How is my single 4 ohm speaker a 8 ohm load?

troy mcclure · #1 01-24-2011, 10:46 PM

I have a single 18 cab and it has no crossover, just some kind of circuit breaker type reset. The rear of the cab says 8ohms and I pulled out the driver and it says 4 ohms? It is the original driver according to everything I read on Harmony Central... any takers..

it is an old yorkville sub if you are wondering...

DanRJBrasil · #2 01-25-2011, 02:25 AM

use a multimeter and find out, the chances are that is a 4ohms as it is wrtten in the back of the driver

billfitzmaurice · #3 01-25-2011, 06:55 AM

Either the factory installed the wrong driver or the wrong plate or the driver has been replaced. Harmony Central is hardly a definitive source, if you want to pursue it further check w/Yorkville.

JTE · #4 01-25-2011, 07:42 AM

I do know that Peavey's FH-1 folded horn cabinet had a different driver than the system's stated nominal impedance. The explanation Peavey gave (this was in the mid '80s) was that the air loading on the driver affected how the speaker reacted (dang, I wish I'd listened more to Len that day) and made the impedance the amp saw to be different than the nominal impedance of the voice coil.

John

**mikeddd** · #5 01-25-2011, 08:01 AM

Maybe it's a dual voicecoil driver (2, 4-ohm vc's) and the coils are wired in series? That would explain the 8-ohm rating from a "4 ohm" driver. Though I've never seen a dual vc driver in a bass cab, anything's possible I suppose.

troy mcclure · #6 01-25-2011, 08:09 AM

yorkville doesn't have this product archived on thier website. I am thinking they made a mistake on the face plate. They were using RCF drivers from Italy, not sure who makes their drivers now.

billfitzmaurice · #7 01-25-2011, 08:26 AM

Quote:

Originally Posted by JTE

Peavey's FH-1 folded horn cabinet had a different driver than the system's stated nominal impedance. The explanation Peavey gave...was that the air loading on the driver affected how the speaker reacted... and made the impedance the amp saw to be different than the nominal impedance of the voice coil.

John

True.

father of fires · #8 01-25-2011, 09:09 AM

Quote:

Originally Posted by billfitzmaurice

True.

Really?

I was waiting for you to debunk this.

Could you explain it all?

BurningSkies · #9 01-25-2011, 09:12 AM

Quote:

Originally Posted by father of fires

Really?

I was waiting for you to debunk this.

Could you explain it all?

Ahhh...the mysteries of impedance curves.

alexclaber · #10 01-25-2011, 09:24 AM

Quote:

Originally Posted by father of fires

Really?

I was waiting for you to debunk this.

Could you explain it all?

The horn loading adds acoustic impedance. It's the same for some of Bill's horn subs. If you stick enough identical direct radiator cabs in a small space you get this too, though to a lesser degree.

JTE · #11 01-25-2011, 09:24 AM

From Peavey's website... (http://www.peavey.com/support/techno...mpedance_3.cfm)

"WHEN FOUR OHMS IS NOT FOUR OHMS
There is an enclosure in our product line that we have been making for twenty years called, the FH-1 low frequency enclosure. We use a four ohm loudspeaker in this enclosure; however, as long as the enclosure is operated above its cut-off frequency of 60 Hz, the actual load impedance that the power amplifier sees is nominally eight ohms. Likewise, we use a four ohm loudspeaker in the Mid bass horn of HDH-4 and HDH-1 speaker enclosures. As long as these horns are operated above their cut-off frequency of 300 Hz, the midbass of the enclosure will exhibit an eight ohm load to the amplifier.

The mechanical loading of the loudspeaker by the horn makes an impedance transformation so the amplifier sees a load impedance of 8 ohms within the horns operating bandpass. I mention the horn's operating bandpass because if you operate any horn below its cut-off (-3 dB down point on the low frequency portion of its response curve), the driver reverts back to its original lower impedance. As long as you send horn loaded enclosure frequencies that are above the cut-off, the system will offer a higher load impedance to the power amplifier.

The DC resistance of the loudspeakers discussed above is 3.2 to 3.8 ohms. Mounting the loudspeaker on a horn doesn't change the DC resistance, but a power amplifier driving that horn will see a load impedance that is more than twice that of the nominal four ohm impedance of the individual speaker. Hopefully some of us now understand how a four ohm loudspeaker can become an 8 ohm loudspeaker system when mounted on a properly designed horn. "

John

greenboy · #12 01-25-2011, 09:34 AM

Yep, and similar was on their Black Widow cutsheets as far back as I can remember, when talking about the 1504DT or the several horns it was used in.

troy mcclure · #13 01-27-2011, 07:16 AM

Getting these reconed and the owner of the reconing firm told me these are very good speakers.
If I cross these over as recomended 100, my amp will see tem as 8 ohm loads and it is safe to wire them in parallel and run my 4 ohm amp in mono?

Ben Clarke · #14 01-27-2011, 07:46 AM

probably the SW-800?

Remember impedance varies with frequency, and low freq enclosures will generally have their lowest impedance in the lower range of their operation, which is why Peavey was referring to LF cutoffs and making sure the speakers in question were not run below them.

Best to email Yorkville to be sure. If it were me, I would move to the 8R 7465 used in current models (a B&C neo), but they are expensive.

Yorkville uses B&C, BMS, and 18 Sound in their better stuff these days. Also Eminence and Celestion in mid-line and entry stuff. Some no-name Chinese factory woofers in entry level PA.

Robby Hoinsky · #15 01-27-2011, 09:00 AM

But your single 18" is horn loaded or not? My guess is not, so I don't see how it would become 8 ohms. Even DC resistance in the crossover wouldn't add 4 ohms.

Quite the mystery.

Robby

Ben Clarke · #16 01-27-2011, 09:09 AM

It likely is (why would you guess?). The vast majority of Yorkville subs out there are horn loaded in some way and do not use passive networks.

Robby Hoinsky · #17 01-27-2011, 09:12 AM

Quote:

Originally Posted by Ben Clarke

It likely is (why would you guess?). The vast majority of Yorkville subs out there are horn loaded in some way and do not use passive networks.

my bad, I completely read his post wrong. All this New England snow shoveling has gotten to my brain

Robby

PaulMacCnj · #18 01-27-2011, 09:16 AM

This was touched upon, but it's worth clarifying. A load rating on a speaker is the impedance, which is a combination of resistance and reactance. A multimeter will read the resistance only of the speaker coil. As previously stated, a 4 ohm speaker will read around 3.2 ohms. An 8 ohm speaker will read around 6 ohms.

Robby Hoinsky · #19 01-27-2011, 09:36 AM

Quote:

Originally Posted by PaulMacCnj

This was touched upon, but it's worth clarifying. A load rating on a speaker is the impedance, which is a combination of resistance and reactance. A multimeter will read the resistance only of the speaker coil. As previously stated, a 4 ohm speaker will read around 3.2 ohms. An 8 ohm speaker will read around 6 ohms.

right, and a 4 ohm speaker put in a horn will read the same resistance but a higher reactance.

Robby

Ben Clarke · #20 01-27-2011, 02:09 PM

Quote:

Originally Posted by Robby Hoinsky

my bad, I completely read his post wrong. All this New England snow shoveling has gotten to my brain

Robby

I can dig it!

...get it?