(Apr 1, 2013)
1" Titanium Compression Driver
PH715 Asymmetric horn
(Bi-Amp) at 1,500Hz (18dB/oct)
In the Nightingale-IV,
the Dayton RS180s 7" is replaced by HiVi's
M8a. With a slightly larger woofer, I hope to get
a better bass response. The horn section remains
the same, a Pyle PH715 Asymmetric Horn coupled to
a Selenium D220Ti 1" Compression Driver.
buyers should be aware that the mounting holes of
the PH715 do not comform to standard 3" hole
to hole spacing. New holes must be drilled to mount
a "bolt-on" driver.
I measured the M8a, my
Thiele & Small Parameters differed greatly
from HiVi. After much thought, I eventually decided
to load the M8a in a Closed Box of 20L. Though it
may not go as low as a Bass Reflex, I have the comfort
of knowing that the mid-bass will be preserved.
aspect that was rather disconcerting is the cone
breakup. A sharp peak just after 2,000Hz is visible
in HiVi's Frequency Response (Fig 1). Obviously,
this driver is meant to be used in a 3-way more
than a 2-way.
I would usually pick a frequency one octave, if
possible, two octaves away to avoid that peak from
intruding into the highs. Unfortunately, it would
mean using a 2" compression driver which I
want to avoid.
1 - HiVi M8a Frequency Response
out the M8a
plots below (Fig 2) are the In-Room responses of
the M8a, taken on-axis with the cone. The Black
trace is the M8a without any crossover. The cone
breakup is indeed recorded at just beyond 2,000Hz.
The Red trace is with the Synergy crossover at 1,750Hz.
I'm not too comfortable with this frequency because
it doesn't seem to suppress the peak enough. The
Blue trace is at 1,500Hz. Now, this looks much better.
I can of course, use a notch filter but that would
incur additional cost. If the offending peak can
be suppressed by judicious selection of crossover
corner frequency, so much the better.
2 - M8a In-Room Frequency Response at 1,750Hz and
meter - On-axis with M8a
M8a with D220Ti / PH715
Red trace below (Fig 3) is of the M8a crossed at
1,500Hz to the D220Ti/PH715. As with the Nightingale-III,
an 8.2uF capacitor is in series with the D220Ti.
No other passive components are used. The compression
driver is connected in Reversed Phase. Measurements
are taken with the microphone placed On-Axis with
3 - M8a with D220Ti/PH715 crossed at 1,500Hz (18dB/oct)
Compression Driver with 8.2uF (connected Reversed
1 meter - On-axis with PH715
the Nightingale-IV for Music