Basic/generic Speaker Questions

[Reggie1503562260]

Some REALLY basic queries on setting up the speakers on my LG AR702BR AC Receiver + 6.1 surround speakers if someone is good enough to help out.

I need to extend the wires on the side & rear speakers. The supplied speaker wire is quite thin (sorry, don't know the gauge) - much thinner than the cables supplied with the Krix speakers I bought many years ago.

1/. Can someone point me to a guide on maximum length of run vs gauge of cable

2/. Given the relative low end quality of this system (it was a promotional giveaway with the 60" plasma) - is the gauge/length of the cable going to make any perceivable difference?

3/. Is there any issue with putting two speakers into one speaker out post on the receiver - or will this 'half' the sound output? (I want to run my old Krix speakers from the receiver out to the outside entertainment area for playing music CD's.) - If this is OK, I'd use the front speaker outs - right??

4/. Is it the 'done thing' to sit the centre speaker directly on top of the sub?

I appreciate these are very basic (& probably dumb) questions for most here, but I'm learning (I hope!!).

[Meld]

1/. Unless you live in a large mansion you'll be ok. I've used ultra-cheap give-away speaker cable before and it's satisfactory. One thing to look-out for though is because the wire is so thin, if you accidentally place heavy furniture on the wire, your signal may get attenuated. The rear channels don't pull as much current from your amp compared to your front speakers so you don't need heavy gauge cable for them. You could always double up on the thin wire if you wanted to, effectively doubling its gauge. My point is use it, don't bin it.

2/ Is the gauge/length of the cable going to make any perceivable difference? It all depends on the channels being driven and the amount of current they draw. In average, real-life set-ups some would say, "not really", as long as you are comparing wire that is meant to be used as speaker cable. You wouldn't for instance use microphone cable as speaker cable, as it may melt and cause a fire.

There are some audioholics out there that claim to hear minute differences in sonic quality between hi-end cable and bell wire. For every one of these there are a million who can't. You need to determine yourself if you are a superhero (at least a superhero to hifi salesmen)... or not.

3/. Yes you connect to the main left/right speaker binding posts. If the amp outputs 80 watts RMS per channel, then you share that power between two speakers, each speaker only gets 40 watts. Trying to turn the volume up too much will give you distortion or activate the amp's protection circuits. It'd be better to use some sort of speaker switching device if your amplifier doesn't provide it in the way of A & B terminals.

4/. The center speaker should be below or above your speaker to create the illusion that the dialogue is actually emanating out of the actor's mouths. That some people place it on their sub is prob. because of convenience or lack of space. Hell, put it on your lap for a more in-yer-face sound.

Edited May 11, 2008 by Meld

[geoff888]

3/. Yes you connect to the main left/right speaker binding posts. If the amp outputs 80 watts RMS per channel, then you share that power between two speakers, each speaker only gets 40 watts. Trying to turn the volume up too much will give you distortion or activate the amp's protection circuits. It'd be better to use some sort of speaker switching device if your amplifier doesn't provide it in the way of A & B terminals.

Not exactly how it works.

You can connect 2 different speakers to the same speaker terminal but it is not recommended unless you are playing it at low volumes. An extra set of speakers on the same terminal (connected in parlallel) results in the lowering of the impedance the amp "sees". To simplify: 1 speaker (8 ohms), 2 x 8ohms speakers =4 ohm load (1/[1/R+1/R]). When the power output of an amp is quoted, it is usually accompanied by an impedance. Eg 80W RMS at 8 ohms, 160 W at 4 ohms. So if you have a really well designed amp it should be able to double it's output when impedance is halved.

However these amps are usually expensive Hi Fi amps and not in cheap receivers (or even expensive receivers). So if you are presenting your amp with lower impedance it will try and draw more current to meet the load and if it is not up to it will either distort/clip, or shut down, or worse - fry.

In your situation cable lengths and gauges will only affect resistance and therefore the volume/output from your speakers. Long runs of thin cable can reduce volume maybe upto 1-2 db (I know, I've tried)

Put your centre speaker above or below your TV.

Edited May 11, 2008 by EndoGuy

[Meld]

Afaik, on my Yammy receiver that has A & B terminals, if you use the B terminals for a second pair of speakers and these speakers are exactly the same impedance as the first pair of speakers, when you engage both A & B pairs of speakers at the same time, the impedance loading is effective halved.

Engaging both A & B pairs would be exactly the same as if I just wired the pairs of speakers to the same L & R binding posts in parallel.

My logic could be a bit faulty but this is the way I understand it:

If your amp has a power supply, and the max power it can supply to one channel is 80 watts RMS, then decreasing the load on one channel from 8 ohms to 4 ohms is not going to give you 160 watts RMS.

