Understanding Distributed Speaker Systems

Distributed speaker systems are also known as “100 volt line” or “70 volt line” speaker systems. They are used extensively where multiple speakers are required. Distributed speaker systems are commonly used in airports, shopping centers, schools, churches, clubs, offices, car-parks, sports grounds and anywhere multiple speakers are required. They can also be used in homes for background music systems.

Advantages of Distributed Speaker Systems

The main advantages of distributed speaker systems are:

  • No need for complicated calculations of total speaker impedance – simply add together each speaker’s wattage (see below for more details)
  • Many speakers can be connected to an amplifier.
  • Extra speakers can normally be added to the system
  • The volume of each speaker can be adjusted independent of the main volume (so the toilet speakers are not as loud as the foyer speakers).
  • Smaller cables can be used. Distributed speaker systems use much less current through the speaker cables
  • Longer speaker cables are possible with minimal line loss. Cables runs can be 100’s of metres or 1000’s of feet.

Disadvantages of Distributed Speaker Systems

The main disadvantages of distributed speaker systems are:

  • Each speaker requires a step-down transformer
  • The transformers affect the quality of the sound – typically the lower frequencies are not transferred as well as a speaker system without transformers.
  • Without using expensive transformers, use is often limited to paging, voice and low level (background) music installations.

Distributed Speaker Systems Overview

The basis of distributed speaker systems is similar to the way electricity is distributed. Power stations use step up transformers to distribute power as high voltage, which means low current, and therefore low line losses and thinner cables. Each town and/or street then converts this high voltage/low current down to low voltage/high current (through step down transformers) for use in your home.

Distributed speaker systems use a similar principle. The amplifier normally has a step-up transformer built into it, producing a high voltage/low current output. Then each speaker has its own step down transformer to convert the signal back to low voltage/high current. This allows the cable to be very long without having any significant line losses.

distributed speaker systems overview

100 Volt Line Speaker System

The most common “high” voltage used in distributed speaker systems is 100 Volts. In many countries distributed speaker systems are known as “100 Volt line” speaker system.  In a 100 Volt line speaker system the output of the amplifier is marked “100 volt”. Indeed at full output, the amplifier puts out 100 volts RMS. Each speaker then has a transformer to reduce the 100 volt line level down to normal speaker level.

70 Volt  Line Speaker System

In North America the most common “high” voltage for distributed speaker systems is 70 Volts. This is because years ago, some states had laws stating that any cable with a maximum voltage greater than 100 Volts peak had to be installed in conduit. This was time consuming and costly to install. So they developed a system where the output voltage of the amplifier was a maximum of 100 Volts peak. This equates to 70.71 Volts RMS. This is commonly known as a “70 Volt line” speaker system. The principle is the same as for 100 volt line systems, but uses a maximum output voltage of 70 Volts. While 70 volt line systems are still the most common in the USA, some 100 volt lines systems are being used.

50 Volt Line and 25 Volt Line Speaker Systems

Less common, but still seen on some amplifiers are 50 volt line or 25 volt line outputs. The principles are the same for all voltages, but the lower the voltage, the more current, therefore the shorter the maximum cable length without significant line losses.distributed speaker systems terminals

In practice, many commercial amplifiers have multiple outlets. They may have 100 and 70 Volts, or 70 and 25 Volts, as well as 4 ohm and 8 ohm outputs for normal speakers (without transformers). Normally you should only use one output of a amplifier, that is, either the 100 volt line output, or the 70 volt line output or the 8 ohm output, not all at the same time.


Every speaker in distributed speaker systems needs to be connected to a step down transformer. This converts the high voltage level down to normal speaker level.

One side of the transformer normally has a common (or “0 volts”) and a 4 ohm and 8 ohms connection.  An 8 ohm speaker would be connected to the common and 8 ohm taps, while a 4 ohm speaker would be connected to the common and 4 ohm tap.

