Impedance matching

[sipleybeck]

I thought I had decided to buy a Countryman Type 85 instead of a Klark Teknik LBB100 - then I remembered one question I forgot to ask.

The Klark Teknik has an output impedance of 150 Ohms, which matches exactly the input impedance of the signal processor I intend to plug it into.
The Type 85 does not publish output impedance in its specs. But another box I was considering is rated “Max. Output Level: +8dBu into 600 Ohms or greater."

How critical is it to match output impedance to input impedance, and what happens when they are not close?

 

[mixsit]

Generally the impedance of output devices are alot lower than inputs, so that small variations won't affect the signal comming into it.
The 'Type 85' spec is showing output power. It wants to see 600 ohms or greater, but most line inputs are much higher, so...
Wayne

 

[sipleybeck]

I’m confused.

First: Why isn’t there a standard for publishing specifications? Here are published specs for three similar products (DI boxes).

1) “-100dBu, 20Hz to 20kHz unweighted, with input terminated by 10k resistor”
2) “<-105dB unweighted, 22hz-22khz, rms*”
3) “149 dB SPL, 1 kHz at 1% T.H.D.”

Q1: Which one is quietest?


Second: Symetrix 528E specs state:

Equivalent Input Noise -126dBv (150-Ohm source,20 Hz to 20 kHz)
Line Input Type and Impedance 10kilohm Transformerles, Balanced Bridging

(Somehow, I have gotten the impression that the E.I.N. spec relates to mic input)

And: The following specs describe Output impedance characteristics for three DI boxes:

1) “+8dBu into 600 Ohms or greater”
2) “150 Ohms” “Min. Load 600 Ohms”
3) “<no specs>”

Q2: Which one is best matched to the 528E?