Adding speakers in parallel

[ukbulls]

We have a Crown CE 1000 amp and two OHM MR228 speakers that are rigged up in a church.

We now need to have two more speakers added to the system so that everyone can hear well enough.

 

The specs of the amp are:

 

120 VAC, 60 Hz Units, Stereo mode, per channel, both channels driven

2 ohms - 560 W

4 ohms - 450 W

8 ohms - 275 W

 

120 VAC, 60 Hz Units, Bridge mono mode

4 ohms - 1,100 W

8 ohms - 900 W

 

The speakers are 200 Watts I believe.

 

Any advice on adding another couple of speakers in parallel?

What rating should they be? If they're not identical to the OHM MR228 speakers already wired in will that be a problem?

 

Any help gratefully received!

[paulears]

Adding speakers in parallel like this isn't a problem, and if your amps are happy with the resultant load, that's fine. The only real snag is that for the people near the speakers, the volume will drop. This isn't an issue if you only run it gently, because you can simply turn it up.

 

The issue is that of the extra speakers are for a different area of audience, you have no scope for controlling volume - you could end up with something rather horrible - where it's too loud or too quiet, and the parallel wiring is not really the issue.

 

Personally, cheap budget amps are available, or indeed powered speakers - but another amp gives you extra power, and most importantly, the ability to turn the new speakers up to their own optimum volume.

 

I have no concerns slapping an extra pair of speakers with short jumpers, and aiming them slightly differently, but if this means you are putting more speakers in at a distance, I'd be more cautious.

 

There is also the question of aligning them in time - especially if your building is an old type church rather than a newer build with less reverberant acoustics. Your distant set may well not work well if people can hear both sets - and then you are into delays and proper zone controls and it gets harder, quicker.

[Simon Lewis]

I have installed dozens of MR228s into churches, and found them go be sturdy little units. They did play around with the components somewhat over time, and there have been several model revisions since the 228. It's now the Ohm CW28 and has a different high frequency horn arrangement.Your speakers halve a pretty good horizontal coverage - so it might possibly be worth having someone look at you existing setup and making sure it is all working and positioned correctly?If possible, when adding more units, it's better to keep the same speakers on the same amp channel. Depending on how your system is cabled that might not be easy to do. Also, depending on what you need to achieve, I would personally prefer to keep additional speakers sounding the same as the ones they are supplementing. That might be possible if you add more Ohm units. However, CW8s aren't a budget unit, and the cost of an extra amp would possibly be small compared to the overall speaker cost.

If you are a CofE can your diocesan technical advisor help (presuming they have one?).

[Oldradiohand]

If the speaker placement is reasonably symmetrical and both are set at the same volume then there is a simple answer. Rewire the existing speakers in parallel off one half of the amp and wire the new speakers in parallel off the other - each side of the amp is seeing a matched pair of speakers (so the volume per speaker in each pair will be the same) and you will have control over the differential volume between the old and new speakers.

[ukbulls]

Thanks for the advice - wow, I'd never heard of a diocesan technical adviser. I'll see if there is one.

 

Will the stereo effect be lost with the solution suggested by Oldradiohand?

[Oldradiohand]

Yes, but most of the congregation don't hear the stereo anyway - especially with two pairs of speakers. I think you'll find that a lot of people on here only use mono PA and sound reinforcement anyway.

[Bazz339]

Thanks for the advice - wow, I'd never heard of a diocesan technical adviser. I'll see if there is one.

 

Will the stereo effect be lost with the solution suggested by Oldradiohand?

 

Which diocese are you in?

[ukbulls]

We're in Chester diocese - on the border with Manchester diocese.

[richardash1981]

We have a Crown CE 1000 amp and two OHM MR228 speakers that are rigged up in a church.

We now need to have two more speakers added to the system so that everyone can hear well enough.

 

The specs of the amp are:

 

120 VAC, 60 Hz Units, Stereo mode, per channel, both channels driven

2 ohms - 560 W

4 ohms - 450 W

8 ohms - 275 W

The speakers are 200 Watts I believe.

 

Any advice on adding another couple of speakers in parallel?

What rating should they be? If they're not identical to the OHM MR228 speakers already wired in will that be a problem?

 

To do the boring maths:

Your speakers are 8 ohms impedance - it probably says that on them. At the moment I assume one is connected to each amp channel, so the amp is driving 8 ohms load.

If you add another 8 ohm speaker, you lower the load on the amp to 4 ohms. This is OK, because it is rated to cope (not all amps are, and you can overdo this with lots of speakers ...)

 

Although the amp output rises to 450W into 4 ohms, half goes to each speaker, so they only get 225W instead of 275W when the amp is flat out. If they are 200W speakers, then that shouldn't worry you! This is why the existing speakers will get a bit quieter, although because of the way you hear sound, probably not enough to notice - to make system significantly louder, you usually need to double the rating in watts, so the 50W you loose from the existing speakers is fairly small change.

 

The point about control is a good one, but the trick Oldradiohand describes will probably solve your problems, because tying to do stereo is rarely a good idea in a Church context. A good deal of the congregation will be far enough to one side or the other to only hear one channel, and so complain about the sound (in opposing directions) if you don't keep the pan controls dead central. Many older systems were rigged in pure mono with only one amp channel to both front speakers, so you got no choice!

 

What paulears refers to at the end of his post is that you rarely have as simple a situation as adding new speakers in isolation - in practice they are in the same building, so some (maybe quite a lot) of people will be getting sound from both old and new pairs. This opens a can of worms, and can sound pretty dreadful (I know of one system where clarity was considerably improved by disconnecting the second pair of speakers!). The problem is that sound travels very fast down the speaker leads, and quite slowly through the air. This leads to people who can hear both sets of speakers hearing two sounds spaced apart in time. If this was far enough apart to be heard as an echo this would be bad enough (think train station PA ...), but small delays are actually worse, because the two lots of sound combine, making some pitches sound very loud and others quiet (and effect known as Comb Filtering).

 

The solution (as Paul says) is to delay the sound from the second speaker set by the right amount to line it all up - but that isn't trivial to do right, and may well need extra equipment you haven't got.This is where some advice knowing the specifics of the situation will serve you well!

[Simon Lewis]

Thanks for the advice - wow, I'd never heard of a diocesan technical adviser. I'll see if there is one.

 

We're a rare breed ;-) Not every diocese has one and there may be even less need after the faculty system goes fully online...

 

 

 

[TonyMitchell]

Not every diocese has a 120v supply at 60Hz, either :huh:

 

@OP - on a serious note, as you're in the UK, recheck your amplifier spec (I guess you've cut & pasted and yours is in fact 230v at 50Hz), however the ratings may be slightly different.