Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is my lecturer incorrect or did I just misunderstand? (sound quality)

  1. Jan 12, 2016 #1
    I'm a first year electrical engineering student and I had a lecture on Analogue and power electronics today. The main topic the lecturer was talking about was headphones and stereo systems etc.

    We learned about frequency responses and looked at product specifications and circuit analysis and he concluded that there is NO difference in quality between expensive or cheap products. For example £10 headphones as opposed to £300 Bose ones or beats or something. He said that our biases are due to placebo effects/ listening to one device at a higher volume makes you think it sounds better and so in shops they turn the more expensive devices up higher.

    Is this really true, or did I misunderstand something? Or is he just talking about in theory because even though I've seen the analysis, I'm finding it hard to believe all products are created equal.

    Hopefully someone can clear this up for me.
  2. jcsd
  3. Jan 12, 2016 #2


    User Avatar
    Science Advisor

    Well, that is stretching it a bit. I will agree that there is no difference in specifications between expensive or cheap products. But quality is much more than specifications.
  4. Jan 12, 2016 #3


    Staff: Mentor

    Qualities not seen in the electrical specifications can include reliability, ruggedness, longevity, and resistance to corrosion. The more expensive brands may or may not have more of those qualities. It is almost impossible for consumers to get verifiable information about those secondary qualities.

    Every headphone/earbud I ever owned (cheap or expensive) seemed to die by failure of the lead wires after I stuff them in a pocket.
  5. Jan 12, 2016 #4


    User Avatar
    Homework Helper
    Gold Member

    I would agree about quality other than specs. I think comfort is a very important feature.

    Are people saying testing would not reveal any differences, or just that all marketing people put the same label on the box?

    Some reviewers complain that one manufacturer may give freq. response as a 3dB range, others a 6dB range and others don't specify any level.

    I had assumed that specs like 20-20kHz 3dB meant that response did not deviate by more than 3dB over the quoted range, but looking at the example below, perhaps these are just the highest and lowest frequencies at which response is within 3dB of some level (not stated - perhaps average or maximum?), but that in between dips can be any depth.
    Looking at the test results for a pair of $1900 headphones there appear to be 15dB dips in the response inside the claimed 5 - 20kHz range. (AFAI can see, they don't specify the dB level for their range.)
    If cheap phones truly have a flat, within 3dB, response over the 20-20kHz range, would these expensive ones need to be very comfortable indeed?
  6. Jan 12, 2016 #5

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    Good integrated circuit amplifiers have got so cheap there's no reason for manufacturers to try cutting a corner there.

    That said, a manufacturer with lush budget can afford low noise resistors to minimize hiss, expensive potentiometers to give the controls that buttery-smooth gliding feel, luxurious padding to make them feel good around your ears, and robust electrical cord & connectors for longevity. He can afford to solder the connections and assemble the parts with fasteners instead of snap-together .

    So called Audiophile stuff is often hyped to prey on naivete . I found some "Monster speaker" cables at a yard sale. Lampcord works just as well.

    Speakers are where you can improve sound quality for not really much investment. Open some headphones and study the little speakers inside. I dont own any audiophile headphones but would expect to find something like this


    perhaps a $4 driver vs a $0.50 driver in cheap phones
    this one was on sale for 99 cents and sold out quickly. Lots of DIY'ers in audio

    It's a fun hobby i hope you get interested.
    Last edited: Jan 12, 2016
  7. Jan 12, 2016 #6
    Really I would say there is not a true correlation between cost and quality - esp sound quality. There is no material to an earbud - and with Sony's history ( looking back at making low cost good quality headsets / then earbuds) -- I'll take my chances with a $20 set of Sonys vs some "popular" $120 pair from Beats -- As for for over the ear sets ( Studio quality ) or Active Noise Cancelling - there are some brands probably worth more money than others.
    BUT - if you are listening to MP3 - or god forbid Sirius / XM -- nothing will make them sound good,.
  8. Jan 12, 2016 #7


    User Avatar
    Science Advisor
    Gold Member

    At one time there was a $10,000 reward offered to anyone who could hear the difference in car audio amps in a blind test. Frequency response was corrected ahead of the amps and of course the power output had to be matched. As far as I know, no one has every been able to tell the difference. There are those who claim they can tell and refuse to take the test because equalization ahead of the amps is considered to be 'dumbing down' a high end amp. The challenge basically says that no one can hear things that test equipment cannot measure. The challenge is NOT saying that all amps sound the same no matter what. It is more geared to prove audiophiles wrong. But this has been next to impossible as well.
  9. Jan 12, 2016 #8


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I agree with Svein. He is exaggerating a bit to make a point. However these days you don't have to pay much to get equipment that is pretty darn good. You could buy equipment that costs 10x or 100x more but you won't always notice a significant difference. Quality is also a very subjective term. Sometimes equipment sounds better even though on paper it's worse. Some people are buying vinyl records again because they prefer the sound.

    Many speakers have distortion figures of around 1 to 3%. Not all manufacturers want you to know that..

    For everyday use I buy ear bud headphones that cost £1 (about $1.44) but that's because they just happen to be a comfortable design.
  10. Jan 12, 2016 #9


    User Avatar

    Speakers/headphones genuinely do vary quite a bit in performance, and you can easily hear the difference in a level matched blind test. You can also easily measure the difference. There isn't always a perfect correlation of cost to quality (sometimes, a more expensive product can actually sound worse than a cheaper one), but there's definitely a significant difference between, say, the headphones you get for free on an airplane flight and these.

