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During the last room acoustics project i also came across the need (or more to say: will) to calculate a primitive root diffusor. The seemingly most used online calculator for these good looking devices is the one written by the austrian producer/DJ Oliver Prime (www.oliverprime.com/prd/). This one is great already, but the user is left alone in finding the usable coprime pairs specified by the corresponding RPG patent (US Patent #5401921), or the primitive roots which can be used.
This new PRD calculator comes with the following features:
Calculation of PRD diffusers (2-dimensional) according to the RPG patent 5401921
All values which are not very common for audio people (the mathematical stuff) just has to be chosen by the user from a set of proposed options in a range which can be chosen. For example, most of the time we have an expectation about the overall size, so the number of columns/rows are expected to be within a certain range. This is done by letting the user enter the desired range for columns/rows first, the calculator then presents the possible combinations (coprime pairs), and you just have to select the right one for your application.
Every change of any value or checkbox instantly is reflected in the overall result at the moment the user leaves the changed input field etc. This way you can just play around until the result is satisfactory, as every input calculates a valid PRD diffuser.
There are several options (buttons) which enable the user to start with any value he wants to start with first (as a given), and then adjust the other parameters which are not critical for the purpose accordingly.
There is a little 3D visualization included, which can also be rotated with the mouse 🙂
Like in the old calculator, the shopping/parts list is also displayed, along with the plan for assembly.
Inspired by the great experiments done by Gernot Ebenlechner (G.E. on Gearslutz), i did some own tests with this bass trap design he babtized „EPA’s“ (Enhanaced Porous Absorbers), as described in these two threads:
The design described works with the well-proven porous absorbent Caruso ISO-Bond WLG 035, which is known for having superb deep bass absorption properties when used in higher thicknesses. The experimental results of G.E. showed that, by adding a 2mm DC01 steel plate sandwiched by the ISO-Bond, the deep bass absorption below 100Hz is getting pretty effective also with overall thickness down to 10cm. Details about the construction are published by G.E. in the threads linked above, also a in-detail documentation about the construction of our new mixing room is published on this website soon, therefore i just outline the major results in this post – which are pretty astonishing 🙂
These are the before/after spectrograms (made with REW) of a test with an empty small room, measurement microphone in the upper corner of the front wall, the speaker (a Tannoy System 12 DMT) at the corresponding lower corner, and the installed bass trap (if present) at the opposite corner of the mic/speaker. The reduction of the 50Hz mode (1-0-0) is pretty drastic for a bass trap just 10cm thick!
ps.: The foto is taken in another room with the monitor placed differently than during measurement, but the EPA construction during the test was exactly the same.