Two subs increases bass headroom by 6 dB, as well as significantly reduces peaks and nulls from room modes. You can’t EQ out a null, which can be 15 dB or more deep, and worse, the nulls are in different parts of the room, so even measuring them is tricky. Two (or more!) subs fill in for each other, since they are separated from each by many feet (preferably as far apart as possible).
A 6 dB increase in headroom is nothing to be sneezed at. 3 dB comes from having twice the power (two plate amps instead of one) and the in-phase in-room summing doubles speaker efficiency, so the net gain in headroom is 3+3 dB, a fourfold power gain. That’s equivalent to either getting 6 dB more efficient speakers (think horns) or 4X the power amp, assuming perfect loudspeakers with no power compression.
In reality, speakers with efficiencies in the 87 to 90 dB/meter range typically experience power compression with amplifiers more powerful than 100 watts, so a 500-watt Class D power amp is not necessarily the answer ... any loudspeaker will sound audibly "squashed" or distorted if too much goes in. Remember, a 92 dB/meter/watt speaker is only 1% efficient, with the other 99% of those expensive audiophile watts doing nothing more than heating the voice coils.
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Hi Kevemaher!
Hate to tell you this, but loudspeakers are very imperfect devices, and frankly there has only been limited progress over the last fifty years. The field is mostly limited by materials science and the cone and dome materials we have to work with. Software synthesis has advanced crossover design since the crude efforts of the Sixties, but cone materials and magnet design are only a little better.
It’s a fact of life that dynamic compression is a problem with low efficiency loudspeakers, which why they are unsuitable for PA, concert, or movie theater use. Watts are nearly free these days, but a multi-kilowatt amplifier at home will do nothing more than destroy the loudspeaker. It comes down to voice coil temperature. Copper has a temperature coefficient, which means it gets less conductive as it gets hotter. Not only that, the heating/cooling cycle is quite slow, on the order of several seconds, much slower than the dynamics of the music being played.
So in practice, just throwing watts at the loudspeaker does not solve the problem of dynamics. If you really want 110 dB peak dynamics, you need more efficient speakers, not a kilowatt amplifier. But scaling down is a reasonable goal, say, maybe 95 dB peaks. With speakers that are 85 to 88 dB/meter/watt efficient (very typical real-world numbers for audiophile speakers) 60 to 100 real watts should be plenty, with any extra just there for headroom.
If you crave headroom, bigger amps are not the solution. Go ahead, try a 500-watt Class D amp and see if it sounds more dynamic. Maybe a little, but much less than you would expect. On the other hand, try a 95 to 100 dB efficient loudspeaker and you will be physically stunned at the headroom, and your craving for more power will disappear.
What’s going on is the more efficient speaker is throwing away less power in the voice coil for a given SPL level. Hot voice coils are very undesirable, and not just for reasons of reliability. There’s no good mechanism for active cooling, nothing like a tiny fan or anything like that. The heat radiates into the thermal mass of the magnet, which in turn gets hot, and that heat convects into the enclosed air of the cabinet. Don’t worry, there’s no risk of fire unless you feed that 500-watt amp with full power sine waves.
But ... if the speaker is four times as efficient (6 dB higher), guess what, there’s four times less heat radiated by the voice coil for the same SPL at the listening position. And the amp can be four times smaller too. However ... there’s no free lunch. The bass enclosure volume grows in direct proportion to the efficiency (if the F3 low-frequency cutoff is held constant). So efficient speakers are necessarily bigger, or have higher cutoffs in the bass region, or a combination of the two.
These is a long-winded way of saying don’t expect big dynamics from small speakers, no matter what the reviewers say. And 500-watt amplifiers don’t necessarily cure the problem, although you can certainly try and find out for yourself.
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Well, if you want ruler-flat response and headroom, your choice is made for you: professional studio monitors, not audiophile-focused speakers. Audiophile speakers typically have woefully low efficiency, 85 to 88 dB/meter/watt, which is frankly as low as it gets. Worse, the well-known audiophile speakers that get glowing reviews in the glossy magazines also have wacky response curves, which is the worst of both worlds ... low efficiency and boom-and-tweet responses tuned to reviewer’s tastes. Not going to name them, but they’re the brands that appear in $100,000+ systems and are owned by the reviewers.
You don’t want either: ergo, avoid products marketed to audiophiles. I would recommend pro monitors made by UK and European companies, which sometimes have amplifiers built right in ... amps of very high quality, considering the intended market. They have tons of headroom and do not require equalization, and make audiophile speakers sound like a joke. I’ve heard them, and they are very very good.
