[ctviggen]

Below is a link to an article entitled "Loudspeakers: Effects of amplifiers and cables".  I thought some might be interested in this.

Audio Design Article

Perhaps this should be in The Lab?

(PS -- I haven't had time to read it; with a newborn, I don't have time to do anything but go to work, hold her, and figure out when to take naps on the weekends!  So, if the article is bad, I apologize in advance.)

[Ethan Winer]

Below is a link to an article entitled "Loudspeakers: Effects of amplifiers and cables".  I thought some might be interested in this.

Philip Newell is really great. I'm a huge fan of his work.

--Ethan

[Bob Reynolds]

Thanks for bringing the article to my attention. It was worth the read and has prompted me to order their book. However, I do take issue with this comment:

Moreover, as no amplifier can improve the accuracy of the signal which it is passing, the only conclusion which can be drawn is that the combination of amplifier and cable can only degrade the signal.

Why is "improve" and "degrade" the only choices? What happened to "no change"? Of course, that raises the question of how the signal is measured to determine "no change".

This one is spot on in my mind:

Similarly, the popularity of valve amplifiers in many domestic hi-fi systems is widely attributed to the pleasing 'musical' sounding even harmonics which they tend to produce. Again, this will be discussed further in Chapter 8, but as these effects are totally subjective in terms of their desirability, it is very difficult to deal with the subject in any definitive way. Therefore, what we will attempt to do in this chapter is look at the problems of amplifiers and loudspeaker cables when accuracy of reproduction is the goal, and which we can deal with in an objective manner.

He makes a subtle point here that audiophiles fall into two groups (not necessarily subjective or ojective): those desiring a pleasing musical sound and those desiring accuracy of reproduction.

As the following article clearly shows, it's not only the reactive load of loudspeakers that determines the sound, but the output impedance of the amplifier relative to that loudspeaker load.

http://stereophile.com/reference/810/

I think both articles make strong arguments for active speakers.

[Ethan Winer]

Why is "improve" and "degrade" the only choices? What happened to "no change"? Of course, that raises the question of how the signal is measured to determine "no change".

Because, theoretically anyway, "no change" is impossible. Now, the change might be inaudible, and possibly even unmeasurable. But all circuits have some amount of nonlinearity (fancy word for distortion), and all cables have some resistance, capacitance, and inductance. If you define "no change" as adding less than 0.01 percent distortion, and not skewing the frequency response by more than 0.1 dB throughout the audible range of 20 Hz to 20 KHz, then you are correct to call that "no change."

He makes a subtle point here that audiophiles fall into two groups (not necessarily subjective or ojective): those desiring a pleasing musical sound and those desiring accuracy of reproduction.

If a system reproduces sound with high accuracy, then it will be pleasing to me. But many vinyl and toob fans prefer the added distortion and possible loss of high frequencies from those mediums. It's not up to me to say they're wrong, but I personally do not find that pleasing.

I also agree with you about active speakers. I have Mackie 624s in my living room home theater, and they're amazing. One reason active speakers can be superior is they are typically bi-amped. Another, at least as implemented in the Mackies, is the speaker's cone motion can be included in the amplifier's negative feedback loop. This lowers distortion quite a bit.

--Ethan

[Bob Reynolds]

Why is "improve" and "degrade" the only choices? What happened to "no change"? Of course, that raises the question of how the signal is measured to determine "no change".

Because, theoretically anyway, "no change" is impossible. Now, the change might be inaudible, and possibly even unmeasurable. But all circuits have some amount of nonlinearity (fancy word for distortion), and all cables have some resistance, capacitance, and inductance. If you define "no change" as adding less than 0.01 percent distortion, and not skewing the frequency response by more than 0.1 dB throughout the audible range of 20 Hz to 20 KHz, then you are correct to call that "no change."

That's the nit I was picking. Logically, there are 3 choices. I would have liked the authors to present the 3rd choice as you did.

He makes a subtle point here that audiophiles fall into two groups (not necessarily subjective or ojective): those desiring a pleasing musical sound and those desiring accuracy of reproduction.

If a system reproduces sound with high accuracy, then it will be pleasing to me. But many vinyl and toob fans prefer the added distortion and possible loss of high frequencies from those mediums. It's not up to me to say they're wrong, but I personally do not find that pleasing.

Nor do I. The goal of my audio system is to let me hear what is on the source. If it's a crummy recording, so be it.

I also agree with you about active speakers. I have Mackie 624s in my living room home theater, and they're amazing. One reason active speakers can be superior is they are typically bi-amped. Another, at least as implemented in the Mackies, is the speaker's cone motion can be included in the amplifier's negative feedback loop. This lowers distortion quite a bit.

--Ethan

I've never heard the Mackies, but considered them a good value.

Ethan, I believe I read that you use JBL speakers in your main audio system. Do you have any thoughts on the JBL LSR4300 series? http://www.jblpro.com/products/recording&broadcast/LSR4300/index.html

[Ethan Winer]

I believe I read that you use JBL speakers in your main audio system. Do you have any thoughts on the JBL LSR4300 series?

