The Quads are for classical! What are you listening to on them Richard? Led Zepplin? 😀
If you need more bass, why not augment them with a good sub?
(neat trick in post #96 by the way)
If you need more bass, why not augment them with a good sub?
(neat trick in post #96 by the way)
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There's a big difference between voltage drive with a bit of impedance and current drive, those two things are not to be compared. I see potential in a true current drive, as it has the potential to override some of the mechanical resonance issues of modernday voltage driven speakers and drivers. Adding output resistance to voltage drive is just an attempt to compensate for poor speaker designs.
" output transformer " ?
Jan,
I think you are thinking of the normal SS amp with
the output taken from the emitters or sources of
the final output stage where the output Z is, in fact,
low like you say. But if the output is taken from the
collectors or drains the impedance (sans any feedback)
is theorietically infinite.
If I had the money, I would buy these from eBay, item 121084484485: Dali Megaline III
http://rover.ebay.com/rover/1/711-5...io01-20&ipn=psmain&kwid=902099&mtid=824&kw=lg
I listen primarily to Blues and World Music. Some jazz and R&R if it has a strong blues influence to it. Most have beats and rhythms set with drums and bass guitar. I have a 5 string Padulla (bass) that I am fumbling with... need lessons, i think.
I drag out the Quads and use them as test equipment for critical listening sessions.
#96.... I thought so, but not enough people read TAA so it didnt get the attention it deserves... glad there was a place here to bring it up again. Thx.
But I also want to find out more about current drive -- issues/pro/con and some real-world tests, hopefully.
-Richard
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Led Zep? Good idea... got to go find it and play it again !! In High Def digital download, perhaps?
Dali? That 400$ shipping is a deal breaker for me. 🙂
-RNM
Dali? That 400$ shipping is a deal breaker for me. 🙂
-RNM
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Actually true Current Drive exacerbates 'mechanical resonance issues'.
ie if a speaker has a mechanical resonance problem, it will be even more obvious with true Current Drive. This is not a Golden Pinnae thing but easily heard on a sine sweep.
In the scope shot below, yellow is the voltage driven to one coil of a DVC woofer. Blue is the current in the driven coil. Purple is the open circuit voltage of the un-driven second voice coil.
There is about 3A RMS forward. The speaker is about 12 ohms at resonance.
I had thought that the driven current distortion is due to the phase of the back emf. It appears I was wrong. It looks like back emf distortion may be the culprit compliments of the non-linearity of BL.
The back emf is non-linear and asymmetric.
The The driven coil current distortion is quite visible at 1.2A rms.
There is about 3A RMS forward. The speaker is about 12 ohms at resonance.
I had thought that the driven current distortion is due to the phase of the back emf. It appears I was wrong. It looks like back emf distortion may be the culprit compliments of the non-linearity of BL.
The back emf is non-linear and asymmetric.
The The driven coil current distortion is quite visible at 1.2A rms.
An externally hosted image should be here but it was not working when we last tested it.
Kgrlee, yes assuming you use a normal driver in normal voltage based environments. then current drive would worsen the scenario, to exploit the possibilities you would have to rethink the driver and cabinet solution. The culprit is for sure the low woofer resonance.
Err.rh! Classical Music. Dynamic Range. Remember loud bits and soft bits?
Even Led Zep with mostly constant mezzo forte can do with pretty small amps & speakers for bleeding ear levels without audible distortion. It's Britten's War Requiem that needs the 1000W/channel amp and 4 pairs of ELS63s at LF for no audible distortion.
4 pairs of ELS63s would have less audible THD than any moving coil sub I can think of at high level.
Mr. Marsh, you would need a new listening room for my Ultimate speaker system. I'm happy to design that for you too 🙂
Thats looks like an accoustic mixing from cabinet and mass effect.The back emf is non-linear and asymmetric.
E: Mass effect should be forced to be minimum, and accoustic mixing should be allowed as it is, thats something difficult driving. It most difficult is in HF.
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I've spent a long time 'rethinking' this issue from both a drive unit as well as cabinet, design perspective. Alas, the solutions all involve reducing efficiency to much lower levels.
And the good solutions are even more effective when used to improve 'normal' voltage drive speakers.
If you know of other solutions, please let us know.
Even if you have a 'speaker system optimised for current drive'[*], any unwanted mechanical resonances (eg cabinet panel resonances) would still be exacerbated cos the current drive.
[*] Technology & 'know how' for this exists. Just need some Unobtainium.
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The woofer is suspended in free air. It is operating at resonance. When I adjust drive level, I adjust the frequency for speaker resonance.
Woofer, this is a very high level 36Vrms at resonance 😱
How much is the cone moving (+/- ? mm) ?
Can you do another scope pic with the cone moving at Xmax and another at 1/2 Xmax?
QUad of Quad ESL for woofer? Hmmmm Only need 3 more pairs. only. About the same as a Dali.
I have a sloping 13-21 foot ceiling so no problem. Nice for dispersion. Tall enough and large room volume for listening.
