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WSRnewsletter125/10/0710:13 AMPage 5FROM The ArchivesLoudspeaker AccuracyHow Impulse, Step, And Phase Response , FrequencyResponse, Waterfall Measurements , And InputImpedance Affect The Music — Part 4JO H NDU N L A V YThis is the fourth in a series of articles onthe topic “Loudspeaker Accuracy” that Ihave written for Widescreen Review as aguest editorialist. In this article, I haveincluded a discussion of frequencyresponse and waterfall measurements,which originally were to be presented asParts 5 and 6 in the original outline of“Topics To Be Covered,” which appeared inIssue 58, March 2002, plus a discussion ofinput impedance versus frequency.The Necessity Of AnAccurate Set OfAnechoic ChamberMeasurementsIt is probably difficult for the averageaudiophile, perhaps lacking an appropriatebackground in mathematics, to understandthat from a measurement of the “impulseresponse” of a loudspeaker, a computercan calculate its frequency response, stepresponse, phase response, etc. This isaccomplished using a FFT (Fast FourierTransform) program, such as MLSSA(Maximum Length Sequence SpeakerAnalysis) designed by Doug Rife of DRALabs. It is not an inexpensive program but,if used regularly and properly, is worth everycent it costs—and then some.However, many of the same measurements can also be made within a good,large anechoic chamber (like the two chambers I built at Dunlavy Audio Labs—DAL)that are approximately 30 feet long, 20 feetwide, and 16 feet high, with all internal surfaces covered with large wedges of highdensity open-cell acoustical foam.But, even with two large anechoic chambers, MLSSA is still used to ensure the highest possible accuracy for all DAL loudspeaker measurements.Some loudspeaker designers attempt totake their measurements outdoors, but it isseldom that the “ever-present wind,” evenwhen it is difficult to “feel,” drops to a lowWIDESCREEN REVIEW NEWSLETTER 12enough velocity not to affect the accuracyof measurements. Many loudspeakerdesigners (and magazines) attempt to circumvent this problem by measuring thebass response of their loudspeakersindoors at a distance of only a few feet (typically placing the instrumentation microphone almost up against the woofer cone)and “splicing” the data to measurementsmade at higher frequencies over a greaterdistance (typically one meter). But realistically, nobody listens to a large-size loudspeaker at such a close distance, andtherefore such a near-field measurement willtypically not convey the loudspeaker’s performance at the normal listening distance of8 to 12 feet. (And, for several other goodtechnical reasons, this seldom yields a setof measurements with reliable and/or consistently usable accuracy.)direction that is more than about 12 to 15 dBbelow the level of the positive peak. Thisshould be followed by no more than about200 to 500 microseconds of additional ringing (with a maximum amplitude at least 15to 20 dB lower than the peak amplitude ofthe impulse). Ringing is an undesirablecharacteristic for all audiophile componentsincluding loudspeakers, amplifiers, preamps, signal sources, etc. A large overshoot and/or ringing of substantial amplitude and duration can have the effect ofblurring complex musical transients ordulling the impact of fast rise-time musicalsignals. Ringing can be described as repetition of the original impulse in the timedomain. Such pronounced overshoot and/orringing can also turn a sharp “tic” soundinto a dull “toc” sound and significantly alterthe quality of plucked strings, orchestralImpulse, Step, AndPhase ResponseAn acoustical impulse is a very brief “tic”sound that, surprising to most people,simultaneously contains all audio frequencies. The measured impulse response of aloudspeaker is important because it defineshow faithfully a given loudspeaker canreproduce complex or short-duration musical transients without “blurring.” While nontechnical people may find it difficult to imagine, “mathematically,” an impulse containsall of the information needed by a computerrunning a FFT program to accurately derivethe frequency response, step response,cumulative spectral decay (waterfall)response, and phase response. Impulseresponse is usually based upon using a rectangular pulse having a very fast rise timeand a width of less than about 20 microseconds. (See Figure 1, Impulse Response.)A well-designed loudspeaker should possess an impulse response with a rapid risetime, a steep drop from the maximum, followed by an “overshoot” in the negative5Figure 1—Dunlavy Signature Series SC-VFigure 1—An Expensive Audiophile LoudspeakerMAY 2007 - www.WidescreenReview.com

