Not Blowing Out Cabs w/ My Powerful Amp

[ryromofo]

I have a Stewart World 1.6 stereo amplifier, and I'm trying to figure out the best cab setup for this amp.

Amp specs:

880W @ 2 ohms single channel
650W @ 4 ohms single channel
390W @ 8 ohms single channel

(or you can bridge both channels for more power out of a single channel)
1600W x 1 @ 4 ohms bridged
1150W x 1 @ 8 ohms bridged
600W x 1 @ 16 ohms bridged

I have a Markbass 151p cabinet (1x15 speaker) that is rated at 400W @ 8 ohms.

Running out of one of the channels of the stereo amp (390W), it seemed too quiet for what I needed. So I ran it mono bridged (1150W), and kept the volume less than half on the amp.

Well it blew the speaker after 6 months.

So as I try and see if I can get the speaker fixed, I'm trying to figure out what would be the best solution for getting suitable volume and tone and not blow the speaker(s) out so easily.

Should I pair the (repaired) Markbass 151p with one of their 102p cabs (2x10 speakers also rated at 400W @ 8 ohms), and run them in parallel out of one of the amp's channels? That should then knock it down to 4 ohms, so i'd be getting 650W out of the single channel on the amp (right?). Would the addition of the 2nd cab help with my volume problems?



Thanks in advance. Would love to figure this out!

[JimmyM]

You just learned two important lessons here:

1. Your amp has a volume knob. Use it.

B. Manufacturers often lie about how much wattage their cabs can take.

I've played that cab, and there is no way it could take 400w real world. 400w is the point where the voice coil blows up. You can cause it to stress out and wear out with less wattage than that. It's probably closer to 250w that it takes real world.

If you want to play loud, you have to have a big cab rig, simple as that.

[ryromofo]

Originally Posted by JimmyM

You just learned two important lessons here:

1. Your amp has a volume knob. Use it.

B. Manufacturers often lie about how much wattage their cabs can take.

I've played that cab, and there is no way it could take 400w real world. 400w is the point where the voice coil blows up. You can cause it to stress out and wear out with less wattage than that. It's probably closer to 250w that it takes real world.

If you want to play loud, you have to have a big cab rig, simple as that.

Thanks, yeah I thought I would be able to hear if I was overdriving it, but I guess it snuck up on me.

From experience, do you or anybody else think in my situation a combination of 1x15 and 2x10 cabinets would be better, or maybe a 4x10 on its own?

I guess I'm also trying to figure out if it's a better idea to drive the cab(s) on mono bridged mode with a lot of watts but the amp turned down, or run it on a single channel mode with less watts, but the amp turned up all the way?

[JimmyM]

Mixing cabs can work, but the results are unpredictable, whereas using matching cabs always works.

[BassmanPaul]

+1 to Jimmy's post. As a rule of thumb, a cabinet can make use of about half it's thermal power before it's cone runs out of travel (excursion). Adding more power after that just gets wasted as heat melting the voice coil. The cab will get no louder.

[IntrepidCellist]

With that kind of power? Either you need a super-driver (like one of the Eminence Kappalites) or a hell of a lot of other drivers.

If you're trying to put 1000W through a small cab to keep up, you need more speakers.

[ryromofo]

I believe the Stewart amp is a Class H amp.

The thing can deliver quite a lot of power when mono bridged.

But I guess I should only run out of one of the channels then, to avoid giving the speakers too much power.

They make a companion cab to the one I'm getting fixed, so I would think those would pair nicely with each other.

Do you think I'd risk another blowout running two 400W cabs through the amp at 650W? Would making sure I never turned up amp volume more than half way help?

Thanks guys.

[BassmanPaul]

A power amps volume control has no effect on the amount of power that the amp can give. All they do change the amount of signal needed to get that power.

[ryromofo]

Originally Posted by BassmanPaul

A power amps volume control has no effect on the amount of power that the amp can give. All they do change the amount of signal needed to get that power.

Hmm, good to know. Thanks.

So I really should be aiming at delivering the exact same amount of power to the speaker cabinets as they are rated?
I always thought there was some reason to have an amp that could deliver more.

There aren't really any 650 watt 4 ohm speaker cabinets out there though. How would I go about matching it?

[Munjibunga]

Why bridge the amp? If you ran just one side, the amp would be at 390 watts. Your cabinet can only go so loud. Hooking an 1,100-watt amp up to a 400-watt speaker just invites the temptation to turn it up past the power it can handle. For more volume, you need more speakers.

[Muckaluck]

What about something like an Acme B4. Andy usually advocates for more power with those speakers. Could be a good match?

[Munjibunga]

Originally Posted by ryromofo

Hmm, good to know. Thanks.

So I really should be aiming at delivering the exact same amount of power to the speaker cabinets as they are rated?
I always thought there was some reason to have an amp that could deliver more.

