What Power Amplifier Should I Buy?

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

@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.

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.

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.

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.

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

@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.

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 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?

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".

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.

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.

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.

@lynn_olson 

@atmasphere 

I've enjoyed this discussion.

I have built my own full range speakers in the past. I understand how difficult a task it is.

I can get one of the Hypex modules and check it out. Past that I really can't afford even one item you've recommended. Fixed income , yada, yada.

I do wish I could grab the gear you've recommended, but I just can't.

@8th-note +1

For driving inefficient speakers I bought a Perreaux 2150B. $900 on eBay. Power in watts: 340/680/920wpc@8/4/2 ohms. Weight 65 lbs. This would really wake up your Revel's!

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.

The brands I think of are horrible choices: ZU Audio and Klipsch.

@kevemaher I don't see any problem with the ZUs. They easily keep up with the studio monitors @lynn_olson was recommending. The Klipsch, harder to say; if you want the most dynamics you get one of their horn systems but as far as I can tell they are (IMO) entry level to horns. I should qualify that by saying I've not heard a set in a controlled environment for quite some time. I would not be surprised to find out they are using computer optimization in their horns- anyone who doesn't do that these days is missing a bet!

I'm a fan of horns also; they have controlled directivity so can be used to minimize side wall reflections which otherwise contribute to harshness and of course they are much easier to drive!

You might consider a set of Deadalus loudspeakers which are typically about 95dB (meaning you'll need about 1/10th the power to get the same sound pressure in your room as opposed to the speakers you have now) and are reasonably priced. There are plenty of other choices.

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.

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.

@lynn_olson 

Thanks for the recommendation.

Gee, those are some expensive speakers. My budget is $5K. I need to stay near that price.

What is your opinion of the Revel f208 speakers? I bought them mostly because I liked the small bookshelf speakers they make (now in the lo-fi TV system that my SO likes a lot) and by Amir's g;lowing review on ASR.

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.

@lynn_olson 

@atmasphere 

My thanks to both of you. I agree with all that was said. I agree my speakers are mostly 4 ohms. My previous measurement indicated that even for the 4 ohm load, the voltage I measured at the speaker input terminals (pink noise input) was 3V. This is 9/4=2.25 W. The amp is rated to 180 W at 4 ohms. This is why I've given up the search for a new power amp.

I agree that higher efficiency speakers will provide more headroom.

The brands I think of are horrible choices: ZU Audio and Klipsch. I want a more neutral speaker, not these.

I've not based my speaker searches on efficiency, rather I chose a speaker that was neutral.

Can you suggest a brand that might be more neutral?

I have an FR curve from my last tuning. And I have just discovered what a pain it is to upload a jpg into this forum. So I won't. I'll attempt to describe it to you.

I tuned the FR to have a 1 dB/octave slope from 20-20K Hz (actual REW calc is 1.23 dB/octave). There are no big dips. Deviation from the 1 dB/octave slope is +/- 5 dB maximum throughout the spectrum. The phase plot indicates a problem (room resonance) near 300-400 Hz. But otherwise it is well behaved. I consider this a pretty good FR. I enjoy the sound. My measurements were done at about 85dB SPL, which is near the SPL I normally use for music. And I am evaluating the FR using the VAR filtering REW offers.

In reality, speakers with efficiencies in the 87 to 90 dB/meter range typically experience power compression with amplifiers more powerful than 100 watts,

@lynn_olson To be clear, the amplifier power is only part of that, the other being the lower the efficiency of the speaker, the more thermal compression regardless of the power of the amp. The exceptions of course are ESL loudspeakers since they don't have a voice coil. 

@kevemaher Its a bit of a stretch to call your speakers '8 Ohms'! If you look at the impedance curve on the ASR site, you'll see that other than the box resonance, the impedance curve is closer to 4 Ohms (or less) in the bass region, where the power is most used.

There's a bit of math here; the woofer array of this speaker uses two 8 Ohm drivers wired in parallel for 4 Ohms. Since the sensitivity of the speaker is a Voltage measurement (2.83 Volts at one meter) the impedance of the speaker makes a difference.

