Speaker with the highest sensitivity?

[Woodstockz]

Interesting... I was unaware that it was frequency dependent. I probably should have thought of that, but it is a very important consideration. Would it be reasonable to assume it also varies based on operating temperature and therefore power put in?

From my investigation, a lot of speakers seem to be sensitivity rated right at 1 kHz. Their plots are all over the place, but the advertised sensitivity is at 1 K.

Now I know that some average their ratings, but some are peaks and some are dips.

 

[Woodstockz]

You'd be surprised how loud 5 watts of Class A tube power can be if you use high efficiency drivers like the JBLs, EVs, or Altecs (15").

Used to plug an old Fender VibroChamp into either a single EVM-15B or two JBLs for practice or even acoustic jams with an acoustic guitar and hand percussion.

+1.

1 Watt at 1 kHz is pretty freaking loud if you are standing right next to the speaker. As you go below 1 kHz you need more power.

 

[Woodstockz]

Bogeybass, I may do a push-pull set up. Depending on biasing, they are still class a, as both devices conduct for the full cycle. It would make transformer choice easier since there isn't any DC in the windings. I was thinking of MOSFET or even power JFET amp to mess with using current feedback/ defined output impedance. I was considering a scaled down version of Nelson Pass's Zen amp.

dhsierra, I am rather fond of that site. It's where I've learned a lot of what I know. I keep rereading the articles and I get something new every time.

astack, I think I have Alex's articles saved somewhere. I definitely need to look over them again. He knows quite a bit. I don't know when this rig will happen. I'm trying to get all the details in order first. Most of the time I just throw things together, but I'm sure the results will be better with proper planning. Don't know how much I'll spend on it, I assume it will cost quite a bit if I want to do it right.

This thread is a good read. A lot of topics covered.

I am also thinking about building a MOSFET amp eventually...I wouldn't put JFETS in a power amp, just the pre-amp...Pass shuns feedback...As Pass says, the first Watt is the most important, cause if the first Watt is bad, then any following Watt will be bad as well.

At the low powers mentioned in this thread, just a few Watts, I don't think that compression is something to worry about.

Kappa Lites and Alpha 6 were mentioned...this thread on efficiency seems to outline why fEARfuls are so loud and popular. There is a reason that fEARfuls specify those drivers.

 

[Derek Balonek]

I like to cover the interesting topics. One learns quite a bit.

They do make power JFETs; they have the advantage of being easier to drive. Less voltage drop and lower gate capacitance. I was thinking of some feedback (mixed voltage and current) so I can vary the output impedance. Amp plans need its own thread though.

The fEarfuls are popular for a very good reason. Greenboy made good designs and they're very effective at what they do.

 

[agedhorse]

This thread is a good read. A lot of topics covered.

I am also thinking about building a MOSFET amp eventually...I wouldn't put JFETS in a power amp, just the pre-amp...Pass shuns feedback...As Pass says, the first Watt is the most important, cause if the first Watt is bad, then any following Watt will be bad as well.

I would like to address this particular statement because IMO, it's taken quite out of context.

First of all, I am familiar with Nelson's work, and in fact we both graduated from the same university engineering program and worked for the same company while in school. I hold his work in high regard.

If you read the attached article, and you study the circuits of Nelson's designs, he doesn't believe in no feedback. He does believe, as do I, that feedback is not a free lunch and that feedback used with reckless abandon can cause more problems than it solves. It should also be noted that many of his feedback comments are related to global feedback and multi-stage global feedback and NOT local feedback. The comments also address specific issues related to THD and IMD but do not address the tradeoffs related to things like stability, improvement in output impedance, input impedance, frequency response linearization, etc.

There are good reasons for using feedback (stabilization of performance, linearization across production quantities of parts, and in the case of low frequency local and global feedback, the stabilization of DC operating points). There are also bad uses of feedback (to attempt to improve performance of a poor design or poor choice of parts and the desire to show vanishingly low THD numbers at the cost of added artifacts.)

