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Messages - PJ

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1
General Discussion / Re: Building a Music Room
« on: January 07, 2010, 12:20:19 PM »
Given a corner location for the bass speakers, it becomes important to look at the first few room modes. If we assume an adequate amount of low-frequency acoustic absorption - and that's a might big if, as well as being ill-defined! - then you can simplify to the longitudinal modes in the expectation that the 2- and 3-wall modes are more heavily damped.

Given that, the smoothest bass response is going to happen when the modes, and hence the room dimensions, are space at 1/3 octave intervals. That means room dimensions in the 1:1.26:1.59 ratio. For example, a room 20 feet by 25 feet, with a 16 foot ceiling.

Adequate damping is an issue. Corner horns like the Klipsch require rigid walls or else the bass gets absorbed before it escapes to the room, but the rest of the room is going to get its bass absorption from wall vibrations or massive amounts of tube traps, tuned appropriately.

This is only talking about the very low frequencies, say below 100 or 150Hz. Others have made excellent points about initial reflection delay time, diffusion, live/dead distribution, all of which are relevant in the more critical midrange and high frequencies and may have constraints incompatible with the bass requirements. It's not a subject with a simple answer!

2
General Discussion / Re: Building a Music Room
« on: November 25, 2009, 10:20:39 PM »
For smoothest response, the ratio of 1 : 1.25 : 1.6 is best, as it spreads out the frequencies of the standing waves the most.  But it would be even better to build the room without any parallel walls.
For what it's worth, you can do nearly as well with 1:1.6:2.5 ratios, which is often more amenable to normal house construction. The point of both is to space the axial resonances evenly - the higher order resonances bounce off more surfaces, are more easily damped, and hence less important. The ratio 1.6 is pretty close to the "golden ratio" which may be why both seem to work.

The point of non-parallel walls is to diffuse slap echoes, where high-frequency harmonics stay in phase with repeated reflections. In the really great old concert halls, they did this by accident using lots of marble statues in niches in the walls, Cyrill Harris accomplished the same goal here in Seattle at Benaroya Hall (home of the Seattle Symphony) using very shallow truncated pyramids - the deviation from parallel is only a few degrees. There are many ways to minimize absolutely parallel surfaces without seriously compromising normal rectangular construction methods.

3
Suggestion Box / Re: More orchestral blockbusters
« on: November 01, 2009, 04:26:23 PM »
A Mahler symphony, preferably one of the "Wunderhorn" symphonies (2,3,4). I'm open to suggestion with respect to performances. Klemperer maybe for 2? Kletzki for 4? Bernstein for 3 (if good sound can be obtained)? ...
Second the Bernstein Mahler 3, this is the recording that opened my eyes to Mahler. But it's nearly 2 hours, not gonna fit on a couple reels. Same problem with most of the Mahler symphonies I'm afraid. Mahler 2 is another beloved piece; I have a terrific reading by Haitink and the Concertgebouw - Elly Ameling sings the soprano. Nice!

I like the other suggestions as well...

4
General Discussion / Re: Speed Question
« on: October 29, 2009, 02:30:53 PM »
...Off hand I think the -3DB is 18 Khz for 7 1/2' and 20 Khz for 15 ips, ...
I'm sure you're right in many realistic cases, but theoretically (i.e. with the same head gap and a low enough head capacitance) you should be able to get another octave at twice the tape speed.

5
Suggestion Box / Re: More on Mahler 1
« on: October 27, 2009, 05:35:39 PM »
I'm not registered with the Mahlerites so I didn't vote. But my vote would certainly be Leinsdorf/BSO by RCA, "mastered on RCA magnetic tape". Says so right on the album cover. I'm not a collector, just a fan, but I always thought that was the definitive recording. I once had a 7.5ips tape, might have given it to Dan S. The recording is quite good, and I at least find it musically the best of any I've heard, live or recorded.

I fully agree, the First is the most accessible. Actually the Fourth is pretty accessible as well, but it has never moved me like the First.

The only other M1 I have at hand is the Barbirolli (Halle). The recording is in stereo, but unpleasant sounding and quite noisy - possibly because my pressing is on Vanguard-Everyman. Label says "A Pye recording - 1967".