Most transformers have a selection of input taps. The example in this picture has taps for 20 Watts, 15 Watts, 10 Watts and 5 Watts. The feed cable is connected to the common and any one of the other taps. This allows the relative volume of the speaker to be set during the installation. For example the speaker in a high noise room might be set on 20 Watts, while the speaker in a small, low noise area might be set on 5 watts.

All amplifiers designed for use with distributed speakers systems have a step-up transformer built-in. It is also possible to add an external transformer to an amplifier without an integrated transformer. Simply use a speaker transformer in reverse – that is, connect the common and 8 ohm transformer connection to the common and  8 ohm speaker output of the amplifier.  Just make sure the amplifier and transformer are rated with enough power to drive all the speakers to be connected (see Connecting Multiple Speakers below).


Any speaker can be used in a distributed speaker system, as long as a step-down transformer is used. Many manufacturers produce speakers with integrated transformers for use in distributed speaker systems. ceiling spkr for distributed speaker systems

Ceiling Speakers

Ceiling speakers are used in many distributed speaker system installations to cover large areas and/or multiple small rooms or areas. The speaker cable is normally connected directly to the transformer.  To change the power settings you need to connect the speaker cable to a different transformer tap. In the speaker pictured, this is a simple matter of moving the speaker wire to a different terminal connector.

Cabinet Speakers (Speaker Boxes)

100 volt box speaker for distributed speaker systems

Speaker boxes come in all sorts of shapes and sizes. Many manufactures make a version of their cabinets with an integrated transformer. Connections are often by some form of speaker terminals. To change taps, simply rotate the switch to the desired power setting. Often these switches also have a position for 8 ohms (bypassing the transformer) – this makes them very versatile speakers for the installer. Speaker boxes are used where ceiling speakers aren’t practical, or where higher sound levels are required.
rear of horn speaker for use with distributed speaker systems

Horn Speakers

Horn speakers are very efficient, but not very good quality. They are mostly used outdoors when coverage of a large, or high noise, area is required. For example in car parks, sports grounds, school yards and other outdoor areas. In the picture shown, the rear of the horn has a selector switch which needs a flat bladed screw-driver to operate. This is useful to reduce the likelihood of inadvertent changing of the settings after the install.

Connecting Multiple Speakers

This is the fun bit, because there is no need to calculate the total impedance. To connect multiple speakers in distributed speaker systems, just wire them all in parallel and add up the total watts.

Example 1: A PA amplifier is rated at 120 watts @100 volt line. Therefore you could connect:

  • 20 x 5 Watt (100 volt) ceiling speakers (total 100 Watts), or
  • 40 x 2.5 Watt (100 volt) ceiling speakers (total 100 Watts), or
  • 10 x 5 Watt (100 volts) ceiling speakers and 20 x 2.5 Watts (100 volt) ceiling speakers (total 100 Watts), or
  • any combination of speakers that add up to no more than 120 Watts.

Example 2: A small church has a small 25 Watt (70 Volt) PA amplifier with 4 small speakers mounted in the church (2 down each side). They now want to add a speaker in a separate room for an overflow and creche area.

  • 4 existing speakers can be wired at 2.5 Watts (70 Volt), total of 10 Watts
  • A new box speaker can be wired at 10 Watts (70 Volt), this allows it to be louder than any of the small church speakers (since the creche area has much more ambient noise levels).

As shown, it is easy to add the individual speaker watts together. This is much easier than calculating the total impedance.This makes installation much simpler.

Calculating Watts from Speaker Impedances

Sometimes manufacturers of speakers designed for distributed systems only mark their speakers with the impedance of each tap, rather than the Watts. Also, many impedance meters tell you the impedance, and you need to calculator the wattage.

