• Please note that Audiokarma will be offline briefly for updates early on Monday morning, September 28th.

impedance question?

C

chameloman72

Active Member
This might be a dumb question, but I have to ask. If I have a pair of speakers and an A + B channel selection on my amp. If I take one 8 ohm speaker and hook it to the positive of say A side left and negative to A side negative right and do the same with the second speaker on the B channels will my amp read the speakers as 4 ohm? Thanks for your responces in advance! Basically, you have left and right on A and I took positive of one speaker to the left and negative to right negative. Does this do anything to the impedance?
 
Register to hide this ad
In most (but not all) amps the negative terminals are common so it really doesn't matter if you connect to the left or right negative or A or B negative.

The B speaker outputs are merely switched off the amp just like the A outputs so you're not gaining anything by using them...except the ability to turn off the speakers independently.

If you connect both speakers to the left side A and B, it will depend on how your amp connects them as to the resulting impedance. Most A+B switches put the speakers in parallel. So, if that's what you're doing, then yes, it will be 4 ohms.

If you're connecting to Left A and Right B, then the receiver/amp will see 8 ohms just as if they were connected to A only...assuming the A+B switch parallels the speakers. If it's one of the rare ones that puts the speakers in series, you'll get no sound because there isn't a corresponding speaker on the other A or B side to complete the circuit.

Why, may I ask, are you using (or pondering) this odd style of connection?

IMHO...you should just connect it up normally. There isn't any magic (except maybe magic smoke) to be found by some odd connection scheme.
 
whoaru99 said:
Why, may I ask, are you using (or pondering) this odd style of connection?

IMHO...you should just connect it up normally. There isn't any magic (except maybe magic smoke) to be found by some odd connection scheme.
Click to expand...

Well...I am trying to lower the impedance in my two speakers to gain more power! The amp is rated 200 wpc into 8 ohms and 270 wpc into 4 ohms. Any idea as to even a possibility of doing this?
 
chameloman72 said:
This might be a dumb question, but I have to ask. If I have a pair of speakers and an A + B channel selection on my amp. If I take one 8 ohm speaker and hook it to the positive of say A side left and negative to A side negative right and do the same with the second speaker on the B channels will my amp read the speakers as 4 ohm? Thanks for your responces in advance! Basically, you have left and right on A and I took positive of one speaker to the left and negative to right negative. Does this do anything to the impedance?
Click to expand...

The impedance of a pair of speakers won't change by wiring it in a strange way. The negatives are common unless the amp is dual mono and everything is completely isolated or it's a stereo tube amp, which would have a separate output transformer for each channel and connecting the negatives will cause problems. You'll need to either accept the speakers as they are or get A) another pair to use on the Spkr B output or get a pair of 4 Ohm speakers.

Also, you need to know that a speaker's impedance can dip below what it's rated. The speaker output goes to the A/B switch before the terminals- it would need to be a 4 channel amp to develop more power by using A and B terminals. Using resistors will only waste energy and can cause other problems. I have worked on houses that had wire wound resistors attached to floor joists and the joist had a charred area around the resistor, caused by the heat. The load will drop but the result will only be heat, which is the result of the wasted power.

How much louder do you want it?
 
chameloman72 said:
Well...I am trying to lower the impedance in my two speakers to gain more power! The amp is rated 200 wpc into 8 ohms and 270 wpc into 4 ohms. Any idea as to even a possibility of doing this?
Click to expand...

You're confusing apples and oranges. The load (the speakers) connected to a source (the amp) will "draw" whatever current it will draw, based on Ohm's Law. (It's actually more complicated than that when you're talking about speakers and crossovers, but for this example it will do.) If you halve the resistance (or impedance) of the load, the current draw will double, or, in other words, the power drawn from the source (the amp) will have to double as well. If the amp can handle it, it will deliver it. If not, no.

This increase in the power drawn by the load has NOTHING to do with how "loud" your speakers will be.

When an amplifier manufacture says that its amps can deliver 200 watts into an 8 ohm load or 400 watts into a 4 ohm load, they're promising you that the amp can maintain its specifications into either load, without melting. Or going into protection, or blowing a fuse.

Nothing to do with "more power" or "louder".
 
Last edited:
Thanks guys! The amp can be bridged into mono for a whopping 580 watts! I guess I will have to acquire another one! I have a pair of JBL L150's and according to the specs they sound best with an amplifier rated at 300 wpc rms!
 
Huh?

