# 45 Ohm speaker replacement options?

#### wayneh

Joined Sep 9, 2010
17,160
My home intercom/music system uses 45 ohm speakers, with a series pot to control (reduce) volume at the speaker. I have one speaker outdoors that's gone bad, and the OEM replacement is outrageously priced. I can't find one for less than $50. I'm looking for any reasonable solution that saves money. http://www.linearcorp.com/product_detail.php?productId=512 I've tested a normal, lower impedance speaker and it does work, although I'm concerned it would eventually cook the amp. I could eliminate that concern by adding a cheap$20 amp such as:
http://www.parts-express.com/pe/sho...t&utm_content=310-300&utm_campaign= Flyer_10F

But I don't have power installed near the speaker. It's not too far away though. Short of adding a power amp, are there other clever solutions to consider?

#### R!f@@

Joined Apr 2, 2009
9,758
What is the intercom power requirements.

U can use a cheap LM386 with an 8 ohm speaker

Better yet, post the intercom amp specs

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#### wayneh

Joined Sep 9, 2010
17,160
Huh, that's a thought, change the amp. There is power and a little room in the "command center" cavity in the wall. It'd be easy to lodge a small circuit in there, and run the wires for the outdoor speaker from the new circuit instead of the intercom PCB.

I haven't been very impressed with the LM358 [correction: LM386] circuits I've played with, but I wasn't really trying something like this. What would it take to have it sound decent? (Intercom decent, not hi-fi decent.) The existing system sounds better than you'd expect, and gives decent volume to the outdoor speaker.

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#### R!f@@

Joined Apr 2, 2009
9,758
Recheck the post.. made a boo boo!!

#### R!f@@

Joined Apr 2, 2009
9,758
The 50 ohm ones are driven with quite a power and sounds pretty descent.

why don't u try a 16 ohm one with a series resistor

#### wayneh

Joined Sep 9, 2010
17,160
Well, that's almost so simple as to be cheating!

I might even have a workable transformer already in my parts box. I suppose internally this thing has a turn ratio of ~2.5:1, so that the impedance ratio is roughly 2.5^2 = 6.25:1 (45Ω versus 8Ω)?

#### R!f@@

Joined Apr 2, 2009
9,758
Impedance matching should be 45Ω primary to 8Ω secondary if 8 ohm speaker is to be used.

Byfar this is the simplest method

If mismatch occurs power will be reflected back into the amp.
This cause excessive power being dissipated by the amp. If the amp has poor heat dissipation, it will burn quickly

To recap, the OEM speaker from Linear Corp. couldn't be found for less than ~$45 delivered. http://www.linearcorp.com/product_detail.php?productId=512 http://www.discounthomeautomation.c...base&cvsfa=1970&cvsfe=2&cvsfhu=4d4d534e523850 Since it's really just a cheap speaker, I didn't want to pay that much for it and started looking for options. I didn't want to use just any "normal" 8Ω speaker for fear of burning up the intercom amp. Thanks to this forum and especially Kermit2's slap-the-forehead-simple suggestion, I went looking for a 8Ω speaker+transformer to replace the 45Ω speaker. I found one here: http://www.parts-express.com/pe/showdetl.cfm?&DID=7&Partnumber=300-020 It's perfect, a speaker and transformer sold together for less than$20 delivered. The speaker fit the existing enclosure exactly. The transformer offered several wiring options.