Hi,
http://www.waset.org/journals/waset/v41/v41-21.pdf
From personal experience I find 6dB less maximum SPL are acceptable. However, as the Amplifier has to cover only a fraction of the spectrum, we can reduce power more than that.
If you had (say) a 100W Amplifier putting out pink noise and you used an active crossover to remove everything below 2KHz you would only need around 30Watt, but with 6dB less SPL needed it would be 7.5Watt.
Plus Tweeters are often more efficient than Woofers, so it may be possible to drop power levels even further.
HOWEVER, some music may contain peaks to nominal 0dB even at high frequencies, so it would be prudent to use an amplifier of around halve the power of the woofer section, biased for Class A operation up to a few Watt.
With enough heatsinking and CCS on the output an LM3875 Chipamp can do surprisingly well in this application.
Feed it a stabilised +/-25V and you get up to 40W for peaks into the typical (6 Ohm Impedance) tweeter, which should make sure no clipping is encountered. Add a 0.7A current source (LM317 & resistor will do) to the output and you get around 2.83V or the nominal "first watt" in SE Class A.
For the midrange section you can use pretty much the same Amp, bridged Pairs of LM3886 (one pair per nominal 8 ohm Woofer) run on +/-30V without Class A biasing can complete the woofer section for a nice 3-Way home solution that is easy to implement.
Personally I'd use Pass B1 style buffers for the crossover ahead of these chipamps. The result would likely be not bad at all if the driver selection and crossover design are competent.
Of course, we can improve the Midrange and Treble performance by using current drive and use some form of motional feedback on the Woofer in a 3-Way system where the results could be quite exceptional.
Seas has 5" or 6.5" Coaxials that would be very suited to the Job of Midrange/Treble (and which last time I looked had low enough Qm to be very usable with current drive)... Woofers can be found.
Ciao T
http://www.waset.org/journals/waset/v41/v41-21.pdf
From personal experience I find 6dB less maximum SPL are acceptable. However, as the Amplifier has to cover only a fraction of the spectrum, we can reduce power more than that.
If you had (say) a 100W Amplifier putting out pink noise and you used an active crossover to remove everything below 2KHz you would only need around 30Watt, but with 6dB less SPL needed it would be 7.5Watt.
Plus Tweeters are often more efficient than Woofers, so it may be possible to drop power levels even further.
HOWEVER, some music may contain peaks to nominal 0dB even at high frequencies, so it would be prudent to use an amplifier of around halve the power of the woofer section, biased for Class A operation up to a few Watt.
With enough heatsinking and CCS on the output an LM3875 Chipamp can do surprisingly well in this application.
Feed it a stabilised +/-25V and you get up to 40W for peaks into the typical (6 Ohm Impedance) tweeter, which should make sure no clipping is encountered. Add a 0.7A current source (LM317 & resistor will do) to the output and you get around 2.83V or the nominal "first watt" in SE Class A.
For the midrange section you can use pretty much the same Amp, bridged Pairs of LM3886 (one pair per nominal 8 ohm Woofer) run on +/-30V without Class A biasing can complete the woofer section for a nice 3-Way home solution that is easy to implement.
Personally I'd use Pass B1 style buffers for the crossover ahead of these chipamps. The result would likely be not bad at all if the driver selection and crossover design are competent.
Of course, we can improve the Midrange and Treble performance by using current drive and use some form of motional feedback on the Woofer in a 3-Way system where the results could be quite exceptional.
Seas has 5" or 6.5" Coaxials that would be very suited to the Job of Midrange/Treble (and which last time I looked had low enough Qm to be very usable with current drive)... Woofers can be found.
Ciao T
T,
When woofers are designed to produce flat frequency response curves that requires reducing the efficiency. Woofers that show pistonic response are often more efficient than tweeters.
So in home use tweeters will see much less energy than woofers.
When I started doing big joints even the acoustical consultants seemed to believe that. Turns out there is 20 db or more loss at 8,000 hertz than at 150 hertz. The tweeters being horn loaded are more directional than the lower frequency devices so that appears to improve the output level. However to get the best results at long throws 200 meters or more the high frequency drivers require more power than the woofers. The midrange drivers are often horn loaded and really get to loaf. So at an American football stadium I can have 60,000 watts on the woofers, 8,000 watts midrange and 80,000 watts driving the 150 or so compression drivers!
Now the secret to using compression drivers at high power is that you can compress air almost infinitely but you have a very well defined limit on the rarefaction side! So by deliberately adding distortion you can decrease the compression time and increase the rarefaction time of the cycle. Now when you consider the distortion results of doing this realize the same air losses apply. So if I have 300% distortion at 8,000 hertz. The third harmonic would be reduced to .3% at the listeners position, just by the air loss!
The same actually holds true for a tweeter only home use amplifier. Higher order distortion products such as the 11th would have a hard time making it out of the tweeter and get some additional attenuation from the air loss! So designing a tweeter only amplifier is a bit different than just a low power HF only version of a basic amplifier. As well noted here crossover distortion would be a super - ultra - mondo - major issue. So it actually might not be unreasonable to use an (Shudder, groan, exhale) IC power amplifier with an output biased to class A! The THD just might not be as important an issue.
Of course lets talk bandwidth and layout, those would be much more important.
When woofers are designed to produce flat frequency response curves that requires reducing the efficiency. Woofers that show pistonic response are often more efficient than tweeters.
So in home use tweeters will see much less energy than woofers.
