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TPA3255: Distributed Speaker Installations.

Rudjeev Gunawardana
Prodigy 30 points

Part Number: TPA3255

I plan to use TPA3255 in medium sized PA systems in buildings and outdoors (e.g. schools). The wires will be long and I am aware that I will need to match impudence to optimize power transfer. The outdoor systems are likely to use horn speakers.

Given above, will there be problems related to long wires and/or characteristics of horn speakers? I believe EMI concerns are covered but again, I would be interested in comments relating. I am more interested in possible problems or precautions to be taken at circuit level or limits on number of speakers and wire length.

Also, are there other concerns such as OP latching and/or static damage.

Raj Gunawardana

  • 0
    TI__Genius 11490 points

    Rudieev,

    How is the impedance of the longwire?  you can estimate from wire's diameter/length/material. 

    How much power are required to for the speaker?

    With above information, we can estiamte how much power required at TPA3255 output side, or how better the wire should be.

    Dylan

  • 0 in reply to Dylan Yao
    Prodigy 30 points

    Thank you for getting back. On impedance, we would be using 16 AWG at around 1 Ohm/1000 feet and so the wire impedance will be low. Horn Speakers have typical 16R value but we can adjust with serial-parallel combinations. I am really not too concerned with maximum power transfer as there is plenty of headroom.

    It is, if anything, more likely that the application will present too high an impedance than too low. This kind of match is not discussed in datasheets presumably because the challenge is to drive power into lower impedences (2R is mentioned in the TPA3522 datasheet).

    My concerns are practicalities of use.

    Are you aware of TI Class D being used in similar applications and if so, are there any problems or precautions to be observed beyond those recommended in datasheets?

    It would be good to present the problem to a TI expert on the topic... I believe the application type is a menaningful possibility for the high power devices.

    Thank you; Raj Gunawardana

  • 0 in reply to Rudjeev Gunawardana
    TI__Mastermind 19080 points

    Hi Raj,

    Could you tell us the cable length in your design?

    Please note that the impedance is not only the resistance. The parasitic inductance also plays a role. 1m wire can have a roughly ~1uH distributed inductance. and the audio signals are AC signals.

    We do have seen some customers are using a few meters length cable, and not much issues here. Just take care of the EMC considerations, as the long cable will enlarge the parasitic capacitance with reference ground.

    Regards,

    Sam