mazeroth said:
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.
bhg41088 said:
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.
Attachments
Mats J said:
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)
mazeroth said:
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.
mazeroth said: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.
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!
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!
Re: another "stupid" question
Sure, that makes perfect sense. A lot of my crossovers look like that. It looks like a standard 2nd order crossover with a cap and a coil, but the first coil is large enough to also address the rise from baffle step. Here's a perfect example for a 4 ohm MTM speaker with a 1700hz crossover:
The woofers have a mild rise after being mounted in the box (blue curve):
raw driver curves
The first coil in the crossover looks kinda large for a 4 ohm speaker:
crossover
It takes care of the baffle step and results in 4th order rolloff:
resulting driver curves
jdybnis said:
Sure, that makes perfect sense. A lot of my crossovers look like that. It looks like a standard 2nd order crossover with a cap and a coil, but the first coil is large enough to also address the rise from baffle step. Here's a perfect example for a 4 ohm MTM speaker with a 1700hz crossover:
The woofers have a mild rise after being mounted in the box (blue curve):
raw driver curves
The first coil in the crossover looks kinda large for a 4 ohm speaker:
crossover
It takes care of the baffle step and results in 4th order rolloff:
resulting driver curves
FR and impedance graphs are there
better than I expected from MarkK's nearfield measurements:
RS125: + 5dB 1.5 - 3 kHz, drop beginning 4.5 kHz, first peak at 7.5 kHz
RS150: very flat out to 3.5 kHz, where drop begins, first resonance at 6 kHz
RS180: reasonable flat out to 3.5 kHz, dip at 4 kHz, resonance at 6.5 kHz, downside: cone edge reflection (-1 dB) at 500 Hz), broad hump (+2 dB) 700 - 2 kHz
This drivers is almost a broad as the RS150 but seems floppier.
RS225: drop begins at 2 kHz, 3 dB hump 800 - 2 kHz, extremely broad resonance around 6 kHz (floppy cone?)
RS270: extremely flat out to 1 kHz, first dip at 1.2 kHz - this could work as the bass of a traditional 3-way!
better than I expected from MarkK's nearfield measurements:
RS125: + 5dB 1.5 - 3 kHz, drop beginning 4.5 kHz, first peak at 7.5 kHz
RS150: very flat out to 3.5 kHz, where drop begins, first resonance at 6 kHz
RS180: reasonable flat out to 3.5 kHz, dip at 4 kHz, resonance at 6.5 kHz, downside: cone edge reflection (-1 dB) at 500 Hz), broad hump (+2 dB) 700 - 2 kHz
This drivers is almost a broad as the RS150 but seems floppier.
RS225: drop begins at 2 kHz, 3 dB hump 800 - 2 kHz, extremely broad resonance around 6 kHz (floppy cone?)
RS270: extremely flat out to 1 kHz, first dip at 1.2 kHz - this could work as the bass of a traditional 3-way!
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.