I have JBL 4430s in my home studio, but those are very different from the smaller models JBL sells these days. The LSR series are perfectly fine speakers, but their Room Mode Correction is not the solution JBL would have you believe. Just yesterday someone elsewhere asked about that feature, and below is my reply. This is not to indict JBL, because they're certainly not the first company to wrongly claim that EQ can solve all room acoustic problems. In fact, I noticed they've toned down the hype in their more recent magazine ads. My Audyssey critique HERE examines this in much more detail. Now I see even more companies including EQ built into active speakers, and sold with similar specious claims.

Here's a related side story: Earlier this year I was invited to speak about acoustics at the NARAS division of the Grammys, which was held at the Hit Factory / Criteria studios in North Miami. They set up three pairs of speakers in a lounge room typical of the size people use for home studios. The audience auditioned all three speakers with and without acoustic treatment, using the same music repeatedly. (I had brought one of our Standard Room Kits.) We also played the JBLs with and without RMC engaged. I forget some of the exact speaker model numbers, but one was a pair of JBL's LSR series, another was a pair of Genelecs, and the third was Yamaha NS-10s. Besides myself and the audience, there were four high-profile engineers there including Charles Dye and Eric Schilling who mixed all of Gloria Estefan's big hits from years past. At dinner afterward all four professional engineers said they thought the JBL speakers were "okay," but only when the EQ was disabled.

--Ethan

I would like to know if those [JBL speakers] can be a solution for those who can not treat a room, if it can be a good substitute solution.

No, it's basically marketing hype, intended to appeal to people who want to avoid treating their room properly. (Why do so many people love buying gear, as long as that gear is not bass traps?)

There are three main problems when reproducing low frequencies in small rooms through loudspeakers:

* Peaks, where the reflections from the walls, floor, and ceiling arrive at your ears more or less in phase with the direct sound from the speaker(s).

* Nulls, also caused by reflections, but arriving out of phase.

* Modal ringing, which sustains some, but not all, bass notes even after the bass player stops the strings.

Active EQ like in the JBL speakers can only help with peaks, and even that is only a partial solution. If you measure the response in your room with a microphone, then move the microphone even six inches, the response measured will now be very different. So any "correction" applied by EQ will not help as much for the person sitting next to you. It can't even fix the response for both of your ears at the same time. The EQ is also sure to make the response worse somewhere else in the room, possibly even as close as a few feet away.

This is not to say that reducing peaks with EQ is of no value, but it is not the "total solution" the marketing hype would have you believe. Contrast that to bass traps and other room treatment which always improve peaks, nulls, and ringing at all locations in the room.

--Ethan

[Freo-1]

I take issue with so called "added distortion" from valve amplifiers. While certainly many of the vintage valve amps would have distortion characteristics due to circuit topology and component age, so do vintage solid state amps (think McIntosh).

A properly designed valve amp should not have any more distortion than a solid state setup.  However, there are sonic differences between valve and solid state, not all of which can be readily explained. I have a Sony DA9000ES, a 70 pound 200 watt behemoth that when connected to the fire wire input of a Denon 5910, provides outstanding sound to Polk LSIs (the vifa tweeter in the LSI's are really nice). Very neutral reproduction. Yet, for two channel. I prefer my custom 60 WPC custom valve amp. The amp is basically a HK Citation II frame and transformers, totally redone power supply, bias, and uses 5687/7044/7119 front end. A customized Audio Research SP 12 provides the preamp stage. Subjectively, the music sounds closer to live than any solid state setup I've heard, regardless of price.

This is a link to a very interesting article about valves. One of the curious items is the difference between a 6AU6 and a J-FET when a signal is passed through. The noise floor is LESS with the 6AU6.

http://www.spectrum.ieee.org/archive/1640

This is a very difficult and somewhat subjective subject to nail down.  Enjoy reading the threads. Always learn something new.

[art]

Did anyone notice this part:

"Figure 6.4 shows a step function after passing through an amplifier whose response is 3 dB down at 15 Hz and 30 kHz in (a), then 3 dB down at 30 Hz and 15 kHz in (b), with 12dB/octave roll-offs in each instance."

That would imply that it is a tube (valve) amp. No solid state amp could ever look that bad. Even an amp with low BW, like the first Ayre amp, would only have a 6 dB/octave roll-off.

OK.......what do those 2 attribute to how SS amps and cables interact? Just curious.

(Not sure they have the answer.)

Pat

[Bob Reynolds]

Ethan, thanks for reposting your previous response about the JBL LSR speakers. I agree with your comments. I believe that Floyd Toole states the same things in his papers on the Harman site. Marketing people are, well, marketing people. Also, thanks for the link to your article on the Audyssey system.

The fundamental issue I have with room treatments is that I simply have no room in our living room. With a dedicated media room, treatments would definitely be used. So, for those of us in this "fix", EQ can provide some assistance. I don't expect it to be a "cure-all".

