Have seen a lot of discussion about speaker damping and many applications seemed to be ad-hoc. Admittedly, even the use of damping for Directiva r1 was more of a guess than I was comfortable suggesting. Having acquired many different types of materials from different DIY projects, I felt it was time to better understand how effective they are. There are many ways a speaker can resonate and potentially affect the sound quality. The driver(s) have resonances, and the cabinet and various parts (panels, vents, terminals, etc.) can resonate at many frequencies (and harmonics of those frequencies).
This study is mainly targeted to see how effective various damping materials are for a target speaker. As is relatively inexpensive and had some extra parts around from the one I built for Amir's testing, the target speaker is the Dayton C-Note. The C-Note has some good sound qualities but also exhibited some issues common to many speakers. That said, it is a small speaker and so panel resonances are not a major focus. Also, most materials used for panel damping require adhesives and would require more resources and testing to ensure each speaker cabinet was acoustically identical.
The test setup uses REW, a UMIK-1 microphone, my MOTU m4 and a Hypex amp to drive the C-Note speaker, Measurements were taken in nearfield at the center of the C-Note port (zero distance). The measurements are unsmoothed and gated at 200 ms (which yields 5 Hz resolution). Here is the initial measurement for the undamped C-Note as supplied by Parts Express....
Can see the primary output of the port is around 38 Hz using the specified 7 inch port length. While there is another slight resonance just below 300, the real concerns are the ones around 600 to 1600 Hz. Some of this is low enough in frequency and high enough in magnitude to flow around the baffle and shows in Amir's Klippel measures. As we get much above 1000 Hz or so, the speaker more fully transitions to 2pi space and you are less likely to hear those resonances. Still might explain rippling between 1000-2000 Hz in Amir's results. The woofer has some known ringing around 7 kHz but the crossover kicks in and does not make an appearance (and at over 40 dB below is not audible and so did not show it).
Next will look at how adding some Sonic Barrier (per the designer) affects the port output.
This study is mainly targeted to see how effective various damping materials are for a target speaker. As is relatively inexpensive and had some extra parts around from the one I built for Amir's testing, the target speaker is the Dayton C-Note. The C-Note has some good sound qualities but also exhibited some issues common to many speakers. That said, it is a small speaker and so panel resonances are not a major focus. Also, most materials used for panel damping require adhesives and would require more resources and testing to ensure each speaker cabinet was acoustically identical.
The test setup uses REW, a UMIK-1 microphone, my MOTU m4 and a Hypex amp to drive the C-Note speaker, Measurements were taken in nearfield at the center of the C-Note port (zero distance). The measurements are unsmoothed and gated at 200 ms (which yields 5 Hz resolution). Here is the initial measurement for the undamped C-Note as supplied by Parts Express....
Can see the primary output of the port is around 38 Hz using the specified 7 inch port length. While there is another slight resonance just below 300, the real concerns are the ones around 600 to 1600 Hz. Some of this is low enough in frequency and high enough in magnitude to flow around the baffle and shows in Amir's Klippel measures. As we get much above 1000 Hz or so, the speaker more fully transitions to 2pi space and you are less likely to hear those resonances. Still might explain rippling between 1000-2000 Hz in Amir's results. The woofer has some known ringing around 7 kHz but the crossover kicks in and does not make an appearance (and at over 40 dB below is not audible and so did not show it).
Next will look at how adding some Sonic Barrier (per the designer) affects the port output.
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