Sound Engineer Posted November 18, 2014 Share Posted November 18, 2014 Hi chaps, I'm on a corporate event this week. Bog standard conference set up, KV2 fronts, delays and fills, LS9 at control and a load of Sennheiser G3 lavaliers. I've worked in this room before without problem so was pretty confident that it would sound ok, but today I was having to battle the system the whole day to avoid feedback (around 500Hz to 1kHz After a bit of faffing, I realised the G3 beltpacks were set slightly less sensitively (-30dB as opposed to my usual -27dB) so I upped them by 3dB and dropped the gains on the LS9 by 3dB accordingly. Immediately the feedback problem was gone and it was business as usual. Comparing two identical mics and capsules side by side, it was apparent that there's quite a significant tonal change between running the gains at -26dB and -23dB on the console, in particular as you cross the -25dB threshold where you get the relay click as it drops the voltage to the pre-amp. When you get above -25dB of gain, there is a significant jump in the level of reproduction of the mid-range. Anyone else ever encountered this? It was driving me absolutely mad until I fixed it Link to comment Share on other sites More sharing options...
Oldradiohand Posted November 18, 2014 Share Posted November 18, 2014 Is that relay also changing the input impedance? Mic input is usually a couple of hundred ohms and line is tens of thousands. Link to comment Share on other sites More sharing options...
Sound Engineer Posted November 18, 2014 Author Share Posted November 18, 2014 That's a good question, I'd have to check the specs. As there's no hard switch between line and mic level it must come somewhere in that range. I'm using an SB168 Ethersound stagebox which I don't often have which may explain why I've seen differences this time that I've not noticed before. I've not yet compared the onboard pre-amps to the external box. Link to comment Share on other sites More sharing options...
Brian Posted November 18, 2014 Share Posted November 18, 2014 Mic input is usually a couple of hundred ohms...Not usually they're not; more like a couple of k. Link to comment Share on other sites More sharing options...
Oldradiohand Posted November 18, 2014 Share Posted November 18, 2014 Mic input is usually a couple of hundred ohms...Not usually they're not; more like a couple of k. I stand corrected. Link to comment Share on other sites More sharing options...
Electrolytic Posted November 19, 2014 Share Posted November 19, 2014 yeah the LS9 preamps are one of the main reasons it gets a lot of hate. Link to comment Share on other sites More sharing options...
Bobbsy Posted November 19, 2014 Share Posted November 19, 2014 If I had to guess...and I stress that this is only a guess...I'd be more likely to think that the gain change on G3 is the culprit. With the use of pre-emphasis/de-emphasis circuits on the RF, it would be pretty easy for this to change the frequency response slightly. Indeed, I've often thought (but never measured) that I can hear slight changes to the tone (and not just the level) when changing the sensitivity on the Sennheiser belt packs. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.