I haven't kept up on Piezo tweeters, but unless I'm mistaken they represent a capacitive load to the amp, and as the frequency goes up, the impedance goes down. Though I'm more than willing to be correct on that.
Because at lower frequencies they present a high impedance, they are in effect their own crossover.
Though I've not heard of anyone else using this technique, I put a 10 ohm resistor in parallel with the Piezo horn to allow it to be used with a normal crossover. I've not noticed any problems with this method. It sounds fine, and the crossover seems to be where it is suppose to be.
To make ideal or better crossovers, you use the impedance of the Drives at the crossover frequency rather than the generic nominal impedance.
For example, take these two driver - Dayton Classic 6.5" and a Dayton Dome tweeter -
http://www.parts-express.com/pdf/295-305s.pdf
http://www.parts-express.com/pdf/275-045s.pdf
If we assume a 2khz crossover, then according to the spec sheet. The woofer is 21.5 ohms and the tweeter is 10.3 ohms. Your crossover will be more accurate if your use these numbers rather than a generic 8 ohms.
Also, I'm not recommending this combination, these were just the first two Dayton drivers to come up in the list.
I've never had trouble with oscillation with Piezo horn tweeters. But I'm crossing very high, and have a standard 12dB crossover network connected to it. Though I have heard of using a series resistor to control the impedance. So, that might be a valid technique.
However, unless you are building a REALLY cheap speaker system, There is no need to use Piezo tweeters. When I used them in a speaker system, I was a starving college student, so that is my excuse.
But given that you can get a nice tweeter in the $15 to $25 range, there is no reason to use Piezo unless you are dead broke.
But then ... that's just my opinion.
Steve/bluewizard
Because at lower frequencies they present a high impedance, they are in effect their own crossover.
Though I've not heard of anyone else using this technique, I put a 10 ohm resistor in parallel with the Piezo horn to allow it to be used with a normal crossover. I've not noticed any problems with this method. It sounds fine, and the crossover seems to be where it is suppose to be.
To make ideal or better crossovers, you use the impedance of the Drives at the crossover frequency rather than the generic nominal impedance.
For example, take these two driver - Dayton Classic 6.5" and a Dayton Dome tweeter -
http://www.parts-express.com/pdf/295-305s.pdf
http://www.parts-express.com/pdf/275-045s.pdf
If we assume a 2khz crossover, then according to the spec sheet. The woofer is 21.5 ohms and the tweeter is 10.3 ohms. Your crossover will be more accurate if your use these numbers rather than a generic 8 ohms.
Also, I'm not recommending this combination, these were just the first two Dayton drivers to come up in the list.
I've never had trouble with oscillation with Piezo horn tweeters. But I'm crossing very high, and have a standard 12dB crossover network connected to it. Though I have heard of using a series resistor to control the impedance. So, that might be a valid technique.
However, unless you are building a REALLY cheap speaker system, There is no need to use Piezo tweeters. When I used them in a speaker system, I was a starving college student, so that is my excuse.
But given that you can get a nice tweeter in the $15 to $25 range, there is no reason to use Piezo unless you are dead broke.
But then ... that's just my opinion.
Steve/bluewizard
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On the other hand.... This is the first set of
Speakers I am making so literally cheap is fine, learning the processes etc. so I'm getting drivers with supplied thiele small parameters (cant measure myself yet). Going to go with 8 inch woofer so what kind of high freq
Driver would be good? The reason I have been lookin at piezo horns is that this learning is all going towards building a PA system from scratch and they seem standard for that.
Thanks
Speakers I am making so literally cheap is fine, learning the processes etc. so I'm getting drivers with supplied thiele small parameters (cant measure myself yet). Going to go with 8 inch woofer so what kind of high freq
Driver would be good? The reason I have been lookin at piezo horns is that this learning is all going towards building a PA system from scratch and they seem standard for that.
Thanks
You are throwing in a lot of complication. Stick to focusing on one project.
So, 8" woofer in a 2-way system. Does that sum it up?
The problem is finding an 8" woofer that will go high enough to effectively cross over to the tweeter, or conversely finding a tweeter than can go down low enough to cross in the working range of the woofer.
Just as an illustration, take the Dayton 8" Classic -
Dayton Audio DC200-8 8" Classic Woofer 295-310
http://www.parts-express.com/pdf/295-310s.pdf
At the second PDF link, zoom in on the frequency response graph. Notice, it is going to have a hard time above 1khz. Also notice the peak in the upper frequencies at 2.2khz. You are probably going to have to put a notch filter to suppress that peak.
