[preeble]

I have a 987.1 Boxster S with Bose (CDR24). I am using an FM Transmitter (made by Roav/Anker) to allow me to connect me to stream music and talk from my phone. The functionality works perfectly with one issue (and a rather annoying one) - on some songs, I get repeatable distortion coming from my speakers (in other words, at the same point in the song, I get distortion every time). In some songs, I get no distortion at all and in others, lots of distortion. Some additional notes/comments:

- An example song is Michael Jackson's Rock with You at the 6th second of the song (I played it from the Google Play app)
- The distortion seems to be a static sound cutting in that overlays the music. The distortion/static seems to come at a mid-level music frequency (i.e., not at a bass or treble-heavy section).
- I have tried different FM frequencies with the same result
- I have tried music from different sources/apps with the same result
- I have tried this FM transmitter in two different cars and have not heard the distortion mentioned above (in fact, I never heard distortion at all)
- I have even pulled another car next to the Porsche and transmitted from that car (the CDR24 picked up the signal fine) and have heard the distortion in the Porsche, but not the other car

Based on my tests above, I don't think it is the music source or the FM transmitter because I cannot replicate the issue in any other car. The best I can conclude is that the FM transmitter is transmitting music outside of the CDR24's range and when it receives this signal it throws static because it doesn't know what to do with it.

Is this even possible? I am sort of at a loss here.

 

[danschy]

Could be the FM Transmitter is modulating a little too far for the CDR24 to handle. Selectivity in an FM radio is a balance between maintaining low distortion on-channel and rejecting off-channel signals. Could be the CDR24 has a narrower band-pass filter than other radios you've compared and it can't handle the signal of the Roav/Anker FM transmitter. If you turn the volume down on your phone, does the distortion go away? I have used a couple different transmitters in my 07 Cayman with CDR24 and they both sounded fine.

 

[preeble]

Thanks for the insightful response. If I turn the volume down on my phone (to about 50%), the distortion does seem to go away, but it is very hard to tell because I have to turn up the volume to almost the max on the CDR24 (40) to hear music at a reasonable level and when I do that, I hear the typical FM static/background noise. As such, that is not an acceptable solution.

Also as an FYI - the phone I am using is a Samsung (S10+); I have tried different EQ settings, turning on/off Dolby, etc. and I still get the distortion noise. I did read a suggestion somewhere else to muck around with the developer options that deal with sound to see if that changes anything. I haven't tried that yet. I may also try to use an iPhone to see if that changes anything. Lastly, I just may try another FM transmitter to see if that rectifies it.

 

[eyeofthetiger]

a bit of guessing here - hope these points help...

there are 3 things worth looking at:
1. the stock speakers are a bit old about now and it may be worth having a look at them first
2. test the bose amp
3. stuffing the bose subwoofer (see this example - https://www.planet-9.com/987-cayman-and-boxster-electronics/232515-re-post-subwoofer-pillow-hack-instructions-please.html?highlight=)

 

[preeble]

When I listen to a CD or even the radio, the speakers sound good (or at a minimum fine). One of my original thoughts was that perhaps the amp was going, but I think I would hear this type of distortion across all sources.

I will have to consider the Bose mod...

 

[eyeofthetiger]

some players have separate sound settings for different sources....does the CDR24 have that?

 

[preeble]

Your responses were helpful - after more investigation, it looks like the static is coming from the high frequencies. If I turn down the two highest frequencies in my phone equalizer (I have an android), the static/distortion is greatly reduced when using the FM transmitter. Again, what is strange is that I get no distortion when playing normal radio or when playing a CD, which sort of rules out an amp issue.

Oh well, this band-aid will have to be good enough. If any of your are using an FM transmitter on a CDR24 without distortion (that you bought sort of recently), can u let me know which one you are using?

Thanks

 

[danschy]

Yep that makes sense since higher frequencies would produce higher FM deviation on the RF signal and thus stress the filter more than low freqs. I now use a TranzitBlu, but prior to installing that I used a "GOgroove FlexSMART X2 Bluetooth FM Transmitter" which sounded good. I bought mine in 2013, but looks like they now have a 2019 model - not sure how they compare.

 

[preeble]

Yep that makes sense since higher frequencies would produce higher FM deviation on the RF signal and thus stress the filter more than low freqs. I now use a TranzitBlu, but prior to installing that I used a "GOgroove FlexSMART X2 Bluetooth FM Transmitter" which sounded good. I bought mine in 2013, but looks like they now have a 2019 model - not sure how they compare.

I purchased the model you mentioned and still have the same distortion. My solution is to turn the higher frequencies down on my phone equalizer and the distortion goes away.

 

[danschy]

I purchased the model you mentioned and still have the same distortion. My solution is to turn the higher frequencies down on my phone equalizer and the distortion goes away.

Sorry. That unit is the best sounding one I've heard - way better than the TranzitBlu I replaced it with. I'm half-way through a road trip and have begun to hate the sound from the TrazitBlu, so plan to replace the head unit when I get back home and be done with the external blue tooth solutions.

 

[preeble]

Sorry. That unit is the best sounding one I've heard - way better than the TranzitBlu I replaced it with. I'm half-way through a road trip and have begun to hate the sound from the TrazitBlu, so plan to replace the head unit when I get back home and be done with the external blue tooth solutions.

Yep - that is the route I ultimately plan on going.