So if 2.83Volts into 8 Ohms is 1 Watt, but that same Voltage into 4 Ohms is 2 Watts- a 3dB difference. If you were using the 8 Ohm taps on your Cary, it would have been struggling and no surprise you didn't get that 'tube sound'!

With tube amps the Efficiency spec (1 Watt/1 meter) is more useful since tube amps don't double power as the load impedance is halved. We already know the numbers, you simply subtract 3dB from the sensitivity value if a 4 Ohm load to arrive at the Efficiency, so only about 85dB.

If you want 'more dynamic' I really would consider getting a speaker that is both higher efficiency and also higher impedance (like actually 8 Ohms instead of '8 Ohm compatible' or '8 Ohms Nominal').

You don't lose any resolution by having a speaker that's easier to drive. In fact you may get more since hard to drive speakers cause power amplifiers to make more distortion, and distortion obscures detail. You want your amplifier to be loafing to do its job! That is when it will be the most musical.  

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.

Hey OP,

If your speakers still lack oomph close up it’s not your room for the most part, but it could be your overall levels. Can you post your full range response, including sub and mains?

I should mention, I have a Hsu 15" sub as well and well integrated with the main speaker's it's never lacked for guts.

@erik_squires 

Thanks for the suggestions.

I use REW to characterize and help me improve my sound system. I have extensive traps from a company called "Real Traps". I know where the resonances are. I understand that dips in FR are hard to compensate electronically.

I normally test every component. First, electronic performance and second, in-room performance (listening).

My speakers don't sound any different close up.

What kinds of measurements am I not doing that you think would help me to further understand the performance of my system?

Thanks.

Also, of course, having a room that is too reflective acts as a tone control, making the speakers sound brighter and short of enough bass.

In these cases some damping around the room can really help the bass bloom, in addition to improving imaging and clarity.

A good test for this is to get close to your speakers.  Do they suddenly sound much better, with a better bass to mid and treble balance?  Then it's your room.

OP:
 

Measuring your speakers at your listening room could really help understand what oomph you are missing.

@lynn_olson 

I agree that another sub would help.

I'm confused by your statement about power requirements. Did you mean to say that any amp over 100 W will push the drivers into compression (does this mean non-linear?).  Therefore any amp over 100 W is not recommended for speakers that have the sensitivity that the Revel f208 does.

@erik_squires 

Moving the EQ to the sub path is a good idea. I do however, make adjustments to frequencies higher than the 120 Hz I now use as XO.

What kind of measurements are you referring to?

It's a shame you don't have measurements.  Also, putting an EQ just in the path of your sub is a very good idea. 

You may be suffering peaks that need to be clipped that would let you raise the sub level. 

For an amp with Oomph I like Luxmans, which have amazing bass extension but this may not help you much with a sub and high pass filters.

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.

Both Stereophile and ASR test show plenty of bass down to 30hz. Your 14x19x8h room looks fine, but the other impedance show the F208 is harder than average to drive. Conclusion is that you don’t have enough power. Also, if one defines “average” needed power to run most speakers, seems to be in the 150-300watt at 8ohms range, somewhat doubling down to 4ohms.

If you love your amp, I suppose you could try to fill in the missing bass, but my preference would be to get the bass from the speaker since it’s matched to the other transducers (mid treble).

Maybe you can test by borrowing a more powerful 4ohm amp?

@kennyc 

Just looked at Bryston's published spec. It is rated at 180 W into 4 ohms. So it is rated at 4 ohms. However, I was cautioned that if the impedance was below 4 ohms for a large part of the spectrum, especially in the midrange, there could be problems.

I have never seen any of the overload lights turn red, although maybe that doesn't mean much.

I really haven't experienced anything audible or measured any parameter with REW that would indicate problems.

Am I thinking properly here?

@kennyc 

Thanks for reminding me about this. I've seen the impedance plot on ASR. There is a dip to 3.7 ohms at about 100 Hz and 3 KHz.

I also measured the voltage into the speakers while I had the SPL at the listening position using pink noise. I found that I needed about 3 V, which is about 1 W for 8 ohms and 2W for 4 ohms.

