Crossover question

[moody]

I'm in the process of fixing up an old pair of 2x15 speaker cabinets for rehearsals. I've replaced the speakers with 4 cheap p.audio woofers.

 

I know that the horns work.

 

I am not certain, but I have reason to believe that the crossovers may have been wired for 16ohms rather than the 4ohms that are more normal for boxes of this type. The people owning them were somewhat less than technical so I really don't know if they were wired correctly when I got them and they can't give me good info for how they were wired. All I've been told is that they were designed to be run two per side plugged together and 2ohms doesn't seem at all likely for the age of the cabs.

 

Is there any way of telling at all? I have a multimeter. These crossovers are very much home made (components on a wooden backing board).

 

If I can't tell, would it be best to wire them 4 or 16ohm? (which is least likely to cause damage if wired incorrectly?).

 

I do know the basics of speaker impedence related to the power amp, it's just the crossover that's stuffing me.

[laidback]

DC resistance is easily measured with a cheap and common multimeter. It won't be the same as impedance, but the 2 numbers will "track': figure dc resistance of around 6 or so for a nominal 8 ohm loudspeaker.

 

Other things at play here are that the crossover frequency will be dependent on driver impedance, and how you plan to run these. If I were paralleling these boxes, I'd wire them for 16 ohms each to give 8 ohms total. You could bridge your power amp to regain the lost volume from higher impedance. Or you could wire them for 4 ohms each and run 1 on each side of the amp, an arrangement that might be a little more flexible.

 

Of course, If you guys aren't ungodly loud at rehearsal you might just unhook 1 woofer altogether. You might get better vocal clarity and less low-mid mud.....

[moody]

ok.

 

Thanks for your help, but you didn't tell me anything I didn't already know (sorry).

 

I need to find out what the crossover frequency will be given particular impedence, basically I don't know what the crossovers are (wouldn't mind knowing if they are cheap / easy to rewire for different impedence?).

 

Also, disconnect one loudspeaker? It's a massive box already, I didn't think that it was advisable to run single drivers in absolutely massive vented boxes because there would be to much 'give' to the quantity of air behind them.

[moody]

 

Originally posted by laidback Of course, If you guys aren't ungodly loud at rehearsal you might just unhook 1 woofer altogether. You might get better vocal clarity and less low-mid mud.....

 

 

This isn't my rig and I'm basically setting it up to how the owner wants it. The band which will be using these is a fleetwood mac tribute band that don't play to loud. They will basically be running vocals, keys and possibly bass with a cheap behringer mixer and a single 15 band eq .

 

I would prefer to run them as 4ohm boxes if the crossover is set up for that. While we have plenty of smaller pa equipment and this is intended to be permanently set up, in an emergency it is conceivable that they could be used to gig with on occasion

[tlbonehead]

Originally posted by moody I'm in the process of fixing up an old pair of 2x15 speaker cabinets for rehearsals. I've replaced the speakers with 4 cheap p.audio woofers. I know that the horns work. I am not certain, but I have reason to believe that the crossovers may have been wired for 16ohms rather than the 4ohms that are more normal for boxes of this type. The people owning them were somewhat less than technical so I really don't know if they were wired correctly when I got them and they can't give me good info for how they were wired. All I've been told is that they were designed to be run two per side plugged together and 2ohms doesn't seem at all likely for the age of the cabs. Is there any way of telling at all? I have a multimeter. These crossovers are very much home made (components on a wooden backing board). If I can't tell, would it be best to wire them 4 or 16ohm? (which is least likely to cause damage if wired incorrectly?). I do know the basics of speaker impedence related to the power amp, it's just the crossover that's stuffing me.

If you know that the woofers are 8 ohms each,why not just look at whether the woofers are wired together in parallel or series. And you said that "the crossovers are wired for 16 ohms rather than 4 ohms" which makes no sense. What do you mean by that? Do you mean that the crossovers were built using values intended for 16 ohm operation,or what? What is the impedence of the horn driver and what components do the crossovers consist of? What is the value of the caps?

[kevinnem]

You don't really get to choose what the impeadance of the box is, it is based off of the parts on the inside.

