Author Topic: Series/parallel (Read 268 times)

gbarchus · « **on:** November 13, 2005, 06:46:38 PM »

I'm interested in a 4X10 cabinet and am wondering if there is any audible difference between a cabinet that's wired all parallel (four 16 ohm speakers to get a 4 ohm load) and one that's wired series/parallel (four 8 ohm speakers to get an 8 ohm load). I'd like an 8 ohm cabinet to be able to add another if needed. My amp (eden vt300) will only go down to 4 ohms.

kmh364 · « **Reply #1 on:** November 14, 2005, 06:17:38 AM »

There shouldn't be much difference in sound speaker-wise within a single speaker cab RE: parallel vs. series wiring, but the amp may change sonically. Adding another cab (parallel load) will change the sound and apparent volume level.

Ohm's law mainly dicates here. The lower the overall impedance of the load an amplifier sees, the easier it is to produce higher power outputs, to a point. Output current will increase as well. Some amps, like my Eden WT-550, can safely drive 2 Ohm loads (i.e., two 4 Ohm D-210XST cabs in parallel), and others cannot produce the current required at that impedance. Remember, that impedance specs for a loudspeaker or speaker array is an average. A loudspeaker is a reactive load, meaning impedance changes with frequency. I have old Infinty IRS Kappa 9 loudspeakers rated at 4 Ohms nominal that drop to an output device-melting 0.5 Ohms at 50hz! Not every amp can deliver the current required without blowing the mains fusees, activating thermal protection, or destroying the output transistors.

Damping factor (i.e., the ability of the amplifier to 'control' the excursion of the drivers) tends to decrease as output impedance decreases, meaning flabbier speaker response. This may be a good thing, if the resulting sound is desirable.

There are other factors as well regarding loudspeaker loading and it's effects on amplifier behavior, but I think you get my drift. FWIW, I'm an electrical engineer (power) and a hi-fi/MI/electronics nut, but I'm not an audio engineer. This is a club site not an AES forum, so there you have it, LOL!

In short, paralleling cabs will tax your amp a little more, but you will get an apparent increase in volume due to increased overall driver area and increased peak power output of the amp. Remember, every increase of 3dB (i.e, a clearly appreciable/perceptible increase in volume level) in loudness requires a DOUBLING of amplifier output power. In other words, a 600W amplifier output is NOT twice as loud as a 300W amplifier output, all things being equal. The resultant reinforcement and/or cancellation at certain frequencies with two cabs paralleled will certainly change your sound as well, so experimentation is the order of the day, LOL!

Enjoy!

Kevin

gbarchus · « **Reply #2 on:** November 14, 2005, 06:31:31 AM »

thanks Kevin!

I have this perception (not based on theory) that the flow of current is distributed more efficiently if the speakers are wired in parallel. I may not have a good grasp of the concept, but if the speakers are in series, the current would run through one speaker first and then on to the next. Whereas, in parallel, they both get the power at the same time. Maybe I'm trying to get at something that doesn't exist.

kmh364 · « **Reply #3 on:** November 14, 2005, 08:13:42 AM »

Not quite, but you're part of the way there. Don't confuse voltage (=V, in Volts), current (=I, in Amperes) and power (=P, in Watts). Ohm's law states that P = VI, where V = IZ (Z=Impedance, in Ohms).

In a parallel circuit, the voltage across each 'device is constant, but the current varies (Kirchoff's Current Law, or current divider). In a series circuit, the current through each device is constant, but the voltage across (i.e., voltage drop) each varies (Kirchoff's Voltage law, or voltage divider). As such, in a series circuit each device sees the full amount current flowing in that circuit. In a parallel circuit, current is divied up amongst the elements in the circuit. What does happen is that the impedance is additive in series circuit elements (i.e., Ztotal = Z1 + Z2+ Z3...), and is proprtional in Parallel circuits (i.e., 1/Ztotal = 1/Z1 + 1/Z2 + ....). In other words, two 8 ohm speakers wired in series are equivalent to a 16 Ohm load. The same two 8 Ohm speakers wired in parallel result in a four 4 Ohm Load. The difference in total impedance affects the max. power produced by the amplifier. That's the main difference. In a multi speaker array, like a 4X10 cab, you'll find they wire some drivers in series and some in parallel, depending on the nominal impedance desired. As you might imagine, this is called series-parallel wiring.

Confused yet? LOL!

(Message edited by kmh364 on November 14, 2005)

(Message edited by kmh364 on November 15, 2005)

j_gary · « **Reply #4 on:** November 14, 2005, 03:51:59 PM »

OH YEA! I CAN LIFT AN AMPEG 810 CAB ALL BY MYSELF, NA NA NA!!! ( Once )

Jeeze Kevin, you keep that stuff up your gonna have to start playing a six string. If you only had one arm I'd want you in my band.

So if I'm following you correctly, (not a chance) if you are sending power to two cabinets from one amp, you would be wiser to run two speaker cables from the two individual outlets rather than powering both from a single outlet.

BTW, would you have the skinny on speaker cable vs. instrument cable? I think I knew once, but now I cannot tell them apart at times.

