Polk SDA 2 compatibility with Amplifier

audioluvr

invalid wrote: »

If you look at measurements from stereophile or any 3rd party you will find that the 8ohm measurements are underrated, when you have the actual 8ohm measurements it will not be double.

I have to call BS on that. When I had my B&K's refreshed they were load tested at 1000 and 10,000hz and they showed 200w @8ohm and 400w at 4ohm. He told me that other amps such as Hafler's, Aragon etc. will also produce these results.

I'd say if an amp/integrated/receiver outputs 75% more wattage at 4ohm than 8 it's probably got pretty solid current capability.

invalid

You can call BS all you want, but I'm telling you it isn't possible, it would be perpetual power, they can come close but not quite accomplish that feat.

honestaquarian

When you break it down to it’s most basic, an amps capacity to drive low impedance loads is needed. Meaning an amp that has high current capability.
Voltage drives high impedance.
Current drives low impedance.
Current times voltage equals power (but there are many variables in how that works out) into a load (ohms)
If the power supply is expected to output higher power into a lower impedance then it must have a more robust power supply (*this is where most of the money and weight in the average amp goes*) that can hold it’s voltage steady in order to be able to increase the current output into lower impedances.
Hence more power.
If the voltage sags under load (cheap power supply)then even if the current increases you won’t get more power output into lower impedances.

invalid

Try load testing it at 20hz.

pitdogg2

audioluvr wrote: »

invalid wrote: »

If you look at measurements from stereophile or any 3rd party you will find that the 8ohm measurements are underrated, when you have the actual 8ohm measurements it will not be double.

I have to call BS on that. When I had my B&K's refreshed they were load tested at 1000 and 10,000hz and they showed 200w @8ohm and 400w at 4ohm. He told me that other amps such as Hafler's, Aragon etc. will also produce these results.

I'd say if an amp/integrated/receiver outputs 75% more wattage at 4ohm than 8 it's probably got pretty solid current capability.

Basically what @invalid said as I took it is, most are tested and rated at an easy load 1khz for example. When you test at 20hz-20khz you get a whole other set of specs. What a receiver can output at 1khz can be dramatically higher than the full frequency spectrum.

Yamaha used to severely underrate their receivers. My 992 was rated at 85 watts per channel times 5. It could get a full 85 watts per channel times 5 with all 5 channels playing. In two channel it was realistically closer to 150 watt per channel. These days the magic number is like 100 times 5 or 150 times 5 and none of them can get it but just barely at two channel.
Then you see the magic * @ 1khz in 2 channel only. By the time you get 5 speakers wanting power you're at barely 40wpc.


Most amps have better power supplies and receivers are a jack of all trades and master and none it costs a lot of money to put a big power supply in a receiver and they just don't do it because of cost.

BlueFox

The Absolute Sound and Stereophile test amps using the standard power measurement standard of 20Hz to 20KHz when they measure amp power. In over 20 years of reading those magazines I have never seen them say they are under rating the 8 ohm measurements. They measure to the power measurement standard, and many amps double their power into 4 ohms. So, I will believe their measurements, and ignore invalid.

invalid

I'll use your stereophile example the krell ksa250 is 250 watts into 8ohms but it measured 325 so the manufacturer underrated it.

Gardenstater

What did the mfg. Krell say it would supply into 4 ohms? Or did they just not say?

invalid

Gardenstater wrote: »

What did the mfg. Krell say it would supply into 4 ohms? Or did they just not say?

250 watts

honestaquarian

The KSA250 is a typical overbuilt Krell amplifier.
250wpc @ 8 ohms
500wpc @ 4 ohms
1000wpc @ 2 ohms
2000wpc @ 1 ohm

Gardenstater

According to Stereophile's measurements even this SuperAmp doesn't quite make the doubling of power for every halving of impedance ideal standard:



PS: I doubt anyone who owns one is complaining much

invalid

honestaquarian wrote: »

The KSA250 is a typical overbuilt Krell amplifier.
250wpc @ 8 ohms
500wpc @ 4 ohms
1000wpc @ 2 ohms
2000wpc @ 1 ohm

This amp is a great match for the sda2A's

audioluvr

I stand corrected.

honestaquarian

@Gardenstater did you look at the voltage drop at the wall outlet that they measured when doing those tests?
It dropped all the way down to 106 volts.

Gardenstater

Yep it's right there in the spreadsheet ^^^

But I think maybe the Power should be adjusted by the ratios of the squares of the Voltages.

That would give 102.3% not 98.8 which is over 100% (maybe inaccuracies or rounding error)
73.9% not 70.9
62.1% not 53.4

invalid - too bad it costs probably 8x what someone would pay for the SDA 2A's

honestaquarian

Gardenstater wrote: »

Yep it's right there in the spreadsheet ^^^

But I think maybe the Power should be adjusted by the ratios of the squares of the Voltages.

That would give 102.3% not 98.8 which is over 100% (maybe inaccuracies or rounding error)
73.9% not 70.9
62.1% not 53.4

invalid - too bad it costs probably 8x what someone would pay for the SDA 2A's

Could you come back down to earth and speak English to us non engineering types please??

invalid

too bad it costs probably 8x what someone would pay for the SDA 2A's



Look how much more the pass labs x600 cost new compared to Darqueknights 1.2tl's. I have a ksa300s I run my sda2Atl's with. Look at it this way, a great price on a decent speaker that can be upgraded, so more money for an amp.

bynum03

Hi everyone! I’m new here, just picked up a pair of sda 2a on a whim. Hoping to piggy back on this thread a bit. All of my amps are from the 60s-70s, my most powerful is a Kenwood ka 907 integrated, then a realistic sta 2100 receiver , then pioneer sa8800 integrated, etc. I was hoping that the ka 907 would be a good option here but I believe it is dual mono, I could be wrong but kinda don’t want to take that chance. From what I’ve read dual mono is a no no with these speakers.

I have yet to do the common ground test on any of these amps, but was wondering if anyone knew if any of these amps would be an ok option to run the sda’s with. I’m a bit partial to 60-70s amps and would prefer not to have to buy a newer one to run the sda’s efficiently.

Any thoughts/suggestions would be great!

Thanks!
Blake

F1nut

Welcome Blake. The Kenwood certainly appears to be dual mono. While rated to drive 4 ohm loads such as your SDA's the 4 ohm wpc rating isn't much more than the 8 ohm, which indicates it's not exactly a high current amp. SDA's like high current amps. The Pioneer appears to be common ground and rated to drive 4 ohm loads, but again not exactly a high current amp. I didn't check the Realistic.

You need to do the common ground test and go from there.

bynum03

Thank you sir! I appreciate all of the help!