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Fuse Protecting multiple speakers

Manchophile

Manchophile

New Member
Hi everyone. I am new to this forum so be easy on me. I know just enough to get in trouble.

Any speaker gurus out there, this is for you. I have a Phase Linear 400 II and I want to hook up multiple speakers. 4 pair to be exact. If you are not familiar with the Phase Linear it only has contacts for 1 pair of speakers. If I run the 4 speakers in parallel using the given contacts, does the equation I = sqrt(P/4R) work as I think where the power is the total power of all speakers or would it be I = sqrt(P/(x)R) where x is the number of speakers? pairs of speakers? It might be a dumb question but if 4 is a constant and P is the sum of all speakers in parallel then I am ok. I just want to make sure that when running speakers in parallel and fuse protecting them on the + terminal I would add the total amount of power of all speakers in parallel and just use 4R(in my case 32 since all speakers are 8 ohms) in the equation. Also, is the speaker power (P) in the equation the Maximum Input Power or Rated input power? I have sansui 2500's, and it says 80 ohms. Other speakers I have give two former values.140 ohms and 70 ohms respectively. Thanks in advance.
 
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What does that mean?
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Whoa, whoa. You're in for a world of hurt if you try to hook them up that way.

The number of speakers connected to an amplifier does not increase the amount of power available. The total output power is determined by the speaker impedance and the power supply of the amp (not to mention the actual design of the amp). Now, if you connect a pair of speakers in parallel to an amp, in theory you double the amount of power that the amp is capable of outputting. However, very few home amps are capable of doubling their output when your halve the impedance (many car amps can do this, up to a point, because they are designed to work with lower impedance speakers). The amount of power seen by each speaker will be some fraction of the total output of the amp, but this probably isn't that important anyway (see below for more)

What you really need to worry about is the impedance that the amp will see. If you connect four pairs of speakers in parallel, assuming they're all 8 Ω speakers, you're talking about a 2 Ω load seen by the amp. I doubt your amp will react kindly to that. In your situation, you have at least two ways to do this:
  1. Connect the speakers in a series/parallel arrangement. Connect each pair in series, then connect the pairs in parallel. If all the speakers are the same model, this will work fine. Each speaker will get 1/4 of the total amp power. If the speakers are not the same, you will probably end up with different volumes at the different speakers.
  2. Get a speaker switching system that allows you to maintain a constant impedance even if you have multiple speakers connected. The Niles SS-4 is one example. More expensive models have separate volume controls for each speaker.
Now, the reason that the total power seen by each speaker isn't that important is that you've got a 350 watt amp. Even with 85 watts being sent to each speaker, that's probably more than you're going to need (and if it's not, I suggest you consider using multiple amplifiers). If you think you need more than that, you might tell us what your application is and the models of the speakers.
 
Woodj, is right. If you hook 4 sets of these Sanusi speakers in parallel and attempt to put any power to them, your problem isn't fusing to protect the speakers. Your amp will struggle with this awful load and possibly take out the output transistors.

The way to do this and protect your amp is to wire two pairs of Sansui's in series. You can then safely wire these series connected pairs in parallel. Resulting impedance would then be 8 ohms as opposed to 2 ohms.

Regards,
Jerry
 
Manchophile said:
I have sansui 2500's, and it says 80 ohms. Other speakers I have give two former values.140 ohms and 70 ohms respectively.
Click to expand...
Just noticed this at the end of your OP. I think they probably say 80 watts/140 watts or 70 watts. No home speaker is going to have an impedance that high. The highest I've ever seen is 32 Ω, and that's pretty rare. Most speakers have impedance of 8 Ω. A little more rare is 6 Ω or 4 Ω. Some older (i.e. from the 1950s or 60s) speakers were 16 Ω.
 
ok guys. I got it. Your a tough crowd. I knew this would happen.

Let me simplify so I can get some help instead of popcorn watchers and blue smoke comments. I want to fuse speakers so i do not blow them as the Phase Linear documentation and research done has me inclined to do so. I have not heard back from a member that makes a circuit that protects speakers yet and I want to hear the the thing work. I have a pair of sansui 2500's ( Max power 80W and 8 ohms). I have a pair of Coral BX1000's (Max power 50W and 8 ohms), I have a pair of Wharfedale W25 (max power25W and 8 ohms). I also have a pair of kenwood (Maximum Input Power and Rated input power of 140W and 70w respectively and they are 8 ohms). I have a phase linear 400 and a Kenwood kr4070 amp receiver(40WPC). For now I have the signal from the headphone jack of the receiver to the phase linear input. I was ASKING about the equation variables and I included the instructions on wiring in series and how they said to fuse. I assume you all know the equation. I am planning on getting a pre amp to control the volume and planning a lot of things of which I would really appreciate your help if I ask. From my conclusion on my arrangement I see a total of 225W of speakers wired in SERIES with all of them being 8 ohms. If I do the equation I get a fuse coming off the phase linear of 2.65 Amps. My question is simple. Am I doing this right? I attached the phase one fusing guideline. Thank you again.
 