6
General Discussion / Re: Equalization curves
« on: October 01, 2009, 10:45:01 PM »
Perhaps this will help.

RIAA has three corner frequencies. Practical IEC has two. Theoretical IEC has only one.

7
...
PJ, you sure are up late tonight. I'm watching the qualifying for the Grand Prix in Valencia Spain. What's your excuse?
Huh - my Saturday night post disappeared, so this comment now seems out of context ... but I posted after I got home from the Seattle "Gotterdammerung" so of course I was pretty late! Incidentally, many people did not like our Brunhilde, but I loved her. Finally, a signer who looks and sounds like a tomboy virgin maiden Valkyrie instead of a 45-your-old prison guard! OK, her low and middle range could not overpower the orchestra in full force - what do you expect from a kid?! - but her high register could, and she never got tired. Never! And youthful exuberance, in voice and acting, to match Siegfried. What a treat!

8
Tape Project Machines / Re: Nagra T Audio available
« on: August 23, 2009, 01:52:02 AM »
Dave is an old friend from VALVE days, and yes he really is one of the sweetest people on the planet. Not that you will get anything past him when making a deal - did I mention smart as well?  :^) 

And yes, at an early VSAC show Bottlehead showed a system with Dave's Ampex 350 playing 30ips tapes from Paul S. Took "best of show" from several journals, and while I'm proud to have helped design the amps and speakers, I think that was because we had the best damn source by a very wide margin!

IIRC there was a good deal of exceptional Scotch involved as well (not the tape) but that's another story.

9
Sorry I missed this thread until now. I usually concentrate on the hardware forums, but I am personally a mostly-classical listener.

I'd just like to mention that I agree with Paul S. - analogue tape is uniquely suited to capturing the spectrally dense sound of a large orchestra. I don't know technically why digital gets so messed up in the high frequencies when there is more than one or two things going on, but I sure as heck hear it! Only the very best vinyl comes close in my experience. And since this is the music that moves me the most, I'm quite enthused about more of it on good tape.

I'm in the middle of the Ring performances in Seattle right now, so of course I'm thinking of that. The touchstone is still (I think) the London ffrr set with Solti and the Vienna Philharmonic - Flagstad, Svanholm, Nilsson, Ludvig, Windgassen, Sutherland, Fischer-Dieskau, ... so many great voices are on this set. OK, I know it's 30 tapesbut there are some SERIOUS Wagner fans out there! I'm just sayin'...

10
Tape Project Machines / Re: Tape project Machines page updated
« on: April 30, 2009, 02:57:49 PM »
I think this question has been addressed before on these pages, somewhere.

The basic problem is that RIAA equalization falls at 6dB per octave above 2100Hz, while tape equalizations are flat above the upper-midrange corner frequency. Unless you modify the equalization network inside the phono preamp, you will need additional gain to restore the high frequencies. In my experience, even if you have 20-30dB excess gain available, it would still be uncertain whether you could place the equalization in a way that did not make mincemeat of the signal-to-noise ration of the system.

It should not be difficult to change the equalization, and I would be surprised if deParavicini has not been asked this question before. However, based on our experience with the Bottlehead circuits, it would be much more difficult to make the equalization switchable - finding a place for the switch, and wiring it is such a way that the various stray capacitances and interference signals do not corrupt the sound, are significant difficulties that do not show up on the circuit diagram!

11
...  Appears that the components affecting the HF are mounted on a little turret board on the front panel near the EQ switch.  The HF "pole" components are a 47 NF cap in series with a 1.06K resistor, which gets shunted by a 2.48K resistor when the EQ switch is in the IEC position.  Played with adding resistance to the 1.06K and found that an additional 220 ohms upped the HF response so it is now within a dB at 10K and down 2 dB at 20Khz.  ...
Actually, this illustrates a big part of why these Repro amp do not have a high degree of adjustability.

For a "perfect" tape head, the equalization in the high frequencies has a single corner at a few kHz; the actual frequency depends on which equalization curve is being followed, This is in the midrange, and tape heads in general have a flat response in the midrange. Consequently, this is not an appropriate place to adjust the high treble - it will unbalance the critical midrange if you make adjustments. The proper reason for such adjustment would be to compensate out-of-tolerance resistors and capacitors, or drifting tube parameters. Modern precision components make it unnecessary, and careful design can make the equalization insensitive to tube parameter changes.