In either case, you can use this simple calculator:

Tips for Using Distributed Speaker Systems

Following are some practical tips for installing distributed speaker systems:

  • Keep all the speakers in phase. This means the the “O volt” or the “Com” of the amplifier speaker terminal should be connected to the “O Volt” or “Com” of each speaker transformer.
  • It is good practice to design distributed speaker systems to use up to only 80% of the amplifier’s total available power. For example, a 120 Watt PA amplifier should only be connected to a maximum of around 100 Watts of speakers. This helps avoid the amplifier’s transformer distorting from saturation (overload), allows for inefficiencies in the system, and allows an extra speaker to be added if required in the future.
  • When designing distributed speaker systems, calculate the total watts of the speakers, and select an amplifier larger than required. For example, If an install requires 10 speakers at 5 Watts each (total load of 50 Watts), a 60 Watt amplifier could be used, but selecting a 100 Watt or 120 Watt amplifier will allow speaker taps to be changed or extra speakers added in the future. It is a relative small increase in price to up-size the amplifier before purchase, rather than have to buy a new one later.
  • When selecting speakers, chose a higher power one than required. For example: If a 5 Watt ceiling speaker is required, chose a 10 Watt or 15 Watt speaker and use the 5 Watt tap on the transformer. This again reduces the likelihood of overloading cheaper transformers, and gives the ability to increase the power level (volume) if required.
  • When connecting many speakers, it is good to have multiple feed cables. For example; if connecting 60 speakers, it is possible to use one speaker cable run and loop in and out of each speaker. However it is better to have several feed cables to smaller groups of speakers. This way if a fault occurs, it is easier to isolate which feed the fault in on.
  • It is possible to get some speakers with a built-in attenuator to control the volume of the speaker. This is useful in situations when you want the listener to control the volume. For example in a creche. It is also possible to get external attenuators to control the volume in a room or for an individual speaker.
  • If possible, measure the impedance of each speaker feed cable before connecting the amplifier. This is best done with an impedance meter. If installing a number of distributed speaker systems, an impedance meter is very useful. For examples of impedance meters, view Amazon’s range here.
  • Don’t connect a 4 ohm or 8 ohm speaker directly to a 100 volt line or 70 volt line speaker cable. Apart from severely overloading the speaker (and possibly burning it out) a 4-8 ohm speaker effectively puts a short circuit on the speaker line and overloads the amplifier. See the calculations below for the mathematical explanation of this.
  • If a 100 Volt line amplifier is overloaded, connecting the load to the 70 Volt line effectively halves the load on the amplifier and it will not be overloaded.
    • Example 1: The total watts of all the (100 Volt) speakers totals 200 Watts. If connected to the 100 Volt line speaker terminals of a 120 watt (100 Volt) amplifier, the amplifier will be overloaded. Connect the same speakers to the 70 Volt line terminals of the same 120 watt amplifier and the amplifier will only see a load of 100 Watts.
    • Example 2:  The total watts of all the (70 Volt) speakers totals 50 Watts. If connected to the 70 Volt line speaker terminals of a 40 watt (70 Volt) amplifier, the amplifier will be overloaded. Connect the same speakers to the 50 Volt line terminals of the same 40 Watt amplifier and the amplifier will only see a load of 25 Watts.
    • You can use the calculator above to see this by selecting the different system voltages. For those whose like to know, the mathematical explanation of this is below.


Distributed speaker systems are ideal for multiple speaker installations. They allow long speaker cables and calculation of the total load is easy. Distributed speaker systems are normally mono (not stereo). They are mostly used for paging and background music situations. Although normally used for commercial installations,  they can be used in domestic installations for background music systems

Below are some of the major calculations used with distributed speaker systems (you can stop reading now if you are not into calculations).

Calculations for Distribution Speaker Systems

The following calculations are for those who like to understand the mathematics behind the principles outlined above. You don’t need to understand these calculations to use distributed speaker systems, but it will help you understand and design systems better.

Several principles of distributed speaker systems have been outlined above. A mathematical explanation of each principle is now given under the following sub-headings:

Adding the Power of Each Speaker

As an example, four 5 Watt speakers are connected together (in parallel) to a 100 Volt line amplifier.

The simple way to calculate the total load is to add 5 + 5 + 5 + 5 = 20 Watts.

