We should reject hard-to-drive speakers more often

@phusis :

You're welcome, glad you liked it :-)

Mike

@ditusa --

Very good article by Floyd E. Toole - thank you :)

@atmasphere

i completely follow what you are saying... i actually used paul’s zeros years ago when i was trying to run maggies driven by roger mojeski’s rm9 tube amp... you are right, when the amp really can’t handle the load, the autoformer poses no tradeoff... its autoformer or no music...

i was curious on the sonic degradation if used on an easy to drive speaker

also, i had never thought of using them with solid state amps! makes perfect sense, the autoformer provides any amp with greater electrical 'leverage'  irrespective of amp type...  ok i am going to try to find those zeros in my storage closet this weekend, maybe i still have em!

in your experience ralph, when an autoformer is used to better couple tube amps with lower impedance speakers, is there a meaningful sonic penalty?

@jjss49 IME a tube amp often won't deal with low impedances, particularly something like 1 or 2 Ohms. In those cases, there are no tradeoffs- the autoformer makes it possible to drive the speaker where it was not possible before. Its when the speaker is a bit higher impedance (4 Ohms or slightly more) where you might encounter tradeoffs.

BTW this holds true for solid state amps as well. Even though they might easily double power into a lower impedance, that's not the same as saying they sound their best doing that- and you can also measure the increased distortion. Paul Speltz, the guy that makes the ZEROs, has a letter from Steve McCormick (who makes very competent solid state amps) that says exactly that: it sound better driving 4 Ohms thru the ZEROs than doing it directly, despite being able to easily double power into 4 Ohm from 8.

Thinking about this thread for a while and I realize I should have inverted the headline.  What I wish I had written was:

We shouldn't praise speakers specifically because they are hard to drive.  A speaker that is discerning of amplifiers because it is hard to drive is not necessarily any good at playing music.

My bad.

I give you permission to reject hard to drive speakers, on my behalf. Keep up the good work.

@phusis Wrote:

Overly damped (i.e.: "tight") bass isn’t natural bass to my ears, nor is the inverse scenario - it’s certainly about finding the right balance in relation to one’s (p)reference and context.

 Couldn't agree more! See article below:😎

Mike

http://diyaudioprojects.com/Technical/Papers/Damping-Damping-Factor-and-Damn-Nonsense-Floyd-Toole.pdf

@phusis  I couldn't agree with you more about overly damped bass.

@erik_squires wrote:

At some point significantly below Xmax I believe there begins to appear evidence of compression, both within the FR and distortion.

In addition to thermal issues this would only stress the importance of headroom, and also as a phenomenon somewhat equivalent to thermal modulation as an effect that has sonic implications well before the typically assessed limits, both thermally and mechanically. These "grey areas" definitely need more attention. 

@ditusa wrote:

In my opinion, a high powered amplifier that can drive lower impedances will never be a proxy for a speakers lack of true efficiency.

I fully agree, Mike.

@mrdecibel wrote:

The times I used tubes for mids / highs, and ss for bass, I always was aware of the " transition " between the two.

Even via my horn hybrid, actively configured main speakers using different SS amps for the top horn section (~600Hz on up) and bass bin it doesn’t go unnoticed that they "speak" slightly differently when compared to using two identical amps here, not least when the identical amps are bi-amped vertically. The difference is likely somewhat more subtle vs. the scenario of tubes + SS you’re describing, but it goes to show there are points in coherency to gain with extra attention invested here.

The SS amp chosen for the subs below ~85Hz is less critical wrt. ultimate coherency, but to my ears what is critical in this region is choosing an amp that doesn’t go totally bonkers with a damping factor in the thousands as a means in itself, but this is obviously also a matter of proper subs-amp-room matching and what sounds the most musically full and natural here, or whatever one finds appealing. Overly damped (i.e.: "tight") bass isn’t natural bass to my ears, nor is the inverse scenario - it’s certainly about finding the right balance in relation to one’s (p)reference and context.

I have been around the block with Apogee speakers back in the day, including the Scintilla ( I actually owned, for a year, the Duettas ). My question was, as stated, " adequately " drive? I am not fond of tube amps ( low / poor damping factor ), which is a shame, as I own horns. The times I used tubes for mids / highs, and ss for bass, I always was aware of the " transition " between the two. Listen, I have always said, " whatever the listener enjoys, that is fine. I like what I like, and I don’t like, what I don’t. My best, and enjoy ! MrD.

