material is delivering 15 db of dynamic range but with head end ringing being uncontrolled, the dynamic range is reduced to only 4 dB. Music suffers from a lack of dynamics because of the masking effect due to head end ringing. The music sounds as if it is compressed with a limiter. Secondly, is that we lost the ability to hear the lower 11 dB of the audible attack transient. We’ve lost the ability to hear more of the attack transient because lingering sound from head end ringing has back filled into the short period of electronic silence that actually is in the original music track. Not being able to hear more low level detain in the attack transient limits our ability to perceive upper partial musical detail.

But Why TubeTraps?

And so, finally we have discovered the connection between adding TubeTraps into the front of the listening room and how the treble range clarity is improved, and along with it, musicality, dynamics, imaging and sound staging. It is about sound masking. When we add TubeTraps to the front of the room, we dry up the build-up and storage of perpendicular sound, head end ringing, as it is being created, and as well, during the quiet time between each tone burst.

One might be tempted to say that when TubeTraps are cleaning up head end ringing, they are fixing the room acoustic problem before it was even heard. This is unlike RT 60 adjustments in traditional room acoustic work. Here, the problem has already taken place and all that is being done is to more quickly get rid of the bad sound, which has already been created and listened to.

And finally, we look at the TubeTraps themselves: The things that are doing this work. We need to absorb as much vibration out the head end ringing while it is being created as possible. For this we need the most aggressive sound absorption possible. We have very little time to knock down the level of head end ringing, we’d like to reduce it by 10 dB in at least 1/16th second. This corresponds to a RT60 of 0.3 seconds in the deep bass range in the front of the room compared to 1.2 seconds RT60, later when the whole room dies down.

There is only so much room in the front of the room. TubeTraps are very volumetric aggressive, they provide more absorption per cubic foot of bass trap volume than any other bass trap built. TubeTraps out-perform all other bass traps while taking up less space in the front of the room. Pressure zones are not huge and bass traps don’t work outside of these pressure zones. A 50 Hz pressure zone fills the volume out some 2 feet from the wall. Small, highly efficient bass traps are needed to fit nicely inside bass range pressure zones.