What Power Amplifier Should I Buy?

You’ve heard the expression, "A Quart in a Pint Pot"? Yeah, like that. A little woofer sounds little. Maybe a 500-watt amplifier will make the 6.5" woofer sound bigger. Maybe. But I am dubious.

Which is where subs come in. Two of them have twice the radiating area, twice the amplifier power, and twice the first efficiency of a single sub. That’s a 6 dB gain in headroom, which is definitely audible. But ... restricted to under 40~80 Hz, depending how your crossovers are set.

And you have a $5000 (or less) spending constraint. I’ll be honest, if you are not into DIY builds or hacking old Klipsch loudspeakers, your options are limited. Commercial speakers with 15" woofers are usually aimed at the party speaker market, not hi-fi. Studio monitors with 15" woofers are serious money unless you buy used, and you have to be very careful buying anything that’s seen professional use (more likely abuse).

A big problem are the high profit margins built into high-end audio products. 40% for the dealer, and another 5~10% for the regional distributor. If imported from Europe or the UK, another 10~15% for the USA agent. Audio companies need a minimum of a 3 to 4 times ratio between total assembly cost and the retail price to turn a (minimal) profit. This means building at least the wood cabinet in China is a good idea, and maybe the drivers too.

Looked at as a strict cost exercise, a small 2-way sitting directly on top of a subwoofer with a 12" driver, and an electronic crossover between the two of them, is the smart and economic choice. The little guy gets an electronic highpass filter between 80 and 120 Hz to stop the 6.5" woofer moving, which makes it a midrange driver. That also takes the power burden from the mid/high amplifier, so anything beyond 30 watts is plenty. You might even go Class A and enjoy the clarity and lack of fatigue of Class A sound. I am a big fan of Class A operation, whether solid-state of vacuum tube.

Vera-Fi Audio makes a $400 subwoofer with a 12" driver and 500-watt Class D amplifier called the Caldera. From what I can tell, it’s a solid product. I bought one for my son as a Christmas present.

Slap one under each Revel, and get a good electronic crossover between the Revel amplifier and the plate amp of the subs. With the subs directly underneath the Revels, or any other compact loudspeaker, you can set the crossover as high as desired, and decrease the IM distortion many times. With a setup like that, I would ditch the traditional Class AB amplifier and try something else.

@lynn_olson 

I forget if I had posted previously that I am running a single 15" HSU sub right now, 800W plate amp. I xover at 120 Hz using a K231 from Sublime Acoustic. The two channels are combined in the sub.That value is higher than most recommendations. I chose 120 Hz because it helped to minimize a big null in the Revels at 80Hz.

So the load on the Bryston is significantly reduced. I'm not sure how much, but probably less than 50%, more than 25%. I'm thinking about adding a second sub.

I listened to and liked Coherent model 18 on the Montreal Audio show. These speakers are very sensitive and sound very easy and uncompressed (in the way like my Altec 604E) but with deeper bass and more smooth and extended high frequencies. They also have Model15 that should be very similar to model 18.

It is still more expensive than Klipsch Cornwall but IMHO it sounds better.

https://www.coherentspeakers.net/coherent-audio-gra-15-reference

Looks like quite a good loudspeaker, and surprisingly, fairly priced for what you get. Thanks for the link! Always good to see high efficiency speakers with quality drivers.

Definitely a solid alternative to the Tannoy and 604 Duplex loudspeakers.