Bests & Worsts Reviews from Amazon

In this article from the New Yorker, January 28, 2013 “Music To Your Ears.” Daniel Levitin (https://en.wikipedia.org/wiki/Daniel_Levitin) “pointed out that most of the lowest notes on most pianos are actually inferred rather than heard. The soundboard on most pianos isn’t long enough to produce the bottom octave, but the brain hears the right overtones, which the piano can produce, and neurons in the brain begin to fire at the frequency of the missing bass note.” In days of yore (1950s – 1960s) this psycho-acoustic quirk was used in the design of “hi-fi” consoles to produce a semblance of deep bass without actually having an extended low frequency response. And so it is with the Rumble 25. I measured the response of this combo as shown in the graph. The red curve is with all controls set to 12 o’clock. The blue curve shows it can actually produce a reasonably flat response from 90 Hz to 2.5 kHz, +/-3 dB with the controls set as follows: Bass @ 12 o’clock, Mid @ 9 o’clock, High @ fully ccw. This means that it can only reproduce the 2nd harmonic of the lower bass octave (40 Hz to 80 Hz). Because of the normal 18 dB/octave roll-off for a vented enclosure, the 10 dB down point is about 70 Hz. As to the 2.5 kHz frequency, note that the 12th harmonic of a high A (220 Hz) on a bass is 2.64 kHz. The driver is low compliance and the box appears tuned to about 100 Hz, both of which are consistent with the measurements. These curves are smoothed with a 1/3 octave cepstral algorithm to remove insignificant non-audible variations in the measurements. There is a large resonant peak just over 3 kHz = 1/2 the driver diameter. This is tamed pretty well with the High control fully ccw, but still sits almost 7 dB above the average level. Given that the paper cone is quite stiff with no attempt in its design to damp sound waves travelling through the cone material, this resonant peak is not at all surprising. This peak corresponds to the 16th harmonic of the 220 Hz high A on the bass. This peak is probably a good “feature” for the attacks of slap bass (which I don’t do). Otherwise it is actually of little consequence. All this said, the Rumble 25 works well for me. It was low cost, is small, lightweight, and, in spite of lacking any usable output much below 100 Hz, it nonetheless “sounds” like a decent bass loudspeaker. With the controls set as noted for the flattest response, it works well for both my electric and acoustic basses, both of which sound best through a flat response system. The former is an all-original, ’63 Fender Jazz and the latter uses an NS Design “Copperhead” pick-up, a prototype kindly given to me by Ned as a present for mentoring one of his sons on bass. For acoustic gigs, even those using a PA for rooms sized for around 75 -100 audience, the Rumble 25 does the job in terms of sound quality and loudness. For larger rooms and louder gigs that’s why I have my “big” rig. This is custom set-up with a ruler flat response from 40 Hz to 2.5 kHz. However, It consists of a separate EQ, amplifier, and loudspeaker = much more to set up, is five times heavier, and it cost over 20 times more than the Rumble 25. That is what prompted me to try the Rumble 25 for smaller gigs. For what it's worth I play most all genres of music from classical to rock. One feature I like is Fender's built-in, non-adjustable, "Delta-Comp" limiter. This seems to work really well, holding things in check when the amplifier is over driven a bit. Push it hard over the limit point and some high frequency artifacts do appear. However, when running the amplifier near its limits it is virtually unnoticeable except for subtlly limiting the loudness. In spite of its measured performance, I'm giving the Rumble 25 five stars because its doing just what I need it to do.