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Observe: Paul Dicomo was a superb 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 superb man who taught a period of audio/video journalists the easiest way to understand the merchandise that we cowl.

Paul contributed numerous great 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 greater: Speaker A with a frequency response range of 45Hz to 18kHz or, Speaker B with a selection of 20Hz to 25kHz? The truth is there’s merely not enough information in these numbers to know one thing of value. Taken out of context and with out totally different information, a straightforward set of numbers don’t let you already know quite a bit about precise world sound top quality. Nevertheless people make audio looking for selections based mostly totally on printed specs, such as a result of the frequency response spec, regularly. I’d want to demystify the strategy for you; help you in on a bit bit commerce secret about “The Frequency Response Spec.”

My Frequency Response

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

You don’t want the speaker to range the “mix” of tones; which may harm the timbre of voices and units, making them sound unnatural. Ideally, you want the sounds which could 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: must you made a recording of all the audible tones on the same amount and carried out that recording through a speaker, you’d want all the audible tones to return 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, all the sound!”). The flat line on the graph signifies that the speaker is “flat”; it reproduces all the 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 obtained’t impose its will on the music nevertheless 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 really exist, and neither does Unobtainium. Presently’s utilized sciences allow speaker designers to get nearer to the “flat” supreme than ever sooner than, nevertheless they nonetheless fall far wanting “perfection.” So if a frequency range spec shouldn’t be sufficient, what’s?

Frequency Response In Context

A large enchancment could be a frequency response amount that moreover comprises 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 larger than 3 Decibels from the center line. The “plus or minus 3dB” spec is considered an atypical of sorts. The thought 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

Take a look at Decide C. This speaker has response that could be specified as 20Hz-20kHz +/- 3dB. Take a look at Decide D; it, too, can have the exact same specification as Speaker C! Do you suppose they’ll sound associated? NOT! They obtained’t sound even remotely like one another. Speaker C might have “one discover” bass and might make voices and totally different units sound unnatural, nevertheless Speaker D will sound straightforward and further pure.

speaker response curves
Decide D

If I needed to resolve on strictly by the response curves, I’d choose speaker D because 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.

Industrial. Scroll to proceed learning.

smooth frequency response
Decide E

Now take a look on the response of the speaker in Decide E. This speaker reveals a straightforward response curve with low amplitude variations so that you simply’d rely on a fairly pure sound; however, 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 range 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 identify this “The Smile Curve.” It’s not the fascinating trait it seems like but it surely 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 may ask: “does the frequency range inform us one thing the least bit?” Positive, it does. As long as you notice the amplitude tolerance (+/- 3dB), the frequency response range 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 will probably be the upper, additional pleasing speaker, nevertheless on the very least I’d know one factor of value.

And now that you simply know 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 counsel it. No matter many advances in experience over the earlier 20 years, frequency response measurement is an imperfect science. The an identical speaker measured by two utterly totally different labs might yield utterly totally different response graphs. And some companies merely plain cheat after they publish response curves. If it appears hand drawn, it probably was. (Positive, the graphs had been hand drawn for illustration features.)

The Third Dimension
Up to now we’ve talked about frequency (the X axis of the graph) and amplitude (Y axis) nevertheless 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 availability sound stops it’s altering, or “coloring,” the sound of the distinctive recording. And that’s harmful.

Decide FDecide G

Decide F reveals a bandwidth restricted impulse signal. You may even see that it begins and stops abruptly. Decide G reveals that exact same impulse coming out of a speaker. You may 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 objective to see to what extent and at which frequencies the “ringing” is occurring, we use a cultured computer algorithm generally known as MLLSA (affectionately generally known as “Melissa” by engineers who don’t date quite a bit) 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. Think about it as a group of slices with each slice being a frequency response graph taken at a novel time restrict.

If we had been to measure the suitable speaker the MLLSA graph would look 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, harking back 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 larger sounding speaker.

Decide HDecide I

Whereas no measurement technique can completely describe the subjective sound of a loudspeaker, MLLSA and totally different frequency response measurements are of good help to Polk engineers in rising greater sounding audio system. Solely a fool would design a speaker based mostly totally on measurements alone and solely an entire fool would design a speaker based solely on subjective listening. A speaker which can sound good on a selected recording might really be flawed – it might need what’s normally generally known as a “euphonic coloration.” It might be pleasing to the ear beneath certain circumstances, but it surely 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 superb help in pointing us within the applicable design course, avoiding errors which is able to come once more to chew us later. The measurements give us a manner of selecting which experimental designs are worth listening to.

Nevertheless now we have now to be glad with the whole 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 lot of expert listeners should be all ears to a proposed design and sign off on the sound sooner than a model might 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 can be additional helpful, but it surely 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 the easiest way to interpret them. Further power to you!

No matter how adept you is probably at deciphering frequency response information, it should solely be one information stage amongst many in deciding on a speaker. There could also be quite a bit additional to a speaker’s effectivity than merely its response – like its dispersion and imaging, dynamic range and aspect resolution along with dimension, cosmetics and worth. Looking at good frequency response information might enable you to eradicate audio system with obvious and obnoxious errors. Whenever you’ve eradicated the rise & tizz pseudo-fi audio system, chances are you’ll settle all the best way right down to cautious listening and making a additional educated different.

How Polk Specifies Frequency Response

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

Industrial. Scroll to proceed learning.

I merely wrote this massive article making the case that these types of numbers is not going to be terribly useful in making looking for selections. So why does Polk use them? For greater 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 larger question will 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 important 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 picks. Lastly, the variation in measurement methods might make evaluating graphs from two utterly totally 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 Subject vs. Components. Which is Best For You?

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