Loudspeaker Designs and Articles for the DIY Enthusiast
In keeping with the goals of this design, the crossover point was set higher than my normal propensity, with steep slopes. To keep the component count and
costs down, the design is a 2.5 way. I looked into making it a 2.5.5 where the woofers furthest from the tweeter were rolled off more than the intermediate
woofers, but I found no real advantage that would offset the additional cost of the components.
The two woofers flanking the tweeter are connected in series, as are the middle pair and the bottom pair. The 3 pair are then essentially paralleled. This
results in a woofer system minimum impedance of about 5 ohms, and a gain in system sensitivity of almost 10 dB over a single driver for the same excitation
voltage. The source signal is first fed through the common 2nd order electrical low pass filter Consisting of L0011 and C0021. Additionally, a shunt resistor
R0031 provides some response shaping, specifically ameliorating a small response peak around 2.5K. The low passed signal is then sent to the two
woofers flanking the tweeter. This low passed signal is also sent to the lower quad of woofers through a series inductor which counteracts the woofers’ rising
response up to the crossover frequency. The acoustic transfer function of the upper woofers resembles a 4th order LR crossed at 4 kHz, however the
combined woofer response pulls the measured crossover point lower.
A series attenuation resistor R4011 precedes a 2nd order electrical high pass filter, consisting of C3021 and L3031. The transfer function results in a low
Q, 3rd order acoustic roll off at about 3.5 kHz. While I modeled a 4th order acoustic transfer function, which modeled slightly better, in the end the extra
expense of the additional capacitor didn’t provide any useful sonic benefit. While I didn’t run any long term high power tests, I recommend R3011 and
R3012 should be at least capable of 10 watts of power dissipation each.
|A high sensitivity / high SPL
design offered for PA, Music
and Home Theater
Tips and Tricks:
All drivers are connected with normal polarity.
Each woofer pair represents roughly a 16 ohm load, so
16 gauge, or even 18 gauge internal hookup wiring will
be more than sufficient in this instance.
The Common Net provides the low pass filter to cross
over to the tweeter. It connects to the binding posts and
its output feeds the inputs of Net 1 and Net 2
Net 3 is the tweeter network, and it is connected
directly to the speaker binding posts.
Net 2 is the woofer pair flanking the tweeter, connected
in series and wired across the common network.
Net 1 is the four lower woofers and also wired to the
Common Net These woofers can be installed in any
order on the baffle. I made the lower pair a series pair
as the upper pair, and paralleled those two pairs, but
as long as they are series parallel, it makes no
R0031 and R0032 in the Common Net are spec'd as 40
ohm 10 watt resistors in series, for a total resistance of
80 ohms, and 20 watts. This should be about twice the
capability they need at maximum SPL's but may get
warm, so insure they are mounted to obtain sufficient
R3011 and R3012 in Net 3 are 4.7 ohm 10 watt
resistors, paralleled to obtain a value of 2.35 ohms
capable of 20 watts of a power dissipation. At max SPL
these could get quite warm, so take the same
precautions to mount them away from the board, with
sufficient air convection.
To satisfy personal preferences, the value of the
tweeter resistors can be reduced to increase the
tweeter output, but this will directly impact the system
impedance above 5K. Eliminating them entirely for
instance, will result in a system impedance minima of
below 2 ohms at tweeter frequencies.
Fort Tube Amplification Affectionarios:
The impedance normalization network shown below
connects before the crossover, or directly across the
binding posts. This will significantly reduce the
impedance bump at 900 Hz, which may make the
speakers a bit too forward with higher source
impedance amplifiers. See the measurements page for
an impedance plot showing the effects of this optional
circuit. Because of the series resistance, the DCR of
L4011 is of no consequence. Use a 20 gauge here. A
NPE cap is fine for C4011. You might want to parallel 3
10uF NPE's to keep the ECR down, otherwise a single
30 uF poly cap will be fine.
BOM: Click here or on the crossover layout or wiring
images below for larger drawings.
The top two interconnect diagrams below are provided courtesy of Soundslike on the PE forum, followed below by
my originals. All drawings are electrically equivalent, but illustrate slightly different grounding methodology.