1st order xover question - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

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 September 2013, 07:30 PM   #1
diyAudio Member
 
Join Date: Aug 2005
Default 1st order xover question

My question concerns a pair of Altec Lansing Model 1 acoustic suspension 2-way bookshelf loudspeakers.

It use a 8" woofer running full range w/o any xover, in typical Altec design.
The 2" paper cone tweeter w/ metal dust cover uses a simple 1st order xover w/ a single cap and variable L-pad.
Both drivers are 8 ohm and Altec's spec say the xover is at 3 khz.
The single cap is 2.0 uf. All the on-line crossover calculators figure about a 6 uf cap. The reason for my question is that I would like to try a soft dome tweeter. (Or at least replace the cap because while the original tweeters work they sound distorted and harsh to me.)

I've found a budget dome tweeter that is a drop in.
Goldwood GT-510 1" Soft Dome Tweeter 270-176
Should I replace the xover cap with a 2uf or go with the calculators that say about 6 uf?

Or is there any benefit to replace with this paper cone tweeter?
Goldwood GT-25 4" Cone Tweeter 270-018
  Reply With Quote
Old 26th September 2013, 07:36 PM   #2
diyAudio Member
 
tuxedocivic's Avatar
 
Join Date: Jan 2011
Location: Ladysmith, BC
You sure the distorted and harsh sound is the tweeter and not the woofer running freely up in it's breakup region?
  Reply With Quote
Old 26th September 2013, 08:30 PM   #3
diyAudio Member
 
Join Date: Aug 2005
Tweeter for sure. Anyway what do you think about the capacitor value?
  Reply With Quote
Old 26th September 2013, 10:32 PM   #4
diyAudio Member
 
Join Date: Jun 2007
How sure are you that the existing Capacitor is actually 2.0uF?

When you say Altec says the crossover is 3000, who says that? Did you look that up on-line? Did you contact Altec? Are you sure they new specifically what Model you were speaking of?

According to the Crossover Calculator I used, 2uF crosses to 8 ohms at 9500hz. That seem unlikely.

How sure are you that the existing tweeter is really 8 ohms? If the tweeter were 16 ohms, for a 3khz crossover, then the capacitor would need to be about 3.3uF. WIth a 16 ohm tweeter, a 2uF capacitor would give a crossover of about 4500hz.

Do you have an ohm meter to measure the Tweeter. The DC Resistance is about 2/3rds to 3/4ths the rated impedance. That might give us a clue.

Again, does the capacitor say clearly and indisputably 2uF?

I think if you use a new tweeter, you use the calculated value appropriate for that tweeter. It is best if you can find a tweeter that has a full SPEC Sheet. That way you can design the crossover to the specific impedance of the tweeter at the crossover frequency.

Dayton and other high brands typically do have full Spec Sheets available. Goldwood ... not so much.

The Dayton DC28F-8 1-1/8" Silk Dome is popular, and reasonably priced, though certainly there are many others. Here is a link to the full spec sheet -

http://www.parts-express.com/pdf/275-070s.pdf

If you look at the Impedance Graph, at 3khz, the actual impedance is about 6.2 ohms.

Just a few thoughts.

Steve/bluewizard
  Reply With Quote
Old 26th September 2013, 10:37 PM   #5
Speakerholic
diyAudio Moderator
 
Cal Weldon's Avatar
 
Join Date: Jan 2004
Location: Near Vancouver
Quote:
Originally Posted by mjatabor View Post
Tweeter for sure.
If it's both tweeters the same, make sure it's not your amp.
__________________
Next stop: Margaritaville
Some of Cal's stuff | Cal Weldon Consulting
  Reply With Quote
Old 26th September 2013, 10:59 PM   #6
diyAudio Member
 
Join Date: Aug 2005
Quote:
Originally Posted by BlueWizard View Post
How sure are you that the existing Capacitor is actually 2.0uF?
I looked at both crossovers and they each have a 2uf 50v cap

When you say Altec says the crossover is 3000, who says that? Did you look that up on-line? Did you contact Altec? Are you sure they new specifically what Model you were speaking of?
Altec Lansings spec sheet say 3khz
http://www.lansingheritage.org/image...ome/page09.jpg


According to the Crossover Calculator I used, 2uF crosses to 8 ohms at 9500hz. That seem unlikely.
Exactly my sentiments

How sure are you that the existing tweeter is really 8 ohms? If the tweeter were 16 ohms, for a 3khz crossover, then the capacitor would need to be about 3.3uF. WIth a 16 ohm tweeter, a 2uF capacitor would give a crossover of about 4500hz.
That is what I came up with. The measured resistance of each tweeter is 5.9 and 6.1ohms

Do you have an ohm meter to measure the Tweeter. The DC Resistance is about 2/3rds to 3/4ths the rated impedance. That might give us a clue.
I've read specs on other tweeters and it seems like many have 6.2 ohm resistance for a 8 ohm tweeter

Again, does the capacitor say clearly and indisputably 2uF?
Yes clearly with out a doubt. I'll take a photo tomorrow.