    Now, for amplifiers, DACs, and cables? There's almost no reason to spend more than a relatively minimal amount on those. Even pretty cheap ones are to the point now that they're audibly perfect.
  11. Jan 12, 2016 #10


    User Avatar
    Gold Member

    Your professor is WAY wrong. There is a HUGE difference between headphones that have the same frequency response specs. (and I am not an audiophile talking about subtle unscientific things. And, I deal with headphones professionally)
    1. The transducers are not linear (they distort), have resonance and intermodulation effects, different mechanical damping factors, etc. There are cheap transducers, and expensive transducers, and they can have the same frequency response specs and sound totally different.
    2. The acoustic chambers are not the same which changes the sound (mostly flatness/resonances). There is a huge difference between "over the ear isolating", "over-ther-ear-open", "in-ear", "on_ear". You have no idea what model was used to measure the headphone (headphones are tested with HATS, such as http://www.bksv.com/Products/transducers/ear-simulators/head-and-torso )
    3. Power levels/sound pressure level capacity of different transducers are different.
    4. Impedances are different (which affect loudness achievable with a given device)
    5. Acoustic matching between ears can be very different, affecting acoustic imaging

    If he ever listened to a beats and then to a studio monitor headset with the same specs, he would never say such a thing. The effect is BLATANTLY OBVIOUS. It is not placebo effect.

    BTW, these effects are all measurable, not psychological. There is much more to sound measurement than frequency response.

    It's like he said that all speakers with 20 to 20KHz frequency response are the same. That's ridiculous. I can adjust cheap speakers to have the same frequency response as expensive ones. And, the differences are measurable. Damping factor, distortion, intermodulation, acoustic chambering, multiple transducers with crossovers, etc etc etc.

    There is no difference between a ferrari and a ford mustang. They can both go from 0 to 150MPH.
  12. Jan 12, 2016 #11

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    Last edited by a moderator: May 7, 2017
  13. Jan 13, 2016 #12


    User Avatar
    Gold Member

    Jim, did you look at the head and torso simulator? We have a couple at work. They even have different ear material inserts because it affects the acoustics. The microphone is a cochlear simulator to emulate the loading of the ear canal. They include the torso because of reflections that can impact the headset microphone and noise cancellation.

    The OP's instructor has no idea of the real engineering involved in the design, manufacture and calibration of even a cheap headphone, much less a really good one. And it isn't audiophile mumbo-jumbo. It is all verifiable (measurable) quantified effects. (I'm so anti-audiophile it isn't funny)

    Even the natural resonances that happen in an earphone due to the length of the ear canal have a huge impact on sound. Some people try to compensate, some don't.

    Here is some pictures of the effects I listed in my previous post. Again, these things are all real and have an impact on the sound. It is not audiophile mumbo-jumbo (like 99% oxygen free cables) http://www.headphone.com/pages/evaluating-headphones

    The one thing that does vary is what people like. It's possible to actually prefer a sloppy headphone (like a beats --- YEECH) or a consumer tweaked Bose (they have the sauce many people like, but it isn't accurate). It isn't possible to say it is not different.

    Here is an application that tries to compensate for the enclosure effects. http://mathaudio.com/headphone-eq.htm
  14. Jan 13, 2016 #13

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    no i hadnt - i guess seeing word 'simulator' i assumed it was a computer program instead of something real .

    Very interesting links, that's the fun of PF somebody has interest and knowledge in most any area.

    I particularly like the square wave tests. They show directly what's damping and natural frequencies, in situ including enclosure.....

    I was never around any high end headphones. I will likely "soup up" my next thrift store find with better drivers like i pictured above.

    My own taste has changed for two reasons
    1. I've come to really enjoy classical music. And one can stream it, KBYI 's Moron Tabernacle sunday broadcasts are a favorite with me.
    2. My old ears dont hear highs and i have so much tinnitis that what sounds 'right' for me is unbearably squawky to others

    Thanks !

    old jim
  15. Jan 13, 2016 #14


    User Avatar
    Gold Member

    I just talked to one of our headphone experts. He started sputtering and saying ridiculous when I read what the instructor was concluding. He said that it is nearly impossible to get two different headphones to sound the same. In his statistics of signals class he developed filters that equalized three headphones to sound the same (just based on linear response). He used recordings from our HATS mannequin to develop the filters. Just making them equal loudness was difficult, but once he was done you had to use A/B tests to detect the differences. The filtering was substantial.

    He said that it difficult to make two headphones sound the same even if the only difference is the plastic used in the housing (we can 3D print our own stuff)

    If the OP wants them, I can post the audio recordings made on the HATS to show how different headphones really sound. (sennheiser, bose with ANC, bose without ANC, sony)
    Last edited: Jan 13, 2016
  16. Jan 14, 2016 #15
    IMO, the differences do not scale with price. You are nearly as likely to find a cheap set with good sound as you are an expensive set with poor(ish) sound. Equipment brand names likely matter as some are built by audio engineers. But some high end equipment is likely built by accountants, so it's a crap shoot as to who's in charge of what brand in any given decade.

    I buy my earbuds at the dollar store. I buy four or five, and a couple work -- for a while. But that's still a lot cheaper than paying $20 and still having them malfunction.

    I am not an audiophile though. Comfort, style, and keeping up with the Joneses argue against my approach.

    Audio engineering makes a big difference but pretty much only in/after the transducer stage. Sound waves are tricky and rightly have their own engineers. The problem is telling which company hires good engineers and which hires good accountants.
  17. Jan 14, 2016 #16


    Staff: Mentor

    You'll see me right behind you at the dollar store checkout Jeff. But I almost never listen to music, only speech. Also, my ears hear nothing beyond 2 kHz. Thus the only quality I'm interested in is how long they last. Like you, I found that the expensive ones fail just as rapidly as the dollar store ones.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Similar Threads for lecturer incorrect misunderstand
Simple Battery Misunderstanding