 

I am a little rusty on my electical engineering, but it should be very apearent from looking at the cross over. if all you see is a set of the same caps and inductors, and a pad for the tops (cause they would likely be more effecent) then you are likely wireing it for operation so the impeadance of the horn matchs the woffer (aka make the ohms of the lows the same as the highs).

 

In fact I would say it is likely no matter what the cross over looks like, that you need to wire it for 4 ohm. It will be appeaent once you hook it up, cause if it is made for 16 ohm, and you are loading it to 4 ohm your cross over point will be way different. it would also may a huge inbalance between the volume of the tweeter and woffer. (if it is made for 4 ohm and you hook it up 16 then the volume will be way lower)

 

what are the values/toplology for the the cross over

 

Kev.

[tlbonehead]

Originally posted by kevinnem You don't really get to choose what the impeadance of the box is, it is based off of the parts on the inside. I am a little rusty on my electical engineering, but it should be very apearent from looking at the cross over. if all you see is a set of the same caps and inductors, and a pad for the tops (cause they would likely be more effecent) then you are likely wireing it for operation so the impeadance of the horn matchs the woffer (aka make the ohms of the lows the same as the highs). In fact I would say it is likely no matter what the cross over looks like, that you need to wire it for 4 ohm. It will be appeaent once you hook it up, cause if it is made for 16 ohm, and you are loading it to 4 ohm your cross over point will be way different. it would also may a huge inbalance between the volume of the tweeter and woffer. (if it is made for 4 ohm and you hook it up 16 then the volume will be way lower) what are the values/toplology for the the cross over Kev.

There is usually no problem with having a 4 ohm low frequency and 8 or 16 ohms on the high frequency device,as long as the crossover is design to take that into consideration.

[dboomer]

 

Originally posted by kevinnem In fact I would say it is likely no matter what the cross over looks like, that you need to wire it for 4 ohm. It will be appeaent once you hook it up, cause if it is made for 16 ohm, and you are loading it to 4 ohm your cross over point will be way different.

 

 

Yes ... but once you change the drivers the crossover summation pretty much goes to hell anyways ... frequency response, level matching, etc. These things don't just fall off of trees ya know

[tlbonehead]

Originally posted by dboomer Yes ... but once you change the drivers the crossover summation pretty much goes to hell anyways ... frequency response, level matching, etc. These things don't just fall off of trees ya know

Yep. I thought maybe if we kenew the values of the crossover components,maybe we could get an idea of how it was originally wired,although the current woofers are not original either.

[agedhorse]

I think everyone here is missing Moody's real question... that is given a box with an unknown crossover AND a pair of 8 ohm speakers in each box AND a horn, how can you tell what impedances the existing crossover is designed for.

 

Short answer... without an LC meter, or marked components, you really cant without setting up the crossover into a known resistive load, sweeping the crossover and measuring the response.

 

If you haven't changed the horn, you can (maybe safely) assume that the high pass portion is working properly. There's no way to know what the configuration or slope ofthe low pass section is.

 

As far as the original nominal impedance of the box, I would expect that 16 ohms would be very odd since amps that could deliver any kind of 16 (or even 8) ohm power was severely limited by the semiconductor technology of the time. It was MUCH easier to build amplifiers with higher current, lower voltage output.

 

My educated guess it that those were originally 4 ohm boxes. I would also bet that the original crossovers may have been a home-brew prokect of dubious quality as well. You might look at just replacing those x-overs with a known commercial replacement product???

 

Hope this helps.

[tlbonehead]

Originally posted by agedhorse I think everyone here is missing Moody's real question... that is given a box with an unknown crossover AND a pair of 8 ohm speakers in each box AND a horn, how can you tell what impedances the existing crossover is designed for. Short answer... without an LC meter, or marked components, you really cant without setting up the crossover into a known resistive load, sweeping the crossover and measuring the response. If you haven't changed the horn, you can (maybe safely) assume that the high pass portion is working properly. There's no way to know what the configuration or slope ofthe low pass section is. As far as the original nominal impedance of the box, I would expect that 16 ohms would be very odd since amps that could deliver any kind of 16 (or even 8) ohm power was severely limited by the semiconductor technology of the time. It was MUCH easier to build amplifiers with higher current, lower voltage output. My educated guess it that those were originally 4 ohm boxes. I would also bet that the original crossovers may have been a home-brew prokect of dubious quality as well. You might look at just replacing those x-overs with a known commercial replacement product??? Hope this helps.