Do the specs actually say "they sound best with an amplifier rated at 300 wpc rms" or simply that they can handle that?
 
Yeah, impedance is a complex thing. Load specs on amps and speakers are 'nominal' only. The actual value varies around this nominal rating according to frequency, mechanical movement of the voice coil within the pole-pieces, etc. Impedance is frequently confused with its rough DC equivalent, resistance.

Most high quality amplifiers, both modern and vintage will usually specify if a 2 Ohm load is safe without freaking up the output stage or tripping protection, etc.

Speakers in series will present ( nominally ) double the load on the output stage and placing them in parallel will halve the load.
 
chameloman72 said:
Thanks guys! The amp can be bridged into mono for a whopping 580 watts! I guess I will have to acquire another one! I have a pair of JBL L150's and according to the specs they sound best with an amplifier rated at 300 wpc rms!
Click to expand...

Bear in mind that it takes 10 times more power to sound twice as loud.

So, starting with your current 200w setup you would need 2,000w of power, with all other things equal, to sound twice as loud.

Going from 200w to 580w is a meaningful enough change to notice a difference, but that difference will be mostly (IMO) headroom. This added headroom should give you a "cleaner" sound when you've got it cranked up.

But, in terms of sheer volume, that 200w to 580w would result in ~4.5dB increase. Again, it's a meaningful (noticeable) difference, but not that much in terms of sheer volume.
 
whoaru99 said:
Bear in mind that it takes 10 times more power to sound twice as loud.

So, starting with your current 200w setup you would need 2,000w of power, with all other things equal, to sound twice as loud.

Going from 200w to 580w is a meaningful enough change to notice a difference, but that difference will be mostly (IMO) headroom. This added headroom should give you a "cleaner" sound when you've got it cranked up.

But, in terms of sheer volume, that 200w to 580w would result in ~4.5dB increase. Again, it's a meaningful (noticeable) difference, but not that much in terms of sheer volume.
Click to expand...

I totally understand this and it is headroom I am trying to achieve! More power better sound and less the amp has to work to achieve it!
 
Not sure which amp you have, but I'm sure you've seen the pro audio amp discussions going on here.

Pro amps are worthy of serious consideration if you're looking for big, clean power at a (relatively) reasonable price.
 
chameloman72 said:
I totally understand this and it is headroom I am trying to achieve! More power better sound and less the amp has to work to achieve it!
Click to expand...

Your existing amp may not be the right one for what you want to do. Is it an integrated amp or power amp? If it's integrated and you like the sound, your preamp section may be fine and if you look around, I'm sure you can find a good deal on a power amp that will do this. Pro audio amps are a good choice when you want headroom, in many cases.

Remember- if what you listen to is mostly recent recordings, not everything has much headroom. Many CDs are recorded for MP3 and iPods, which are not exactly HiFi, unless the player can support .wav or other lossless recordings and don't need compression.
 
I have read the thread and links

as well as this one: http://www.audiokarma.org/forums/showthread.php?t=60386
But being a none technical guy I am still a bit unclear.
Let me just ask directly,

I have the Dali Mentor 5, here are some specs.
Nominal impedance [ohms]
6
Recommended amp. power [Watts]
40 - 200
Sensitivity (2,83 V/1 m) [dB]: 88,0

I drive them with a Nad C372
2 x 150W Minimum Continuous Power into 4/8 ohms
220W, 340W, 460W IHF Dynamic Power into 8, 4 and 2 ohms, respectively

Is this to much power, not enough?
Should I have any concerns either for blowing a speaker or overheating the amp at loud sustained listening sessions?
 
Power wise, I don't think it's too much. If your looking for very loud, the choke point might be the 88dBspl @ 1m with 2.83 volts applied. Those are about medium sensitive speakers. Adding more power for more output might be a diminishing returns exercise.

That is not too much power for the speakers. really, you get into more trouble damaging speakers by having an underpowered amplifier. When the low powered (or any powered) amp clips, loads of high order harmonics (high frequencies) are generated and the high power, high frequency content heads right for the tweeters. ...making them ill.:puke:

That is a fine power for your speaks. It looks to be about 42VACrms can be delivered to the load (@ 8 ohms). If the power supply holds up, that means about ~290Watts into 6 ohms. That's plenty. You want the big power reserve for peaks. Music has a very large peak to average ratio (except the new Metallica Death Magnetic) so average power is rather low. You want to have a lot more amp (which you have) waiting for peaks.
 
You must log in or register to reply here.
Back
Top Bottom