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Getting a 15" cab...

S

Skavenger

May 26, 2002
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#1
I have a Pro Fet IV amplifier from Warwick. It has 400w of juice and under that I have a W411 cab for the time being. The w411 is a 4x10" cab with a high-frequency horn and clocks in at 600w RMS.

The questions are: I'm buying a 15" Ampeg to get that bottom end more present, do I need anything extra or do I simply plug it in the back of the amp using the speakon contact? My 4x10 cab also has an extra speakon contact on the backside, does that allow me to plug the 15" cab together with it? Should I maybe invest in a frequency filter so that the bass goes to the 15" and the treble goes to the 4X10?

If I'm in my cheapest mood and end up buying only the cab with speakon cable, will it work at all?

Bear with me, I'm a complete beginner when it comes to amps and cabs.
 
#2
I'm going to assume that your amp's minimum impedance is 4 Ohms, and each of your cabinets is 8 Ohms (together, they meet the minimum load, and you'll get the max wattage out of your amp; anything lower than 4 Ohms, and you'll damage your amp; anything higher, no issues - you'll just get less wattage out of your amp). I'm also assuming that your amp has two speakon outputs.

1) If your amp has two speakon outputs, you simply run two speakon cables from the amp - one to each cabinet. Nothing else to do - it's as simple as that.

2) If you have just one speakon out... then that's where the 4x10 cab's extra output comes into play. You'd basically "daisy-chain" your two 8-Ohm cabinets: Amp => 4x10 => 1x15.

I haven't seen too many setups like option #2, though.

If your cabinets or amp have different impedance specs (Ohms), let us know before you decide to plug in anything.
 
#3
you have to check the impedance of the cabs and of your head. The impedence of the cabs is written on them somewhere most likely beside the input jack it's measured in ohms. Your head can only work dowm to a minimal impedence, if you go lower than that the currents that flows in the components will be too great and there's a lot of chances you'll fry your head.

Most heads go down to 4 ohms some go down to 2 ohms. If your head goes down to 4 ohms and your current cab is 4 ohms, you're pretty much screwed because there's no way you can hook up a 4 ohm cab with another one without going down to 2 ohms.

To calculate the total impedence of x number of cabs you use this formula: (1/(1/firstcab+1/secondcab+1/cab3 and so on...))
for example: two 4 ohms cabs (1/(1/4ohms+1/4ohms))=2ohms

an 8ohm cab with a 4 ohm one : (1/(1/8ohms+1/4ohms))=2.67ohms

so if your head goes down to 2 ohms you can hook these cabs together. If it goes down to 4 ohms you're pretty much stuck to using two 8ohms cab. theres another simpler formula you can use to calculate impedance when using only two cabs wich is obviously your case, (8ohmsx8ohms/8ohms+8ohms)=4ohms

Good luck!:hyper:
 
#6
Alright, I checked my amp and cab out and the amp had a 4ohm minimum impedance. The cab had 8 ohms. The one I'm buying also had 8 ohm impedance. So I should be all set, right?

My amp has two outputs and my cab has two outputs as well. Will there be a difference in sound depending on where I hook it up? Is the amp "smart" in any way, meaning that it can separate the lowest lows and send them to the cab better suited for it and vice versa for the highest highs? Another thing, does this mean I can never get another cab to my present gear? What if I wanted to add, say, a third cab to the rig, or do I need another amp for that? Just a philosophical question.
 
#7
Skavenger said:
Alright, I checked my amp and cab out and the amp had a 4ohm minimum impedance. The cab had 8 ohms. The one I'm buying also had 8 ohm impedance. So I should be all set, right?

My amp has two outputs and my cab has two outputs as well. Will there be a difference in sound depending on where I hook it up? Is the amp "smart" in any way, meaning that it can separate the lowest lows and send them to the cab better suited for it and vice versa for the highest highs? Another thing, does this mean I can never get another cab to my present gear? What if I wanted to add, say, a third cab to the rig, or do I need another amp for that? Just a philosophical question.
Click to expand...

