Hi,
I am currently desiging some crossovs for a 3 way set of speakers I am building. I need a question answered that I cant use my powers of google to find.
My Low sections has 2 x woofers in series both are 3.7ohm resistance for a total of 7.4ohms resistance.
My questions is when desiging the x-over for the low section do I use the total resistance for the speakers (i.e. 7.4) or the resistance of an individual speaker (3.7)
thanks>
I am currently desiging some crossovs for a 3 way set of speakers I am building. I need a question answered that I cant use my powers of google to find.
My Low sections has 2 x woofers in series both are 3.7ohm resistance for a total of 7.4ohms resistance.
My questions is when desiging the x-over for the low section do I use the total resistance for the speakers (i.e. 7.4) or the resistance of an individual speaker (3.7)
thanks>
Thanks for the replies.
What is the reasoning behind not wanting to run the woofers in series?
I will need to run omething in series as 3 x componets in parellel (8,5,8 ohms) would give a load of only 2.2ohms which would blow my amp.
You better do it in parallel if there is no issue with impedance. With parallel you get more efficiency and probably more.
The reason to put in series is to prevent the impedance of the speaker to go very low. Four ohm woofers are usually must go with series to give the "standard" 8 ohm woofer. If you put it in parallel it will be 2 ohm or so.
Many amplifiers cannot handle low speaker impedance. Or huge amount of current will be drawn from the amplifier, causing heat and transistor destruction.
The reason to put in series is to prevent the impedance of the speaker to go very low. Four ohm woofers are usually must go with series to give the "standard" 8 ohm woofer. If you put it in parallel it will be 2 ohm or so.
Many amplifiers cannot handle low speaker impedance. Or huge amount of current will be drawn from the amplifier, causing heat and transistor destruction.
You are missing how passive crossovers work. Here is impedance of a speaker with a 2-way crossover. The blue line is the woofer impedance with the crossover in-circuit, and the red is the same for the tweeter. The black line is the total impedance. You can end up with the drivers essentially in parallel over some ranges (and thus too low impedance) if the crossover is not designed well, but it's not how it's supposed to work.
This is a totally separate issue from series/parallel when you are trying to use two drivers as one driver, i.e. play the same frequency range as each other. When you're doing that, you treat them as one driver, with combined impedance, and a crossover for that impedance.
An externally hosted image should be here but it was not working when we last tested it.
This is a totally separate issue from series/parallel when you are trying to use two drivers as one driver, i.e. play the same frequency range as each other. When you're doing that, you treat them as one driver, with combined impedance, and a crossover for that impedance.
re:"What is the reasoning behind not wanting to run the woofers in series?"
- for guitar or PA systems, small variations in Re will mean uneven power handling, which may lead to catastrophic failure. For domestic systems, this shouldn't be a problem
... unless you like it really loud....
But Moondog's right, when calculating your low section use twice the impedance value of the speaker AT THE CROSSOVER FREQUENCY... you'll need an impedance graph of the driver to get this...
- for guitar or PA systems, small variations in Re will mean uneven power handling, which may lead to catastrophic failure. For domestic systems, this shouldn't be a problem
... unless you like it really loud....
But Moondog's right, when calculating your low section use twice the impedance value of the speaker AT THE CROSSOVER FREQUENCY... you'll need an impedance graph of the driver to get this...
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Hi Jester,
You have DC resistance measurements. They will not be very useful for crossover design in and of themselves unless you have some plans to extrapolate from that data, combined with other data, some realistic impedance around the intended crossover.
I'd be willing to bet that the impedance you will want to use for component selection will actually be quit a bit higher than ~8ohm. Learn to use a crossover simulation program for best initial results.
Eric
You have DC resistance measurements. They will not be very useful for crossover design in and of themselves unless you have some plans to extrapolate from that data, combined with other data, some realistic impedance around the intended crossover.
I'd be willing to bet that the impedance you will want to use for component selection will actually be quit a bit higher than ~8ohm. Learn to use a crossover simulation program for best initial results.
Eric
Speaker impedance is a function of frequency. But you can get the "picture" from woofer impedance. 3x 8 Ohm in parallel is 2.67 Ohm by the formula 1/Rt = 1/R1 + 1/R2 + 1/R3.
Too low or not it depends on your amplifier. Tube amps have different requirements than most solid state. Solid state amps also have different requirements.
With lower impedance load, most solid state (not all) will give more power, more distortion. But it is because of the more power the amp may go into destruction. But certain system (usually car amps) can accept quite low impedance load. And some subwoofer amps are designed to handle 2 Ohm load or less.
If your amp is using STK chips, Sanyo recommend a minimum of around 6 Ohm. Four Ohm and without sufficient heatsink the chip will get very hot (high volume of course) and may burn out.
Amplifiers that can handle low impedance load usually has parallel output stage.
Parallel is better soundwise (as long as the crossover is correct), as long as you can accept the consequences with your amplifier.
It is a little more complicated than that, the amplifier sees the total impedance of each driver AND each crossover so the drivers are not really all in parallel together at all frequencies, have a look at the posted impedance plot posted earlier
Amplifier will reproduce music. Music consists of sounds of varying frequency. For high frequency signals (treble) speaker impedance is very high. For low frequency signals (bass) speaker impedance will be lower (in average). So from the "security" point of view, the lowest impedance is what you may be interested with.
Security is one thing. Another thing is you want to design a crossover to "blend" woofer with tweeter. There are many considerations here. For example, in the process you may find it easier to accomplish the job if the tweeter and woofers have similar impedance and sensitivity.
Security is one thing. Another thing is you want to design a crossover to "blend" woofer with tweeter. There are many considerations here. For example, in the process you may find it easier to accomplish the job if the tweeter and woofers have similar impedance and sensitivity.
Hi,
The trouble with the "powers of google" is it invariably leads to
descriptions of how to design speakers and x/o's by halfwits
who don't even know they are going about it the wrong way.
Good 3 way design is a complicated business, anyone asking
such a basic question is simply in way over their head, if they
are trying to design and make a high quality speaker design.
rgds, sreten.
Possibly in over my head but I have to start somewhere and am trying to learn as much as I can before I go ahad and build them. In the past I have made some 2 way systems and they have came out allright so I want to have a go at a 3 way. (in more ways that one ;p )
So basically in parallel becuse the impendance is dynamic because of the frequeny that is being played my 3 x speakers will infact be more than 2.6ohms and won blow my amp(yamaha) that needs a min of 4 ohms? Is that about right?
So with that in mind with 3 x drivers 8,8,8 ohms in parallel and the xo as well it should nomally be above 4 ohms
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