I think if you use a new tweeter, you use the calculated value appropriate for that tweeter. It is best if you can find a tweeter that has a full SPEC Sheet. That way you can design the crossover to the specific impedance of the tweeter at the crossover frequency.

Dayton and other high brands typically do have full Spec Sheets available. Goldwood ... not so much.

The Dayton DC28F-8 1-1/8" Silk Dome is popular, and reasonably priced, though certainly there are many others. Here is a link to the full spec sheet -
http://www.parts-express.com/pdf/275-070s.pdf
I've thought about that too. I want to make sure it has 4" dia so I can replace original tweeters if I sell later on.
If you look at the Impedance Graph, at 3khz, the actual impedance is about 6.2 ohms.

Just a few thoughts.

Steve/bluewizard
Steve, thanks for all the thorough questions I hope I answered them all for you.

Last edited by mjatabor; 26th September 2013 at 11:03 PM.
  Reply With Quote
Old 26th September 2013, 11:00 PM   #7
diyAudio Member
 
Join Date: Aug 2005
Quote:
Originally Posted by Cal Weldon View Post
If it's both tweeters the same, make sure it's not your amp.
The HK 870 amp is perfect with every other speaker, both 8 and 4 ohm speakers.
  Reply With Quote
Old 26th September 2013, 11:14 PM   #8
diyAudio Member
 
Join Date: Jun 2007
I never was a fan of Cone Tweeters.

If you can find a drop-in replacement in a dome tweeter, I think it would be an improvement.

How are the surrounds holding up on the Tweeter? Any signs of wear, tear, or deterioration?

Can we get a date on these, any idea when they were manufactured?

Can you tell what kind (electrolytic, non-polar electrolytic, Film) capacitors? If any kind of electrolytic and if they were manufactured a few decades ago, then likely they have deteriorated. A Poly or Mylar or Metal Film Capacitor would be a big step up and last for many more decades. Quality capacitors need not cost a fortune, but I recommend only using the non-polar electrolytic if you are on a starvation budget. Otherwise, the various film capacitors are you best choice.

Just a few more thoughts.

Steve/bluewizard
  Reply With Quote
Old 26th September 2013, 11:31 PM   #9
Dissi is offline Dissi  Switzerland
diyAudio Member
 
Join Date: Sep 2012
Location: Winterthur
Closed cone tweeters often have a huge SPL peak at the resonant frequency. For example, the graph of the Goldwood GT-25 shows a 10 dB peak at 1.3 kHz. The small capacitor in the crossover is a hopeless attempt to suppress that resonance.

If you want to keep the vintage style of your speaker, there is only one replacement option IMO:

Phenolic Ring Tweeter 8 Ohm 270-252
  Reply With Quote
Old 26th September 2013, 11:47 PM   #10
diyAudio Member
 
Join Date: Aug 2005
Thanks Dissi.

I can't find it now but in my research I noticed the peak of paper cone tweeters. That is the irritation I must be hearing. I was wondering if a 6 db roll off of a 1st order crossover can lower it enough.

I looked at the Phenolic Ring tweeter to keep my Altec vintage, yet upgrading, and I like the look. As I began my search I got swayed by soft dome tweeters because I'm familiar with their sound.

The Phenolic Ring tweeter's resonant frequency is 1084 so I can easily cross it over at 3khz or 3.5khz. Would you consider 5.5uf-6.5uf cap to cross over it? Or where do you recommend I cross it at?
  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
2nd order or 1st with notch, that is the question Bill poster Multi-Way 22 24th August 2013 10:36 AM
1st order Passive Line Level Crossover + 2nd order Highpass? alexclaber Multi-Way 11 4th January 2008 07:15 PM
deceptive perception ? 1st order-2nd order question poldus Multi-Way 4 10th April 2007 11:58 PM
2nd Order Xover question johninCR Multi-Way 7 10th August 2004 08:15 AM
1st Order Tweeter, 3rd Order Woofer? Jay Multi-Way 8 8th May 2004 09:29 PM


New To Site? Need Help?

All times are GMT. The time now is 04:30 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