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Splitting signals for a hearing aid and headphone - Balance XLR on the Phonitor 2

monophreak

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Hello Everyone at Audio Science Review!

This post is a little bit niche but I can see there is a substantial amount of expertise on this forum. My situation is as follows. I have been Single Sided Deaf (left ear) for most of my life (with a working ear on the right). Fortunately, I recently have some hearing restored in my left ear through a BAHA and I am looking for a way to split a balanced signal from a SPL Phonitor 2 to two devices. I wish to send one signal to an Audio-Technica ATH-M70x speaker (single - other speaker unhooked) and one to the line in of my hearing aid (unbalanced). Latency on the left/right channels can be controlled successfully through Audio Hijack.

Specifications:
Phonitor 2 manual: https://spl.audio/wp-content/uploads/Phonitor_2_BA_EN.pdf -
  • Neutrik XLR, balanced, Pin 2 = (+)
  • Headphone output: 6.35 mm TRS connector
    "Warning: Never connect a mono jack cable to the headphone output (front panel stereo jack). Make sure that the stereo jack is fully inserted, otherwise a short circuit might damage the headphone amplifier!"
Hearing aid line in connection via TV Streamer: https://mss-p-007-delivery.sitecore...t/aceb75afdf2547808ce81473ef450f25?v=f6ef89fa or Mini Mic 2.


Do you know if it is possible to do any of the following and what would the implications be:

Option 1:
BACK Balanced XLR out LEFT via XLR to unbalanced RCA (or 3.5mm jack)--> Hearing Aid Adapter.
BACK Balanced XLR out Right via XLR to (unbalanced) 3.5mm headphone jack -> Single Audio-Technica speaker.
Option 2:
Headphone output on the front (TRS) --> TRS female/female left/right splitter.
Splitter left TRS to 3.5mm jack --> hearing aid line in.
Splitter right TRS to 3.5mm jack --> Audio-Technica M70x.
Option 3:
RME ADI-2 Pro FS BE where I would use the Mac (DAW) --> USB --> ADI-2 Pro (DAC).
ADI-2 Pro main XLR balanced outputs --> Phonitor 2 XLR balanced inputs.
I use the Phonitor 2 monitor angle, cross talk, m/s isolation and general mixing and spacial features.
Phonitor 2 output signal ---> back to the RME ADI-2 Pro balanced XLR/TRS inputs.
ADI-2 Pro headphone out 1/2 --> Audio-Technica.
ADI-2 Pro headphone out 3/4 --> hearing aid line in.
In this scenario (if it works), would I then increase the volume on the ADI-2 Pro or the Phonitor 2 (or leave them 50/50 or another config).
Option 4:
I use some sort of splitters that takes a balanced output from the Phonitor 2 and divides the signal in two.
I can then use one signal --> hearing aid line in.
The other --> Audio-Technica ATH-M70x
Option 5:
Anything else that would help me take advantage of the mixing capabilities of the Phonitor 2.

Thank you for your time and expertise. Dividing balanced stereo signals and their associated configurations is a new world to me. I used to just plug in a headphone and away I go (using one ear) but I want to harness the new opportunity to hear again.
 
OP
monophreak

monophreak

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Thanks AnalogSteph,

I completely agree with your opinion on Option 3 being overdressed. I think I will go for that though because I have no idea how the SPL 120V rail technology acts with unbalanced cables and at least I can make a loop of balanced in/outs. Plus, I intend to upgrade my DAC anyhow and the RME ADI-2 Pro version has two headphones out. I can see that being really useful for various hearing aid applications.

From the sounds of it, I think I can put the Pro into a multiple in/out mode.

When it comes to hearing aid adaptions, I will have to give it a go and then I will add information about my findings to my blog so that there are more experiences available, showing attempts on how to hook up these types of systems.

After reading the SPL Phonitor X review from Audio Science Review (link), I can see that "But if you have a 300 or 600 ohm headphone, this thing sings. And sings really loud!". This makes me think I should have a lower volume from the RME ADI-2 Pro entering the Phonitor 2 and then raise the volume higher on the Phonitor itself - to drive the unit. Do you know if I have interpreted this correctly?
 
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monophreak

monophreak

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After re-reading your reply AnalogSteph and checking the manual, I noticed that (I think) the front headphone out isn't balanced which gives me more options related to Option 2 and I understand your post.

