Isothermal TubeTrap – How It Works
We developed the IsoThermal TubeTrap to aggressively manage typical HiFi rear wall bounce phase-cancel effects. What we got was a major performance boost across the entire bass spectrum. And we did it without altering the fundamental voice of a TubeTrap.
Check out the absorption data for the new 16″ Isothermal TubeTrap compared to a standard 16″ TubeTrap. Power is doubled in the sub-bass range, while the LF rolloff is extended by over half an octave! The efficiency of the unit is a solid 40% greater all the way up through the “muddy” range of bass.
We were even more impressed when third party theoretical calculations made in ESI’s NOVA software (a multi layered acoustic simulator used in advanced acoustic engineering) corroborated our data to an uncanny degree.
As with standard TubeTraps, larger diameter units reach to lower frequencies. However, with the IsoThermal upgrade, the operating frequency of each size TubeTrap has come to match that of the next model size larger, approximately. This means that if you previously used and loved the sonics of a 16″ TubeTrap, you can now replace your old tubes with new 13″ IsoThermal TubeTraps, with very similar voicing. Better yet, if you always wished you had the space in your room and money in your wallet to fill your corners with deep-breathing 20″ TubeTraps, now you can simply upgrade your system with 16″ IsoThermal TubeTraps to manage that 35 Hz rumble.
What is the IsoThermal effect? The short story begins with the statement that when you compress gas, it heats up, while when it expands, it cools down. High pressure sounds entering the acoustic capacitor of a TubeTrap cause a rise in pressure, or compression. When the air pressure inside the TubeTrap reaches that of the ambient air outside it, the capacitor is essentially “full.” The air then cools off fairly rapidly due to thermal and hydraulic losses, and returns to low pressure, ready to be filled up again.
The frequency of this “filling-up” is proportional to – you guessed it – the frequency of the sound. Therefore low frequency sounds “fill up” the capacitor much more quickly, due to the slowness with which they propagate through the media. A larger capacitor (think of a 24″ TubeTrap) takes the longest to fill, and so reaches the lowest frequencies.
The conversion of the capacitive section of a TubeTrap into an isothermal vessel alters this behavior in a very beneficial way. The low-pressure air inside the capacitor is prevented from rising in temperature upon being subjected to a high-pressure pulse. Through this action, the effective size of the capacitor is increased by 40%, almost as though the IsoThermal TubeTrap is 40% larger than it appears! (This comparison is not quite accurate, since other factors come into play regarding the resistance of the absorptive material among various TubeTrap models, but it is a good approximation).
How do we achieve converting our capacitors into isothermal vessels?
We evenly distribute fibers, a single micron in width, through the air cavity of a TubeTrap, spaced a few dozen microns apart. Such an exposure of surface area provides very rapid, very aggressive thermal action upon the gas molecules, which return to room temperature extremely quickly. This added speed allows the operating frequency of any diameter IsoThermal TubeTrap to be lower than a non-isothermal variety.
Unlike some prior attempts to allow our TubeTraps to reach deeper operating frequencies, the IsoThermal upgrade is the first which enhances deep LF absorption without changing the familiar upper range acoustics of the TubeTrap.
Rear Wall Bounce Benefits
While the IsoThermal TubeTrap is very similar to our Standard TubeTrap, its extended low frequency absorption makes it perfect for treating the rear wall of your room. In any listening environment, the rear wall bounce creates the most bothersome of LF low frequency problems: the phase-cancel effect, also known in HiFi as a “suck-out”. If someone has an 8 dB suck-out at 49 Hz, they usually get tired of hearing the same note drop out of double bass riffs.
The Rear Wall Bounce Explained
Imagine listening to your HiFi outside. Your speaker has a flat frequency response and the sound waves are flying right past you at the speed of sound.
Now imagine someone drops a wall a few feet behind you. Now, the sound that used to fly right past you and out of your life forever bounces off the wall and flies past you again a few milliseconds later.
It was the wall bounce that wiped out your flat frequency response. When the timing of the rear wall bounce is just right, the incoming wave gets canceled by the outgoing wave. The frequency this happens at (Fx) is 282 ÷ D where D is the distance between the listener and the rear wall.
If the reflection is just as strong as the direct, then the phase cancel effect is 100% and the sound level drops to zero. If the reflection is not quite as strong, then the phase cancel effect is not quite 100% and some sound is heard.