WSRnewsletter125/10/0710:13 AMPage 6FROM The Archivesshould also exhibit good impulse and stepresponses. Conversely, a loudspeaker withan excellent step response should exhibit asmooth curve of both amplitude and phaseversus frequency, with no time domain distortion or irregularities. Thus, a loudspeakerwith poor phase response (resulting in apoor transient response) can be expectedto create an audible “blurring” of complexmusical transients, etc.Figure 2—(Top) Dunlavy Signature Series SC-III.AA 5,495 Per Pair Audiophile Loudspeaker(Bottom) An 11,000 Per Pair RespectedAudiophile Loudspeakerthe “transfer-function” of a device, is ameasurement that reveals how accurately aloudspeaker can reproduce the shape of arectangular pulse having a very long duration(greater than 100 milliseconds). A “perfectloudspeaker” would reproduce such a signalwith little or no initial overshoot, followed by anexponential roll-off in amplitude versus time,until the amplitude eventually approachedzero. (See Figure 2, Step Response.)Step response also reveals a great dealabout the overall properties of a loudspeaker because the shape of the reproducedcurve provides an easy, visual picture ofboth amplitude and phase versus frequency, crossover network parameters, and driver time alignment. An accurate stepresponse reveals whether a loudspeaker istruly accurate with respect to its frequencyresponse, phase response, impulse response,and waterfall response. Therefore, a properly reproduced step response is a reasonable guarantee of a truly accurate soundingloudspeaker, capable of preserving thespectral properties of the original live musical performance, all else being equal.Phase response is related to the timedomain response of a loudspeaker, i.e., theability of the loudspeaker to accuratelyreproduce complex signals over a widerange of frequencies without any time domaindelays or distortion (including the ability of aloudspeaker to accurately reproduce squarewaves). Phase response is directly relatedto the impulse and step responses of aloudspeaker and is therefore relevant to theaccurate reproduction of complex musicaltransients. A loudspeaker with excellent frequency and phase response propertiesWIDESCREEN REVIEW NEWSLETTER 12Frequency ResponseThe frequency response of a loudspeakeris the modulus (variations) of amplitude versus frequency. Measured accurately withina good anechoic chamber (preferably inconjunction with a state-of-the-art FFTmeasurement program such as MLSSA), itreveals a loudspeaker’s spectral balance,i.e., its ability or inability to reproduce all frequencies or musical tones with equal intensity or volume. This is an essential propertyif the reproduced sounds of familiar musicalinstruments are to be heard as possessing“live” properties.It is usually considered the most important performance property because it is theeasiest for the average person to evaluatewhen listening to loudspeakers. Anomaliesin frequency response are most detectablewhen the direct arrival “curve” departs fromthe “average level” by more than about 2dB over a range of more than about onefourth to one-third of an octave in frequency(See Figure 3, Transfer Function MagnitudeFrequency Response). (An octave is a twoto-one ratio of frequency, e.g, 100 to 200Hz, 1 to 2 kHz, 4 to 8 kHz, etc.)However, a truly accurate loudspeakershould possess an amplitude versus frequency curve that falls well within 1 or 2dB limits, with excursions of less than about 1 dB within any given