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### Re: MicMix MasterRoom XL-305 Spring Reverb Clone

Posted: **Sun Feb 03, 2019 8:14 pm**

by **mediatechnology**

**I just finished cutting and assembling springs for a client.**
Sample sound file:

http://proaudiodesignforum.com/content/ ... 5_Demo.mp3
*As a kid doing sound in high school and college I always looked for a stairwell, hall or small room that sounded like this.*

### The equally-tempered tuning of the MicMix Master Room reverb.

Posted: **Wed Mar 13, 2019 6:49 pm**

by **mediatechnology**

**I wanted to provide a mathematical and musical analog to explain the Master Room spring timings.**

The equally-tempered musical scale has a ratio between neighboring notes that is equal to the 12th√2 or 1.059463. (plus change)

An octave spans a factor of two - there are 12 notes in each octave.

For example "A4" is 440 Hz; "A4#" is (440 * 1.059463) = 466.16 Hz.

B4 is 1.059463 * A4# or 493.88 Hz.

**Open the lid of a piano, hold the damper open and sing into it.**

It will be some of the smoothest reverb that you've ever heard.

For smooth reverberation, like that of a piano, the goal is to make the delay timings of the springs equally-tempered in the time domain.

If the springs are equally-tempered in the time domain, they will be equally-tempered in the frequency domain similar to the musical scale.

There's one simple difference: An octave is a ratio of "2."

Springs produce an initial delay we'll call T.

An impulse at the driver will produce an initial impulse in the pickup at T.

That first pulse is reflected off the pickup and back to the driver where it is reflected again back into the pickup.

The initial pulse appears at time T, but the reflected pulse of the second echo has to transverse the length of the spring twice.

The second-order echo appears at time 3T. (T+2T=3T).

**An equally-tempered octave has to span a frequency ratio of 2 in 12 steps; an equally-tempered spring reverb has to span a time ratio of 3 with a number of steps equal to the number of springs.**

The Master Room XL-305 had 12 springs.

For the twelve springs to span a ratio of 3 in equally tempered steps the ratio is the 12th√3 or 1.0959.

If you take the 13.5 ms delay of the first spring and multiply it by 1.0959 you come up with 14.8 ms.

Multiply the 14.8 by 1.0959 and you get the delay of the third spring.

Repeat the series and you wind up with the same numbers in the original table.

**The point is that the Master Room reverb is tuned musically - to an equally-tempered scale.**

*I've been contacted by a manufacturer who may want to make these in a rack unit similar to the original XL-305. Stay "tuned."*

### Re: MicMix MasterRoom XL-305 Spring Reverb Clone

Posted: **Thu Mar 14, 2019 7:53 am**

by **emrr**

well spotted!