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Old 2nd January 2018, 06:30 PM   #3741
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by billshurv View Post
yeah a lot of 'popular' music does hang around -12dB. Or at least used to. I have a track with -6dB RMS and Tom has worse on his website.
5-6 dB is the worst case reported in the Sound on Sound article I link to in the Crest Factor section of my Taming the LM3886 article series.

From the data above, it looks like 27-30 dB is a probable best case, though I would never design an amp for that. My recommendations are based on the average CF of 14 dB reported by SOS. I also design for a max heat sink temperature of 60 C with an ambient temperature of 25 C. That means that a design which is right up against the limit will get quite hot (but survive) with sine wave operation. It may trip the thermal protection in the LM3886 after an hour of operation with a continuous sine wave into a 4 Ω load at the worst case dissipation, but will barely get lukewarm in operation with a music signal at normally loud critical listening levels with speaker loads and music signal.

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Originally Posted by nycavsr2000 View Post
Good discussion. I’ve been reading Toole’s 3rd Edition of “Sound Reproductions” <highly recommended> and he discusses this in detail on Chapter 16. He doesn’t mention a DF ratio though so I presumed 1:10 was adequate. Do you have a source for your 1:20 recommendation?
I'd be interested in the source for the 1:20 recommendation as well. I'd also be interested in the perceived effects of a lower DF (scientific results, not subjective so-and-so-on-the-internet-said opinion).

Tom
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Old 2nd January 2018, 10:39 PM   #3742
billshurv is offline billshurv  United Kingdom
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I'd never design thermals for best case CF, but it's useful for one of the upper bounds on how much power you need, even if the number of albums that require it are small. Telarc 1812 has a (badly clipped) 38Hz fundamental on the cannon shot on the CD version. And it's interesting to have a collection of oddities in one's music library
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Old 2nd January 2018, 11:13 PM   #3743
soongsc is offline soongsc  Taiwan
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Having stood beside firing tanks, I think it would be highly unlikely to hear these levels reproduced.
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Old 2nd January 2018, 11:26 PM   #3744
billshurv is offline billshurv  United Kingdom
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Of course not, but when the cannon blast on the telarc 1812 is 26dB* above the orchestra if you have the orchestra at 75dBa then you need to have enough power for approx 101dBa* from whatever produces your bass at 38Hz. Assuming 85dB/W and nearfield listening that's 40W. BUT if you have the orchestra at 85dBa, which some do although I would suggest a tad louder than I listen you need 400W. Suddenly a plurality of powered subs seems a good idea! (or listen at more sensible levels).

Not realistic cannons, but for a hifi torture track does the job. And a data point on how much power you need, even if sizing your system for 90 seconds of music is a level of daft beyond that which most audiophiles will go

*There is evidence for the CD release that they wimped out and cut 6dB from the cannons. I need to prove this.
**arm wavy calculation well aware that there are several places where reality could tip things 3dB one way or the other.
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Old 2nd January 2018, 11:43 PM   #3745
soongsc is offline soongsc  Taiwan
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There are much more related with good cannon sound reproduction, since the cannons actual have a quite wide spectrum, the phase/group delay is important and much more difficult to achieve in a small room. The size of the drivers to produce the SPL necessary is also critical, the Linkwitz site has some quick calculations of what surface area that might be necessary to accomplish this. The driver data I have seen on Klippel measurements suggest an 18 driver reach max excursion around 25~30 volts, another consideration when working with high SPL low frequency reproduction.
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Old 2nd January 2018, 11:59 PM   #3746
billshurv is offline billshurv  United Kingdom
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luckily there is only one classical piece that calls for cannons and I have several recordings that use real cannons. It's an edge case and not one I would optimise my personal system for. I'm only allowed one 18" black cube in the living room so I am limited to around 100dBa peaks in the bass. That will do me and envelope says that, in combination with the apogees running actively off mod-86 I am good for all but wild parties, which I don't have
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Old 4th January 2018, 12:37 PM   #3747
Johnny2Bad is offline Johnny2Bad  Canada
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Quote:
Originally Posted by nycavsr2000 View Post
Good discussion. I’ve been reading Toole’s 3rd Edition of “Sound Reproductions” <highly recommended> and he discusses this in detail on Chapter 16. He doesn’t mention a DF ratio though so I presumed 1:10 was adequate. Do you have a source for your 1:20 recommendation?

Best,
Anand.
Yes and no. It's from some discussions I read a few years ago, when I was interested in the subject. So it might have been a magazine interview with someone who was designing amps in the 60's and 70's, maybe a Rane Note, there were a few other places I dug up and read.