octave (without anyamplitude or bandwidth “smoothing.”).MLSSA provides a “smoothing function” thatallows the measurer to manipulate a frequency response that measures 3 to 5 dBand make it look like one that appears to beonly 1 or 2 dB. Some designers will arguethat room reflections will modify the frequency response heard by a listener by greatervalues than this amount. However, the effectof room reflections, as long as they arrivemore than about 5 to 10 milliseconds (soundtravels approximately one foot per millisecond) later than the direct arrival sound, aregenerally aurally processed and recognizedas such by most experienced listeners.WaterfallMeasurementsTime domain response is viewed by6Figure 3—(Top) Dunlavy Signature Series SC-III.AA 5,495 Per Pair Audiophile Loudspeaker27-20,000 Hz 1.5 dB Measured(Bottom) An 11,000 Per Pair RespectedAudiophile Loudspeakermeans of a Cumulative Spectral Decay plot(often called a waterfall plot). It provides asequence of individual frequency responsecurves, each delayed by a short time interval from the preceding plot. It is anotherexcellent tool for gauging the accuracy of aloudspeaker’s ability to reproduce complexmusical passages possessing significanttransient details without blurring or smearingof complex details in the frequency or timedomains. (See Figure 4, CumulativeSpectral Decay—Log Frequency—Hz.)Input Impedance VersusFrequencyThe ability of a loudspeaker to be “amplifier-friendly” is often related to the loudspeaker’s input impedance versus frequency. This is especially true with regard totube amplifiers and some solid-state amplifiers using minimal inverse-feedback. This isbecause the internal output impedance ofsuch amplifiers is often higher than 1 ohm,which when feeding a loudspeaker whoseinput impedance might vary from 1 or 2 ohmsto a maximum of 20 or 30 ohms or more, canresult in such a system no longer possessing a flat frequency response (amplitudeversus frequency and/or accurate impulseand step responses). A well-designed poweramplifier should have an output impedancelower than a few tenths of 1 ohm because ahigher output impedance, feeding a loudspeaker with an input impedance varyingfrom 2 ohms to perhaps 30 ohms (or more) canpotentially create audible fluctuations in freMAY 2007 - www.WidescreenReview.com

WSRnewsletter125/10/0710:13 AMPage 7FROM The ArchivesFigure 4—Dunlavy Signature Series SC-VFigure 4—An Expensive Audiophile LoudspeakerFigure 5—Dunlavy Signature Series SC-VFigure 5—An Expensive Audiophile LoudspeakerConclusionhigher output impedance, feeding a loudspeaker with an input impedance varyingfrom 2 ohms to perhaps 30 ohms (or more)can potentially create audible fluctuations infrequency response. Therefore, a welldesigned loudspeaker should have an inputimpedance that does not drop below about3 ohms over the audio spectrum, especiallyat higher frequencies, e.g., 3 to 5 kHz. It isnecessary, for accurately evaluating a loudspeaker’s input impedance with respect toits being amplifier-friendly, to have availableboth its resistive and reactive components.This is because many tube amplifiers, orother Class A amplifiers, that exhibit a relatively high output impedance can alter thefrequency response and time domainresponse of a system using loudspeakershaving an input impedance that varies significantly with frequency. (See Figure 5,Impedance Bode Plot—Ohms.)While loudspeakers that do not measureaccurately may sound musically good, satisfying, etc., they can never reproducemusic with the audible accuracy of loudspeakers that measure truly accurate in allof the above mentioned categories. IIAbout John DunlavyJohn Dunlavy, MAES, FIREE, etc., is a well-knownand highly-respected engineer and scientist with anumber of patents to his credit, and 40 years at theforefront of audio innovation. John’s special interestis loudspeaker accuracy, a notion he’s been workingon and talking about for decades. Agree or disagreewith him, we can all learn something valuableabout the world of audio reproduction, sitting atJohn’s knee. That’s why I’ve invited him to pen thisGuest Editorial column for the next several monthsto provide us all a “short course” in acoustics andaudio reproduction. I’m looking forward to it, as Ilook forward (as always) to your comments.Gary Reber, Editor-In-Chief, Widescreen ReviewDigital VideoEssentialsinAvailable Now AtWidescreenReview.com!WIDESCREEN REVIEW NEWSLETTER 127MAY 2007 - www.WidescreenReview.com