I concluded that I have enough headroom to allow for a little higher SPL and for the low impedance at the above frequencies (100 Hz goes to my self-powered sub).

@kevemaher

Your Bryston 2.5B cubed specs show:

Power Output (per channel): 135W @ 8Ω | 180W @ 4Ω

However, Stereophile F208 review here suggests you need more current:

…. F208 will need to be driven by a good 4 ohm-rated amplifier…..

and that there was plenty of bass. Therefore a more powerful amp with adequate current is likely better than adding subs

Generally, a speaker rated at 8 ohms only hints at being average to easy to drive, while a 4 ohm is harder. But a further look into the frequency vs impedance/phase test/chart of the F208 reveals it needs more power

I'm not sure if anyone is still paying attention, but...

My time with the BP-17 has come to an end. I could not get rid of the sibilance that drives me crazy. The ergonomics are OK, but nothing like the Levinson 38s. I've listed it, but not on Audiogon yet.

Now I use my old, old Paragon System E as a line preamp and a phono preamp. I still use the 38s, but now it is relegated to volume control because it has a remote. The Paragon does not.

This is the best sound I have gotten so far. I have rebuilt the Paragon PSU, replacing all components except the transformer, so it should be good for a while.

The Paragon is a tube preamp with six 12AX7 tubes. I've got new tubes (JJ). It was sold in the late 70s through the mid 80s. I bought mine new.

I'm finished with this quest. Although I have not found the Grail, I am quite pleased with the relics that I have. I've firmly decided I don't need an amp with more power output.

Gotta go buy some records. My gear search has ended.

After all this discussion of power, I bought a Bryston BP-17 cubed preamp. I'll get it next week. This discussion has convinced me that I have enough power from my power amp. So I decided to see if the much newer BP-17-3 can outperform the aged Levinson #38s. I hope so.

@kevemaher - I suspect the crossover is not the biggest issue. I actually own a Sublime K235 (their newer model) and it seems pretty good although I don't currently have in my system. The graphic equalizer has many more lower-quality op-amps and capacitors in the signal path, so I think this is probably the bigger issue. 

If you really need equalization, I'd suggest looking for a decent DSP preamp, such as the Anthem STR or DEQX Pre-4.

Another option is the Danville Signal DSP Nexus. This isn't quite as fancy from a case-work perspective, and the software is quite complex (but there is good support), but the sound quality is pretty good using the latest AKM DACs. I also have a DSP Nexus 2/8 that I've been playing around with. 

And then there are the Trinnov systems although I don't know if their products support a phono preamp or even analog input.

@jaytor Yeah, I have always had concerns about the EQ. But some form of EQ is needed to help tame some of the FR variations from the room.

I have traps which are very effective. I don't need more, except for the floor to ceiling mode. But the "rules" prevent me from doing that. I have worked very hard at positioning the speakers and the sub to get the best FR, but there are still +/- 6 dB variations in the bass. I am restricted to near the present locations. I have tried a miniDSP Flex. It doesn't affect the time domain at all and is barely better than the analog EQ. I ditched that. And I enjoy the idea that I have an all analog signal path (except for the CD/DVD and music files).

So the dBx EQ is a somewhat "necessary" evil. I could live without it, but the engineer in me strives to have as perfect FR and TR (Temporal Response) as I can manage to obtain.

The XO does a very good job, far better than the Rane I once used. I don't like the idea of running the f208s full range and band limiting the woofer. However I haven't tried this in a while. Might be worth a shot.

Are you aware of any reviews on the Sublime XO?

Very helpful advice. Thanks.

My guess is that the dbx equalizer and sublime crossover have more to do with the lack of dynamics than anything else. These are both low cost devices with inexpensive opamps. In the case of the equalizer, you have dozens of opamps and cheap slider pots that you are running the signal through. 

The CODA 07x preamp also has dual XLR outputs (I think it also had an RCA).

It is a warmer tubey sounding preamp than the LA4. I kept the LA4.