Wisely used, feedback is a good tool for improving a variety of performance parameters. In many cases, it is impossible to achieve acceptable performance across a large number of products without feedback. To say that feedback is always bad is overlooking an awful lot of potentially positive and beneficial attributes.

https://passlabs.com/articles/audio-distortion-and-feedback

Here's a link to the Alpha 30/60 schematic and there is both global as well as local feedback being used:
http://www.diyaudio.com/forums/pass-labs/217061-aleph-60-building-thread.html

 

[Woodstockz]

I would like to address this particular statement because IMO, it's taken quite out of context.

First of all, I am familiar with Nelson's work, and in fact we both graduated from the same university engineering program and worked for the same company while in school. I hold his work in high regard.

If you read the attached article, and you study the circuits of Nelson's designs, he doesn't believe in no feedback. He does believe, as do I, that feedback is not a free lunch and that feedback used with reckless abandon can cause more problems than it solves. It should also be noted that many of his feedback comments are related to global feedback and multi-stage global feedback and NOT local feedback. The comments also address specific issues related to THD and IMD but do not address the tradeoffs related to things like stability, improvement in output impedance, input impedance, frequency response linearization, etc.

There are good reasons for using feedback (stabilization of performance, linearization across production quantities of parts, and in the case of low frequency local and global feedback, the stabilization of DC operating points). There are also bad uses of feedback (to attempt to improve performance of a poor design or poor choice of parts and the desire to show vanishingly low THD numbers at the cost of added artifacts.)

Wisely used, feedback is a good tool for improving a variety of performance parameters. In many cases, it is impossible to achieve acceptable performance across a large number of products without feedback. To say that feedback is always bad is overlooking an awful lot of potentially positive and beneficial attributes.

https://passlabs.com/articles/audio-distortion-and-feedback

Here's a link to the Alpha 30/60 schematic and there is both global as well as local feedback being used:
http://www.diyaudio.com/forums/pass-labs/217061-aleph-60-building-thread.html

Agedhorse,

Firstly, I would like to genuinely thank you for your input. Talkbass needs the gurus.

To address the reason for my response.
The OP mentioned feedback: "I was thinking of some feedback (mixed voltage and current) so I can vary the output impedance".
I just wanted to warn the OP of the dark side of feedback, and to mention that any feedback should be carefully considered. Probably should have said just that.

I would like to say that I never said "no feedback". I never said that feedback is always bad. Your words, not mine.
Instead, I chose to use the word "shun" feedback instead of "no"; shun as in reference to a necessary evil: use it if you have to, and don't use it if you don't have to.
Since I didn't get the word shun from Mr Pass, I probably should have used a direct quote. Shun was just the gist that I got...
Feedback is a complicated subject. [And has some complicated math behind it].
I should have made a better attempt at explanation. Thank you for your explanation, it was better than mine.

I learned decades ago that feedback can help stabilize an amplifier.
My professor said that one way to make a good oscillator, is to make a bad amplifier. So we learned about feedback. [And the complicated math behind it]

Thank you for that awesome link. I have seen it before, and it is great to re-read anything from Mr. Pass. I read Pass a lot, and I learn more each time.
[But in addition to a regular job, I also learn songs and practice scales. So much to do, so little time.]

I would like to illustrate a couple of points.

Pass starts out: "Audiophiles seem to revel in minor controversies"
[He doesn't have to stop at Audiophiles. That could be Audiophiles, or bassists, or engineers, sound guys, or people on the internet in general.]
I am not being trying to revel in minor controversies here, just trying to move things forward in the spirit of collaboration.
This is not a controversy, actually, I think that we are on the same page.

Some quotes from the website that you mentioned:

"We use negative feedback in audio amplifiers to stabilize the gain, increase the bandwidth, lower the output impedance and lower the non-linear distortion."
This is what I was taught in class many years ago, so I think that we can agree to this so far.

Further on down, Nelson says this:

"As the feedback figure exceeds 20 dB or so, you find that all the measurements will improve by the amount of additional feedback....
...
Sounds like something for nothing, doesn't it?
Not quite. I think it's a bit more like a credit card – convenient if used wisely, but carrying interest payments and penalties when it's not.
Negative Feedback and Higher Order Harmonics
Years ago Peter Baxandall pointed out that while negative feedback reduces distortion, it creates additional higher order harmonics in the process. Others have confirmed this phenomenon experimentally and in computer simulations."