WSRnewsletter125/10/0710:13 AMPage 8I Want ToKnowThe Studio ScoopRumors, Reports, & RamblingsJack KelleyBuena VistaDo you know from where the nameBuena Vista (as in Buena Vista HomeEntertainment) comes? Well, it is the nameof the street Walt Disney built his headquarters on way back in 1937. Since, BuenaVista has been the umbrella for such studios as Miramax, Touchstone, Dimension,and, of course, Walt Disney. But that isabout to change. According to Walt DisneyCEO Robert Iger, in an effort to “focus moreon brands and build brand strength,”Buena Vista Home Entertainment will soonget a name change. Most likely it willmorph into something like “Walt DisneyHome Entertainment,” or somethingequally as clever, yet I think this wouldbe a great marketing opportunity for alittle consumer participation.be shot in widescreen (or I wouldn’t be ableto write about it), The Hollywood Reporter isreporting (as that’s what they do) that JustinTimberlake’s FutureSex/LoveShow WorldTour will be taped for HBO when it stops atNew York’s Madison Square Gardens onAugust 16th. "When Justin said he wasgoing on tour, it was a no-brainer. It just feltright—he is a classic HBO star, it feels likethe right time, and he’s the right guy," saidNancy Geller, Senior ViceDreamWorksLooks like Laura Ramsey, JenaMalone, and Shawn Ashmore will bejoining Jonathan Tucker when theyhead to Queensland, Australia in lateMay to begin filming The Ruins, whichwill be based on Scott B. Smith’s novel.Don’t worry, I am way ahead of you.Laura Ramsey played Gabrielle fromThe Lords Of Dogtown (Issue 101),Jena Malone was Lydia Bennett inPride & Prejudice (Issue 107), ShawnAshmore became Iceman in X-Men:The Last Stand (Issue 114), andJonathan Tucker acted as JoshOckmann in Pulse (Issue 116). You see, youmay not yet recognize actors by name, butyou will know them by the films in whichthey star, which are thoroughly reviewed ineach and every issue of WidescreenReview. Do you have your subscription?(Disclaimer: Management suggested I worksubscription opportunities into my Scoop.Mission completed.) Oh, The Ruins is athriller about when a Mexican vacationtakes an evil turn.MGMAnd MGM makes it four, as they willbegin selling movies on Apple’s iTunesStore. It has been reported that 25“classic” (there’s that word again) films,such as Dances With Wolves andRocky, will be the first to be made available for purchase. But it seems that therelease of catalog titles versus recentlyreleased titles may be hurting iTunes.According to Daily Variety, iTunes’downloads have fallen by 600,000, from1.3 million copies for the first quarter of2006 to 700,000 for the same time period in 2007.New LinePresident, HBO Entertainment. Look for thisspecial to air on September 3, 2007. I’m notsure if he’s a “classic HBO star,” but hedoes star in Alpha Dog, which will bereviewed in Issue 122 in both DVD and HDDVD.LionsgateKeeping my fingers crossed that this willForget the family-values type stuff fromthe last two newsletters, and mark your calendars for June 8, 2006, when Eli Roth’sHostel: Part II tortures its way onto the bigscreen. I wouldn’t recommend you seeingthis film without first watching Hostel, whichWIDESCREEN REVIEW NEWSLETTER 128HBOwas reviewed in Issue 108. I haven’t seenthe first one, nor will I probably see the second, yet I know I am not going to vacationin Slovakia anytime soon. I like to drink anddance, not be bound and gagged.Back in the day, it was SheriffTaylor and Opie. Then we had MikeBrady and Greg, Peter, and Bobby. Andnow, we have Master P and Romeo, thereal-life father and son rappers. You canlook for them on June 26 in Uncle P, andall for just 19.99, as New Line looks torecapture its urban glory of the mid-’90s.