@jon_5912 Wrote:

 High power class D amps more than make up for the difference in dynamic contrast between low and high efficiency speakers. 

In my opinion, a high powered amplifier that can drive lower impedances will never be a proxy for a speakers lack of true efficiency. 

Mike

@mrdecibel  there are a few tube amps that can power the apogee scintilla and full range, most of them have 1ohm taps. There is a guy that used to post on the apogee forum that is powering his apogee full range with Tube Research Labs amps, four monoblocks with 1200 watts total, and he has owned quite a few of the usual suspect solid state amps that are supposed to be used with this type of speaker. He says the tube amps do the best job.

in your experience ralph, when an autoformer is used to better couple tube amps with lower impedance speakers, is there a meaningful sonic penalty? seems to me that what is happening is many many more metal windings are being placed between tube amp's built in transformer (leaving aside the otl’s for a moment) -- and so my guess is that there must be more of the classic wooly, expansive, slightly echo-y transformer sound that is introduced into the music, more or less....

of course, this point and my question is moot for speakers that could never be driven by the tube amp in the first place, but have you done an experiment with a more ’normal’ higher impedance speaker... then adding the autoformer ... then trying hearing the sonic change from the additional transformer present in the chain?

just curious

Ralph, so the answer is = none. My best, MrD.

Back in the early 90s, TAS did a review of our MA-1 OTL amplifier. OTLs are not known for driving low impedances. The reviewer, Steven Stone, had a set of the old Apogee Full Range speakers, which were 1 Ohm. At the time we made an outboard autoformer called the ZMusic (similar to the ZEROs) that we installed between the amp and speaker- the ZMusic had a 1 Ohm tap. The result drove the Full Ranges quite well- despite the impedance, they otherwise were a resistive load and didn't need a lot of power. Steve commented it was the first time he had ever heard the speaker with a tube amplifier. 

Ralph, so the answer is = none. My best, MrD.

What tube amps ( tubes used in the output stage ) can " adequately " drive 1 ohm Scintillas ? I am not aware of any, and would like to know, so I may sleep better tonight. My best, MrD.

If you use an outboard device like the ZEROs then its possible.

My speakers are Kef Blade 1. When my 250/425 wpc amp drove them to realistic levels I thought I was golden, but as time passed and I found low volume listening was boring I decided to borrow a more beastly product and the Mc 611's are staying. I think of the Horsepower vs torque analogy but have no clue what amp measurements would apply? 

If they sound good, get amps which are stable for 2Ohm and below!

close thread 

Eric, that's why I use dealers and purchase from them. They are the ones who do the work as they carry what will work together best and what will be reliable (they can't make money when things break down).  

Too often folks just buy 'top rated' this or that or component of the month.  I found a speaker I love and then I listen to the dealers as well as what the manufacturer uses and it's a start.  

When reading posts online, you see where spec defy reality.  There are just too many factors like room size, ones own hearing, what's in the room (room sound) etc...  Yes, trial and error is a huge part of this hobby isn't it?  I may read threads and mags, but my ears are always the final factor.  Just because a high efficiency speaker seems easy to drive, that doesn't mean it the electronics will sound good with them, just that they can 'drive' them.  I'm not an engineer, nor do I need to be to know what sounds good.  

I don't have the money for trail and error purchasing and selling like so many seem to have (or they do it and keep loosing money on the treadmill) so I audition before purchasing.  It's very rare that I don't and that includes my high priced cables and cords.  That's just me. We all have our own way to purchase and I'm not dissing anyone else's way.  It's all good and it's still all about the music for me.

What tube amps ( tubes used in the output stage ) can " adequately " drive 1 ohm Scintillas ? I am not aware of any, and would like to know, so I may sleep better tonight. My best, MrD.

Why do some tube amps have the power to drive apogee scintilla and full range speakers, the specs certainly don't tell you this would work.

As long as you have the system to match your speakers, you’ll never have to worry about specs and how hard or easy a speaker is to drive.

Well, how exactly do you match those without a lot of trial and error, or social knowledge if you can’t actually rely on specs?

As a consumer this seems like a ton of work. Sometimes this work is a lot more because vendors ( looking at you, KEF ) completely mischaracterize their products.

