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#1
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How can I make a spk simulator load
I want to put a load on small tube amps that simulates the reactive load of a speaker, not just a resistor... I know that spk models are very complex, but a simple circuit should be possible. I'm thinking of a regular full range spk like a guitar amp speaker, shouldn't be too hard? I saw such a circuit before but can't locate it. Thanks anyone. |
#2
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Robbie wrote:
I want to put a load on small tube amps that simulates the reactive load of a speaker, not just a resistor... I know that spk models are very complex, but a simple circuit should be possible. I'm thinking of a regular full range spk like a guitar amp speaker, shouldn't be too hard? I saw such a circuit before but can't locate it. How about... a speaker? If you don't want to disturb the neighbors, try hiding it in the fridge. The insulation of the fridge should muffle the sound. |
#3
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robert casey wrote:
Robbie wrote: I want to put a load on small tube amps that simulates the reactive load of a speaker, not just a resistor... I know that spk models are very complex, but a simple circuit should be possible. I'm thinking of a regular full range spk like a guitar amp speaker, shouldn't be too hard? I saw such a circuit before but can't locate it. How about... a speaker? If you don't want to disturb the neighbors, try hiding it in the fridge. The insulation of the fridge should muffle the sound. I would have throught an amp connected to a transformer which is then connected to a to a resistor load would be pretty similar to a speaker. |
#4
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"robert casey" wrote
How about... a speaker? If you don't want to disturb the neighbors, try hiding it in the fridge. The insulation of the fridge should muffle the sound. genius! But not when it's on, or spk will get damp when taken out or, perish the thought, ice up within. cheers, Ian |
#5
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"Mark Harriss" = net stalking, criminal ****WIT I would have throught an amp connected to a transformer which is then connected to a to a resistor load would be pretty similar to a speaker. ** ROTFL !! This bull****ting arsehole from Brisbane cannot even spell "thought" let alone have one !! ......... Phil |
#6
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"Robbie" I want to put a load on small tube amps that simulates the reactive load of a speaker, not just a resistor... I know that spk models are very complex, but a simple circuit should be possible. I'm thinking of a regular full range spk like a guitar amp speaker, shouldn't be too hard? I saw such a circuit before but can't locate it. ** Figure 2 in this article has what you are asking for: http://sound.westhost.com/vi.htm The resonant frequency of the parallel tuned circuit is 50 Hz . You could alter the inductor to 10 mH and the 22 ohms to 33 ohms for simulating a guitar speaker. BTW The speaker hidden in the fridge idea appeals - maybe wrap it in a plastic bag first. ............ Phil |
#7
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On Wed, 27 Jul 2005 20:00:54 -0400, Robbie
wrote: I want to put a load on small tube amps that simulates the reactive load of a speaker, not just a resistor... I know that spk models are very complex, but a simple circuit should be possible. I'm thinking of a regular full range spk like a guitar amp speaker, shouldn't be too hard? I saw such a circuit before but can't locate it. As Robert has posted, for guitar amp (single driver, full range) testing, a real speaker is the only believable load. Speakers are both complex load impedances and motors, which include mass controlled reactive voltages. Since you haven't mentioned any teensy bit about what you want to observe, we're all just panting for data.... Amplifiers for monitoring or living room reproduction are sometimes tested into a modestly reactive load intended to approximate some "typical" loudspeaker. Not. We need data, Mon, Chris Hornbeck |
#8
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"Chris Hornbeck" Robbie As Robert has posted, for guitar amp (single driver, full range) testing, a real speaker is the only believable load. ** Robert Casey posted no such comment - plus it is utter bull**** anyhow. Speakers are both complex load impedances and motors, which include mass controlled reactive voltages. ** Far as the driving amplifier is concerned, it is just an electrical network. ............. Phil |
