Active compensation... - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 9th September 2005, 06:57 PM   #1
barossi is offline barossi  Germany
diyAudio Member
 
Join Date: Oct 2003
Location: Hamburg area
Question Active compensation...

Hi,
i am using an active 2-way system.
I use a Onken bass with a parasound transistor amp.
For the high frequ. >800 Hz i am using a 45 single ended tube amp (2-stages Bugle Amp)with a 288-16K Altec driver.
The problem is, that the 288- Altec driver begin rolling off at ~7 kHz.
Is there any possibility to compensate this behaviour with the 45 SET amp?

Greetings Barossi


  Reply With Quote
Old 9th September 2005, 07:26 PM   #2
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
Default Wild guess

Of course. You need to insert a step network at the input of your SET amplifier. The problem is that you need to know reasonably accurately what the response of your HF driver is like. Still, I'll take a wild guess and assume that it's about 4dB down. We make a 4dB attenuator out of a 360k resistor and a 620k resistor. The 620k resistor replaces your existing grid leak resistor. Next we put a capacitor across the 360k resistor to short circuit it at HF so that although you have 4dB of attenuation at LF, you have none at HF. Try a 68pF capacitor. If that gives too much effect, reduce it, if too little, increase it.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 9th September 2005, 07:37 PM   #3
barossi is offline barossi  Germany
diyAudio Member
 
Join Date: Oct 2003
Location: Hamburg area
Hi Ec8010,

it look nearly like this:

Greetings Barossi

BTW i don't understand how the network will look like
Attached Images
File Type: png 288-16k.png (2.9 KB, 226 views)
  Reply With Quote
Old 10th September 2005, 11:15 AM   #4
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
I'm afraid you need something rather more sophisticated than a simple network to deal with that driver. It needs an op-amp or an LC network, and even then I doubt if it would make it sound better.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 10th September 2005, 06:20 PM   #5
vuki is offline vuki  Croatia
diyAudio Member
 
vuki's Avatar
 
Join Date: Jun 2002
Location: zagreb, croatia
Hi Barossi,

you could start with simple RC correction before 288. Here is how it looks like with 10R||4u7.

Regards,
Vuki
Attached Images
File Type: jpg leccor.jpg (52.1 KB, 164 views)
  Reply With Quote
Old 10th September 2005, 07:50 PM   #6
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
That 15K peak will be pretty fierce; this is a job for a notch filter, or possibly modifying the driver if that's practical.
__________________
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 10th September 2005, 08:03 PM   #7
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
look for Jean Hiraga's passive EQ-ed xover for altec A7 ,anf try to implement that in your EQ.
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 11th September 2005, 01:06 AM   #8
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: USA
> the 288- Altec driver begin rolling off at ~7 kHz.

It's been decades since I stood in front of a 288. But the driver starts falling at 2KHz-3KHz. The Old Men knew this, and designed the horns to compensate. That's easy in theater use (and I don't think you should use 288 in any room smaller or liver than a theater): make the horn less directional below 2KHz and more directional above 4KHz. The sweet thing is: that's what an exponential horn does anyway! The tough part is getting a proper match between driver droop and horn on-axis rise, while still hitting all the paying customers.

Oh, and in a small room, the wide dispersion at 500Hz and the tight beaming at 15KHz mean a very odd off-axis and reverberation sound.

Oh, and any practical horn will have many cross-modes causing dips and lumps in the response. That 13KHz peak may be a throat cross-mode, and will almost certainly move or vanish if you move the microphone a foot left or right, up or down.

About 1975, fashion changed to Constant Directivity horns. These have the same pattern 1KHz to 10KHz. When used with a max-efficiency driver (288 is close enough) they drop above 2KHz, but the same all over the room, and a simple R-C network like EC8010's will get back to pretty-flat everywhere. And since the efficiency of the 288 is SO high, you can (as Vuki says) equalize between power amp and driver: put 50 ohms in series with the 288, bypass the 50 ohms with about 1uFd. That works for Constant Directivity horns; it won't be right for classic Exponential or Sectoral horns such as you seem to have. Vuki's plot does slump less, but the peak-dip will be more annoying than before.

Personally, I think you need to change the horn. No, I don't have a suggestion: I made my own out of lumber and fiberglass until Altec, JBL and EV got their CD horns into production. And the commercial CD horns are mostly not very CD or much too big for the home (my JBLs are 4 feet long, some MantaRays were longer).

Here is another trick. Take the horn off. Use the driver without a horn. With the 1" or 2" opening, dispersion will be VERY wide and uniform up to the top of the audio band. In a home, this is a better sound than a big honky-horn. The drawback is lower efficiency and a VERY low power handling at 500Hz. However I have used JBL 2440 this way in a home, at high listening level. Yet another technique, for some drivers, is to take the back cover off and listen to the diaphragm. A 2440 is a killer 4" direct radiator. I only tried that once because my 2440s are the rare Beryllium model, and that stuff is toxic. Every other driver ever made is aluminum or phenolic, quite safe to health. Of course children and cats are dangrous to diaphragms.
  Reply With Quote
Old 11th September 2005, 02:08 AM   #9
diyAudio Member
 
Brett's Avatar
 
Join Date: Jan 2002
It seems to me that if you boost the top end all you're going to be doing is to exaggerate the breakup modes of the driver. Roll it off earlier into another driver and flare.
  Reply With Quote
Old 11th September 2005, 09:56 AM   #10
vuki is offline vuki  Croatia
diyAudio Member
 
vuki's Avatar
 
Join Date: Jun 2002
Location: zagreb, croatia
Here is the measurement of the raw driver at 5 inches from exit.
The 12kHz peak is still present. It vanishes when measuring somewhat off axis.
Attached Images
File Type: jpg 288al.jpg (51.4 KB, 103 views)
  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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Active Crossovers & Baffle Step Compensation Mikett Multi-Way 21 8th June 2014 10:40 AM
Impedance Compensation in Active Systems ShinOBIWAN Multi-Way 11 13th February 2006 10:39 AM
Impedance compensation needed for active speakers? tcpip Multi-Way 31 19th August 2005 02:39 AM
Baffle step compensation in an active X/O sunil Solid State 6 12th November 2003 09:52 AM
Baffle step compensation in an active X/O sunil Multi-Way 0 26th October 2003 08:47 AM


New To Site? Need Help?

All times are GMT. The time now is 10:42 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