There aren't really any 650 watt 4 ohm speaker cabinets out there though. How would I go about matching it?

Bergantino makes made a 600-watt 212, the AE212. I run a 900-watt amp through it all the time. It's all about knowing the limitations of your cabs, and using the volume knob accordingly.

[ryromofo]

Thanks, I'll check the Bergantino cab out.

Does anybody know the general differences between one big speaker in a cab versus many smaller speakers in a cab? I always liked the 15" speaker best for getting the biggest low end, but it seems like a cab with multiple smaller speakers will be able to move more air with the same power. Do you lose some of the bigger low end but gain volume with the multiple speaker approach?

[RickenBoogie]

What you want is alot more speakers. A single 15 is no match for that amp. If you like it, use more of the same. Matching cabs are ALWAYS best. Seems like you *could* run up to 4 of them, 2 a side. OR, consider larger cabs, like 810's. Volume is produced by speakers, not wattage. And spkr cabs are rated at their thermal limit. They can really only handle HALF what the rating says. (as has been mentioned, but worth repeating). And no, low end comes from the cab design, and has nothing at all to do with the size of the spkr.

[ryromofo]

Well I like the 151p for it's nice low end, but i think my tone could use a bit more in the midrange. That's why I was thinking of pairing it with a cab with 2x10. But you're thinking if I added a cab to my existing 1x15 i should just double up with the same cab again?

[scottbass]

You need more volume. More volume is produced by moving more air. Each speaker moves air according to it's surface area and the total excursion (back and forth motion). Unless you get into high-excursion (and high-cost) drivers like the Eminence Kappalight 3015LF, every instrument speaker has more or less the same maximum excursion, about 4 mm.

A 15" driver has about 177 square inches of surface area. A 10" driver has about 78.5" of surface area. So you can see a 15" driver has A LITTLE more surface area (about 13% more) than two 10" drivers.

For many years a very popular combination was to run one single 15" cab along with a 2x10" cab. Another popular combination was to run one single 15" cab along with a 4x10" cab. 2x15" cabs were very popular many years ago, became less popular, and are starting to regain popularity recently.

All of these speaker combinations are for the same purpose: to move more air, thereby creating more volume. You were obviously trying to move too much air with too little surface area, thereby creating an over-excursion situation that resulted in speaker failure.

I am of the school that believes too many watts is never the problem; it's too little air movement and/or too few watts that cause the problem (in the extreme case where you turn up your amp to the point of distortion which results in over-excursion).

If you use two speaker cabs that have the same impedance AND similar efficiencies, it is most efficient to run them in parallel from a bridged amp. If, however, the cabs have significantly different efficiencies you might want to drive each one using one side of your amp in stereo mode in order to balance the volume levels.

[agreatheight]

2x15?

[billfitzmaurice]

Originally Posted by JimmyM

You just learned two important lessons here:

1. Your amp has a volume knob. Use it.

B. Manufacturers often lie about how much wattage their cabs can take.

Lesson 3: If you're not an expert where gear is concerned never bridge, all you're likely to end up with is blown drivers. Not loud enough? You don't need more watts, you need more and/or better speakers.

And if you don't know your amp's output voltage swing capacity and the voltage required to drive your speakers to full excursion you're not an expert.

[staindbass]

to the original question- a compressor helps by reducing huge peaks in the signal, if you are not using one already. saves many speakers.

[ryromofo]

Originally Posted by scottbass

You need more volume. More volume is produced by moving more air. Each speaker moves air according to it's surface area and the total excursion (back and forth motion). Unless you get into high-excursion (and high-cost) drivers like the Eminence Kappalight 3015LF, every instrument speaker has more or less the same maximum excursion, about 4 mm.

A 15" driver has about 177 square inches of surface area. A 10" driver has about 78.5" of surface area. So you can see a 15" driver has A LITTLE more surface area (about 13% more) than two 10" drivers.

For many years a very popular combination was to run one single 15" cab along with a 2x10" cab. Another popular combination was to run one single 15" cab along with a 4x10" cab. 2x15" cabs were very popular many years ago, became less popular, and are starting to regain popularity recently.

All of these speaker combinations are for the same purpose: to move more air, thereby creating more volume. You were obviously trying to move too much air with too little surface area, thereby creating an over-excursion situation that resulted in speaker failure.

I am of the school that believes too many watts is never the problem; it's too little air movement and/or too few watts that cause the problem (in the extreme case where you turn up your amp to the point of distortion which results in over-excursion).

If you use two speaker cabs that have the same impedance AND similar efficiencies, it is most efficient to run them in parallel from a bridged amp. If, however, the cabs have significantly different efficiencies you might want to drive each one using one side of your amp in stereo mode in order to balance the volume levels.

Thanks, that's a lot of really useful info. I've heard cabs with multiple smaller speakers are more efficient with their power than a larger 1 speaker cabinet. Do you know if that's true?