# BFD for Karaoke



## ScruffyHT (Sep 23, 2008)

I asked a question in another forum about whether people use Karaoke in their Home Theaters and one of the responses was to be sure to use a feedback destroyer to avoid wrecking the speakers

Some background :

I have a HTPC with a Karaoke Builder CD+G Player installed and I was running it for my kids.

The setup included ... HTPC + cheap RS mixer + cheap RS microphones + Altec Lansing speaker/sub for PC ( My theater is under construction but I built the PC early to test with )

I figured out later that my speakers were wrecked because the cheap microphones created too much distortion ( + kids that think they are rock stars  ) for the volume level they were using it at.

A friend that has a rock/blues band told me that Shure Microphones are what he uses in his band and I looked them up online and they are fairly reasonably priced ( not " sure " which model is best for my situation but I can cross that bridge when I get to it  )

So that leaves the question of how best to protect my Home Theater speakers once the theater is done and I hook this all up in there ... 

I am thinking in the Home Theater I would have the output of the PC ( karaoke Program ) go into the mixer ( microphones into mixer as well ) and then output into the AVR

I dont know anything about a feedback destroyer ( except the name probably says it all ) but if this was something that would be beneficial in this case how and where would a feedback destroyer fit into the picture ?

I hope this is the right forum to ask this question


----------



## Wayne A. Pflughaupt (Apr 13, 2006)

ScruffyHT said:


> I asked a question in another forum about whether people use Karaoke in their Home Theaters and one of the responses was to be sure to use a feedback destroyer to avoid wrecking the speakers.


The BFD would only be needed if you were having feedback problems. As you indicated, that's not what killed your speakers.



> I figured out later that my speakers were wrecked because the cheap microphones created too much distortion ( + kids that think they are rock stars  ) for the volume level they were using it at.


The problem wasn't the mics. It's that your system was under powered and as such maxed out. 

When an amp is operating safely within its limits, its voltage output with regular program material constantly varies. When that happens, the speaker's cone moves in and out. The varying voltage and cooling effect of the movement of the cone keep the speaker's voice coil from over heating. By comparison, when an amplifier is maxed out, its output is a flat line of constant voltage. Cone movement is at full excursion and holds there. The combination of the steady-state voltage and no cooling from cone movement causes the voice coil to overheat. Eventually the winding will burn through, and you no longer have a working speaker. It's fried. To get an idea of what I'm talking about, hook a 9-volt battery up to a bare speaker. You'll see the cone move to maximum excursion immediately, and sit there. Keep the battery connected long enough and it will burn out the voice coil.



> So that leaves the question of how best to protect my Home Theater speakers once the theater is done and I hook this all up in there ...


What you need is a limiter. It will keep output at a pre-set level, no matter how hard the input is driven. Another thing that can destroy your speakers instantly would be if someone dropped one of the mics. The limiter will protect against that, too.



> A friend that has a rock/blues band told me that Shure Microphones are what he uses in his band and I looked them up online and they are fairly reasonably priced ( not " sure " which model is best for my situation but I can cross that bridge when I get to it  )


Model 58 or 57.



> I dont know anything about a feedback destroyer ( except the name probably says it all ) but if this was something that would be beneficial in this case how and where would a feedback destroyer fit into the picture ?


It (as well as the limiter) would connect between the RS mixer and your HT system.

Regards,
Wayne


----------



## ScruffyHT (Sep 23, 2008)

Hey Wayne ... thanks for the reply !

quick question ... the mixer iirc can control output so can I use that as my limiter ?

also as far as a bfd I wont know I need one till too late maybe right ?

also I am building GOM enclosures for the L & R speakers so they are hidden beside the screen ... would you just use a separate set of speakers to run the Karaoke or would you trust it to your main speakers ( just nervous after the incident with the PC speakers ) I understand the theory of overdriving a amp but I thought the microphones did not help


----------



## Wayne A. Pflughaupt (Apr 13, 2006)

> the mixer iirc can control output so can I use that as my limiter ?


That's merely a master volume control for everything that's hooked up to the mixer. Sure, you can make sure you keep the volume down low enough and avoid any problems, but that's not the same thing as a limiter. Recommended reading:

http://www.mediacollege.com/audio/processing/limiter/
http://www.ethanwiner.com/compressors.html



> also as far as a bfd I wont know I need one till too late maybe right ?


If you mean "too late" as in you've fried the speakers, it's not as bad as all that. If you find you're having feedback problems, then the BFD might be beneficial. You can also just keep the mics away from the speakers.



> would you just use a separate set of speakers to run the Karaoke or would you trust it to your main speakers ( just nervous after the incident with the PC speakers )


It would certainly be the best option to have a dedicated amp/speaker system for the karoke. Home equipment isn't really designed for the demands of live sound applications.

Regards,
Wayne


----------



## salvasol (Oct 31, 2006)

> ... the best option to have a dedicated amp/speaker system for the karoke. Home equipment isn't really designed for the demands of live sound applications..


I second this suggestion ... get a pair of speakers and a mixer/amp for your karaoke :yes: ... you can even get some used on ebay :bigsmile:


----------

