mesa / boogie 400+ mismatched cabinets

[turdferguson]

i've run 2 4 ohm cabinets off the 400+ in the past and it's been stable at 2 ohms. I'm toying with the idea of running one 8 ohm 4x10 cabinet and one 4 ohm 2x15 cabinet which i believe will produce a total system impedance of 2.6 ohms.

and if i understand correctly, 2/3 of the output / power will go to the 4x10 and 1/3 will power the 2x15. my question is has anyone run such a mismatched load on this particular amp, or any other high-wattage tube power amp. i'm not afraid of the low impedance, since it's always been stable at 2 ohms, but i tend to overthink things. so i'm looking for input from anyone with experience with such a setup, since i do not actually HAVE an 8 ohm 4x10 cabinet and i'd rather not buy one just so i can try it out.

thanks, and i hope everyone is doing well.

 

[waltdogg]

Aside from the speaker matching police saying otherwise about the unmatched cabs. You should be good. I'm not 100% sure which cab will see more power either.

As impedance is somewhat relative anyways and the amp handles the load you are going to be connecting it to; I don't see how you could do any harm. I've run my V-4 into an 8x10 and 2x15 at 2 ohms. Worked well enough, it wasn't an impedance mismatch, however. It was just two 4 ohm cabs.

 

[StraightSix]

"...if i understand correctly, 2/3 of the output / power will go to the 4x10 and 1/3 will power the 2x15."

I think you have that the wrong way round - the 215 is four ohms so it will see roughly 2/3 of the power.
Also, it is my understanding that all-tube amps put out their full power at any of their recommended output impedances, so you should get full power out of the 400+ into four or two ohms.

If you get a modern 215 such as the Fearless Dually or F215, you will probably not need the 410.

Fearless review from Bass Player magazine: Greenboy Audio Fearless F112 Cabinet Reviewed | Bassplayer

 

[BassmanPaul]

Tube amps tolerate running into a lower impedance than the tap but it will reduce the lifespan of your output tubes. It is always advisable to match tap and load.

 

[walterw]

i think you can do a trick where you plug the 8Ω box into the 8Ω jack on the amp, then plug the 4Ω box into the 4Ω jack, and the amp will "see" essentially a matched 2Ω load.

or maybe it's achieved by plugging the 8Ω cab into the 4Ω jack and the 4Ω cab into the 2Ω jack? i forget, because i've never tried it and would never try it.

 

[Korladis]

First of all, you have it backwards. The cab with the 4 ohm impedance will see 2/3rds of the total impedance.

Secondly, not trying to be dismissive, but what are you hoping to accomplish here?

 

[iualum]

First of all, you have it backwards. The cab with the 4 ohm impedance will see 2/3rds of the total impedance.

Secondly, not trying to be dismissive, but what are you hoping to accomplish here?

Fine question. I think the answer is along the lines of just wanting to do it to see what happens because the 2 boxes are around .

 

[Mr. Foxen]

Mixing up cabs is messy, better just using whichever one sounds best, for all practical purposes.

 

[walterw]

Fine question. I think the answer is along the lines of just wanting to do it to see what happens because the 2 boxes are around .

but they're not, the 4x10 was just an idea. (not a good one, either)

 

[turdferguson]

thanks everyone for your thoughtful responses

 

[mikeswals]

You should call Mesa and ask if their 400+ head is happy with mismatched impedance cabs.
Because I remember when I got my Bass 400 (non +), I asked them about running two 4ohm Boogie cabs. They told me it was fine as long as ran two matching impedance cabs, and not mismatched loads. Now the difference we know is the Bass 400+ has two ohm taps, and most 400 non+ doesnt.

