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
>

* 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, what are your thoughts on transmission lines? Transmission lines have much smoother impedance curves through the bass region than most other enclosure types. One current commercial design that I'm familiar with uses an "8-ohm" woofer and the impedance peak in the bass region doesn't go over 11 ohms. There may well be others that do even better.

Or what about pressure-relief enclosures? No time-delayed output from the damped opening, and once again a much smoother impedance curve in the bass region.

Seems to me either of these approaches are inherently even less resonant than a sealed box.
Transmission lines have potential but are phenomenally hard to build and fine tune. Given that most manufacturers can't design / build simpler products, i don't hold much faith in them getting a more complex product like a TL right.

As a side note, AudioXpress had some recent articles about a TL design. From what i walked away from that article with, my thoughts about them being very complex / hard to optimize were only reinforced. Tons of higher frequency rippling taking place, etc... along the length of the tunnel. Even more than a poorly designed port. Obviously, one would have to do a lot of experimenting with different types, densities and placement of damping materials to get things dialed in. As such, sealed and stuffed is hard to beat from either a mass production or hand built / tweaker point of view. In many cases, simpler really is better.

As far as "pressure relief" enclosures go, are you talking about Aperiodic's aka "vario-vents"? Sean
>
Re: transmission line speakers, mechanical & electrical modelling is now available for quarter-wavelength speaker design. Never tried it -- but thanks to a few audiophile engineers it looks like we've taken a large step forward from the trial & error situation of yesteryear. D Dlugos' site has general info on the subject and, of course Martin J King who actually developed the computer-based mechanical modelling.
Cheers
In my opinion, and with 50 years of experience building speakers (mostly by the old fashoned trial and error method) transmission lines are the best boxes, but as sean says are hard to get right. Sealed boxes are almost idiot-proof, and so, in the real world, in most cases will outperform TLs. Furthermore, because of their gradual and well controlled roll-off, electronic equalization is effective. The key to speaker building is "don't screw it up". It's too easy to do that with a TL.
Phew! Lots of reading....
Glad to see that "Q" was discussed. Balancing enclosure size, driver characteristics, vent frequency and sensitivity is certainly an art. Not having heard the 20T, I would nonetheless find it a bit difficult to believe that Mike Kelly would purposely let a bloated high Q speaker out the door at 23k. Likewise I've learned that JA's cut 'n patch fr curves can be a bit misleading...as are most such attempts at describing response in a real environment. My assumption is that the 20T is for LARGE roms, where the big bass plateau can be appropriate. These ARE big speakers in my book....
I think it may be a bit too easy to criticize vented designs. Certainly if the vent frequency is low, and the driver well-controlled with a very low Fs, in an appropriate nonresonant enclosure, excellent results can be had. I understand the nherent problems, yet had moderate success loading a 3-way (8+5+0.75, vent 32-35Hz) a while ago. The problem wasn't so much the bass response, but other issues higher in frequency (matching driver sensitivities with loose OE specs!). Yet the speaker did have characteristic "vent" sound. Maybe we're all too much used to it, and Sean is partly right....
So it was quite a shock to hear how clean and tight the response is from my now-3yr old Verity Ausio Parsifal Encores, for example (8+5+1). Stunningly fast bass response that matches its incomparably-quick midrange. I asked Pelchat et al at VA how they did it, and mentioned that the Encore was predominantly about getting an extremely "fast" woofer custom spec'ed from Dynaudio, for which they pay a fortune. Sounds it...really hard to believe there's a lagging vent huffing and puffing in this design.... I suspect a low Q keeps things quick and flat, too, as I measure fla response to 30Hz in-room, falling precipitously below that, of course, as is typical of a tuned vent. You should listen to this speaker, Sean, before castigating all vented designs further....
Comments about boom-cha favored response (the old West Coast saddle-curve...aka Bose?) I find intriguing, and can't comment upon whether current designers are influenced by unnatural bass level pop music tastes....
Some posters correlate that flat bass frequency response is somewhat correlated with price. certainly this is only slightly true, vis a vis enclosure size cost. It's really not harder to design a $1k speaker with a reasonably flat and "chosen-Q and vent freq" than a $20k one. Thiele/Small, Q, vent geo, etc., are givens, so Aeriel's $23k speaker doesn't have smoother bass than the $6k Legacy for THAT reason. Hell, my Spendor 3/1p ($1400) have a nice smooth bottom. It's just good design....
There's too much to comment on here later....
Cheers. Ern