Just found this thread again.  I completely agree with you about your post Sounds_real!  Too many folks read specs etc… and forget to put a true ‘system’ together.  As long as you have the system to match your speakers, you’ll never have to worry about specs and how hard or easy a speaker is to drive.  

I’ve always marveled at how many folks just assume speakers with lower efficiency ratings assume they are hard to drive etc…, but in fact they may end up being easy to drive in real life.  

there are so many things we should reject. Not sure hard to drive speakers are at the top of my list. 

@steve59,

What speakers do you have?

Mike

@steve59 

Typically, speakers respond to the amount of current available…. Basically the number of electrons instantaneously available when a bass note comes along. Watts does not measure this. Amps do. I remember getting my first truly high powered amp it was 250 wpc… but could put out around 4 amps… that was roughly what my arc welder put out at work. When you have that much power in your amp, it just grabs your speaker and says…”do this”, and compliance is mandatory. It does it. 

@steve59 Wrote:

Shouldn't any amp have power to spare at 1 watt? 

Maybe this will help. Why is the first watt important? See below:

https://www.firstwatt.com/

Mike

@steve59 

https://youtu.be/AhB8uL12gtk

this may help...

... also don't confuse input sensitivity of an amplifier with its power output

I watched the video, not sure PM did the job of explaining the difference between the quality of a Cambridge audio watt vs the BHK.  How would somebody confuse power output with input sensitivity or is input sensitivity a possible reason for the low volume differences I'm hearing?

@erik_squires Wrote:

There’s a reason JBL professional drivers are so expensive, and one of the main reasons that is that they are built specifically to avoid thermal compression even at constant power levels that would make most audiophile systems weep.

100% correct! See articles below: Power compression Vs Thermal distortion in loudspeaker drivers:

Mike

https://pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/Harman_Int%27l/AES-Other_Publications/LS_Heat_Dissipation-Thermal_Compression.pdf

https://www.linkedin.com/pulse/power-compression-vs-thermal-distortion-loudspeaker-alexander-wilson/

@steve59 

https://youtu.be/AhB8uL12gtk

this may help...

... also don't confuse input sensitivity of an amplifier with its power output

This thread got seriously above my IQ this page, I've been able to play in waters previously too deep because my family took care of me in their passing and I was living within my means before that. Anyhow I learned the hard way about how dull and lifeless a pair of speakers can sound without enough juice. 

Here's where I get confused and I hope somebody can explain it in simple terms. Why does huge power matter when I'm listening between .5-5 watts? My speakers sounded dull and lifeless until I turned the volume past 90 db so I swap out my 300wpc and replace with a couple mc 611's and suddenly low volumes sound dynamic? Shouldn't any amp have power to spare at 1 watt?  I've shipped several very highly regarded speakers out because 250 wpc wasn't enough to 'wake them up'. I only mentioned the mac model because IDK if output transformers on a SS amp are a factor in my question.

The alternative is to own amps that will drive anything.  I was lucky enough to buy several Class  A amps that were stable into 1 ohm loads early in my audio hobby - a pair were driving the heck out of Apogee Scintillas at 1 ohm setting. 

which compression per se as a mechanically induced phenomenon isn’t relevant.

@phusis I don’t claim to be an expert in all measurements but this seems not to go along with what I’ve seen or measured.

At some point significantly below Xmax I believe there begins to appear evidence of compression, both within the FR and distortion.  I'm not sure how we could attribute any/all of it to thermal without tone burst testing. Take a look at the SoundStage speaker measurements, just about any of them, since they are the only mag I know of that takes compression measurements regularly.

@erik_squires wrote:

Then I’d really like to know what you think happens when your reach the maximum excursion of a driver. Either they have limited excursion, and therefore compression, or they have infinite excursion and no compression.

That’s indeed what I’m talking about in regards to mechanical compression, but how often do we reach, let alone exceed X-mech? My point is, before that happens the driver’s suspension has a range of motion within which compression per se as a mechanically induced phenomenon isn’t relevant. What’s arguably more relevant mechanically is hysteresis (or magnetically, hysteresis distortion) as that which happens through the range of cone movement, but that’s hardly a compression issue, no?

Although: smaller (<10"), low eff. woofers certainly makes their effort in reproducing the range <40Hz at elevated, but hardly prodigious levels be known, and when you’re used to a pair of corner loaded, high eff. tapped horns fitted with 15" pro woofers in 20cf. enclosures where the cones barely more than a few mm’s at bonkers SPL’s, it’s all the more obvious. With smaller hifi woofer cones working hard it’s likely a combo of mechanical noise and -compression, as well as the onset of thermally induced compression.

