The DIYRM-A, Two way Dayton RS150P and RS28 Tweeter-60 Page Design Guide - diyAudio
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Old 23rd February 2015, 03:23 AM   #1
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Default The DIYRM-A, Two way Dayton RS150P and RS28 Tweeter-60 Page Design Guide

So, what started out as a quick little writeup about crossovers...turned into a bit more...about 60 pages more.

The DIYRM-A is a Do-It-Yourself Reference Monitor....much along the lines of an LS3/5a. Can be used a bit more broadly and works better with modern music.

The writeup can be found at:

https://dl.dropboxusercontent.com/u/...sion%201_0.pdf



The document covers:

Introduction
Design Goals
Driver Selection
Enclosure Design and Construction
Design Measurements
Crossover Design
Listening Notes
Crossover Power Handling Testing
Conclusion

They are excellent for a variety of applications from near-field monitoring, two channel stereo where space is a concern and surround sound applications, again where space prevents the use of larger designs.

I hope you enjoy.

Scott "SpeakerScott" Hinson
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Old 23rd February 2015, 03:24 AM   #2
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So I got into a bit of a debate/question answer session over PM regarding the number of components in the crossover. One of the concerns was that there was no way that a crossover with this many components would be "linear".

By definition a system with linear components, no matter how many there are is still a linear system. This is a pretty fundamental tenant of electrical engineering rigorously supported by a bunch of mathematics I vaguely remember knowing at one point in my life.

Physical components will always have some amount of non-linearity caused by a junction of dissimilar metals, hysteresis of materials etc. In the DIYRM-A crossover the single most suspect component is the 1.5mH laminated core inductor. The lamination will suffer from both hysteresis and saturation resulting in some amount of distortion.

I can't actually remember seeing if someone has ever tested an iron-core inductor for distortion under multi-tone conditions, so I thought I'd give it a shot.

*NOTE: I did this test using the FFT function of an oscilloscope...which has either an 8-bit or 10-bit front end...I will need to re-do this test with a device with enough resolution to actually measure the distortion induced, since this setup did not have enough capability to actually measure the distortion. That said...(spoiler alert) the distortion was lower than I expected.

So I set up a circuit with a 5mH ERSE air core inductor from the same line as the 1.5mH used in the DIYRM-A, in series with a 4 ohm resistor. I used my Carver TFM-25 amplifier to put a two-tone test signal, total signal amplitude of 17.5VRMS across the resistor of 20Hz and 200Hz, equal magnitude.

The 17.5VRMS across the resistor equates to 4.375ARMS. Into an 8 ohm load that current equals 153 Watts continuous power.

That's a lot for a speaker intended for nearfield use.

No...that's a $%#@$ lot of power for a speaker intended for nearfield use. Well more than you should ever put into a 6" woofer you're sitting within 1-10 of.

Under test I could feel the inductor core vibrating due to magnetostriction, or the property of magnetic materials to change shape under a strong magnetic field.

No single harmonic of the 200Hz or 20 Hz signal came within 40dB of the applied signals. 40dB down is 1% distortion...please trust that at these signal levels the woofer will show well higher than 1% distortion...as will nearly every 6" woofer.

So...in summary, I have even less concerns regarding using a iron core inductor than I did before. To get the equivalent series resistance in an air core part would require a large inductor that would cut into the interior volume of the speaker and be tough to fit on that back panel.

Attached picture of the oscilloscope screen during testing.
Attached Images
File Type: jpg Inductor Distoriton.jpg (641.4 KB, 124 views)
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Old 23rd February 2015, 07:35 AM   #3
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Quote:
Originally Posted by SpeakerScott View Post
I can't actually remember seeing if someone has ever tested an iron-core inductor for distortion under multi-tone conditions, so I thought I'd give it a shot.
Way back in 1988 Dutch mag Elektuur published distortion tests on core inductors. Then modern developments such as Corobar and Ferrobar cores from German distributor Intertechnik showed that distortion with these materials was no issue (<0,4%) with currents related up to 1000W on 8Ω. Nor with laminated cores by the way. All loudspeakers show far bigger distortion figures under such powers.
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Old 24th February 2015, 09:23 PM   #4
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Quote:
Originally Posted by markbakk View Post
Way back in 1988 Dutch mag Elektuur published distortion tests on core inductors. Then modern developments such as Corobar and Ferrobar cores from German distributor Intertechnik showed that distortion with these materials was no issue (<0,4%) with currents related up to 1000W on 8Ω. Nor with laminated cores by the way. All loudspeakers show far bigger distortion figures under such powers.
Is that article online? I'd love to see it, I did a few quick Google searches and came up empty.

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