Another "Help Me Understand Amp/Cab Pairings, Ohms, etc" Thread

[Obese Chess]

Don’t crank it up beyond what the speaker can SAFELY handle.

Would I be correct in assuming that there's no way for a layman to objectively measure what the speakers can safely handle, just "use your ears and turn it down if it's distorting?"

 

[agedhorse]

Would I be correct in assuming that there's no way for a layman to objectively measure what the speakers can safely handle, just "use your ears and turn it down if it's distorting?"

Many players can’t hear when a cabinet is in danger, and sometimes it’s just not possible.

 

[Hoochie Coochie Man]

I bet some players could blow a cabinet rated for 1200 Wrms with an amplifier rated to produce 1200 Wrms output power.

 

[agedhorse]

I bet some players could blow a cabinet rated for 1200 Wrms with an amplifier rated to produce 1200 Wrms output power.

Indeed they can.

 

[Obese Chess]

Okay, so I guess I'm stumped now and I'm confident this is just an issue where you're all leading me to water I haven't figured out how to drink, so tp speak. If I am careful, use good judgment, and don't crank it up beyond what the speaker can safely handle, I'll be fine, but there's no way for me to know if and when I'm cranking it up beyond what the speaker can handle?

 

[agedhorse]

Okay, so I guess I'm stumped now and I'm confident this is just an issue where you're all leading me to water I haven't figured out how to drink, so tp speak. If I am careful, use good judgment, and don't crank it up beyond what the speaker can safely handle, I'll be fine, but there's no way for me to know if and when I'm cranking it up beyond what the speaker can handle?

This is where having reasonable expectations comes into play.

The other way is to crank it until the speaker fails, then back it off a bit...

 

[D to the C]

The other thing you need to be aware of, is some speaker mfg use RMS ratings, which is the mean or average, while others use peak! So you really do need to use common sense. If you are playing loud enough to shake the room think of how much that speaker is moving, or the distance it is traveling in its frame (excursion). This generates heat, It’s only going to bang against its frame for so long before failure. You and your judgement are the best defense against speaker damage!

 

[Stylee Mousse]

How about a mesa subway 410, rated at 1200 watts.

Is there a scenario where that isn’t loud enough?

 

[Pontiac Thrasher]

This is where having reasonable expectations comes into play.

The other way is to crank it until the speaker fails, then back it off a bit...

Or, the scenario that led me to seek knowledge from agedhorse and others here, cranking it up till it sounds really cool while watching the E140-8 JBL drivers trying to jump out of the cabs, backing off, and then building up my system to meet the demands at that time.

How about a mesa subway 410, rated at 1200 watts.

Is there a scenario where that isn’t loud enough?

Loud was not the only issue for me a couple of years ago, since I was the bass player, and I was up against 16 twelve inch guitar drivers (two good quality tube driven full stacks, one a Marshall fed lead from a Les Paul, one an Orange fed rhythm from an SG.)

So would the SW410 have been heard, sure, but an fair match to support those 16 twelves?

I buried the lower frequencies of those two stacks with two JBL 15's, plus two JBL 18's, and it was not so much the power as the quality combined with cone size, I tried 300 watts at 2ohms after one of the two amps that day blew, and we made it thru rehearsal like that, but they turned down a little. Threw around 1400 watts at it the next week, that was stunning. Nobody wanted to get any louder after that. Tried the Mesa Subway D800+ several weeks later cranked 800 watts at 2 ohms, and it was great too, and sounded the best.

: )

 

[beans-on-toast]

in terms of wattage capacity, some cabs are rated more conservatively than others. So when comparing, the numbers are not the only guide. Always use your ears as well. Your best bet is to use a cab and amp from the same company where that has been matched to work well together. Otherwise, a cab’s RMS rating that twice that of the amp’s RMS output is considered very conservative and safe. Matching the amp’s RMS rating with an equal cabinet rating has to be done with care. It depends on both the amp and the cab’s design. Certain playing, hard continuous or popping, can push the amp beyond it’s RMS rating.