The BP17 is great with the 2.5, best match I had with those amps. There is a brand synergy there for sure. I haven’t heard the BP19 or BR20. The Benchmark LA4 is one of the best preamps I’ve ever had, especially as far as neutrality goes. It is a gem and at its price a tremendous deal. But for synergy with Bryston amps I’d probably get a Bryston preamp, if it were me. Plus as you mentioned you get the dual outputs.

Lastly, another option if you want to stick with Bryston and/or save some $$ and shelf space, the B135 integrated has preamp outs.  So you could use that with your 2.5B to horizontally biamp.  

@kevemaher thats why I recommend not using them as monoblocks, which is what Bryston is talking about. In this case they are bridged and each amp becomes one channel and doubles the power into 8 ohms. Try to find specs though on what they put into 4 ohms when bridged. It’s not recommended for speakers like Revels.
If you use one channel though from each amp to power the highs and lows of a speaker you let the amplifier ‘see’ a much easier load than if it was powering the whole speaker, and offering much more headroom. Active speakers (like ATC) have an amplifier for each driver in the speaker. You’re right, and as I mentioned in my first post you need a preamp with two sets of outputs or you can get a y-splitter for your preamp. Incidentally, when I had two 2.5s I tried them in this configuration as well as bridged monoblocks, powering the Revel 228 Be. It sounded ok as monos but not as good as the other way. A bit muddy. And two amps definitely sounded better than one, but the difference was not huge.

I don’t think you could go wrong with a 3B or a 4B, but I was looking at it from a price perspective. Probably cheaper to pick up a used 2.5. But also, from a power perspective, 2 smaller amps may be better than one larger. The 2.5 is conservatively spec’d. It’s basically a 150/300 w amp into 8/4 ohms. So biamping, at 4 ohms you’re getting 300 w/ch into the mid and tweeter, and 300 into the woofers, and each amp channel sees an easier impedance load. With something like a 4B you would get 500 w/ch into each speaker and it will see the combined load of the whole F208.

@scm I deliberately crossover at 100-120Hz because of a nasty room resonance at 40Hz. This creates a big dip at 80Hz that can't be EQed away very effectively. This dip is very strong with the f208 speakers. It is much smaller with the sub. I've placed the XO frequency a reasonable distance from that resonance. I've used REW and other tools to guide me.

I've listened to sub only at 75, 100, and 120 Hz. I cannot hear voices at all. Frequencies below 200 Hz are radiated into a half sphere, with no dependence on angle. How can this muddy the sound?

Of course, I could be wrong. Could you explain how this higher XO frequency creates muddiness? Thanks.

Two subs may be the way to go.

@jimmy2615   @perazzi28 

I've talked to Bryston about bi-amping. They recomment against doing it because the speakers drop below 4 ohms at the xover to the highs (2.2 KHz), although they hedged saying I moght be OK because there's not much power/current needed at that frequency.

I'm not taking that chance.

Biamping will give me more power only if I use two outputs from the preamp. Not very many preamps have two (balanced) outputs. The ML 38s doesn't. But the Bryston BP-17 cubed does!

What's the word on this preamp? I've looked at it before thinking I would try it or the Benchmark LA-4. I wound up getting a Cary tube power amp. That didn't change the sound very much, so I went back to the Bryston amp.

Two things come to mind.  The vintage pre-amp may not be up to the task. Ensure that you choose a preamplifier with 2 outputs.  Ultimately consider bi-amping, running the Bryston's on the low-end and something else on the tweeters.  Could be another stereo amp or monoblocs?  You have options with the Bryston's like "jimmy2615" stated.

I have three ideas for you but one was already mentioned. Adding a second complimentary subwoofer would help. It's adding more watts, more sound and also taking some load off your main amp (which you like). When I did this, it really opened up the overall soundstage and I felt more amp was producing more realistic organic sound. The second idea I offer is to do the first thing (add second subwoofer that is the same model) and add mono amps of the kind you have. Bryston makes good amps, and if they offer mono amps, I think that would keep that good sound you stated you like. Third idea is to change speakers. I know this maybe a less popular idea, but the facts are some speakers are MUCH easier to drive than others and still sound great. I have had my share of speakers and that is simply an easy solution. Good luck.