From the manual:

Outputs
Headphone output
Warning: Never connect a mono jack cable to the headphone output (front panel stereo jack). Make sure that the stereo jack is fully inserted, otherwise a short circuit might damage the headphone amplifier!
  • 6.35 mm TRS connector
  • Pin wiring: Tip = Left, ring = right, sleeve = GND
  • Impedance: 0.18 ohm
  • Attenuation factor: 180 @ 40 ohms
  • Frequency range: 10 Hz to 300 kHz ( -3 dB)
  • Crosstalk at 1 kHz: -90 dB
  • THD & N: 0.00091% (at 0 dBu, 1 kHz, 100 kohms load)
  • Noise (A-weighted): -103 dB
  • Dynamic range: 134 dB

In relation to the Audio-Technica ohm resistance which I believe to be 650ohm, I think I can reduce the output on the hearing aid item through an in-line dial I bought a while back.

As a result, do you have any ideas if I could just use something link this (link) - 6.35mm 1/4" Jack Adapter Y Splitter TRS Cable Male to 2 Female - to split the signal in 2. Split 1 stereo jack signal into 2 jacks.

Or even better this: (link) Large Stereo Jack Dual Mono Splitter Y Adaptor which I assumer would make the left mono one side and right mono the other.

In relation to the warning, as all of the TRS tips have two lines (for stereo), do you know if this could cause any problems if one of the ends of a splitter was not connected? (or switched off in the case of the hearing aid line in)
 
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AnalogSteph

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As a result, do you have any ideas if I could just use something link this (link) - 6.35mm 1/4" Jack Adapter Y Splitter TRS Cable Male to 2 Female - to split the signal in 2. Split 1 stereo jack signal into 2 jacks.
As long as something playing in the M70X on the side with the hearing aid is not a problem, this should work. Assuming you can reconcile the level needs of the hearing aid input and headphones decently enough, that is.
Or even better this: (link) Large Stereo Jack Dual Mono Splitter Y Adaptor which I assumer would make the left mono one side and right mono the other.
Yes. Do note that mono output (TS) always ends up on the left channel. You may need a mono to stereo adapter in addition (TS plug to TRS jack) so the headphones also emit sound on the right ear.
In relation to the warning, as all of the TRS tips have two lines (for stereo), do you know if this could cause any problems if one of the ends of a splitter was not connected? (or switched off in the case of the hearing aid line in)
Unconnected is not a problem, you're just not supposed to short a channel to ground or both to each other. Leaving the hearing aid transmitter connected but not powered on may or may not be a problem depending on what kind of input / input protection circuitry it uses. Its specs aren't very detailed, so if in doubt one may have to consult the manufacturer.
 
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monophreak

monophreak

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Yes. Do note that mono output (TS) always ends up on the left channel. You may need a mono to stereo adapter in addition (TS plug to TRS jack) so the headphones also emit sound on the right ear.

Unconnected is not a problem, you're just not supposed to short a channel to ground or both to each other. Leaving the hearing aid transmitter connected but not powered on may or may not be a problem depending on what kind of input / input protection circuitry it uses. Its specs aren't very detailed, so if in doubt one may have to consult the manufacturer.
Thank you for this AnalogSteph, your help has been amazing. I did not know that the mono output ends up on the left channel and this has definitely saved me time when troubleshooting and for preparation.

Due to my late night posting, I managed to get my Audio-Technica model mixed up. I have an ATH-R70x (not the M70x) but interestingly, I think the mixup has helped. While looking at the M70x cable, I realised that this could work on my R70x for one speaker. The R70x cable split in two 2.5mm jacks whereas the M70 stays as a single 2.5mm jack. I wanted to avoid the second 2.5mm jack from dangling down but by using a single jack M70x cable instead, this will not be an issue.

Due to the mono signal (which would be from the right side of the splitter) travelling on the left, my thoughts are I can run this cable into the left headphone speaker. I think this should give me the sound on the right.

My final challenge is understanding the nature of a short. Using a TRS splitter to TS (left), TS (right) - it would be really great to understand what happens when I plug the headphones TRS cable into the right.

Would it be as simple as that since only one channel is coming out from the Phonitor (as it has been split) the TRS cable itself would only receive one signal down the left. In this case, does the TRS part itself short and can this cause an issue? or, has this issue has already been solved at the TRS splitter section where it was split into two TS signals already so nothing can go up or down at that point?

Thank you so much. I am learning a lot.
 
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