Attachments

If you just want to connect one pair at a time to hear the amp work, you don't need a fuse if you exercise some common sense:
  1. Make sure all your connections are clean and corrosion-free (especially between the amp and the receiver). This especially applies to the input jacks on the amp.
  2. Make sure your volume control doesn't produce any static (hook up a pair of speakers to the receiver and turn it on with no input, then move the volume up and down. You should hear nothing)
  3. Don't make any connection changes with any of the equipment powered on
  4. Keep the volume at a reasonable level
Power ratings on speakers are almost completely meaningless. What can kill speakers is peaks or distortion ("clipping") due to underpowering. With that amp you won't have to worry about the latter, but the former can be caused, even at lower volumes, by noisy controls.

ETA: OK, after having thought about your question for a while, I've finally figured out how to answer it. The problem is that your post was confusing and inconsistent with your later post (first you mention parallel, then series). In any event, keep in mind that the fuse is to protect the speaker, not the amp, so if you want to hook up multiple pairs of speakers, you should fuse each speaker separately based on, if you like, the stated power handling of that speaker. The problem is that fuses won't always help you - the rated value may prevent you from overpowering a woofer, but not necessarily a tweeter, which requires a fraction of the power (I'm surprised more speakers don't have separate fuses for each driver).

At any rate I believe the conventional wisdom is to use fast blow fuses, since some peaks may be high enough to melt a tweeter's voice coil but too fast to trip the fuse.
 
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Thank you swechsler. I have done all that. I would like to hear all three sets of my speakers (not the kenwoods as they are not vintage) at once real loud. Can I just hook up as attachment says + 1 more set with a fuse for my OCD and Paranoia? So that would be a total of 175 W of speakers? I will just add on more set to the diagram ilustrated in instuction and then get the proper equipment. Thank you.
 
Manchophile said:
Thank you swechsler. I have done all that. I would like to hear all three sets of my speakers (not the kenwoods as they are not vintage) at once real loud. Can I just hook up as attachment says + 1 more set with a fuse for my OCD and Paranoia? So that would be a total of 175 W of speakers? I will just add on more set to the diagram ilustrated in instuction and then get the proper equipment. Thank you.
Click to expand...
I think I already answered this in my edited response, but as long you keep the impedance >= 4 ohms and fuse each speaker separately you should be fine.
 
I guess my simple most basic question is if I hook speakers up in series does the equation work with total power of all speakers for fusing? I am dyi ng to hear this thin g crank.
 
Manchophile, you forgot the little detail that your 4 pairs of speakers are all DIFFERENT!

You realize that when you start putting these speakers in series the chances they will sound anything like the manufacturer intended is remote at best. Even when you put them in parallel, you have no way to balance anything. I mean they'll sound OK, but one set will dominate over the other.

That drawing will only allow you to connect 2 set of speakers to the Phase Linear. So, I guess you'll connect the other two to the Kenwood.

Just be careful with the headphone connection to the PL. The voltages on the headphone outputs are way, way higher than the typical line voltages that are applied to the PL inputs.

Jerry
 
dont get so hung up about supposed speaker power ratings and concentrate on the speaker impedance matching to the amplifier .. my test speakers are something like 40w or 60w 6 ohms aiwa bookshelf and have handled 600 watts without a problem . short periods only .mainly my ears at risk there ..
as mentioned earlier a series parallel arrangement to wire the speakers is a good way forwards ... i did make boxes to do just this for my pa system .
 
Here is another problem that you may not have considered. Fuses can't tell the difference between AC and DC. When an amp clips, it likes to send DC, which blows up speakers by melting the voice coils.
 
Did you look at the attachment? It shows two pairs of speakers being fused on + terminal. It does not say anything about them being the same speaker or the same watts per the equation. I think everyone is missing the point here and I do not mean to be condescending or act like I know what I am talking about. How about this.
1. I like vintage equipment
2. I have speakers with different Watts. ALL ARE 8 Ohms.
3. I would like to use my PL with some or all of them. Whatever is safe. Darkblue is obviously just an antagonist and he has had nothing to add but negative comments and cliche stuff found on speakers and amps for dummies.
4. What would be the best solution to add the PL into my listening experience. I am fine with whatever is logical and safe. I am smart.
5. Should I ditch the speaker fusing and just use my common sense? IE, just manage my volume and my common sense? I want to be happy and listen to loud music. I have what I have and have to work with it. It is a problem and can be solved. If my phase linear can only control two sets of speakers in series of the same manufacturer then so be it. I can use in basement and line feed off the pre amp. I can use other two off kenwood and be happy.
6. I am looking for a solution. I wish I was as smart as you guys but at least I am not stupid and can take constructive criticism. Not negative.

Thank you again

Mike
 
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