Using two cabs: one 8 ohms, the other 4 with a Carvin B1500

[11Rob]

Can you wise folks here on talkbass enlighten me!

I have a Carvin B1500 head which is a "mono block" head (one power supply). I also have a 4 ohm 4x10 and an 8ohm 1x18.

Can I use both cabs with this head?

If so, should I run each off the head or should I chain them together?


Thanks!

[Got2SadowskyNYC]

It's not good to mix ohms like this, because you get an uneven rating.

2 8ohms cabs make a 4 ohm load.

2 4 ohm cabs make a 2 ohm load.

A 4 and an 8 would get you about a 3 ohm load. Not good on the amp.

depending on the speakers in the 4x10 you may be able to rewire it for 8 ohms.

[basscooker]

Originally Posted by Got2SadowskyNYC

depending on the speakers in the 4x10 you may be able to rewire it for 8 ohms.

do tell....

[smogg]

Q: Can I use both cabs with this head?
A: Yes, your amp is 2 ohm stable.
8ohm + 4ohm = 2.6ohm which is less than the 2ohm minimum.
Rough guesstiment power output about 75% of the 2ohm output rating with twice the power going to the 4ohm cab vs the 8. (do the battery test to make sure the two cabs are IN phase)

Q: If so, should I run each off the head or should I chain them together?
A: No difference.

[LowEZ]

Originally Posted by Got2SadowskyNYC

A 4 and an 8 would get you about a 3 ohm load. Not good on the amp.

Wrong. It would be fine 'on the amp'.

depending on the speakers in the 4x10 you may be able to rewire it for 8 ohms.

Wrong. Impossible.

[gearhead1972]

Originally Posted by smogg

Q: Can I use both cabs with this head?
A: Yes, your amp is 2 ohm stable.
8ohm + 4ohm = 2.6ohm which is less than the 2ohm minimum.
Rough guesstiment power output about 75% of the 2ohm output rating with twice the power going to the 4ohm cab vs the 8. (do the battery test to make sure the two cabs are IN phase)

Q: If so, should I run each off the head or should I chain them together?
A: No difference.

This
http://www.carvinguitars.com/manuals/B1500.pdf

[Downunderwonder]

Does amp handle sub 4ohm loading? If not it's a good time to trade up to a nice matching pair of 2x12 if you must have stupid loud.

At least the impedances are compatible with the probable power handling capacities of the two cabs. It could easily sound muddy as hell though.

[Downunderwonder]

Originally Posted by Got2SadowskyNYC

It's not good to mix ohms like this, because you get an uneven rating.

2 8ohms cabs make a 4 ohm load.

2 4 ohm cabs make a 2 ohm load.

A 4 and an 8 would get you about a 3 ohm load. Not good on the amp.

depending on the speakers in the 4x10 you may be able to rewire it for 8 ohms.

Suggest familiarising yourself with the amps forum sticky contents before dishing out any more advice this year.

[smogg]

Originally Posted by Got2SadowskyNYC

It's not good to mix ohms like this, because you get an uneven rating.
A 4 and an 8 would get you about a 3 ohm load. Not good on the amp.

AFAIK/and to the best of my limited knowledge, that concept only applies to all tube amps and maybe real old school SS amps that were passively cooled. That Carvin is a modern fan cooled SS amp that can handle a 2.6 load no problem.

[Jaco who?]

Originally Posted by 11Rob

Can you wise folks here on talkbass enlighten me!

I have a Carvin B1500 head which is a "mono block" head (one power supply). I also have a 4 ohm 4x10 and an 8ohm 1x18.

Can I use both cabs with this head?

If so, should I run each off the head or should I chain them together?
Thanks!

Yes, you can. You will have a 2.667 Ω load. Your amp is rated @ 2 Ωs minimum load.

You can run each off the head or chain them together, the result will be the same, a parallel 2.667 Ω load with either method.

[jumblemind]

Would the 4ohm cab overpower/overshadow the 8ohm in the mix?

[Downunderwonder]

Originally Posted by jumblemind

Would the 4ohm cab overpower/overshadow the 8ohm in the mix?

Yes, and that would likely save the 18 from being blown out.

Multiple 10's handle more power and move more air as a collective than a similar sized cab with 15". Afaik 18's are in a similar boat to 15's.

Without full disclosure of what drivers are in the cabs we can't say if the 18 might still be struggling to keep up with the 4x10, even with the impedance handicap but it's certainly possible.

Assuming the 18 adds something rather than handicapping the 4x10, some amount louder is usually "better" unless nasty phasing happens.

We don't know the sensitivities but it's a pretty good bet the single 18 lags behind, making less use of its 1/3 share of power. Probably not going to add nearly as much "louder" as hoped.

Personally I can't imagine this experiment sounding very good but it doesn't automatically fail on account of the impedances making it dangerous for the amp or the speakers.

Beware of farting. Highly distorted tones make it hard to hear the farts when you're in the middle of business.

[gumtownbassman]

good to see bad advise is being corrected,
seeing too much of this lately.

[bertbass666]

I used a B1500 for a few years and always ran it at 2 ohms, no problem at all. Using both cabs, the 4x10 will be louder than the 1x18.

[11Rob]

Thanks for the advise everyone! I appreciate everyone's feedback.

The 18 is a Carvin BRX18 (8) rated at 800W. I also have an Ampeg PR410HLF (4) which is rated at 600W (1200 peak).

I used them together last night. It sounds like they are probably in phase because combined they are much louder and there is no loss of bass.

In fact, from the basement, I knocked some dishes off the shelf upstairs at my drummers house.

Yes, I do want my bass rig to be "stupid loud". My drummer is very aggressive and the guitar player insists on practicing at face melting levels. We are a rock band. Our practice level are around 85 dB. I wear ear protection.

I play a 5 string dropped 1/2 step. The 18 does a nice job with the sub bass freqs.

Oh, and with the B1500 in a heavy tour case my bass rig is outrageously heavy!

[11Rob]

Here's the stats on the two enclosures:

18

- Power handling: 800 Watts
- Reproduces Frequencies from low B (26 Hz to 2 kHz)
- Freq. Resp: 30 to 2K Hz ± 5 dB
- Sensitivity: 98dB @ 1w and 127 dB @ 800W


410

RMS Power Handling: 600-Watts
Frequency Response (-3dB): 33Hz - 18kHz
Usable Low Frequency (-10dB): 29Hz
Crossover Frequency: 4kHz
Nominal Impedance: 4-Ohms
Sensitivity: 96dB
Maximum SPL: 124dB

[bertbass666]

85db isn't loud.

[smogg]

Originally Posted by bertbass666

85db isn't loud.

It is in a 10x20 concrete basement.

[11Rob]

I used a phone app to measure the SPL. Maybe its not the most accurate. I have ran it side by side with a real meter at a venue and they appeared to agree.

[Downunderwonder]

85dB is the same wherever. It's not loud on the rock band scale. Shaking stuff off shelves your practice room is probably more like 120dB most of the time and peaking higher.

If the 18 was all its specs say I'd be very surprised.