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Amplifier Comparison SpeakerPower SP2-12000 and Powersoft K20-DSP-Aesop

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Here is something interesting in the way that REW interprets input levels for folks who may not know...

 

This is the highest clean level that a class A/B chipamp can produce @ 30Hz without clipping the waveform:

e9c197cc341df38494dff3e457f2e122.png

 

Now here is the same amplifier pushed into clipping.  Neither REW's or the soundcard's input was clipped, only the signal into them was. 

88a634051e663f9484d5dee6b11603fc.png

 

The peak voltage into REW's input does not go any higher when the amp was pushed into clipping because the amp had already reached it's output limit but REW still shows a 1.7-1.8dB increase in level because it senses an increase in RMS level. 

 

This is another example for why I think it is less confusing for most people to stick to peak values and not focus on RMS.  After all, the amps are rated in peak power values anyway. 

 

 

 

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 The long term sine wave testing at this lower impedance load is a little more interesting. The K20 exhibited some limiting during this and was held about 3-4dB below clipping for large sections of the sweep. The general trend is that the K20 would produce near full power for a section of the sweep then reduce output for a while and then ramp back up and then limit a bit for awhile. We can see that the K20 starts off with a bit higher output down in the resonance of the earth frequencies of 2-5Hz and then the SP2-12000 takes over from 5-15Hz. The K20 rises back up and takes back over from 16-34Hz. Then the SP2-12000 takes over or runs even with the K20 over the 35-70Hz octave. The K20 comes back on from 70-120Hz and produces a bit higher output again. To me this looks like long term current limiting going on in the K20. The Digam series of amplifiers has a number of settings for limiting the amplifiers output or matching it to the circuit that it is on. The maximum current setting is 33A which is a long term average which is there to prevent tripping breakers. With typical content I doubt that this is ever an issue but the sine wave measurement used here is 100% duty cycle for 23 seconds or so and with the relatively low impedance minimums and the amplifier being run at full output I suspect this may actually be coming into effect and the software may be limiting the current a bit. The most notable area of the K20's measurement is between 30-40Hz where clearly the output is limited abruptly for a bit.  If this set of sweeps is compared with the impedance curve of the driver provided earlier we can see that the output squishing happens in the areas of high current demand. I will say that there is no way that I could hear anything happening or tell anything different during this measurement by ear. The entire house was being shook violently and a reduction of a couple dB in output simply doesn't audibly register to me when my home and body is being punished like that. Perhaps outside...I don't know. Anyway I'd call the 2 ohm long term sine wave test a draw or a slight win for the SP2-12000.

 

 

attachicon.gifsp2-12k 2 ohm stereo vs k20 4 ohm bridge.jpg

 

Good job on your testing! It has been a pleasure to interact with you during the process. I feel you have been very fair and well grounded in reality. The results are about what I expected. The K20 has a higher voltage power supply so I expected it to take the honors on the burst test and it did. The SP2-12000 is not your average amplifier designed for light duty cycles and higher frequencies. It shines at very low and infrasonic frequency performance and high duty cycles. It takes special testing to reveal this performance.  My long term sine wave testing is done a single frequency at a time. The initial input level is set to get the maximum undistorted short term power level. Then I graph the output power versus time. This allows you to see how the amp loses power at lower frequencies, how long it holds full power before it cuts back, how smoothly it cuts back (some go into oscillation, some cut off) and what power level it eventually settles at. In your test, the back and forth of which amp is higher may be due to the time constant of the protection circuits interacting with the sweep rate of the test signal as the impedance changed in the load. I don't mean to criticize; it just demonstrates how hard it is to test this stuff. 