#9
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On Thu, 28 Jul 2005 13:41:43 +1000, "Phil Allison"
wrote: ** Robert Casey posted no such comment - plus it is utter bull**** anyhow. "On Thu, 28 Jul 2005 00:48:16 GMT, robert casey wrote: How about... a speaker? " Speakers are both complex load impedances and motors, which include mass controlled reactive voltages. ** Far as the driving amplifier is concerned, it is just an electrical network. Except when it isn't. Speaker drivers are motors and transducers; either label transcends the "electrical network" model. A model that includes diaphragm mass and conversion efficency might become interesting. Otherwise, please spare me. ** Thanks, Chris Hornbeck |
#10
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On Thu, 28 Jul 2005 13:21:04 +1000, "Phil Allison"
wrote: "Robbie" I want to put a load on small tube amps that simulates the reactive load of a speaker, not just a resistor... I know that spk models are very complex, but a simple circuit should be possible. I'm thinking of a regular full range spk like a guitar amp speaker, shouldn't be too hard? I saw such a circuit before but can't locate it. ** Figure 2 in this article has what you are asking for: http://sound.westhost.com/vi.htm The resonant frequency of the parallel tuned circuit is 50 Hz . You could alter the inductor to 10 mH and the 22 ohms to 33 ohms for simulating a guitar speaker. Hey thanks a lot! I notice the 6r8 resistor and the coil - should I compensate these values, EG if the coil was 6r8 then I wouldn't need the resistor? Just from experience I expect a 1mh coil to be around 200 turns free air... maybe a few ohms depending on the wire I can find. Also, that cap is big, I guess a back-to-back electrolytic? Thanks again! |
#11
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On Thu, 28 Jul 2005 00:48:16 GMT, robert casey wrote:
Robbie wrote: I want to put a load on small tube amps that simulates the reactive load of a speaker, not just a resistor... I know that spk models are very complex, but a simple circuit should be possible. I'm thinking of a regular full range spk like a guitar amp speaker, shouldn't be too hard? I saw such a circuit before but can't locate it. How about... a speaker? If you don't want to disturb the neighbors, try hiding it in the fridge. The insulation of the fridge should muffle the sound. Hey cool Idea!! But seriously folks... I want to experiment with a small single ended 6BQ5 amp driving a P-P-P 6L6 100 watt power amp... I want the compression of the little amp to be amplified by the larger amp (as a feature, not necessarily full time) and I was thinking that I need the speaker to 'activate' the crunch of the little amp properly, the way the transformer interacts with the speaker during clipping... I could have 2 outputs on the amp, one for 5 watts practice level and one for 100, but also the option of not having the smaller speaker connected. The small amp driving the big amp would be the 'high gain' effect. This is for a real gigging amp for my cousin, he loves my little 6BQ6 but needs 100 watts or more for stage, his bass player has 400 watts... so this might work... Hey it's fun too! |
#12
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"Chris Hornbeck" "Phil Allison" ** Robert Casey posted no such comment - plus it is utter bull**** anyhow. "On Thu, 28 Jul 2005 00:48:16 GMT, robert casey wrote: How about... a speaker? " ** What happened to the comment - you schizoid ****WIT !!!!!!!! Speakers are both complex load impedances and motors, which include mass controlled reactive voltages. ** Far as the driving amplifier is concerned, it is just an electrical network. Except when it isn't. ** Go tell your head shrinker hat one - ****wit. .............. Phil |
#13
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On Thu, 28 Jul 2005 03:33:10 GMT, Chris Hornbeck
