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[Christopher Greco]

I have 4 dual 18 subs that I bought used a few years back and when I read the DC resistance on the drivers which are wired individually to an NL4, driver 1 to +&-1 and driver 2 wired to +&-2. In my experience of measuring speaker drivers with a DVM I am accustomed to seeing slightly less  that the stated impedance on the driver. For an 8 ohm speaker I have seen in tbe neighborhood of  6 ohms DC resistance resistance. Now on my Paudio 18s I am seeing as low as 3ohms across the board. The speakers sound fine but I am wondering if the DC resistanceni am reading is a result of a miss spent youth where overheating the coils might have lessened thier resistance. These seem to be original cones and look like factory glue jobs. I would think if someone reconed them to 4 ohm that they would have put some sort of label or sharpeed over the 8. Any one have insite on this phenomenon ??

[Tim McCulloch]

I have 4 dual 18 subs that I bought used a few years back and when I read the DC resistance on the drivers which are wired individually to an NL4, driver 1 to +&-1 and driver 2 wired to +&-2. In my experience of measuring speaker drivers with a DVM I am accustomed to seeing slightly less  that the stated impedance on the driver. For an 8 ohm speaker I have seen in tbe neighborhood of  6 ohms DC resistance resistance. Now on my Paudio 18s I am seeing as low as 3ohms across the board. The speakers sound fine but I am wondering if the DC resistanceni am reading is a result of a miss spent youth where overheating the coils might have lessened thier resistance. These seem to be original cones and look like factory glue jobs. I would think if someone reconed them to 4 ohm that they would have put some sort of label or sharpeed over the 8. Any one have insite on this phenomenon ??

So go to pAudio's web site, download the spec sheet for the driver and see what the listed DC resistance is for the voice coil.

[Steve-White]

They drivers are probably nominally rated at 4 ohms.

[Paul G. OBrien]

In my experience of measuring speaker drivers with a DVM I am accustomed to seeing slightly less  that the stated impedance on the driver. For an 8 ohm speaker I have seen in tbe neighborhood of  6 ohms DC resistance resistance.

That matches my experience.

Now on my Paudio 18s I am seeing as low as 3ohms across the board.

Yeah that sounds like 4ohm drivers to me, I don't think you could work a driver hard enough to permanently lower it's DC resistance without being seconds away from blowing it. 
I have some Yorkville dual 18s that contain 4ohm drivers that were factory wired in parallel and somehow given a nominal box rating of 4ohms. I don't know why a manufacturer would do this because most amplifiers aren't too happy about being bridged into a 2ohm load... which is how most people powered a box like this in the days before class D. I rewired the cabs to power each driver with a separate amp channel.

[Geoff Doane]

What kind of cabinets are they in? (I did a quick Google search, but just came up with raw drivers.)

Horn loading will tend to raise the impedance.  A 4Ω nominal driver may very well measure 8Ω or above in the frequency range you're interested in.

GTD

[Matthew Knischewsky]

What kind of cabinets are they in? (I did a quick Google search, but just came up with raw drivers.)

Horn loading will tend to raise the impedance.  A 4Ω nominal driver may very well measure 8Ω or above in the frequency range you're interested in.

GTD

He could be referring to any of the Elite Double 18's... SW1000, ES1004, LS1004... I seem to remember that this was a "thing" but it's been a minute since I have refreshed my memory of these cabinets.

SW1000 used either with L18/851 drivers or L18Y800.
ES1004 used L18Y800
LS1004 used 7458, and later 7465.

All of those except the 7465 seem to be rated at 4 ohms as per the Yorkville Parts Catalogue, so that would seem to indicate that a double 18" cabinet would be technically rated at 2 ohms. But I'm going to guess that since all of these "sub" cabinets are tuned fairly high (40Hz or so) there is a large impedance peak due to the cabinet tuning that makes the entire system (two drivers and the cabinet) close enough to 4 ohms that amplifiers are not unhappy with the load. Or maybe they just took a chance thought "no one will buy a 2 ohm sub cabinet, we will just say it's 4!"

