Opinion poll: another bc208, additional 1x12, or something entirely new

[meisi]

Assuming the cabs are as close as possible, the sensitivity goes up 3dB theoretically. Real world will probably be a bit less. If the usable power increases, you get additional SPL.

Normally when you add a cab, it's connected in parallel with first cab. Assuming both cabs are the same:
1. Combined impedance = 1/2
2. Combined power handling = 2X
3. Combined sensitivity = +3dB

Tube amps put out the same power as long as they see the expected loud. So if you have an 100W tube amp with 4 and 8 ohm outputs, you get 100W with one or two 8 ohms cabs. Since the power stays the same, adding a matching cab gets you +3dB.

Solid state amps typically produce more power as the impedance goes lower. This is not always the case, so check the specs. When the impedance is cut in half, the power may double, increase by something like 70%, or stay the same. In some rare examples, the power may also decrease.

If the power doubles you get another +3dB. So total increase is 3dB from increased sensitivity and 3dB from increased power. 3 + 3 = 6dB total

If the power increases by 70% you get ~+2.3dB. So total increase is 3dB from increased sensitivity and 2.3dB from increased power. 3 + 2.3 = 5.3dB total.

If the power stays the same you only get +3dB from increased sensitivity.

so in my case, bam200 @16ohms vs 4ohms into the exact same 2x8, I'm getting at most a 6dB total change.

my ears agree.

 

[Wasnex]

so in my case, bam200 @16ohms vs 4ohms into the exact same 2x8, I'm getting at most a 6dB total change.

my ears agree.

I think you mean at 8 ohms and 4 ohms. Assuming the amp makes 100W at 8 ohms and 200W at 4 ohms, then adding a matching cab should get you ~ +6dB of headroom. +3dB from increased sensitivity and +3dB from doubling usable power.

 

[meisi]

I think you mean at 8 ohms and 4 ohms. Assuming the amp makes 100W at 8 ohms and 200W at 4 ohms, then adding a matching cab should get you ~ +6dB of headroom. +3dB from increased sensitivity and +3dB from doubling usable power.

mentioned the setup earlier - it's a 2x 8" 8ohm drivers wired so I can do series or parallel for 16 or 4 ohms respectively or for fun I can also do 1x 8" at 8ohms.

So if I were to wire it

2x8 @ 4ohms 0dB
1x8 @ 8ohms -6dB
2x8 @ 16ohms -6dB

No?

As far as loudness goes, it's around what my ears think

 

[Wasnex]

2x8 @ 4ohms 0dB
1x8 @ 8ohms -6dB
2x8 @ 16ohms -6dB

The relative values are correct, assuming the amp produces the same voltage at 4, 8, and 16 ohms.

Given the amp and cabs, what is the benefit of wiring the cabs in series?

The sensitivity of one cab is 93dB 1W/1m. The sensitivity of two cabs will be ~96dB 1W/1m, assuming perfect coupling.

Let's assume the amp holds the voltage constant:
Voltage for 200W at 4 ohms is sq rt(200 x 4) = ~28.28V.

Power at 8 ohms = (28.28 ^ 2)/8 = ~100W
Power at 16 ohms = (28.28 ^ 2)/16 = ~50W

Calculated SPL

2x8 @ 4ohms = 10Log(200) + 96 = ~119dB
1x8 @ 8ohms = 10Log(100) + 93 = ~113dB
2x8 @ 16ohms = 10Log(50) + 96 = ~113dB

At 16 ohms the combined 1W/1m sensitivity of two cabs is still +3dB, but usable power is down -3dB. The tone will be a bit deeper/thicker, but you don't get more SPL.

 

[meisi]

The relative values are correct, assuming the amp produces the same voltage at 4, 8, and 16 ohms.

Given the amp and cabs, what is the benefit of wiring the cabs in series?

The sensitivity of one cab is 93dB 1W/1m. The sensitivity of two cabs will be ~96dB 1W/1m, assuming perfect coupling.

Let's assume the amp holds the voltage constant:
Voltage for 200W at 4 ohms is sq rt(200 x 4) = ~28.28V.

Power at 8 ohms = (28.28 ^ 2)/8 = ~100W
Power at 16 ohms = (28.28 ^ 2)/16 = ~50W

Calculated SPL

2x8 @ 4ohms = 10Log(200) + 96 = ~119dB
1x8 @ 8ohms = 10Log(100) + 93 = ~113dB
2x8 @ 16ohms = 10Log(50) + 96 = ~113dB

At 16 ohms the combined 1W/1m sensitivity of two cabs is still +3dB, but usable power is down -3dB. The tone will be a bit deeper/thicker, but you don't get more SPL.

Deeper/thicker (fuller, fatter, etc) is exactly what my ears hear, too.

More speakers area the better at the same SPL is my takeaway. Not just the air you move but how you move it, I guess.

 

[mrbell321]

The BAM200 is rated at 200watts continuous at 4ohms. Bc200 is rated 200watt continuous but 8 ohms.
So bam200 with 1 bc208 is 100watt .
Adding a second bc208 cuts the total impedance to 4 ohms, so boot the power to 200 watt. But as been pointed out that's all max rating.
And it's also been pointed out the sensitivity of these cabs is rated rather low. That's a trade I'm ok with to keep it he weight down.

Those markbass cabs are quite interesting, tho… much more expensive

 

[mrbell321]

Wow, I need to refresh more… 2 new posts I didn't see in my last response…

 

[Wasnex]

Deeper/thicker (fuller, fatter, etc) is exactly what my ears hear, too.

More speakers area the better at the same SPL is my takeaway. Not just the air you move but how you move it, I guess.

AFAIK the reason for the change in tone is coupling is most effective at lower frequencies. The wavelength gets longer as the frequency goes lower. AFAIK couplings become close to optimum as the center to center spacing approaches 1/4 wavelength.


I generally prefer the tone of a single driver over multiple drivers.

 

[Wasnex]

And it's also been pointed out the sensitivity of these cabs is rated rather low. That's a trade I'm ok with to keep it he weight down.

Those markbass cabs are quite interesting, tho… much more expensive

The Trace Elliot ELF 2x8 should a bit more efficient than the BC208. I believe the ELF 2x8 uses a pair of 16 ohm Faital 8PR200. The sensitivity for this driver is listed as 94dB 1W/1m. So a pair should be 97dB 1W/1m.

I haven't compared these two cabs, so I can't say if the difference is as big as the specs suggest or not. Also, the ELF 2x8 is approximately double the price of the BC208.

 

[mrbell321]

the ELF 2x8 is approximately double the price of the BC208.

Yeah...exactly. The value just isn't there for me on that, I don't think.

 

[Artman]

This is what is needed. This, drum lessons, or both.

 

[Aloe]

tho… much more expensive

well, as always:
* light
* loud
* cheap

pick any two. you won't get three together.

I did some math and believe one 102 energy even in 8 ohms will be louder with your head than two bc208s.
and, uhm, twice lighter.