 

[Jim Bergantino]

I think many are missing the point about power concerns and damaging speakers. As many of you probably know we just introduced a new 2000 watt @ 4 ohm amp. And I will recommend this over any <300 watt amp for the best bedroom experience. Just like I would enjoy driving an 8 cylinder vehicle in the city as much as driving it on the highway over any 4 or 6 cylinder vehicle. It’s about how it responds. It’s that simple. It’s not about the ability to go faster or play louder, it’s about how it responds dynamically at lower speeds or lower volumes. You’re only going to blow up your speakers if you're a complete $@*%^! ;-)

 

[agedhorse]

Unfortunately, a lot of players damage speakers Jim.

Sometimes it’s an accident (partially unplugged cord, pedal board issue, etc.), sometimes it’s due to unrealistic expectations, sometimes it’s because of poor judgement.

There’s a lot less safety margin when the amp grows beyond the safe mechanical power handling of the speaker (which is usually less than the often specified thermal power handling).

 

[Jim Bergantino]

Unfortunately, a lot of players damage speakers Jim.

Sometimes it’s an accident (partially unplugged cord, pedal board issue, etc.), sometimes it’s due to unrealistic expectations, sometimes it’s because of poor judgement.

There’s a lot less safety margin when the amp grows beyond the safe mechanical power handling of the speaker (which is usually less than the often specified thermal power handling).

While I agree with your point Andy, I also believe it’s far easier to mechanically damage a speaker with too little power than with more power. The reason being as you drive the amp into its power rails, its ability to control the woofers movement is compromised, and it’s this inability to retain control over the woofers motor that, IMO, leads to far more speaker failures than having “too much” power.
And given todays size and weight of Class D amps and $/watt value, I also feel it’s inexcusable for any serious bass player to go to a gig under powered. It’s a disservice to yourself and your band. This is all IMO of course but it’s how I feel about this subject. I’m all about headroom. Your rig will always sound better and last longer without issues when it’s not run into, or close to, its limits.

 

[agedhorse]

That’s not been my experience, sure the output impedance increases a little as the amp goes into clipping, but the open loop output impedance is still very low, especially with class D amps.

The low impedance contributes to the damping, lower is “better” but on a class D amp the difference isn’t that much.

 

[Jim Bergantino]

That’s not been my experience, sure the output impedance increases a little as the amp goes into clipping, but the open loop output impedance is still very low, especially with class D amps.

The low impedance contributes to the damping, lower is “better” but on a class D amp the difference isn’t that much.

Appreciate the insight Andy. I'm not sure we're talking about damping here, but I'm not absolutely sure to be honest. Given you allow user adjustment on your WD800 design, I'm sure you wouldn't do so at the risk of potentially causing harm to the speakers, or if your implementation of the design itself effects the actual damping of the Class D module. The incidents I recall involved moderately powered Class A/B bass heads. Anyway, my main point in all this is the importance of headroom. I believe it adds a whole other level of playing enjoyment and experience where you don't have to play to the shortcomings of your rig, but just enjoy serving the music! ;-}

 

[agedhorse]

Our old Walkabout and Carbine power amps had no global NFB which increased output impedance and reduced damping factor. This results in a little looser feel, but even open loop the output impedance is low relative to the speaker (especially at resonance).

With greater power comes a need for more responsibility.

 

[Obese Chess]

Ahhh, that's the conversation I wanted to read. Really interesting stuff. Unfortunately to Jim's point, I have been described by many as "a complete $@*%^!" but the principle makes sense. It seems to me that the implication is that the amps themselves are rated for, say, 800W RMS at 4 ohms, but there's no serious, major risk of physically damaging the speakers themselves - which may physically and mechanically be able to handle more than that - unless I crank the volume or do something else reckless, though it is still a real possibility.

There's a few different ways I can get the tone I'm looking for - volume isn't really the concern, I'd likely be more interested in that that Peavey if it were 600W - without having to tetris the trunk of my car at every gig and this gives me a lot to chew on. Thanks y'all.