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Current Trends in multi thousand dollar speakers

Have any of you been paying attention to the current trends in larger multi-woofer speakers that cost multiple thousands of dollars? So that many of you can follow along, i'll use the Legacy Focus 20/20's at $6K, the Piega C8's at $15K and the Aerial 20T's at $23K as points of reference. All of these have been reviewed in Stereophile over the last few months. If you're not familiar with these, all of them are vertical dynamic designs using multiple woofers in vented cabinets.

If you look at the response of of these speakers, they all have very pronounced bass peaks with elevated low frequency plateau's taking place. Of these three, the Legacy's are by far the worst of the bunch. Not only do they diverge from neutrality the most ( +7 dB peak @ 100 Hz ), their elevated bass output or "low frequency plateau" levels out at 40 Hz and at 400 Hz. That is over 3+ octaves of "extra" output that wasn't on the recording. Above 400 Hz, the output levels off with very noticeable rippling slightly above that point in the midrange and multiple large peaks with a dip up in the treble response. Below 40 Hz, the output drops like a rock. The reason that the plateau levels out at 40 Hz is because of the associated sharp roll-off associated with vents below their point of resonance.

To sum things up, this speaker, which Paul Bolin raved about in Stereophile, is anything but "smooth" or "linear" in reproduction. As can be seen in the graphs, there is a very definite "boom & sizzle" type of response taking place here. As a side note, i found that the Legacy Signature III's showed a similar large bass peak centered at appr 100 - 110 Hz, so this would seem to be a consistent design attribute / "house sound" / "family voice" to Legacy speakers.

Moving onto the Piega's, their overall response looks to be measurably smoother than the Legacy's from the midrange on up. As far as bass goes, the Piega's peak occurs at an amplitude of +5 dB's and is centered at appr 85 Hz. Their "bass plateau" is quite wide, actually just as wide as that of the Legacy. Both show the same appr "elevated output" aka "bloat" from about 40 Hz to 400 Hz. Much like the Legacy's, the Piega shows the typical sharp roll-off below 40 Hz due to the output of the vent being out of phase with that of the undamped woofer. Even though both speakers show very similar plateau's and a similar F3 ( -3 dB point ), the Legacy's bass plateau has both a higher peak and a higher average.

Moving up to the $23K price range, we've got the Aerial 20T's. Similar to the Piega's, the Aerial's are reasonably smooth in response from the mids on up with a few low amplitude peaks and dips. Side by side comparisons though, it would appear that the Piega's are a little "flatter".

When it comes to low frequency performance, the Aerial's produced a +5 db peak centered at appr 60 Hz. Of the three speakers mentioned here, the amplitude of the peak is the same of the Piega's ( +5 dB's ), which is much lower ( 66% reduction ) than that of the +7 dB peak of the Legacy's. Even with this 66% reduction of the peak amplitude at resonance compared to the Legacy's, we are still talking about a divurgence of +5 dB's here!!!

As far as the "bass plateau" goes with the 20T's, this speaker is much more linear than either of the above. While the Aerial's also level out at appr 40 Hz and drop like a rock below that point, the upper end of the bass region is MUCH smoother. Whereas the others were contributing added output up to appr 400 Hz, the Aerial's are leveling out at appr 120 Hz or so. In effect, the Aerial's appear to offer the most controlled bass with the least amount of bass colouration. Then again, they are by far the most expensive also.


As far as low frequency extension is concerned, the Aerial's resonance peak is centered the lowest of the three i.e. 60 Hz for the Aerial's vs 85 Hz for the Piega's and 100 Hz for the Legacy. Even though the Aerial's have a resonance that is 25 Hz below that of the Piega's and 40% lower in frequency than the Legacy's, all of their -3 dB points are within a very few Hz of each other. While the graph's aren't completely legible, it appears that the F3 ( -3 dB point ) for all of these speakers are right about 34 - 38 Hz or so. How do such different designs achieve similar F3's? It has to do with the tuning of the vents and the amplitude of the peaks at resonance.

By creating a huge peak at resonance, it takes longer for the amplitude of the signal to fall off. As such, the Legacy's much larger peak at resonance allows it to achieve appr the same F3 on paper that the other designs worked harder to achieve. As such, were the Legacy's designed this way because they like the sound of massive bloat? Were they designed this way so that they could claim a lower F3? Could it be a combo of the two? We'll probably never know.

