Audio Systems: Medical Office Audio, receptionist position, listening zone

Question
QUESTION: Hi

I am putting in an audio system in a medical office. There a total of 12 speakers that will be installed. The idea is to provide background music. They are considering Yamaha NS-IW480 or Polk Audio RC80i but are open to stereo speakers. My questions are:

1) Mono vs Stereo speakers - Which ones should I be focusing on?
  I am thinking mono speakers should be sufficient but I am not   
  sure

2) Do I need a speaker selector?

3) Can you recommend a receiver good enough for this job?

Thank You
Sanjay

ANSWER: See my comments below.

1) Mono is best for BGM (background music) because you don't know where people are going to sitting or standing relative any one of the speakers.  Stereo is intended primarily for one positioned in between two speakers in a stereophonic playback configuration and who it primarily listening seriously to the music program.

2) Placement of the individual loudspeakers and their audio level is a serious matter and depends on what the activity is in the listening zone of a particular speaker.  In a receptionist position it should be switchable and adjustable for circumstances such as poor phone connection or concentration on client or patient.  Same for areas where patient is in counsel with a professional.  And, in the best world, each speaker should be at least adjustable even though the loudness setting may need adjustment only occasionally.  See the next comment.

3)  Connecting several speakers to one amplifier is a problem.  The impedance load to the amplifier is very important and it is quite difficult to do with home audio class products.  It is true the several speakers can be wired up in parallel/series combination that will load properly but it leaves you with no control over the loudness of each speaker/zone.  The better way to do it is with a 70v or 25v line system.  In the voltage distribution method each speaker unit is driven by a transformer which has wattage level taps on it allowing that speaker to have the amount of power into it that you want for the audio and acoustic situation of its space.  Speaker units can be added and deleted as the office space may change from time to time or as the usage is altered in the normal course of business.

I am not recommending the following system, but it is instructive on how such a system will be employed.  You can source the products as you please.  The speakers you referred to are just fine.  A distribution amplifier is easily searched out at a good commercial audio place or google shopping, etc.

http://www.alectrosystems.com/audio/Distribution/70volt.htm

http://www.a1components.com/25-70volt.aspx

http://www.ticcorp.com/25v_70v_100v_systems.htm

Note:  70v and 100v systems are used mostly for where the speaker wires must go quite a long distance.  The 25v system is often preferred where building codes require conduit for the speaker wire if the voltage is over 25v.  Something to discuss with your electrician or audio system installer.

Let me know if you have further questions.



---------- FOLLOW-UP ----------

QUESTION: Thank you for your response. I really appreciate it.  My installer plans to run the wires in a star  configuration with home runs to receiver. He is planning on using 2 monster cable 6 speaker selectors. He is also putting in 9 volume controls around the clinic.

Do you think it's an acceptable way of installing the speaker system?

ANSWER: Your response does not address the matter of impedance matching or loading to the amplifier which is very important.  If the matching is not correct it will cause damage to the amplifier output section.

But, as to the wiring scheme, switches and volume controls it sounds fine.  

But, getting back to the amplifier load, it really depends on how the amplifier is being loaded. If the speaker switching scheme allows too many speakers in parallel it will place a "too low" impedance on the output of the amp and overload it.  That is my only concern with what you have proposed thus far.  Therefore, I would suggest you ask the installer for an explanation of how the impedance loading on the amplifier is managed.

All the best.



---------- FOLLOW-UP ----------

QUESTION: Thanks for your response. I am thinking of connecting each 8 ohm speaker to its own 70 volt transformer. My questions are:

1) 70 volt transformer - How many watts do I need for the background  
  music? Do you think 15W or 20W be sufficient or do I need more?

2) Do I need a receiver in addition to the 70V amplifier?

3) Will this below setup eliminate the low impedance problems faced by the
  receiver:

  Receiver => 70V Amp => 12 speakers in series with each one connected to   
  its own 70v transformer.

Thanks
Sanjay

Answer
1) 15W is plenty.  Usually, even 5W is considered okey for bgm in small rooms.

2) Receiver is helpful if you are going to tune into radio such as fm, but if you are planning to just play mp3 or ipod you can feed directly to the amplifier.  BUT: if you are going to add emergency announcements or paging annunciation then you will need some kind of mixer or receiver to add those functions.

3) Yes, it will do the job.  

Best wishes.