Taming harshness in horn tweeter

[rongon]

I hope I can get some help from the group. Thank you in advance...

I have a pair of Klipsch KG 4.5 I've been, er... tweaking.

So far, I've applied Duct Seal to the woofer frame and magnet, and to the backside of the tweeter horn and around its magnet. That made a noticeable improvement in midrange clarity.

After that, I bought the upgrade titanium tweeter diaphragms from Bob Crites. That improved the highs, noticeably smoother.

The most recent tweak has been lining the cabinet walls with polyester felt, and putting a layer of felt around the tweeter horn on the front of the baffle, which helped the imaging and clarity a bit more.

The final frontier is how to get that last bit of horn harshness out of the tweeters. There is a hardness and sizzle to vocal sibilants and cymbals.

I don't want to mess up the midrange around the crossover region, which is pretty good right now.

I thought I'd try a Zobel network on the tweeter, to see if that would make the trebles sound "softer." I don't have specs on the Klipsch K-85-K tweeter, and can't find them anywhere, so I don't know what the voice coil inductance is (Le). I can tell you the voice coil resistance (Re) is an unexpectedly high 8.1 ohms.

Can I assume the tweeter impedance is 8 ohms and use an 8 ohm resistor? Or should I go with 1.25*Le and use a 10 ohm resistor?

What would be a typical Le value for a cheap-ish horn tweeter like this? 0.05mH?

I have available 7.5 to 10 ohms for R and capacitor values from 0.22uF to 2.2uF for C, at least to start with. I put a zobel using 0.47uF and 10 ohms in last night, but haven't listened to the speakers at full listening levels yet.

I just read that a resistive attentuation circuit actually damps horn resonances better than a zobel. So I could calculate an L-pad and use that instead. But once again, I'm confounded by the Re of 8.1 ohms for these tweeters. Should I calculate the L-pad values based on an 8 ohm impedance, or something like 10 ohms instead?

I could try a 1.5 or 2 ohm series R with a 50 ohm parallel R. That should just pad down the tweeter by about 1.5dB.

I've already tried paralleling the tweeter with 100 ohms, but removed it before I upgraded the tweeter diaphragms and added the felt layers to the cabinet. I will try this again.

--

[bwaslo]

Try some reticulated foam in the tweeter horns.
For example:
Red Spade Audio: Miniwaves foam mod
http://redspade-audio.blogspot.com/2...-foam-mod.html
Or google "reticulated foam waveguide".

[tomtt]

Originally Posted by rongon

The final frontier is how to get that last bit of horn harshness out of the tweeters.

There is a hardness and sizzle to vocal sibilants and cymbals.

hardness and sizzle?

electrolytic caps would do something like that.

[Michael Chua]

Originally Posted by rongon

There is a hardness and sizzle to vocal sibilants and cymbals....

I thought I'd try a Zobel network on the tweeter, to see if that would make the trebles sound "softer."...
--

That "Glare" may not be from the tweeter. Could well be from the cone breakup of the 10" Carbon Graphite Cone woofer. If there's cone breakup, a zobel on the woofer can tame that sizzle. The other way is to apply a notch filter.

Another cause could be the tweeter is resonating. This happens when it's crossed near it's resonance frequency. For this, you'll need a conjugate network (LCR).

[rongon]

Thanks for the replies.

I got home and took a quick listen to the speakers with the zobel networks on the tweeters. The zobels took all the life out of them. Definitely rolled off the highs above 10kHz, but left them sounding too polite and reserved.

For test listening, I use a Denon CD of Ravel's Ma Mere L'Oye (Orch National de France, Eliahu Inbal, cond.) that has nice triangles, col legno violins and cellos, spooky muted violins and some nice blatty trombone blasts. Lots of good high frequency stuff.

Right now I've got 100 ohm 5W wirewounds in parallel with each tweeter. No series resistor. It smooths out the trebles just a hair. I guess they sound pretty OK.

Originally Posted by bwaslo

Try some reticulated foam in the tweeter horns.

That's an intriguing idea, might just be the ticket. I took a quick look to find some for sale, but couldn't. Where to buy in the USA or NYC? Canal Rubber?

Originally Posted by tomtt

hardness and sizzle? electrolytic caps would do something like that.

No electrolytics in the tweeter circuit (all are small metallized mylar), but there is a 33uF 100V non-polarized electrolytic in the woofer circuit. The crossover board is really small, so fitting a 33uF film cap would be difficult to impossible. Maybe a much better quality Panasonic NP 'lytic would improve things? I'll take a look at DigiKey, Mouser...

Originally Posted by Michael Chua

That "Glare" may not be from the tweeter. Could well be from the cone breakup of the 10" Carbon Graphite Cone woofer. If there's cone breakup, a zobel on the woofer can tame that sizzle. The other way is to apply a notch filter.

Another cause could be the tweeter is resonating. This happens when it's crossed near it's resonance frequency. For this, you'll need a conjugate network (LCR).

Food for thought! Yes, that makes sense. I think I'll try a zobel on the woofers. I can't seem to find specs for these Klipsch drivers. It's easy to get the Re of the woofer, but I doubt I can find the Le (I have no L meter). I could ballpark guess, it I suppose. It's Re * 1.25 for the R, and something like 22uF to 33uF for the C, correct?

I wonder if anybody knows what drivers Klipsch used in these. They didn't make their own, correct?

