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Phase Plugs: Technical opinions wanted
Wessel Dirksen wrote:
I use loudspeaker drivers with phase plugs frequently because I like them. I have looked into what makes them functionally different from standard moving dustcap models. The primary difference, and the reason for having the phase plug is that it halves the effective diameter thus allowing smoother response an octave higher than what would ordinarily be the case for the loudspeaker driver size in question. 1 Phase plug drivers leak. Ql is always (slightly) lower. Because of this they act like mini ARU's. I don't know what an ARU is, in a closed cabinet it probably doesn't really matter, for bass reflex it probably does make a difference as I recall a recent contribution in another thread by Dick Pierce. 2 They leak through the voice coil gap which appears to improve thermal compression effects and power handling. Can we have that difference in dB's please .... O;-) 3 Sd is slightly lower because the phase plug is immobile This is probably not a large issue, also because not all center domes are rigid, nor airtight. 4 Frequency response is smoother in the passband with slightly less THD. Explained initially. Could this be due to improved excursion linearity? No. I'm thinking this is possibly an effect similar to what the spillhole does in a parachute. No. 5 Frequency response is extended probably due to reduced dynamic moving mass. No. Explained initially, some kind of "semi horn loading" of the sound from the voicecoil edge may also occur, dunno for sure. Is this because of #3 or are there other factors? Two factors seem to me to matter when phase plugs are deployed: the shape of the space between the phase plug and the membrane and the fact that standing waves "across" move an octave up in frequency. In my opinion the occasion for using a unit with a phase plug is when one has to use a larger unit than desirable, most probably for power handling reasons, possibly for downwards bandwidth in case of a midrange unit - that too is mostly a power handling concern. I may be wrong. Wessel Kind regards Peter Larsen -- ******************************************* * My site is at: http://www.muyiovatki.dk * ******************************************* |
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