John Curl's Blowtorch preamplifier part II - Page 1923 - diyAudio
Go Back   Home > Forums > Member Areas > The Lounge

The Lounge A place to talk about almost anything but politics and religion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 14th December 2011, 06:28 PM   #19221
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by SY View Post
Ditto the AD MIMS accelerometers. The +/-100g unit is appropriate.
I haven't really thought out how one would do it with pressure, but they make a nice calibrator for a piston chamber, the .5% laser trim translates to about .05dB SPL which is better than anything less than NIST traceable B&K reference mics or something like that.
__________________
"Greetings from The Humungus! The Lord Humungus! The Warrior of the Wasteland! The Ayatollah of Rock and Rolla!" aka the Wizard of Wrestling.
  Reply With Quote
Old 14th December 2011, 06:29 PM   #19222
diyAudio Member
 
Chris Hornbeck's Avatar
 
Join Date: May 2011
Location: Little Rock
Quote:
Originally Posted by scott wurcer View Post
best = most?
Although you meant this rhetorically I think there's an undercurrent of more truth to it. Just as a side effect of being *able* to make a lot of air move, the radiating diaphragms often/typically move less to make any particular amount of air movement, so less FM. FM's fundamental to diaphragm movement, so yada yada.

Thanks,
Chris
  Reply With Quote
Old 14th December 2011, 06:32 PM   #19223
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Quote:
Originally Posted by scott wurcer View Post
I haven't really thought out how one would do it with pressure...
You don't have to, they're tiny and when glued to the dustcap, they give an excellent signal.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 14th December 2011, 06:34 PM   #19224
diyAudio Member
 
Steve Eddy's Avatar
 
Join Date: Sep 2002
Location: Sacramento, CA
Quote:
Originally Posted by scott wurcer View Post
best = most?
Heheh. His was definitely a qualitative rather than quantitative assessment.

Quote:
The room rattlers at BA did pretty well. Dick Burwen uses 30' concrete horns which are part of his foundation. There was a French fellow doing this even bigger, lost the pics.
Yeah, I've seen those. That's bordering on insanity though.

se
__________________
The Audio Guild
  Reply With Quote
Old 14th December 2011, 08:36 PM   #19225
diyAudio Member
 
Join Date: Nov 2008
Location: Oakmont PA
Quote:
Originally Posted by Wavebourn View Post
Simon, do you understand I disagree on any extremism that inevitably throws out baby with dirty water?
I have low wattage zero feedback designs to drive effective full-range speakers. I have designs to drive speakers with complex crossovers that sometimes have close to zero impedance dips. I have some designs to drive subwoofers by a negative output impedance. All of them satisfy requirements to drive own speakers. But if to select amps by criterion how close their output resistance is to zero we gain nothing but satisfaction of own meaningless criterion. Thanks God there is no such standard, so we still have some freedom to explore different possibilities.
Anatoliy,

I see in the stars that you have a new job, congratulations, hope it meets your needs.

I think there needs to be a bit of clarification. All real amplifiers have a complex output impedance that is also non-ohmic. In a typical solid state amplifier such as Bob Cordell's examples there is a maximum power output that increases with decreasing loads. In theory the power out should double as the load impedance halves. This is rarely the case due to what can be modeled as internal resistance in the power supply section. But even Thorsten knows that!

Then there is the output impedance of the output stage. This may or may not be reduced by feedback or specific design techniques. Most solid state amplifiers provide damping factor numbers to show just how low this output impedance can be at some given test frequency.

The standard for loudspeaker specifications used to assume the power applied to the loudspeaker under test was determined by the voltage measured at the device under test input terminals. This was then listed as a wattage based on the rated D.U.T. impedance. My one contribution was to start listing this as a voltage as that is what was actually measured and loudspeaker impedance is a complex number and issue.

So for now a loudspeaker is expected to be specified with a very low source impedance.

Now as many seem to have noticed you can make almost any given loudspeaker perform better for some tastes and musical genres with a non minimum impedance amplifier output.

Now in the case where you are designing an amplifier for a specific driver transducer this is quite a powerful approach and works well.

Now when you design an amplifier for a full range loudspeaker system advantages may be had for specific systems and combinations. This is of course boutique design. It is a valid design method, but it is not a general purpose design. A general purpose design most likely will never work as well as a boutique designed system, when done by a competent designer.