Thanks again for the suggestions.

--

[AllenB]

Before you go adding this RC circuit (or any zobel compensation), you should consider the potentially double-edged effects...

An RC circuit like that usually doesn't help when it affects the top end where the crossover is just passing the sound through, because you need components between the amp and speaker which are effective at those frequencies, and unless you measure....hence the fact it is rarely used this way.

However since you said it did make a difference, it has obviously altered a part of the impedance that was under the influence of the crossover and this is the point...when you add a zobel for zobel's sake, you should do it before adding the crossover. When you add it after, you not only change the expected behaviour of the crossover but you add a new level of complexity to it with results that can be hard to predict.

If you are going to add components to the crossover you will want to consider the entire circuit in the bigger picture. Some here might be able to make this easier if you wanted to post your crossover (if you can).

lining the cabinet walls with polyester felt

If this is the thin felt, then it may not have a noticeable effect on the walls but might be useful around the rough edges behind the woofer.

Using felt on the baffle may be a good idea, especially if it is a little more thick. It wouldn't hurt to try covering the entire baffle.

I could try a 1.5 or 2 ohm series R with a 50 ohm parallel R. That should just pad down the tweeter by about 1.5dB.

This may be worth trying as it's intended effect is likely to be greater than its side effects.

You need to be sure you've considered all reasonable options with damping materials first. Then if you need to change the tone of the speaker, it should be done as a whole. In other words, if you want to bring down the upper treble, you should prevent changes in the tweeter down near the crossover. Maybe all you need is an RC with different values, or a shelving network.

Hope this helps.

[phivates]

Filters are a problem. Zobels help on woofers, tweeters not so much. And horns magnify everything. Why isn't this simple?

[tinitus]

Originally Posted by AllenB

when you add a zobel for zobel's sake, you should do it before adding the crossover.

When you add it after, you not only change the expected behaviour of the crossover but you add a new level of complexity to it with results that can be hard to predict.

ahh, now I know why it takes me months to adjust those bloddy zobels

I also spend months to get tweeter filter/attenuation combination right

dull or harsh sound is easily caused by crossover malfunction
and the differences where this change happens can be ridicoulusly small

[bwaslo]

for reticulated foam, try an aquariumshop.
its used for filters.

[rongon]

Originally Posted by AllenB

...when you add a zobel for zobel's sake, you should do it before adding the crossover. When you add it after, you not only change the expected behaviour of the crossover but you add a new level of complexity to it with results that can be hard to predict.

If you are going to add components to the crossover you will want to consider the entire circuit in the bigger picture. Some here might be able to make this easier if you wanted to post your crossover (if you can).

Easy enough, here it is:

Originally Posted by AllenB

If this is the thin felt, then it may not have a noticeable effect on the walls but might be useful around the rough edges behind the woofer.

Yes, it's the thin felt. What is "around the rough edges behind the woofer"? Do you mean the baffle and mounting hole? Or the back wall, directly behind the woofer (i.e. soften the back wave reflection)?

Originally Posted by AllenB

Using felt on the baffle may be a good idea, especially if it is a little more thick. It wouldn't hurt to try covering the entire baffle.

Yup, thicker felt. Not wool felt, but it's thicker polyester felt with adhesive backing, from Home Depot.

Originally Posted by AllenB

...(L-pad) may be worth trying as it's intended effect is likely to be greater than its side effects.

I have a 100 ohm resistor parallel to the tweeter now, and was listening earlier. It makes a very slight difference, sort of softens the highs in the 8kHz and up area.

I wonder if Michael Chua's suggestion is accurate, that the sibilance might be caused by resonances closer to the crossover region. Maybe 4kHz or so? That could be... If that's the case, a zobel across the woofer might help. But this one's tricky. There's already that 33uF cap in series with 2 ohms to ground. Sort of looks like a zobel already, right? But that 2 ohms is way lower value than the voice coil resistance (which is 7.2 ohms on these woofers). If I do go with a zobel on the woofer, I calculate its values as R = 9 ohms, C = 22uF. Even just electrically, that would interact with the 33uF and 2 ohms in series from woofer + to ground, would it not?

Originally Posted by AllenB

You need to be sure you've considered all reasonable options with damping materials first. Then if you need to change the tone of the speaker, it should be done as a whole. In other words, if you want to bring down the upper treble, you should prevent changes in the tweeter down near the crossover. Maybe all you need is an RC with different values, or a shelving network.

I wish I knew exactly what the problem is. I thought I did, but now I have doubts. It could be the lower end of the tweeter response that has a resonance causing harsh sibilants. Or it could be cone breakup at the top end of the woofer's response. Or it could be an overly elevated treble above 10kHz. Measuring tools and more knowledge and expertise than I have are required, I think.

I'll try an L-pad over this weekend, to see what that sounds like. Easy to experiment with that.

I could also try a simple series resistor and nothing else. I gather that reduces output down at the crossover end of the tweeter's response, leaving the highest frequencies relatively untouched. If there's a resonance or peak in the upper mids, then that could mellow it out. Another easy thing to do.

If that doesn't do it, I'll try a zobel on the woofer, on the off chance that cone breakup is causing a problem. Again, easy to do.

If none of that does the trick, well, I suppose I'll have narrowed down the options.

Originally Posted by AllenB

Hope this helps.

It sure has! Thanks for replying.