“The films that defined New Line in the ‘90swere Friday and House Party. We basicallywant to take the title and reimagine themafter today’s market,” explained KevinKasha, New Line Senior VP of Acquisitionsand Programming. No news on Uncle P inh-def.but that would be da bomb.ParamountRemember Babel? (If you don’t, just referto Issue 119 for the complete review.) Well,it seems about 50 or so Japanese moviegoers will have a hard time forgetting it.and,in this case, that’s not a good thing. Sinceits Japanese premiere last week (April 28),50 people have become ill while watchingthe film, and that number is expected torise. And, as this outbreak is from severalMAY 2007 - www.WidescreenReview.com

WSRnewsletter125/10/0710:13 AMPage 9Continued from page 8.venues, not just one, there goes that “itmust-be-something-we-ate” theory. “Wehave issued warnings to the public thatthey may feel unwell by watching the film,”said Mimi Ichikawa, spokesperson forGaga Communications. Personally, I didn’tlove the film, but I never became ill whilewatching it. Well, there was that onescene.Sony PicturesOkay, I was going to tell you about howSpider-Man 3 broke overseas’ recordsupon its opening, and how it is going tokick some Spidey-butt this weekend (May5), but we already know that, so to other,older news.Okay, we’ve all made choices we regret,but most of us have not had them shownon the big screen and then immortalized onDVD. Well, according to IMDb, ChloeSevigny is “still traumatized” (some threeplus years later) by her unsimulated (read:real) sex act on then-boyfriend, VincentGallo, in The Brown Bunny (reviewed inIssue 100). Luckily for her, it only brought in 366,000, so it was only seen by a handfulof moviegoers. To research further, I wentto YouTube and entered “Brown Bunny,”coming up with a mere five pages, andmost of clips appeared to be of the fourlegged and long-eared type, but a couplelooked to be made of chocolate.20th Century FoxMove over Hillary. Step aside Barack.Make room Arnold (as in Schwarzenegger,Governor of California). Borat is in thehouse.and on the pages of Time magazine. Sacha Baron Cohen (aka: Borat) hasbeen chosen as one of the 100 MostInfluential People by the decades-old magazine. I’m not sure if there is any sort ofceremony to honor these 100 movers andshakers, but if there is (and I am keepingmy fingers crossed), Stacey, ourSubscriptions Manager, would love to seeMr. Cohen sport his lime-green uni-thongas he receives his well-deserved kudos. (Toview all 100 in slideshow fashion, visit:http://www.time.com/time/Universal PicturesThose involved are hoping the secondtime’s a charm, knowing the first Hulk had aless-than-stellar boxoffice performance,bringing in 62 million its opening weekend. For round two, The Incredible Hulk (or,perhaps, Hulk 2), will be directed by LouisLeterrier (Transporter 1, Transporter 2,Unleashed), with Edward Norton as BruceBanner and Liv Tyler as Betty Ross, hislongtime love interest. Look for it to be theatrically released in June 2008.in all of itsgreen glory.Warner Bros.In less than two months (July 3), BloodDiamond (Issue 120) will be Warner’s firsthi-def title to be released with web-enabledfeatures. This feature will “allow viewers touse the players to participate in the studio’sonline polls and view bonus features, suchas maps of conflict in war-torn Africa.” Alsoincluded on the HD DVD will be, of course,the In-Movie Experience. Now, if you are inthe Blu-Ray Disc camp, you can pick upthat version on June 5, but it won’t have theweb-enabled features found on the HDDVD. Both titles will be available for 28.99,so from a features-to-cost perspective, itlooks like HD DVD is the winner in thiscase. Contrary to popular opinion, Research/ProductionEditor Jack Kelley is not responsible for anyrelease date changes, price changes, or anyother perceived errors contained within. He canb

Onkyo TX-S805 THX Ultra2 receiver Onkyo TX-SR605 A/V Receiver Onkyo TX-SR505 A/V Receiver. Onkyo HT-SR800, shown in silver finish WIDESCREEN REVIEW NEWSLETTER 12 4 MAY 2007 - www.Wid