 

[turdferguson]

i love the sound and the low end i get from the 15's and i like the punch i get from the 10's. and i'd like to be able to use both simultaneously but it seems like a 410/115 combination might make more sense. i found a good deal locally on a 410 (constantly searching craigslist for stuff i do not need) but it clearly doesn't make sense.

furthermore, i suppose my initial post should have stated "if i remember correctly" rather than "if i understand correctly" i'm pretty sure i knew how the distribution of the mismatched load worked a long time ago, but that was a long time ago.

thanks again all for taking the time to read/respond.

 

[ThisBass]

@turdferguson

From the manual:

"Slight mismatches are not a major problem, but they will cause slightly lower output and may shorten tube life."

As your total load is around 2.7 Ohm you can use both 4 Ohm outputs or both 2 Ohm outputs. The sound will be slightly different by comparison. So get with the output "matching" you like best soundwise.

I do not believe it's a good idea talk a thing bad that isn't proved yet.
The 1/3 vers 2/3 power distribution predicts +3dB of loudness for the 215 cab. So it depends on cab/speaker efficience if both cabs in combination will complement one another.
Although it results in a considerably big tower I'd stack the cabs vertically to improve horizontal dispersion.

Don't mix ported cabs with sealed cabs!

Understanding the 400 plus outputs:

OT 8 Ohm tap
- 2 x "8 Ohm" jacks parallel wiring

OT 4 Ohm tap
- 2 x "4 Ohm" jacks parallel wiring

OT 2 Ohm tap
- 2 x "2 Ohm" jacks parallel wiring

If a single 8 Ohm cab is plugged into one of the "8 Ohm" jacks the amplifier expects a 8 Ohm load. Impedance matching is fine so far.
If a second 8 Ohm cab is plugged into the other "8 Ohm" jack the amplifier still expects a total load of 8 Ohm but then gets 4 Ohm in total because both "8 Ohm" jacks are parallel wired.

Conclusion, two 8 Ohm cabs in parallel gives 4 Ohm in total, therefore the "4 Ohm" jacks provide correct Ohm matching to the OT for two 8 Ohm cabs.
Two 16 Ohm cabs was fine (in this case) to provide a total load of 8 Ohm for "8 Ohm" jacks

Same is for two 4 Ohm cabs. Total Ohm load is 2 Ohm therefore the "2 Ohm" jacks provide the correct matching to the OT.


If there are two cabs one with 8 Ohm the second one with 4 Ohm, the 8 Ohm cab connected to the "8 Ohm" jack and the 4 Ohm cab to the "4 Ohm" jack,
the amplifier then expects a 5.3 Ohm total load but "gets" 2.7 Ohm in total.

For correct impdance matching of two different cabs (4 Ohm and 8 Ohm) it can be managed this way:

The 8 Ohm cab is plugged into one of the 4 Ohm outputs
the 4 Ohm cab is plugged into one of the 2 Ohm outputs.
In this case the amplifier expects 2.7 Ohm total load and indeed gets 2.7 Ohm in total.
In this case of "wrong looking" connection to the amplifier both cabs get the same power! Impdance matching to the amplifier is fine in this case.
Some easy understanding words how that works,
try to imagine the 8 Ohm / 8 Ohm configuration. Both cabs are plugged to the "4 Ohm" jacks for matched impdance. Now one of the 8 Ohm cabs is swapped for a 4 Ohm cab. The remaining 8 Ohm cab remaines plugged into "4 Ohm" jack, the new 4 Ohm cab then goes to the "2 Ohm" jack to achieve matched impedance. Both cabs then again "see 1/2" of their Ohm number at the amplifier output jacks.



As impdance matching is somewhat tricky with this amp (same is for strategy amp and 400 amp) It wouldn't make me wonder if a very lot of those amplifiers out there runs with impdance mismatching. As long as a user does not notice the mismatching soundwise and/or powerwise and is happy so far, so what!

 

[turdferguson]

thanks a lot. and thanks for bringing up the sealed/ported thing. i never even considered that that would/could become problematic. the 2x15 is an old acoustic 106 cab and it is ported, though i rarely have the room (or the need) to use both simultaneously.