When I started doing big joints even the acoustical consultants seemed to believe that. Turns out there is 20 db or more loss at 8,000 hertz than at 150 hertz. The tweeters being horn loaded are more directional than the lower frequency devices so that appears to improve the output level. However to get the best results at long throws 200 meters or more the high frequency drivers require more power than the woofers. The midrange drivers are often horn loaded and really get to loaf. So at an American football stadium I can have 60,000 watts on the woofers, 8,000 watts midrange and 80,000 watts driving the 150 or so compression drivers!
Now the secret to using compression drivers at high power is that you can compress air almost infinitely but you have a very well defined limit on the rarefaction side! So by deliberately adding distortion you can decrease the compression time and increase the rarefaction time of the cycle. Now when you consider the distortion results of doing this realize the same air losses apply. So if I have 300% distortion at 8,000 hertz. The third harmonic would be reduced to .3% at the listeners position, just by the air loss!
The same actually holds true for a tweeter only home use amplifier. Higher order distortion products such as the 11th would have a hard time making it out of the tweeter and get some additional attenuation from the air loss! So designing a tweeter only amplifier is a bit different than just a low power HF only version of a basic amplifier. As well noted here crossover distortion would be a super - ultra - mondo - major issue. So it actually might not be unreasonable to use an (Shudder, groan, exhale) IC power amplifier with an output biased to class A! The THD just might not be as important an issue.
Of course lets talk bandwidth and layout, those would be much more important.
Ed,
Well, in concert systems (my stuff) we usually dealt with such extremely long throw situations with deploying delayed towers downrange, much less headaches. This may not be possible in certain sports venues etc. for sports events, but that is a quite esotheric are of sound and somehow I feel you may not be deploying class A Amp's on these midranges and tweeters...
Yes, Neumann designed a similar into LP cutting lathes in the 1960's and it was very widely used since. The funny bit is that this distortion cancellation system on LP only works if you have a spherical playback stylus, use anything else and you actually get added, not subtracted distortion...
I proposed a similar system to apply to domestic and studio speakers (where the problem is generally at LF) in the 1990's on the "Bass" List to an overwhelming silence...
Ciao T
Well, in concert systems (my stuff) we usually dealt with such extremely long throw situations with deploying delayed towers downrange, much less headaches. This may not be possible in certain sports venues etc. for sports events, but that is a quite esotheric are of sound and somehow I feel you may not be deploying class A Amp's on these midranges and tweeters...
Yes, Neumann designed a similar into LP cutting lathes in the 1960's and it was very widely used since. The funny bit is that this distortion cancellation system on LP only works if you have a spherical playback stylus, use anything else and you actually get added, not subtracted distortion...
I proposed a similar system to apply to domestic and studio speakers (where the problem is generally at LF) in the 1990's on the "Bass" List to an overwhelming silence...
Ciao T
Is there any reference available actually showing this work? I would think traceing pre-distortion could be computed for any stylus geometry, but I would also think traceing distortion goes down at low frequency somewhat for any geometry. So then what is the point of line contact stylii if the records were cut for spherical ones?
My experience is that tones above a few kHz have so much distortion that it would be a challenge to see a difference.
Hi,
AES E-Library Development and Application of a New -Tracing Simulator-
Yes, but in the 70's and 80's spherical stylii where prevalent in consumer grade gear, so that is what they cut for...
There where several systems at the time, only Neumann and Teldec (with DMM) achieved an wide spread penetration.
Nonwhatsoever?
Did you use a decent quality cartridge with a spherical stylus (not elliptical or line contact)?
They where compensating some 10% + of TD...
Ciao T
AES E-Library Development and Application of a New -Tracing Simulator-
Yes, but in the 70's and 80's spherical stylii where prevalent in consumer grade gear, so that is what they cut for...
There where several systems at the time, only Neumann and Teldec (with DMM) achieved an wide spread penetration.
Nonwhatsoever?
Did you use a decent quality cartridge with a spherical stylus (not elliptical or line contact)?
They where compensating some 10% + of TD...
Ciao T
They were decent but not spherical, would the Denon 103 with the spherical option be a decent choice and how does one find out if the pre-distortion was used. I'm interested in this in an intellectual sense. There seems to be some disconnect going on with high-end cartridge makers and what's on the LP's. I have also seen no mention of this in the context of laser or ultra-high res optical LP scanning neither of which has tracking distortion.
John, what about your direct to disk experience?
BTW that Neumann paper was dated 1970, when was the system rolled out?
EDIT - there should be a transform between stylus geometries especially much better tracking ones.
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Interesting, the Crystal Clear records that I have heard would not have benefited from any pre-distortion (IMHO), but then how would I know?
Phono reproduction is a very ad hoc, seat-of-pants endeavor that wouldn't have even been attempted if anyone had been able to do a real engineering analysis back in the day. Like bumblebees, they can't fly. Contact pressures in the tons per square inch, temperatures of 400F (some say up to 700F), dirt bigger than most signal and significant signal in the optical wavelengths.
One part of this contraption not often appreciated is that the actual geometry being traced extends considerably *into* the medium, with significant elastic deformation a critical part of the geometry. Those non-contact surface-only scanners, besides the insane noise issues, actually trace the*wrong* geometry.
Thanks,
Chris
They probably do better with archiving old shellac 78's where they can average up and down the groove wall.
Vinyl in speakers out, well, it still can sound fine even though it looks hopeless.
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