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Good job on your testing! It has been a pleasure to interact with you during the process. I feel you have been very fair and well grounded in reality. The results are about what I expected. The K20 has a higher voltage power supply so I expected it to take the honors on the burst test and it did. The SP2-12000 is not your average amplifier designed for light duty cycles and higher frequencies. It shines at very low and infrasonic frequency performance and high duty cycles. It takes special testing to reveal this performance.  My long term sine wave testing is done a single frequency at a time. The initial input level is set to get the maximum undistorted short term power level. Then I graph the output power versus time. This allows you to see how the amp loses power at lower frequencies, how long it holds full power before it cuts back, how smoothly it cuts back (some go into oscillation, some cut off) and what power level it eventually settles at. In your test, the back and forth of which amp is higher may be due to the time constant of the protection circuits interacting with the sweep rate of the test signal as the impedance changed in the load. I don't mean to criticize; it just demonstrates how hard it is to test this stuff. 

 

Welcome to the forum, SP :)

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Thanks Brian.

I always try to be unbiased and fair. It is not easy sometimes I will admit. Anyway I think both amplifiers performed extremely well. Each has particular strengths and features. The fact that the 12K fans do not run most of the time is a huge plus for home theater installs. I'm thinking about building a hush box or remote locating my K20's now. Their fan noise is less than most amps I've used but compared to silence it's no contest. I can see why the SP plate amps have become so popular. It is such a big step up in power from the other choices available. The typical "1000w" plate amps are toys in comparison.

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I have always been chatting with Dgage(SP dealer also) about them. Although I heard many also get them from Seaton also.

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I haven't doubted the raw output data, but I do question the 1 ohm operation claim. Again, I don't doubt certain situations permit that sort of stupid-high current draw, but I don't think your system presents such a situation. I don't believe you operate anywhere near 1 ohm.

 

If you have any data to the contrary, please post it. :)

 

 

No need to get petty about this Luke, you've only been asked to verify your claim which is not out of the ordinary for these discussions.  If you haven't measured your system's voltage and current while playing your demo track then all you have is a theory, which is also fine with us. 

 

i purchased a Fluke 117 and also borrowed another Fluke meter from a buddy of mine so I could take amperage and voltage readings at the same time.

 

I ran sine waves, one frequency at a time..., and started at 1 volt of output from the amp.  However, that was getting too loud so I lowered it to ~.5 volts for the remainder of the measurements.

 

 

21ipal%20impedance_zpsusaktkcx.png

 

 

Taking a measurement during one of my favorite dubstep tracks had an average reading of ~2 to 2.1 ohms, and after hooking up SpecLab, I found out what I thought was ~30hz was really ~33hz so that made sense.

 

So, I tried another track, this one with several seconds straight of ~27hz, and the reading was a repeatable 1.217 ohms.

 

I pushed this track to levels over 135db at the seats with just the Othorns playing and it resulted in no clipping and idle fans.  Amp barely warm to the touch.  

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So, I tried another track, this one with several seconds straight of ~27hz, and the reading was a repeatable 1.217 ohms.

 

I pushed this track to levels over 135db at the seats with just the Othorns playing and it resulted in no clipping and idle fans.  Amp barely warm to the touch.  

Volts and amps draw was what for 135dB?

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Yeah that's what I want, a random voltage. :rolleyes:

 

Comon man, keep up.  You wrote: "So, I tried another track, this one with several seconds straight of ~27hz, and the reading was a repeatable 1.217 ohms.

I pushed this track to levels over 135db at the seats with just the Othorns playing and it resulted in no clipping and idle fans.  Amp barely warm to the touch."

 

Then I posted: "Volts and amps draw was what for 135dB?"

 

So... play the several seconds of 1.217 ohms at 135dB and measure the RMS voltage.  Tell me that number and I'll tell you the power.  No fibbing. 

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Yeah that's what I want, a random voltage. :rolleyes:

 

Comon man, keep up.  You wrote: "So, I tried another track, this one with several seconds straight of ~27hz, and the reading was a repeatable 1.217 ohms.

I pushed this track to levels over 135db at the seats with just the Othorns playing and it resulted in no clipping and idle fans.  Amp barely warm to the touch."

 

Then I posted: "Volts and amps draw was what for 135dB?"

 

So... play the several seconds of 1.217 ohms at 135dB and measure the RMS voltage.  Tell me that number and I'll tell you the power.  No fibbing. 