But, the problem is now finding a tweeter that can cross over at 1khz. You might find a tweeter with a 1khz rated low end, but you can not crossover there and expect must power handling.
One solution I have, though I don't know if it has been tested, is to use a small full range speaker. Say something like this -
Tang Band W3-926SDF 3" Full Range Speaker 264-912
http://www.parts-express.com/pedocs/specs/264-912-tang-band-w3-926sdf-specifications.pdf
Pretty flat from 100hz to 20khz, so crossing in the 500hz to 1khz range would be fine. Note this particular speaker is 4 ohms. Keep that in mind.
There are other Tang Band or Dayton or others that are full range speakers of a similar nature. Finding a standard tweeter for a small Bookshelf design is going to be difficult. Now you don't have to use the Dayton 8" Classic, there are plenty of other 8" bass drivers to consider. But what I'm doing is illustrating the process of matching drivers to a purpose. The Dayton Classic demands a low crossover, but it is very hard to find tweeters to cross that low, so you either go for a 3-way or you get creative on the tweeter.
A huge part of any design is finding two speaker that are remotely capable of working together. Once you have that, you work on the cabinet size and the crossovers. Both complex processes.
Again, search long and hard for an existing design that meets your needs and copy it. Consider it a learning process.
Just a few thoughts.
Steve/bluewizard
So, 8" woofer in a 2-way system. Does that sum it up?
The problem is finding an 8" woofer that will go high enough to effectively cross over to the tweeter, or conversely finding a tweeter than can go down low enough to cross in the working range of the woofer.
Just as an illustration, take the Dayton 8" Classic -
Dayton Audio DC200-8 8" Classic Woofer 295-310
http://www.parts-express.com/pdf/295-310s.pdf
At the second PDF link, zoom in on the frequency response graph. Notice, it is going to have a hard time above 1khz. Also notice the peak in the upper frequencies at 2.2khz. You are probably going to have to put a notch filter to suppress that peak.
But, the problem is now finding a tweeter that can cross over at 1khz. You might find a tweeter with a 1khz rated low end, but you can not crossover there and expect must power handling.
One solution I have, though I don't know if it has been tested, is to use a small full range speaker. Say something like this -
Tang Band W3-926SDF 3" Full Range Speaker 264-912
http://www.parts-express.com/pedocs/specs/264-912-tang-band-w3-926sdf-specifications.pdf
Pretty flat from 100hz to 20khz, so crossing in the 500hz to 1khz range would be fine. Note this particular speaker is 4 ohms. Keep that in mind.
There are other Tang Band or Dayton or others that are full range speakers of a similar nature. Finding a standard tweeter for a small Bookshelf design is going to be difficult. Now you don't have to use the Dayton 8" Classic, there are plenty of other 8" bass drivers to consider. But what I'm doing is illustrating the process of matching drivers to a purpose. The Dayton Classic demands a low crossover, but it is very hard to find tweeters to cross that low, so you either go for a 3-way or you get creative on the tweeter.
A huge part of any design is finding two speaker that are remotely capable of working together. Once you have that, you work on the cabinet size and the crossovers. Both complex processes.
Again, search long and hard for an existing design that meets your needs and copy it. Consider it a learning process.
Just a few thoughts.
Steve/bluewizard
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Correct.
Close enough. They can be run straight from the amp unlike a dynamic tweeter because of the capacitance.
Here's a article that may help H Burch. It's what you said with a little more added.
diyAudio.com Wiki - projects by fanatics, for fanatics
Quite common actually. Around these parts they're referred to as a F.A.S.T. system.
The industry for a loudspeaker driver uses twice the minimum impedance across a given bandwidth as the rated impedance. The bandwidth is typically 20 - 20,000 Hz for a full range loudspeaker system.
Note that a loudspeaker driver is not the same as a loudspeaker system!
A competent amplifier designer will be sure a 4 ohm rated amplifier can drive 2 ohms without damaging itself. That does not mean the distortion will be the same for 2 ohms vs 4 ohms.
Only in near field loudspeaker systems does the tweeter see the least amount of power. Depending on humidity to keep a loudspeaker system's frequency response flat at 50' or more the tweeter may require more power than the midrange to make it to 20,000 Hz. At 500' to get to 8,000 Hz the tweeter requirements begin to approach those of the woofers!