The downside of boutique design for the consumer is that although they may purchase the same amplifier and loudspeakers that perform very well as a set, they may not have a similar listening environment or musical tastes. Then again they may combine all individually well rated boutique components into a very bad system, due to not understanding why each part went best some other gear.

Now as we all have design preferences that will influence our views on how others design, listen and perform.

For example you often use tubes. They have several specific advantages over solid state parts. They also have some liabilities. The issue I find most interesting is they inherently have much greater out of band noise rejection. So it is quite reasonable that you find almost any power cord works well with your designs.

I for example have a power cord design the significantly reduces interference without adding any resistance. I can design this cord into a system as part of my power supply. Using other cords may degrade the performance of the entire system. But as it reduces costs and provides benefits I may choose to do so. That is a design decision.

Then there is the issue of power cord resistance. Most of the solid state capacitor filtered power supplies seem to have peak current draws 3 to 4 times the average current, some much more. In those cases a thinner wire gauge power cord can actually make a difference. (Not really a surprise.) But if you always use a choke filter power supply you may find there is no difference from something as simple as the small power cord resistance difference. This yields the classic story of the blind men examining the elephant.

Then the other issue raised was producing clean power from your own power plant. The issue in designing a rotating machine to produce electricity for low distortion is simple. The rotor has windings on several cores. You must have a gap between the cores to allow the wire in to be wound! This produces gaps in the magnetic field when the rotor moves. These gaps create disturbances in the power produced. So while you could design a lower distortion generator for the small power market, you wouldn't sell very many. Then people would tell you how unethical you are for charging such a high price for a product that is almost exactly the same as...

ES

Last edited by simon7000; 14th December 2011 at 08:39 PM.
  Reply With Quote
Old 14th December 2011, 09:09 PM   #19226
diyAudio Member
 
jacco vermeulen's Avatar
 
Join Date: Oct 2004
Location: At the sea front, Rotterdam or Curaçao
Send a message via Yahoo to jacco vermeulen
Quote:
Originally Posted by simon7000 View Post
boutique generator
Oehh, I/i know of a plastic surgeon who's both very proud of his collection of paintings, his audio set, and his backup generator setup.
Think i'll save this low distortion power plant story for the next upcoming wino art exhibition soirée.
__________________
The buck stops Here
  Reply With Quote
Old 15th December 2011, 01:15 AM   #19227
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
Hi guys, solved all the world's problems when it comes to woofers? I am for a simple, large box with a really big loudspeaker or two. Of course, what do I know? '-)
  Reply With Quote
Old 15th December 2011, 01:50 AM   #19228
PHEONIX is offline PHEONIX  Australia
diyAudio Member
 
Join Date: Jul 2004
Location: Australia
Quote:
Originally Posted by john curl View Post
Hi guys, solved all the world's problems when it comes to woofers? I am for a simple, large box with a really big loudspeaker or two. Of course, what do I know? '-)
Hello John

Is the large box sealed or vented.
  Reply With Quote
Old 15th December 2011, 01:51 AM   #19229
diyAudio Member
 
Chris Hornbeck's Avatar
 
Join Date: May 2011
Location: Little Rock
Quote:
Originally Posted by john curl View Post
Hi guys, solved all the world's problems when it comes to woofers? I am for a simple, large box with a really big loudspeaker or two. Of course, what do I know? '-)
I can add a ringing (Arf) endorsement for what's become known as a Linkwitz transform, but was originally just an almost overlooked little circuit element in S. Linkwitz's old 1980 _Speaker Builder_ article (not in the AES paper). It uses one inverting feedback gain stage to change any F_c and Q_c to (almost) any other F_c and Q_c.

Once, given the task of choosing an F_c and Q_c for a really really big woofer system (8 18"ers sealed boxes for home use) our small group settled on 8Hz and Q=0.5 - but your mileage will vary.

Might even be something that could be integrated into a high dollar preamp as a (very) custom option. Needs to be the same quality level, fersure.

Thanks,
Chris
  Reply With Quote
Old 15th December 2011, 02:02 AM   #19230
diyAudio Member
 
Join Date: Mar 2002
Although this is second hand, a speaker designer friend of mine told me that some of the best bass he's ever heard was in a system that used a pair of these. The enclosures were a simple truncated pyramid. It wasn't really an enclosure per se as the bottom was left open and the drivers mounted at the top. The bottom was held up off the floor by about 4 to 6 inches with some simple feet.

> Sorta kinda like listening to an open baffle from the side ...
and rotated to appear a table ......
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 08:26 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2