What Power Amplifier Should I Buy?

Oh, by the way, the Klipsch Cornwall is the most "civilized" of the classic Klipsch speakers, and in stock form has more or less flat response. The latest model is expensive, but there are lots and lots of beat-up old ones around (which are cheap), and modifying Klipsch is a cottage industry.

Basically, you put in felt lining and fiberfill (or use NoRes automotive damping pads), reinforce the cabinet a little bit, and use better caps in the crossover. That’s it. All done. Way better than any speaker with a whizzer cone. And super efficient around 95~97 dB/meter/watt.

I once owned the little brother, the Klipsch Forte, which has a 12" woofer and is about 2/3rd’s the size of the Cornwall, and that was pretty decent too, after I modified it with good caps.

I was surprised how flat I got the Fortes after I twiddled with the crossover a bit. Since you’re into EQ, you might also be surprised what you get with an old Cornwall or Forte.

By contrast, modifying classic Altec or JBL is a serious project that requires serious crossover mojo. Not for the faint of heart and definitely not for the beginner. Klipsch is way easier since they are basically simple speakers that respond positively to even minor upgrades. You might question the horns but the 12" or 15" woofers are the real deal.

P.S. Beware of modifying Klipschorns, LaScala’s, or Heresies. Those have much more uneven responses and modifying them changes their basic character. I think Paul Klipsch wanted to try his hand at a mainstream "hifi" speaker, and he came pretty close with the Cornwall. In other words, they’re 80% there, and just need a little nudge to get to 90% to 95% there.

Hi @lynn_olson 

Are you familiar with JBL 4430/4435?

https://www.audioheritage.org/html/profiles/jbl/4430-35.htm

They have a smooth sounding horn section compared to other vintage speakers.

Sorry, not a JBL guy. "Smooth" is not the word that comes to mind when I think of JBL. They have their fans, I’m just not one of them.

I prefer modern horns if possible ... see the Australian AH425 Azurahorn, which was designed by Bjorn Kolbrek using BEM computer simulation. The AH425 simulation became part of his Doctoral Thesis in Norway, and the physical horns were built in Perth, Australia by Martin Seddon.

Azurahorns

AH425 Frequency Response

They were part of a project to design a modern successor to the Altec Model 19, which I have set aside, but the AH425 was a nice spin-off from the project. The other half of the project was an Altec/Great Plains Audio 416 woofer in a 4 cubic foot closed box with a crossover in the 640~800 Hz range.

Going back to the OP, I still think, given his budget constraints, he should try a much more powerful amplifier (not just another 30 watts) and see if dynamics improve. I doubt it will, but I’m not the OP, and the experiment should be tried. In my experience, speakers usually limit the dynamic range of a system, not the amp. The true Theile/Small efficiency of the woofer typically sets overall speaker efficiency, and that in turn sets the overall system headroom. To a first approximation, 1% conversion efficiency in the T/S sense results in 92 dB/meter/watt efficiency for the bass driver, which is almost never attenuated in the crossover.

From previous conversations, the T/S efficiency of the compact Revels appears to be in the 0.2% to 0.3% range. This would imply only 10 watts/channel are needed to reach 95 dB at a one meter distance. Allow another 2X for a 2 meter listening distance, and maybe we need 20 watts/channel.

Anything more is just there for additional headroom, and to allow for the occasional transient peak. The fact that a 100 watt amplifier is falling short points to marginal amplifier design, or the speaker itself running out of steam. More likely it’s the speaker, if a 6.5" woofer is all we have to work with.

Speaker manufacturers like to brag about "long excursion", but an old rule of thumb in the loudspeaker biz is: "If you can see the cone moving, it’s distorting". Still true today.

One of the jokes we used to tell back when I did this for living was: "If the amp is bigger than the speaker, something ain't right".

@lynn_olson 

I will probably buy the Buckeye Hypex NC502MP 2-Channel amp. Spec is 500W in to 4 ohms at 1% THD. I'm not happy with that way of specifying, but the power should be far more than the Bryston and should allow me to discover what more headroom will get me

I notice that in your last post, you seem to be implying that the amp may not be the problem. I've come to that conclusion. So the upcoming test will probably highlight any deficiencies in the Revels.

I am quite comfortable using REW. Is there a measurement in REW that will highlight the speaker non-linearities? Distortion perhaps?

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.

Hi @lynn_olson ,

In the Montreal show were the Coherent speakers Model 18 (18" coaxial Radian driver with Neodymium magnet and aluminum diaphragm).

In 2022 they used a 300B Allnic Audio T-1500 300B SET stereo amplifier. This setup sounded the best. And in my opinion it was the best on this show.

In 2023 it was M-2500  Allnic 300B Push pull monoblocs. It sounded good too. But I liked the more warmish SET sound.

And in 2024 they use other speakers with 12" coaxial and 2x 15" woofers with transistor amplification. I didn't like this sound at all.

Why do most modern 15 inch drivers like modern JBL and Tannoy are made for very powerful transistor amplifiers?  These drivers have a very high moving mass and are designed to survive very high power. It is done in compromise in sound quality and sensitivity. It shows the big audio industry players ignore low power amplifiers lovers.

@lynn_olson 

I've dragged my Levinson no 27 Power Amp out of storage. It is now 30+ years old. I have had it for 20 years. A few months ago, I replaced all the big power supply caps (8 of 'em) with brand new ones and thoroughly cleaned it up. I broke the caps in with about 50 hours of music. But then I put it away. This amp is rated minimum 100W into 8 ohms and 200W into 4 ohms. No 4 ohm speaker limitations. It weighs about 90 lbs.

I've had about 1 hour listening, so maybe too fresh. My initial reactions were that voices were better articulated than the Bryston. Dynamics might be better. I need more listening time, but I am pleased with the change so far.

Good news! Nice that the Revels respond to an amp swap. You're probably hearing better current delivery thanks to the massive supply.