The harder way (which is why its not normally done) is to calculate the impedance of one speaker, and then calculate the total impedance of 4 such speakers in parallel, and then calculate the total power.

So the impedance of a 5 Watt speaker on a 100 volt line:

Impedance={\Large\frac{Volts ^2}{Power}=\frac{100 ^2}{5} = \frac{10,000}{5} =}\, {\large 2,000}\, ohms

That’s right, the impedance of a 5 Watt speaker with a 100 volt transformer is 2,000 ohms. Now to calculate the total impedance of four of these connected in parallel:

\frac{1}{R_{Total}}= \frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+\frac{1}{R_4}  so  \frac{1}{R_{Total}}= \frac{1}{2000}+\frac{1}{2000}+\frac{1}{2000}+\frac{1}{2000}=\frac{1}{500}

therefore R (total) = 500 ohms.

Now the total power of 100 Volts with a total impedance of 500 ohms can be calculated:

Power={\Large\frac{Volts ^2}{Impedance}=\frac{100 ^2}{500} = \frac{10,000}{500} =}\, {\large 20}\, Watts

Low and behold, that is the same as simply adding the speaker watts together – which is much simpler!

Changing the Amplifier Connection Halves the Load

Example 1: The total impedance of 200 watts of 100 Volt speakers can be calculated:

Impedance={\Large\frac{Volts ^2}{Power}=\frac{100 ^2}{200} = \frac{10,000}{200} =}\, {\large 50}\, ohms

Now look what happens when that same 50 ohm speaker load is connected to the 70 Volt terminal of the amplifier:

Power={\Large\frac{Volts ^2}{Impedance}=\frac{70.71^2}{50} = \frac{5,000}{50} =}\, {\large 100}\, Watts.

Amazing, the same 50 ohm load draws 200 watts of power on a 100 volt line system, but only 100 watts on a 70 volt line system.

Example 2: The total impedance of 50 watts of 70 Volt speakers can be calculated (remember 70 Volt line is actually 70.71 Volts):

Impedance={\Large\frac{Volts ^2}{Power}=\frac{70.71 ^2}{50} = \frac{5,000}{50} =}\, {\large 100}\, ohms

Now look what happens when that same 100 ohm speaker load is connected to the 50 Volt terminal of the amplifier:

Power={\Large\frac{Volts ^2}{Impedance}=\frac{50^2}{100} = \frac{2,500}{100} =}\, {\large 25}\, Watts

This principle is very handy to the installer if the power required by the speaker load is greater than what the amplifier can deliver. Simply move to the lower line voltage speaker connection and the power drawn is halved.

A 8 Ohm Speaker will Overload a Distributed Speaker System

In the examples above we saw the speaker impedance of distributed speaker systems is reasonably high. For example a 5 watt speaker on a 100 Volt line has an impedance of 2,000 ohms. Even a 125 Watt load of 100 Volt speakers is 80 ohms. So imagine the load if the total impedance is only 8 ohms. It should be 10 times the load right? This scenario can be calculated:

Power={\Large\frac{Volts ^2}{Impedance}=\frac{100^2}{8} = \frac{10,000}{8} =}\, {\large 1250}\, Watts

That’s right, connecting a low impedance speaker (4 or 8 ohms) to distributed speaker systems will drastically increase the load on the amplifier.



  1. Thanks Geoff – Great article that answer a lot of questions I have had over the last few years.

    You mentioned moving equipment from 100V to 70V to reduce the load. Does that also work moving devices down from 70V to 25V?

    Most of the systems I work on are running 25V. The speaker/horn spec sheet states “The unit shall have a 70V/25V transformer with power taps of 4, 2, 1, 0.5, and 0.25 watts, selectable by rotary switch.” The device has separate leads when connecting to 70V or 25V. Does that mean it is applying (correct term?) a different impedance based on the watt selected? e.g. 4W@70V would need 1250 Ohms whereas 4W@25V would need 156.25 Ohms (if i followed the math correctly).


