Speakers in serie, what happens to SPL ?

[WrineX]

ok quick and maybe stupid question but i really dont know exactly ! and could not find a simple conclusion on the net.

The thing is is there SPL gained when putting them in serie ? i got one speaker that is not loud enough to get allong with the rest, paralel is not an option because the DC resistance is already 1,5 ohm.

in paralell its 3dB i gues

or when putting in serie i just improve powerhandling?

[pjpoes]

it's a bit of a complicated topic, so this is an overly simplistic answer.

Yes, it will increase the output for a given wattage. Basically, if you mounted two woofers in close proximity and wired in parallel, you would gain (relative to the other drivers in the system) 3db's for the doubling of woofers, and 3db's for reducing the impedance. The logical conclusion of a series system is that it's the same, no net gain, as you have 3db's for double woofers, and -3db's for increased impedance. What really happens though isn't consistent with this, and you would end up with a small amount of gain (expect less than 3, but more than 1).

Now as to the issue here, what woofer are you using with a 1.5 ohm dc resistance, and in what type of system? I think a better explanation will help others help you. For instance, if this is a car subwoofer, which I suspect it must be, and it's connected to it's own amplifier, then that changes things drastically as compared with a woofer in say a 3-way system.

If this is a subwoofer designed for a car, you may be asking it to do something it wasn't intended to do. These woofers are typically designed with high moving mass and high BL, allowing efficient bass in a small box. However, they are pretty inefficient as compared with other drivers for the rest of the range they can cover. They also have high coil inductance typically, making their upper range quite limited. If it's being used as a sort of powered subwoofer and isn't keeping up with the mains, then turn the amp gain up. If the woofer is incapable of keeping up with the mains, then you need more cone area, and two woofers will give you that. The increase in efficiency and sensitivity gained from using two woofers vs one in a powered subwoofer is really somewhat arbitrary to the overall issue I have described here.

[PeteMcK]

I think pjpoes is correct, but he's assuming the impedances of the drivers in series are the same. If they're different, you're going to have the power shared in proportion to their impedances (ignoring any acoustic differences due to different surface areas..)

[WrineX]

sorry for the lack of info,

its a little ribbon i tried , with low power magnets, so SPL is not that great, in the range of 80 dB or something. i whas wondering if i stil could use it for something if i used more. but this is a dead end because the more units ill use the more i increase the weight as well. wich is the reason to use a ribbon .

but thanks allot for your quick reply !

[cuibono]

Originally posted by pjpoes
The logical conclusion of a series system is that it's the same, no net gain, as you have 3db's for double woofers, and -3db's for increased impedance. What really happens though isn't consistent with this, and you would end up with a small amount of gain (expect less than 3, but more than 1).

Would you talk a little more about this? I have been thinking of putting two Eminence Alpha15a in series because they have a Re of 5.88ohms and I didn't want to try driving a 2.95ohm load. I had assumed that although there wouldn't be any net gain in output for a given input level, I would gain 6dB of 'headroom' - ie, my maximum output level would be doubled. Would someone talk a little more about the details here?

[planet10]

Double the number of drivers (assume they are the same) you gain 3dB of efficiency. Series or parallel doesn't matter. Power handling doubles.

Connecting in parallel halves the impedance. Connecting in series doubles the impedance.

Now what does the amp do with the change of impedance?

If it is a "perfect" voltage amp, power doubles when the impedance halves, power halves when impedance doubles, so parallel gains 3dB and series loses you 3dB.

Because a lot of voltage source amps current limit into low impedances this needs to be taken into consideration. (distortion most often increases as impedance drops as well).

If it is a "perfect" current amp, powerhalves when the impedance halves, power doubles when impedance doubles, so series gains 3dB and parallel loses you 3dB.

If you have a transformer coupled tube amp, with the load connected to the proper taps, power remains unchanged.

If you have an OTL, they don't like low impedances and there is a range where they behave much like a current amp.

dave

[pjpoes]

Originally posted by WrineX
sorry for the lack of info,

its a little ribbon i tried , with low power magnets, so SPL is not that great, in the range of 80 dB or something. i whas wondering if i stil could use it for something if i used more. but this is a dead end because the more units ill use the more i increase the weight as well. wich is the reason to use a ribbon .

but thanks allot for your quick reply !