 

If you want something specific, ask for something specific.  We obviously weren't on the same page.

 

The voltage for that will have to wait for another night when the wife is out of the house.  

 

You guys wanted measurements and I provided them.  I went one frequency at a time to capture the impedance at each, and also captured the volts/amperage  during a track which also lined up almost exactly with my graph.  

 

What's next after I capture this next thing?  

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My 8 and 6 year old had an argument with almost that exact same use of words.  

 

"If you're not going to let me play with your toys I won't want to play with them anyway!!"  

 

 

It seemed obvious to Josh and Brian that the use of this particular driver would cause problems for a lot of amps, and Powersoft eve made an amplifier module just for this driver rated at 8000w into...you guessed it...1ohm.

 

I'm fine with it that you don't think I'm approaching 1ohm loads,  but it's up to you to prove I'm not if you're really that concerned about it.  

 

 

I missed this gem ^^

 

My kids are grown men but when they were young if someone asked them a question they didn't have the answer to they just said "I don't know" or went and got the actual answer. :)

 

8,000 watts into 1 ohm requires 90 amps of current. So, you might see why someone reading your name-dropping, spec-citing posts might ask for actual measurements, or might be curious about your 220V/30A circuit and SP 1-6000 driving the iPAL/DIY Horn?

 

I appreciate what you've posted as a start.

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I missed this gem ^^

 

My kids are grown men but when they were young if someone asked them a question they didn't have the answer to they just said "I don't know" or went and got the actual answer. :)

 

8,000 watts into 1 ohm requires 90 amps of current. So, you might see why someone reading your name-dropping, spec-citing posts might ask for actual measurements, or might be curious about your 220V/30A circuit and SP 1-6000 driving the iPAL/DIY Horn?

 

I appreciate what you've posted as a start.

 

 

I regret my snippy comment.  I shouldn't have said it and I apologize.

 

I allowed your posting style, which I would describe as frequently sarcastic and passive aggressive, to put me in a grumpy mood when I posted that.  Won't happen again.  

 

Josh had direct experience with an IPAL in an Othorn, so if he tells me the load drops to ~1.1ohm between 25-30hz, why should I doubt him?  Before purchasing the SP amp I was also chatting with Brian, who I found out also had experience with this specific driver, so naturally I had some questions for him.  I also PM'd you about the A14k during this time as that amp was on my list of potentials for this specific project.  

 

Do you have some issue with me talking about some of the details of my casual conversations with Josh and Brian?  

 

I also don't see the problem with the 90A requirement that delivering 8kw into 1ohm would necessitate.  My limited understanding is that the 8kw figure is a burst/peak wattage number like the rest of the Powersoft output specifications, and I also assume they recommend at least 240v/30A mains for that module.  A 90A draw for a few fractions of a second shouldn't give a breaker that size any trouble, should it?

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since it was mentioned how much current the wall will allow and by extrapolation then the max power, that depends greatly on the "time current curve" of the breaker.  they vary quite a bit.  i just quickly searched on a ge 30 amp 240v breaker and was then cross-referenced to this link (ge industrial series ges-6112c available in amperages from 15-50, voltages from 120-240, and 60hz lines).  it seems representative if not specific.

 

http://apps.geindustrial.com/publibrary/checkout/GES-6122C?TNR=Time%20Current%20Curves%7CGES-6122C%7Cgeneric

 

if the "bursts" that luke was drawing were less than one second in duration, the breaker may actually allow current to about 7 times its rating.  for a 30 amp breaker that is obviously 210 amps.  on a 240v line, that is 50,400 watts for a second.  woohoo...

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I regret my snippy comment.  I shouldn't have said it and I apologize.

 

I allowed your posting style, which I would describe as frequently sarcastic and passive aggressive, to put me in a grumpy mood when I posted that.  Won't happen again.  

