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need help! 8 ohm amp, and 4 ohm speakers, can it work?

Discussion in 'Monitoring / Headphones' started by Auxsam, Apr 5, 2005.

  1. Auxsam

    Auxsam Guest

    hello all,
    I know it isnt the most interesting topic, but i have an 150 watt amp with a load impedance of 8 ohms and i just got event 20/20's and they are 4 ohm speakers that peak at 200 w. Is there any way i can wire up these speakers to that amp with hurting either one? i know in series the ohms add up, but can i do that with a stereo power amp? wouldnt that work with only the right side or left side of terminals? i need help because i desperately need to know if i need to buy another power amp. any advise is much appreciated! thank you
    S
     
  2. TeddyG

    TeddyG Well-Known Member

    The Event 20/20 manual says "NO"! Event says you may harm the amp itself?!?!(I'm not a tech, just parroting the manual here.)

    There may be workarounds(Conversion circuitry, whatever.), but a 4 ohm amp - by Alesis, Crown, QSC, etc., would be a better(Albeit 300 to 500 dollar?) option.

    Teddy G.
     
  3. Massive Mastering

    Massive Mastering Well-Known Member

    I'd triple-check with the amp's MFG or manual if you have one...

    A lot of amps are rated at (X) watts @ (X) ohms and will work fine under a lower load. Of course, there are amps that don't like the lower loads also (Events are only 4 ohms?!? What the hell are they thinking?). You certainly don't want to cook the amp.
     
  4. Auxsam

    Auxsam Guest

    yeah, the manuals and such have been lost for years, and all i know is that the amps load impedance is 8 ohms and that its 150 w(75 a side).
    Ive searched everywhere for a manual, the amp is a technics se-9060, old unit.
    Im gonna have to buy another power amp. thank you , you guys have been helpful, i apreciate it!
    S
     
  5. TeddyG

    TeddyG Well-Known Member

    I found the manual for the speakers on the web within a few minutes of reading(Then responding to ) your first post...

    Event says: NO! No 8 ohm amp! They said it, I didn't(And neither of us sell 4 ohm amps, as far as I know..?).

    Indeed, though, 4 ohms, what were they thinking? Lots of things have gone to 4 ohms, like car stereos, ham radios, etc. Wonder why?

    TG
     
  6. Massive Mastering

    Massive Mastering Well-Known Member

    With an amp that'll drive a 4-ohm (or 2-ohm, for that matter) load, you can always go higher. You can't go lower than the rated load.

    I was asking on that amp as a lot of MFG's just give the wattage at the load but usually, they give the lowest load / highest power to impress.

    10,000 WATTS!!! peak, at one ohm - or 120 watts rms at 8 ohms...
     
  7. Markd102

    Markd102 Well-Known Member

    LOL, ain't that the truth!

    Auxsam, you really would be better off with a genuine reference amp anyway. Maybe watch Ebay for a secondhand Hafler.
     
  8. Auxsam

    Auxsam Guest

    Got another question,
    Whats up with those power amps that change impedance and wattage depending on the speakers impedance? I'd never heard about that, but sure enough i was looking at crowns catalogue and i saw many amps that had different wattages depending on the impedance it was outputting( or that the specific speakers could handle). Can anybody clear me on this? and example was the crown 402 and so im just not sure if its safe, and my speakers are new and i want to be very careful with them.
    Thanks again, Later.
    S
     
  9. Kev

    Kev Well-Known Member

    V=IR

    lower the load the more current that wants to flow.

    If the amp can deliver the current it should double into 4 and then double again into 2.

    Most amps can't and that's OK ... to a point. A 100W at 8 that then backs up with 180W at 4 is a good result and will be fine for your speakers.
    BUT
    if this amp were to drop to 120W at 4 then I feel it is under rated.

    This is not a new situation and this is also true for line level stuff at 600 ohm or bridging inputy.

    The KEY point here is CLIPPING.
    no amp clipping is permitted.
    Voltage OR Current limiting. If you experience clipping then you need a bigger amp.

    Even so your continuous RMS level need to be below the thermal rating of the speaker.

    Sorry to get all technical but this is just how it is.

    Don't let people over complicate things and the simple rules with simple tests will set you straight.
    You will be fine .... no clipping
     
  10. dpd

    dpd Active Member

    As Kev infers you'll do more damage to your speakers (primarily the tweeter) by sending it clipped (limited) waveforms. But the amp will work with your speakers. It's just a matter of how loud the speakers get - if you crank it up and it sounds distorted on the peaks, then lower the volume or risk damaging the speakers.

    As far as power amps go - they are designed to approximate a pure voltage source. What that means is, theoretically, the amp can put out infinite current without dropping voltage. In other words x watts at 8 ohms, 2x at 4, 4x at 2, 8x at 1, etc. When the amp power doesn't double each time the load impedance halves, that tells you about the power supply and/or the heat dissipation capacity of the amp.

    Amps do NOT have 8 ohm output impedances. They do NOT try to match impedances from source (amp) to load (speakers) for optimum power transfer like radio transmitters do into antennas.

    The more power capacity in the amp the better - ensures the amp won't clip, and keeps the amp as linear as possible, and as cool as possible (assuming it's not a Class A amp).
     
  11. karbomusic

    karbomusic Active Member

    Amp Safety & Why

    This is my first post here. I hope you will have me as a new member. There seem to be many intelligent people here. I just wanted to add a couple of thoughts to this post:

    The simple answer:

    Is it is best to use an impedance equal to or higher than the amps rating. Anything less causes the amp to overheat. It will work but the amp will die sooner than it would have, whether it is 2 years or 2 minutes later.