wrote: On Wed, 27 Jul 2005 20:00:54 -0400, Robbie wrote: I want to put a load on small tube amps that simulates the reactive load of a speaker, not just a resistor... I know that spk models are very complex, but a simple circuit should be possible. I'm thinking of a regular full range spk like a guitar amp speaker, shouldn't be too hard? I saw such a circuit before but can't locate it. As Robert has posted, for guitar amp (single driver, full range) testing, a real speaker is the only believable load. Speakers are both complex load impedances and motors, which include mass controlled reactive voltages. Since you haven't mentioned any teensy bit about what you want to observe, we're all just panting for data.... Amplifiers for monitoring or living room reproduction are sometimes tested into a modestly reactive load intended to approximate some "typical" loudspeaker. Not. We need data, Mon, Chris Hornbeck I'm having some net trouble tonight but I'll try to respond... My cousin loves my little 6BQ5 guitar amp, it has great compression and crunch, but he wants to use a quad 6L6 amp on stage, 100 watts. I told him I could put a high gain circuit into his amp but it wouldn't be the same, for tons of reasons I won't go into here, so we though we could mic the little amp into the big amp. Then we thought better, we could install the small amp into the big amp and use it as the high gain channel... but now the rub becomes the speaker load... I think the spk contributes to the 'crunch' of the amp, so any dummy load would have to be like the spk. I guess if we have to we'll run a small speaker all the time, but that's so NOT scientific! |
#14
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On Thu, 28 Jul 2005 14:50:43 +1000, "Phil Allison"
wrote: you schizoid ****WIT !!!!!!!! Cool, want to discuss the topic (load simulators)? Otherwise, please direct your masterbatory semen elsewhere. We're getting tired of it around here. Chris Hornbeck |
#15
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"Chris Hornbeck" "Phil Allison" you schizoid ****WIT !!!!!!!! Cool, want to discuss the topic (load simulators)? ** Not with a stinking, bull****, spewing, autistic lunatic like YOU . Otherwise, please direct your masterbatory semen elsewhere. ** PKB Fuuuucckkk Offffffffff !!! ........... Phil We're getting tired of it around here. Chris Hornbeck |
#16
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"Robbie" "Phil Allison" I want to put a load on small tube amps that simulates the reactive load of a speaker, not just a resistor... I know that spk models are very complex, but a simple circuit should be possible. I'm thinking of a regular full range spk like a guitar amp speaker, shouldn't be too hard? I saw such a circuit before but can't locate it. ** Figure 2 in this article has what you are asking for: http://sound.westhost.com/vi.htm The resonant frequency of the parallel tuned circuit is 50 Hz . You could alter the inductor to 10 mH and the 22 ohms to 33 ohms for simulating a guitar speaker. Hey thanks a lot! I notice the 6r8 resistor and the coil - should I compensate these values, EG if the coil was 6r8 then I wouldn't need the resistor? ** Correct. Also, that cap is big, I guess a back-to-back electrolytic? ** Two 1000uF, 50 volt electos, neg to neg in series is fine. ........... Phil |
#17
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On Thu, 28 Jul 2005 00:55:03 -0400, Robbie
wrote: My cousin loves my little 6BQ5 guitar amp, it has great compression and crunch, but he wants to use a quad 6L6 amp on stage, 100 watts. I told him I could put a high gain circuit into his amp but it wouldn't be the same, for tons of reasons I won't go into here, so we though we could mic the little amp into the big amp. Then we thought better, we could install the small amp into the big amp and use it as the high gain channel... but now the rub becomes the speaker load... I think the spk contributes to the 'crunch' of the amp, so any dummy load would have to be like the spk. I guess if we have to we'll run a small speaker all the time, but that's so NOT scientific! The greatest thing I ever saw in my own personal sorry life was Patti Smith's gig on Saturday Nite Live about three decades ago. Her opening number was Van's "G-L-O-R-I-A" and the closing number was a Who cover of "My G-G-Generation", including trashing the stage and her PigNose exiting. In stage terms, voices, mic'd amps, etc. etc. are all same-same. Still no clue what you're about, based on your postings. But it sounds like you want to be mic'ing the geetar speaker. Good fortune, Chris Hornbeck |
#18
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On Thu, 28 Jul 2005 15:07:37 +1000, "Phil Allison"
wrote: ** Not with a stinking, bull****, spewing, autistic lunatic like YOU . Fuuuucckkk Offffffffff !!! Kiss and make up? You act like you don't love me anymore, Chris Hornbeck |
#19
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1. connect a 4 or 8ohm resistor ( depending on the impedence of the 5w
