Barefaced 2 Cabs vs 1volume question

[Bill Fitzmaurice]

Using identical 8 ohm drivers the 2x10 is 4 ohms and the 4x10 is 8 ohms. In that case 600w into the 2x10 could be some 6dB louder than 400w into the 4x10. That's because in the 2x10 each driver will be receiving 48 volts, in the 4x10 each driver will be receiving 28 volts. The 4x10 would equal the 2x10 if the drivers were all parallel wired, but that would take a 2 ohm capable amp. But this is academic, due to the displacement limited power handling of the drivers. Very few tens can take 300w, and those which can tend to be PA subs. Electric bass tens tend to be displacement limited to 100 watts, in which case you wouldn't be able to put 600w into the 2x10, and by dint of that the 4x10 would go louder.

[alexa3020]

4 hours ago, Bill Fitzmaurice said:

Electric bass tens tend to be displacement limited to 100 watts, in which case you wouldn't be able to put 600w into the 2x10, and by dint of that the 4x10 would go louder.

Hi Bill, thanks for all your input, it’s been really useful. 
I am trying (but struggling) to understand this. Are you saying there’s no point in having an amp that can push more than 200w to a 2x10 cab, because each driver can’t handle more than 100w each?

if that’s the case, why are these cabs rated as much higher wattage (barefaced 2x10 is rated at 500w or up to 800w if clean).

I know it will be louder with 2x 210s, but ultimately I’m trying to understand if it’s worth me spending another £600 on a cab, if the difference in volume will be marginal.

I would also like to point out that I’m really happy with the 210 & on its own is in most circumstances plenty loud enough. It’s certainly the loudest 210 I’ve ever used.

[Phil Starr]

11 hours ago, Jack said:

Doesn't that '+6dB' logic only hold true if we were talking about 1x 12R cab being doubled to 2x identical 12R cabs though? I think what's being lost in this is that, if only using one cab, we can use the 4R setting to cheat the impedance/power game a little. 

 

I guess the real question is: what's the volume difference between 600W into a 2x10 and ~400W into a 4x10? Which after all that doesn't really change the answer, it's going to be the 4x10.

Hi Jack, you have it right, more or less. the 6dB gain is made up of two parts, there's a 3dB gain due to the halving of the impedance and the amplifier providing double the power (if it can, more later)

The other 3dB is due to the increase in efficiency of converting the cone movement into air movement by doubling the cone area. Which is available simply by adding the extra cab.

The complexity is in the amp. The amp provides a voltage across the speakers which determines the maximum power but providing tht power continuously depends upon the power supply built into the amp. If you move from 16ohms to 8 then the power will almost always double. For most commercial bass amps if you then halve again to 4ohms then the power supply won't be able to provide enough current and the amp won't quite be able to double the power. Typically most current amps will do something like 300W into 8ohms and 500 into 4 so the increase in power by doubling will be more like 2dB than 3dB and the increase in sound nearer 5dB than the theoretical 6dB. A few designed for 2ohm operation will still double at this point but will then run out  of the ability to double the current  going from 4ohms to 2. Power is voltage x current and the power from an amp can be voltage or current limited.

The Barefaced is interesting as it has a crossover inside so the switch from 4ohms to 12 is achieved by changing both the crossover and the wiring of the speakers. Quite slick really. Impedance in any case changes across the frequency spectrum and the ohms quoted are for any speaker are an average.

So to answer @alexa3020 's question.

doubling up the BF 210's will give you extra volume. How much will depend upon the exact design of the amp you are using. You'll gain 3db from the extra speakers but how much power you will lose depends upon whether the amp is current limited or voltage limited at 6ohms. My guess is that it  will be voltage limited and will provide roughly the same power into 6ohms as it will into 4. Overall you'll be 2-3dB louder, but it isn't as simple as this. By adding the extra cab you are going to lift the top speaker to ear level and changing the radiation pattern for the audience. You are also reducing the current and power to each of the 10's and this reduces the amount they heat up and power compression at high levels as well as distortion. There will also be changes in the coupling of the speakers with the floor as this is dependent upon the distance of each driver from the floor.

The important thing is how this sounds. Adding the 2-3dB isn't huge but will be noticeable but I think you will experience a cleaner sounding and more authoritative sound and you'll be able to hear yourself more clearly above the band. Two speakers stacked vertically is a lovely experience for a bassist and if you can afford it then it will probably become your go to setup even at smaller gigs. 

[Beer of the Bass]

I know doubling my speakers at the same amp output (valve amp with multiple taps) makes more difference to the perceived "bigness" of the sound than I had anticipated from written explanations of it. So I'd concur with Phil's post above.

Edited October 28, 2020 by Beer of the Bass

[Bill Fitzmaurice]

4 hours ago, alexa3020 said:

Hi Bill, thanks for all your input, it’s been really useful. 
I am trying (but struggling) to understand this. Are you saying there’s no point in having an amp that can push more than 200w to a 2x10 cab, because each driver can’t handle more than 100w each?

if that’s the case, why are these cabs rated as much higher wattage (barefaced 2x10 is rated at 500w or up to 800w if clean).

One advantage to having more power than the speakers can handle is clean headroom. Another good reason is because amp manufacturers tend to be, shall we say, optimistic in how much continuous power their amps can actually deliver. As for speaker power ratings, all speakers should have two sets of numbers, thermal and mechanical. Those companies that do provide mechanical power ratings are, unfortunately, very rare exceptions. Never forget that truth in advertising is an oxymoron, and always has been. The phrase 'caveat emptor', after all, was coined when Latin was still a living language.

[Phil Starr]

this shows pretty much what Bill is talking about and i happened to have it on screen. I'm designing a speaker for a practice amp and this is a plot of the maximum power handling for a 6" speaker.

The flat line at the top of the graph is where the power handling is limited by the heat in the voice coil (100W in this case) Between 100 and 250Hz the speaker has to move a long way to move the air so the speaker can only handle 20W without distorting. The flat bit at around 90Hz is where the port will be making the sound and the speaker stops moving. Below that the speaker is effectively in free air as the port stops being a barrier and the power handling drops to almost nothing. 

This is a tiny speaker I'm proposing to use with a battery powered amp so it's fine for this job but the general shape of this graph will be the same for most drivers.

Speaker manufacturers quote the thermal limit because it's easily measured and checkable. The rest depends upon the cabinet and frequency so they can't really give a definite figure but the cab designer can work it out. You don't really need to know this to buy a cab except that it is useful to know that sounds below the port frequency can damage speakers if you drive them hard and that driving any speaker to it's thermal limit isn't great.