In the case cited here, by changing the resistor you moved the corner so there is a shelving rise in the midrange, which raised the 10kHz and 15kHz levels as well. The measured numerical deviation may be smaller, but the midrange shelving is likely to be more audible.

The very high frequency response is determined by the tape heads - the gap, the inductance, and the parasitic capacitances in particular. In the case of high-output, high-inductance heads which will exhibit an inductance/capacitance resonance in the audible range, the damping of that resonance can be adjusted by the preamp input loading resistance to obtain a modicum of control, and some Repro amps have this adjustment installed. It must be placed at the most critical location, at the preamp input, so a quality fixed resistor is always preferable sonically if it is possible to do so. These heads are most likely to be found on older tape decks with tubed electronics.

Some tape head preamps employ various kinds of equalizer circuits to compensate for poor high-frequency response. Such additional circuitry will inevitably degrade the sound, however subtly. Fortunately, good modern heads of medium sensitivity, such as those used on the Technics 1500, Otari MX5050, Ampex ATR, etc., are now available, and they do not need compensation. If such a head has lost treble response due to wear, it should be re-lapped rather than equalized. Bottlehead sends heads out for re-lapping frequently, and they come back with full response restored. If the response can't be restored, then the head is worn out and should be replaced. Even the best heads cost no more than a Tape Project album or two!

The remaining candidate for adjustment is the bass response where "head bumps" may give a less than flat response. Again, a complex set of parametric equalizers would be needed to fully compensate, and in this case very difficult and time-consuming to adjust correctly. Usually such adjustments are found only in the preamps built into certain high-end tape decks where the designer of hte electronics knows what the head bumps are like because he also specified the tape head to be used, and the electronics are tuned to that particular head (and tape speed). Fortunately (again) extended-response heads with minimal head bumps are available and are a sonically superior solution in our opinion.

Those are the considerations that led to the Bottlehead Repro amp having so few adjustments available.

12
General Discussion / Re: Outboard Electronics
« on: April 08, 2009, 11:00:19 AM »
...
Hey PJ,.. I was just wondering if Michael had those big Meyer Sound X10's when you listened? ...
I think it might have been the TADs at that time, but if not it would have been the X10s (which - I agree - are a great speaker).

13
General Discussion / Re: Outboard Electronics
« on: March 31, 2009, 11:44:26 PM »
...My greatest fear is that in a controlled double blind test I would pick high bit rate digital over my beloved analog sources...
A couple years ago I was present at the Mission Street studio, listening to a really high-end, high bit rate, high resolution A/D and D/A. This was seriously good stuff, not yet commercially available at the time. Paul S. brought in a 1" two-track, 30IPS I think, recording which was routed to the digital stuff or bypassed with the flick of a switch. Trust me, you do NOT need to have this fear. Really good digital may be miles better than CDs (yes indeed it is!), but it still ain't analog and it's not difficult to tell, if the source and system are good enough.

People often claim added distortion of the pleasant sort will explain the preference for tubes, but in this experiment it was clear that added digital distortion damaged the sound. And I'm pretty confident that the measured distortion of the digital system was orders of magnitude less than the usual SET amp. And, for what it's worth, this was not a tube system either - ATR-100 to Michael's console, amps, and speakers.

14
General Discussion / Re: Tape fairy strikes again
« on: March 23, 2009, 10:14:35 PM »
For those of you who read about the acquisition of the Mercury tapes in another thread, I am happy to report that today the TF (Tape Fairy) left a brown bag at my office with a selection of RCA/Reiner/Chicago
recordings. I have not yet had a chance to inventory what's in there, but I think there just might be some real goodies...
Lucky you! There are some real gems with Reiner/Chicago - long ago I had a Mahler 4 on tape. I still have vinyl of the Heldenleben, that performance is head and shoulders above any other I've heard. And God knows Strauss really NEEDS the clarity of tape.

Did I mention I like the Romantics?  :^)

15
Tape Project Machines / Am I mistaken ...
« on: March 11, 2009, 11:54:37 PM »
Or is that a Technics RS-1500?

http://www.wapsisquare.com/index.html
(this is for 3/12/09; may have to search if it's not Thursday)

Hey, newspapers are disappearing fast - gotta find your own comics on the web to read.  :^)  any strip with a demon barista has to be good!

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