Using a stereo amp from a mono signal? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 7 Old 05-23-2009, 07:11 AM - Thread Starter
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Im setting up a system in my basement and i wanted to use an older set of speakers my dad has. He built them in the 60s so im sure the drivers are shot. They still work but im sure they cant handle any kind of power.

What i thought ide do is keep them around because they look nice but replace the driver with a sub and just use them as sub cabnets.

The reciver i was going to use has a mono signal output, his receiver still works so what i thought was maybe i could use his receiver as the poweramp to drive the subs from the sub preamp of the receiver im going to use.

My question is, since his stereo has stereo in my output is mono can i just use an RCA splitter and just split the mono signal from my receiver out to his then just hook up the speakers as normaly?

When running a mono signal can i run the subs out of phase to get a better bass sound?

I remember when i messed around with car audio and i ran 2 subs i got way better bass when i ran them both out of phase from each other. (as one fired out when a bass note hit, the other woofer would pull in giving this feeling of more bass or somthing.

Will there be any ground loop problem or any feedback or somthing weird when i split the signal and send the same signal to both inputs?

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post #2 of 7 Old 05-23-2009, 07:16 AM
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I don't fully get what you are trying to do, but splitting a mono signal to stereo inputs should work fine.

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post #3 of 7 Old 05-23-2009, 08:08 AM - Thread Starter
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Sorry i ramble sometimes.

My dad has some old speakers from the 60s he built but i wanted to keep them because he built them. You cant see the driver because of the grills he put on them. They look nice so i wanted to keep the cabnets but replace the driver for a sub. 2 nice old cabnets with 2 new subs.

Now my receiver im going to use with the surround sound format has all the ins and outs but it also has a pre sub output. What i thought ide do is keep his old receiver but use it as a power amp for the subs im gona put in his cabnets. Use his receiver as a sub power amp to power his cabnets with my new subs in it. They are a nice size for a 12" sub.

Since they were once full range home stereo speakers there is 2 so i thought insted of using a mono sub like most systems have use the stereo amp to power 2 of them

I was just wondering if ide have any problem running both inputs into 1 because my receiver just has the "mono pre sub out"

His receiver also has a 7 band EQ so i could evenremove alot of the high end in the signal if there is any

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How can you tell a point is a reflection point?
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sit in normal spot
have friend slide mirror on wall
see speaker? bingo!-Max
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post #4 of 7 Old 05-23-2009, 08:14 AM
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Far as I know, that should work. Note though, that subs need more power than other speakers, or at least need to be able to hit higher SPLs.

For movies, the LFE level is 10 dB higher than the other channels (see https://www.avsforum.com/avs-vb/showthread.php?t=748147)

And if your bass is being sent to the sub from the other channels, that will also increase the SPL your sub needs to deliver, but I don't know how much.

That being said, I have a powered sub in my system rated for only 100 watts or so, and it seems to handle my needs fine.

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post #5 of 7 Old 05-23-2009, 08:37 AM
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Quote:
Originally Posted by BowerR64 View Post


When running a mono signal can i run the subs out of phase to get a better bass sound?

It will work, usually you can set the crossover point in the main receiver for the LFE out (mono). The receiver you are using for the subs will just get the bass signals, the eq may not be necessary. But could come in handy to tame certain room boom nodes, if it has enough trims in the low end (32hz, 50hz, 100hz.) which is possible being a 7 band. You just need an Rca one male to two female splitter and a regular stereo Rca cable to hook this up. Furthermore, I don't know exactly how you were able to get more bass by running the subs out of phase in your car audio, but do not recommend doing so with the setup here as running speakers out of phase with each other would normally cancel out critical bass frequencies.
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post #6 of 7 Old 05-24-2009, 03:29 PM - Thread Starter
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Well it was in a car, you know how tight cars are. The first setup i did this with the subs were in the same cabnet but ive had it happen with a devider also.

It was by accedent once and i jammed on it for a while then i rewired everything and found it lost alot of bass so i messed around with it and figured out what was going on. I then asked a car audio guy and he told me it was called "out of phase"

I havnt really been able to hear it work on home audio equipment. Either its somthing that only happens with DC or in small cars or it was just somthing that happened with amps back in the 80s and 90s.

I even remember amps with switched on them called reverse polarity that you could flip and hear the difference when you flipped it.

I do notice with home audio the bass sounds the best in the center directly between both speakers. With the out of phase setup it didnt do this. The bass was good anywhere.

Quote:
Originally Posted by donsantos
How can you tell a point is a reflection point?
Quote:
Originally Posted by maxcooper
sit in normal spot
have friend slide mirror on wall
see speaker? bingo!-Max
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post #7 of 7 Old 05-24-2009, 03:38 PM
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Out of phase implies that an input wave arrives at your ears at different times from multiple speakers. There are multiple ways this could happen. Speaker location, accoustics, or somewhere in your signal path are three ways I can think of.

In other words, a instant moment in time of an audio track would ideally arrive at your ears at the same time for each speaker it was playing out of.

If the sound from two speakers are arriving in phase, they will reinforce each other - ideally, a 3 dB gain if I am not mistaken.

If the sounds arrive 180 degrees out of phase, they will negate each other. This is the principle behind noise reduction headphones.

If the sounds somewhere in between, they can either reinforce or reduce each other depending.

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