But what would I do with those two 18 inch TC-Sounds sub woofer drivers and the massive current-drive or motional feedback amps needed for them?
Woofertester --- I never got back with you from last year --- took off for Asia.... but did you find an amp for your project -- mine are 900W/4 class AB balanced/bridge amps at <.01% mono amps.... dont know what the 1% power output is. What needs to be done to use them for a current-drive amp or?
These are the same amps I designed for Dave Wilson's subs a few years back and the ones I was planning to use with the TC-Sounds (if I dont use a gang of QUADS instead). .
-Richard
I have a sloping 13-21 foot ceiling so no problem. Nice for dispersion. Tall enough and large room volume for listening.
But what would I do with those two 18 inch TC-Sounds sub woofer drivers and the massive current-drive or motional feedback amps needed for them?
Woofertester --- I never got back with you from last year --- took off for Asia.... but did you find an amp for your project -- mine are 900W/4 class AB balanced/bridge amps at <.01% mono amps.... dont know what the 1% power output is. What needs to be done to use them for a current-drive amp or?
These are the same amps I designed for Dave Wilson's subs a few years back and the ones I was planning to use with the TC-Sounds (if I dont use a gang of QUADS instead). .
-Richard
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Simultaneous Measurement of Impulse Response and Distortion with a Swept-Sine Technique was Angelo's first paper on the subject.
All his papers are available on his website but might need some finding. http://pcfarina.eng.unipr.it/Public/ but see eg
http://www.nvo.com/winmls/nss-folder/electro1acoustics/Measuring%20impulse%20resp%20and%20distortion%20with%20swept%20sine%201341AES00.pdf
I developed the theory for this circa 1990 for production testing of speaker response & THD in the shortest theoretically possible time. But the computing power, and particularly good A/D & D/As, were too expensive for what we wanted. I'm quite happy for Angelo to take the credit cos he was first to publish.
Returning to civilisation after more than a decade in the bush, I found the cheapest IBM/Lenovo laptop had all the necessary hardware. Alas, I'm still in the 20th century with my DOS compiler which severely limits the size of data I can process .. and worse, machines that can run DOS will soon be extinct.
But it was wonderful to hear again the dulcet tones of a B&K 2010 driven by a 2307 chart recorder .. swept sines as God intended. 🙂
I use a mixture of Audacity and my own DOS programmes.
http://ap.com/kb/show/9 is AP's announcement of their first product to use this.
_________________
Flog them to the "never mind the quality .. just feel the weight" brigade 😀
Yes - but in my den, no need to hit the same levels as a concert hall - I use 'phones for that!
Its a real pleasure to have your experience here as one who has been in the trenches and knows.
BTW -- Can you still get chart paper for that recorder? What have you been measuring, lately?
Speaking of old systems used with old computers.... but still gives good data.... I have a MLSSA/MLS card and Linear X / LMS card that work fine in a 486 box computer [with a color monitor]. Have any computer that old to use them with?
-RM
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Chart Recorder paper isn't a problem. All my software prints to 2307 size & aspect ratio so you can compare curves by the time honoured method of aligning two plots and holding them up to the light. 🙂
The problem is getting the steam to power a B&K 2307 and 2010 .. even in Cooktown 😀
THAT brings back nostalgic memories!
I mentioned IBM/Lenovo laptops having good 16b soundcards. Alas, they are no more. Today, only a couple of Macs have good 16b inputs. I spent a small fortune (to a beach bum) buying old IBM laptops from eBay.
But computers like that are all 10+ yrs old and probably dead or dying. None of the new PCs have the slots or the drivers or good sound cards. I think AP System 1 owners have a similar problem.
I gave up and bought a new Windoz 7 laptop. Alas Windoz 7 won't run DOS at all so I re-formatted it to XP so I can run Virtual PC to run Windoz 98 which can run DOS sensibly. 😱 Du.uuh! About time I entered the 21st century.
The MOTU Traveler I use as a quality sound card is actually Angelo Farina's. He visited in 2007 and brought presents cos he had to use up some funds.
I'm a REAL beach bum. Lifeguarding at the local swimming pool puts food on the table ... and I get a good view of the tastefully clad young ladies. 🙂
I do some work on microphones for friends but there is a general ennui in dis beach bum life due to old age.
eg I've got the carcases of 3 big PA amps which I scored but haven't even opened them up. Also 8 speakers for my planned supa surround system that have sat in their boxes for nearly 5 yrs.
The DSP power in even the cheapest PC these days means I can do stuff which was only a theoretical dream in the 90's. But finding the energy to do serious DSP work is a problem when the beach calls. It's a hard life 🙂
Apologies for an old man's drooling ..
Attachments
Yes I know; maybe I have lost track here but isn't Nelson using an output xformer? He mentioned 80 ohms in parallel to the output and I think I have seen that during some of his presentations as an 80 ohms resistor in parallel to the output xformer primary.
Jan