Acoustic Response Series 707
Overview and Measurements
The Acoustic Response Series 707 speakers are 12" 3-way white van speakers from the early 90's. The manufacturer is listed as Innovative Sound Solutions from Anaheim, CA and the speakers say they were made in the USA! They are called studio monitors but I seriously doubt any studio ever used these as such.
The set I have here came from my uncle who wanted them gone after they had been in his basement for the past couple decades. This set was in surprisingly good shape considering they are 30 years old at this point (serial number shows a '92 build date). He did mention that he really did buy these from a guy selling them out of a van at the time and regrets ever spending any money on them.
Features & Specs:
As mentioned they are a 3-way design and looking at other versions of these speakers online the cabinet finish and woofer appear to have varied over the years.
These cabinets are carpet covered and the 12" woofer has a translucent poly cone woofer with paper dust cap and foam half roll surround. The speakers also utilize a 4" paper cone midrange and 3" paper cone tweeter.
Impedance is listed as 8 ohms nominal and power rating at 125w.
The front label also mentions they are liquid cooled which I take to mean the tweeter and/or midrange use ferrofluid in the voice coils. They also feature two potentiometers on the front to control the level of the tweeter and midrange which are listed as high and low frequency.
The cabinets measure 27.25" high x 15.25" wide x 11.5" deep, they are made from 3/4" particle board and ported with a 2.75" diameter x 5.25" long port tube.
The terminal cup in the back uses standard spring style connectors and also features a resetable circuit breaker.
Digging into the cabinets themselves we find that the drivers are nothing special, in fact the 12" woofer used in these speakers has a magnet comparable in size to that found on many 4" woofers. In addition no damping material or bracing is used in the cabinets.
The pots are listed as 20 Ohm 5w and connected in series only with the tweeter and midrange. Like many cheap designs of this era there is virtually no crossover to speak of. The woofer is connected directly to the input terminals and allowed to run fullrange while bi-polar electrolytic caps are is placed in series with the midrange (10uF) and tweeter (4.7uF) to provide some low frequency protection. Surprisingly both capacitors in this speaker that I opened up measured out to the correct value when I tested them, I attribute that to seeing little use and being kept at room temperatures over their entire life.
I found the circuit breaker on both of these speakers to be adding quite a bit of resistance fluctuating between 2-4 Ohms so I ended up bypassing them before testing.
Here are the T/S specs of one of the woofers, both woofers measured similar but I must have forgot to save the second set:
* This data was exported from DATS the Dayton Audio Test System
* Piston Diameter = 248.9 mm
* f(s)= 28.93 Hz
* R(e)= 4.854 Ohms
* Z(max)= 36.31 Ohms
* Q(ms)= 6.064
* Q(es)= 0.9359
* Q(ts)= 0.8107
* V(as)= 234.1 liters (8.267 cubic feet)
* L(e)= 1.474 mH
* n(0)= 0.5778 %
* SPL= 89.72 1W/1m
* M(ms)= 42.99 grams
* C(ms)= 0.704 mm/N
* BL= 6.367
Stock Crossover Schematic:
Frequency response from the individual drivers:
Note - I took these measurements after the full spin below and had added some damping in the cabinet at this point to see how it helps, this is why the 500-2000hz range looks a little smoother then the main measurements.
Since the woofer is allowed to run fullrange and the tweeter and midrange only highpassed there is terrible comb filtering or interference between the drivers as you move anywhere off axis. Since the tweeter and midrange are offset side to side this even occurs horizontally which would not normally be the case if the drivers were lined up vertically like most normal speakers. Even directly on axis the drivers do not blend correctly as there is no real time alignment or phase correction between the drivers.
I hooked one up to listen real quick and it was pretty clear why my uncle was disappointed in these, they sound pretty terrible, not broken just bad. You move at all and the sound changes drastically as the overlapping output from all three drivers fight it out canceling each other out and adding up at different frequencies. This can be clearly seen in the off axis plots below which are a mess.
The following measurements were performed on my 10' tall outdoor turntable, measurements taken at 2.83v / 2M with the mic aimed at the cabinet center halfway between the midrange and tweeter.
SPL has been scaled 6dB to approximate 2.83v/1M level.
The measurements are gated at 14ms and blended to diffraction adjusted nearfield woofer response below 250hz.
Smoothing applied is 1/48th octave.
The two level adjustment potentiometers on this speaker were centered.
On Axis Response
CTA-2034 Style Spin
Acoustic Response Series 707 Harmonic Distortion at 85, 95 and 100
Compression at 85/95/100/105 normalized against 75dB:
Acoustic Response Series 707 Impedance:
Next I'll see how much improvement can be made with a simple but properly designed 3-way crossover for this speaker.