John Curl's Blowtorch preamplifier part II

[morinix]

Originally Posted by Tom Danley

If you want to hear how accurate a loudspeaker is, make a generation loss recording with a measurement mic in a semi anechoic condition (outdoors on a quiet day). Like any part of the chain, the more passes it will tolerate before transmogrifying the signal, the more accurate it is.
At work, we used this at work developing our loudspeakers (large scale sound) and it was eye opening many times.. It is surprising how few passes even some good loudspeakers will last, each generation an increasing caricature of what is wrong.
Best,
Tom Danley
Danley Sound Labs

A super-practical nugget of wisdom

[fas42]

Originally Posted by RNMarsh

256W but at 1 meter from the speaker. Depending on room volume/size and speaker directivity, distance to the listening position, room characteristic et al, the power needs will be greater than this minimum number. And, most speakers are much lower than 94db. Lots more power needed.

No, still not happy ... remember I only was working with a single speaker, the stereo pairing adds 6dB in the "sweet spot", so now that 256W/channel is pumping 118 + 6 = 124dB into your skull at 1 metre. Okay, back off to listening distance used by many, 2 meteres, roughly lose 6dB, still around 118dB. And we haven't taken into account additive effects of room reflections ...

Now, I know how many systems appear to lack grunt, but IME this is all about the quality of the sound ... lack of distortion. All my experience has shown me that a nominally low powered system working correctly creates the subjective impression of high impact, dynamic reproduction.

Frank

[fas42]

Originally Posted by Esperado

Did-you mean two hours of Spinal Tap music with your volume at 11 each time you want to listen at " A Little Night Music " ?

Pretty well that. If I kick off straightaway with classical it will be all very polite and somewhat innocuous, but it will lack life, the dynamics of the real thing. The treble has to be right for the sparkle, the punch of real music to emerge, and dynamic drivers as a class all seem to suffer this to some degree, the need for conditioning the suspensions from cold. Probably one reason why panels generally hit the "right note" on casual hearing for many ...

Frank

[Wavebourn]

Originally Posted by fas42

That's what my main agenda is ... I believe, very strongly, because I've experienced it many times, that the illusion can be maintained no matter how close one gets to the speaker drivers. It's all a matter of degree, the system has to be absolutely correctly aligned for this to happen, requires extreme fussiness about every detail, but when you get it right there's no questioning about the effect: the ear/brain is happy to be fooled into thinking that the speakers aren't in the room, no matter what. And all the adjectives that people throw around about impressive sound all make sense ...

Still, planars and line arrays in this regards are best. They genetare kind of more uniform field, so stereo image is heard on much wider area than with point source speakers. Even when stereo image gets uncertain the volume is still heard.

[fas42]

Originally Posted by john curl

Horn throat distortion is real. It can be VERY critical, although JBL and others have attempted to minimize it with better horn drivers and faster flare (for the actual working range) throats in RECENT years. I must say that JBL did NOT appreciate my input, 40 years ago on the same subject. Now you would think that they improved things, just because they could. '-)

Probably completely irrelevant, but the ambitious JBL at the recent hifi show, with horn midrange and treble, 94dB sensitivity, just wasn't in the game -- as soon as there was real volume the thought, PA sound, popped into one's head ...

Frank

[Chris Hornbeck]

Originally Posted by fas42

... remember I only was working with a single speaker, the stereo pairing adds 6dB in the "sweet spot"

My turn to nitpick, I guess. Uncorrelated signals add 3dB, like noise. The line sources being discussed have another advantage; if they're very big (compared to a wavelength) direct sound falls off linearly.

Thanks,
Chris

[fas42]

Originally Posted by Wavebourn

Still, planars and line arrays in this regards are best. They genetare kind of more uniform field, so stereo image is heard on much wider area than with point source speakers. Even when stereo image gets uncertain the volume is still heard.

My experience with planars is not particularly positive ... yes, they generally are very pleasant to listen to but they typically do weird things with the treble because of the size of the radiating area -- the microscopic sweet spot effect, not my cup of tea.

My goal is for the stereo image to be experienced everywhere in the room, that there is no such animal as a sweet spot ...

Frank

[fas42]

Originally Posted by Chris Hornbeck

My turn to nitpick, I guess. Uncorrelated signals add 3dB, like noise. The line sources being discussed have another advantage; if they're very big (compared to a wavelength) direct sound falls off linearly.

Thanks,
Chris

But the signals are correlated, if the piano is centre then a note struck is very close to being purely additive, from the 2 channels.

Note that all professional active monitors sold are always spec'd on using a stereo pair, such that there is 6dB gain for the typical listening position. The top Dynaudio's do 133dB at 1 meter - what!!! - yes, assuming a stereo pair, this now makes more sense ...

Frank

[Wavebourn]

Originally Posted by fas42

My experience with planars is not particularly positive ... yes, they generally are very pleasant to listen to but they typically do weird things with the treble because of the size of the radiating area -- the microscopic sweet spot effect, not my cup of tea.

My goal is for the stereo image to be experienced everywhere in the room, that there is no such animal as a sweet spot ...

Then try arrays. No sweet spot at all. Dispersed sound, like it goes from beyond the speakers. The next year I will bring on BAF 3-row arrays, open baffles: open baffles and dipoles are getting popular.

My arrays at home are currently in walls.

[Chris Hornbeck]

Originally Posted by fas42

But the signals are correlated, if the piano is centre then a note struck is very close to being purely additive, from the 2 channels.

Note that all professional active monitors sold are always spec'd on using a stereo pair, such that there is 6dB gain for the typical listening position. The top Dynaudio's do 133dB at 1 meter - what!!! - yes, assuming a stereo pair, this now makes more sense ...

Try it for yourself with a music source. Except at very low frequencies, the precision needed for correlation is an impossible hurdle.

Thanks,
Chris