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Old 16th February 2010, 06:14 PM   #1
pjanda1 is offline pjanda1  United States
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Default discussing Whizzers

I sometimes write lengthy emails in response to simple questions. I've been discussing speakers with a gent new to DIY. He saw that a few folks here are interested in whizzer-less widebanders and asked, "why?". I shared a few thoughts with him. He thought I should post some of this info, and given that I've certainly fielded similar questions in the past, I'll just copy and paste the entire message (with one little edit). This was hastily composed, and I certainly have additional thoughts. But I thought it might make for some discussion as well.

Paul



Aaron,

The whizzer reproduce all the frequencies above 8Khz or so. Those using the WOW versions (with-out-whizzer) are using other tweeters. High efficiency tweeters are expensive, and a good crossover can be tough to design. Some folks know what they are doing and are working on some interesting applications, others are stabbing in the dark, but having fun.

Whizzers have some drawbacks. They aren't really linear transducers. They are more like sympathetic resonators that produce some high frequencies. They have peaks and dips, and don't go terribly high. (BTW, the same can be said of some very expensive soft dome tweeters). They have some upsides too. First of all, they are cheap as can be: the same cost as a dustcap (you need something to keep stuff out of the gap). Though folks often think of them as part of the cone, they really act like another driver with a mechanical crossover, and that crossover is essentially free. They are perfectly concentric. I think that has huge advantages, and it is nearly impossible to achieve otherwise on a driver with a small voice coil (and a small voice coil is necessary to get the main cone up into the high treble). I think a concentric, flawed high frequency transducer may well be better than a perfect one in another place.

In general, I think whizzers are excessively maligned. First of all, measurements-oriented guys don't like the fact that they are non-linear, but there is nothing about a single driver speaker that the measurements crowd (in general, there are exceptions) will like. Second, many single driver speakers have some very real drawbacks. Many larger speakers have excessive high frequency rise when implemented in many typical ways. Folks hear the brightness, and see the whizzer, so they blame it unfairly. All larger fullrange drivers are operating non-pistonically, in some form of "breakup" above 2Khz or so. That means there are some peaks in the frequency response (for those of us that like single drivers, this is another drawback offset by the benefits). Folks see the whizzer, and blame it for that brightness too. Some cut the whizzer off to alleviate either of these problems, and the speaker does indeed sound less bright! But there is no high treble, and the problem is still there.

Those problems occur down between 3Khz and 7Khz where we can hear very well. The whizzer operates from 8Khz or so on up, in a range where nobody over the age of 15 can hear very well. Even if you can hear the frequencies, they are much like low bass. You can tell they are there, but you don't have much ability to discern differences. This also means, IMO, that there are better ways to spend one's money than on expensive super tweeters. That doesn't stop folks from disliking the lowly whizzer though.

Then, you also have folks who like whizzers, but who are looking for something different. Many of us enjoy DIY because you can have something nobody else has. If you order a custom speaker, it puts you in a smaller crowd. Then put it in a box of your own design, and you've got something unique. For example, my tube amps are highly customized. I'm not really attracted to building the Nth identical Simple SE. (I felt compelled to order a custom transformer and use a chassis nobody else had for my chip amp). I really like single driver speakers, but I've built a bunch of them. So, I'm working on an OB with a helper woofer. For that matter, I didn't want to use one of the popular woofer choices either, so I've got something that is a surplus, limited availability OEM unit! I'm honestly curious about trying a tweeter above 5K or so. And it is mostly because I've had so many single driver systems. Try as we might to find the perfect thing for us, curiosity and boredom quickly set in.

So, don't worry about the whizzer. If you someday crave a fancier implementation of the Betsy, a "whizzer-ectomy" is a simple procedure. Then you can make your own phase plug! You can also use a simple low pass filter, and thus keep the whizzer from really operating. Either way, I'd try the single driver first. If you want to pursue more advanced implementations of the Betsy (the main reasons would of course be curiosity, boredom, and the general neurosis that pervades our hobby), there are plenty of things I'd mess with before tweeters.

Paul
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Old 16th February 2010, 06:48 PM   #2
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Quote:
Originally Posted by pjanda1 View Post
If you someday crave a fancier implementation of the Betsy, a "whizzer-ectomy" is a simple procedure. Then you can make your own phase plug!
Good treatise Paul.