SE amp's secondary) with a .75 mH air core inductor in series with the output of the 5W amp. 2. get a 100V commercial speaker line output transformer and hook its 8 ohm secondary in parallel to the RL network and mesure the primary's output. 3. make an apporpriate voltage divider network to attenuate the 20 or so volts comming out of the line transformer and feed that into the phae splitter of the 100W 6l6. also consider a 1.0 UF poly cap between the transformer and a grid screening resistor of like a 100k before your grid bias resistor as an alternative circuit This circuit would most likely to load an amp simular to a Marshall Powerbrake |
#20
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"Chris Hornbeck" wrote
...A model that includes diaphragm mass and conversion efficency might become interesting... http://www.ivesonaudio.pwp.blueyonder.co.uk/driver1.gif mechanics and electricity are in the same world. For testing amps, pretty much any reasonable approximation will do, as Phil has explained. The main problem is that speakers are much less linear systems, especially at high displacements. Getting the cranked up sound the same with a dummy load may be difficult. The following power amp will be running clean, so there will be no sound of a saturating output transformer struggling with non-linear cone behaviour...that kind of stuff. It's a subject that has been extensively discussed ad infinitum since the dawn of time. There are umpteen hardware "solutions" available. The usual thing is to mike the amp AFAIK. cheers, Ian |
#21
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In article , Chris Hornbeck
wrote: On Thu, 28 Jul 2005 13:41:43 +1000, "Phil Allison" wrote: ** Robert Casey posted no such comment - plus it is utter bull**** anyhow. "On Thu, 28 Jul 2005 00:48:16 GMT, robert casey wrote: How about... a speaker? " Speakers are both complex load impedances and motors, which include mass controlled reactive voltages. ** Far as the driving amplifier is concerned, it is just an electrical network. Except when it isn't. Speaker drivers are motors and transducers; either label transcends the "electrical network" model. Chris, sometimes you can really be stupid. Those mechanical elements have electrical analogies, it's just a matter of how much detail you want to include in the electrical representation of the mechanical system. A model that includes diaphragm mass and conversion efficency might become interesting. Otherwise, please spare me. I think "diaphragm mass and conversion efficency" are some of the more elemental parts of a speaker, and are both included even in Phil's bare bones model. Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
#22
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"Robbie" wrote in message ... I want to put a load on small tube amps that simulates the reactive load of a speaker, not just a resistor... I know that spk models are very complex, but a simple circuit should be possible. I'm thinking of a regular full range spk like a guitar amp speaker, shouldn't be too hard? I saw such a circuit before but can't locate it. **This is a pretty good one (for a relatively easy load). http://www.stereophile.com/reference/60/index.html -- Trevor Wilson www.rageaudio.com.au |
#23
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On Thu, 28 Jul 2005 17:15:15 GMT, "Ian Iveson"
wrote: ...A model that includes diaphragm mass and conversion efficiency might become interesting... http://www.ivesonaudio.pwp.blueyonder.co.uk/driver1.gif This looks really good. Thanks, Chris Hornbeck |
#24
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Phil Allison wrote: "Robbie" I want to put a load on small tube amps that simulates the reactive load of a speaker, not just a resistor... I know that spk models are very complex, but a simple circuit should be possible. I'm thinking of a regular full range spk like a guitar amp speaker, shouldn't be too hard? I saw such a circuit before but can't locate it. ** Figure 2 in this article has what you are asking for: http://sound.westhost.com/vi.htm The resonant frequency of the parallel tuned circuit is 50 Hz . You could alter the inductor to 10 mH and the 22 ohms to 33 ohms for simulating a guitar speaker. BTW The speaker hidden in the fridge idea appeals - maybe wrap it in a plastic bag first. ........... Phil About a year & half ago I built a Loud Speaker Simulator very much like that shown in Phil's article. For the input L I have a 90 microhenry aircore choke followed by a 7.5R, 10 watt resistor. The low freqency resonance is formed by a Mallory 220 microfarad NP motor starting cap in parallel with a Hammond 159ZC choke ( 60 mh, 0.7R). All works very well & does a good job confusing the amplifier in test. Cheers, John Stewart |
#26
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On Thu, 28 Jul 2005 17:15:15 GMT, "Ian Iveson"
