Stereo to mono

[karatestu]

I have been thinking of this recently ever since I heard my sister's single speaker B&O system. It worked really well. Obviously you don't get stereo effects like different instruments from different speakers or say a full kit drum roll panned from one speaker to the other. Thing is I didn't miss it at all

The left and right channels are summed and just come out of the same speaker. I have had the thought that listening mono through one speaker would get better results when using omni directional type speakers. Semi omni would be better than point a squirt if you weren't in the sweet spot but not as good as a true omni or quasi omni.

My diy speakers have tweeters mounted firing forward, upwards, downwards, backwards and to each side (six in all). Whilst not a true omni it is closer than a semi omni. With the bass and mid bass upward firing then that takes care of itself - it is just the tweeters to worry about with their directivity and power off axis.

The good thing about mono with omni or quasi omni is that the left and right channel information is coming from the same driver(s) so you can't be further away from one than the other. You can still be further away from the mid bass than the tweeter but that is a topic for another thread.

So what is the best way to combine the left and right signals from our stereo sources ? I don't know yet I need to do some more research or ask somebody who knows - anybody here know ?

You can't just join the two channels together and hope for the best. The signals will fight each other and the magic smoke will surely appear Get an amp with a mono switch ? Nope don't want to do that. The only two ways I currently know of how to do it is to combine the two channels before or after the power amplifiers.The following is all my limited knowledge on the subject so far and could be wrong.

Combining the signals after the power amp involves bridging the two amplifier modules. Doc did not endorse this in anyway as it resulted in repairs Essentially the bridged amplifier see's the speaker load as half of what it originally was. So an eight ohm load becomes a four ohm load. If the speaker's impedance dips down at a certain frequency then you could be in trouble. Same if you tried to bridge the amps and the speaker is rated at four ohms nominal impedance. The amp would see a two ohm load and if it was NVA (along with many others) would probably overheat and destroy the output transistors and god knows what else.

The other way that i know of and done before the power amplifier is to join the two channels to a common point but with series resistors in each line just before the join. The 0V of each is just joined together. I don't know the pros and cons of this method. I have seen 1K resistors mentioned as a good resistance to start with so that the two channels are adequately isolated from each other but who knows. There must be signal loss with a resistor in line, possible sq degradation and possibly other issues concerning impedance.

Anybody got views or experience on this ?

[karatestu]

I am now listening to Donald Byrd in mono through one speaker

Thanks to Nick (Lurcher) for a bit of advice on audiotalk .

I need to my speaker now as it is not central on the wall. Some early thoughts. Overall volume is about the same. I thought the bass was lower volume at first but I think it is just clearer now. Maybe the room is having less of an effect in the bass now ? I gather most recordings mono up the bass below about 100 Hz anyway.

It is taking a bit of getting used to but there are good things to say about it. The imaging seems better ie the instruments are as clear as a bell but there is not much sound staging going on. I think my set up is doing well with up firing bass and mid bass along with the tweeters pointing in six directions.

The experience is different to stereo of course and there are some things I think the mono is doing better but I need to be exposed to this much longer to work out which I prefer.

Going to move my speaker now and listen again.

[Latteman]

Moved the speaker. It's bloody heavy .

Now half way along the wall, pushed nearly right back and right in front the main listening position.

The central image is rock soild Sounds exactly the same wherever I go

[karatestu]

I ended up using the 10K series resistors in my potential divider volume control to isolate the two channels from each other and connected the two channels together after those at their junction with the 680R resistors I have going to ground. Removed one of the 680R resistors as it is no longer needed and disconnected the now unused TIS and speaker cables.

No components added

[Latteman]

At first I was intrigued by the sound of mono. But it is now giving me a headache and not sure why. Led Zep 2 sounds very odd with no panning. Everything huddled together in the centre is a bit crap as well.

For me stereo summed to mono through one speaker is officially bums.

