Combining 8-Ohm and 4-Ohm Subs with PA

[walterw]

...I'm not so sure there is easy and cheap access to an L-pad type attentuator that would safely manage a potential 500+ watts being thrown at it.

BTW, have any of you actually tried running different ohm'd cabs?

Thinking outside the box, is there a way to somehow rig a resistor/capacitor or something that would reduce just the 8-Ohm speaker two 4-Ohms? I would think if I only had the 8-Ohm hooked up, this could be done easily with something in-line, but how could this be done without affecting the 4-Ohm speaker since the 4-Ohm is being daisy-chained?

nope, doesn't work that way at all, it has to be done "upstream".

you'd need to give each box its own amp channel, and adjust the signal levels going into those amps to get them at roughly equal volume.

also, trying to use resistors to change the load from 4Ω to 8 or back is no good either; the resistor just takes half of the amp power the speaker would have gotten, negating the point of the exercise.

 

[MrLeadFoot]

I mix subs. I have a Peavey 118 that I reloaded with an 18" Eminence driver and I have a Carvin RL118. Both are 4 ohm. The Eminence driver hits harder than the Carvin does. Other than that no problems. I push each of them with 1000 watt power amps though and I match the output level by ear.

Thanks for chiming in. Nice to hear real world experience. Have you ever mixed impedance, if only just to see what you hear? How's that for an oxymoron?

 

[MrLeadFoot]

nope, doesn't work that way at all, it has to be done "upstream".

Not sure what you meant by that.

you'd need to give each box its own amp channel, and adjust the signal levels going into those amps to get them at roughly equal volume.

I am trying to keep the 2nd channel open, which is why I am exploring this.

also, trying to use resistors to change the load from 4Ω to 8 or back is no good either; the resistor just takes half of the amp power the speaker would have gotten, negating the point of the exercise.

OK, so I would end up converting that 8-Ohm speaker to 4-Ohms, but:

Let's say there are 700watts output to one 8-Ohm speaker, but there are 1800watts total output to a 2-Ohm-ish load, which is the one 4-Ohm and one 8-Ohm speaker. You said the 4-Ohm speaker would take 2/3, so that would be 1200 watts, and the 8-Ohm would get only 1/3, which is 600 watts. Quite the imbalance. Putting a resistor in the chain would give me
essentially three 4-Ohm power-drawing devices, 2 of them being speakers and one being a "power-soak". Those 1800watts split up evenly over all three devices, is 600 watts apiece. While the resistor is basically throwing away its 600watts, that still leaves 2 speakers running 600watts apiece, wouldn't it? And, wouldn't that be better than the one speaker getting 700watts?

Yes, I could run just the Carvin (if it were indeed 4-Ohms), which would give that Carvin 1100 watts (according to the 4-Ohm load rating), but the Carvin is a much lesser speaker being 400 watts Continuous, vs. the 8-Ohm sub's 1000 watt RMS, so I was thinking it there was a way to run these two in parallel, I might have more spread.

Or, am I missing something else that's key, here? Not that I want to go through the hassle of inserting a resistor somewhere; just trying to understand what it is that you're trying to tell me.

 

[Floyd Eye]

Thanks for chiming in. Nice to hear real world experience. Have you ever mixed impedance, if only just to see what you hear? How's that for an oxymoron?

I have mixed impedance on monitors. I used to daisy chain a 16 and an 8 on the same channel. No issues for the short time I did it, but I quickly got more power amps and now I don't daisy chain anything except a pair of Yamaha tops. And I don't think I would do it with subs. Anything less than 1000 watts for a sub is pretty anemic anyway. If it were me, I would get enough amp to push 1000x2 @ 4 0hms and then get a couple 4 ohm subs. Preferably matched, but I can tell you that mismatching subs is not always a bad idea. Not always a good idea, but.......

