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#### gonar

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

what is the difference between 4ohm and 8 ohm speakers? (I know, 4 ohms! but seriously folks...)

why would you want 4ohm vs 8ohm?

why are most DIY plans ~4ohms?

why are most commercial speakers 8ohm?

I ask these questions mostly because I was thinking it would be fun to make a pair of MTM towers and am having trouble finding 8 ohm designs, and my receiver (yamaha htr-5860), while it will support 4ohm speakers, is really intended for 8 ohm commercial speakers.

#### Paul Scarpelli

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No speaker is a pure resistive load. The resistance varies with frequency. An 8 ohm speaker can be 40 ohms at one frequency, and the impedance curve can drop to 5 ohms at some frequencies. Whether a speaker is 4 ohms or 8 ohms tends to be a coarse generalization, based upon an estimate, and maybe with where the minimum impedance is.

MTMs tend to be 4 ohms (on average) and they generally use two 8 ohm woofer/midrange drivers. I suppose you could use two 16 ohm drivers to make an 8 ohm system...

Have fun.

#### bear paws

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Paul

Explain to him the diff in 4,6,8 Z and why one would use one over the other. I'm too tired.

Bear!

#### jedi.night

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I'm interested in learning this as well.

I've noticed on some receivers the Wattage doubles for powering 4 ohms, why is this?

IE. 50 X 2 into 8ohms......100 X 2 into 4 ohms?

#### ekb

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Quote:
 Originally Posted by jedi.night I'm interested in learning this as well. I've noticed on some receivers the Wattage doubles for powering 4 ohms, why is this? IE. 50 X 2 into 8ohms......100 X 2 into 4 ohms?
That's because an amplifier is supposed to look like a perfect voltage source. So if the impedance (ie ohms) drops in half, the current needs to double to maintain that same voltage. So with the same voltage but double the current you have double the power. The reason many amplifiers will not double in power is beacuse they can't supply enough current. You need a beefy amp and power supply to supply unlimited current.

Ed

#### bear paws

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OK, lets try.

Speaker are matched to the amps ability not the other way around.

THe ability of a amp is by design dictated by cost and type. Class A, A/B , D, or Mosfet. [C&F is used in radio freq.stuff] and that is a whole chapter by itself.

When "they" design a amp to meet a certain price point it dictates what "they" use for components.

The current out put is determined by the final out put transistors [ or tubes] The higher current transistors and more of them with cooling fans \$\$\$\$\$ will result in its ability to provide more current at the same voltage.

This is not a good analogy but will give you the idea. Take a 12 volt car battery and a bunch of [8] D-cell flash light batts. Both will give you 12 volts but the car batt will power a head lamp while the 'D's" barely light a parking lamp. THe head lamp has less resistance [ohms][closer to a short] draws more power than the small park bulb that has higher resistance [ohms] and draws a lot less current.

The head lamp won't be very bright , if at all, and cause the 'Ds" to get hot. "like a hernia" but the park lamp will coast on the big car batt. burn at full rated brightness BUT give you a lot less light than the head lamp on the car batt.

Ok, the amp with more and higher current out-put transistors will power lower resistive speakers without burning up the finals.

If the amp is rated down to 4 ohms than it can saftly power high draw {low ohms] speakers as well as higher ohms like 6,8,12,16, etc.

BUT the higher in ohms value you go the less power it will draw and thus for the same efficiantcy speaker you get less volume [SPL- sound pressure levels] [less light output]

Now there is theory amongst many that the higher the impedance [ohms =Z] the less harsh and cleaner the speaker will sound for a number of reasons like less chance of amp clipping [distortion]. AS in every thing else there is a point of diminishing return, where you run out of loud knob [Read as current control for now] . There is more, but thats for another day.

LIke a light bulb, if you combine 2 equal speakers in series than it will double the resistance and thus draw less current and each one will not be as bright but the combined light of the 2 will be that of 1 alone.

If you combine the 2 speakers in parallel it will draw twice the current , [be twice as bright combined as one alone but will deplete the batt twice as fast]. Create more heat in the amp that it may not be able to get ride of and you FIZZ WAP the amp.

By trying to keep it simple it does get complicated

Bear!

Consumer "commercial' speakers 8 ohm are for the vast majoity of amps on the market and can easyly be driven by 4ohm type amps.

Most, not all, DIY amps are 4 Z because the cost is within reason to get the higher current and a great many are Mosfit type. [cheap good and easy] but may not satisfy some "audiophiles" golden ear bone. [They hear things I never knew existed]

#### ekb

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Isn't it MOSFET (ie Field Effect Transistor)?

Ed

#### bear paws

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 My finger was getting tired.

Bear!

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