I did a search of my current HD, nothing there (well, some, but related to turntables). If I remember, next time I read some of my archived drives, maybe I saved something.

The more interesting part about DF was how it became an issue in the first place. In the early and mid 1960's, when solid state amps began to enter the HiFi market (versus the "Teen Beach Party" FM/AM radio market), naturally there was a competitive nature to the marketing, and SS amps had these very low output impedances. So it was proposed as an inherent quality advantage over transformer-coupled vacuum and SS (the McIntosh patent) amps; the ad copy of the day touted it as a feature.

Somewhere in all that (not withstanding the ad copy) it seemed there was a consensus amongst those who dismissed the high DF argument that "a DF of 20 was adequate". I remember those exact words. A lot of the reasoning behind that is the combined impedances of everything after the binding posts, making the SS amps DF a little less impressive.

I also took note of the "lunatic fringe" car audio guys, running 2 and sometimes 1 ohm bass drivers, and no-one is complaining about lack of woofer control, at least amongst the Sound Quality (SQ) guys (there are a lot of bad car audio installations out there). In that crowd they almost without exception prefer high power and ported LF drivers, so you have to wonder what all the fuss is about. Plus you see ads for car audio amps rearing the DF "advantage" once more, which I find suspicious since these ads are not touting the "best sounding" power amps according to the car audio guys. That's a weird market, to be sure.

My own personal experience led me to the conclusion that high power did a better job of controlling the woofer's back-EMF than a high damping factor seemed to. I'm just lucky I was in a position to be exposed to so much gear that my suspicion was raised. For example, when I first heard the Bryston 4B, although it's a flawed amplifier, especially on the top end, it has stunning bass control.

One of those things where the audio reviewers might start talking about "huge differences". And on almost anything you threw at it ... big woofers, dual big woofers in huge boxes, horn loaded woofers, electrostatics. There is a lot of variation in impedances there. But they would measure out to 250wpc or 480w or therabouts in mono, yet the output impedance wasn't different than other amps using sand, and that was a time when people were just starting to talk about cable, so the combined impedances probably weren't anything to rave about.

It's not a subject I really want to go back to, unless I come across new information that challenges my current position, which is I'm buying what the DF:20 guys are selling, for now at least. Maybe Toole is right, and DF:10 is the magic number, but 20 isn't too hard to achieve with SS, and I also own a transformer-coupled vacuum state power amp (Anthem Amp1; 40wpc, EL34's, and it sounds best on the 4 ohm taps) and I see no reason to fault it on woofer control.
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Last edited by Johnny2Bad; 4th January 2018 at 01:07 PM.
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Old 4th January 2018, 01:10 PM   #3748
Johnny2Bad is offline Johnny2Bad  Canada
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Correction:
Bryston 4B (1970's version) 200wpc 8 ohms stereo, 800 wpc 8 ohms bridged into mono. And we used them in mono for a bunch of DIY subwoofers, plus a lot of full-range speakers. Bryston warned us about using them in mono with 4 ohm loads, but we never had problems with things like big Infinity's, three-panel Magnepans, Dayton-Wright XG8's, and the usual conventional woofers of the day. I can't remember breaking even a single one, and I can't say that for a lot of highly touted amps of the day on some of those loads.

Maybe Tom can chime in (or anyone else who knows) but is the output impedance halved or doubled when you bridge the output transistors?
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Last edited by Johnny2Bad; 4th January 2018 at 01:32 PM.
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Old 4th January 2018, 01:25 PM   #3749
billshurv is offline billshurv  United Kingdom
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There is of course this on damping Impedance, and how it affects audio equipment . For me it's a system consideration.
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Old 4th January 2018, 02:38 PM   #3750
anatech is online now anatech  Canada
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Hi Johnny2Bad,
The amplifier will see the load resistance as 1/2 it's actual value in bridged mode. The damping factor rises to 1/2 it's normal value.

I can't recommend the practice of bridging amplifiers. To many negatives compared to a little positive. I think you would be further ahead running each channel into it's own speaker.

The old 4B was a piece of junk. They were right in telling you not to attempt running them in bridged mode. THe fact you didn't have any problems says one of two things.

Either you didn't need to put them in bridged mode, or
You were so very, very lucky.

My advice to anyone today is the same. Don't do it.

-Chris
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Last edited by anatech; 4th January 2018 at 03:31 PM. Reason: one "Chris" too many
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