@weltersys made a comment recently which has confused me. I recently acquired an Audica SUB10 with a faulty plate amp. I discarded the plate amp and made the unit passive. However, the plate amp was housed in its own 6 litre compartment. I used a hole saw to make a 60mm hole through to the main chamber, adding the 6 litres to the main cabinet volume. @weltersys informed me that I'd created a Helmholtz absorber @200hz.
What does this mean?
What are the benefits of making another hole?
What does this mean?
What are the benefits of making another hole?
Surtsey,
Helmholtz absorber means muffler in common terms.
Helmholtz resonators are widely used in noise control. A common example of Helmholtz resonator is the muffler, a device used to reduce the sound emitted by an internal combustion engine's exhaust system.
Part of the incident sound energy is absorbed by the Helmholtz resonator with maximal sound reduction at its resonant frequency.
https://community.sw.siemens.com/s/...he-Transmission-Loss-of-a-Helmholtz-resonator
Your plate amp compartment shrunk since last month ;^).
The absorption/cancellation Helmholtz frequency would depend on the chamber volume (8 liter), the hole diameter/radius (60mm/30mm) and depth, which you did not specify.
I used 25mm as a guess, resulting in around 200 Hz in this calculator:
https://www.omnicalculator.com/physics/helmholtz-resonator
The benefits of making another hole would be the chamber connections would have more area, less restriction and chuffing noises.
I don't know if those internal noises could even be heard through the external bass reflex port (s).
The Helmholtz resonance frequency of the secondary chamber would be higher, whether that is a "benefit", and the depth of narrow band "muffling" achieved would require testing.
Art
Helmholtz absorber means muffler in common terms.
Helmholtz resonators are widely used in noise control. A common example of Helmholtz resonator is the muffler, a device used to reduce the sound emitted by an internal combustion engine's exhaust system.
Part of the incident sound energy is absorbed by the Helmholtz resonator with maximal sound reduction at its resonant frequency.
https://community.sw.siemens.com/s/...he-Transmission-Loss-of-a-Helmholtz-resonator
Your plate amp compartment shrunk since last month ;^).
The absorption/cancellation Helmholtz frequency would depend on the chamber volume (8 liter), the hole diameter/radius (60mm/30mm) and depth, which you did not specify.
I used 25mm as a guess, resulting in around 200 Hz in this calculator:
https://www.omnicalculator.com/physics/helmholtz-resonator
The benefits of making another hole would be the chamber connections would have more area, less restriction and chuffing noises.
I don't know if those internal noises could even be heard through the external bass reflex port (s).
The Helmholtz resonance frequency of the secondary chamber would be higher, whether that is a "benefit", and the depth of narrow band "muffling" achieved would require testing.
Art
Attachments
Perhaps it would be enough to know that energy could be diverted and focussed in the box, and that it would be frequency dependent. It may also be preventing the additional volume from acting as part of the overall volume. Art's calculations show that it's at a frequency of interest.
I'm still intrigued. Is the resonator a benefit? I'd imagine a sub with reduced output @ 200hz would be a benefit in certain circumstances.
I'm asking because I've performed the operation on another cabinet.
I'm asking because I've performed the operation on another cabinet.
It also depends where the resonator opening is. Its effect will be small if it is located at a pressure minimum of the respective frequency. However, there will always be some effect, because it is at the enclosure boundary.
I once tested the enclosure resonance absorbing effect of an internal helmholtz resonator for a vented speaker here:
https://www.diyaudio.com/community/...rbers-and-port-geometries.388264/post-7434471
I once tested the enclosure resonance absorbing effect of an internal helmholtz resonator for a vented speaker here:
https://www.diyaudio.com/community/...rbers-and-port-geometries.388264/post-7434471
Elipson used this technique as well as Fostex ( Fostex double/Elipson triple resonnator).
I heard some Elipson* from circa 1975 using this and the low mid was really really clean for a bass reflex. Very low box coloration.
Fostex goal was to extend in low freq. Elipson to make cleaner low mid. I never heard a Fostex.
*Contrary to BBC, ORTF often used third parties for some of their specifics needs and for loudspeakers it was from Elipson.
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