speaker impedance please help

[jgcable]

Guys, I am loosing my friggin mind after a long weekend. Please help.
I have a cabinet with 2 12" Altec Lansing Speakers in it. The model #'s are 417-8c
They are clearly marked 8 ohms.
When I wire them in series I only get 8 ohms!!
I put my meter to the + and - of one of the speakers and it is reading 4 ohms. How can they be 4 ohms if the speakers are clearly marked 8 ohms? Heck... even the part # confirms they are 8 ohm speakers. Are there such things as switchable impedance on speakers??

[MountainDog]

Re: speaker impedance please help

You are actually measuring the Voice Coil DC resistance, which doesn't usually exactly match the impedance. The actual impedance is found from a curve of the speaker in its box when it is fed a 20hz to 20khz signal from a sine generator. That said, usually the Voice coil resistance is fairly close to the impedance.

It is well known in the industry to rate speakers as a certain impedance, but when you measure it, it comes out less.

From an Altec own site, I couldn't find a 417 8C spec sheet, but I found a 416 8c one, and the DC resistance is 6.5ohms. Also, I found a 417 16lf spec, which would mean 16 ohms, that says the Re(ohms) is 11.50:
http://websearch.cs.com/gw/boomframe.jsp?query=altec+lansing+417+8c&page=1&of fset=0&result_url=redir%3Fsrc%3Dwebsearch%26reques tId%3D230883e83b0c3b2%26clickedItemRank%3D2%26user Que ry%3Daltec%2Blansing%2B417%2B8c%26clickedItemURN%3 Dhttp%253A%252F%252Fnleinternet.net%252Falteclansi ngunofficial%252FThiele-Small.html%26invocationType%3D-%26fromPage%3DGWYResults% 26amp%3BampTest%3D1&remove_url=http%3A%2F%2Fnleint ernet.net%2Falteclansingunofficial%2FThiele-Small.html

All that said, your's should be measuring closer to 6.50ohms. Did someone recone and use a different lower impedance voice coil?

But it all comes down to your amp. Is your amp asking for 16ohm loads? If it is a solid state amp, most run fine on 8ohm. If your amp can handle the 8ohm in series load, then you can use these speakers no problem.

[jgcable]

Re: speaker impedance please help

It is a Soldano Astroverb 16 and it asks for a 16 ohm load. When I wire the 2 Altec Lansing speakers up in series it measures 8.7 ohms at the output jack.

I also took a look at my 4 x 12 Carvin cabinet.
It is loaded with Peavey Scorpion speakers in it. I measured the individual speakers and they measured 4 ohms each. I always thought that Peavey Scorpions were 8 ohm speakers. I wired them up in series and the cabinet measures 13.2 ohms at the output jack. I read online that to compensate for using a digital multimeter I should multiply the measurement I get by 1.3.
This means my 2 x 12 cabinet reads 11.31 ohms and my 4 x 12 cabinet reads 17.16 ohms. What gives... What does a stock 4 x 12 cabinet measure? How about a 2 x 12?

[MountainDog]

Re: speaker impedance please help

Tube amps are very particular about impedance so I wouldn't use the 2x12 altec cab with the Soldano. Your carvin cab should be close enough.

How a cabinet will measure is based on what the manufacturer decided to use as a voice coil resistance vs. what they decide to rate the speakers at.
a 4x12 w/four 16ohm speakers (that really measure close to 16ohm) would be 4 ohm in parallel/parallel wiring, and 16 ohm in series/parallel (like a marshall 4x12).
a 4x12 w/four 8ohm speakers would be 2 ohm par/par and 8ohm ser/par.
a 2x12 w/two 16ohm speakers would be 8 ohm in parallel and 32 ohm in series
a 2x12 w/two 8ohm speakers would be 4 ohm in parallel and 16 in series


I suggest you try to find some speakers that measure much closer to the sticker'd rating (Celestions are known to be close) so you know your amp is safe.