I wish I could find them but I remember seeing tone burst tests showing that thermal compression could happen in a tweeter in less than half a second. You could see the first tone burst perform perfectly, and then half way through the second compression sets in.

Interesting; I take it what could also be referred to as thermal modulation as a more dynamic phenomenon. It’s a shame this area isn’t more well documented, leaving us with the more general ’thermal compression’ description and correlation as heat build-up in the voice coils over longer time.

As a mechanical compression artefact this is hardly true for all drivers

@phusis

Then I’d really like to know what you think happens when your reach the maximum excursion of a driver. Either they have limited excursion, and therefore compression, or they have infinite excursion and no compression.

I wish I could find them but I remember seeing tone burst tests showing that thermal compression could happen in a tweeter in less than half a second. You could see the first tone burst perform perfectly, and then half way through the second compression sets in.

"Some compression occurs in planar drivers, including ESLs, because the membranes are stretched across a frame. The mechanical impedance is not linear."

True for all drivers, except perhaps the massive fan subwoofers. I think the difference in measurement/thinking about thermal compression vs. mechanical is that thermal compression changes the behavior of the speaker in time, sometimes within milliseconds, while mechanical compression is always there, until you blow the driver. :)

As a mechanical compression artefact this is hardly true for all drivers. Dynamic drivers have suspensions, and the "stretch" of a membrane here wouldn't occur in a way comparable unless the suspension iself is (getting close to being) mechanically edged out. 

I do think it’s odd audiophiles have fixated on thermal compression, specifically, as being the only one that matters, though I do agree that higher efficiency drivers seem to be at an advantage here.

Question is when, and perhaps not least how thermal compression starts becoming prevalent and an actual audible effect. Thermal 'modulation' may be a better term to explain or correlate what happens sonically; thermal compression impacts SPL envelope and ultimately driver failure, but it also appears to dull transient cleanliness and snap at a much earlier juncture as a very dynamic phenomena. 

There’s a reason JBL professional drivers are so expensive, and one of the main reasons that is that they are built specifically to avoid thermal compression even at constant power levels that would make most audiophile systems weep.

Other pro brands would do equally well, and at a cheaper price, but yes pro drivers are simply on another level here. 

The very thin aluminum foil with considerable surface area is essentially self cooling. This test was extreme.

That was kind of where I was going with that. 99% of the surface area of the conductor is directly exposed to air, unlike an actual coil where you may have multiple layers of windings or the former acting as insulators.

Some compression occurs in planar drivers, including ESLs, because the membranes are stretched across a frame. The mechanical impedance is not linear.

True for all drivers, except perhaps the massive fan subwoofers. I think the difference in measurement/thinking about thermal compression vs. mechanical is that thermal compression changes the behavior of the speaker in time, sometimes within milliseconds, while mechanical compression is always there, until you blow the driver. :)

I do think it’s odd audiophiles have fixated on thermal compression, specifically, as being the only one that matters, though I do agree that higher efficiency drivers seem to be at an advantage here.

There’s a reason JBL professional drivers are so expensive, and one of the main reasons that is that they are built specifically to avoid thermal compression even at constant power levels that would make most audiophile systems weep.

Nope!

get an amp that has enough power and you will be fine

sunfire amps

sanders magtech

odyssey monos platinum parts for low Ohm speakers

While Atmasphere is correct in saying that it is possible to achieve thermal compression in planar-magnetic drivers, in practical terms it really doesn’t happen much, at least not in larger drivers. Being involved with Analysis planar-ribbon speakers for almost 2 decades, I have witnessed some very informative testing. In one test the bass panel was subjected to considerable power at low frequencies to test thermal saturation and the mechanical integrity of the adhesives used. Even beyond its usable max excursion practically no heat was generated (short term). The very thin aluminum foil with considerable surface area is essentially self cooling. This test was extreme.

I would not call the planar foil a coil because it’s not, at least not in the case of the Analysis design.

Some compression occurs in planar drivers, including ESLs, because the membranes are stretched across a frame. The mechanical impedance is not linear. The greater the excursion the more power is needed. Analysis speakers address this mechanically induced compression by using a rubber surround. The design is quite effective in reducing compression. Other ways around this inherent quality is by using VERY large panels or subwoofers.