 

Josh had direct experience with an IPAL in an Othorn, so if he tells me the load drops to ~1.1ohm between 25-30hz, why should I doubt him?  Before purchasing the SP amp I was also chatting with Brian, who I found out also had experience with this specific driver, so naturally I had some questions for him.  I also PM'd you about the A14k during this time as that amp was on my list of potentials for this specific project.  

 

Do you have some issue with me talking about some of the details of my casual conversations with Josh and Brian?  

 

I also don't see the problem with the 90A requirement that delivering 8kw into 1ohm would necessitate.  My limited understanding is that the 8kw figure is a burst/peak wattage number like the rest of the Powersoft output specifications, and I also assume they recommend at least 240v/30A mains for that module.  A 90A draw for a few fractions of a second shouldn't give a breaker that size any trouble, should it?

 

If everything about low frequency reproduction could be assumed, this forum would obviously not exist.

 

The question is why would anyone design a subwoofer system to operate at 1 ohm nominal. I see no advantages, only disadvantages. How much transient burst current a breaker can allow before tripping is not predictable and not relevant.

 

The SP-2-8000 muted when operating on a dedicated 120V-30A line at Brandon's GTG, both channels driving a 1.7 resting Re reactive load. Since Paul and I weren't there to test a SP amplifier (didn't even know one was there until Dave Gage pulled it out of his car and brought it in half way through the GTG), there was little more time and equipment available to do more than measure resting Re and speclab cap the scenes being played.

 

I know this; the A14-K amp bridged, driving the series-wired VCs at a resting Re of 3.4 ohms with the same 120V-30A line would have been easily able to damage the HST-24 driver without going into protect.

 

There was speculation by Seaton after the fact that it was "line sag", but there was no indication that line sag or brown out was apparent during the rest of the GTG. Still, no measurements were taken. I still don't know if there is overcurrent protection in the SP line of amps or how one would know what is going on with the amplifier since there are no indicator LEDs on the front panel besides a power on LED and the rear panel only has single signal LED and a clip and a protect LED. Protect can mean several things.

 

I don't see the difference between the songs being played at the GTG and the song you mention playing, but, there's no data here beyond your description. A speclab cap would be nice. Actually, the mic'd version (that clocked 135dB) and a loop through version for comparison. And, the measurements Paul asked for as well as a FR at the mic that clocked 135dB. That data would be helpful vs the 'so and so says so' kinda answers.

 

No one has posted a FR of the amplifiers as well. I really don't get that. It's pretty much the whole shootin' match when making claims about subwoofer reproduction. I know that you filter the low stuff out, but the rest of us don't so it's pertinent to know if the amplifier is doing that for you.

 

Since this thread is about the SP amps, I thought it would be nice to get to the bottom of these issues. I mentioned in my first post in this thread that I don't lend any credence to the SP comparison tests and that sort of info is a marketing ploy to justify the relatively high cost of the SP line, IMO. I'm much more interested in the sort of comparison Josh did in this thread, except that there is still a lot of missing data, IMO, YMMV.

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Couple of things.

 

1.) The SP-12K I have on loan does have front panel clip, signal and protect indicators. Putting them on the back was completely nonsensical to me. Glad that change was made. 

 

2.) I could not get the SP-12K or the K20 to protect with any content above 20Hz in any of the particular scenarios I used. Protect was much more likely below 10Hz with lower impedances. IOW higher current demands. A lower impedance load may be different as may a smaller 120v line, but it is clear that the sub bass stuff is a much greater drain on the amps either way. YMMV

 

3.) I've read a lot about that SI-24 / SP-8K deal and I don't know what happened there. Not enough info. Perhaps the content used really wasn't as demanding on the driver as what is thought or maybe Mark is right and there was severe line sag on the 120v line. I'm confident that the 12K I have would not be able to be let loose on the 24 in the exact box used at that GTG with the GP DB type testing or the 24 driver would need re-coned.

 

4.) I'm going to take the SP-12K and use it to GP test a sealed IPAL-21 which is a much rougher load than when loaded in a horn with a HPF. It will be on 240v. We'll see how that goes. I'll capture the applied voltage and already have the impedance measurement for that enclosure+driver so we will be able to do a rough calculation of the current and power.

