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Observe: Paul Dicomo was a wonderful pal to eCoustics and many individuals over the earlier 2 a few years. Sadly, Paul misplaced a courageous battle with most cancers in 2021 and the commerce misplaced a wonderful man who taught a period of audio/video journalists one of the best ways to understand the merchandise that we cowl.

Paul contributed a whole lot of fantastic articles over time and we hope {that a} new period of readers finds good value in his writing.

By Paul Dicomo

The Secret Behind The Enterprise’s Most-Cited Spec.

Proper right here’s a quick quiz: which of these two audio system sounds increased: Speaker A with a frequency response differ of 45Hz to 18kHz or, Speaker B with an expansion of 20Hz to 25kHz? The fact is there’s merely not ample data in these numbers to know one thing of value. Taken out of context and with out completely different data, a simple set of numbers don’t let you realize rather a lot about precise world sound top quality. Nevertheless people make audio looking for decisions primarily based totally on printed specs, such as a result of the frequency response spec, frequently. I’d want to demystify the tactic for you; let you in on a little bit bit commerce secret about “The Frequency Response Spec.”

My Frequency Response

The Frequency Response specification makes an try to clarify the differ of frequencies or musical tones a speaker can reproduce, measured in Hertz (recognized to old-timers as “Cycles per Second”). The differ of human listening to is normally regarded as being from 20Hz, very low bass tones, through 20kHz (20,000Hz), the very highest treble. Presumably a speaker which may reproduce that change would sound lifelike. Alas, it’s no guarantee. An vital determinant of a speaker’s frequency effectivity shouldn’t be its width or differ, nonetheless whether or not or not it’s capable of reproducing the entire audible frequencies on the same amount at which they’d been recorded.

You don’t want the speaker to differ the “mix” of tones; which may injury the timbre of voices and gadgets, making them sound unnatural. Ideally, you want the sounds which is likely to be on the recording to be reproduced as they’d been recorded, with out the speaker altering the sound. To say it one different method: do you have to made a recording of the entire audible tones on the same amount and carried out that recording through a speaker, you’d want the entire audible tones to come back again out on the same amount. The reality is, that’s a technique of measuring audio system. An indication that’s comprised of all frequencies at equal amount is fed proper right into a speaker that sits in a room with no reflective surfaces. A calibrated microphone is positioned in entrance of the speaker and feeds the speaker’s output proper right into a machine that plots the frequency vs. amplitude as confirmed in Decide A.

frequency vs. amplitude
Decide A

Now take a look at the graph in Decide B. That’s the frequency response of the Erehwon Model 10, with drivers and tweeters manufactured from pure Unobtainium (“Half the carbs, the entire sound!”). The flat line on the graph signifies that the speaker is “flat”; it reproduces the entire musically associated tones on the same amount. That doesn’t suggest {that a} “flat” speaker will play all recorded sounds on the same amount — bear with me proper right here — it signifies that it’ll take care of all sounds equally; it acquired’t impose its will on the music nonetheless will allow you to listen to the music as a result of it was recorded. Flat is sweet. Flat response implies that the speaker reproduces sound exactly.

Erehwon Model 10
Decide B

Too harmful that the Erehwon Model 10 doesn’t truly exist, and neither does Unobtainium. Presently’s utilized sciences allow speaker designers to get nearer to the “flat” supreme than ever sooner than, nonetheless they nonetheless fall far wanting “perfection.” So if a frequency differ spec shouldn’t be sufficient, what’s?