    Rule of Thumb:

    The lower the impedance than what it shoud be... The closer your amp circuit resembles a hot burner on your stove.

    The Long answer:

    less ohms = louder audio but more than sounding bad, it is dangerous to the amp due to increased heat......

    One of the biggest issues with driving lower impedance speakers with an amp of higher reccomended impedance rating is heat and the amp circuitry's ability to deal with it.

    This issue is treated differently between tube and transitor amplifiers. For both types.... As a previous poster said, less impedance or "load" = more power/signal flow. When doing this the amp will try supply every bit of power it is asked for via the lower resitance of the speakers. This means more heat due to the extra power demands and why you get more volume from the speakers when doing this. The wiring in the amp itself, transformers etc can only handle a finite amount of heat before they become red hot and burn things up. This has a lot to do with where those "use this impedance only" specs come from. Stay within them and the responsibility for failure is placed back on the manufacturer!

    With the heat in the picture manufacturers have the opportunity to do something as simple as better job of dissapating that heat, thus a lower impedance rating. Much more goes into this but in this instance heat is first order priority since "it don't matter if it's clippin' if it is on fire."

    Some of the better manufacturers do well at both manufacturing amps that will function at really low impedances as well as also under-rating those specs to give you some latitude. Thats part of the reason for those heat sinks.

    Don't trust your ears on this one. Amps and especially speakers tend to sound "the best the ever have" right before they start smoking! This is why people need lights and indicators on amps and one rare occassion when you should use your eyes and not your ears.

    Hope I didn't ramble too much... I am just returning from a 4 year abscence from the audio world so I'm using this post to start knocking of the dust!

    Best regards-

    Karbo
     
  12. dpd

    dpd Active Member

    ^^^ if you don't play it too loud then the amp CANNOT overheat. Period. The amp can only supply the power to the speakers that you tell it to with your volume control.

    Moral: if you cannot get the amp to play loud enough without audible distortion and/or excessive heat, then you need a more powerful amp.
     
  13. Davedog

    Davedog Distinguished Member

    This last bit is only partially true.It is true that the setting of the final output of a mixer or controller of some sort will limit the voltage to the amp.However, no matter what this setting is, in terms of a signal involving a program such as music, there are many types of transients that the amp will try its best to reproduce,and will try to reproduce them as called for by the wave of the transient.Large bass waves require a LOT of power to reproduce and if the amp is underpowered or is trying to drive an unmatched load at its outputs, this will also create scads of heat and in some cases a heat spike which the overload protections may or may not be able to deal with.This is a recipe for failure at a high rate and (as I have personally witnessed) some spectaculer fireworks to the tune of drivers spitting flames a few feet out on a DC spike from an underpowered amp.
    When I had serious PA gear, I didnt believe in amps with volume controls on em.Everything was either LOUD or off.
     
  14. dpd

    dpd Active Member

    Amps have both voltage gain and current gain.

    The maximum output voltage is controlled by the input signal level times the amplifier's voltage gain. The voltage can clip with no load (speaker) connected to its outputs if driven with too high a signal - frequency be damned.

    The voltage can be in the linear range and the current waveform can be clipped - causing overload and overheating. But, I think, the voltage waveform will distort when the current gets too high. Most speakers have a dip in their impedance - they aren't constant over frequency - somewhere (been too long since I've looked this up but I think it's around the resonance peak of the low freq driver?). So, the current demands on the amp are frequency-dependent which, I think, explains the issue that Davedog was describing above.

    The amp is simply not a perfect voltage source - it has a current maximum determined by its power supply and output stage drive capability. But, amps are not impedance-matched devices like RF circuits.
     
  15. took-the-red-pill

    took-the-red-pill Active Member

    2 ?'s come to mind.

    1-Could the guy get a hold of a 4 Ohm resister and wire it in, to bring it up to 8 Ohm's? What would be the negative issues in this scenario?

    2-If one has a choice, would one generally get better results, sound quality wise, by buying a much more powerful amp, and running it at 1/4 throttle, than buying an amp that is closely rated to what the speakers are and turning it to 1/2-3/4 to get the same volume?

    Jest askin'

    cheers
    K
     
  16. dpd

    dpd Active Member

    1) you will burn up 1/2 of the power in the 4 ohm resistor (assuming the speakers are a constant 4 ohm load to the amp). Forget doing this

    2) IMO, analog systems sound better when they aren't heavily stressed - so, yes
     
  17. To expand on dpd's #2 answer, amplifers are generally overrated and speakers are generally underrated. You also do more damage to speakers by underpowering them. I had to demonstrate this to MY BOSS when I was working for a car audio shop here. We took three 12" subs rated at 500/1000w (same model) and hooked them up to three amps of the same brand and similar specs rated at 400, 500, and 750 (all RMS ratings). We then split the signal from the cd player to each amp/speaker setup. We ran a THX sub test (max output on amp and just below clip on cd player) and guess which one blew first? The 400. The 500 blew shortly thereafter. We kept the 750 going for 12 straight hours before we decided that enough was enough.

    Basically, what I am saying is that power amps are generally rated at what they CAN put out while speakers are rated at what they need to provide what they say they can (like a speaker rated at 85dB output needs x amount of watts to actually put out 85dB). 99% of the time a power amp will not put out near its rated power. It's actually a good idea to use a power amp with 20% more power rated than your speaker. (For subs, I typically go up to 50% more power.) When you underpower speakers, you get distortion before you can drive your speakers where they were made to be driven.

    Oh, in case you're wondering who paid for the test, he did. The bet was covered by the loser's paycheck.
     

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