I assume the coild would need to be disconnected and then measured. Would this give an accurate idea of their inductance? Caps ordinarily would have the rating printed on them I would think. If you know the layout of the crossover and the values of the coils and caps,you might be able to use a crossover chart and figure out the impedence that the crossover was intended for. But,I agree,it might make more sense to just go with new crossovers,or at least replace the components with the right ones for the intended application.

[kevinnem]

 

Originally posted by tlbonehead There is usually no problem with having a 4 ohm low frequency and 8 or 16 ohms on the high frequency device,as long as the crossover is design to take that into consideration.

 

 

I know, .. my point was, that IF the components values are the same on each 1/2 of the cross over, then the resistive load it was designed for will be the same for each 1/2 as well.

[kevinnem]

 

Originally posted by dboomer Yes ... but once you change the drivers the crossover summation pretty much goes to hell anyways ... frequency response, level matching, etc. These things don't just fall off of trees ya know

 

 

yea, I see what you are saying, but in context of the "we have a old box, make it make noise" I think we can let seom of the details fall by the wasteside.

 

no one has even adressed the fact that the box might be totally wrong for the drivers being used.

 

Kev.

[tlbonehead]

Originally posted by kevinnem yea, I see what you are saying, but in context of the "we have a old box, make it make noise" I think we can let seom of the details fall by the wasteside. no one has even adressed the fact that the box might be totally wrong for the drivers being used. Kev.

That wasn't the question.

[dboomer]

I stand corrected, aye? .... it will make noise.

[moody]

Wow... lots of nocturnal activity.

 

I have no doubt that these boxes were originally designed for 4ohms. My problem is that they could easily have been changed to 16ohm since then (based on the homemade look of the crossovers combined with cryptic comments from the owner).

 

I know that these aren't the original drivers for the box. I have winisd and the box dimensions and it should work fine. (the speakers I had in them were missmatched between the two speakers).

 

As I said, I have a multimeter, I can measure values of components if I know what I'm measuring. Each crossover appears to be two coils and a mass of components (4 or 5) in a bunch (all glued together with thick glue, so I can't read anything on them).

 

If I don't get a decent response I'll wire them 4ohm and hope for the best. If they are set up for 16ohm what will it sound like??

[bigmike216]

If the crossovers are designed for 16 ohm drivers, and you hook it up to a 4 ohm load, the crossover points will be wildly different. It should be apparent.

[agedhorse]

 

Originally posted by bigmike216 If the crossovers are designed for 16 ohm drivers, and you hook it up to a 4 ohm load, the crossover points will be wildly different. It should be apparent.

And vis-versa.

 

You can't measure the inductance of a coil without an inductance meter. Not many coils have the value printed on them (though some do).

[Dookietwo]

If I don't get a decent response I'll wire them 4ohm and hope for the best. If they are set up for 16ohm what will it sound like??

 

Hello

In boxes for guitar it may be normal to series speakers for a 16 0hm load but in PA speakers it is rare. Series speaker boxes have a loose undampened sound with poor control of the cone. Again great for guitar but PA systems generally want to reproduce the sound as close to the source as possible. There are some out there but it is not as common as parelled cabinets.

If the crossover was designed for a 2,000hz crossover point with the 2 15's connected in parrell or a 4 ohm load then if you wired them in series to 16 ohms the "APROX" crossover point would be between 7,000 to 8,000hz.

 

2,000hz at 4 ohms

4,000hz at 8 ohms

8,000hz at 16 ohms ( Again approx)

The two 15's would be overlapping the horns area and that would cause allot of problems in the horns area.

