How to Spot a Psychopath

A reader writes:

I have a quick question regarding speaker sensitivity as I'm somewhat confused. I've always liked nice sound, but it's not a big passion of mine, recently a read a review on a small tube amp and thought that might provide me with a good starting point to sit and listen to some albums at home rather than just listen to things on the train/bus.

Anyway, this small tube amp is cheap and cheerful, putting out a beastly sum of 3.5 watts/channel @ 8 ohms.

So I started to look for speakers to match the amp. If you want something with a high sensitivity, as they recommend, you start running into some big dollars, which to me kinda negates the cheap amp! Reading around people recommend a 90db+ @ 1m set of bookshelf or similar speakers (Even as far as 97db @ 1m!). I happened to come across these large 3 way tower Jamos for a mere $500 delivered, offering a sensitivity of 89db @ 1m, which is better than say bookshelf speakers such as the AudioEngine P4 which are 88db @ 1m!

I guess ultimately I want to know can this tiny amp power such large tower speakers and still be listenable in my small lounge room (in my small apartment)? Also am I right in saying if you got both sets of speakers (Jamos and the AudioEngines) the Jamos would be noticably louder given the same wattage inputted?

Thanks for your assistance and hope you can help!

Travis

First up, I implore you to spend less money and get a proper transistor amplifier. Not because the little valve amp you're looking at has feeble output power - which it does, but that's really not very important - but because tube amps do not actually sound better.

Tubes in guitar amps, that are meant to be driven into distortion, sound very different from transistors, and you may well find yourself turning up a tiny tube amp far enough that it goes into clearly audible distortion, but this is a bad thing. Hi-fi amps are not meant to have any audible distortion, and at normal volumes for normal amps this is the case for all of them. In this situation, tubes and transistors sound exactly the same. Various golden-eared audiophiles insist that this is not the case; none of them score better than chance in blinded tests.

Speaker design can make a huge difference to the sound of a hi-fi system; amplifier design does not, unless there's something terribly wrong with the amp (which doesn't mean audiophiles won't still insist it's awesome).

OK, lecture concludes.

As regards getting decent listening volume from a weedy amp, your room and how close you are to the speakers matters more than the raw loudspeaker efficiency numbers (which are measured with a 1kHz test tone, and so don't take bass or treble response into account; you may prefer quieter speakers if they have a flatter response curve). In your little room in your little flat, you'll probably be able to get away with just about anything.

It's perfectly possible to get room-filling audio from a few watts per channel. That's all that most listening actually ever needs, because of the logarithmic response of the human ear - you need something like ten times as much power to make the music sound twice as loud. Extra wattage is nice to have for parties, or extraordinarily low-efficiency speakers, and an amp with high burst current capacity can make sudden crescendos, the cannons in the 1812 Overture, et cetera, sound better. But low output power is not a big deal for most purposes.

There are, by the way, many perfectly-fine low-wattage amps in the the Class D or "Class T" categories, which even many audiophiles appear to like, possibly because of some warped sense that these amplifiers have as little output power as a frou-frou tube amp, and so they must sound good. There's no pressing reason to get a Class D amp instead of an ordinary one if you're not short of space or want an amp that'll run from 12 volts, but there certainly are a lot of super-cheap 12V Class Ds on eBay these days.

As a general rule, sealed-box loudspeakers have terrible efficiency of about 1% at best, but even they can be OK from a few watts per channel if the room's small and/or the speakers are close to the listener. Ported (or "bass reflex") loudspeakers still only have an audio efficiency of a few per cent, but they beat the heck out of sealed boxes for loudness and can be tuned to have a response hump down around the bass-drum area, which is why practically every low-end speaker these days is ported. There are other designs - transmissions lines, horns, electrostatics and several more - but they're all in the pretty-darn-expensive-unless-you-build-it-yourself category.

You definitely can connect a tiny amp to big speakers, by the way, and that's actually a good way to get plenty of sound from a small amplifier. As a general rule, the bigger the speaker, the higher its efficiency. This is why the best way to upgrade a cheap-'n'-crappy plastic department-store midi system is to replace the standard speakers with much, much bigger ones. You can actually blow up big speakers with a small amp, if you turn it up way past the audible-distortion line and it starts sending some really nasty waveforms to the speakers; generally, this happens at parties when everyone's too drunk to notice how awful the music suddenly sounds (and how it gets progressively worse, as the tweeters die first, then the midranges...). As long as you know that, though, there's no down side to pairing big speakers with a small amp.

If you know which end of a screwdriver is which, I recommend you check out nearby loudspeaker-kit companies; you can get great speakers very cheaply if you do just a little bit of screwing and gluing. Also, remember thrift shops and garage sales; most of the speakers you'll find there will be pretty awful or need significant repairs, but you could just as easily find some nice full-sized three-ways from 1985 whose only problem is that some kid poked the woofer and put a dent in the dust cap. (Which, by the way, won't hurt the sound. If the speaker's been poked so hard that the voice coil scrapes on the magnet, or if it's a fragile little dome tweeter that's been crushed, that's bad. Damaged or missing dust caps on bigger drivers don't matter, though. It's also possible to replace rotted or ripped roll surrounds around big drivers, either with a repair kit that comes with surrounds the exact right size, or more annoyingly with a reel of straight roll surround.)

Try eBay, too, avoiding surprise expenses by searching for speakers within whatever distance you find acceptable of where you live. I'm up in the mountains without a whole lot of nearby options, but searching for used speakers within 25km of my mum's house in the Sydney suburbs shows me some awesome Seventies Technics monsters in good condition, various little brand-name surround-speaker sets that can be perfectly fine even without a subwoofer, some Tannoys that'd be great except some loony will probably bid them up to a zillion dollars, some odd-looking little Mission bookshelf speakers, some nice little Gale bookshelfs too (Gale are sort of the very top of the off-brand mountain; good designs, low prices), and the list goes on.

Above all, don't think that you have to get something with a Major Hi-Fi Brand on it to get decent sound. The Jamos you mention look very nice for the money (not so nice for their much higher alleged list price), but they might not be great for a small room, because they have a rear-firing bass driver and port, so you can't push them hard up against a wall at the back without losing a lot of bass. But there really are a lot of other options.

I dunno - maybe I just enjoy shopping for used speakers in the same way many blokes enjoy shopping for used cars!

And now, let the argument in the comments about valves and transistors... commence!