 

[MrLeadFoot]

We are a local 200 mile radius variety cover band. I have plenty of amperage between my QSC, Yamaha and Mackie amps. I've been scaling back so I don't have to deal with the weight of that Mackie, and dual subs, so the single 1000 watt sub is all we typically run. The QSC I have is the PLX3402, and the sub sounds darned good running the QSC in stereo mode on one channel, which is rated at 700 watts per channel in stereo. And, it's plenty for indoor and small outdoor gigs, like tented wedding receptions, small winery concerts, corporate events, etc., at which I typically push 70% power. We're not like many other bands that play so loud people can't even shout at each other, and we use the sub to provide some kick thump and reinforce low bass frequencies, but we don't try to blow people's hair back or anything like that. We were just contracted to do a lucrative outdoor gig, and the bass player mentioned that he had that "spare" Carvin bass 18", so I thought I would explore the possibility.

 

[modulusman]

OK one more time. What is the other sub model/brand? It doesn't matter if it is different ohmage what matters is how efficient it is. If the sub you are currently using is more efficient it could possibly be louder than the carvin. Whether or not they will work well together is also determined by the subs design. So if you want to dick around with resistors go ahead. Or you could answer my question and maybe then you will know whether you are wasting your time. 25 replies to this thread when it could have been answered in 2or 3.

 

[walterw]

Not sure what you meant by that.

I am trying to keep the 2nd channel open, which is why I am exploring this.

it means you wouldn't be able to keep that second channel open, sorry.

Putting a resistor in the chain would give me
essentially three 4-Ohm power-drawing devices, 2 of them being speakers and one being a "power-soak". Those 1800watts split up evenly over all three devices, is 600 watts apiece.

ever bought a 600w resistor? how about the fan-cooled box you'd need to keep it in?

forget it, this is a blind alley.

 

[modulusman]

We are a local 200 mile radius variety cover band. I have plenty of amperage between my QSC, Yamaha and Mackie amps. I've been scaling back so I don't have to deal with the weight of that Mackie, and dual subs, so the single 1000 watt sub is all we typically run. The QSC I have is the PLX3402, and the sub sounds darned good running the QSC in stereo mode on one channel, which is rated at 700 watts per channel in stereo. And, it's plenty for indoor and small outdoor gigs, like tented wedding receptions, small winery concerts, corporate events, etc., at which I typically push 70% power. We're not like many other bands that play so loud people can't even shout at each other, and we use the sub to provide some kick thump and reinforce low bass frequencies, but we don't try to blow people's hair back or anything like that. We were just contracted to do a lucrative outdoor gig, and the bass player mentioned that he had that "spare" Carvin bass 18", so I thought I would explore the possibility.

You should bring the mackie for this one job and use both channels of the PLX for the subs. If this is a lucrative job then rent another sub like your first one instead of using a bass cabinet. Wrong tool for the job.

 

[MrLeadFoot]

OK one more time. What is the other sub model/brand? It doesn't matter if it is different ohmage what matters is how efficient it is. If the sub you are currently using is more efficient it could possibly be louder than the carvin. Whether or not they will work well together is also determined by the subs design. So if you want to dick around with resistors go ahead. Or you could answer my question and maybe then you will know whether you are wasting your time. 25 replies to this thread when it could have been answered in 2or 3.

It is a Seismic Audio Enforcer II. I know they get a bad rap for being so inexpensive, but I used to have a powered Mackie 15, and honestly, this Seismic Audio sub sounds better outdoors than the Mackie did. We then tried a powered Mackie 18 and while it sounded good under a tent, it was only OK when when out in the open. And, it weighed way too much to be worth effort.

No, I don't necessarily want to mess with resistors. I only brought it up in case it was something easy, and might be something worth exploring.

 

[MrLeadFoot]

You should bring the mackie for this one job and use both channels of the PLX for the subs.

While I could do that, I really don't even want to have to cart the second sub. And, we may not even need to, if it's going to be a hassle. I wasn't even thinking about a second sub. It's one of those things that because I know it's available, I want to see if it's a viable option.

If this is a lucrative job then rent another sub like your first one instead of using a bass cabinet. Wrong tool for the job.