Now if the crossover was designed for 2,000hz at 16 ohms and you wired it for a 4 ohm load it would be around 500hz aprox. There would be a big hole between the horns 2,000hz horns cutoff and the 500hz upper limit of the 2 15 inch drivers.

 

One more thing to add. It is normal to roll the bottom 15's freq response off at around 200 to 250hz so it does not interfer with the upper 15's response from 250hz or so and above. What allot of box designers do is have the bottom woofer go from say 40hz to 250hz. The next 15 does the full 40hz to 2,000hz and rolls off to the horn. Only the middle 15 covers the full 40-2,000hz. With the bottom 15 rolled out at 250hz or so the two drivers are not reproducing the same freq which is good because of the distance they are apart that would cause cancelation. Allot of speaker companies make them this way. Peavey makes a great sp4 speaker and they call this type of box Quasi 3 way if I remember right.

 

Is there any chance there was 3 wires coming out of the crossover? One for the bottom 15 , one for the middle and one for the horn?

 

Kindest Regards

Dookietwo

[ctardi]

Just go to Steel Sound (will re-direct you to MSC), and spend the $10 on a new crossover.

[bigmike216]

 

Originally posted by ctardi Just go to Steel Sound (will re-direct you to MSC), and spend the $10 on a new crossover.

 

 

Not quite that easy. He'd probably be alot worse off with one of those crappy $10 ready made crossovers.

[tlbonehead]

 

Originally posted by Dookietwo If I don't get a decent response I'll wire them 4ohm and hope for the best. If they are set up for 16ohm what will it sound like??

 

 

Hello

In boxes for guitar it may be normal to series speakers for a 16 0hm load but in PA speakers it is rare. Series speaker boxes have a loose undampened sound with poor control of the cone. Again great for guitar but PA systems generally want to reproduce the sound as close to the source as possible. There are some out there but it is not as common as parelled cabinets.

If the crossover was designed for a 2,000hz crossover point with the 2 15's connected in parrell or a 4 ohm load then if you wired them in series to 16 ohms the "APROX" crossover point would be between 7,000 to 8,000hz.

 

2,000hz at 4 ohms

4,000hz at 8 ohms

8,000hz at 16 ohms ( Again approx)

The two 15's would be overlapping the horns area and that would cause allot of problems in the horns area.

Now if the crossover was designed for 2,000hz at 16 ohms and you wired it for a 4 ohm load it would be around 500hz aprox. There would be a big hole between the horns 2,000hz horns cutoff and the 500hz upper limit of the 2 15 inch drivers.

 

One more thing to add. It is normal to roll the bottom 15's freq response off at around 200 to 250hz so it does not interfer with the upper 15's response from 250hz or so and above. What allot of box designers do is have the bottom woofer go from say 40hz to 250hz. The next 15 does the full 40hz to 2,000hz and rolls off to the horn. Only the middle 15 covers the full 40-2,000hz. With the bottom 15 rolled out at 250hz or so the two drivers are not reproducing the same freq which is good because of the distance they are apart that would cause cancelation. Allot of speaker companies make them this way. Peavey makes a great sp4 speaker and they call this type of box Quasi 3 way if I remember right.

 

Is there any chance there was 3 wires coming out of the crossover? One for the bottom 15 , one for the middle and one for the horn?

 

Kindest Regards

Dookietwo It isn't that simple though,when you are talking about 12 or 18db rolloff crossovers.

[ctardi]

 

Originally posted by bigmike216 Not quite that easy. He'd probably be alot worse off with one of those crappy $10 ready made crossovers.

 

 

Then buy the stuff to make your own.

[tlbonehead]

Originally posted by ctardi Just go to Steel Sound (will re-direct you to MSC), and spend the $10 on a new crossover.

They look pretty junky to me. I'd just replace the components with correct values or get decent crossovers for not much more than the Steelsound price.

[tlbonehead]

Originally posted by ctardi Then buy the stuff to make your own.

You can buy an Eminence 600 watt 18db high-pass model with protection for about $15. Then just put the proper coil on the woofers to roll the highs off. A 14-15 gauge coil would be under $5. Or get a Dayton Audio model 12db 2-way for under $20. Or make your own. Its pretty simple.