To the OP, I think people like what they like for a variety of reasons. Some people like large aluminum boxes with tons of power because they think they are cool, others like tube amp with exposed tubes because they think they are cool. Some people are fulfilling their audio dreams from a time before they had the money to buy their dream gear. There are valid arguments for high and low efficiency speakers. There are also trends.

Personally I lean toward high efficiency speakers. Our Apollo series OB line array speakers are high efficiency for several practical reasons, mainly because HE speakers always sound much more lively (linear dynamic contract) to me. Live music sounds lively. It’s one of the main elements that creates the experience. We will be showing our Apollo 9s at AXPONA using 300B amps if anyone wants to hear high efficiency OB line arrays.

If we are talking about the original Apogee true ribbon 1 Ohm speakers, this would be news to me.

Technically Atmasphere is correct, they use the aluminum panel as the voice coil

the reasons for thermal compression in actual voice coil speakers can't possibly apply here.

Hence my use of the word 'possible'... In the case of a magnetic panel speaker like the Apogee, the 'voice coil' for lack of a better term can be heated.  It seems to me that would take some power. If it heats, then less current can be applied because the impedance is higher. That's what causes thermal compression. The thing about thermal compression is that it can happen with individual bass notes; IOW the 'voice coil' is heating and cooling dynamically with the music. If the speaker is using a magnetic principle then this can happen. How much it happens is a different matter.

Technically Atmasphere is correct, they use the aluminum panel as the voice coil,

That’s just it. They are a panel, not a coil. There’s no "coil" there. They are however electromagnetic instead of electrostatic. In addition, the very large size and direct exposure to ambient temperature makes them behave in an entirely different manner thermally than a tightly wound coil in limited distance between round magnets.

I’m going to go with the Wikipedia article, that specifically calls a voice coil as consisting of a former, collar and winding, as proving these speakers have no voice coil to speak of.  Even if they did, the reasons for thermal compression in actual voice coil speakers can't possibly apply here.

https://en.wikipedia.org/wiki/Voice_coil

Technically Atmasphere is correct, they use the aluminum panel as the voice coil, and they still use magnets. I highly doubt that apogee's suffer from thermal compression, the area is much larger to dissipate heat. I listened to a pair of Diva's that were driven by over 2,000 watts and they had effortless dynamics.

Apogees have a voice coil and so thermal compression is possible.

If we are talking about the original Apogee true ribbon 1 Ohm speakers, this would be news to me.

@atmasphere wrote:

The signal itself is the source of dynamic contrast. Loudspeakers only take away from that; if you value dynamic contrast, using a speaker that has the least thermal compression will bring you closer to your goal. In this light, ESLs have the least thermal compression owing to no voice coil at all; a close runner up is higher efficiency loudspeakers [...]

Which only gets you so far being ESL's have the lesser macro-dynamic range compared to horns/high efficiency designs, unless extremely (unrealistically?) large and rid of bass signals. Before thermal compression would ever become an issue with horns, other potential factors like horn material resonance and truncated horn size in the midbass horn in particular would be the primary concerns. While ESL's don't compress per se - and as such some of their implementations can have an advantage over low eff. direct radiating, dynamic driver designs - it's well known that when they limit out they do so abruptly, not least when applied full-range. 

I don't think ESL's are the only loudspeakers that don't suffer from thermal compression, what about full range panel speakers like apogees?

Apogees have a voice coil and so thermal compression is possible.

I don't think ESL's are the only loudspeakers that don't suffer from thermal compression, what about full range panel speakers like apogees?

mrdecibel

2,746 posts

03-29-2023 at 06:31pm 

@bdp24 I have no idea what was said by kenjit, as I pass him over when reading

You're a smart man.

we buy ESL speakers because we like how they sound, realizing we need the right amp...

speakers make the sound we hear in our rooms... and wonderful sound is what we are striving for in our rooms

speakers should be evaluated when performing at their best, which is properly set up in room, driven by a suitable amp to get peak performance (or something very close to it) from them

efficiency of the speaker, and the requisite amp, are all part of the tradeoffs to get the sound we really want

all others things equal, yes, easy to drive, efficient speakers are nice to have... but it is foremost about the sound... that is the big dog that wags the tail of efficiency and amplification