100v Line Speakers

[JimWebber]

Hello,

 

Please bear with me, being a bit of a lamp tramp, being given a scary job in the audio world!

 

I have fairly recently joined a local Hospital Radio station, as a presenter, but as soon as they discovered I had a background in technical theatre, I have been landed with all manner of technical "bits".

 

We fairly regularly take an OB to local supermarket car parks and the like, and play lots of music in order to encourage shoppers to put money into our collecting tins.

 

I have been tasked to source replacement speakers, complete with stands, ready for use with our existing amplifier. Not a problem normally, but looking at the amp, it appears that it is a 100V line version. What I know about 100V lines could be written on a match-box. Without having to take the matches out.

 

Looking at the PDF at the link, it says that it can be used on 100V, 70V and "Low Impedance (4 Ohm)"

 

Am I right in assuming that I can connect either:

 

Two 100V speakers, in parallel, without thinking too much about the impedances to the 100V terminals (Although the label on the speaker output states 83 Ohm)

 

Two 8 Ohm "Normal" speakers in parallel to the 4 Ohm terminal (Although this states 22V)

 

I think what is confusing me is the voltage specification on the 4 Ohm terminal, and the Impedance spec on the 100V terminal.

 

I appreciate this is a simple question, but it is all new to me!

 

In fact, can I be cheeky and ask another question - In this situation, would people recommend the 100v route, or the "Normal" route?

 

Many thanks.

 

Jim

[bruce]

Either stick 2x 8ohm speakers, in parallel, across the "common" and "4ohm" terminals

OR

any number of speakers (up to the rated output of the amp) in parallel across the "common" and "100v"

 

Don't do both together.

 

In general, if short cable runs are appropriate, low impedance is generally simpler. Using the 100V route gives the option for long cable runs over thinner cable, and by tapping each speaker differently (there will be a multitap tarnsformer in each cabinet) you can alter the volume of individual speakers.

[Simon Lewis]

A pair of low Z loudspeakers will probably sound better for music playback...

[bruce]

I'd agree - and disagree - with that... :)

 

Fundamentally, there's little difference in audio terms. Inside each of the Hi Z speakers, you'll find a multitap transformer, which converts the 100V input to something suitable for the drivers - typically 8 or 16 ohm, or something like that.

 

However, most of the "off-the-shelf" 100V speakers you get are intended for paging/ceilings/shops/factories, so tend to be a bit shrill and lacking in bass.

 

In my garage, I've got a pile of 100V transformers, which had been retrofitted into some fairly nice speakers, and then installed in a concert hall...

[David Duffy]

If you're only putting two speakers on it, then low impedance would be the way I'd go too.

 

The 100V line route would be better if you have a variable number of speakers (depending on the OB venue) to hook up.

 

Either way, make sure you use double insulated cable (not old style figure 8) for safety and durability.

[Jivemaster]

How long a speaker lead will you need to use? IMO Sub 50m use the 4 ohm connector, above 100m use the 100v selectoin.

 

Think of 100v line as like mains! Voltage specified then you put a load to draw some of the available power.

 

100v line means that the resistance of the cable is largely insignificant as very little current is needed.

 

100v speakers can be nasty sounding for paging or nice sounding for music. Usually they have a transformer inside with tappings to select the power taken from the supply.

[ceecrb1]

Welcome to the hospital radio world! I was with EHBS untill I moved to spain...

 

Its pretty much as has been said already.

 

I do the maintenence at Valencia´s "Heron City"... there are HUNDREDS of 100v line speakers over a stack of 10 amps.... been doing it 3 years and I havent needed to learn much.

 

100v lines are to be honest, even simpler than normal speaker systems to work out... no 1/r=1/r1 + 1/r2.......... just Pt =p1 + p2........

set the speakers to a wattage.... and off you go..

 

Imagine you had a 100 watt amp

You could add up to 10x 10watt speakers

or 50x 2watt speakers...

(all in parallel.)

 

Its a basic system thought out for normal "home" sparkies to be able to work out during an install or shopfit they might do, using gash twin&earth they might have lying around etc.

 

a more standard system with 2x 8ohm speakers will sound better...

 

Many 100v speakers on the market are switchable (if not close to all).. most will have options from very low to high wattage, and then a bypass of the internal transformer and direct connection to the speaker itself, be it an 8 or 4 ohm system etc..

 

Finally, with a hospital radio OB, think about your audience and the music you will be playing.

At ours we used radio 2 as a rough guide, if they´d play it, we would....

So you can rull out the need for sounding like an Ibiza super club or an aerobics class... no not too much bass needed...

would most of the "live audience" be of an older generation and not too interested in a fully ranged system, rather than the ability to just hear?

Just last week a client opted for 2 100v line ceiling speakers on a job, over some really nice mixing studio monitors, as the "ceiling speaker are more aesthetically pleasing"..... after a demo of both....

Also, how good are your presenters/techs...... the 100v system and its lack of frequencies might actually be a great HELP to you in terms of mic feedback....