You are right, I could rent another if we really needed it. And, acutally, the Carvin is not the wrong tool for the job. According to a tech at Carvin, the bass subs speakers are exactly the same as the PA subs, but the cabs were designed slightly smaller to ease transportation for the bassist. The guy also told me that technically what I was curious about doing would indeed work, and this setup just happened to be the perfect amount of power for both subs. Of course, we did not get into the practical aspects, such as one being louder or more "efficient" than the other, but at that stage of inquiry I was just making sure it was a technically sound option, and I came here to get some feedback and thoughts about the practicality of the application. So far, the consensus seems to me that it's not a smart thing to do. Granted, only one person has actually tried something like this, and I still don't even know if the Carvin sub is 8-Ohms or 4-Ohms. At this point I am just trying to get my ducks in a row to determine whether or not a simple test is even in order. I will know the rating of the Carvin this afternoon. And, honestly, I don't know if I am hoping it turns out to be 8-Ohms or 4-Ohms. On one hand, if it is 4-Ohms then I may end up carting the Mackie amp and the extra sub, which I really don't want to, or might not even need to do. On the other hand, if it's 8-Ohms, whether we need it or not, I may end up carting it just because I know I can! Provided of course that the two sound decent together.

 

[modulusman]

Well it looks like it is a simular design as the carvin so they may work fine if you decide to centercluster. I guess it is up to you to decide based on crowd size and type of gig as to whether you need it or not. If you are playing to more than a 100 people who are actually there to watch the band one sub isn't going to cut it IMO.

 

[MrLeadFoot]

OK, the Carvin sub is indeed 4-Ohms. I daisy-chained it with the Seismic 8-Ohm, and I gotta say they sounded great together. Yes, the Carvin was louder, but it sure did not seem to be 2/3 louder. I put a 50 watt L-pad I already had in-line with the Carvin to attentuate the volume a bit, and we rehearsed for 2 hours. I periodically checked the L-pad, fully prepared to yank it at the slightest indication that it was going to be a problem and it didn't even get hot. What gives? I mean, why did the L-pad work fine, even though it's only 50 watts? And, what would happen if it did fail? Would it simply stop working without getting hot? Would it melt? More importantly, could it damage either the amp or either sub?

 

[c2thej2theizzo]

If you have to use different makes and resistance(ohms) cabinets. The best practice is too never run them in parallel if you can help it. Run them in different channels so you can control them differently. Most subs and amps are blown when bands do this. What I would do if I were you since you only have two channels is to choose between one of the subs. This way you wont be pushing the 4ohm cab too hard and not getting enough from the 8ohm. Obviously ur best bet is too buy or borrow another amp so you can run the two subs and monitors separately - but as you mentioned its just one gig. Dont waist any time thinking about center clustering - etc, you only have two subs. In your case Its all about placement at the venue. Just figure out where in the room the bass will reflect and fill a room Ie: if the stage is near a wall on one side place it next to the wall, not in open space. experiment when you get to the venue, if you can.

 

[oerk]

OK, the Carvin sub is indeed 4-Ohms. I daisy-chained it with the Seismic 8-Ohm, and I gotta say they sounded great together. Yes, the Carvin was louder, but it sure did not seem to be 2/3 louder. I put a 50 watt L-pad I already had in-line with the Carvin to attentuate the volume a bit, and we rehearsed for 2 hours. I periodically checked the L-pad, fully prepared to yank it at the slightest indication that it was going to be a problem and it didn't even get hot. What gives? I mean, why did the L-pad work fine, even though it's only 50 watts? And, what would happen if it did fail? Would it simply stop working without getting hot? Would it melt? More importantly, could it damage either the amp or either sub?

Still a stupid idea, sorry to say.

Did you rehearse at outdoor gig levels? Chances are, you did only put a few watts through it, which would be plenty for an indoor rehearsal space. The L-Pad can take that. At outdoor gig levels, the wattage is exponentially higher and can very well destroy the L-Pad. There's a reason you need a huge power soak for a 100W guitar amp. An L-Pad is inteded for a tweeter, where 50W is plenty.

