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 9th May 2007, 06:41 AM   #1
diyAudio Member
 
Join Date: May 2007
Default Piezo as supertweeter in Large Advent

Greetings!

The New Large Advent loudspeaker has a reported frequency response of 33Hz to 17,000Hz +/- 3dB. I thought I might try to extend the high frequency of the Large Advent by adding a Radio Shack Piezo Tweeter 40-1218 http://support.radioshack.com/suppor...oc63/63021.pdf or the Motorola/CTS KSN-1005 (4kHz-27kHz). Although no crossover is needed and this driver supposedly does not significantly affect the impedence of the speaker it is wired to, I found the following ‘crossover’ circuit and modifications to the driver that is said to eliminate its "spitty and lispy" fatiguing harshness:
1. 8 ohm/20 watt resistor across the piezo terminals (Radio Shack part # 271-120, $1.49 each) This resistor makes the piezo appear to the system as an 8 ohm driver?
2. 0.47 uf capacitor wired in series (Hovland, $1.50 each from Madisound) I assume this only allows frequencies above 15,000 Hz (based on 12dB filter parameters) go to the piezo tweeter.
3. Application of damar varnish on the piezo’s cone element is said to add refinement to the sound and almost completely reduce the fatiging sibilance:
a. Remove the three screws from the back of the piezo
b.Coat the paper cone with one coat of damar
c.Remove ‘pooling’ of damar with a tissue
d.Let dry overnight
e.Reattach horn
4. An application of rope caulk to the back and sides of the horn helps to deaden any plastic sound. (See attachment)

I want to incorporate a CTS KSN-1005 piezo into a New Large Advent speaker. I'm attempting to get frequencies about 17 kHz and above passed to the piezo. I will be making the piezo appear as an 8 ohm driver with an 8 ohm/20 watt resistor. Even though this will limit the output of the piezo somewhat that will probably be OK as the piezo is much more efficient than the Large Advent system. Is a .22uF capacitor wired in series the correct device to get a 17 kHz rolloff as a 12 dB filter at 8 ohms? From the 2nd order crossover charts I have seen, a .47uF capacitor will provide a 15 kHz rolloff at 8 ohms. Does it then follow that a .22uF capacitor will provide a 17 kHz rolloff for an 8 ohm 12 dB filter?

Thanks for any help you can provide.
Attached Images
File Type: jpg piezo.jpg (19.2 KB, 581 views)
  Reply With Quote
Old 9th May 2007, 12:05 PM   #2
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi,

If it is a classic loudspeaker adding a piezo is not a good idea.

Click the image to open in full size.

You could try something a lot more subtle e.g. a small neo :

http://www.partsexpress.com/pe/showd...number=275-025

And use something like a first order series c/o with the tweeter at 10KHz.

/sreten.
  Reply With Quote
Old 9th May 2007, 01:46 PM   #3
diyAudio Member
 
Join Date: May 2007
Thanks for the reply. The Dahlquist DQ-10 is about as classic a loudspeaker as it gets and it uses the KSN-1005 as a super tweeter.

When one has 6 pairs of Large Advents a few it would seem would be open for some experimentation. The Large Advent does fine to 17 kHz, I would like to experiment with something that would take it higher from there. Not having a command of crossover networks I am just trying to devise a simple circuit to attenuate frequencies below 17 kHz.

For a conventional crossover the piezo tweeter must be made to look "resistive" in order to work with the crossover. This can be done by wiring an 8 ohm resistor across the piezo tweeter. Then I assumed it is a matter of establishing an 8 ohm 12 dB filter for cutoff at 17 kHz with a .22uF capacitor.

For straight level attenuation a simple non-polar capacitor can be wired in series after a 50 ohm, 2 watt resistor wired in series is established to eliminate ultrasonic resonance interaction between the tweeter and amp.

Either way, I'm just trying to figure out what the value of the capacitor must be to acheive the 17 kHz cutoff. Any ideas would help, thanks.
  Reply With Quote
Old 9th May 2007, 02:27 PM   #4
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
I don't know how deep those go (although I do know that they wewre once very popular in the US). But keep in mind that you may probably not like the sound because it can get unbalanced if they don't go very low (rule of 400,000).

Regards

Charles
  Reply With Quote
Old 9th May 2007, 03:35 PM   #5
diyAudio Member
 
Join Date: May 2007
The frequency response of the KSN-1005 is 4 Hz - 27 kHz. It won't hurt them a bit to attenuate them to a 17 kHz - 27 kHz response.

I know of one application where the piezo was successfully working with an 8 ohm 12 dB filter using a .47uF capacitor for a cutoff of 15 kHz.

So, the critical question in my mind is:

Is a .22uF capacitor wired in series the correct device to get a 17 kHz rolloff as a 12 dB filter at 8 ohms? If not, what value capacitor will?
  Reply With Quote
Old 9th May 2007, 03:50 PM   #6
Speakerholic
diyAudio Moderator
 
Cal Weldon's Avatar
 
Join Date: Jan 2004
Location: British Columbia
Quote:
Originally posted by jackfish
So, the critical question in my mind is:
I have two for you.