Frequency Response In Context

A large enchancment is usually a frequency response amount that moreover accommodates the amplitude tolerance, expressed as “XHz-YkHz +/- 3dB.” This tells you that the amplitude of the speaker’s response relative to frequency doesn’t deviate better than 3 Decibels from the center line. The “plus or minus 3dB” spec is regarded as an bizarre of varieties. The concept is that 3dB variations are “merely perceptible,” so a speaker whose response curve lies inside that tolerance window is a reasonably right speaker. Let’s see if that idea holds water.

speaker frequency response
Decide C

Try Decide C. This speaker has response which may be specified as 20Hz-20kHz +/- 3dB. Try Decide D; it, too, can have the exact same specification as Speaker C! Do you suppose they’ll sound associated? NOT! They acquired’t sound even remotely like one another. Speaker C could have “one discover” bass and might make voices and completely different gadgets sound unnatural, nonetheless Speaker D will sound simple and additional pure.

speaker response curves
Decide D

If I needed to determine on strictly by the response curves, I’d choose speaker D on account of its amplitude variations are smoother and gentler. In distinction, speaker C’s amplitude variations are additional extreme and “spikey.” Experience has confirmed speaker designers that these quick changes in response produce a sound that’s additional fatiguing, a lot much less pleasing and subjectively a lot much less right.

Business. Scroll to proceed finding out.

smooth frequency response
Decide E

Now take a look on the response of the speaker in Decide E. This speaker reveals a simple response curve with low amplitude variations so that you simply’d rely on a fairly pure sound; nonetheless, the bandwidth of these errors might be very broad, and experience has confirmed us that even low amount variations are audible within the occasion that they cowl a broad differ of frequencies. On this case, Speaker E would have rich bass, excellent treble and be significantly recessed or “laid once more” throughout the midrange. Audiophiles title this “The Smile Curve.” It’s not the fascinating trait it seems like however it absolutely’s a extremely “sellable” trait to naive shoppers.

My Response To Frequency

Now that you simply notice the importance (and limitations) of amplitude variations in frequency response graphs, you might ask: “does the frequency differ inform us one thing the least bit?” Positive, it does. As long as you notice the amplitude tolerance (+/- 3dB), the frequency response differ or width tells you methods extreme or low the speaker goes. A speaker rated as 20Hz – 25kHz +/- 3dB will play lower bass and higher treble sounds than a speaker that measures 40Hz – 20kHz +/- 3dB. I wouldn’t guess money that it will likely be the upper, additional pleasing speaker, nonetheless on the very least I’d know one factor of value.

And now that you simply understand how to interpret these numbers, you’re capable of run correct out and buy a speaker just by wanting on the response curve, correct? I wouldn’t recommend it. No matter many advances in experience over the earlier 20 years, frequency response measurement is an imperfect science. The equivalent speaker measured by two fully completely different labs might yield fully completely different response graphs. And some firms merely plain cheat after they publish response curves. If it appears hand drawn, it most definitely was. (Positive, the graphs had been hand drawn for illustration features.)

The Third Dimension
So far we’ve talked about frequency (the X axis of the graph) and amplitude (Y axis) nonetheless we ignored a necessary third dimension: time. When a speaker responds to an impulse, as an example a rim shot — “THWACK!” — it ought to start instantly and stop the second the instrument stops making sound. If the speaker retains vibrating or resonating and making sound after the provision sound stops it’s altering, or “coloring,” the sound of the distinctive recording. And that’s harmful.

Decide FDecide G
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Decide F reveals a bandwidth restricted impulse signal. You might even see that it begins and stops abruptly. Decide G reveals that exact same impulse coming out of a speaker. You might even see that the sound persists after the impulse enter has stopped — it resonates or “rings.” The speaker is altering the timbre or character of the distinctive recording. With a goal to see to what extent and at which frequencies the “ringing” is happening, we use an aesthetic laptop algorithm often called MLLSA (affectionately often called “Melissa” by engineers who don’t date rather a lot) to measure the response of a speaker in frequency, amplitude and time. Decide H is a MLLSA spectral decay graph of a prototype speaker. The third axis of this graph is time, so graph traces closest to you’re measurements taken later than these throughout the once more. Contemplate it as a set of slices with each slice being a frequency response graph taken at a singular time restrict.

