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 30th July 2007, 01:19 PM   #11
ssmith is offline ssmith  France
diyAudio Member
 
Join Date: Aug 2005
Location: Paris
Quote:
Originally posted by AndrewT
Does anyone disagree with the two octave rule?
I'd asked various people about this, and read and heard the more the better (withing reason) -- although anything from 'around' 1.5 octaves is just fine if using a 4th order active. At the same time, was also advised that a slightly lower value film cap is better than a more ideally valued bipolar electrolytic cap due to long-term stability issues.
Cannot back this up with any experience or measurements, it's just what I've read and heard from various people (dealers included).
  Reply With Quote
Old 30th July 2007, 02:15 PM   #12
Svante is offline Svante  Sweden
diyAudio Member
 
Svante's Avatar
 
Join Date: Feb 2004
Location: Stockholm
Quote:
Originally posted by AndrewT
Does anyone disagree with the two octave rule?

Svante recommends reducing the active filter slope by one pole and integrating the protection cap into the required overall filter type. I like this, except for the accuracy required and the fixed Q=0.71 that must be compensated by altering the Q of the active filter. Although LR2 can be achieved with an active single pole (q=0.71) and passive single pole (q=0.71). LR4 and Butterworth require more thought.

yes and use hot melt glue or similar to secure the cap to something rigid, otherwise the solid core wire will fatigue and break.
Mja... Dunno if I would propose decreasing the slope of the active filter as a general metod. I just meant that the effects of the passive components should be considered. IMO it is easy to neglect the acoustic effects of the driver, and when it comes to this hybrid type of active/passive filters, it is also easy to neglect the effects of the passive components. Adding a capacitor does not nessecarily result in one extra real pole, it will also result in a tendency to a peak near the driver resonance. It was this effect I had in mind when I commented on the parallel resistor.

Anyway, here is a simulation of a reasonably real tweeter with a rather high fs. The larger capacitor results in a cutoff of 700 Hz electrically according to textbook examples (assuming a purely resistive tweeter). The smaller capacitor results in a cutoff of 1400 Hz. It can be seen on the lowest curve group that the voltage across the tweeter terminals does not follow a standard 1st order HP filter function. In particular, the pink curve has a peak near fs, and it is larger than the light blue peak. This is because the parallel resistor reduces the impedance peak of the driver slightly, even though it does not eliminate it.

It can also be seen in the impedance curves (middle group) that the blue curves (=those with the resistor) presents an unnessecarily low impedance for the amplifier.

So, what is "best" is up to the designer, but IMO all of these effects as a whole should be considered. Changing one component might be just right to compensate for another etc.
In this case it might be easiest to stick with the dark red curve, ie a large enough capacitor in series with the tweeter. Surely it removes low frequencies good enough. However, there will still be a need to integrate the responses of the active filters with the responses of the drivers.

Click the image to open in full size.
__________________
Simulate loudspeakers: Basta!
Simulate the baffle step: The Edge
  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 cross speakers and the tweeter protection cap wigginjs Multi-Way 28 1st May 2012 01:15 AM
tweeter protection in an active speaker Cousin Billy Multi-Way 12 23rd April 2009 02:03 AM
Tweeter protection gizmo for active XO? JoeM Solid State 5 31st March 2009 08:18 AM
Speaker protection with capacitor Jay Multi-Way 14 10th November 2005 11:17 AM
Tweeter protection for active speakers paulspencer Multi-Way 31 26th October 2005 08:40 AM


New To Site? Need Help?

All times are GMT. The time now is 06:52 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