Tweeter opinions (sorry!)

[Tenson]

I just noticed this on Madisound http://www.madisound.com/cgi-bin/ind...28591&pid=2125

Has anyone an opinion about it? My other choice was the RAAL 140-15D. I need a tweeter that can crossover as low as possible, 1.5KHz or even better 1KHz and lower 4th order but still working well up to 20KHz.

I like the look of this as it seems to go smoothly down to 1KHz but also because it is very slim, which means I can mount it semi-coaxially with the 12" woofer far easier than with the RAAL (yes I have time-alignment).

I imagine this is a very, very good tweeter as the other revorlator tweeters gain high praise right? How would it compare to the RAAL though? Domes have lower distortion don't they, but ribbons have faster transient response. The RAAL also goes up to 20KHz easier but I'm sure a bit of a diffraction grill will help the very slightly rolled off off-axis response. Would it give much SPL when crossed over low like 1KHz?

I have high expectations for it as my current speakers use a 34mm soft dome @1.4KHz 4th order and sound VERY good. I would hope these super expensive tweeters sound even better.

[Snickers-is]

You should concentrate on the dispersion pattern and the frequency response. These two factors affects us more than THD if THD is at normal levels or better.

Limiting the dispersion with a horn also helps you in creating a time alignment and achieving some transient capacity in the XO range. It also draws some attention away from crossing over at low frequencies as the tweeter and midrange dispersion patterns could be pretty much the same. It also helps you to lower the off axis frequency curve jump and allows you to implement a high order filter with greater sucess.

[Tenson]

You should concentrate on the dispersion pattern and the frequency response. These two factors affects us more than THD if THD is at normal levels or better.

Maybe but then Linkwiz says to look at phase and cumulative decay over frequency response doesn't he?

Limiting the dispersion with a horn also helps you in creating a time alignment and achieving some transient capacity in the XO range. It also draws some attention away from crossing over at low frequencies as the tweeter and midrange dispersion patterns could be pretty much the same. It also helps you to lower the off axis frequency curve jump and allows you to implement a high order filter with greater sucess.

Thanks for your comments, can you explain more please…

Why does a horn help time alignment?

I don't think dispersion will be a problem. Both drivers will be pretty much fine on and off-axis at 1KHz, with slot loading on the woofer and a sharp Xover.

The off-axis response is fine on the tweeter, except maybe a roll-off at 18KHz which is ever so slightly too steep. I’m sure I can modify it though; I have done a fair amount of work in diffusion. Either way, why would a horn help to implement a high order Xover?

I'm not keen on highly directional speakers in the high frequencies as they sound closed in and have yet to hear a horn system that sounds 'right' to my ears.

[Snickers-is]

Yes, Linkwitz says so, but he does not say "forget the dispersion because phase is more important".

A waveguide could easily end up being the same depth as the 12 inch driver. This makes it time aligned if they are at the same Z axis in front.

The off axis responses at 90 and 180 degrees in baffel are also interesting and should be considered.

If you can not get what you want above 10kHz I would rather recommend you to make a slight boost at the highest frequencies and listen to it a bit off axis. Another alternative is to add a small ribbon at around 12kHz. Then the manin tweeter could simply be a TangBand W4 1337s, and the high tweeter a Fountek Neo CD3.0

[Tenson]

Ahh, I think you missed that I will mount it near-coaxial, mounted in the centre of the woofer. So the waveguide won't do anything for time-alignment as it will nearly be in time already (especially if I removed the dustcap, or inverted it). The waveguide would likely mess up the woofer's dispersion instead.

I Imagine the woofer itself would act as a gentle waveguide at that point probably around 1KHz in fact.

The response easily extends to 10KHz on this tweeter have a look at the PDF. It just starts to roll-off 30 degrees off-axis around 18KHz, like any other good tweeter but does it a little steep for my taste. Boosting HF would make the on-axis response incorrect then. A phase plate would be a better option here I think.

I was really just interested in opinions on the tweeter and its sound quality and if it could handle Xover at 1KHz, 4th order or maybe even 8th order! I don't anticipate high order Xovers being such an issue when the tweeter is coaxial, am I right?