I've never had any experience with Warwick heads, but I'd assume since they're rather nice, there might be a bi-amp button located somewhere on your head. if you were to press that button (if there is one) it would separate your lows to the 15 and highs to the 410.

and for the third cab ----I think you would have to get another amp...but I could be wrong?:eyebrow:
 
#8
kid_squanto said:
I've never had any experience with Warwick heads, but I'd assume since they're rather nice, there might be a bi-amp button located somewhere on your head. if you were to press that button (if there is one) it would separate your lows to the 15 and highs to the 410.

and for the third cab ----I think you would have to get another amp...but I could be wrong?:eyebrow:
Click to expand...

No, you're right.

If you want three 8-Ohm cabs but one amp head, then a 2-Ohm amp would be necessary.

Or, you could get a stereo amp. But that's a different story. I'd imagine that, with a 4-Ohm stereo amp, you could run two 8-Ohm cabs in each channel (Left and Right).

If you like the Warwick preamp section, you could always get a stereo poweramp and bypass the power section on the Warwick amp head (if you run a cable from the "Effects Send" portion of your effects loop, to a separate poweramp, the head's power section is bypassed) . Otherwise, with that amp head alone, I believe you can't do more than 4-Ohm mono (Someone correct me if I'm wrong).

It really isn't bad at all, though. Most people use 4-Ohm mono amps, and two 8-Ohm cabinets (or one 4-Ohm cabinet). I use that setup myself, as GK stuff is built that way.
 
#9
I checked out the Warwick site and your amp does not have crossover capability. Which means you cannot send one signal to your 115 and one to your 410.

Keep in mind that your amp puts out 400 watts @ 4 ohms and your 410 is a 600 watt cab. Adding on a 15, depending on it's wattage, your amp might not adequately drive both spkr cabs.
 
#10
That's what I was afraid of.

But I recall asking about it here and I got the answer that if you have more watts on the speaker than the amp there's less risk to blow it, the amp always delivers 400w of sound if it has the room to do so, and thus having a cab with more watts than the amp is better compared to having a cab with less watts. Does this change when you add another cab?

My amp has 400w, the 4x10 has 600w and the cab I'm buying is at 200w. Will there be, like, no sound at all coming from one of the cabs, sort of like when you pour a glass of water into a bucket...The water is the amp's watt and the bucket the cabs(ie you only fill the bucket up to the "400" mark and the rest is empty, and silent)? How about that analogy :)
 
#11
You'll hear something from both spkr cabs, it's just a possibility that you can underdrive your spkr's causing them to fart (excessive cone movement). Only way to tell is to try it out.

Rule of thumb, you always want more watts (headroom as referred to) then your spkr cabs. I've played through amps that didn't put out what they say they did and my spkr's were farting (excessive cone movement) and I've played through amps capeable of handling more then they say. i.e. the Epifani 502 is 600 watts @ 4 ohms and it can drive the Epi UL410's 1000 watts @ 4 ohms with no problem.

Some spkr's are designed and require good true wattage where others are not.

To simply put it, you can damage a spkr by underdriving it as well as too much power and turning up too loud.
 
#13
Alright, I've checked the FAQ about the underpower issue. Damn...I have to buy a more powerful amp. Seeing as I've used my current setup for 2 years it could be only a matter of time. But I dohave a clip LED warning on the amp and I generally try to keep my playing below that.

The insight that I might damage it in someway just by playing through it on a more powerful cabinet is disturbing to say the least. It's a good thing I found out in time.
 
#14
Good morning Chris. Since you've been playing through your current rig for some time now, I doubt you'll hurt your spkr's.
I'm just saying that before you buy the 15 cab, try it out with your amp and 410 cab to make sure you're happy with it's sound and that you're getting sufficient output to both cabs. You'll know if it's enough when you turn it up some and the spkr's start to fart or you see a lot of cone movement (excursion). No need to go rush out and buy another amp.
Some gigs for you might be okay with just the 410, other gigs you may need to add the 15, or some gigs all you'll need is only the 15. You'll have some versitily this way.:)

Since you mentioned that you're relitively new at this, here's some advice to check and make sure your spkr's are all in phase. (sometimes they get wired up wrong from the manufacturer). Use a spkr cable with (2) 1/4" jacks and a 9 volt battery. Plug one end of the cable into your spkr cab and tap the other end of the cables 1/4" jack to the 9 volt battery (positive to positve and negative to negative) What you should see while doing this tapping of the battery is your spkr's cone should move outward (you'll here a popping sound), if the spkr's cone moves inward, than the wires on the back of the spkr need to be reversed. All spkr cones should be moving outward.
 

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