    • Hi Brian,

      Your math is correct.

      The impedance of the selected tap remains the same, but the voltage applied to it will change the maximum power at that tap.

      As an example, double click on the photo of the horn speaker above. You will see that when the 50 ohm tap is selected it will produce up to 20 watts if 100 volts is applied, or 10 watts if 70 volts is applied.

      Now in your case you have two wires (plus a common), one for 70 volt and one for 25 volt. I haven’t seen that (I mainly deal with 100 volt gear), but I have a thought. I suggest the 25 volt wire is connected to the top tap of the transformer and the 70 volt wire is connected to the 2nd top tap. This makes sure you can’t connect 70 volts to the top tap. This is a safer way than just having a warning (like on the picture above) saying “never connect the higher voltage to the top tap”.

      Does that make sense?


  2. Hi Geoff,

    I am designing Public Address/Mass Notification (PA/MNS) System for Hotels and Offices. Are 6-watts speakers enough to handle this kind of system? Or should I switch to lower (or higher) wattage? My worry is that it may deafen the guests and tenants when PA/MNS pages in.

    This article really help me in the design, by the way. Thanks.

    • Hi James,

      The answer to your question will depend on many things like: What is the background noise level? How loud do you want it? How far are the listeners from the speakers? etc.

      If you are worried that it will be too loud, then run the volume down or set each speaker on a lower tap.

      6 watts or lower is usually fine for offices etc. For Hotel rooms it could be tricky, as you don’t want it too loud in a guest room, but they need to hear any evac notices over the TV etc. One thing you can do is set any paging to lower level than evac messages. This will help the paging not to be too loud.

      You can also set room speakers at lower tap then public spaces.

      hope this helps some,


  3. Hi Geoff
    Our local church has had a p/a system installed a TOA A-1706 60w twop zone amp & four TOA bs-1030w 30W speakers.

    Unfortunatly we are getting bad feedback if we try to increase the volume. At any setting past about 25% a steady buzz starts increasing to a bad howl.

    On checking the installation I find that all four speakers have been multiblocked together & wired into one Direct 100v connection. The returns are also multiblocked together & run into one C connection.

    This seems wrong to me. Can you advise as to the correct wiring system for this rig. Would this be causing the problem.

    Thanks for any help you can give

  4. Hi Geoff, i am designing PA system with 172 number of speakers of 6W @ 70V which are distributed in 7 floors. Probably i will make two zones and will use one central amplifier of two channel of wattage around 500 Watt/channel.
    May i know is it possible to run the speaker cable around 200 to 300 meter from central amplifier?
    Your earliest reply or suggestion will be highly appreciable

    • Hi Jarjeet,

      Long distances can be OK if you use large enough cable, especially for the cable closest to the amplifier as that carries the most current.

      EAW have a good calculator. Once you play with it a bit, you’ll find it very useful.


  5. Hi Geoff
    I just want to know what is the difference when setting your speaker in a 60 watts or 30 watts. Let say I have 4 speakers and an amp of 200 watts. If I set them to 60 watts it will overload. If I set them in 30 watts it won’t overload. My question is should I buy a big amp or the same 30 watts will give me enough sound same as 60 watts

    Sorry for disturbing am just a student in sound

    • Hi Abdulhamid,

      Obviously 60 watts is twice as powerful as 30 watts, but it wont sound twice as loud. It will be 3dB louder, is louder but not by a real lot.

      Whether it will be loud enough for you will depend on what speaker and how many speakers, what area are trying to cover, how much ambient noise there as is how loud you need the system to operate at.

      I’ve just done a zoo, and all the speakers were set at either 10 watts or 20 watts. Some of these speakers were covering up to 50 metres. For a supermarket, I use lots of speakers set to 3 watts or less.

      I would try the speakers at 30 watts with your current amp and see how it goes.


