situation with my 2X10

[eartha5]

hi folks,

hoping some people can chime in with thoughts on this:

i have a 4 ohm Goliath Jr II. the thing supposedly handled 250W stock, and i have been running my Ampeg head into the cabinet for a long time. my head delivers 350W at 4 ohms, so if i pushed it the speaker would start distorting some with the re-coned stock speakers that were in it.

so i ordered a pair of SWR's latest 2X10 drivers (Eminence 200W 8 ohm)--the same ones they're putting in the latest Goliath cab, which is rated at 400W (obviously).

i figured i'd be all set as my 350W head could never crap out a 400W cabinet, right? i drive my 450W-handling SWR 8X8 cabinet all the time at max volume with this head and never get a single dirty note...

but i took this 2X10 out to two gigs now and had to back off the <80Hz and sculpt the EQ toward a ~125Hz bias to keep from getting distortion on lower than F or G on my 5 string at high volume. and if i turn the head up to 10, i get distortion and what sounds like intermittent clipping through this cabinet, even though the limiter is active and obviously working. again, everything always sounds great through my 8x8 with same settings.

as far as i can tell this cabinet is behaving exactly the same with the 400W of speakers in it as it did when it was 250W.

can anyone think of what could be happening here? i've read a bit recently on power mis-match, poor cabling, etc, and i don't see how any of that could come into play here.

i contacted the guy at Fender (can't get anyone at SWR any more since Fender bought them) who helped me order the drivers, and he just said "you must be over-powering the cabinet" and sorry we can't do tech support.

my crazy guess is that maybe the ampeg is rated at 350W output for flat signal, and pumping the EQ toward serious bass is making the amp put out >400W output. but this seems ridiculous. what kind of manufacturer would us a lower number for their output specification than what you can really get from their head?

i'm totally puzzled by this. i don't see how there could be such a giant difference between this supposedly 400W cab and my 450W cab, and how the behavior of this 400W cab is the same, basically as it was at 250W...

another weird thing is i played a gig through someone else's SWR combo recently and it was definitely putting way more clean volume through it's exact same 2 10-in drivers, than i'm able to get with my rig.

any thoughts are greatly appreciated...

[billfitzmaurice]

Originally Posted by eartha5

as far as i can tell this cabinet is behaving exactly the same with the 400W of speakers in it as it did when it was 250W.

can anyone think of what could be happening here?

The driver/cab thermal rating and how much power they can actually use before farting out are not related. Most drivers can't take even half their thermal rating before reaching their excursion limit. Where low end output is concerned Pe (thermal power) is virtually meaningless; Sd (displacement) is what counts.

[JimmyM]

Originally Posted by eartha5

my crazy guess is that maybe the ampeg is rated at 350W output for flat signal, and pumping the EQ toward serious bass is making the amp put out >400W output. but this seems ridiculous. what kind of manufacturer would us a lower number for their output specification than what you can really get from their head?

all of them. the rms wattage of a head is what you can get out of it clean. once the signal starts to dirty up, you're getting into what's called "peak wattage," which can be over twice as much as the rms wattage. adding serious bass eq can not only pump you easily into peak wattage, but you could never even know you're into it because you can't hear dirt in the low end nearly as well as you can the mids and highs.

this and what bill said is why if you're going to push your cabs beyond what they can do, you're way better off adding another cab or getting a big one than replacing speakers in your existing small cab. small cabs are always going to be small cabs and no speaker change is going to make them behave or sound like big cabs.

[eartha5]

thanks for the response, bill.

so how then does anyone ever determine if an amp/head combo is going to fart out or not, if you can't just compare the only readily available spec ("wattage")?

why would SWR advertise this cab as 400W if you plug a 400W head into it and it will fart out on you before it can handle the output? could this be the reason they used to rate these things at lower wattage (before Fender bought them)?

i used to have an SVT combo with 2 10's in it. the drivers handled 200W and the head put out 200W and even at straight up full, full volume the speakers would never distort. you can't just extrapolate that experience to all amps?

if you don't feel like fielding my billion questions, could you by chance suggest a tutorial anywhere that explains how Pe and Sd relate to driver design?

many thanks...

[eartha5]

so jimmyM, i understand that you have to add more speakers and get more displacement of air in order to get more "volume", but i assumed that i could get rid of the distortion in my cabinet by upping it's RMS rating. shouldn't upping the RMS rating up the peak handling capacity, too?

[JimmyM]

Originally Posted by eartha5

so jimmyM, i understand that you have to add more speakers and get more displacement of air in order to get more "volume", but i assumed that i could get rid of the distortion in my cabinet by upping it's RMS rating. shouldn't upping the RMS rating up the peak handling capacity, too?

you're assuming that changing the speakers will up the power handling just because the new speakers have a higher rms rating. in many cases, if the box isn't built and tuned correctly for the new speakers, they can fart out way before the old speakers with less power handling did. you're lucky you didn't get worse performance, actually.

now the reason the swr speakers are rated for 400w instead of 200 or 250w? 400w looks more impressive to someone buying a cab, especially bass players who don't know anything about speaker science. and technically, since that's the wattage that the voice coils burn out at, they're not totally lying, although i think it definitely is lying.

now why was the ampeg more in line with what they quote in their sales literature? simple...ampeg is one of the very few companies out there that doesn't lie. their power handling ratings are much more in line with where their cabs start to fart rather than where the voice coils burn out.

[christw]

Originally Posted by JimmyM

you're assuming that changing the speakers will up the power handling just because the new speakers have a higher rms rating. in many cases, if the box isn't built and tuned correctly for the new speakers, they can fart out way before the old speakers with less power handling did. you're lucky you didn't get worse performance, actually.

My first thought. Speakers aren't meant to go in just any box and perform just right.

[eartha5]

thanks for the responses guys. this all makes sense. the reason i didn't think i'd get any issues is that it seemed to me all the goliath jr versions are built the same. i guess that's a stupid thing to assume, though, since i can't see the interior of all goliath versions to see what length the port tubes are and baffles, etc, inside the things.

anyway, the cabinet sounds great short of farting level, so i guess i'll just chalk it up to peaks pushing the drivers beyond their limits in the context of the cabinet. they look like they are maxing out when pushed (the cones look to be travelling their full capacity), so i guess that's that...

i should have just put my $300 towards something else and reserved this cabinet for smaller gigs.

[JimmyM]

hey, we all waste money on stuff that doesn't work. i've probably got a couple grand in stuff that didn't work