BTW due to a manufacturing error i have a number of pre-made Betsy plugs (or more accurately, plugs that fit Betsy) that can be had unfinished for a good price.

dave
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Old 16th February 2010, 07:02 PM   #3
pjanda1 is offline pjanda1  United States
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Dave,

Do you want to post prices and info in another thread so more folks might see it?

Paul
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Old 16th February 2010, 07:12 PM   #4
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You fail to consider the case of one that do not like the look of a whizzer, not will even dare to think to cut out a delicate part of the woofer, don't like the look of any kind of phase plug, don't even mind of crossing over at any frequency with shorter wavelenght than the distance from Betsy/tweeter centers, and just loves the look of a whizzerless/plugless Betsy and the gorgeus midbass, and do not care a dime about subwoofers and/or high frequency (they invented the tweeter for this job)
I'm kidding, of course (or maybe not). Nevertheless in a K-Coupler , for example a standard Betsy featuring would be my choice.
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Old 16th February 2010, 07:13 PM   #5
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Do you want to post prices and info in another thread so more folks might see it?
Done

Phase plugs for Betsy

Thanx for the suggestion

dave
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Old 16th February 2010, 07:40 PM   #6
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just loves the look of a whizzerless/plugless Betsy and the gorgeus midbass, and do not care a dime about subwoofers and/or high frequency (they invented the tweeter for this job)
.
60-10k baby; that's all I need. I don't even like the sounds
I hear outside of this range.
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Old 16th February 2010, 08:25 PM   #7
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Hi Paul

Maybe it's unfair to use the term "non-linearity" wrt to whizzers? Could give folks the wrong impression. Sure the frequency response tends to be a mess, but AFAIK there's no serious non-linearity (as in distortion).

Regarding the "brightness" problem that plagues many wide-range drivers - it seems to me there's two related "problems":
a) Too much treble on-axis.
b) Not much treble off-axis.

It seems to me that an acoustic lens, as used donkey's years ago on horns (and other tweeters) might help with both by widening the dispersion at high frequencies.

Not sure I'd want to try it myself, but if you're looking for something different...

Hmm... Can't find any images of the real oldies on Google, but the attached pics give an idea of the sort of thing I'm talking about (the slanted plates in front of the tweeters).

Cheers - Godfrey
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File Type: jpg hs-55.JPG (41.2 KB, 175 views)
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Old 16th February 2010, 10:13 PM   #8
pjanda1 is offline pjanda1  United States
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Godfrey,

As usual, I'm a little out of my league when I apply technical terms. But, whizzer's response tends to be a mess due to the resonances, right? And, wouldn't those resonances would show up as a mess in a waterfall plot? If that ringing after the signal isn't officially "distortion" what is it? It's noise that ain't in the signal. I need to get some real measurement equipment. And again, I'd add that I think whizzers might still be better than many other alternatives.

Re: treble rise and dispersion: I think you can balance them to get a relatively flat in room response. For me, my speakers, which have a rise similar to the FE207E, end up just about right a little off axis in my room(s). More rise is too much for me, even well off axis where the response is more ragged. I do accept that other ears and other rooms might work differently.

I think wide dispersion is highly overrated (in a home audio setting, pro audio/live sound is completely different). I like to put box speakers near boundaries for aesthetic reasons and to help alleviate the need for BSC. If they had wide dispersion, it would reflect of the walls. In addition, it would reflect off room furnishings, etc. I don't want a padded room! I also like the ability to affect treble response by adjusting toe-in. For home audio with only a listener or two, I see no real downside to limited (I use the word controlled) dispersion.

A college I taught at had a pair of giant old PA speakers with 15" woofers and a pair of big horn tweeters with lenses like you pictured. I don't think they were used and the room was usually unlocked and open. I wanted to bring a cart and wheel them home just for fun.

Paul
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Old 17th February 2010, 04:34 AM   #9
freddi is offline freddi  United States
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here's a dried-up old weak motor UC-122 University speaker with Qts above 1.4 and fs ~101Hz - mounted it out of curiosity and it sounded better than a P-Audio 12cx

one of the great Abraham Cohen's patents http://www.google.com/patents?id=xDl...BAJ&dq=2852089

a whizzer can be a good thing and great compromise - note perforations
Click the image to open in full size.

UC-122 side view - did the holes matter?
Click the image to open in full size.

Last edited by freddi; 17th February 2010 at 04:51 AM.
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Old 17th February 2010, 09:42 AM   #10
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Quote:
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.... do not like the look of a whizzer,... .
Except one that looks like this one!!
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