What does all of this add up to? Judged in comparison to each other and strictly talking about bass linearity, the Aerial looks the best on paper by far. Why just on paper? Because we have to factor in the added gain associated with in-room response. Our ears hear the entire presentation i.e. the speaker and how the speaker loads up / pressurizes & excites the room. As such, what looks the best on paper may not be what you like the most in your room. If you're room is properly set-up, the results on paper and the results in the room should pretty well jive. That is, at least as far as frequency response & linearity go. There are a LOT of other factors going on here though, not to mention personal preference.

What happens if the room isn't properly set up? Compared to anechoic responses, all speakers will have greater output / added extension when placed in an average listening room. While specific speaker placement comes into play in terms of the extension and amount of boost, most rooms will produce maximum ouput somewhere in the 50 - 80 Hz range. Obviously, this varies with the size and shape of the room.

The net effect is that these speakers are going to produce even MORE bass than what they already show in these graphs. Not only are we picking up low frequency output from what is called "room gain" ( "cabin gain" in a vehicle ) by pressurizing the room, we are also going to be exciting the resonances of the room too. All of this adds up to GOBS more "apparent bass". Add in the fact that this bass lacks speed and control* and you've got "bloated, ill-defined thump" running rampant.

Other than that, one has to wonder just how extended the bass response of these designs would be if they didn't have such HUGE peaks? After all, the higher the peak at resonance, the lower the -3 dB point of the speaker appears to be. Do we have to add "bloat" to get extension? How do you get around all of this and still keep good sound? That's easy but it is a completely different subject : )

What i want to know is, what do you folks think about this type of performance at these price levels? Is there anything that we can learn from this? Do we see a specific trend taking place here and in other parts of the audio market? Inquiring minds want to know : ) Sean
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* vented designs all suffer from a lack of transient response, increased ringing, over-shoot and phase problems. In this respect, a well designed port is typically "more linear" than a passive radiator.
sean
audiokinesis
2,753 posts
 
Sean, methinks you paints with a wide brush:

"For sake of clarity, these figures are based on the accepted principles that vented systems fall at a rate of 24 dB's an octave and sealed designs fall at a rate of 12 dB's an octave..."

Either type can be tuned to have a different rolloff rate in practice. And especially in the case of a vented system, it's the exceptions to the 24 dB "rule" that are by far the most interesting.

Note that, given a 90 dB reference level (longterm exposure to which will lead to permanent hearing loss), a signal that's -12 dB at 25 or 30 Hz isn't much above the threashold of audibility. Of greater real-world interest would be the -6 dB frequency, in my opinion.

It really is quite easy to design a vented system with an approximately second order characteristic over the first octave or so of rolloff, below which what's happening is of relatively minor audible significance. Such a system would be about twice the size of a Qtc = .7 sealed box using a comparable woofer, but would have about 1/2 octave greater extension. Obviously this would involve a much lower tuning frequency than would be the "rule" for that size vented enclosure. But it's often the exceptions to the rules that are the most interesting.

If we're comparing equal-size enclosures, both with an approximately second order characteristic over the first octave or so of rolloff, having very similar -3 dB, -6 db and -12 dB points, then the optimal woofers would of course be very different. The sealed box woofer would be approximately 1.8 dB less efficient than the vented box woofer. In addition, the vented box woofer's parameters would be better suited for good midrange performance, which might make a significant difference in a two-way system. I know it's not quite as simple as I've made it out to be here (I've ignored the issue of minimizing coloration from the vent itself, for example), but my point is it's quite possible to design a vented system that embodies many of the desirable characteristics of a good sealed system.

Duke
sean OP
6,231 posts
 
Duke: How many "exceptions to the rule" that you describe above do you know of that are being marketed?

Aside from the aspect of roll-off rates, changing the box alignment still doesn't deal with the lack of transient response / out of band port leakage / lack of damping / potential for over-excursion that comes with all vented designs. You simply can NOT take an out of phase signal and use it to reinforce the in-phase signal without multiple drawbacks / repurcussions. With that in mind, it is up to the designer to prioritize which trade-offs are most / least important. When one can avoid most all of these and achieve relatively similar / better results ( except for sensitivity ), there is only one reason to accept the trade-offs that come with vents. That reason would be a lack of available power, which is no longer applicable with modern day designs / technology.