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If everything about low frequency reproduction could be assumed, this forum would obviously not exist.

 

The question is why would anyone design a subwoofer system to operate at 1 ohm nominal. I see no advantages, only disadvantages. How much transient burst current a breaker can allow before tripping is not predictable and not relevant.

 

The SP-2-8000 muted when operating on a dedicated 120V-30A line at Brandon's GTG, both channels driving a 1.7 resting Re reactive load. Since Paul and I weren't there to test a SP amplifier (didn't even know one was there until Dave Gage pulled it out of his car and brought it in half way through the GTG), there was little more time and equipment available to do more than measure resting Re and speclab cap the scenes being played.

 

I know this; the A14-K amp bridged, driving the series-wired VCs at a resting Re of 3.4 ohms with the same 120V-30A line would have been easily able to damage the HST-24 driver without going into protect.

 

There was speculation by Seaton after the fact that it was "line sag", but there was no indication that line sag or brown out was apparent during the rest of the GTG. Still, no measurements were taken. I still don't know if there is overcurrent protection in the SP line of amps or how one would know what is going on with the amplifier since there are no indicator LEDs on the front panel besides a power on LED and the rear panel only has single signal LED and a clip and a protect LED. Protect can mean several things.

 

I don't see the difference between the songs being played at the GTG and the song you mention playing, but, there's no data here beyond your description. A speclab cap would be nice. Actually, the mic'd version (that clocked 135dB) and a loop through version for comparison. And, the measurements Paul asked for as well as a FR at the mic that clocked 135dB. That data would be helpful vs the 'so and so says so' kinda answers.

 

No one has posted a FR of the amplifiers as well. I really don't get that. It's pretty much the whole shootin' match when making claims about subwoofer reproduction. I know that you filter the low stuff out, but the rest of us don't so it's pertinent to know if the amplifier is doing that for you.

 

Since this thread is about the SP amps, I thought it would be nice to get to the bottom of these issues. I mentioned in my first post in this thread that I don't lend any credence to the SP comparison tests and that sort of info is a marketing ploy to justify the relatively high cost of the SP line, IMO. I'm much more interested in the sort of comparison Josh did in this thread, except that there is still a lot of missing data, IMO, YMMV.

 

It remains a mystery what happened with the SP2-8000 and the HS-24.  Everyone was shocked by the outcome, although no one is denying it happened.

 

I admit I was a bit cranky when asked for all the additional information about my 1ohm claims, but I’ve learned a lot in the last week so I’m glad I dug into it deeper.  I found out my favorite dubstep demo track wasn’t anywhere near 1ohm but rather even over 2ohm in fact once measured. 

 

I also confirmed (at least to myself) that on the very next track I picked with 27hz content that a consistent ~1.2ohm load is being presented to the amp many  times throughout that track.  I’ll provide a SpecLab capture of the track and also of my several second loop of the track which I used for the voltage/amperage capture. 

 

Me merely providing a DCR of a driver and a track name wasn’t enough info for you, and I get why after the last week of impedance measurements I performed. 

 

However, this is exactly the limited information you’ve provided about the SP2-8k/HS-24 debacle.  We have a DCR of the driver, and a track name from “imagic” on AVS.  I imagine if someone stated something like “We bridged an A14K to a single driver with a DCR of 2.9ohm and got it to mute the outputs on “tracknamehere” you’d understandably want more information such as the exact things I’ve been asked for in this thread:  Speclab captures of the track, voltage and amperage draw from the amp, and a RMS voltage from the amp while at the limits.  Maybe even a voltage reading from the mains to see if there was voltage drop? 

 

That information was never gathered and can’t be provided from this GTG a few years ago, so it’s going to remain a mystery.  If it were the A14K in that scenario with the same limited information, you wouldn’t be happy it was brought up every time a A14K is mentioned because we simply don’t have enough information to know what caused it.

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