Thanks, Gary

lbpesq · « **Reply #5 on:** November 14, 2005, 04:21:05 PM »

IIRC instrument cable is shielded, speaker cable isn't. Do I have this right?

Bill, tgo

David Houck · « **Reply #6 on:** November 14, 2005, 04:40:05 PM »

Bill; yes, that's it!

bob · « **Reply #7 on:** November 14, 2005, 09:38:43 PM »

Umm, I'm not exactly an EE...

Yes, instrument cables are usually shielded, to protect the very low level signal.

But I think the more critical factor is that speaker cable has to carry lots of current - possibly enough to fry an instrument cable and/or the connectors.

So using a speaker cable on your instrument might not sound so great, but an instrument cable to your speakers could be downright dangerous.

I think???

gbarchus · « **Reply #8 on:** November 14, 2005, 11:14:06 PM »

I guess it would be possible to run two 4 ohm cabinets in series (with some kind of external box). I guess the problem is having too many connections. Again, I have the perception that the shorter the distance and more direct the contact is best between speakers and amplifier. I COULD internally wire the two output jacks in series on my amplifier but then I would always have to use two cabinets.

I'm still not sure where I get the idea that four 10 speakers would sound better if they were all wired in parallel rather than a series/parallel configuration.

Wouldn't an instrument cable have a much higher impedance than a speaker cable which would have an effect on the amplifier. Intrument cable is not a very thick gauge, which is more efficient for bass. Also speaker cable is not shielded and wouldn't work for an instrument without a lot of noise.

I appreciate everyone's input!

Gale

keith_h · « **Reply #9 on:** November 15, 2005, 05:09:11 AM »

You need a shielded cable for an instrument to avoid noise. These days the better ones are made from wire/insulators designed for musical instrument use.

Speakers need cables capable of carrying high currents. The high signal level precludes the need for shielding. I use 12 gauge cables for all of my speaker connections. The ideal situation is to use as short a cable as possible and as heavy a gauge as you can to avoid power loss in the cable. For a short run (

kmh364 · « **Reply #10 on:** November 15, 2005, 05:27:28 AM »

Gary:

You mean six-string bass? I already play guitar (I'm primarily a guitarist that also pretends to be a bassist), LOL!

It's not necessary to run TWO separate cables from the amp, i.e., one to each cab...remember my diatribe above...the speaker connections at the amp AND at your cabs are in PARALLEL, not in series! It matters not weather you have two separate speaker jacks on your amp or one (per channel). As long as your cabs have PARALLEL jacks on the back, you can cable from the amp to the first cab, and then from the first cab to the second cab, etc. Just use the highest quality, heaviest guage cable you can find. Oh yeah, and if possible, do like I do and use SPEAKONS wherever practicable. They are, unlike 1/4 phone jacks, designed for high current connections/transmission (and they positively lock in place, which is a nice bonus). I not only use 'em on my Eden bass amp rig exclusively, but I also have 'em on my new Custom Straub Cantus Hot-Rodded Plexi style tube guitar amp half-stack (with the custom matching greenback-loaded cab by Sultone for Straub) which I use exclusively, even though I have locking Neutrik 1/4 jacks as well (for a backup just in case a speakon cable goes bad, and only a phone jack-equipped cable is available).

(Message edited by kmh364 on November 15, 2005)

kmh364 · « **Reply #11 on:** November 15, 2005, 05:36:38 AM »

Gale:

I reiterate Keith's comments: You DON'T wanna mess with the internal amp wiring. You can rewire a cab anyway you want to change the overall impedance. Just bear in mind that the dual jacks on any cab are in PARALLEL. You would have to break the internal connection between the two jacks and wire them separately. Make sure you do your math if you attempt to modify the speaker wiring. Too much impedance will give your amp a hard time driving the load (and reduce power output), to little impedance and the excess current required could fry your amp.

Keith: Thanks for the additional comments. I forgot to mention about the power dissipation of each element in the circuit. That's why you can use 25W Celestion Greenbacks in a 4X12 cab with a 50 or 100W Marshall head, LOL!

kmh364 · « **Reply #12 on:** November 15, 2005, 05:47:37 AM »

There's a nice discussion on the WeberVST speaker site RE: wiring spekers for different nominal impedances. Click on the link below, and go to the Let's Talk Speaker FAQ section and scroll down. There's a diagram to help understand the answer.

http://www.tedweber.com/

BTW, If you're not familiar with them, Weber makes some outstanding MI speakers, especially modern takes on old, discontinued gems, for reasonable prices.

keith_h · « **Reply #13 on:** November 15, 2005, 06:08:42 AM »

Kevin,
I also use Speakons on my newer cabinets. My older stuff is all 1/4 but Neutrik makes a plug that will handle 12 ga wire so I use those.

Keith

bassdr · « **Reply #14 on:** November 15, 2005, 09:24:25 AM »

I prefer double banana plugs in my rigs when possible- you can stack them to achieve parallel conections and they have excellent surface contact which minimizes resistance. I also use Speakons or the old Hubble twistlocks. 1/4 jacks just do not have the surface contact and are generally less reliable in hostile environments- like playing parties and Bars Michael (Flame Koa Essence)