[Variac]

Are you going to remove the dustcap of a big woofer and mount the tweeter on the end of the pole piece? If you get a woofer with a 4" voice coil it should work!

It is pretty efficient too, maybe use it with a pro audio driver?
Often they are made to go to higher frequencies such as the 1k or more that you are mentioning.

I hope someone who has tried the tweeter sees this thread and comments.

[Tenson]

I'm planning to use an Eminence Magnum 12HO, which does indeed have a 4" voice-coil. It extends to 3KHz, but beaming starts around 1KHz so I need an Xover around that and a sharp slope.

I wasn't thinking of putting it on the pole piece but rather just have some 'arms' that reach from the side of the speaker to hold it in place. What would be involved in mounting it on the pole piece?

In fact... what is involved in removing the dustcap? Does it not affect the woofer's performance? If the tweeter was on the pole piece (is this the piece the voice-coil is wrapped around and connects to the cone?) then the tweeter would add to the mass of the woofer cone wouldn't it?

Edit: I have added a picture of a woofer with all the bits I know labelled, if someone could add the bits I don't know that would be great! Maybe it should even be a sticky

[Tenson]

Ah okay I cut open a crappy Dayton driver I had. The pole piece is the bit that is in the centre of the voice-coil and voice-coil former, correct? Most seem to be vented with a hole. I could fix something to that

[angsuman]

Well if your going to mount it coaxial you need a big voicecoiled woofer to fit in that huge tweeter. If you want to DIY yourself a coaxial i think I remember many threads on it but using a small Neodymnium tweeter. There are many great coaxials made by seas if you really want the time alignment and even dispersion pattern. If you have measuring equipment then you could try the coaxial idea. But you should look at the type of cone. I'd figure an exponential expansion on the woofer cone profile is much better than a straigt profile.

The tweeter you mentioned seems to use a lot of technology from the VIFA dx25. The dispersion is very very good for a dome tweeter i wouldn't worry about the drop-off after 18khz. Waveguiding the tweeter would be a better option or atleast more predictable than a coaxial arrangement with a woofer. If you're really considering the use of this rather pricey tweeter in a project it'd probably be best to use it as it was designed.

If you decide to go with a ribbon the RAAL appears to be one of the best ribbons out there. They even publish their distortion specs.

[Variac]

EDIT: Just saw that you posted, you understand what the pole piece is! END EDIT

Well, first, the Magnum series has a very good reputation so in that way its a good choice.

Generally, you can remove the dustcap by just carefully peeling it off the cone helped with very carefully cutting at the glue with a razor knife. It will affect efficiency and response a little bit, but not much on a 12" driver. With te MAgnum it shouldn't chanfge the sound at all...


The voice coil is wrapped abround a light tube called the "former" which is attached to the cone.

The pole piece is that thick tube hooked to the magnet that the voice coil and former are outside of. It doesn't move.

OK , the magnum is a special case in that it has a very gauzy dust cap that you can partially see through, like those sheer tops womwen wear with a lacey bra underneath ,.... OK where was I ? OK moving on...

UNDER the Magnum "dust cap" is a phaseplug/ heat sink attached to the pole piece, bullet shaped, like those....er never mind....MOVING ON....

So anyway, the first step is to install the tweeter as you suggest. As a further tweak, if you are thrilled with the setup, you could later remove the gauzy dust cap exposing the phase plug which would look cool. Then you could see if you could remove the plug so that the tweeter could replace it and then reinstall it. OR maybe you could just epoxy some PVC tube on the end of the bullet/phase plug and mount the tweeter on it. Looks like it might work.


The idea is to get rid of the area between the back of the tweeter and the cone that will resonate. Also I think you want to get the tweeter about half way into the cone for proper phase . Because of its special construction, I think the MAgnum will have less resonance than most in this area.

Overall, the MAgnum is probably a little harder to use as I suggested....A driver with a standard polepiece and dustcap would be easier. I've been suggesting this hoping someone would try it. Would work great with a 4" tweeter and 4" voice coil..
I should do it I guess....

You can probably cross overr a bit higher if you have too.....