Extremely difficult: Tweeter with best low-end performance...Please help!

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I need to choose a tweeter for a 2-way standmount design. My goal is to build a high-end yet inexpensive satellite monitor that has lowest possible distortions. The woofer will be Usher 8945P 7". But it is difficult to choose a tweeter. The most important criterion for the choice is clean low-end performance because I'll use 1.5 kHz as an XO frequency for acoustic LR4. This will be achieved by electric 2nd or 3rd order on the tweeter, depending on the tweeter's natural slope.

The reason why the choice is difficulst is that there are multiple candidates! I cannot decide on one out of the following three:

1. Peerless HDS
2. Dayton RS28A-4
3. Seas 27TBFC/G (H1212)

I already checked with distortion measurements reported by John Krutke, Mark K, and Joe Rasmussen. My conclusion is that all these three are EQually excellent in their nonlinear distortions! The more I look at their measurement data, the more difficult to choose one! (Note: RS28As measured by John must have some problem since Mark K's more extensive measurement shows RS28s are as good as Seas and Peerless).

So, I have to consider other factors:

1. Peerless HDS tweeter

Pros: 1) Good off axis performance; 2) nice metal face plate

Cons: 1) Most costly out of three; 2) a 2dB dip at 6.5 kHz (not sure what kind of effect it'll have in real-world listening); 3) the low end starts to roll off from 2.5 kHz, which means a higher order XO will be needed to obtain good phase alignment with the midwoofer.

2. Dayton RS28A-4

Pros: 1) Elegant look of mesh grill and metal plate; 2) the low end runs flat to 1 kHz (easy to work with in my application)

Cons: 1) a wide 5 dB dip at top end (again I'm not sure what kind of effect it'll have in actual listening); 2) high frequency but mild breakup node (but I agree that it's not audible); 3) QC consistency problem reported (but I confirmed from Darren Kuzma that this problem was due to misspecified tooling and has been addressed after the first product batch); 4) 4 ohm load but it's alright in my application.

3. Seas 27TBFC/G

Pros: 1) Inexpensive; 2) no notable FR dip or bump

Cons: 1) Cheap look of polymer plate and Hexa grill; 2) peaky breakup node at 26.5 kHz (may not be audible)


That's all I can consider. But still can't decide!

Can anyone suggest other factors that can help me make a decision? Please help...

- Jay
 
Peter,

Breakup modes show themselves further down the frequency spectrum. For the 27TBFCG - you can see the ultrasonic breakup appearing in Zaph's harmonic distortion 3rd order at 8.7KHz, then 5th order at approx 5.25KHz (= the approx 25KHz F1 breakup node)

Both F3 and F5 are significantly down in dB to not be heard over the signal so the breakup of the 27TBFCG should not be audible, although you could argue any harmonic distortion colours the sound.

Cheers,
David.
 
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I hate talking about first hand experience, because really it means very little.

It is the end product that matters, there are other confounding factors such as drivers, cabinet, crossover etc will influence the perceived treble quality.

Unless you experiment with the different 3 tweeters on the single woofer, and design 3 crossovers to match the basic parameters like FR/phase alignment, it is impossible to make valid comparisons.

I have the ZaphAudio L18RNX/P+27TBFC/G, and in THIS 2-way the treble quality is consistent with the measurements- so little extra colouration, there is very little to write home about it.

I always hear about airiness, shimmer, and floating treble, soo tangible, you-can-almost-touch-it treble when people talk about some great dome tweeters, and more commonly ribbon tweeter, and they argue that these tweeters are more realistics.

But I'd argue that these are distortion artifacts.
Ask yourself, when did you notice this kind of phenomena at a real-live (unamplified) concert?

Consistency wise, probably 27TBFC/G tweeters probably have the best low end performance. This is important if you don't have measurements gear that allows you to test for non-linear distortion performance.
 
Hartono said:
try to choose the tweeter that don't need series resistance to pad down the volume. series resistor in tweeter degrade dynamic and sound quality audibly.

Unfortunately, a series resistor is required in my design for any of these tweeters. BTW, I think people agree that a resistor is the least harmful component of a passive XO. An inductor is the worst. Am I wrong?
 