If we had been to measure the appropriate speaker the MLLSA graph would seem like a straight line in once more with no traces in entrance. Precise audio system fall far wanting this supreme and proceed to resonate after an impulse has stopped, paying homage to in Decide H. Decide I is a Polk LSi9, and we’re capable of see that the speaker stops responding sooner throughout the midrange than the speaker pictured in Decide H, indicating that the LSi9 is a better sounding speaker.

Decide HDecide I
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Whereas no measurement technique can completely describe the subjective sound of a loudspeaker, MLLSA and completely different frequency response measurements are of good help to Polk engineers in rising increased sounding audio system. Solely a fool would design a speaker primarily based totally on measurements alone and solely a whole fool would design a speaker primarily based solely on subjective listening. A speaker which can sound good on a selected recording might truly be flawed – it might need what’s normally often called a “euphonic coloration.” It might be pleasing to the ear beneath certain circumstances, however it absolutely optimistic ain’t correct.

We use every measurements and subjective listening to design and take into account audio system. The measurements save us time and are a wonderful help in pointing us within the acceptable design course, avoiding errors which can come once more to chew us later. The measurements give us a means of selecting which experimental designs are value listening to.

Nevertheless we’ve now to be glad with the complete subjective experience sooner than a model new design turns right into a Polk Audio speaker. We spend quite a few hours listening to music and flicks. A variety of expert listeners should take heed to a proposed design and sign off on the sound sooner than a model could even go into manufacturing. The Mission Supervisor, Strategies Engineer, VP of Engineering, Product Line Supervisor, and significantly Matthew Polk, all should agree that the prototype delivers the kind of rewarding listening experience that you simply simply rely on from Polk Audio.

What’s Your Frequency?

You now know the important thing: a frequency response specification is a extremely weak predictor of the actual effectivity of a loudspeaker. A frequency response chart will probably be additional helpful, however it absolutely’s missing the important time measurement. You now know to seek for normal curve smoothness and to stay away from quick swings in amplitude. Some magazines and evaluation web sites publish MLSSA graphs of reviewed audio system, and now you’ll understand one of the best ways to interpret them. Further vitality to you!

No matter how adept you is probably at deciphering frequency response data, it should solely be one data stage amongst many in choosing a speaker. There could also be rather a lot additional to a speaker’s effectivity than merely its response – like its dispersion and imaging, dynamic differ and component choice along with dimension, cosmetics and worth. Having a look at good frequency response data could enable you eradicate audio system with obvious and obnoxious errors. Once you’ve eradicated the rise & tizz pseudo-fi audio system, chances are you’ll settle all the way in which right down to cautious listening and making a additional educated various.

How Polk Specifies Frequency Response

Polk Audio publishes two frequency response specs: “Normal” and “-3dB.” “Normal” describes the frequency differ limits of the speaker inside an amplitude drop off of 9dB. Any frequency reproduced better than 9dB down from the rest of the frequencies will contribute little to the sound. The “-3dB” spec describes the frequency differ limits of the speaker inside an amplitude drop off of 3dB.

Business. Scroll to proceed finding out.

I merely wrote this huge article making the case that these types of numbers won’t be terribly useful in making looking for decisions. So why does Polk use them? For increased or for worse, these numbers are the norm throughout the audio commerce.

To not publish them would go away an impression that our merchandise weren’t aggressive. A better question might be: why don’t we publish frequency response and MLSSA graphs together with the simple numbers? We actually really feel that these graphs wouldn’t be vital to the overwhelming majority of shoppers.

It takes years of working with measurements and loudspeakers sooner than you get an excellent sense of how the graphs correlate to subjective sound top quality. Incorrect interpretation of graphs can merely lead to misinformation and harmful alternatives. Lastly, the variation in measurement methods might make evaluating graphs from two fully completely different labs or producers unreliable and misleading.

Paul Dicomo

By Paul Dicomo, Polk Audio – Promoting and advertising Supervisor

Initially Revealed: September 28, 2005

Further Articles by Paul Dicomo:

All You Should Know About Bass Administration

Residence Theater in a Area vs. Parts. Which is Best For You?

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