I'm not an expert on this, but I suspect the L-Pad could melt, creating a short circuit and damaging the amp. Not to mention the potential fire hazard.

I don't get why you entertain the thought of bringing an extra sub for a (well-paying) gig, but don't want to bring the necessary extra power amp for it (that you already have).

Either do it right, or don't do it at all. Converting power to heat in a resistor for bass speakers is never a good idea.

 

[MrLeadFoot]

Hey, I'm just exploring all avenues, but your point about us already bringing the extra sub is well-taken. We might as well bring the other amp.

 

[Floyd Eye]

I wouldn't exactly call the Carvin "The right tool for the job". It is decent, but as a stand alone sub? Nah. I use a 4 ohm Carvin 118 in conjunction with another 118 and it gets the job done, though I still hesitate to call it "The right tool for the job".

And my band is not trying to blow anyone's hair back either. We are a hard rock band, but let's face it, we play in bars most of the time. The rooms are not big enough, nor is it really appropriate to push your subs to the point that everyone in the place has heart palpatations every time the kick hits.

Nevertheless, I stand by my statement that anything less than 1000 watts is pretty anemic for a sub.

 

[modulusman]

I wouldn't exactly call the Carvin "The right tool for the job". It is decent, but as a stand alone sub? Nah. I use a 4 ohm Carvin 118 in conjunction with another 118 and it gets the job done, though I still hesitate to call it "The right tool for the job".
And my band is not trying to blow anyone's hair back either. We are a hard rock band, but let's face it, we play in bars most of the time. The rooms are not big enough, nor is it really appropriate to push your subs to the point that everyone in the place has heart palpatations every time the kick hits.

Nevertheless, I stand by my statement that anything less than 1000 watts is pretty anemic for a sub.

I don't know if you were talking to me with this reference. BTW my bands powered QSC HPR151s and 181s only have a 700 watt amp. They get plenty loud.

 

[Floyd Eye]

I don't know if you were talking to me with this reference. BTW my bands powered QSC HPR151s and 181s only have a 700 watt amp. They get plenty loud.

Sorry, I was not directing this at you. I have absolutely zero experience with powered speakers of any kind. I would lean towards listening to your advice if I were ready to go in that direction. I am pretty much only speaking from the experience I have had with the passive 18s I have owned and the QSC and Crown amps I have powered them with. I'm sure the quality of the boxes makes a big difference as well. My boxes are not Meyer or anything, but the subs I am using are both fed 1000 watts and, in my case anyway, they sound anemic to my ears trying to feed them less.

 

[MrLeadFoot]

The powered Mackie 15" I had previously only had a 350 watt internal amp, but it was a monster all by itself at indoor gigs, like bars and restaurants, etc. The 18" Active Mackie I had was only 800 watts, and it did well by itself outdoors, and we never had to run it at full power. But, at 150lbs. taking it to gigs got old real quick. I also did not like that both of these were painted finishes, instead of carpet, so they began to look like crap in real short order. In fact, if you bumped them into something or scooted them along the ground, pieces of the cabs would just chip off. They both sounded great, but what a crappy design.

The Carvin bass cab sub is smaller than its counterpart PA sub cab (same woofer), but it still sounds punchy, albeit, so far I've only run it in conjunction with the Seismic sub, and they sound great together. But, because the cab is smaller it doesn't "fill" as well as the Seismic does alone. Surprisingly, the Seismic sounds pretty darned good alone outdoors. But because the Carvin is spec'd significantly less than the Seismic, and that the Carvin has a smaller cab, I think it would be pointless to try running it alone outdoors.