This is what I am getting at, I wanted the Op to consider the dark side.
Pass continues: "Negative loop feedback creates higher order distortion harmonics, and there seems to be an implication that you might want to use lots of feedback if you plan on using any at all. Some designers look at it this way, others to use feedback sparingly, and some refuse to use it at all."
I'm in the sparingly group of cautious consideration. So I say go ahead and use feedback to stabilize the circuit if you have to. Just don't add more than you need just for good measure cause it seems like a good idea.

It's like the old Nissan commercial: Everything that you need, nothing that you don't.

Thanks again for your input, and better explanation than mine.
As Derek mentioned, an amp build needs its own thread. I look forward to that thread, and your input.

Best Regards.
Woodstock

 

[dhsierra1]

+1.

1 Watt at 1 kHz is pretty freaking loud if you are standing right next to the speaker. As you go below 1 kHz you need more power.

yes, I'm familiar with Fletcher-Munson curves. For low sound level practice and even acoustic jamming I've found the 5 watts below 1 kHz are adequate unless you're doing acoustic versions of metal tunes with a 5 stringer YMMV, IME etc

 

[Woodstockz]

I like to cover the interesting topics. One learns quite a bit.

They do make power JFETs; they have the advantage of being easier to drive. Less voltage drop and lower gate capacitance. I was thinking of some feedback (mixed voltage and current) so I can vary the output impedance. Amp plans need its own thread though.

The fEarfuls are popular for a very good reason. Greenboy made good designs and they're very effective at what they do.

Thanks for mentioning power JFETs. Very interesting. I will look into them.

I respect Greenboy's design for the fEarful. I also respect his driver choices. They are very efficient.

From the fEARful website:
"fEARful™ enclosures utilize Eminence Kappalite 3012LF or 3015LF high-excursion neodymium woofers and 18Sound 6ND410 / 6NM410 neo (for most designs) or Eminence Alpha6A"

From the fEARful FAQ:
Question: Can I substitute [some other speaker(s)] instead of what the plans call for?
Answer: In a word, no....

I have gone around and around on this. In terms of efficiency, fEARful is hard to beat.

Looking forward to an amp build thread.

 

[ThisBass]

From the fEARful FAQ:
Question: Can I substitute [some other speaker(s)] instead of what the plans call for?
Answer: In a word, no....

Answer in four words,
yes it is possible.

 

[agedhorse]

I should have also mentioned that global feedback can have large negative implications under some overdriven amplifier applications where too much can cause the amplifier to stick to the rails or oscillate. What happens when an amplifier clips is that the feedback loop loses control of the amp (the amp essentially goes open loop) and when it comes back out of clip into the linear region, the feedback loop may have difficulty regaining control if there's not enough stability margin and the frequency is high enough.

This is why I prefer (generally) fairly modest amounts of feedback. It's like cooking, use just enough spices to attain the effect you want. Too much of a good thing stops being a good thing

 

[Derek Balonek]

Yeah, you want your amplifier to be nice and stable before feedback is applied. It can't make a bad amplifier good. To echo what agedhorse said, if you want to add lots of feedback and have decent gain, the open-loop must be massive, which can mean unstable before feedback is applied. So feedback is best for helping a good amplifier out, not salvaging a bad one.

 

[agedhorse]

Correct, feedback generally will not make a bad amp good but too much can make a good amp bad (or at least one heck of a power oscillator).

 

[Woodstockz]

...

This is why I prefer (generally) fairly modest amounts of feedback. It's like cooking, use just enough spices to attain the effect you want. Too much of a good thing stops being a good thing

I agree 100%.

 

[Bassmec]

Some people thought all that way back in 1968 that it's important enough to have a rotary switch for precise adjustment of negative feedback on the front panel.
Invalid Link Removed
Matamp! They offer it still for custom build, No jfets in fact not even got a semiconductor rectifier, Just all tube goodness that's all it relies on.