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

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