  6. I am trying to replace the amp in a building that currently has a 25v and common group connection. There are about 15 speakers in the building. Is there a way to replace this amp with a powered mixer and if so, what should I look for to ensure it will work?


    • Hi Dave,

      I wouldn’t normally try to use a powered mixer to drive these speakers. The amps in a powered mixer are normally designed for 8 ohms speakers, not 100 volt. While you could use a transformer on the output of the powered mixer, I wouldn’t like to do it.

      It would be helpful if you know or could find out what wattage the speakers are. Or rather, what wattage tap from the transformer the speaker is connected to. Most likely whatever one is set to the others will be the same. Let’s they are at 5 watts each. 15 lots of 5 watts is 75 watts. Once you know the total load in watts, you will know what size amp you need.

      How many inputs do you need to mix? Mostly distributed systems are used for paging and background music. Maybe a couple of mics and a couple of music inputs. That is why most mixer/amps have 4 or 6 inputs and 70/25 volts out.

      If you know a bit more of the needs I’ll try to help some more,


  7. Hi Geoff,

    I am a complete newb at this. however, we have a toa 2060 60w amplifier manual, driving 4 ceiling mounted @30w kramer galil 6-c speakers totalling 120w on the 100v line, from reading your site i feel that the amp is not powerful enough. can you please confirm this?



    • Hi Phil,

      You are correct, four 30 watt speakers @ 100v will give a 120 watt load on your 60 watt amp.

      However an easy solution is to simply set the taps on each of the speakers to 15 watt. This will give a total load of 60 watts.


      • Hi Geoff thank you for your quck response,

        i was wondering, does setting the speakers to 15w bi-pass the transformer on the speakers?

        Sorry for my ignorence.



        • Hi Phil,
          No, using the different taps on the transformer does not bypass the transformer. It is simply a way of balancing the load and the levels.

          You only bypass the transformer if you select 8 ohms. But any of the 100 volt or 70 volts taps are fine


      • Don’t you want to allow a 20% headway between the total speaker wattage pull compared to the wattage of the amp to prevent issues?

        • Hi Erica,

          You are correct, it is best practice to leave at least 20% headroom on your amps. This is what I outlined in the 2nd point under “tips for using distributed speaker systems”. Sorry if I have mislead the readers with any other comments.



  8. Geoff,

    I have a Frankenstein monster in a retail environment. The majority of the retail space is 70V; but I need to try and get this paging system audio feed into a commercial Sonace amp. The Sonace amp is what is being used to drive one small part of the store. Is it possible to integrate these two systems for paging purposes?

    • Hi Dave,

      I think you are asking how to connect the output of a 70 volt amp to the input of a Sonance amp. If this is correct, then there are two common ways to do this:
      1) if the both amps are physically close to each other, then you can normally connect the tape out of 70 volt amp to the line in of the 2nd amp.
      2) alternatively, you can use a converter box to convert the 70 volts speaker level down to line level to connect to the 2nd amp. Something like this should work.

      hope this helps,


  9. Hi Geoff, I have been tasked with setting our sporting complex PA system up in a more permanent manner and would like your advice.
    Current equip:
    • Amcron Geodyne 1 (2 channels rated at 300w per chan @ 4 ohms, 220w @ 8 ohms. Circa 1992)
    • Behringer Xenyx 502 mixer
    Proposed equip:
    • 2 x Outdoor horn speakers – considering Australian Monitor MP30 (30 watts)
    • 4 x indoor speakers – considering Turbosound TCI32T (30 watts continuous)

    I have a few questions
    1. Can the mixer be set up to feed into both channels, thereby allowing volume control on each channel? This would also allow:
    a. a single microphone, music source, etc
    b. 2 zones for the speakers (outdoor/indoor)
    2. We may also have a third zone which is occasionally used so was eyeing off your article on speaker switches.
    3. Are we better off just buying a new amp and setting up a 100volt distributed system and allowing for expansion of the system should it be needed?

    Many thanks & great job on your website.

