Question on using mixed cabs with different sensitivity

Power should be shared evenly.

 

Yes half power to each cab when they have the same impedance.

Do both cabs have the same number of drivers? That can be a thing if you aren't careful.

 

The farther apart the sensitivity, the less the lower sensitivity cabinet will contribute to the overall SPL.

 

Yes, both cabs will receive the same power. The difference in sensitivity means that the cab with the lower sensitivity will produce less volume despite the power being the same to each.

hth

 

If one were being truly pedantic wouldn't it be both cabs will receive *on average* the same power? If I understand this stuff correctly won't there be points at the lower end of the scale where the actual impedance at given frequencies is significantly different on each cab? And if so doesn't this mean one or other cab will be receiving a rather larger proportion of the signal at different frequencies? Or is this a negligible concern in practice due to complexity of signal unless you send the cabs pure sinewaves from a bass synth?

 

If the gap in sensitivity is big you get no extra volume from the extra cab until you pump a whole lot of extra power in.

 

In general negligible.

 

About the only way around that disparate SPL is to use a dual powerblock amp. I had a similar problem with a very boomy GK115 cab I had and a not-boomy acoustic B410. The GK115bpx was boomy and louder than the B410. I'd drop the bass EQ from flat to about 10:30 to get rid of the boominess. If I ran just the 410 at that it sounded pretty thin.

Then I bought an old Eden WT500 upgraded to 800 watts bridged. It is a dual-powerblock amp. The Eden WT500, WT600, and WT800 were all dual powerblock amps as is their current WTP900. That means that they had two separate power amps inside. I would plug one cab into one side and the other cab into the other side. But what did the magic to my sound from doing this was the "Balance" knob on the front of the amp. You could use it to direct more power to one side than the other. So I just turned that knob a little bit towards the 410 and put the bass EQ back to flat. Voila' much better sound all around.

Not a lot of amps around anymore that are dual powerblock, but plenty of power amplifiers that are. You might consider getting one of those and just running you a cord from your amp's effects-send to that power amp. In effect, you are using your amp as just a preamp at that point. Make sure the power amp has a balance knob on it though or separate volumes for each side or it won't do you any good.

Conversely you could by an old Eden dual powerblock or their new WTP900 amp and have everything in one. Odds are there are some other current amps out there that have that dual powerblock, but I don't think that's very common any more.

 

Both cabs are getting the same power. There is no way to overcome the sensitivity difference, unfortunately. Sorry it is so noticeable!
This is why the sensitivity of a cab is so important - makes much more difference than amp power.
AMP - takes 10X power (+10dB) to "sound" twice as loud. Cab - takes only 2x sensitivity (+3dB) to "sound" twice as loud.

 

I think it’s a great that somebody actually took sensitivity into account. A few years ago, I saw a recommendation for a either a Pyle or Dayton speaker as an economical replacement for a failed speaker in a 2x10 bass cabinet. Out of curiosity, I looked up the recommended speaker and the sensitivity rating was 89db....

 

Sensitivity is just as important as power handling and other parameters used to define the performance of a speaker.

 

Do it. Start with the volume low. Raise the output until the least robust speakers approach failure, don't ever go any louder than that.
Google pictures of Entwistle, Bootsy, Watt, Wooten, McCartney, Geddy Lee, there are thousands of professional bassists who do this reliably. Just start low and see how high you can go. Don't tell anyone here, just do it. You'll know in seconds if it sounds like you want it. As long as you don't start at max level you won't damage anything. I know, we all know it's not recommended but in fairness part of that 'recommendation' is a suggestion that you go buy 2 matching speakers, not everyone can do that. You won't blow the speaker without knowing that it is stressed. It's not like bomb. You get a lot of hints. I'm sure you've played loudly enough once or twice that you know what speakers sound like when they are approaching the limit.

 

The problem with the lower sensitivity speaker being the "weak link"" is that it's unlikely that you will hear it straining until the damage is done. The higher sensitivity speaker will mask all the warning signs.

I do see the effects of such combinations, usually because of the need for repairs. That's why I am trying to educate, it seems (based on what I see) that it's still necessary.

 

Maybe if in these discussions we explicity characterized the lower sensitivity speaker in a combined system as literally becoming a "fuse/sacrifical elelment", the point would become more obvious. I mean my toaster or vacuum cleaner rarely alerts me before a breaker trips. Just a thought...

 

The real trick is, "does it produce sound at a level you can gig with?" without risking the speakers. If so, then just go ahead and enjoy. I have an 800 watt amp that I use at 800-watts to drive either of two speaker cabs - either my DNS-210 cab (handles 700-watts rms) or my DNS-410 cab (handles 1400-watt rms).

I can drive either of these cabs to ear-splitting levels without ever turning the master on my 800-watt amp up to 11:00 o'clock. I can run the 410 up to a max of 10 o'clock without being told to turn down at outdoor festivals - 10:30 is too loud. I ran my 210 at 10 o'clock indoors for a not quite large room and made the mistake of having it up close to ear level. Ended up having to move my cab both over and up closer to the front of the stage to get me out of the 60° dispersion cone of the speakers. That level was perfect for the room, but was killing my ears - literally was painful for my ears.

Your Genzler 350 amp will put out a max of 175-watts to each cab though, so you do need to be aware that is more than your S2012 can handle. So if you start playing at higher levels, you need to listen closely to that cab for any farting sounds. Your 2x8 cab will probably be stacked on top of it, closer to your ears, so be aware that may hide any problems with your 212 cab.

 

In a perfect mix of cabs, the absolute theoretical best you can obtain is +3dB due to more cone area, add another 2~3dB if you are running a SS head and going from 8 to 4 ohms. And you get another 2~3dB boost at sub 500Hz frequencies due to coupling of those low frequencies.

That’s a theoretical max if using matched cabs.

Anything other than matched cabs will result in minimal gains using the more sensitive cab as the benchmark.

 

You have doubled up on the coupling effect from doubling cones. 3dB for coupling up twice as many cones. 2 or 3dB from extra power available. That is all.