Would you use a 4 ohm tap with these speakers? - 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 26th March 2009, 05:37 AM   #1
diyAudio Member
 
Join Date: Sep 2002
Location: Oregon, USA
Default Would you use a 4 ohm tap with these speakers?

This is the calculated impedance of a speaker crossover design I'm working on (the individual driver impedances are the measured values). This is just a midrange and tweeter, the amp will have a line level crossover at 450-500Hz so it won't be playing anything below that. Also, this graph doesn't have too many data points below 1K, so take the low frequency region with a grain of salt.

The amp is an SE 2A3, using One Electron UBT-3 OPT's (which is a 3kOhm transformer). I'm using Sovtek 2A3s and driving them slightly hot (~65-70mA), if that makes any difference. The 8 ohm taps are currently connected.

I'll wait till I have real measurements of the final crossover before changing the taps on the OPTs, but I'd like some advice on whether this would be considered a nominal 4 ohm speaker load or not. It seems to me that it should be, it's between 4 and 6 ohms over the region I'm interested in (and even dips a little below 4 at one point).

Also, I understand the general rule of thumb of putting this speaker load on the 8 ohm tap - power output goes up, distortion goes up. Anything else I should keep in mind? Does the fact that I'm driving the tubes slightly hot make any difference here?

Thanks,
Saurav
Attached Images
File Type: jpg impedance.jpg (40.7 KB, 155 views)
  Reply With Quote
Old 26th March 2009, 06:17 AM   #2
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Hard question to answer, certainly with lower impedance primaries the 4 ohm tap might be better, but in a region where either tap may work reasonably well you'll have to try it to see which one provides the best overall performance.

Note that it is not a bad idea to figure out what the amplifier's output impedance is on each tap and using that in the design of your x-o . It's less critical with mids and tweeter drivers, but unlike the nearly perfect voltage source of a solid state amplifier where the two networks are practically speaking independent of each other, with a tube amplifier there can be interaction between the components in the two filter sections of the x-o, their speaker loads, and the amplifier.

The Audio Precision website had a good article on measuring amplifier source impedance based on changes in output voltage loaded and unloaded.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 26th March 2009, 07:14 AM   #3
diyAudio Member
 
Richard Ellis's Avatar
 
Join Date: Sep 2006
Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.
Myself I would go with the Four Ohm tap...The bulk of signal "information" is going to be in the midrange of the scale. And as in your chart that impedence is running at Appx. six ohms. The four Ohm would be the safest choice. As Kevin notes there are almost countless variables to consider.......that's why we have our composite "averages".
The rising impedence at the lower end is of course the Back EMF of the resonant frequency of the midrange, (Probably cone type..6"?)
_______________________________________--Rick....
  Reply With Quote
Old 26th March 2009, 03:11 PM   #4
diyAudio Member
 
Join Date: Sep 2002
Location: Oregon, USA
Yes, the midrange Fs is 117Hz, and it's a 6.5" driver.

Measuring the amp's output impedance is a good idea, I'll keep that in mind. Thanks.
  Reply With Quote
Old 26th March 2009, 03:25 PM   #5
diyAudio Member
 
Join Date: Jan 2002
Location: Tyrone Ga. U.S.A.
What midrange is that?
  Reply With Quote
Old 26th March 2009, 03:42 PM   #6
diyAudio Member
 
Join Date: Sep 2002
Location: Oregon, USA
Audax PR170M0
  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
Studio monitor speakers as Hi Fi speakers? MRod Multi-Way 2 27th March 2009 06:07 AM
Built differences between Guitar Speakers and PA Speakers? agadis PA Systems 7 24th September 2007 09:22 AM
How would you compare your DIY speakers to commercial speakers? AJ Bertelson Multi-Way 20 28th May 2004 04:20 PM
Car Speakers in Theatre Speakers NEED HELP FAST!!! Psionic Multi-Way 9 3rd March 2003 12:11 PM


New To Site? Need Help?

All times are GMT. The time now is 11:08 PM.


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