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SpeakerPower Torpedo SP1-4000 Plate Amp
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<blockquote data-quote="Langston Holland" data-source="post: 31690" data-attributes="member: 171"><p>Re: SpeakerPower Torpedo SP1-4000 Plate Amp (3 of 3)</p><p></p><p>Got an idea today (remember the DI story - ideas can be dangerous) and got it done right before I set off for an 8 hour drive to Orlando for InfoComm. Typing this in the car - A/C is broke and it's 34 degrees Celsius outside even though dark - ugh. Someone else is driving. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /></p><p></p><p>For you chumps that still need to be delivered from Fahrenheit, this'll get you to the new-improved rest of your life: the Celsius #'s you need to know are 0, 20, 25, 37, 100. Respectively that's freezing, lower human comfort level, upper human comfort level, healthy human body temperature, boiling. There, now get with the program!</p><p></p><p>Meanwhile...</p><p></p><p>Don Keele developed a composite bass tone burst test stimulus that is flat from 30Hz to 80Hz and falls off sharper than any crossover slope you'll ever use above and below those frequencies. Crest factor of a single 200ms burst is 8.6dB, and with his 1 second pause between bursts, the overall crest factor becomes 15.4dB. It's very music-like and since it's made of the linear sum of 5 individual sine based tone bursts, distortion is easy to detect by ear or instrument once amps or woofers reach their limits.</p><p></p><p>With a sub that doesn't spec EQ such as the TH118's, you don't need to bother with a loudspeaker processor to perform this test and I didn't. This composite burst only covers the normal operating passband of the sub, thus I just played the stimulus straight into the SP1-4000 and PL380 and connected the output of the amp to both the sub and an oscilloscope. A microphone was not used in this test because I wanted to focus on the amp performance. This would in fact make an ideal sub shootout stimulus and provide a strong dose of objectivity to same. The test rig shown below is a what I used if you ignore the microphone. It's very easy to hear when something is clipping, thus the scope is just for verification and pretty pictures in this post.</p><p></p><p><img src="http://soundscapesweb.com/files/PSW/AmpTests3/KeeleBurstTestRig.png" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>My TH118's are 4Ω and use the lovely B&C drivers. Several interesting and unexpected results came from this test - such as one of my subs has either a driver or cabinet problem. Sounds like a baffle didn't get sealed properly during construction, but I'll find out through the 'ole process of elimination next week. Stay tuned.</p><p></p><p>Other items of interest are the peak voltage outputs of the SP1-4000 and PL380 into a complex load posing as "4Ω". You can do the math for peak watts, but it's deceptive - volts make SPL - watts heat the room. The PL380 proved very strong when bridged into a real loudspeaker that can handle it. I've never tried it bridged until today and it made a single TH118 go places I didn't know were possible with a 160 lb sub. I'm going to do peak acoustic measurements on these puppies pretty soon to put a number on what I heard. This is an outstanding sub.</p><p></p><p>Below you will see 4 traces. The top is from one of the few multitrack recording programs that does the math right on audio waveforms and shows Keele's actual composite tone burst stimulus. The middle left is the output of the SP1-4000 driven pretty far into limiting to get the maximum voltage readout on the scope. The TH118 was quite comfortable at this level, though you could hear the change in the waveform. The middle right is the PL380 in stereo mode also pretty far into limiting to get the maximum possible voltage readout. The TH118 was still comfortable and looking for more. The bottom trace is the output of the bridged PL380 where the TH118 finally said "enough" just as the amp LED's were beginning to kiss red. As you can see, both PL380 traces are nice replicas of the original trace, while I really went too far with the SP1-4000 looking for voltage and it shows a fair amount of what appears to be pre-ringing that obviously factored into the RMS calculation.</p><p></p><p><img src="http://soundscapesweb.com/files/PSW/AmpTests3/SP1-4000_TH118_Burst.png" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>The voltages of 294, 321 and 540 are "peak to peak". Divide each in half to arrive at "peak" voltage. Square the peak voltage, then divide that by 4 to get the nominal "peak watts". If that stuff doesn't mean much to you and you're only interested in how loud can the sub go and still sound good - you are wiser than you may think.</p></blockquote><p></p>