Dave's answer is, of course, a better and more detailed response to your question than mine. The reason I stated relative to the other drivers was for precisely the reason he describes. However, my description was based solely on typical solid state amps, which typically are closer to a voltage source.

Ok now that I know what you are using, a ribbon, the low impedance does make sense, and the issue is more clear. If you add more ribbons, it won't increase the mass of the diagram at all. Each magnet will act on the same mass as before, you are just increasing the overall radiating area. I see no problem with adding ribbons, this is commonly done in ribbon based line arrays.

Now, given the popularity of using ribbons with tubes, I have to ask, what is the amplification? I assumed it to be a solidstate amp given the low impedance (Tube amps don't typically do well with such low impedance), but I now see that assumption was wrong. If you are using a tube amp of pretty much any type short of a solid state output unit, I would strongly recomend using multiple ribbons all in series. You will see an increase of 3db's (roughly) per driver, and an increase in output due to the higher load the tube amp is now seeing. They get along with 16 ohm loads quite nicely, but you will need ten of them.

Another issue that is going to now arise is that, if you due end up with a line array of tweeters, their dispersion becomes quite different. I'm a fan of the Bessel array, or concepts similar to it, and feel it offers better sound and better phase response.

If you have no desire to do an array, or an array doesn't fit your design goals here, you could get away with just 3 and probably work the rest out.

Oh I just realized something else about your comment I hadn't thought about. It sounds like your comment concerning "Keeping up" was more about increased total output, rather than the change in efficiency (how I interpreted it). As Dave said, you always get the 3db increase in maximum clean output for every increase in drivers. If using tube amps, you will see something more like 6db's. Additionally, this max output problem may also be due to increased distortion from the tube amp trying to drive a low impedance load. Even solidstate amps typically produce lower distortion into higher impedance loads. What I consider the most important area to look at, the first watt (really the first 1/100th to 1/10th) is most effected, probably due to increases in switching distortion at lower impedances.

[WrineX]

wow, thanks for the reply, i dont gone use the ribbon i think, it sounded pretty decent but the ribbon has to be around a few meters to get a normal load of 4 ohm haha i got the magnets for it, but as said before they are verry weak, and maybe not ideal for this task. i saw everybody making ribbons with Huge neodyms, and beacuse i had allot of the flexi type magnets from magnepan laying around. i thought wy not try it, and when spl is to low just stack, maybe can even make fullrange if enough ribbon used side by side in series.

but although your saying it wont ad to the weight for each magnet , it will turn out in a speaker that has a high total mass wich i believe is not a good thing but i migth be wrong here.

[oaristys]

Hello all,

I have a question in same subject.

I have two 8 ohm woofer in parallel one side of crossover and a 4ohm tweeter other side.

So the two sides are in parallel. Is that meen a total of 2ohm ?

Now i use a testing vintage solid state amp. But when the fine tune will be done, i will drop in my Shanling STP-80 tube amp. I need to know what plug use. The 8ohm or the 4ohm.


And is it my 4 ohm tweeter cut my loudspeaker total SPL ?

[pjpoes]

Writex: Sorry, I continue to be confused by your response. I didn't realize you were making these ribbons. If you increase the size of the ribbon, as in, make one continuous larger ribbon then, yes, it will increase the mass. This can cause problem with high frequencies, but I've never built a ribbon, and I'm no expert. If you make a series of 2" ribbon diagrams all with the same magnet structures, then the mass for each "system" doesn't increase, and there would be no problems.

Oaristys: Your confusion is very understandable. Think of it more this way. The crossover makes it so the amplifier only can "see" each driver within a given bandpass, set by the crossover. Basically what happens is that the passive crossover, a reactive device, hit's a knee point, the crossover point, where the impedance begins to increase sharply. This means that the amplifier see's something like a 8 ohm load from the low end of the driver up till say 3khz where the crossover is. Then it begins to increase until the load on the amplifier is so high that no appreciable power is being produced, and thus, the driver is no longer producing sound. The tweeter works in reverse, at low frequencies the load is so high that no power is sent to the tweeter, and as frequency raises, it's load comes closer to the drivers actual impedance until around the crossover point, where it will be, roughly, 8 ohms. This is very simplistic, but I think is fine to explain how crossovers function, and why your amp is not seeing a 2 ohm load.