Cube-20X with external speaker?

[YocoYur]

Did anybody tried Cube-20X with external speaker-box?

IMO that amp has potential to push more than little 8" internal speaker.

[randyc]

Why not? There's a cult following of guitarists in the U.S. that love 3 watt amplifiers driving four tens (or similar large cabinets). They are mostly metal people, however.

It's long been known that the entire accoustic output power of a symphony orchestra amounts to about 0.5 watt of accoustic power. Of course the horrible efficiency of loudspeakers requires the drive power to increase by a factor of 100 to provide equivalent volume.

An easy way to improve the listening level of a small amplifier is to increase the area of the speaker cone (some may recall that I posted a l-o-n-g one about loudspeakers some time back). The problem is that the point of diminishing returns is reached quickly. Larger speaker cone and moving coil mass limits upper frequency range. Personally, I LOVE the sound of my 18 inch Showman cabinet but it may not be bright enough for Telecaster afficionados, for example, who enjoy the ice-pick sound.

For jazz, most of us are pretty happy with a wide-range 15 inch speaker although they are definitely not all created equal. There's plenty of internet education available about loudspeaker evaluation and an engineering education isn't required to understand the concepts.

Go for it, Yocoyur !

[YocoYur]

Thanks Randyc!

I wonder, if somebody already tried that, I am interesting about quality of the sound get out that way from Cube 20x and also how loudness increase. I`m thinking about 2x12" box.
Can you tell me, how much the loudness will be (approximately) increase with that kind of box? Is there any formula or system to recalculate this relations?

[randyc]

Well, there are a LOT of variables involved: speaker efficiency, speaker radiating area, human hearing response and more.

But first you should consult the amplifier specifications and make sure that it can drive a pair of 12 inch speakers. You do not want the speakers wired in series and if they are the normal 8 ohm impedance, the parallel equivalent is 4 ohms. It's not likely that the little Cube is configured for that impedance, it's probably designed for the common 8 ohm speaker impedance. This is something that you should check - you may have to employ a single speaker instead of the dual twelves.

Assuming that the impedance characteristics are satisfactory then increasing the diameter of loudspeakers produces an amplitude increase that is roughly proportional to the difference in areas between the two speakers (making the doubtful presumption that speaker effeciencies are identical). As an example, an eight inch speaker has a circular (not conical) area of about fifty square inches while a twelve inch speaker has a circular area of around one-hundred thirteen square inches. That's a ratio of over two to one which superficially sounds impressive.

But human hearing characteristics are logarithmic, not linear, so double the accoustic pressure level is just noticeably detectable. For a human to detect pressure (or power) difference that the brain interprets as DOUBLE, requires an increase in pressure level of about three times.

Note that this is a subjective topic and there are so many variables that it's not possible to provide firm advice. But intuitively, a significant increase in level probably wouldn't occur unless you could use the dual twelve configuration that you're proposing.

If you know the brand and model number of the speakers, you can look up the SPL (sound pressure level) specifications. For example, your eight inch speaker might have a SPL of 92 dB and each of your twelve inch speakers may have a SPL of 96 dB. Doubling the SPL produces an increase of 3 dB so the two twelves together would result in a SPL of 99 dB.

The difference in SPL between your eight inch speaker and the dual twelves would be 7 dB - which is definitely noticeable but would NOT sound twice as loud as the single eight inch speaker.

Among the many variables, by the way, is WHERE the manufacturer chooses to specify the SPL specification, since it is strongly dependant on both frequency and the speaker mounting method is undefined (the test is usually performed with speaker mounted to a baffle but not in an enclosure). Sealed cabinets and open-back cabinets respond quite differently to different speakers.

If you are technically inclined, there are many free software suites on the internet for evaluating speakers and enclosures provided that the loudspeaker manufacturer specifies the "Thiele-Small" characteristics of his product.

In addition to the above confusion, solid state amplifiers react to impedance mismatch (the speaker impedance versus the amplifier design impedance) very differently than vacuum tube amplifiers. If your amplifier is designed for a 6 ohm speaker (not uncommon for small solid-state amplifiers), then it will be louder with a 4 ohm speaker load but the amplifier will be overstressed and get hotter.

This may not be a problem if the amplifier is equipped with a thermal shutdown feature (also not uncommon for solid-state amplifiers). Depending on how loud and for how long you play, you may never experience a problem with a lower impedance speaker but I'm advising you that there IS a risk.

Operating with a loudspeaker impedance HIGHER than the amplifier is designed for will usually produce less volume and greater distortion but there is much less risk of damaging the amplifier.

Good Luck,
Randy C

[YocoYur]

Thanks Randy a lot for this. If I`ll try Cube 20-x with ext. speaker, I will make a report.

Until than I`ll waiting for some other owner experiences with amps like Cube 20-x