Matching amp power to cabs

[Kro]

I actually haven't seen it brought up in any threads I've perused recently, but given the direction that this thread has gone in (discussing the benefits of more speakers vs. more watts), the old rule of thumb still holds true that without also increasing power, simply doubling the same cab (adding another 4x10 to the existing, as noted in post #6) would net roughly +3dB increase from coupling, right?

And then doubling both the cab, and watts, would provide a +6dB increase.

Now, I repeat these from memory as having been learned probably here - maybe reinforced from a few outside sources, but along with those, if not mistaken, I've long understood that a +3dB increase is something like the smallest volume difference that is able to be perceived by most people.

I know that the "more cabs" argument is usually correct in this day in age of cheap watts, but I can't help but personally feel that things might be getting a bit carried away. I know that many hear have alluded to how complex these things are, so I'm not trying to make any blanket statements - especially about people participating in this thread. Just an observation.

Again, I note this just as general concepts that I've understood to be correct as they apply to some of the questions and responses of this thread. I only bring these points up to maybe be corrected where I'm off, and to learn from the discussion of those much smarter than I am.

 

[chris_b]

I have got an Ashdown ABM 600 amp min impedance 4 ohms. Matching this I have an Ashdown ABM 115 (1x15) 300w @ 8 ohms and an Ashdown ABM 410 600w @ 8ohms.

So to get the full 600 watts out of the ABM 600 I know I will need to plug both speakers in to reduce impedance to 4ohms. But after doing this how many watts would go to each speaker respectively? My concern is that 600w to the ABM 115 would damage it as it can only handle 300w.

I'm only a novice at this so I can only do simple explanations.

Are you seriously going to run your 600 watt amp flat out? I'm hard pressed to run my 500 watt amp at half volume and that's incredibly loud.

Anyway, a 600 watt amp into 2 8 ohm cabs could put a potential 300 watts into each cab. Looks like that is OK with the specs of your gear. I would suggest you're really going to put closer to 150 watts into each cab and maybe less, so they will be fine.

 

[Al Kraft]

I actually haven't seen it brought up in any threads I've perused recently, but given the direction that this thread has gone in (discussing the benefits of more speakers vs. more watts), the old rule of thumb still holds true that without also increasing power, simply doubling the same cab (adding another 4x10 to the existing, as noted in post #6) would net roughly +3dB increase from coupling, right?

And then doubling both the cab, and watts, would provide a +6dB increase.

Now, I repeat these from memory as having been learned probably here - maybe reinforced from a few outside sources, but along with those, if not mistaken, I've long understood that a +3dB increase is something like the smallest volume difference that is able to be perceived by most people.

I know that the "more cabs" argument is usually correct in this day in age of cheap watts, but I can't help but personally feel that things might be getting a bit carried away. I know that many hear have alluded to how complex these things are, so I'm not trying to make any blanket statements - especially about people participating in this thread. Just an observation.

Again, I note this just as general concepts that I've understood to be correct as they apply to some of the questions and responses of this thread. I only bring these points up to maybe be corrected where I'm off, and to learn from the discussion of those much smarter than I am.

First off, I make no claim to be smarter than anyone, and it doesn't take long after you get to know me to see how I came to that conclusion. In general, I think you'll find that adding a second IDENTICAL cab in parallel (assuming the amp can operate safely at the lower impedance) will give you approximately a 6dB increase in SPL. This is significant enough to be noticeable and quite useful.

Here is a Bill Fitzmaurice quote that explains how/why it happens: When drivers/speakers are doubled, parallel wired and placed less than 1/4 wavelength apart, mutual coupling gives you 3dB, while the halved impedance load gives another 3dB. Total gain: 6dB

 

[Kro]

First off, I make no claim to be smarter than anyone, and it doesn't take long after you get to know me to see how I came to that conclusion. In general, I think you'll find that adding a second IDENTICAL cab in parallel (assuming the amp can operate safely at the lower impedance) will give you approximately a 6dB increase in SPL. This is significant enough to be noticeable and quite useful.

