Infinity Infinitesimal Speakers

Once again, I was donat­ed a pair of Infinity Infinitesimal speak­ers by the same gen­er­ous per­son, who donat­ed the “System One” rack and three Nakamichi BlackBox series units from a pre­vi­ous post.

These speak­ers are 4 ohms with a pow­er Rating of 15 to 100 watts RMS. They have an EMIT Tweeter (Electro Magnetic Induction Tweeter) and a 5″ (12.7cm) Infinity/Watkins Dual-Drive Woofer. The woofer has two sep­a­rate dri­ve coils which each have dif­fer­ent imped­ances.
The crossover fre­quen­cy is set at 3,000 Hz and the fre­quen­cy response is spec­i­fied at 65Hz-32kHz +/-2dB. There is a 3‑position switch on the back of the speak­er for adjust­ing the EMIT tweet­er response, along with a 2‑position con­tour switch.

In the user man­u­al it is not­ed that by “set­ting the con­tour switch in posi­tion A’ response below 70 HZ is increased and response between 100 and 250HZ is decreased. This is use­ful for cars or mid bass heavy sit­u­a­tions. In posi­tion B’ the response below 70 HZ is reduced and the response between 100 and 250 HZ is increased. This gives a warmer sound and is use­ful in a home environment”.

Overall the speak­ers were in very good con­di­tion with a min­i­mal buildup of dust. The revi­sion 0.2 speak­ers were built between 1980 and 1982 so these speak­ers are at least 43 years old. Probably a good idea to to check out the elec­trolyt­ic crossover capac­i­tors before con­nect­ing them to an ampli­fi­er and crank­ing them up.

Six screws attach the side wood trim and speak­er grill, and four screws each attach the top and bot­tom wood end­caps. The alu­minum enclo­sure cov­er is attached with six screws of which the cen­ter two screws are short­er than the four screws on the corners.

The dual-coil woofer has two pairs of con­nec­tors, The red-black stripe wires con­nect to each coil from a com­mon point, while the sol­id red wire con­nects to the 4 Ohm coil and the black wire con­nects to the 2.5 Ohm coil.
My resis­tance mea­sure­ments of the two coils were 3.78 and 2.14 Ohms.
The EMIT tweet­er wires (light blue) are direct­ly sol­dered to the crossover board and care is need­ed when remov­ing the cov­er not to stress the wires.

The crossover board con­sists of two induc­tors, two non-polar­ized (bi-polar) elec­trolyt­ic capac­i­tors, three resis­tors, and a film capac­i­tor. On the back side of the board are the ter­mi­nals, two switch­es, and tweet­er fuse.

After de-sol­der­ing and lift­ing one leg of each elec­trolyt­ic capac­i­tor I was semi sur­prised to find that the capac­i­tors in both speak­ers were in excel­lent condition.

The 4.5 uF film capac­i­tors were also test­ed in each speak­er with near-per­fect read­ings.
While I had the crossover boards out I took the time to clean the fuse hold­er, fuse, and switch­es with DeoxIT D5 con­tact clean­er.
After that it was time to clean-up the cast alu­minum case and reassem­ble the speakers.

Reassembly is fair­ly easy and the reverse of dis­as­sem­bly. Redistribute the fiber­fill even­ly around the enclo­sure tak­ing care that it does­n’t con­tact the woofer cone, also take care not to bunch up the wires between the woofer mag­net and crossover board.

For their size the Infinity Infinitesimal 0.2 sound excel­lent and have a clar­i­ty that even some of the mid-sized Infinity speak­ers lack. I opt­ed for the cen­ter posi­tion of the tweet­er switch and posi­tion B for the con­tour switch. They are a lit­tle lack­ing on the very low-end fre­quen­cies and could ben­e­fit from a sub-woofer sys­tem.
My cur­rent plans are to build a low-fre­quen­cy speak­er box / box­es and use the Nakamichi BlackBox EC-100 crossover mod­ule with one of the Nakamichi 420 ampli­fiers for each of the high and low fre­quen­cy outputs.