Lynn Olson about speakers

Planar, horn, dynamic...
softspeaker
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Lynn Olson about speakers

Postby softspeaker » 25 Jun 2012, 15:52

http://www.nutshellhifi.com/

Here I'll describe a pair of simple ear-training methods to detect colorations - you won't thank me, since you'll be sensitized for life once you become aware of them.

1) Tweeters have a surprising amount of distortion. To hear the tweeter distortion, play music at a level you're comfortable with, and choose selections that have a continuous line of singing. Now shut off the midbass and woofers, leaving the tweeter playing. The sound will be wispy and insubstantial, and after you listen for a little while, you'll notice that on some passages, it is actually quite distorted. Notice that the distortion comes and goes in an unpredictable and maddening way - just as you start to relax, the thing blats and sizzles like a piece of tissue paper, than the annoyance flits away again.

Now that you can recognize what your tweeter's been doing all along, restore the mids and bass. You can still hear the problem, can't you? Now that awareness will never go away.

2) Cabinets have more coloration than you think. Play a symphonic piece this time, something scored with a lot of density. No chamber music or jazz, no good for this test. Play it a moderate level, and walk up to the speaker and press your ear directly against the side of the cabinet. Repeat for the rear. Try the other side.

Now sit and listen in the usual listening position. You can still hear the cabinet sound, can't you? Yes, it's been there all along, and you didn't know it. Now you do - and you won't be able to ignore it any more!

3) Play a symphonic piece at a moderate level with a fairly continuous line - choose a piece you like, this test won't destroy your faith as much as the first two. Shut down the other channel - you can use a mono source if you want, just choose something with a pleasing and natural-sounding tonal balance.

Walk up to the remaining speaker so you're about a meter away, then walk around it slowly, completing one circle, then keep moving slowly round and round. Stop and listen what the speaker sounds like in the rear quadrant. Most monopoles (nearly all) sound - well - "gurgly" and bass-heavy from the rear. The "gurgly" quality are cabinet colorations at close range (you are close enough so room colorations don't matter) and the dull, muffled quality is the strange, heavily diffracted sound of the tweeter.

This one is so simple it looks really stupid. That doesn't stop me when nobody is looking.

4) Cabinets have really weird-sounding internal standing wave colorations, and especially cabinets where multiple drivers share a common chamber (line arrays, I'm looking at you). If you visit the proud audiophile or manufacturer when the drivers are pulled out, if the baffle opening is big enough, put your head inside (don't get stuck!!!), or if you want to play it safe, put your ear right at the aperture.

Listen for awhile. Note just how different it sounds than when you're several feet away in free air. The cabinet, even if is filled with Miracle Absorbing Material, has a hollow, muffled, resonant - well, boxlike quality, but with odd colorations from the damping techniques themselves. It's not really a simple "box" sound - there's other stuff, too, and hard to describe.

Speaker diaphragms are acoustically transparent, no matter what material they are made from. These weird boxy qualities are there all the time, overlaying their signature on the honest sound of the driver. This is especially severe in line arrays with a common rear chamber - the best reason for using multiple, small, isolated chambers, preferably of dissimilar dimensions.

There. Four listening techniques that will reveal a great deal of the gross and obvious defects of speakers from $100 to $100,000.


You've had a little taste of the speaker-designer world, where speaker defects jump out at you at trade shows and the homes of hifi enthusiasts. I've described only two of the many, many defects of loudspeakers.
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About dipoles, boxes, etc:

Some people prefer a restricted soundstage, and consider extra-width and extra-deep effects artificial. I don't - I've worked in surround sound since 1973 (the Shadow Vector patent and prototype with Audionics) - and know the difference between artificial and genuine reproduction of spatial characteristics. A good dipole, whether electrostatic or dynamic, plays the recorded ambience as recorded, not in a fake-reverb kind of way.

This is because the brain/mind/hearing system assigns sound into different processing "slots": 0-1 mSec is used for localization, 1-25 mSec is used for assigning ambient qualities (how big is the space), and anything delayed more than 25mSec starts to sound like an echo. So measures to reduce diffraction and stored energy in any kind of speaker are worthwhile, since most of the stored energy is going to fall into the 0 to 1 mSec interval, where it damages the sense of localization. Room reflections, including the first one off the floor, are benign - in fact, the floor reflection, although troublesome to measure, actually assists localization.

This is why dipoles don't "create" ambience, the simply allow you to notice what's on the recording. If you're listening to a 1944 Toscanini recording, it's going to sound as dry as the Sahara Desert. Chamber music sounds just like musicians playing in a small, lively room. Symphonies sound like they're in big halls, as they should, although running the solo mikes up and down is really obvious and silly-sounding, since the lucky instrument zooms forward and then scurries away once it leaves the spotlight.

The most noticeable - and unique to prosound dipoles - is the sheer sense of presence of big-sounding instruments like piano and kettledrums. These things sound real, not hifi. Electrostats just don't have the gigantic dynamics these instruments require, and with horns, you don't get that sense of the sheer size of the instrument, although you get the loudness. And to my ears, the audiophile line arrays sound artificial, overhyped, and incoherent. (Not surprising; when you have a multitude of drivers delivering the sound at slightly different arrival times - think of the path-length differences - the sense of impact and coherence isn't going to be there, thanks to the arrivals being smeared over that critical fisrt millisecond.)

Anyway, if anyone reading this little thread is truly ambitious, try the dipole thing with a 15" paper-cone Tannoy, and prepare to be amazed. The less you hear the cabinet, the better a driver is going to sound. If the driver is truly great, you won't hear it's full potential in a box - any box, I don't care what wonder material it's made of.
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About spectral balance:

From what I heard at the show, Siegfried Linkwitz, Jonathan Weiss, Duke, and Bruce Edgar appear to prefer the balance I do (a "traditional" balance), flat with a moderate tilt towards the bass - maybe 1 to 2 dB tilt between 100 Hz and 10 kHz, and no more.

This is a minority taste in the industry today. The high-name-recognition exhibitors (who could afford the largest rooms) were demoing speakers with obviously nonflat balances that reminded me of the TAD Reference Ones I heard a while ago; tipped-up, bright, with breakup artifacts in the 3~5 kHz region, the 100~160 Hz region depressed by several dB, and deep bass overemphasis. This is the sound that magazine and online reviewers seem to prefer, since it's the sound you get with the highly-reviewed name-recognition speakers - Wilson, JMLab, Magico Mini, et al.

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Audiophile vs prosound dynamics:

So when I invent the phrase "audiophile-scaled", I simply mean a speaker that uses typical audiophile drivers, like Scan-Speak, Vifa, Seas, etc.

Contrary to the myths of the glossy magazines, no, you can't pair a $100,000 audiophile speaker with a MBL kilowatt amplifier and have it fill a 500-seat movie theater.
5~7" midrange drivers and 1" dome tweeters can only put out so many acoustic watts. First they compress (around 90~95 dB). Then they distort. Then they distort a lot more. Then they fail, sometimes taking the crossover and amplifier with them.

With permission from Lynn Olson

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