[Geoff.R.G]

Stu, nobody seems to have any answers so let me tell you that in many an amplifier mono is achieved by simply shorting the left and right inputs together. If we go back about 50 years many recordings were in mono and it didn't matter but then along came stereo radio. In the days before the Phase Locked Loop decoder a low RF signal level caused twittering from the decoder when a stereo broadcast was being received, the solution was to switch the tuner to mono and the decoder noises went away. Few modern tuners have a mono switch but some amplifiers retain one. I still have a Leak Troughline tuner and that is pre-PLL with a mono switch, the matching Stereo 30 amplifier also has a mono switch.

Why have a mono switch? Good question but if you play a mono record with a stereo cartridge you also get spurious noises from the left and/or right speaker, switch to mono and they pretty much go away. The same might well apply to magnetic tape though I have never tried. Hence I suspect the mono selection was there to lose unwanted signal. I don't have any mono recordings, except CDs, but if you have any, give it a try.

[karatestu]

Hi Geoff. Yes shorting the letf and right channels together was what i did using the two 10k resistors in my volume control (shunt).

It sounded ok in many ways but ultimately gave me a headache for some reason and I got bored with everything squashed in the centre. Also it was so obvious where the sound was coming from.

Glad I tried it but quite honestly it was pants.

[Geoff.R.G]

I really don't think the original intention was to mix down stereo to mono, if I wanted to do that I would record a stereo track in Audacity and then get the software to sum the two channels or run the two channels through a mixer and set both pan pots to the middle. I think the original idea was to ensure that difference signals were combined when playing a mono recording. The tuner thing was important 50 years ago but far less so now.

[SteveTheShadow]

Now then!
I’ve been having a little play with mono in my system.

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I have a Mo-Fi Studiophono with a mono switch so it was an easy task to throw said mono switch, then just feed the right hand output into the amplifier, then place the right hand speaker across the corner.
Looking back through this thread, Stu wasn’t that impressed, but true mono recordings, played through one speaker in the corner sounds superb in my room. Just shows how different things can turn out over varying systems.

I have some original old Frank Sinatra, Ella Fitzgerald and Louis Armstrong mono LPs (charity shop finds from Malton around 10 years ago. Ten ton pickup damage all present and correct ) and a few 1950s Decca Ace Of Clubs LPs with the eccentric run-out groove and all of these are wonderful over the single speaker setup.
It sounds like a hi-fi version of my parent’s KB valve radiogram when I was a kid: so nostalgic that it actually brought a lump to the old throat.

The great thing about single speaker mono is that all the questions of imaging, and soundstaging go out the window and all one is left with is the music itself. Listening becomes uncritical and of course, where you sit is a complete non-issue.
The fly in the ointment is of course that air and space is completely absent when stereo records are summed to mono.
DSOTM was let’s say ‘interesting’ The pan-potted effects on ‘On the run’ for example were all there in the single speaker, with no level changes as they would have moved across the stereo stage. “Live for today, gone tomorrow, that’s me’ was reproduced perfectly, again with no ‘mono compatible’ changes in level that I could hear, but the huge soundstage was not there, which of course it wouldn’t be. For example, the stereo reverb on Gilmour’s guitar on ‘Time’ caused his instrument to partially cancel itself out, when summed to mono, and it became pushed way back in the mix. Also, Nick Mason’s cymbal work got reduced in level, relative to the other parts of his kit. I can see a real need for a super tweeter with my Fanes now.
Nevertheless as the LP progressed, I became less and less concerned with the lack of space and focussed more on the music being presented. Indeed Roger Water’s bass playing sounded clearer than I’ve ever heard it, so it’s swings and roundabouts.

I like mono on one speaker, and will certainly be exploring it further.

[karatestu]

Glad it's showing promise for you Steve. I don't have many mono recordings. Merging stereo to mono and playing through one speaker had some good things going for it but there were some things about it that I just couldn't live with. I did remember reading something on diyudio called stereolith or some such that is one cabinet which plays stereo (drivers fire to the sides?) Never got far into researching it though.