Here is a Bill Fitzmaurice quote that explains how/why it happens: When drivers/speakers are doubled, parallel wired and placed less than 1/4 wavelength apart, mutual coupling gives you 3dB, while the halved impedance load gives another 3dB. Total gain: 6dB

That seems about right, so going back to the OP - right now he's running a 600w @ 4ohm rated head. It's probably putting out maybe 350w? at @ 8ohm into that single 8 ohm 410. If OP adds another 410, he gets the +3dB from the amp putting out its full 600w (nearly, but not quite double the 8ohm watts), and +3dB for coupling for a total of about a +6dB increase. Did I get that right, or is there something else at play that I'm missing?

Oh Bill - I find myself referencing his old posts all the time. Thankfully we have an awesome current crop of experts that are just as knowledgeable, but even though some found his style off-putting I always enjoyed his posts.

 

[Kro]

Apologies for the double post, but I didn't want to just edit this in - following that same logic (unless I'm wrong!), if you were starting with a 4ohm 410 with any given power source - if you were to swap it with a pair of cabs that were magically functionally identical as that 4ohm 410, with the exception of each being 8ohm, and run it with the same power, you'd only realize a +3dB increase?

Edit, I goofed - I was just trying to think of a scenario where the impedance was halved and failed pretty miserably - from a few different angles actually. Grr. It's still early in the morning, so I might still be wrong, but I guess all I had to say was that going from an 8ohm 410 to a 4ohm 410 should have provided that halved impedance ~3dB increase.

At least I think my post above it is still correct - we'll see if it passes the "finished cup of coffee test".

 

[Al Kraft]

Apologies for the double post, but I didn't want to just edit this in - following that same logic (unless I'm wrong!), if you were starting with a 4ohm 410 with any given power source - if you were to swap it with a pair of cabs that were magically functionally identical as that 4ohm 410, with the exception of each being 8ohm, and run it with the same power, you'd only realize a +3dB increase?

Actually I don't think that would be the case if all the speakers/cabs were of the same efficiency. When we talk about adding another identical cab, it's the additional drivers producing sound that make the first 3 dB and the additional power one can pull from the amp to drive speakers that gets you the second 3 dB. Theoretically if I were making identically scaled speaker cabinets, my 410 should be 3dB more efficient than my 210. Put another way, if my 210 was 8 Ohms and my 410 was 4 Ohms, by the time you add another 210 to the first one the pair should be virtually identical to the single 410 4 Ohm cab efficiency/SPL-wise.

 

[StatesideRambler]

Once again we have a thread demonstrating ample knowledge of arithmetic but limited-to-no understanding of AC networks nor the effects of frequency in said networks.

 

[Gizmot]

As long as you use good judgement, you'll be okay. Listen as you play and don't push it too hard.

Combing speakers is something you'll have to figure out for yourself. I've heard some combinations sound good, others not so much

 

[Al Kraft]

Once again we have a thread demonstrating ample knowledge of arithmetic but limited-to-no understanding of AC networks nor the effects of frequency in said networks.

Are you referring to the fact that the more significant coupling effect will occur in the lower and mid frequencies and somewhat less to not at all in the higher frequencies and/or that the 3 dB number is a nominal maximum value not always achieved in the real world due to other factors not considered in this simplified discussion? I'm not sure I understand your comment but, respectfully, it seems you have something important to add that we've missed.

 

[Kro]

Actually I don't think that would be the case if all the speakers/cabs were of the same efficiency. When we talk about adding another identical cab, it's the additional drivers producing sound that make the first 3 dB and the additional power one can pull from the amp to drive speakers that gets you the second 3 dB. Theoretically if I were making identically scaled speaker cabinets, my 410 should be 3dB more efficient than my 210. Put another way, if my 210 was 8 Ohms and my 410 was 4 Ohms, by the time you add another 210 to the first one the pair should be virtually identical to the single 410 4 Ohm cab efficiency/SPL-wise.

