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Multi-Way Conventional loudspeakers with crossovers

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Old 2nd October 2004, 08:08 PM   #21
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It looks like the 8" driver would be comfortable with a 1.4KHz crossover or so, but definitely not much higher. It would be a great line array woofer.
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Old 2nd October 2004, 09:11 PM   #22
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as for a tweeter to pair with the 8", would the Seas 27tdfc work well?
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Old 2nd October 2004, 09:51 PM   #23
Zaph is offline Zaph  United States
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Quote:
Originally posted by mazeroth
These cross EXTREMELY low...

http://www.partsexpress.com/pe/pshow...=264-555&DID=7

http://www.partsexpress.com/pe/pshow...=264-580&DID=7

They have shielded versions, but they're a bit more.

These are the same tweeters Polk uses in their highly acclaimed LSi series, as well as the Onyx Rockets.
These tweeters have massive harmonic distortion below 2 Khz. I wouldn't recommend crossing them over below 2.5 or 3kHz. Usually, a low Fs means potentialy low crossover points, but not with these tweeters.

Quote:
Originally posted by bhg41088
as for a tweeter to pair with the 8", would the Seas 27tdfc work well?
Yup, now this is one that can cross over low. I just posted a design on my web page using this tweeter with a 1700hz crossover point.
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File Type: gif xt19td00-04-thd.gif (10.3 KB, 280 views)
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Old 2nd October 2004, 10:57 PM   #24
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Quote:
Originally posted by Zaph


These tweeters have massive harmonic distortion below 2 Khz. I wouldn't recommend crossing them over below 2.5 or 3kHz. Usually, a low Fs means potentialy low crossover points, but not with these tweeters.
I don't understand. How can you tell where they have massive harmonic distortion? It looks fairly flat at 1khz and up. Or do you get that by looking at the numbers? I'm still pretty new to this, but I thought I could tell just by looking at the sample response graphs.
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Old 2nd October 2004, 11:22 PM   #25
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Quote:
Originally posted by Mats J


FR's for 8"

Frequency response is the third graph down, the red plot.

Wow, it doesn't look like you'd want to use that much past 1k. I think I'll learn more about crossovers before I consider using this driver since it needs to cross in such an acoustically critical range of the spectrum.

Also, Zaph- am I reading your graph correctly? it looks like you tested that Seas tweeter from 400 to 10k, and it's got very low distortion from 2khz up, with a big hump below that. If that's right, how bad does it really sound as it approaches 1khz? It looks like 1khz has about the same distortion as 1.5 khz- so unless you could push your mid up to 2khz it wouldn't matter between 1khz and 1.5khz (other than power handling)
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Old 3rd October 2004, 02:58 AM   #26
Zaph is offline Zaph  United States
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Quote:
Originally posted by mazeroth
I don't understand. How can you tell where they have massive harmonic distortion? It looks fairly flat at 1khz and up. Or do you get that by looking at the numbers? I'm still pretty new to this, but I thought I could tell just by looking at the sample response graphs.
The curve I posted at the bottom of my message was the total harmonic distortion of the Vifa XT19 tweeter. Notice the big green lump at the bottom, which is the 2nd harmonic. None of that has anything to do with the frequency response. A flat and extended frequency response doesn't imply low distortion.

I also have a curve of the Seas 27TDFC, and it's very low distortion right down to it's Fs.

Anyway, to keep things on topic, yes I think the 27TDFC would be a great tweeter to use with metal cone drivers. Keep in mind that there is much more to deciding on where to cross over than looking at the breakup node. In metal cone drivers, the breakup node can be excited as a harmonic as much as 2 octaves below the breakup.

In general, it's best to cross metal cone drivers 2 octaves below the breakup. Look at some of the Seas Excel HD plots for an idea. In most cases, a driver with a 4kHz breakup node will have a nasty 3rd harmonic distortion at 1.5kHz.
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Old 3rd October 2004, 03:45 AM   #27
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Zaph, the graph you posted was for the 3/4" Vifa ring tweeter, not the 1" tweeter that's a lot more common. What do you have to say about the 1"?

Now, if you really feel like typing, could you explain what the harmonic distortion is and how you figure it out? Sorry for being an idiot
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Old 3rd October 2004, 04:12 AM   #28
Zaph is offline Zaph  United States
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Quote:
Originally posted by mazeroth
Zaph, the graph you posted was for the 3/4" Vifa ring tweeter, not the 1" tweeter that's a lot more common. What do you have to say about the 1"?

Now, if you really feel like typing, could you explain what the harmonic distortion is and how you figure it out? Sorry for being an idiot
No worries, the only stupid question is the one that's never asked.

The 1" has similar distortion tendencies. The tweeter has a low Fs and very flat and extended frequency response, but also suffers from high 2nd order harmonic distortion in the range up to 2khz. Make no mistake, it's a great tweeter, but it needs to be crossed over high to avoid the distortion.

A harmonic is a multiple of the fundamental. For example, if I were to play a 2Khz tone through a Vifa XT tweeter, it would also emit tones at 4khz and 6khz, with those being called the 2nd and 3rd harmonics, respectively. That form of distortion is simply called harmonic distortion, and also "non-linear" distortion.
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Old 3rd October 2004, 04:29 AM   #29
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Gotcha. Where there are peaks at the bottom of that chart is a no-no for a crossover, but where it's flat it's ok, right? Polk crosses this tweeter over at 2.4khz in their LSi line and it sounds fantastic.

When reviewing drivers on Parts Express and other sites I don't ever recall seeing any charts for harmonic distortion. Is there any way to figure it out if there's no chart?

Thanks!
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Old 3rd October 2004, 05:57 AM   #30
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Default another "stupid" question

Does the following make sense? Since the driver has a 6db rise from 500Hz to 1khz, use a 1st order filter at 500Hz to get a flat response up to 1k, and then add a second pole at 1k to get 24db down by 2k including the 12db drop in the drivers natural response?
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