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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
sean OP
6,231 posts
 
El: If such is the case, why not just run an equalizer to fine tune the sonics to what one wants to hear? One can achieve such results without spending much money at all. What does it matter what the source of colourations are so long as one enjoys the final presentation?

I think that a lot of people that were striving for accuracy and thought that they were buying products that would give them that have been lead down the rose path, thorns and all, by the manufacturers and dealers that took their money. Of course, neither the dealer nor the manufacturer could have done this by themselves without some help, so that is where the audio press comes into play. Promoting the "flavour of the month" mentality surely hasn't helped the industry / end-users in the long run.

High end used to be about achieving accurate and musical reproduction of what is on the recording. Non-linear reproduction is not accurate and super-imposing excessive bass / treble or both onto every recording isn't exactly "musical" either. If one prefers such a presentation, so be it. I don't think that most people reading these forums would call such a presentation "high end" though.

Other than that, i think i've more than expressed my point of view on this one. I'll give it a break and leave those that are annoyed alone. Sean
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audiokinesis
2,737 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
3,223 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
2,737 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
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