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Resistor padding often affects phase - its the worst, but impossible or very difficult to do a balanced system without

But if you cant beat them, join them - in other words, its possible to let the padding/phase(delay) work fore you, but its tricky

You could use this little 2" Jordan :D

http://www.ejjordan.co.uk/drivers/jxr6.html

Mounted in a very small chamber it might even almost roll off by itself :cool:

But then I would consider a bass like the 10" Seas CA26RE4X, or similar, preferably with good sensitivity
 
tinitus said:
Resistor padding often affects phase - its the worst, but impossible or very difficult to do a balanced system without

But if you cant beat them, join them - in other words, its possible to let the padding/phase(delay) work fore you, but its tricky

Various ways of resistor padding (a series resistor before the net, a series resistor after the net, two resistor L-pad before the driver, split resistors before and after the net, and so on) all change not only the level but also the FR shape of a tweeter in a unique manner, hence its phase response, too. But this effect on phase is subtle compared to the effect of change of inductor and capacitor values in the network. Moreover, this effect can be predicted by crossover simulation.
 
tktran303 said:
Unless you experiment with the different 3 tweeters on the single woofer, and design 3 crossovers to match the basic parameters like FR/phase alignment, it is impossible to make valid comparisons.

I already designed preliminary versions of three different XOs for these tweeters and the Usher woofer. I simulated these using FRDC tools and Speaker Workshop. I used Zaph's data and minimum phase extraction via Hilbert transform---I found this method can, when PRoperly applied, be even more accurate than poorly implemented actual phase measurement (but to do this correctly, you need some serious learning to know how this method works.)

According to the simulations, all three tweeters are workable with the Usher woofer. The RS28A allows me to obtain the best phase alignment at my design axis (tweeter axis). The HDS tweeter needs a bit tweaked electrical 3rd order XO to achieve an inch or two below tweeter axis as its in-phase axis. The in-phase axis with the Seas is also one or two inch below tweeter axis. Basically, all three give a good phase alignment and frequency response.

This is why it's been so difficult for me to choose among the three!
 
"I think people agree that a resistor is the least harmful component of a passive XO. An inductor is the worst. Am I wrong?"

Basically a misconception here. Not because the resistor sonic per-se, but the damping factor. the larger the resistor in series, the worse the damping factor, this is more to do with the amplifier-speaker interface issue. The same reason to do active subwoofer , not only because power loss, if you use high resistance inductor low pass for passive sub, the cone control would be bad, especially at resonance.



Hartono
 
"The effect of a resistor in a passive XO on damping factor should be negligible especially when we use a high quality solid state amp. A good thing is I don't use a valve amp and will never. "


output impedance of valve amp is higher than solid state. If you add series resistance with the solid state amp, the damping factor would be even worse than valve amp. different output impedance is very audible, not because of frequency response, it affect the dynamic operation of the speaker, But some amp and speaker is designed with this in mind ( current drive amp+speaker). some argue that this even lower distortion, but it definitely will make it worse at resonance, and in your application you want to push the tweeter on it's lower end, this is very audible.

If you don't believe me , add series resistor , try EQ-ing until you got the original frequency response, you will not get the same sound .

1 ohm in series is quite audible.

Hartono
 
"I figured this out before you posted That's why I edited the post."


;) that's cool


"we can use a notch filter to avoid its bad effect. Right?"

notch filter do reduce it but will not eliminate it. adding series resistor might sound ok, but it definitely change the sound. It might even sound better :D , I just want to make sure you aware of the effect of adding series resistor, dynamically, not only the effect on frequency response.

Cheers,
Hartono
 
Hartono said:
I just want to make sure you aware of the effect of adding series resistor, dynamically, not only the effect on frequency response.

Thanks, Hartono. Now I understand better why a low DCR inductor is important in a woofer net. For tweeter, unfortunately, a series resistor cannot be avoided in a passive XO most of the time.

BTW, can you suggest anything to consider I might miss for my tweeter selection?
 
"BTW, can you suggest anything to consider I might miss for my tweeter selection?"

Find tweeter with highest efficiency (reduce flux modulation)and lower impedance peak. Neo magnet (EDIT:smaller magnet which possibly means better venting, reduced flux modulation), shorted turn to reduce inductance, well vented design.

Edit: and short voice coil

ferrofluid alter the sound, not always desirable, some tweeter with ferrofluid sounds good.



Hartono
 
Dave Bullet said:
Peter,

Breakup modes show themselves further down the frequency spectrum. For the 27TBFCG - you can see the ultrasonic breakup appearing in Zaph's harmonic distortion 3rd order at 8.7KHz, then 5th order at approx 5.25KHz (= the approx 25KHz F1 breakup node)

.....

Cheers,
David.

While this is true, it does not matter, because you can't hear the 3rd order harmonic of 8.7khz. The distortion is still ultrasonic.

Dan
 
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