Help, Measured Ohms doesn't match cab rating

[MadAsAHatter]

This is for my Ashdown Rootmaster 610 bass cab.

The cab is rated for 4 ohms. I was looking to rewire it to make it 16 ohms. In checking everything I discovered the measured ohms is off from what the cab is rated.
Each speaker is rated for 8 ohms. Wired in series/parallel that would give a total of 5.33 ohms. I'm guessing Ashdown is saying that is close enough to call it 4 ohms.
Measured I'm getting 7.0 ohms. I measured this several times with different cables plugged in to make sure.

I know Ohms will fluctuate based on frequency and whatnot when playing, but this seems a large deviation when sitting idle. IME other cabs are much closer to calculated ohms when actually measured. Most being no more than a few decimals off; 4.0=4.3, 8.0=7.8, 16.0=16.5, etc.

I'm not going to rewire this cab as originally planned since 6 - 8 ohm speakers will never get me close enough to 16 ohms regardless of the way it's wired. But now it has me worried it's not safe to use with a 4 ohm tube amp.

Is a measured 7 ohm speaker cab safe to run with 4 ohm tube amps?

 

[simonfrewler]

Generally the load will actually measure lower than rated. Such as ...my 8 ohm cabs read about 7 or a little under that...(DC load). because of how it works. Usually about 15 percent lower.

And usually, as a rule, running a higher impedance speaker from a lower impedance tap won't hurt. Just don't do it the other way....your transformer won't like that.

4 ohm tap will definitely run 8 ohm with no issue ...shit, pretty confident you can run 16 as well....not ideal ..but will work.

4ohm into 8 ohm load = half power
4 ohm into 16ohm load = 1/4 power
8 ohm into 4 ohm load = 2x power and nasty smell. Hahaha.


Also, taking all this into account, you have a 8 ohm cab.

 

[NowYou'rePlayingWithPower]

Would guess that you're safe with most amps, but I've seen people say they have issues depending on the amp. Assuming you're running a bass amp into this, does the cab have stereo setting and does the amp have 2x2ohm parallel outputs?

 

[Racerxrated]

You're safe, as others have said. As long as you're at a lower number out on the amp, no worries other than a slight power reduction, maybe a bit darker/thicker tone as well. That's what I've noticed with my set up.
You can also wire 2 16 with 2 8ohm speakers in the same cab, for the same 5.33 ohm result.

 

[simonfrewler]

With this many unknowns, personally, I would test continuity in each driver.... completely rewire the cab to suit your needs and be done.

 

[MadAsAHatter]

Would guess that you're safe with most amps, but I've seen people say they have issues depending on the amp. Assuming you're running a bass amp into this, does the cab have stereo setting and does the amp have 2x2ohm parallel outputs?

Right now I'm using it solely with my BV300. Future plans are to use it with vintage style amps that can be used for both guitar & bass. Like a sunn Model T. I'll use a switcher to have a guitar cab & this bass cab hooked up.

There's nothing special about the Ashdown cab. No stereo or 2x2ohm parallel output or anything. Just a second jack to daisy chain another cab to it.

You're safe, as others have said. As long as you're at a lower number out on the amp, no worries other than a slight power reduction, maybe a bit darker/thicker tone as well. That's what I've noticed with my set up.
You can also wire 2 16 with 2 8ohm speakers in the same cab, for the same 5.33 ohm result.

I've been using it as is and haven't had any issues yet. And I've read amp lower ohms than cab is safe up to double; 4 ohm amp to 8 ohm cab is ok, but don't go 16 ohm cab. I'm also not a fan of purposeful mismatches. In this particular situation the mismatch is what it is. I just needed to be sure it's safe. Sounds like it will be.

With this many unknowns, personally, I would test continuity in each driver.... completely rewire the cab to suit your needs and be done.

I checked each driver, wiring, etc. to make sure all was good. I didn't find anything out of order. As long as it's safe using the 4 ohm tap on my amps it's good to go as is. It just means I won't be able to use that cab mess around with one particular amp that doesn't have a 4 ohm tap. I wanted to see how my new to me Vintage Modern sounded as a bass amp. Like if the low dynamic range mode could sound similar to a Super Bass a la Lemmy.

 

[Greazygeo]

Don’t forget that speakers are rated by impedance and you are trying to measure them by a resistance setting on your meter. They will never read what they are rated.