I got the Seismic as a "hold us over", while we tried to figure out what our next "real" sub would be when we got rid of the Mackies. I was actually going to get the Carvin PA sub, but when I saw how much cheaper the Seismic's delivered price was, I figured it was only temporary, so why not go with the cheaper one. I gotta say, though, that the Seismic is really a nice sub. Like I said above, while the Mackies sounded great indoors, they quickly get lost in the open air, while the Seismic does not. The cab is designed very well, and is structurally sound. They keep their costs down by using copies of materials. For example, they have "twist-loc" connectors, which are undoubtedly Chinese or Taiwanese copies of Neutrik Speakon connectors. I'm sure the handles, pole-mount sockets and passive crossover (which I removed because I have a Rane active corssover) are also some copies. But the Chinese and Taiwanese can copy ANYTHING, so they work just fine. In fact, what today is NOT made in Taiwan or China? In fact, my laquered Mapex Saturn drum kit is manufactured in Taiwan, too, but it's damned nice, which is why I bought it as an upgrade to my Tama, even though I was dead set on buying a Pearl Masters.

During the sound check at this gig, I am going to try both the Seismic by itself, and together with the Carvin. And, if they sound really good together, I just might pick up another Seismic. Yes, I got rid of the Mackie 18 because of weight, but moving two 70 lb. cabs is much eaiser than moving a single 150 lb. cab, especially since that 150 lb. cab has pieces breaking off everytime you bump something! And, I do have plenty of power for two subs with this QSC PLX3402 amp.

 

[modulusman]

The powered Mackie 15" I had previously only had a 350 watt internal amp, but it was a monster all by itself at indoor gigs, like bars and restaurants, etc. The 18" Active Mackie I had was only 800 watts, and it did well by itself outdoors, and we never had to run it at full power. But, at 150lbs. taking it to gigs got old real quick. I also did not like that both of these were painted finishes, instead of carpet, so they began to look like crap in real short order. In fact, if you bumped them into something or scooted them along the ground, pieces of the cabs would just chip off. They both sounded great, but what a crappy design.

The Carvin bass cab sub is smaller than its counterpart PA sub cab (same woofer), but it still sounds punchy, albeit, so far I've only run it in conjunction with the Seismic sub, and they sound great together. But, because the cab is smaller it doesn't "fill" as well as the Seismic does alone. Surprisingly, the Seismic sounds pretty darned good alone outdoors. But because the Carvin is spec'd significantly less than the Seismic, and that the Carvin has a smaller cab, I think it would be pointless to try running it alone outdoors.

I got the Seismic as a "hold us over", while we tried to figure out what our next "real" sub would be when we got rid of the Mackies. I was actually going to get the Carvin PA sub, but when I saw how much cheaper the Seismic's delivered price was, I figured it was only temporary, so why not go with the cheaper one. I gotta say, though, that the Seismic is really a nice sub. Like I said above, while the Mackies sounded great indoors, they quickly get lost in the open air, while the Seismic does not. The cab is designed very well, and is structurally sound. They keep their costs down by using copies of materials. For example, they have "twist-loc" connectors, which are undoubtedly Chinese or Taiwanese copies of Neutrik Speakon connectors. I'm sure the handles, pole-mount sockets and passive crossover (which I removed because I have a Rane active corssover) are also some copies. But the Chinese and Taiwanese can copy ANYTHING, so they work just fine. In fact, what today is NOT made in Taiwan or China? In fact, my laquered Mapex Saturn drum kit is manufactured in Taiwan, too, but it's damned nice, which is why I bought it as an upgrade to my Tama, even though I was dead set on buying a Pearl Masters.

During the sound check at this gig, I am going to try both the Seismic by itself, and together with the Carvin. And, if they sound really good together, I just might pick up another Seismic. Yes, I got rid of the Mackie 18 because of weight, but moving two 70 lb. cabs is much eaiser than moving a single 150 lb. cab, especially since that 150 lb. cab has pieces breaking off everytime you bump something! And, I do have plenty of power for two subs with this QSC PLX3402 amp.

I don't believe Mackie ever made a 350 watt sub. If you had the srs1500 it had a 600watt amp. The design was bad for anything where you needed to throw. The 1501 and 1801 were better. BTW according to seimic audios website your sub weigh 90 pounds