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Ohms question...stupid salesman

rhythmless

rhythmless

Oct 31, 2007
61
13
#1
Ok here's what I've got..

I was running a Firebass 700 through two 410 TVX 4 ohm cabs. The cabs are rated at 350 watts/600 Program, so everything was cool there. I wanted to add a little more low end to my sound, so I looked into buying a TVX115 and trading in one of the 410's.. Went to the local music shop and found one. I specifically asked if it was a 4 ohm or 8 ohm cabinet. The salesman looked at the spec sheet that came with the cabinet, and it had the specs for both 4 and 8 ohms. Then he tells me it has a built-in crossover and will run at 4 and 8 ohms. I was skeptical and contacted Peavey to ask since my 410's were specifically 4 ohm. They tell me that there's an 8 ohm version and a 4 ohm version. There's the backstory...

Now the question.. I've tried researching this and found half the answer on what the ohms would be if you ran an 8 ohm and 4 ohm cabinet together (2.67 ohms). Is this going to screw something up if I run it like this with a 700 watt/2 ohm amp? It would be great if it won't and I can avoid the hassle of lugging that 80 pound beast back to the store, and then waiting two weeks for them to order the 4 ohm 115, but ultimately beats blowing my rig up. Thanks in advance!
 
#5
IMO a 4x10 + 1x15 combination is not that effective. The 4x10 will always overpower the 15 and often the 15 will fail.

Running a 2.67Ω load on a 2Ω stable amp will work fine. However the 4Ω will get 66% of the output power and the 8Ω load the other 33%. With the 15 being 8Ω this is the only way that the mating will be safe. Don't expect the 15 to go lower than the 4x10. It's highly unlikely to happen this way.

Paul
 
#7
If your amp is fine with a 2 Ohm load, it will be fine with a 2.67 Ohm load. The 4 Ohm cabinet will get two-thirds of the power and the 8 Ohm cabinet will get one-third of the power, which may or may not be desirable for you.
Click to expand...


That actually may be the better option. The Peavey customer service guy warned about overloading the 115. It would be getting 100 watts over the RMS if they were evenly split using two 4 ohm cabs. The 410's are rated at 350 watts RMS and 600 program. The 115 is 250 watts RMS and 500 program. I know there has been some debate regarding underpowering cabs, but 233 watts going to the 115 is close enough to 250 right? ;)
 
#8
The Firebass 700 is specified at:
- 700 W into 2 Ohm (= 18.7 A @ 37.4 V)
- 475 W into 4 Ohm (= 10.9 A @ 43.6 V)
- 275 W into 8 Ohm (= 5.86 A @ 46.9 V)

Since the slope of the VI curve is not constant, one cannot precisely interpolate the available output power at 2.67 Ohm. However, I would guesstimate it at 600 W.
Of which 400 W would be delivered to the 4 Ohm load, and 200 W to the 8 Ohm load.
 
#9
PhiDeck said:
The Firebass 700 is specified at:
- 700 W into 2 Ohm (= 18.7 A @ 37.4 V)
- 475 W into 4 Ohm (= 10.9 A @ 43.6 V)
- 275 W into 8 Ohm (= 5.86 A @ 46.9 V)

Since the slope of the VI curve is not constant, one cannot precisely interpolate the available output power at 2.67 Ohm. However, I would guesstimate it at 600 W.
Of which 400 W would be delivered to the 4 Ohm load, and 200 W to the 8 Ohm load.
Click to expand...

Yup. I'd go with that.

I'd try and get the 4 ohm 115, just for that little extra bit of push. But it won't be a huge difference.

I'd also try comparing the 115+410 to your 410+410 first. IMO you're likely to find the 4x10+4x10 bassier (from some experience with peavey 10s and 15s).
 
#11
PhiDeck said:
The Firebass 700 is specified at:
- 700 W into 2 Ohm (= 18.7 A @ 37.4 V)
- 475 W into 4 Ohm (= 10.9 A @ 43.6 V)
- 275 W into 8 Ohm (= 5.86 A @ 46.9 V)

Since the slope of the VI curve is not constant, one cannot precisely interpolate the available output power at 2.67 Ohm. However, I would guesstimate it at 600 W.
Of which 400 W would be delivered to the 4 Ohm load, and 200 W to the 8 Ohm load.
Click to expand...

This is why I come to you guys. I'm an idiot when it comes to this stuff..

@i_got_a_mohawk: The rating for the 115 is 250 RMS. If I get the 4 ohm, it'll be getting 350 watts. Wouldn't that eventually blow the speaker?
 
#13
FunkMetalBass said:
If your amp can handle a 2ohm load, ideally you'd want an 8-ohm 4x10 and a 4ohm 1x15.
Click to expand...

That is completely bass ackwards. The service rep was right. You will overpower the 115 mechanically before the 4x10--the thermal rating of either being irrelevant to this discussion.

A 4 ohm 4x10 + an 8 ohm 115 will work but probably not add the bass you are looking for. What it may do is reduce the mid sensitivity giving the impression of more bass.

A 4 ohm 4x10 + two 8 ohm 115's will be a better match as 2x115 is closer in sensitivity and mechanical power handling to a 4x10 (generally speaking).

Swapping one of two 4 ohm 4x10's for a 4 ohm 115 will be completely counterproductive as the 15 will mechanically run out of nuts way before the 4x10. This is a classic mistake made by players going for "that look" of a 410 on top and a 115 on bottom.
 
#15
rhythmless said:
This is why I come to you guys. I'm an idiot when it comes to this stuff..

@i_got_a_mohawk: The rating for the 115 is 250 RMS. If I get the 4 ohm, it'll be getting 350 watts. Wouldn't that eventually blow the speaker?
Click to expand...

It could blow the speaker but it won't unless you turn it up too loud. Of course, you could just as easily blow that speaker by feeding it a 200W signal with too much bass in it.

Let the 15 thing go. A 15 doesn't inherently go lower than a 10. The reverse is often true.

In this case, you're better off with the two 4x10s unless you really like the way the 15 sounds. In that case you should go with multiple 15s and get rid of the 4x10s all together.
 
#18
Well I guess now that I know it's not gonna split any atoms and blow up the world if I hook it up it's worth a shot to see how it sounds. I have 14 days from this past Saturday to return the 115. Cross your fingers for me and thanks to all of you for your input!
 

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