Home full range loudspeakers often have tweeters that really will fail at only a few watts! As the energy in music may be loosely modeled as an energy peak at 125 Hz. that rolls off at 3 dB per octave it is no too hard to see that a tweeter can be blown out even without clipping a modern solid state amplifier. That is because once you get into separate components power amplifiers have little manufacturing cost differences between low wattage and high wattage! (Basically all you add is transformer core and heatsink!) So it is not very hard to have too much amplifier for a given loudspeaker system.
In pro use we set both compressors and limiters for every driver.
ES
Note that a loudspeaker driver is not the same as a loudspeaker system!
A competent amplifier designer will be sure a 4 ohm rated amplifier can drive 2 ohms without damaging itself. That does not mean the distortion will be the same for 2 ohms vs 4 ohms.
Only in near field loudspeaker systems does the tweeter see the least amount of power. Depending on humidity to keep a loudspeaker system's frequency response flat at 50' or more the tweeter may require more power than the midrange to make it to 20,000 Hz. At 500' to get to 8,000 Hz the tweeter requirements begin to approach those of the woofers!
Home full range loudspeakers often have tweeters that really will fail at only a few watts! As the energy in music may be loosely modeled as an energy peak at 125 Hz. that rolls off at 3 dB per octave it is no too hard to see that a tweeter can be blown out even without clipping a modern solid state amplifier. That is because once you get into separate components power amplifiers have little manufacturing cost differences between low wattage and high wattage! (Basically all you add is transformer core and heatsink!) So it is not very hard to have too much amplifier for a given loudspeaker system.
In pro use we set both compressors and limiters for every driver.
ES
In another home theater forum, there is quite an extensive list of on-going speaker projects as well as completed speaker projects. I might be worth checking out.
On-Going Projects -
http://www.htguide.com/forum/forumdisplay.php?6-Mission-Possible-DIY
Completed Projects -
http://www.htguide.com/forum/forumdisplay.php?39-Missions-Accomplished!
Many of these are Build Details of people building known and trusted designs.
Here is a another Forum that might be helpful -
http://www.htguide.com/forum/forumd...=&pp=25&daysprune=-1&sort=lastpost&order=desc
I'm sure there are many other sites like this with speaker projects.
Zaph Audio has a few designs -
Zaph|Audio
Here is a pretty extensive list of Speaker Design Sites from Part Express forums -
Links to existing DIY speaker designs...
Troels Gravesen, Denmark, is a pretty respected speaker designer -
DIY Loudspeakers
To bad ShinOBIWAN (forum member) doesn't have his own website, he makes some fantastic design. Just out of this world, but you can search DIYaudio - Multi-Way for his username and find many projects by him. They are probably out of your price range, but you still get to see the design process.
They are worth reading just to see the process he goes through. Typically he has a concept which he draws up in 3D, he's a graphic design artist unless I'm mistake, but the initial design concept goes through several changes before he settles on the final design. Then he goes through the crossover design in pretty deep detail. The thread tend to be extremely long as they really do cover every detail, and the discussions get pretty deep.
Here is an extensive list of Websites that have speaker projects from Part Express -
Links to existing DIY speaker designs...
Steve/bluewizard
On-Going Projects -
http://www.htguide.com/forum/forumdisplay.php?6-Mission-Possible-DIY
Completed Projects -
http://www.htguide.com/forum/forumdisplay.php?39-Missions-Accomplished!
Many of these are Build Details of people building known and trusted designs.
Here is a another Forum that might be helpful -
http://www.htguide.com/forum/forumd...=&pp=25&daysprune=-1&sort=lastpost&order=desc
I'm sure there are many other sites like this with speaker projects.
Zaph Audio has a few designs -
Zaph|Audio
Here is a pretty extensive list of Speaker Design Sites from Part Express forums -
Links to existing DIY speaker designs...
Troels Gravesen, Denmark, is a pretty respected speaker designer -
DIY Loudspeakers
To bad ShinOBIWAN (forum member) doesn't have his own website, he makes some fantastic design. Just out of this world, but you can search DIYaudio - Multi-Way for his username and find many projects by him. They are probably out of your price range, but you still get to see the design process.
They are worth reading just to see the process he goes through. Typically he has a concept which he draws up in 3D, he's a graphic design artist unless I'm mistake, but the initial design concept goes through several changes before he settles on the final design. Then he goes through the crossover design in pretty deep detail. The thread tend to be extremely long as they really do cover every detail, and the discussions get pretty deep.
Here is an extensive list of Websites that have speaker projects from Part Express -
Links to existing DIY speaker designs...
Steve/bluewizard
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