Question about speaker effinciency.

[BassNGuns]

Hi, I may be acquiring a Hartke 350w @ 4 ohm head and wanted to add a 4x10 cab to it.
I was thinking of going with an Avatar speaker cab rated at 4 ohms to get the full 350 out of the head, but the Avatar is also rated at 1000w.
There is also a 2-12 version I could get and that would be only rated at 500w.
Which would be more efficient and louder?
Also, is going down to 4 ohms instead of 8 going to give me more headroom?

[Steve Conner]

To answer the question you need to get the sensitivity rating of the cab from Avatar. This is in dB SPL per watt. The higher the figure, the more noise the cabinet makes out of each watt of power fed to it.

You also need to know if the 2-12 cab is 8 ohms or 4: if it's 8 then the amp won't be able to feed the full 350W to it, putting it at a disadvantage in loudness terms. (In other words, yes, all other things being equal a 4 ohm load gives you more headroom.)

You can only connect one 4 ohm cab to your amp, bad news if you want to add another one later.

I suspect the 4x10 will be louder, but the 2x12 might have more of a midrange growl if you like that kind of tone.

[mac1amps]

One factor to consider.....I've noticed in recent years, when you're using a lower impedance speaker cabinet, be aware that the speakers will be drawing more power to them. I've seen a number of cases where [for instance] a user will change an amp's speaker to a lower impedance, with the intention of getting more power out of the amp, but it resulted in prematurely waring out the speaker because it was getting driven harder than it should......IMO, the 4x10 is your best bet.....also remember that even when you're operating the amp @8 Ohms, the lower output power of the amp doesn't make as much difference as most people think it will.

[Wilder Amplification]

One factor to consider.....I've noticed in recent years, when you're using a lower impedance speaker cabinet, be aware that the speakers will be drawing more power to them.

This is incorrect as it applies to transformer coupled valve amplifiers (or any transformer coupled amplifier for that matter). The output transformer secondary taps keep the power the same regardless of load. However, a 4 ohm cab will draw more CURRENT to dissipate the same power as a 16 ohm cab.

Now...sure if you put a 4 ohm cab on a 16 ohm tap, it will dissipate more power as there is double the voltage available at the 16 ohm tap as compared to the 4 ohm tap. But this will cause the valves to red plate at higher output levels as the reflected impedance of the OT will be too low for the B+ voltage and the valve's rated plate dissipation.

However, if you're putting a 4 ohm cab on a 4 ohm tap the power dissipated will be equal to that of a 16 ohm cab on a 16 ohm tap, but @ 2x the current and 1/2 the voltage.

[Steve Conner]

That's all well and good Jon, but this thread pertains to a solid-state bass amp, which has no output transformer, and delivers more power to a 4 ohm load than an 8 ohm one.

Peavey have a patent on a SS amp with an impedance selector switch that changes taps on the POWER transformer. These adjust the rail voltage to give the same power into 16, 8 or 4 ohms. I wish I thought of that one myself.

[g1]

They have a patent on that? I remember an old Traynor SS power amp (PS600 ?) that had an impedance switch which I believe did the same thing, I think it was from the 80's.
Also recall a more recent Yorkville SS amp that actually put out more power at higher than min. impedance. Only time I ever saw that. I think it was rated down to 4R but put out more power at 8R (or could have been 2 & 4 ohm loads).

[Chuck H]

The only info I would add is that if you do want to run two cabinets, say, one 4x10 and one 2x12, and IF you have two parallel outputs, both cabs should be rated at 8 ohms to create a 4 ohm load on the amp. Also... As suggested you will need to learn the efficiency of the proposed cabinet from the MFG. So FWIW a 3dB efficiency increase in the speaker system will provide the same headroom increase as doubling your watts. To sum up, the most efficient (and therefore most headroom) way to run your amp would be into a high efficiency 4 ohm load of whatever arrangement, one efficient 2x12 @ 4 ohms, one efficient 4x10 @ 4 ohms or two efficient 8 ohm cabinets in paralle (for a total load of 4 ohms). The points are that the amp is most efficient at 4 ohms and an efficient speaker offers great advantage in headroom.

[J M Fahey]

These adjust the rail voltage to give the same power into ...

GOSH !!! Are they using MY idea
I think I'll have to use *two* tinfoil hats now, and not take them off even when washing my head or having my hair cut
Well, anyway Mesa will get a patent on that too.

[ThermionicScott]

Is your tinfoil hat properly grounded? It might be acting as an antenna, broadcasting your secrets to the world!!

[J M Fahey]

Dear thermionicscott.
I've stopped worrying about my tinfoil hats .
Yes, you were right, they were not properly grounded, I only used a couple .047x400V paper-in-oil death caps ... but now my problem is other:
Now I'm starting to fear *you*, after seeing your avatar.
Are you sure you are not some High Priest for (whisper) Cthulhu?



Just in case:
"Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn"
Yours, HPL (sometimes also AKA JMF)











Just in case somebody does not know what I'm whispering about, compare TS's avatar with:

[ThermionicScott]

LOL, once you've been driven mad by Cthulhu, you don't have much choice in the matter.

The avatar is a reworking of a panel from the The Misadventures of Hello Cthulhu series.

- Scott