wrote: "Chris Hornbeck" wrote ...A model that includes diaphragm mass and conversion efficency might become interesting... http://www.ivesonaudio.pwp.blueyonder.co.uk/driver1.gif mechanics and electricity are in the same world. For testing amps, pretty much any reasonable approximation will do, as Phil has explained. The main problem is that speakers are much less linear systems, especially at high displacements. Getting the cranked up sound the same with a dummy load may be difficult. The following power amp will be running clean, so there will be no sound of a saturating output transformer struggling with non-linear cone behaviour...that kind of stuff. But wait a second, that's why I intend to put a speaker simulator, and run the little amp full up in crunch! I will have the saturation... and boost it as is in the larger amp. There are tons of theorems around stating that at any particular time, any particular load can be approximated by a resistor and a phase shifting component... of course speakers are weird loads and may have some other property such as time delay effects or whatever, but hey, how far do I really need to go? It's a subject that has been extensively discussed ad infinitum since the dawn of time. There are umpteen hardware "solutions" available. The usual thing is to mike the amp AFAIK. ? afaik ? cheers, Ian |
#27
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On Thu, 28 Jul 2005 05:24:57 GMT, Chris Hornbeck
wrote: On Thu, 28 Jul 2005 00:55:03 -0400, Robbie wrote: My cousin loves my little 6BQ5 guitar amp, it has great compression and crunch, but he wants to use a quad 6L6 amp on stage, 100 watts. I told him I could put a high gain circuit into his amp but it wouldn't be the same, for tons of reasons I won't go into here, so we though we could mic the little amp into the big amp. Then we thought better, we could install the small amp into the big amp and use it as the high gain channel... but now the rub becomes the speaker load... I think the spk contributes to the 'crunch' of the amp, so any dummy load would have to be like the spk. I guess if we have to we'll run a small speaker all the time, but that's so NOT scientific! The greatest thing I ever saw in my own personal sorry life was Patti Smith's gig on Saturday Nite Live about three decades ago. Her opening number was Van's "G-L-O-R-I-A" and the closing number was a Who cover of "My G-G-Generation", including trashing the stage and her PigNose exiting. The greatest thing I ever saw was some drugged out rock star getting his mic caught in the security rope as he twirled it on it's cord, and the security boys had to untangle it while the band (Steppenwolfe) continued repeating the phrase, but I digress... ??? In stage terms, voices, mic'd amps, etc. etc. are all same-same. Still no clue what you're about, based on your postings. But it sounds like you want to be mic'ing the geetar speaker. Sort of, but instead of a mic I want to use a copper pair... Good fortune, 'merci de le cul de mon coeur'... Chris Hornbeck Robbie In Outer Space |
#28
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"John Stewart" About a year & half ago I built a Loud Speaker Simulator very much like that shown in Phil's article. For the input L I have a 90 microhenry aircore choke followed by a 7.5R, 10 watt resistor. The low freqency resonance is formed by a Mallory 220 microfarad NP motor starting cap in parallel with a Hammond 159ZC choke ( 60 mh, 0.7R). ** Such a low value for the input L means you are effectively simulating a speaker that has a copper cap ( inductance damper) on the pole piece - ie as is commonly used for wide range or twin cone speakers. The bass resonance is at 44 Hz but the peak current before saturation is only 2 amps for the 159ZC, so power input is a bit limited. ........... Phil |
#29
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"Trevor Wilson" ... **This is a pretty good one (for a relatively easy load). http://www.stereophile.com/reference/60/index.html ** Sure is an easy one, the worst combination is at about 70 Hz, with an impedance of 14 ohms and a phase angle of 35 degrees. Tuned boxes with their double impedance peaks in the bass are so much harder for an amp to drive. ............. Phil |
#30
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On Thu, 28 Jul 2005 20:56:28 -0400, Robbie