As one tries to achieve greater extension via manipulating the alignment of a vented design, the transient response gets worse. If you want better transient response with a ported design, you have to limit the low frequency extension. Even if you take this approach, the woofer is still unloaded / lacks damping at frequencies below resonance. The fact that you've raised the F3 to obtain improved transient response now exposes the woofer to even greater potential for over-excursion due to having a higher resonant frequency. The higher the resonance, the more potential for woofer overload at frequencies below that point. On top of that, we still have out of band vent leakage to deal with.

One can play all day long with computer simulations, but you can't fight the laws of physics. There are trade-off's involved with every type of design. Rather than try to bend and twist the rules, developing even more problems with increased levels of complexity, why not choose the simplest design with the least amount of trade-offs and work towards optimizing that? It seems that man has a way of making the simplest things in life more difficult than they need to be. Sean
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trelja
3,224 posts
 
I will have the good fortune of having a true transmission line loudspeaker in my main system for the weekend. It will allow me the opportunity to compare and contrast these two alignments in my room, using my system.

Heretofore, my experience with TL bass is that it has been able to achieve more realistic deep bass than ported speakers. Unfortunately, in only one circumstance have I heard them in what is a "good" room in the past. The pair I am considering did not impress me last year, which I in part attributed to the room, but it turns out the line was incorrectly damped and the crossover values were wrong. With the corrections, the bass was improved to a point, but I still feel they were up against the limitations of them being in a difficult room.

My room, being smaller, and possessing boundaries which should definitely show the speaker in a more favorable light, and also being familiar to me, will allow me to get a better handle on things.

One concern I do have is that the achilles heel of the AtmaSphere amps is there lack of low frequency sock. If I begin to feel this is taking away from the experience, I will be switching in the Jadis and/or NAD 2600A to get a broader picture of things.

Personally, despite all the discussion back and forth, I think Sean has laid out some very cogent arguments in this thread. The inherent benefits in the sealed alignment's ease of design and transient response make me wonder why the high end has gone so far in the direction of ported speakers in the past 15 years.

From memory, things were more balanced between sealed and ported in the past. I am unsure of how accurate the conventional wisdom of ported speakers gaining 3 db of loudness over sealed speakers is, but that is normally one of the first arguments thrown out there. I have been under the impression that the resurgence of tube amplification and musical tastes of late account for the scales being tipped in the way they have been, or at least a fair amount of it.
audiokinesis
2,753 posts
 
Hello Sean,

Thanks for your reply. As far as how many production loudspeakers are using a slow-slope vented enclosure, the only ones I know of are the Classic Audio Reproductions models, though I expect there are more. I just haven't really searched for them.

Admittedly my post just above didn't address the topic of this thread, which has to do with trends in megabuck speakers. Rather, my point was that the standard set of generalizations regarding vented systems doesn't acknowledge the implications of more transient-optimized tunings.

One minor point - in tuning for a higher F3 and a more gradual rolloff, you actually use a much lower tuning frequency rather than a higher one - so the woofer is actually better protected against out-of-band signals causing overexcursion than with a more conventional vented tuning.

Improving the transient response of a vented alignment just makes it behave more like a sealed one, raising the F3 but lowering the F12, for instance.

Just for the record, my comments above are based on speakers I have built (or designed and someone else built) as well as on models simulated.

Having experimented with equalized sealed, vented, and transmission line systems, my opinion is that the frequency response curve is a fairly reliable predictor of subjective transient response. I'm under the impression that there's a mathmatical correlation between rolloff rate and transient response, which may or may not imply that it doesn't really matter how the rolloff rate is achieved (whether through enclosure design or speaker/room interaction or equalization). I'm not engineer enough to argue that point one way or the other.

Historically, I've preferred sealed over vented designs (and transmission lines and dipoles over both, though for different reasons). What has driven me to reconsider vented designs (in particular gradual-slope variations) is a heightened awareness of the advantages of very low power compression. You see, the woofers that offer the lowest power compression are best suited for vented or horn loading. And bass horns are just too big in my opinion.