[QUOTE="Langston Holland, post: 31690, member: 171"] Re: SpeakerPower Torpedo SP1-4000 Plate Amp (3 of 3) Got an idea today (remember the DI story - ideas can be dangerous) and got it done right before I set off for an 8 hour drive to Orlando for InfoComm. Typing this in the car - A/C is broke and it's 34 degrees Celsius outside even though dark - ugh. Someone else is driving. :) For you chumps that still need to be delivered from Fahrenheit, this'll get you to the new-improved rest of your life: the Celsius #'s you need to know are 0, 20, 25, 37, 100. Respectively that's freezing, lower human comfort level, upper human comfort level, healthy human body temperature, boiling. There, now get with the program! Meanwhile... Don Keele developed a composite bass tone burst test stimulus that is flat from 30Hz to 80Hz and falls off sharper than any crossover slope you'll ever use above and below those frequencies. Crest factor of a single 200ms burst is 8.6dB, and with his 1 second pause between bursts, the overall crest factor becomes 15.4dB. It's very music-like and since it's made of the linear sum of 5 individual sine based tone bursts, distortion is easy to detect by ear or instrument once amps or woofers reach their limits. With a sub that doesn't spec EQ such as the TH118's, you don't need to bother with a loudspeaker processor to perform this test and I didn't. This composite burst only covers the normal operating passband of the sub, thus I just played the stimulus straight into the SP1-4000 and PL380 and connected the output of the amp to both the sub and an oscilloscope. A microphone was not used in this test because I wanted to focus on the amp performance. This would in fact make an ideal sub shootout stimulus and provide a strong dose of objectivity to same. The test rig shown below is a what I used if you ignore the microphone. It's very easy to hear when something is clipping, thus the scope is just for verification and pretty pictures in this post. [IMG]http://soundscapesweb.com/files/PSW/AmpTests3/KeeleBurstTestRig.png[/IMG] My TH118's are 4Ω and use the lovely B&C drivers. Several interesting and unexpected results came from this test - such as one of my subs has either a driver or cabinet problem. Sounds like a baffle didn't get sealed properly during construction, but I'll find out through the 'ole process of elimination next week. Stay tuned. Other items of interest are the peak voltage outputs of the SP1-4000 and PL380 into a complex load posing as "4Ω". You can do the math for peak watts, but it's deceptive - volts make SPL - watts heat the room. The PL380 proved very strong when bridged into a real loudspeaker that can handle it. I've never tried it bridged until today and it made a single TH118 go places I didn't know were possible with a 160 lb sub. I'm going to do peak acoustic measurements on these puppies pretty soon to put a number on what I heard. This is an outstanding sub. Below you will see 4 traces. The top is from one of the few multitrack recording programs that does the math right on audio waveforms and shows Keele's actual composite tone burst stimulus. The middle left is the output of the SP1-4000 driven pretty far into limiting to get the maximum voltage readout on the scope. The TH118 was quite comfortable at this level, though you could hear the change in the waveform. The middle right is the PL380 in stereo mode also pretty far into limiting to get the maximum possible voltage readout. The TH118 was still comfortable and looking for more. The bottom trace is the output of the bridged PL380 where the TH118 finally said "enough" just as the amp LED's were beginning to kiss red. As you can see, both PL380 traces are nice replicas of the original trace, while I really went too far with the SP1-4000 looking for voltage and it shows a fair amount of what appears to be pre-ringing that obviously factored into the RMS calculation. [IMG]http://soundscapesweb.com/files/PSW/AmpTests3/SP1-4000_TH118_Burst.png[/IMG] The voltages of 294, 321 and 540 are "peak to peak". Divide each in half to arrive at "peak" voltage. Square the peak voltage, then divide that by 4 to get the nominal "peak watts". If that stuff doesn't mean much to you and you're only interested in how loud can the sub go and still sound good - you are wiser than you may think. [/QUOTE]
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