Welcome, Guest. Please login or register.

Author Topic: Quick Question About Ohms  (Read 8149 times)

0 Members and 1 Guest are viewing this topic.

Online Marc Haycook

  • Administrator
  • Location: Jefferson City, MO
  • Posts: 2633
Quick Question About Ohms
« on: September 14, 2011, 09:34:01 AM »
I have a customer who has a Bogen C20 paging amp. They have several horns connected to the amp and one of the horns has gone bad. Some of the horns are 8Ω and some are 16Ω. The horn that is bad is an Executone C23, but I cannot find specs for it to determine if it's 8Ω or 16Ω.

What should I order as a replacement?
Marc Haycook
CCNA
Sport-Touring

Online CMDL_GUY

  • Administrator
  • Location: Mt. Sidney Virginia
  • Posts: 7370
    • www.lscg.net
Re: Quick Question About Ohms
« Reply #1 on: September 14, 2011, 09:39:52 AM »
Here is a link to the spec's for the amp;

http://www.bogen.com/products/pdfs/mixerampspdfs/C10s.pdf

It does list it at 8 ohms but there are taps for 4,8 and 16

I would get the 8 ohm.

Edit; the 8 ohms only is for MOH, speakers are at 4, 8, and 16 ohms.
"Government is not reason; it is not eloquent; it is force. Like fire, it is a dangerous servant and a fearful master." - George Washington

K4LRM

www.lscg.net

Online Marc Haycook

  • Administrator
  • Location: Jefferson City, MO
  • Posts: 2633
Re: Quick Question About Ohms
« Reply #2 on: September 14, 2011, 10:29:41 AM »
We already have the C20, but I am trying to figure out the replacement horn. They have some horns that are 8Ω and some are 16Ω. The cable is old and it's impossible to trace to determine what horns are hooked up to 8Ω and what horns are hooked up to 16Ω on the amp.

I am hoping someone knows that horn and can say if it's 8Ω or 16Ω.

EDIT: I say the cable is impossible to trace because the horn that is bad is mounted on the side of a building, 35 feet from the ground. I needed a bucket truck yesterday just to determine the horn was bad and gave me the model number. I have to go through another supervisor to get someone with a bucket truck and that took a couple of hours yesterday. I know I could throw a tone on the cable and see what port it's connected to on the Bogen, but at this point it's easier to ask if someone knows anything about the horn.
Marc Haycook
CCNA
Sport-Touring

Online hbiss

  • Administrator
  • Location: Westchester County, NY
  • Posts: 2922
Re: Quick Question About Ohms
« Reply #3 on: September 14, 2011, 12:45:14 PM »
To answer your question I need some answers. How many speakers are there and to what output on the amp are they connected? From what you say I hope there are only four 16 ohm speakers connected to the 4 ohm output because that's all you can do. 16 divided by 4 equals 4. Sounds to me like some meathead installed this and if that's the case throw anything in there. It can't be any worse than what it already is.

-Hal
I gotta get out of this business...


COMSYSTEC- Phone Systems | paging systems | background music systems | foreground music systems | retail music | restaurant music

Offline MnDave

  • Moderator
  • Location: Eden Prairie, MN
  • Posts: 340
Re: Quick Question About Ohms
« Reply #4 on: September 14, 2011, 01:34:48 PM »
Connecting multiple horns to a C20 worries me. It's only a small 20 watt amp. Plus, using any output other than 70V is fraught with problems when the next untrained installer adds more speakers. I used to service all the local Best Buy stores and their people were notorious for installing their 8ohm speakers onto the commercial paging amp and thus burn out the amp after a few weeks or months. But like Hal says, putting anything in there shouldn't make it worse. What I recommend when a customer has an amplifier output using either 4/8/16 ohms is to install something like the Phoenix Gold ISM speaker selector to avoid burning out the amplifier.    

Online Marc Haycook

  • Administrator
  • Location: Jefferson City, MO
  • Posts: 2633
Re: Quick Question About Ohms
« Reply #5 on: September 14, 2011, 02:55:35 PM »
From what I can tell, there are three horns. One is in the maintenance shop, one is outside on the side of the main building and one is across the street on the side of another building. There are two audio cables connected to the back of the Bogen. One wire is connected to the 8Ω terminal and the other wire is connected to the 16Ω terminal.