As always, thanks for sharing so much of your time on this forum.

[Steve Eddy]

This is a link to a very interesting article about valves. One of the curious items is the difference between a 6AU6 and a J-FET when a signal is passed through. The noise floor is LESS with the 6AU6.

Where are you getting that from?

The article I'm seeing (the "Distortion" sidebar) shows the noise floor of the JFET about 20dB LOWER than the 6AU6. Even the lowly 2N2222 BJT had a slightly lower noise floor than the 6AU6, albeit with both having higher overall distortion.

Now, when they get to the high voltage comparison, both the BJT and the MOSFET have higher noise floors than the 6AU6. Though their distortion is just like a triode, though higher overall than the 6SN7. Large second, a bit of third, and nothing higher.

se

[Freo-1]

What I was tying to get to was this: (From the article sidebar)

6AU6A pentode: Noise floor is about 120 dB below the fundamental; second harmonic is 48 dB down [red curve, above]. Operating conditions were taken from the resistance-coupled amplifier tables in RCA tube manual RC-21, 1961, p. 438.



2N2222 low-voltage bipolar transistor: The noise floor is about 125 dB below the fundamental; the second harmonic is -30 dB. The circuit was taken from the output stage of "High-Fidelity Preamplifier," p. 609 of RCA transistor manual SC-14, 1973, with a 2N2222 substituted for the (similar) 2N3242A. A 1-k(omega) resistor was used to match the 20-(omega) output impedance of the generator to the transistor.

2N5457 low-voltage junction FET: Unlike the high-voltage MOSFET, the JFET has excellent noise performance (-140 dB) but poor distortion (second harmonic is only 30 dB down). Because of the lower Idss of available junction FETs, the drain resistor was raised to 10 k(omega); the bias was adjusted to give about 1/2 VDD at the output.




MJE2361 high-voltage bipolar transistor: In this test, the transistor was substituted for the 6SN7GTB triode, and the bias was chosen to give the same operating point as the tube. A 1-k(omega) resistor was used to match the 20-(omega) output impedance of the generator to the transistor. The result: a noise floor at about -110 dB, and a second-harmonic level of -46 dB.

IRF822 high-voltage enhancement MOSFET: When substituted for the 6SN7GTB, with bias adjusted to give the same operating point as the tube, the MOSFET exhibited excellent distortion characteristics, which were compromised by its noise floor of -100 dB—about 30 dB above the tube's. Second-harmonic distortion is 41 dB down, which is only 59 dB above the noise.

 Although this is not intended to be an exhaustive examination of all available semiconductors or tubes, the resulting frequency spectra lead us to some conclusions that experienced audio designers have often remarked upon in the past.
      Transistors operating on low-voltage supplies tend to have higher spectral distortion components than tubes.

      If we go to high-voltage transistors, operating on supplies comparable to those of the tubes, the distortion products are less     objectionable. Unfortunately, the noise floor of such devices is much higher. The IRF822 was very triode-like in distortion yet suffered from a noise floor some 30 dB higher than that of the triode.
   
     No other active device possesses both the low distortion products and the low noise floor of the medium-mu triode—albeit at the expense of voltage gain.
   
      The distortion products of transformers are much lower than those of active devices, yet quite different in character. Note that the odd-order harmonic products tend to be higher in level than the even-order products—exactly the reverse of the tubes and transistors.

      It should be obvious that these simple circuit designs can be improved upon, by using differential topologies with constant-current loads and negative loop feedback.

It should also be obvious that the same techniques can be applied to transistors or to tubes; and if this were done, the triode would continue to enjoy some advantages over the semiconductors—and the pentode, for that matter.



When one takes into account the big picture, tubes can provide a transfer function with low distortion and maintain a suitably low noise floor.  I should have made that point clearer in the post.

[Steve Eddy]

When one takes into account the big picture, tubes can provide a transfer function with low distortion and maintain a suitably low noise floor.  I should have made that point clearer in the post.

No, I understood what you were getting at in general. Just that you specifically stated that the JFET had higher noise than the 6AU6 and that just didn't seem right.

Personally though I think transformers out perform transistors and tubes when it comes to signal amplification.

se

[Freo-1]

Thanks, Steve. My typing was phase shifted ahead of my brain there.

A transformer amp would be most cool.  The Germans were big into mag amps "back in the day"

[Steve Eddy]

Thanks, Steve. My typing was phase shifted ahead of my brain there.

Shouldn't that be *ahem* phrase shifted?

A transformer amp would be most cool.  The Germans were big into mag amps "back in the day"

Yeah. Though I'm talking of something different from magnetic amplifiers. Basically taking the typical tube amp topology, turning it inside out, and instead of using the active devices for signal gain and the transformers for impedance transformation, use the transformers for signal amplification and the active devices for impedance transformation.

I think transformers do a better job of signal amplification than tubes or transistors and transistors do a better job of impedance transformation than tubes. Got the notion of doing this some 20 years ago, but only got around to start noodling with it in the past five or six years. The results so far have been very pleasing.

se