Re: Does Anyone Understand Matching Sensitivity?
- From: Mike Rivers <mrivers@xxxxxxxxxxx>
- Date: Sat, 02 Aug 2008 15:07:55 GMT
Davy wrote:
I wish I understood why 0 dBu is 775mV.
That's easy, but it's a long story. It's "0" because that's a standard nominal level from which everything is either higher (+) or less
(-). The 775 mV comes from a telephone company standard.
> Might help if I understood why
sensitivity is measured in dB rather than say 500mV input gives 50W output.
dB is a ratio of two related numbers - but the numbers have to be related, that is, represent the same thing. mV and W are not the same thing. You need another piece of information. If you specified the load impedance (an 8 Ohm speaker, for example) then you could calculate the voltage across the speaker (20 volts) so you could say the sensitivity, or actually voltage gain - the output divided by the input - is 20/0.500 or 40. This can be represented as 32 dB. (look up the formula)
Side note: Someone will complain that this is not correct because dB is only for power ratios, but this is the way WE do it now.
The sensitivity of a microphone is expressed in terms of volts out for a given sound pressure level at the diaphragm. To further complicate things, SPL is often expressed in dB relative to a standard sound pressure level based on air pressure. And voltage out is often expressed as dBu. So you can only compare things if you know how they're measured.
The amplifier is quoted as having an input sensitivity of -10dB/10k ohm unbal.This probably means -10dBu.
Maybe it does but even if it does what would it mean?
First off (if I didn't say this before) it's probably -10 dBV. dBV is voltage relative to 1 volt (rather than 0.775 volts). We didn't use dBV commonly until the "prosumer" gear came along in the late 1970s. They could save money by operating at a lower level than the "pro" standard. Manufacturers wanted to have an equivalent to the professional standard operating level of +4 dBu, and so as not to confuse beginners with yet another odd number, they decided to reference things to a nice even number, and choose their standard operating level as a nice even number (10) of dB lower than the standard.
I have to put the mic not less that an inch in front of my mouth and talk fairly loudly to get acceptable volume on the speakers.
In that case you need more gain somewhere. Try connecting the line output of a consumer audio device like a portable CD player to the amplifier input and see how loud that gets the speakers. If it's plenty loud, then you need to get more signal out of the wireless receiver.
--
If you e-mail me and it bounces, use your secret decoder ring and reach me here:
double-m-eleven-double-zero at yahoo -- I'm really Mike Rivers (mriv...@xxxxxxxxxxx)
.
- Follow-Ups:
- References:
- Does Anyone Understand Matching Sensitivity?
- From: Davy
- Re: Does Anyone Understand Matching Sensitivity?
- From: Scott Dorsey
- Re: Does Anyone Understand Matching Sensitivity?
- From: Davy
- Does Anyone Understand Matching Sensitivity?
- Prev by Date: Re: Alan Blumlein on radio tonight
- Next by Date: Re: Oktava MK-012 mod went wrong :)
- Previous by thread: Re: Does Anyone Understand Matching Sensitivity?
- Next by thread: Re: Does Anyone Understand Matching Sensitivity?
- Index(es):
Relevant Pages
|