My personal favorite horn speakers are the Joseph Crowe speakers made in Canada, which have modern horns with flat responses and low energy storage. They’re basically the modern successors to famous vintage speakers like the Altec 604 Duplex and the Valencia and Model 19 (which have devoted followings to this day). I greatly admire Joseph Crowe’s work ... modern, comprehensive engineering, and zero marketing BS. And they are stunningly beautiful as well.
I’ve migrated to the horn camp over the last two decades, but only consider modern computer-designed horns, not the awful horns of the Fifties and Sixties. They combine effectively unlimited dynamics with silky-smooth sound and accurate, electrostatic-like transients. A correctly designed horn should require very little equalization.
Not cheap, though ... the horns alone are thousands of dollars.
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Not interested in Revel, sorry. I would take Amir’s subjective opinion with a grain of salt, for the simple reason I have yet to meet any reviewer that has the same tastes as I do. I’ve been to their houses (not Amir’s) and didn’t like any of their systems. I don’t trust anyone’s subjective reviews. I'm out of sync with most of the industry.
However, that said, Amir’s measurements of pro monitors are right on the mark. Consider those first. They will have better dynamics than audiophile speakers.
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I should mention there are hard limits on the dynamics of a 2-way speaker with a 8" woofer and 1" dome tweeter. The only dynamic step upwards is a 3-way with a 10" or 12" woofer, 4" midrange, and 1" tweeter. But ... unless superbly engineered, 3-ways usually have a poorer sense of coherence, or integration, than a 2-way speaker. A good 3-way is actually extremely difficult, particularly at a moderate price point.
2-ways are far easier (speaking from experience here). A good crossover and well-chosen drivers, and off you go. But getting coherence out of a 3-way is often difficult, because the midrange driver doesn’t quite match the sonic character of the woofer, and worse, the low-frequency crossover falls in a range where subtle differences in timbre are definitely audible. This is why 3-ways at audio shows often sound disjointed and incoherent, instead of like a single source or like a real musical instrument.
A (very) common problem is the 3-way will sound "right" and coherent at a fairly loud 85 to 90 dB show level, but disjointed and confusing at a 65 dB background level. Something to beware of in show demos ... how do they sound when the playback level is moderate? Is the speaker suitable for background music, or not? Big, complex, expensive audiophile speakers often fail this test.
So the choice between a 2-way and a 3-way isn’t as simple as it first appears, depending on your personal tolerance for incoherence. Once you learn what it sounds like, you can never unhear it, and your choice of acceptable speakers narrows quite a lot.
Historical note: Altec always designed 2-way systems if they had any choice in the matter, while JBL leaned towards 3 and 4-way systems. Part of the reason why the midrange is so different between Altec and JBL in their big monitors.
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Kevemaher, I agree about the Zu’s. I’m not a fan of any speaker with whizzer cones ... mechanical crossovers have a whole host of problems that do not respond to electronic correction. (Mostly time-domain distortion and energy storage.)
The latest generation Klipsch Cornwall is actually pretty refined, but is way out of your price range. To be honest, there aren’t many good, efficient speakers in the $5,000/pair price range. Just finding a well-engineered 2-way, never mind the efficiency, isn’t all that simple. I lean towards British products like Spendor, but they aren’t cheap, and usually need a fair bit of power as well.
I admit I am quite biased because I design my own speakers and electronics, and do not follow the audiophile mainstream. I think the last commercial speakers I owned were KEF 104’s in 1975 or so. Everything after that was by my own hand, and I gradually moved away from the direction that audio took in the 1980’s and 1990’s.
Also, I don’t have the skills to design a speaker that hits the $5,000/pair price point. Value engineering isn’t my thing ... others are way better at that.
To loop around to the original question, you should try a 200 to 500 watt Class D amp and see if that meets your desire for more headroom. My guess is that it will simply expose the dynamic limitations of your existing speakers, but you don’t know until you try. How can you tell? Play the music you know well and compare to your existing amplifier, with no change to your EQ setup.
If you gain headroom, great! You just saved a lot of money. Pat yourself on the back and stop right there. Sell your existing amp and enjoy the brave new world of Class D amps. But ... if it’s your speakers that are the limiting factor, well, you need more efficient speakers, end of story.
And I feel really bad telling you that more efficient speakers might make you more dissatisfied with your existing amplifiers. More efficient speakers have a nasty way of exposing electronic colorations ... not just noise and hiss, but Class AB transitions and grain-n-grit as well. That’s why there is a lively market in the 8 to 35 watt power range.
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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.
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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.
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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".
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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.
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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.
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Good news! Nice that the Revels respond to an amp swap. You're probably hearing better current delivery thanks to the massive supply.
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