Cheers,

Duke
sean OP
6,231 posts
 
Good points Joe. Once again, you've added a brief but very cogent analysis of the how's and why's. In the future, i'll run my mouth / stir things up and you do the final presentation, okay ?? : )

Honestly though, the fact that you typically remain a "third party" in many of these posts and then summarize both points of view expressed sometimes helps me to see things more logically. There have been many times that you and a few others have added to the thread in such a manner that makes us think about the "big picture" and not just the subjects that we've gotten emotionally tied up in discussing in that thread. For that, i am grateful for your input and everyone else that contributes their thoughts. Even if they disagree with my thoughts : )

If anyone didn't follow what Joe was getting at, it looks like "high end" is following a logical progression. Some that never ventured into or just dabbled in a specific part of the "sonic stream" would actually call it "de-evolution" or "moving backwards".

If we think about things logically, most folks traded their warmer and more liquid sounding vinyl rigs as the primary source for more convenient digital based systems. Digital sounded like hell, but we somewhat got used to it over time. In most every case, digital was hard, bright, lean, lacked "PRAT" and was "soul-less" sounding, so in many systems over a gradual period of time, more and more tubes were introduced into the equation. This was done to try and make things both more listenable and "musical" again.

Given the added warmth and natural tendency to soften the treble response, this worked out pretty well. Only problem is, unless you have some of the best and most expensive tube gear available, tubes typically lack power output and current capacity. A such, the end users that didn't have "mega-dollar" / "built like a tank" tube gear ended up with bass was not what they were used to hearing.

To counter the shift in products being used, the manufacturers shifted from speakers that required a good amount of power with a more linear response to those that required less drive. While shifting to more sensitive i.e. "vented" designs, they also found that it was easy to artificially inflate the last few octaves of output. By doing so, the end users now had more bass, albeit all the time with less control, but their amps didn't have to work as hard to deliver low frequency output and current. This is because the speakers were already "hyped" in that region AND sensitivity is up. It was a "win/win" situation for those users that had systems that weren't balanced in operation and manufacturers / retailers that wanted to sell products.

The end result is that tonal balance was returned to sounding "warm & musical", even with using a digital source, but such results were achieved by introducing TONS of errors along the way. One "solution" created other problems that required further "solutions".

Same goes for those that stuck with digital and didn't use tubes. In many cases, they were using SS gear that was high in negative feedback, lacked both bandwidth and high current capacity and sounded "sterile" i.e. lean and hard. By adding quite a bit of measurable bass "weight" with the "new breed" of "audiophile approved" speakers, one didn't tend to notice how bright and piercing the treble was. Manufacturers were able to "kill two birds with one stone" i.e. both tube fans and those using lower grade SS electronics were satisfied.

As such, it would appear that the "high end" industry, their marketing departments and the "paid for by advertising" audio magazines aren't about "accurate musicality" at all. They are about selling complimentary colourations / sonic band-aids and telling you that they are accurate / sound "wonderful". Those that know how to read and interpret spec's know what is going on, but since the mass majority of user's don't know how to do this, the "audio guru's" were and still are "safe". Given the fact that we've been led down the path where "all amps sound the same" and "digital is perfect", most "critical" audio magazines have dropped test procedures and now rely stricly on subjective opinions. Those that can read spec's and interpret data on their own have been further alienated from finding out the "truth" and become disheartened with the industry as a whole.

As a side note, as much as i "bad-mouth" Stereophile, i still LOVE the fact that they provide some type of test bench measurements. Having said that, i still can't understand how someone could listen to a product and NOT know what they are hearing?!?! If all of this were not true, how could you explain someone ( end users & reviewers alike ) NOT noticing that a speaker has phenomenally bloated bass? To them, it doesn't sound "bloated" or out of place. This is probably because they've never heard a "linear" system with "accurate" tonal balance to begin with.

How could such a thing have happened? That's easy. They never had good vinyl rigs / proper phono stages "way back when" and were raised on "perfect sound forever". It's also possible that over the years, they've lost perspective due to lack of familiarity i.e. non-use of a good vinyl system. Obviously, this could skew one's perspective quite a bit.

As such, it seems like the culprit for all of our "troubles" and "major design changes" in the audio industry boils down to the introduction of sonically inferior digital technology some 20+ years ago. The audio industry and end users had to shift gears at that point in time, and looking back now, it would appear that it hasn't been a very smooth transition.

With all of that in mind, if you doubt that "digital is the devil" behind all of this, just ask Albert or Twl. They'll give you the low-down : ) Sean
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PS... If you like what you're listening to, that is what counts. As i've said before, "buy what you like as you are the only one listening to it". Saying and getting someone else to believe that is is "accurate" or "linear in reproduction" may be another story though.
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