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Ohm Question

low down shame

low down shame

Jan 23, 2011
46
1
#1
Hey Talk Bass People ,
I own an SVT 6 Pro that Ampeg claims is 1100 w @ 4 ohms. I've got a Guy who builds Custom Cabs so I called Ampeg to ask a few questions. My question is this, if I'm having a 2x12 built what watt Speakers should I use. I'm looking at Faital Pros and a Ciare Tweeter. Since the Amp is 1100 watts at 4 ohms pegged wide open ( Gain and Volume) I'm assuming I need 2 300 watt @ 8 ohms Speakers rms. If I understand wattage and ohms correctly that would give Me a 600 watt Cabinet @ 4 ohms with a 1200 watt peak. Am I correct and will that work?
 
#5
Downunderwonder said:
That amount of power isn't intended for 2x12. More like 8x12 would be appropriate.

To make best use of those watts without spending a stupid amount on drivers you want to look at 3way cabs with big subs.
Click to expand...

I'd have to concur that there are very few 2-4 speaker cabs that can handle 1100 watts RMS. Eden 410XSTs run at 1000, and that's towards the top end.

IIRC even the fEARful 151566 series will generally only do up to 1500 watts.
 
#7
low down shame said:
Hey Talk Bass People ,
I own an SVT 6 Pro that Ampeg claims is 1100 w @ 4 ohms. I've got a Guy who builds Custom Cabs so I called Ampeg to ask a few questions. My question is this, if I'm having a 2x12 built what watt Speakers should I use. I'm looking at Faital Pros and a Ciare Tweeter. Since the Amp is 1100 watts at 4 ohms pegged wide open ( Gain and Volume) I'm assuming I need 2 300 watt @ 8 ohms Speakers rms. If I understand wattage and ohms correctly that would give Me a 600 watt Cabinet @ 4 ohms with a 1200 watt peak. Am I correct and will that work?
Click to expand...

The limiting factor is usually where the woofers exceed their linear excursion limits and "fart out'. That's not a simple number to come up with, it depends on many things, but it usually happens well before the woofer is close to its rated power handling.

For instance, the Faital 12PR300 is rated at 300 watts, but depending on the specifics of the cab and port tuning (asuming it's a ported cab), and depending on your EQ settings and how aggressively you dig it, it may well run out of excursion and fartout at about 1/3 to 1/2 its rated power.

When choosing woofers, compare them on the basis of how much air they move, rather than how many watts they're rated for. So take the cone area of the 12PR300 (489 square centimeters) and multiply it by the linear excursion (4.92 millimeters, or .492 centimeters), and you get 240.6 cubic centimeters.

If you want to approximate the SPL of a 8x10, make an educated guess about the speakers in it and go from there. The Eminence Beta 10 is probably a reasonable approximation of the average low-cost 10" bass guitar speaker, and it will move 103.5 cc of air, so eight of them will move about 828 cc. So to equal or exceed the displacement of an entry-level 810, you'd probably want to use four 12P300 woofers (or their approximate equivalent).

Note that the Eminence Kappalite 3012LF will move 496 cc, so one 3012LF will fartout at about the same SPL as two Faital 12PR300s, and two of them can rival an 810. But the 3012LF doesn't go up as high. Tradeoffs, always tradeoffs.

Hopefully I'm just going over this for your benefit; hopefully your guy who builds custom cabs is taking displacement into account, and not just looking at watts.
 
#8
wmheilma It would work, but there are a lot of drivers to choose from. If you describe the sound you are after you will get some good direction from the folks on TB.
Click to expand...

Yes, the tone/sound is what matters. Ratings of amps and speakers are more like guidelines.

I can use a 300w speaker @4ohm with your amp and be ok as long as I know my limits. Usually your ears can tell you when a speaker has a hard time. The master volume knob is key in this situation.

If you want to utilize your power rating because this was your intention for clean loud power, then make sure you purchase something that can withstand this 1100w amp. I would recommend a cab that has a rating of at least an extra 1/3 the power rating which is like 1500w.

If your looking for that SVT sound by pushing the gain section and amp section, get a cab set @ 8ohms rated for over 1000w.

Hopefully you understand that you don't have to match perfectly with ratings. Your tone should be more important and not compromised.
 
#9
DukeLeJeune said:
The limiting factor is usually where the woofers exceed their linear excursion limits and "fart out'. That's not a simple number to come up with, it depends on many things, but it usually happens well before the woofer is close to its rated power handling.

For instance, the Faital 12PR300 is rated at 300 watts, but depending on the specifics of the cab and port tuning (asuming it's a ported cab), and depending on your EQ settings and how aggressively you dig it, it may well run out of excursion and fartout at about 1/3 to 1/2 its rated power.

When choosing woofers, compare them on the basis of how much air they move, rather than how many watts they're rated for. So take the cone area of the 12PR300 (489 square centimeters) and multiply it by the linear excursion (4.92 millimeters, or .492 centimeters), and you get 240.6 cubic centimeters.

If you want to approximate the SPL of a 8x10, make an educated guess about the speakers in it and go from there. The Eminence Beta 10 is probably a reasonable approximation of the average low-cost 10" bass guitar speaker, and it will move 103.5 cc of air, so eight of them will move about 828 cc. So to equal or exceed the displacement of an entry-level 810, you'd probably want to use four 12P300 woofers (or their approximate equivalent).

Note that the Eminence Kappalite 3012LF will move 496 cc, so one 3012LF will fartout at about the same SPL as two Faital 12PR300s, and two of them can rival an 810. But the 3012LF doesn't go up as high. Tradeoffs, always tradeoffs.

Hopefully I'm just going over this for your benefit; hopefully your guy who builds custom cabs is taking displacement into account, and not just looking at watts.
Click to expand...

I was actually looking at the Faital 500 and the Kappa Lite LF 12''s. The Kappa's have a higher X-max but Faitals are waterproof. I also hear Bergantino is using them in His Cabinets. Both come in at the 450 to 500 watt range.
 
#13
DukeLeJeune (how cool is that name) is right as usual. For example I have an old Fane 10" that is rated at 200W but farts at about 70-75. I should also mention that if I try to tune it lower than it wants to go, fart out comes sooner.

Many other drivers are similar, with fart out occurring at well below the power rating. I have not tried one yet but I believe that the Kappalite 3012LF does not fart out easily and that is probably why they are so popular.
 

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