Improving Headphones By Voiding Warranties

[Dan] had been wanting a pair of Bluetooth headphones for quite a while. Most of the reviews for wireless headphones in the $50-$80 range complained of tinny sound and dropped bass. Nevertheless, he stumbled upon a $20 pair of headphones with similar reviews and realized that he could switch out the driver and make a decent pair of cans.

The donor drivers came from a pair of Sennheiser HD 540 headphones. These are very respectable headphone speakers that cost about what you would expect for pro audio gear. To to get Bluetooth working with the Sennheisers, [Dan] removed the PCB and battery enclosure and attached them to the headband with velcro.

For his build, he had to cut the cable on the Sennheisers and solder them to the Bluetooth board. There was never any danger of ruining a good pair of headphones, though. If he screwed up he was only out a headphone cable. Now [Dan] has a nice pair of Bluetooth headphones that can reproduce bass. Not a bad deal for a $20 pair of headphones.

34 thoughts on “Improving Headphones By Voiding Warranties

  1. sorry to nitpick (let another flame on negative comment roll), but he did not really switched out the drivers (speakers).
    He used the BT module to drive a HD 540 headphone.

    Aldo it seams silly, it looks a BT headphone in itself seams cheaper than getting a bluetooth headphone receiver for a existing non BT headphone…
    economics, who understands it?

    1. It could still be an improvement over the original drivers, but swapping his 30ohm drivers for the 540s 600ohm drivers would cut his battery life significantly, not to mention lost signal quality going through the BTs built-in amp.

      1. 30 ohm speakers actually use more power than 600 ohm speakers.

        The 600 ohm ones are more sensitive – they make more noise with a smaller current, which is why they’re better for bass from weak signal sources that can’t source a lot of current to drive low-impendance speakers.

      2. @Dax You’re right that higher impedance drivers draw less power at the same volume (as in volume knob position), but the output of the 600ohm drivers would be far quieter.
        Amplification is the major battery drain with wireless headphones, which is why they rarely exceed 50-60ohms. Swapping in 600ohm drivers would require you to turn your volume right up, assuming they can even reach a normal listening level.

      3. Talking in terms of voltage gain and resistance is a bit silly here. A larger voltage gain does not necessarily require more power if the load its driving requires less current. P=IV, Volume = Sensitivity * P. Nothing more.

        Now you may hit a hard volume limit caused either by the gain of the amp or clipping due to the low voltage swing some battery under-powered devices are capable of, but in terms of increased battery drain you won’t notice much of a difference.

      4. @Paul

        It’s not so simple. Higher impendance comes not only from higher resistance, but also from higher inductance which means stronger magnetic field for the same current, so the speaker is more sensitive. It produces more decibels per watt, compensating for the fact that it draws less current from the amplifier.

        There’s also the matter of impendance matching between the amplifier and the speaker. All in all, you get the most power out and the loudest sound when the speaker’s internal impendance is the same as the amplifier’s, but when the speaker’s impendance is much greater, the efficiency of the system increases, compensating for the drop in power.

      5. 600 ohm drivers have greater impedance, will use significantly less power than 30 ohm drivers. Power amp should not have problem with less power required by the headphones. 600 ohm drivers have greater force factor, product of strength of magnetic filed and length of wire in the field, so they should be more sensitive, resulting usually in equal sound pressure with less power used.
        As far as sound quality goes that is at least with headphones usually more related to mechanic and acoustic properties of driver and headphones..

  2. polossatik is right,
    I will say, the rocketfish stereo bluetooth headphones are 70 bucks, and have 5 settings including bassboost which is fantastic, and they have a mind blowing battery life, I’d much rather keep them than make a pair.

    1. Nice, but I can get refurb NOKIA BH503 for $20 with a warranty… I’m not easy on my bluetooth headphones, I use them for everything. Can’t beat a NOKIA.. they take a beating, and keep kicking ass :)

  3. I had a pair of Philips SHN-2500’s and they worked reasonably well. But they had this nasty habit of breaking right at the active noise canceller portion.