Impedance is a curve not a straight line, sometimes designers and marketing departments have to make a call to get a spec "close enough" to something that technicians or musicians know how to work with.

Matt.

[Mike Caldwell]

Impedance is a curve not a straight line, sometimes designers and marketing departments have to make a call to get a spec "close enough" to something that technicians or musicians know how to work with.

Matt.

I'm sure if a cabinet was rated at 6 ohm some would think their amps would not run it.

[Tim McCulloch]

What kind of cabinets are they in? (I did a quick Google search, but just came up with raw drivers.)

Horn loading will tend to raise the impedance.  A 4Ω nominal driver may very well measure 8Ω or above in the frequency range you're interested in.

GTD

Cabinet design will not affect DC coil resistance.

[Caleb Dueck]

I'm sure if a cabinet was rated at 6 ohm some would think their amps would not run it.

That's why Danley had to change the spec for the SH50 - too many calls about how to power a 6 ohm box. 

[Paul G. OBrien]

He could be referring to any of the Elite Double 18's... SW1000, ES1004, LS1004... I seem to remember that this was a "thing" but it's been a minute since I have refreshed my memory of these cabinets.

SW1000's in my case which are just bog standard bass reflex cabs.  The general consensus about these from back in the day was that they sounded loose and flabby, but that is also in my experience what a sub sounds like when the amp powering it is being operated at a lower than recommended load impedance. With the drivers in this box wired independantly to the amp I have no such complaints, output is tight sounding and the drivers seem content to absorb everything the amp(Yamaha P70000) has to offer.

Still I'm not sure why a manufacturer would do this, but at least in the OPs case the drivers were discetely wired to begin with. The OP hasn't come back so we don't know exactly what vintage of SD18 driver and what cab he has, but if the drivers have a relatively low sensitivity this could be a way to make the output seem a bit more "normal". For example there is no advantage of using 94dB 4ohm drivers instead of some other 97dB 8ohm drivers, the 4ohms drivers would consume twice as much power to produce the same SPL.. given the same power amp is in use.

[Art Welter]

Now on my Paudio 18s I am seeing as low as 3ohms across the board. The speakers sound fine but I am wondering if the DC resistanceni am reading is a result of a miss spent youth where overheating the coils might have lessened thier resistance. These seem to be original cones and look like factory glue jobs. I would think if someone reconed them to 4 ohm that they would have put some sort of label or sharpeed over the 8. Any one have insite on this phenomenon ??

Chris,

The current PAudio SD 18 should read 5.2 ohms DC resistance.
Overheating coils temporarily increases their DC resistance.

If the impedance had dropped permanently it would be due to shorted coils, and they would not "sound fine", nor would it be likely eight burnt coils would read within .2 ohms of  each other.

Generic four ohm recone kits are available that will fit the original cones and look like factory glue jobs , good reconers can make them look like originals.
If the person reconing the drivers had used tape to re-lable the impedance to not the change, the seller could have removed the lable to make the drivers look more like "factory original" before putting them back in the cabinets.

At any rate, sounds like they are still the same (wrong) impedance as they were when you asked about them on  July 2, 2023 

Art

[Ivan Beaver]

I'm sure if a cabinet was rated at 6 ohm some would think their amps would not run it.

You HAVE NO IDEA how many people think this.

I once rated a cabinet for 6 ohms (because that best described the overall load on the amplifier).

I got lots of calls asking where to buy a 6 ohm amplifier, because none of the manufacturers listed it.

I then rated it for 4 ohms and the calls stopped.  The cabinet did not change.


The lack of basic understanding in our industry is astounding sometimes

[Brian Jojade]

You HAVE NO IDEA how many people think this.
..
The lack of basic understanding in our industry is astounding sometimes

And that's why $300 power cables exist.

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