Using two 8ohm speakers

[Izzy]

Quite basic question I’m afraid but one I have not been able to find clear answers to with searches although I have tried. Maybe I’m a bit thick.
 

I have a sound fitted tender loco, Hornby J15 with Zimo MX645 + Zimo 8ohm dumbo speaker, that I want to try and add a small 8ohm planar speaker into the smokebox because as it stands the sound is great, but does really seem as if it’s coming from said tender rather than the loco. I’m hoping that this might help balance it a bit better. 
 

As I understand it the MX645 is capable of driving two 8ohm speakers in parallel (4-8ohms at 3W)  but I can’t seem to discover whether polarity is important or not I.e. if the wiring needs to be the same to both or doesn’t matter. And if it does, how to set it up, to tell what the polarities are etc. without blowing up the decoder amp!

 

Can anybody advise please? 
 

Thanks,

 

Bob

[spamcan61]

It may sound a bit odd if the speakers are out of phase, but I don't think there's a universal colour code for speaker polarity, so  'suck it and see' really. You won't damage the speaker by connecting it the "wrong" way round 

[RAF96]

Extract from the Hornby HM7K decoder manual.

Some speakers have a dot to mark polarity, but if not and speakers are the same make adopt connections per the drawing.

Edited February 4 by RAF96
More info.

[Izzy]

As there are no markings on any of these speakers and they are both of similar design, flat with sprung contacts, and able to be fitted into different sized enclosures, I guess I could assume that they are given ‘standard’ polarity I.e. the same orientation, and then go from there.

 

Thanks for the helpful replies.

 

Bob

[Izzy]

I've spent this afternoon testing the theory. Joined up in Parallel the speakers worked fine no matter which way around the wires were. In series one way they were both noticeably quieter one way than the other so that must be the way to judge when they are wired correctly. I got the impression that in Parallel they were louder than in series but this might be because it was all done in the open. Now I am trying to carve out enough space in the J15 smokebox area to fit the small planar, an ESU 15x11mm, when I will test both setups again to try and determine which is best, and if the second speaker actually makes much difference. 

 

Bob

[Albie the plumber]

3 hours ago, Izzy said:

I've spent this afternoon testing the theory. Joined up in Parallel the speakers worked fine no matter which way around the wires were. In series one way they were both noticeably quieter one way than the other so that must be the way to judge when they are wired correctly. I got the impression that in Parallel they were louder than in series but this might be because it was all done in the open. Now I am trying to carve out enough space in the J15 smokebox area to fit the small planar, an ESU 15x11mm, when I will test both setups again to try and determine which is best, and if the second speaker actually makes much difference. 

 

Bob

The greater the impedance , the quieter the sound will be , therefore, wiring in series doubles the impedance  , wiring in parallel halves it .

 HOWEVER ,Wiring in Parallel may well damage the amp on a decoder if the impedance is half the recommended impedance on a decoder .

Many ZIMO decoders are 8 Ohm impedance so will not be suitable for parallel wiring .

sometimes , sticking with one speaker of the correct  impedance is the best option.

 

HTH 

Edited February 4 by Albie the plumber

[Izzy]

8 hours ago, Albie the plumber said:

The greater the impedance , the quieter the sound will be , therefore, wiring in series doubles the impedance  , wiring in parallel halves it .

 HOWEVER ,Wiring in Parallel may well damage the amp on a decoder if the impedance is half the recommended impedance on a decoder .

Many ZIMO decoders are 8 Ohm impedance so will not be suitable for parallel wiring .

sometimes , sticking with one speaker of the correct  impedance is the best option.

 

HTH 

Yes, it does, many thanks. Luckily the Zimo concerned is a MX645 which can do 4-8ohms. So it looks like parallel will be what gets wired in. 
 

Bob

[charliepetty]

In Parallel should be louder, IE 2 X 8Ohms = 4 Ohms.