So if I am understanding things correctly, because there are three horns - one is likely connected to the 8Ω terminal and the other two are likely connected to the 16Ω terminal.

As you can tell from my post, I don't have a lot of information and I don't want to create a problem.
Marc Haycook
CCNA
Sport-Touring

Online CMDL_GUY

  • Administrator
  • Location: Mt. Sidney Virginia
  • Posts: 7370
    • www.lscg.net
Re: Quick Question About Ohms
« Reply #6 on: September 14, 2011, 04:14:31 PM »
You can get a speaker with taps on it so you can change the impedance to what every you need.
"Government is not reason; it is not eloquent; it is force. Like fire, it is a dangerous servant and a fearful master." - George Washington

K4LRM

www.lscg.net

Online hbiss

  • Administrator
  • Location: Westchester County, NY
  • Posts: 2922
Re: Quick Question About Ohms
« Reply #7 on: September 14, 2011, 06:05:36 PM »
There are two audio cables connected to the back of the Bogen. One wire is connected to the 8Ω terminal and the other wire is connected to the 16Ω terminal.

Ouch! You never want to do that. You are supposed to only use the one that is the same or the next one lower than the total of your speaker impedances. So put both of those wires on the 4 ohm output and use a 16 ohm horn. Your total load is going to be 3.2 ohms which is too low for a 4 ohm output but, like I said you didn't do it.

You can get a speaker with taps on it so you can change the impedance to what ever you need.

Yes, those are for either a 25 or 70 volt system, not speakers connected to the voice coil output of an amp. If you want to go that route (and that is the correct route to go) change all the speakers out to ones having line transformers for 70.7v, select the taps on the speaker transformers so that they don't total more than 20 watts and use the 70 volt output on the amp.

-Hal

 
I gotta get out of this business...


COMSYSTEC- Phone Systems | paging systems | background music systems | foreground music systems | retail music | restaurant music

Online telemarv

  • Moderator
  • Location: Ottawa ON Canada
  • Posts: 1336
Re: Quick Question About Ohms
« Reply #8 on: September 14, 2011, 07:20:52 PM »
I would put a 16 ohm. Only because it's better to have a higher impedance load than your output than a lower one.

As in 8 ohm load connected to 4 ohm output rather than a 4ohm load connected to an 8 ohm source. It just won't be as loud.

Even better would be to put transformers on all the existing speakers and use the 70v line.
Marv CCNA


If people had more manners... we'd need fewer laws.

Online CMDL_GUY

  • Administrator
  • Location: Mt. Sidney Virginia
  • Posts: 7370
    • www.lscg.net
Re: Quick Question About Ohms
« Reply #9 on: September 14, 2011, 07:30:06 PM »
Even better would be to put transformers on all the existing speakers and use the 70v line. :054:
"Government is not reason; it is not eloquent; it is force. Like fire, it is a dangerous servant and a fearful master." - George Washington

K4LRM

www.lscg.net

Offline silversam

  • Moderator
  • Location: NYC
  • Posts: 1017
Re: Quick Question About Ohms
« Reply #10 on: September 15, 2011, 06:10:16 AM »
Sorry I missed the thread yesterday (too much else on my mind?).

Marc, all I can do is echo Hal, Dave and the rest of the guys. My suggestion would be to change out the speakers for ones with 70V transformers and then move everything onto the 70 Volt tap. Of course some of those speakers may be wired in series or series parallel  Why? Well, put two 8 ohm speakers in series = 16 ohms. Put two more in series = 16 ohms. Put the two groups in parallel =8 ohms. Now wire the whole shebang to the 8 ohm output. Tada! A hero! Now someone else comes along and wants to add a speaker...Woops!

Being the last one to touch it means that you will own it.


Good luck. You're in a bad situation.

Sam

Online hbiss

  • Administrator
  • Location: Westchester County, NY
  • Posts: 2922
Re: Quick Question About Ohms
« Reply #11 on: September 15, 2011, 03:57:33 PM »
I'm willing to bet that this started out with those two 8 ohm speakers on the 4 ohm output which is correct. Then somebody decided to add that third speaker.

I really wouldn't worry about this, just replace the speaker and collect your money. It worked well enough for them so I doubt you are going to get any support to do anything more. As long as YOU know what is correct, that's all you have to worry about.

-Hal
I gotta get out of this business...


COMSYSTEC- Phone Systems | paging systems | background music systems | foreground music systems | retail music | restaurant music