    So I modified the hell out of it. Resoldered everything and added the ubiquitous hot glue. Dealt with that until I finally got a pair of Mororola MotoRokr S9’s. I actually like those.

  4. Does bluetooth even have the bandwidth to support true “High Fidelity” audio? I mean, sending 96 kb/s is all well and good but that isn’t exactly fully utilizing your quality drivers. Last time I tried to listen to bluetooth music, it sounded great but it was hardly amazing.

    1. I say “amazing” in the context of everyday listening acceptability. Likely complete rubbish by audiophile standards, but for the average person who just wants something to drown out background noise while working on projects in class, and not suffering from tin can treble, this is more than acceptable.

      It is essentially like having wired headphones, but listening to a 96 kb/s MP3. There’s no hissing or glitching, but you indeed know it doesn’t compare to any lossless codec.

    2. 96 kbps, you are very wrong.

      •High Quality – 328 kbps
      •Middle Quality – 229kbps
      •Low Quality – 201 kbps

      Your average mp3 is 128 kbps, but I download everything as high quality as I can, and the iPod’s bluetooth mirrors every single bit of that quality perfectly.

    3. no it doesn’t. BT accepts raw audio (mp3 compression is irrelevant here). It has nowhere near the bandwidth necessary for transmitting audio in a quality good enough that you couldn’t tell it goes over bluetooth. In mono maybe (dunno if the protocol supports higher single channel bandwidth) but definitely not stereo.

      1. Yes it does. The most common and quite outdated bluetooth v1.1 has more than double the maximum bandwidth usable in the MP3 codec. Any audio quality issues are down to the codec being used.

        Modern bluetooth standards have enough bandwidth for reasonable quality video too.

      2. That’s all well and good, assuming you’re streaming the MP3 and decoding it in the headphone, but what you have here is basically a two-step compression, first the MP3 and then whatever bluetooth audio uses for a lossy compression for audio.

        Twice compressed 200 kbps in a lossy codec does not make it 200 kbps at the output, because it tries to compress all the artifacts produced by the first stage codec, and that robs fidelity from the genuine audio data that you’d want to hear.

        The quality is exponentially worse after each recompression step.

    1. I think most, if not all do, but what modern device would use anything older than 4? All I know is my headphones play HD audio, with wicked base, better than the beats by dre headphones one kid brough to school.

    2. Bluetooth v1.2: 700kbps
      Bluetooth v2+EDR: 2.1Mbps
      Bluetooth v3+HS: ~24Mbps (Uses BT to negotiate an 802.11 link)
      Bluetooth v4: Recategorizes previous BT versions and adds the Low-Energy version. No difference in speeds.

      The limiting factor in wireless headphones, like most wireless technology, is the power source. I’m sure you could make some decent wireless headphones if you didn’t mind wearing a laptop battery on your head.

      1. Looks like you could EASILY send FLAC or even Redbook Audio at those bandwidth limits. Obviously real world will limit them some but there is plenty of overhead left over for HQ audio at those speeds.

  5. An interesting mod for sure. I used to have a pair of Motorola bluetooth cans until I snapped the headband. I gutted them for the radio and battery with the intention of transplanting them into something with a bit more thump, until I got my LG HBS-700 for $50 shipped from NewEgg. Bass response is impressive and sound quality is quite good. Unlike my Motorola’s, I’ve only been able to tell twice that I’m listening over bluetooth.

    Either way, the hacks a great solution, I’m just wondering how well the sensitive SH drivers hide/amplify the compression inherent in the bluetooth stream.

    1. The biggest issue I’ve noticed with Bluetooth audio is pitch bending (slight), I would guess because of sampling rate instability? Regardless, sound quality is better than YouTube 240p/360p (not really an official benchmark, but something we can all relate to.)

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