 

Thats what I did in a Bachmann DMU last week, yesterday I did a Cavalex 56 with 2 EM'0' speakers at 4 Ohms wired in series and WOW.  What a noise.

https://www.dckits-devideos.co.uk/index.php?route=product/product&path=223_75&product_id=406

 

Demoing thse this weekend at Doncaster & shortly at Glasgow & Preston

[Roddy Angus]

From what I remember from physics at school, if you wire 2 speakers in parallel, but with opposite polarity, then the sound produced by them will be 180 degrees out of phase.  If this happens, then an interference pattern will be established which will cause some sounds to be louder and others to be quieter, depending on where it is heard from.  In extreme cases, theoretically, the interference could cancel out the sound and nothing would be heard.

 

I hope I am remembering my second year physics correctly.

 

Roddy

Ps this is theoretical and might not be noticeable in practice.

[Stefan88]

I have 2 identical locos, 1 with an ESU Loksound 5 Micro hooked up to a pair of parallel 15x11x5mm 8ohm speakers in a shared enclosure, and one with a Zimo MS580 hooked up to a single 18x13mm 8ohm Dumbo speaker in a custom 3d printed enclosure. Volume and sound quality there is no real difference, only the quality of the sound file seems to have an effect on these (despite both being from the same provider, Zimo is better in this case). That said a pair of Dumbos in separate large enclosures will be better than a single Dumbo, but a single Dumbo is just as effective as a pair of sugar cubes.

[Izzy]

 

Experiments have continued. It seemed just adding the small planar in the smokebox didn't really have the desired effect, the sound volume of the larger Zimo dumbo in the tender overwhelming  it. It was better, but still noticeable.

 

So then I removed it and fitted another of the 15x11 planars in it's place, the idea being they would/should match and thus balance out better. This seems to have worked out. The sound now just seems to come from the loco as a whole rather than a specific area of it as before. This might be helped by the fact the one in the tender is right at the rear of it to match/counter the loco one being right in the front. This is good given all the work I had to carry out on the loco body to obtain the space for the speaker. 

 

Even in parallel at 4ohms however the volume level output couldn't match that of the single Zimo dumbo at 8ohms.  I had it set at 20 (cv266) for my needs in a small room and have had to increase this to 60. Part of this might be because there was no room to add an enclosure to the smokebox one so I didn't with the tender one either so as not to skew too much the balance I was after considering the space in it to act as a soundbox anyway.

 

Bob

[Pete the Elaner]

13 hours ago, Roddy Angus said:

From what I remember from physics at school, if you wire 2 speakers in parallel, but with opposite polarity, then the sound produced by them will be 180 degrees out of phase.  If this happens, then an interference pattern will be established which will cause some sounds to be louder and others to be quieter, depending on where it is heard from.  In extreme cases, theoretically, the interference could cancel out the sound and nothing would be heard.

 

I hope I am remembering my second year physics correctly.

 

Roddy

Ps this is theoretical and might not be noticeable in practice.

 

What you have described sounds a little weird, which is also the best way to describe how speakers usually sound when out of phase.

 

When I bought a new AV amp recently it told me I had my sub put of phase with my standard speakers & I never realised. I guess this was because they deal with different frequencies.

[Nigelcliffe]

The "old way" to tell about phasing was to use a short burst of DC, and observe the cone move.   If both cones moved the same way (in, or, out), then things are in-phase,  if they moved opposite ways, they are out-of-phase.    But tiny modern speakers may not be suitable for such approaches.  

 

- Nigel

[zr2498]

15 hours ago, charliepetty said:

In Parallel should be louder, IE 2 X 8Ohms = 4 Ohms.

 

Thats what I did in a Bachmann DMU last week, yesterday I did a Cavalex 56 with 2 EM'0' speakers at 4 Ohms wired in series and WOW.  What a noise.

https://www.dckits-devideos.co.uk/index.php?route=product/product&path=223_75&product_id=406

 

Demoing thse this weekend at Doncaster & shortly at Glasgow & Preston

Looking forward to the demo at Doncaster. I am suprised there is room for two speakers even though they are smaller than the Cavalex factory fitted.

[charliepetty]

Yes two will fit, very loud here on my desk, but at Noisy model shows its probably just right.  All right stuff at home is always too quiet at shows.

 

Charlie

Edited February 6 by charliepetty