    • Hi Trev,

      I would probably buy a 100 volt amp. Using a 100 volt system makes wiring the speakers very simple. No need for impedance considerations or speaker selector switches. It also allows you to set the indoor speakers at a lower tap then the outdoor speakers so the levels are appropriate for each area.

      You can still switch the inside and outside speakers on and off, but all you need is two light switches.

      The MP30 music horns are good, as long as you only need to cover 30 metres or less. Any more and you might be better off using horn speakers, but they will give less quality, but reach further (more efficient).

      You should be able to use the mixer with the 100 volt amp, but it might be easier and simpler for the operators to get an amp with a mixer built in.

      hope this helps,


      • Many thanks for the advice Geoff – I picked up a second-hand Redback A4085 amplifier which should be plenty for our needs (240 watts)! Also installed are the MP30’s – so far so good.
        I know this question should be in one of your other sections but our mic unit (receiver) went up in smoke after a long layoff. Can you “generally” use the old mic’s (transmitters) with a new/different receiver? If so, how do you sync the channels. I am unsure of the brand.

        • Hi Trev,

          I’m pleased the system is coming together for you – well done.

          In regards to wireless mic systems, it is often difficult to match new and old units. There are several factors:
          – They normally need to the be the same brand, and often the same model
          – older ones may be VHF, most new ones are UHF
          – In Australia, all older UHF frequencies are now illegal, and you need a UHF model in the new frequency range
          – a lot of older units were fixed frequency, while most new ones are multi-frequency.

          So it may be easier and better to get a new system.


  10. Bloody good discriptions and very helpfull.especially about the effeciency of amplifiers.
    You remind me of a mate of mine who lives in Perth,WA

  11. Hi Geoff,
    I’m sure this is an easy one for you, I have existing 100v ceiling speakers that state to be 8ohms but have no setting for this can I just remove the transformer and connect to the outgoing red and black. Want to make sure before I do it and damage the amp.

    • Hi Craig,

      If you are wanting the speakers to be 8 ohms only, then yes you can bypass the transformer and all will be fine. Just be aware of any impedance issue if you are connecting two or more together.
      Also many 100 volt ceiling speakers are only designed for 5- 10 watts, so don’t over drive them too much.


  12. Hi Geoff,

    Hope you can help. I have a set of 8 ohms speakers I want to connect up. The Tap in on the transformers are 0.5w, 1w, 2w, 4w, 6w. What size amp will I require and what is the best way to wire these up?

    Thanks in advance.


    • Hi Ross,

      As outlined in the article, the speaker might be 8 ohm but then it has a transformer connected to it.

      If you want to run it on a normal hifi type amplifier, you need to bypass the transformer, and connect directly to the speaker terminals, rather than through the transformer.

      Alternatively you can use a commercial amplifier with 100 volt or 70 volt outputs, in which case you would connect to the transformer, using the Com and 6 watt tap for maximum volume.

      Either way, you could use any size amp. 10 watts or more would bring maximum volume, but remember no matter what size amp or speaker, if you try hard enough you can always damage them. So if you hear distortion, turn it down.


  13. We are wanting to install a system with an attenuator at each speaker (30 speakers). The wattage of the total speakers is less than the Amplifier and the attenuators exceed the wattage for each speaker.
    Is it possible to overload the amplifier because of too many attenuators?
    The total impedance to the amplifier will be much less than the total impedance if attenuators were not used.

    • Hi Phil,

      There should be no issue with your approach. Each attenuator simply puts less load (less of the speaker impedance) on the amp, so no problems there.

      The only possible trap I can think of is if all the attenunators are set low, and then the amp is running flat out to get enough level. Set the amp level with the attenuators up full, then each attenuator will reduce the level as required, and the amp won’t be pushing uphill with the hand brake on.

      hope this helps

  14. Hi Geoff,

    Fairly straight forward question. I have a 70V PA system with a chain of speakers going down a concourse, through a wall and into two public bathrooms. The bathroom speakers are a larger size than the concourse. The lowest tap settings equal the highest tap settings on the smaller speakers, and they’re simply too loud for the bathrooms while the concourse is too quiet. I want to install a wall mount attenuator between these two zones. Do I need the power rating of the attenuator to equal the total amount of wattage from the speakers *after* the attenuator, or all speakers in the chain?