1. Piezos are not known as a good sounding tweeter. Mods or not, they still sound like a piezo. They are inexpensive and are useful for small PA gear and perhaps annoying your pets but I wouldn't consider using them in a hi-fi application. What is your interest in using a piezo?

2. 17 Khz is beyond what most of us can hear and there's very little program material up there. XO at 17K will mean you are hearing mostly the roll-off below the XO point.
__________________
Next stop: Margaritaville
Some of Cal's stuff | Cal Weldon Consulting
  Reply With Quote
Old 10th May 2007, 03:11 PM   #7
diyAudio Member
 
Join Date: May 2007
1. The Dahlquist DQ-10 is a decent sounding vintage loudspeaker with a substantial following. The piezo was used as a super tweeter to extend the high frequency range beyond what the tweeter provided. The KSN-1005 piezo (not the cheap knock offs) with modifications can be a pleasant, non-fatiguing driver to add some air or presence to the high frequency output of a speaker with relatively little in the way of circuitry. There are other examples of DIY loudspeakers that have successfully used the piezo and achieved good sound, particularly as an accessory to full range drivers.

2. I think most people are well aware that while 20 kHz is considered the audible limit for humans that most with age people cannot hear frequencies above 16 kHz. However, that does not stop loudspeaker manufacturers from creating products that extend above 20 kHz, some to 40 kHz. This is mostly marketing, but there is substantial evidence that there are psychoacoustic benefits to loudspeakers which extend beyond the upper frequncies of human perception and some support to the idea that a system that can go beyond what frequencies can be perceived will do a better job with those frequencies that can be. If the piezo driver is straight line attenuated, which is the way I am now leaning, there is no roll-off below the crossover point.

Besides I have nothing better to do than play around with this to see what happens. I'm glad I'm actually getting helpful information and support from other quarters.
  Reply With Quote
Old 10th May 2007, 10:59 PM   #8
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Single cap and resistor will be a first order network (i.e 6dB) and assuming that you are well within the passband of the piezo tweeter this should result in a first order roll off. This should be ok for the purposes of your experiment.

Whether or not this is a worthwhile exercise I leave to you to determine. Something in the range of 1.0uF + 0.22uF in parallel or thereabouts is likely to get you close with an 8 ohm resistor. This is ~ -3dB @ 16.3kHz and can be realized with available film caps.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 12th May 2007, 12:37 AM   #9
diyAudio Member
 
Join Date: May 2007
Well, after some research (Thanks Godzilla!) I am ready to try my experiment. I purchased two CTS KSN-1005A piezo tweeters, two 20 ohm 20 watt resistors, pairs of a variety of caps; 1.0uF, 0.68uF, 0.47uF, 0.33uF, 0.22uF, and 0.10uF, 4 ounces of Dammar varnish, and some ACE Hardware rope caulk. I have a bunch of 3/4" MDF left over from making my FleXy Table.

I will varnish the piezo's cone element and apply rope caulk to the sides and back of the horn. The resistor will be soldered across the piezo's terminals. I have made a pair of small boxes out of 3/4" MDF just big enough to put the piezos in, the back remains open so I can get at the capacitors. I will then experiment with various attenuations provided by the capacitors wired to the positive terminal of the piezo. I bought an extra pair of 0.33uF to go with the 1.0uF for 1.33uF. I think 1.5uF will let too much of the piezo through. I can try some other combos to get intermediate values. The supertweeter system is then just wired to the speaker terminals of the Large Advent. I will also try the piezo facing forward and backwards on top of Large Advent cabinet. There is some suggestion that facing backwards might improve the sound.

We will see if this will add some pizzazz to the New Large Advent without harming the overall sound quality and report back with my findings. Total cost is under $50.
  Reply With Quote
Old 12th May 2007, 10:29 PM   #10
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
The values I mentioned were intended for use with an 8 ohm resistor, you'll need to scale accordingly. The one other thought I had was that this simple network makes no provisions for level matching should the piezo be more efficient than the advent. You could use an 8 ohm Lpad to address this issue in conjunction with cap values around the range mentioned in my previous post.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  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
FS: Large inductors, Large Ports, and Leaky Holes luvdunhill Swap Meet 10 6th March 2009 03:01 PM
supertweeter help... one1speed Full Range 12 30th March 2006 09:12 PM
Modifying Advent AW-820 clarkdv Multi-Way 2 24th April 2004 03:17 AM
Re: Advent Legacy II's? Tell me all you know... JeremyD Multi-Way 9 12th May 2003 02:09 AM
advent vs jbl FlMike Multi-Way 1 12th January 2002 07:45 PM


New To Site? Need Help?

All times are GMT. The time now is 04:02 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