wrote: In stage terms, voices, mic'd amps, etc. etc. are all same-same. Still no clue what you're about, based on your postings. But it sounds like you want to be mic'ing the geetar speaker. Sort of, but instead of a mic I want to use a copper pair... Cool. Believable simulations are complex, but very do-able. Ian's is a great framework: http://www.ivesonaudio.pwp.blueyonder.co.uk/driver1.gif More elaboration would begin to include distortion effects and such... But do ya really need to? Good fortune, Chris Hornbeck |
#31
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Phil Allison wrote:
"John Stewart" About a year & half ago I built a Loud Speaker Simulator very much like that shown in Phil's article. For the input L I have a 90 microhenry aircore choke followed by a 7.5R, 10 watt resistor. The low freqency resonance is formed by a Mallory 220 microfarad NP motor starting cap in parallel with a Hammond 159ZC choke ( 60 mh, 0.7R). ** Such a low value for the input L means you are effectively simulating a speaker that has a copper cap ( inductance damper) on the pole piece - ie as is commonly used for wide range or twin cone speakers. The bass resonance is at 44 Hz but the peak current before saturation is only 2 amps for the 159ZC, so power input is a bit limited. .......... Phil The loudspeaker simulator has a nice measured peak at about 45 Hz. The rise of impedance caused by the 90 microhenry choke starts at about 4KHz & is well up at 10 KHz, similar to a real speaker. All of the parts were in my pile, so easy to put together. I've also got one each of the Hammond 159ZE & 159ZJ chokes, so other conditions are possible. In all, very useful. Cheers, John Stewart |
#32
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"John Stewart" Phil Allison wrote: About a year & half ago I built a Loud Speaker Simulator very much like that shown in Phil's article. For the input L I have a 90 microhenry aircore choke followed by a 7.5R, 10 watt resistor. The low freqency resonance is formed by a Mallory 220 microfarad NP motor starting cap in parallel with a Hammond 159ZC choke ( 60 mh, 0.7R). ** Such a low value for the input L means you are effectively simulating a speaker that has a copper cap ( inductance damper) on the pole piece - ie as is commonly used for wide range or twin cone speakers. The bass resonance is at 44 Hz but the peak current before saturation is only 2 amps for the 159ZC, so power input is a bit limited. The rise of impedance caused by the 90 microhenry choke starts at about 4KHz & is well up at 10 KHz, similar to a real speaker. ** As usual, you are totally wrong. Your circuit only rises to 9.4 ohms at 10 kHz while typical woofers have inductance figures of 0.5 to 2.5 mH - depending on coil size. The impedance at 10 kHz is 20 to 30 ohms, unless a copper shorting ring or pole cap is fitted. Then the figures are like your circuit. ......... Phil |
#33
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Phil Allison wrote:
"John Stewart" Phil Allison wrote: About a year & half ago I built a Loud Speaker Simulator very much like that shown in Phil's article. For the input L I have a 90 microhenry aircore choke followed by a 7.5R, 10 watt resistor. The low freqency resonance is formed by a Mallory 220 microfarad NP motor starting cap in parallel with a Hammond 159ZC choke ( 60 mh, 0.7R). ** Such a low value for the input L means you are effectively simulating a speaker that has a copper cap ( inductance damper) on the pole piece - ie as is commonly used for wide range or twin cone speakers. The bass resonance is at 44 Hz but the peak current before saturation is only 2 amps for the 159ZC, so power input is a bit limited. The rise of impedance caused by the 90 microhenry choke starts at about 4KHz & is well up at 10 KHz, similar to a real speaker. ** As usual, you are totally wrong. Your circuit only rises to 9.4 ohms at 10 kHz while typical woofers have inductance figures of 0.5 to 2.5 mH - depending on coil size. The impedance at 10 kHz is 20 to 30 ohms, unless a copper shorting ring or pole cap is fitted. Then the figures are like your circuit. ........ Phil Thankyou for your indication of confidence in my work. I actually measured that thing & those are the results. Perhaps something else is going on there. But I've got lots of other things to pursue! Cheers Anyway, John Stewart |
#34
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Phil Allison wrote:
"John Stewart" Phil Allison wrote: About a year & half ago I built a Loud Speaker Simulator very much like that shown in Phil's article. For the input L I have a 90 microhenry aircore choke followed by a 7.5R, 10 watt resistor. The low freqency resonance is formed by a Mallory 220 microfarad NP motor starting cap in parallel with a Hammond 159ZC choke ( 60 mh, 0.7R). ** Such a low value for the input L means you are effectively simulating a speaker that has a copper cap ( inductance damper) on the pole piece - ie as is commonly used for wide range or twin cone speakers. The bass resonance is at 44 Hz but the peak current before saturation is only 2 amps for the 159ZC, so power input is a bit limited. The rise of impedance caused by the 90 microhenry choke starts at about 4KHz & is well up at 10 KHz, similar to a real speaker. ** As usual, you are totally wrong. Your circuit only rises to 9.4 ohms at 10 kHz while typical woofers have inductance figures of 0.5 to 2.5 mH - depending on coil size. The impedance at 10 kHz is 20 to 30 ohms, unless a copper shorting ring or pole cap is fitted. Then the figures are like your circuit. ........ Phil I think I screwed up in my response, so I will take the easy way out. The number is missing a zero & should be 900 microhenries. At the time I built this thing it was part of another project for which I was working against a time limit. Checking back I can see the error is both in my schematic & in the text of the subject article. Luckily, the speaker simulator was only a very small part of a much larger work. As usual, Phil checks everyone's work with a magnifying glass & then comments (sort of)! Cheers, John Stewart |
#35
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"John Stewart" Phil Allison wrote: "John Stewart" Phil Allison wrote: About a year & half ago I built a Loud Speaker Simulator very much like that shown in Phil's article. For the input L I have a 90 microhenry aircore choke followed by a 7.5R, 10 watt resistor. The low freqency resonance is formed by a Mallory 220 microfarad NP motor starting cap in parallel with a Hammond 159ZC choke ( 60 mh, 0.7R). ** Such a low value for the input L means you are effectively simulating a speaker that has a copper cap ( inductance damper) on the pole piece - ie as is commonly used for wide range or twin cone speakers. The bass resonance is at 44 Hz but the peak current before saturation is only 2 amps for the 159ZC, so power input is a bit limited. The rise of impedance caused by the 90 microhenry choke starts at about 4KHz & is well up at 10 KHz, similar to a real speaker. ** As usual, you are totally wrong. Your circuit only rises to 9.4 ohms at 10 kHz while typical woofers have inductance figures of 0.5 to 2.5 mH - depending on coil size. The impedance at 10 kHz is 20 to 30 ohms, unless a copper shorting ring or pole cap is fitted. Then the figures are like your circuit. ........ Phil Thankyou for your indication of confidence in my work. I actually measured that thing & those are the results. ** What a liar - you posted no figures at all. ............ Phil |
#36
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"John Stewart" Phil Allison The rise of impedance caused by the 90 microhenry choke starts at about 4KHz & is well up at 10 KHz, similar to a real speaker. ** As usual, you are totally wrong. Your circuit only rises to 9.4 ohms at 10 kHz while typical woofers have inductance figures of 0.5 to 2.5 mH - depending on coil size. The impedance at 10 kHz is 20 to 30 ohms, unless a copper shorting ring or pole cap is fitted. Then the figures are like your circuit. I think I screwed up in my response, so I will take the easy way out. The number is missing a zero & should be 900 microhenries. ** I suspected as much. As usual, Phil checks everyone's work with a magnifying glass & then comments (sort of)! ** Speaker impedance v. frequency behaviour is a topic I have been very well acquainted with for 30 years - so errors like your stick out like dogs balls. In the mid 1970s, I was designing and building SS guitar and PA amps using single and twin cone speakers. One way a speaker voice coil might become damaged was if the SS amp broke into supersonic oscillation. The particular speaker maker I was dealing with here in Sydney believed this to be a common cause of burnt voice coils on speakers sent back for warranty claims. The manager tried to deny warranty to me on this basis. A few simple measurements showed that due to inherent series inductance, it was totally impossible to overheat the voice coil of the 12 inch driver I was using any audible frequency with the SS amplifier concerned. The impedance at 20 kHz rose (from 8) to 24 ohms, the current therefore reduced to 1/3 and the power dissipation to 1/9 th. That is true unless the speaker was one of their twin cone types, with a copper cap on the pole piece, holding the impedance down a high frequencies. ........... Phil |
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