You'll still only get a max. of 80 watts RMS, which is shared between all the speakers connected to that channel.

[geoff888]

Afaik, on my Yammy receiver that has A & B terminals, if you use the B terminals for a second pair of speakers and these speakers are exactly the same impedance as the first pair of speakers, when you engage both A & B pairs of speakers at the same time, the impedance loading is effective halved.

Engaging both A & B pairs would be exactly the same as if I just wired the pairs of speakers to the same L & R binding posts in parallel.

My logic could be a bit faulty but this is the way I understand it:

If your amp has a power supply, and the max power it can supply to one channel is 80 watts RMS, then decreasing the load on one channel from 8 ohms to 4 ohms is not going to give you 160 watts RMS.

You'll still only get a max. of 80 watts RMS, which is shared between all the speakers connected to that channel.

The rated power output from an amp varies depending on the load and what parameters you put on it. The full info should read eg 80W @ 8 ohms at 0.05% THD (total harmonic distortion). You can quote the same amp at 100W @ 8 ohms @ 0.1% THD if you want and it would be still correct but as you can see it may be able to ouput 100W but it would have higher distortion. Same goes for impedance if you reduce the impedance the output would be higher. A short circuit has virtually zero impedance (apart from the wire) therefore your amp is trying to deliver impossibly high outputs and either shuts down or blows up.

There are 2 ways to connect speakers (1)in series eg daisy chain or (2)in parallel like with A/B connections. When connectiong in parallel you are if fact halving your impedance of the speakers if they have the same impedance (Ohms Law). To put it your way if an amp has 80W output it will try and output 80W to both speakers effectively trying to output 160W in total if it is capable but often it may only output 120W because it just runs out of puff. If you connect them in series then the impedance is doubled and the ouput is halved. You will find that if you have an A/B switch and you switch both speakers on at the same time then you will get a louder sound. Mine you doubling the output form an amp only increases the loudness by 3 db.

[Reggie1503562260]

Thanks for your replies guys - altho' I did get a little lost on the impedance/harmonic distortion/etc (I think I get the basic gist).

It'd be better to use some sort of speaker switching device if your amplifier doesn't provide it in the way of A & B terminals.

My receiver doesn't have any facility for a separate set of speakers - so can I go somewhere like Jaycar & get some type of 'switchbox' ?? (like the A/B serial/parallel switch boxes you used to see in offices driving printers/modems/etc). Do such animals exist for speaker switching?

[Meld]

Jaycar has a Five Way Speaker Switch for $30.

[Roderick]

The purists will say 14AWG speaker wire, or thicker, is needed, but ordinary figure-of-eight 240-volt light flex at 18AWG is a lot better than the "bell wire" they supply with cheap surround sound systems. Light flex is only 70 cents a metre -- less if you buy in bulk.

There will be a slight drop in power over long distance runs, but probably not enough to notice (1 decibel maybe). In any case, the setup procedure on your receiver will compensate for this, and the surround speakers are much less important than your fronts.

Rod

[dvduser]

4/. The center speaker should be below or above your speaker to create the illusion that the dialogue is actually emanating out of the actor's mouths. That some people place it on their sub is prob. because of convenience or lack of space. Hell, put it on your lap for a more in-yer-face sound.

Good Rule-of-Thumb - The centre should be at approximately the same height level as the tweeters in the FL/FR mains.

[geoff888]

Thanks for your replies guys - altho' I did get a little lost on the impedance/harmonic distortion/etc (I think I get the basic gist).

My point was to quote the power output of an amp you need to quote other parameters to make it meaningful. It's like when asked "How big is your room?" and you reply "5m long". Now that means little without the height and length.

So if you say an amp is 100W it's also important to know into how many ohms speakers and at what level of distortion. Some speakers are 4 Ohms, some are 6 and 8 (nominally). Each one of those speakers will get a different output from an amp. As I mentioned an "ideal" amp may output 100W into an 8 ohm speaker but if it was connected to a 4 ohms speaker it would output 200W.

I once had an el cheapo Pioneer receiver that quoted 5 x 120 W on the front panel. When you read the manual it was actually 5x120W into 8 ohms at 10% THD. Thats a huge amount of distortion. A real world acceptable distortion figure for a multichannel receiver would be 0.01% maybe. But at that low level of distortion, that Pioneer amp would probably be only outputing maybe 50W.

As an example the (S. Australian) Halcro DM38 stereo amp ($20K) outputs 180W into 8 ohms and 350W into 4 ohms at 0.0007%THD which is considered ultra accurate (in terms of distortion).