(radio opp´s and live opp´s generally dont think alike).

[JimWebber]

Wow.

 

Thanks for all your replies people! They are all very helpful. Lots to think about, but at least my mind has been put at rest about the 4 Ohm terminal – the 22V stated made me think that I had come across some form of strange 22V line – The Trabant version of PA systems perhaps…

 

After reading that lot, I think I will go with the low impedance route The distances are short – A few metres yards from the commentary box at most, and I think that my choice will be wider (and cheaper). Dodgy Dave's Disco Emporium here I come! :)

 

Colin,

 

I had not even thought about music – as you say, the average playlist is not going to require bass levels high enough to loosen fillings. To be fair our presenters are quite good really (Well, I have got to say that haven’t I?) but you do make an interesting point about feedback…

 

Once again many thanks!

 

Jim

[Simon Lewis]

I'd agree -

and disagree - with that...

It's something of a catch 22 situation... Most 100V line systems get used for paging, so the speakers and transformers used cater more for speech frequencies, and in many cases are built to a low price point. Also, transformer cores are liable to saturate at low frequencies, so many 100 Volt line amplifiers have a fixed high pass filter to prevent core saturation. This can lead to loudspeakers that are somewhat lacking in quality and low frequency response.

 

Granted, a properly designed transformer and good quality loudspeaker will yield good music performance in a 100V line system, but I'd be inclined to try low Z approaches first, unless the specific advantages of 100V line opperation were needed for that job.

 

Simon

[j_b]

To lay your mind to rest on some of the technical points:

 

The amp is a 120W amp, worked this out from the figures you give: 100V line, 83 ohm (P = V² / R) gives Power as 120W. Likewise, with 22V at 4 ohm, gives about the same.

 

You simply have an output transformer with a choice of taps including 4ohm and 83 ohm. To get maximum power out, you need to plug speakers in to match your amp, and 100V line systems give easy to calculate figures, i.e. get 12x 10W speakers in parallel (if you re-arrage P=V²/R to give R=V²/P you get 10W @ 100V = 1kohm therefore each speaker has an input impedance of 1k), so 12 of these in parallel gives 1000/12 = 83 ohm, which is an ideal match for your amp.

 

Same theory, just less sums to do.

 

Furthermore, higher impedance runs see see less losses along a piece of cable, so lend themselves well to public address 'Tannoy' systems. The compromise here is that it is more difficult to make low bass frequencies happen well in higher impedance environments, due to something called the 'damping factor'. - http://en.wikipedia.org/wiki/Damping_factor

[JimWebber]

.........

 

Same theory, just less sums to do.

 

........

 

Of course!

 

'sobvious really!

 

Thanks People!

 

Jim

[MarkPAman]

Dodgy Dave's Disco Emporium here I come! :)

Before you visit Dave - read the PM I sent you!

[Jivemaster]

I often found that Richer Sounds had interesting speakers usually last years model at last year's price, so may be budget friendly, if there is a local one.

[Canal]

To lay your mind to rest on some of the technical points:

 

The amp is a 120W amp, worked this out from the figures you give: 100V line, 83 ohm (P = V² / R) gives Power as 120W. Likewise, with 22V at 4 ohm, gives about the same.

 

You simply have an output transformer with a choice of taps including 4ohm and 83 ohm. To get maximum power out, you need to plug speakers in to match your amp, and 100V line systems give easy to calculate figures, i.e. get 12x 10W speakers in parallel (if you re-arrage P=V²/R to give R=V²/P you get 10W @ 100V = 1kohm therefore each speaker has an input impedance of 1k), so 12 of these in parallel gives 1000/12 = 83 ohm, which is an ideal match for your amp.

 

Same theory, just less sums to do.

 

Furthermore, higher impedance runs see see less losses along a piece of cable, so lend themselves well to public address 'Tannoy' systems. The compromise here is that it is more difficult to make low bass frequencies happen well in higher impedance environments, due to something called the 'damping factor'. - http://en.wikipedia.org/wiki/Damping_factor

 

What would the situation if you reach the limit of 120w Amp @ 100v line to run the system at 70V instead of 100V A company who are doing some work (They worked in radio broadcasting and We need 2 more 10W speaker and they said it would be safe to lower voltage to 70v tapping enough to save buying a 240 w Amp

[Owain]

What would the situation if you reach the limit of 120w Amp @ 100v line to run the system at 70V instead of 100V A company who are doing some work (They worked in radio broadcasting and We need 2 more 10W speaker and they said it would be safe to lower voltage to 70v tapping enough to save buying a 240 w Amp

 

You get less sound out of the speakers, as the speakers are receiving a lower voltage.

 

 

100V speakers match a 70V amplifier at half the speaker power, i.e. you can run ~240 watts of 100V speaker load on a 120W 70V amp. This is useful if you want to run lots of very low power speakers (such as hospital bedhead units, to return to the topic). However dropping the amp voltage to 70V for the sake of an extra 2 x 10W speakers would be daft as all the other speakers would be on half power output.