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15" Bass Speaker Recommendation

S

stingray_666

Mar 6, 2008
29
0
Massachusettes
www.myspace.com
#1
So it seems the cab I just bought has different speakers than the tag (not to mention it blew out the tubes of my V4) I got a Marshall 2x15 cab that was supposed to have 250w celestions at 8ohms. I turned on my V4 and after a few it went HUUMMMMM crapout!!! So I opened up the cab and found (2) JBL D130F @ 8ohms each making it a 4 ohm load... I'm selling those speakers and will look for a suitable replacement....any recommendations would be appreciated.
Bill
 
#2
your saying that plugging into a 4 ohm load instead of 8 blew your tubes? halving the load can be a bit harder on tubes, but its not a big problem. are you sure that the speakers were correctly connected to the input jack on the cab and you had a working lead connecting the 2? try testing the cab with a multimeter. it should read about 3 ohms dc resistance if it is a 4 ohm cab.

and for speaker reccomendations, how is the cab configured? is is ported or sealed? whats the internal volume? if ported, whats the tuning (or just measure the ports so someone can figure it out).
 
#4
stingray_666 said:
My amp tech told me that running the amp at 8ohms with a 4 ohm load can cause a power problem in one or more than one of the tubes. The cab is a marshall 2x15 with a 6 inch port between the 2 speakers. The speakers are wired in series and set diagonal.
Click to expand...
As I recall the original V4B was a 4 ohm cab. Tube amps can have problems handling higher impedance loads, but are seldom affected by lower impedance loads. OTOH if the drivers are 8 ohm series wired that would be a 16 ohm load and could be a problem.
 
#5
billfitzmaurice said:
Tube amps can have problems handling higher impedance loads, but are seldom affected by lower impedance loads.
Click to expand...

Bill, this is different from my experience with transformer-coupled home audio tube amps, wherein a higher-than-designed-for impedance load is usually more benign than a lower (voltage limiting vs current limiting). I'm not disputing you, just interested in knowing the reason(s). Perhaps it's as simple as, in a tube bass amp, the output transformers are wound with the expectation of a four-ohm load?
 
#6
DukeLeJeune said:
Perhaps it's as simple as, in a tube bass amp, the output transformers are wound with the expectation of a four-ohm load?
Click to expand...
Could be. It's a pretty safe bet that if an amp's got jacks to plug in more than one speaker that it will happen. I remember running Fenders with even 1 ohm loads with never a complaint back in the day. Said Fenders were wired with a closed circuit output jack that shorted the transformer secondary when there's no speaker plugged in, as a no-load can toast it. I've also seen guys run into problems running with the 'correct' load with very low Qts drivers that have higher impedance peaks than cabs with high Qts drivers.
 
#8
stingray_666 said:
My mistake, the speakers were wired in parallel. I had my amp set to 8 ohms and the load was 4 ohms.
Click to expand...
That still shouldn't have bothered it. Assuming this is a sealed cab it's impedance will look similar to this chart of a Fridge:

SVT8x10impedance.jpg


Impedance is not a static figure, it varies with frequency. SS amps don't work well when the lowest value drops below their rated minimum, while tube amps are the opposite, not working well when the peak impedance value is higher than the output transformer is designed for. You might have problems running a 16 ohm nominal load on a 4 ohm tap, but running a 4 ohm nominal load on an 8 ohm tap shouldn't be problematic.
 
#10
stingray_666 said:
So it seems the cab I just bought has different speakers than the tag (not to mention it blew out the tubes of my V4) I got a Marshall 2x15 cab that was supposed to have 250w celestions at 8ohms. I turned on my V4 and after a few it went HUUMMMMM crapout!!! So I opened up the cab and found (2) JBL D130F @ 8ohms each making it a 4 ohm load... I'm selling those speakers and will look for a suitable replacement....any recommendations would be appreciated.
Bill
Click to expand...

Did you get any sound from the cab before the mishap?
 
#11
This sounds a bit fishy to me. I have to think it is a coincidence. I've had a V4B and now a V4 and have run them with various speakers that have not always been matched to the output impedance and have had no problems (by the way I used to use my V4B with a 2x15 cabinet with JBL K140s). As BillF posted, speaker impedance isn't constant anyway so unless there is a gross mismatch and you're pushing the amp to it's limits there shouldn't be a problem.

Sounds like something was about to go in your amp and it happened to pick the time that you used this speaker. Is your amp hosed right now?
 
#14
As I recall, the D130 was more of a guitar speaker than a bass one. However you now have to start the exercise of finding what speaker will actually work in your cabinet. Measure the cabinets internal dimensions and the porting and try to match them up with a suitable driver. WinISD is your friend here.

Paul
 

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