I think that matches up with what I was saying, or was trying to say... Edit: NOPE! I royally screwed up my example by adding double the speaker, and butchering the impedance. I added a corrective edit in that same post above... All I was trying to do was create a scenario where only the 3dB increase from halved impedance was realized and failed almost impressively (from the standpoint of me looking back on it in hindsight).

Thanks Al for bearing with me and being so patient when trying to correct me. Ha!

 

[Kro]

Once again we have a thread demonstrating ample knowledge of arithmetic but limited-to-no understanding of AC networks nor the effects of frequency in said networks.

In all seriousness, then instead of just calling it out and sitting back, clue me in. I stated in my earlier post that I was just noting some of the rules of thumb that I've heard primarily here as they may apply to this thread, and was eager to be corrected.

I'm not carrying this discussion from the standpoint from an expert, but from that of a student.

 

[Al Kraft]

In all seriousness, then instead of just calling it out and sitting back, clue me in. I stated in my earlier post that I was just noting some of the rules of thumb that I've heard primarily here as they may apply to this thread, and was eager to be corrected.

I'm not carrying this discussion from the standpoint from an expert, but from that of a student.

+1...I'm always eager to learn.

 

[Kro]

So even if I had 2 410 cabs at 600w, the volume would be no louder. As each would take 300w from the amp

So I wanted to revisit this comment from the OP in light of some of the more recent discussion that's taken place in this thread - discussion that may be too technical for some, and much to general for others.

If you were to add another matching 8ohm 410 to your rig, you'd apparently get roughly close to a 6dB increase - which as far as I can tell from googling, would potentially lead to a nearly 50% increase in perceived loudness (Invalid Link Removed).

 

[jw23mind]

Great discussion. I just thought it worth pointing out that this all applies to SS amps which increase power output with increased (lower ohms) loading, and not tube amps. In the case of a tube amp, by this logic there would only be the +3dB from mutual acoustic coupling.

 

[Ric5]

you can run a 100 watt amp into a cab rated 600 watts ... no problem

if you run a 600 watt amp into a cab rated 100 watts then you can easily blow a speaker if you turn up the volume

 

[MDBass]

So even if I had 2 410 cabs at 600w, the volume would be no louder. As each would take 300w from the amp

Incorrect.

Watts tell you very little about how loud a rig will be, the cabs involved are much more important: a 100 watt amp through eight 10's will be MUCH louder than a 1000 watt amp through a single 10.

 

[Kro]

Incorrect.

Watts tell you very little about how loud a rig will be, the cabs involved are much more important: a 100 watt amp through eight 10's will be MUCH louder than a 1000 watt amp through a single 10.

I dunno, the sound of that single 10 cab exploding might be pretty loud...

 

[TDokland]

Keep in mind that impedance is frequency dependent so the exact power distribution will depend on each speaker's frequency characteristic. It won't necessarily be 50/50.

 

[dbsfgyd1]

I have got an Ashdown ABM 600 amp min impedance 4 ohms. Matching this I have an Ashdown ABM 115 (1x15) 300w @ 8 ohms and an Ashdown ABM 410 600w @ 8ohms.

So to get the full 600 watts out of the ABM 600 I know I will need to plug both speakers in to reduce impedance to 4ohms. But after doing this how many watts would go to each speaker respectively? My concern is that 600w to the ABM 115 would damage it as it can only handle 300w.

I'm only a novice at this so I can only do simple explanations.

Each cabinet will get 300 watts. The 410 will produce higher decibel levels, or sounds louder than the 1-15 cab, as there is more speaker area.

 

[dbsfgyd1]

I dunno, the sound of that single 10 cab exploding might be pretty loud...

I think he was making a point that Increasing speaker surface area is a better option than increasing wattage if you want to be louder.