    • Hi Kyle,

      Good question.

      The attenuator needs to cope with the total load of the speakers connected after the attenuator. So a 50 watt attenuator could control 10 x 5 watt speakers, or a 10 watt attenuator could control a 1 or 2 five watt speakers.


  15. I am upgrading a 70v system that currently has 2 small 60W amplifiers and about 10 speakers. I want to add additional 8 speakers and only have one large 70v amp. My question is wiring. In the past I have always daisy chained one speaker to the next. Is it possible to add one chain of 6 speakers and another 4 and the additional 8 (I am adding) on one ch without damaging the amp?

    • Hi Chip,

      Yes, with 70 volt systems you can add speakers any which way you like. They can be all on one long speaker run, or you can have as many branch lines as you like.

      Just count up the total wattage of the all the speakers, and make sure the amp is larger than that amount.

      does this help?


  16. Geoff, I would like to install 7 Soundtube CM500I in-ceiling speakers at about 50watts each on a 70v system. One of the speakers will be in the nursery. I would like to add an independent volume control to the nursery speaker for the nursery workers. The amplifier I’m eyeballing is the QSC CX302V.

    First, will this amplifier have enough power for my application?

    Second, if I install something like the Lowell 50LVC-D volume attenuator, will it affect the volume of the other speakers in another room? Will this attenuator even be the right fit for my application? Thanks for your help.

    I have an additional 4 speakers installed being ran by a conventional amplifier that I would eventually like to convert to a 70v system as well, but that will be down the road, each with its own volume control.

    • Hi Tim,

      Looks like you are on top of this install.

      The speakers you mention will have a max power of 33 watts when using the 70 volt input. Depending on your application you may not need this much power. Even so, 7 lots of 33 watts is a total of 231 watts which is just about what the amp can handle. If you reduce the wattage of one or two then there would be no issues what-so-ever with power from one channel. Alternatively, you could split the speakers between the two channels.

      The volume control you mention also looks fine. It will cope with a speaker of 50 watts, and you will only have a 33 watt (or less) load on it. If you only connect one speaker to the output of volume control, then it will only affect the level in that one speaker.

      hope this helps,


      • Perfect! Thanks Geoff, that is exactly the confirmation I needed and I do plan to drop the wattage on a few of the speakers that are closest to the, um, speaker. ;~) Another question about the other 4 speakers I have currently in an 8 ohm conventional setup. Could I run those from the other channel of the QSC 70v amp? Or should the loads on each channel be similar? Thanks again, and in advance.

        • Hi Tim,

          Yes, both amps are effectively separate, so you can have different loads on each. However good practice would suggest you try to balance the loads, rather than have one amp at close to full power and one amp doing not much. I assume you will add transformers to the existing speakers before connecting them to the 70 volts amp.


  17. Geoff, I have a 70 volt system in a fire station. Our amp went out a month ago. Got a new one, It is going into protect mode and the temp light is coming on, was found to be very hot to touch. Put a spare one in its place worked for a day now its hot as well. What could be causing them to get so hot and shut down?

    • Hi Randy,

      There are a few reasons amps get hot and shut down. The most common one is they are overloaded. The most common way of doing this is by adding a normal (8 ohm) speaker without a transformer. This effectively puts a demand of 650 watts on the amp, which is enough to make most amps sweet.

      It could also be caused by a faulty cable (maybe caused by a rodent) which could short out the load.

      The easiest way to trouble-shoot this is to disconnect half the speakers. If the sound increases in the ones left connected, the fault is probably in the section disconnected. Keep disconnecting sections/speakers until the culprit is found. Or the easy way is to ask if anyone has added an extra speaker.

      does this help?



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