Will a ribbon help or ruin single driver sound?

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JLM

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Re: Will a ribbon help or ruin single driver sound?
« Reply #40 on: 10 Apr 2010, 11:18 am »
Danny said: "... keep in mind that a full range driver still has inductive reactance and that does cause a shift in phase."

Huh??   :scratch:

What's inductive reactance?  And why wouldn't any driver have some (since all drivers have to cover a range of frequencies)?

roymail

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Re: Will a ribbon help or ruin single driver sound?
« Reply #41 on: 10 Apr 2010, 11:33 am »
Jim (jredman) pointed out... whether you can "hear" anything above 10-12 khz, there is an effect which cannot be denied and definitely adds positively to the listening experience.

That being true, the effect may or may not be desireable depending on the listener.  Apparently, from all I've read the Tonian's get it right, but I doubt that's an easy task.  :|

RennoVattio

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Re: Will a ribbon help or ruin single driver sound?
« Reply #42 on: 25 Apr 2010, 12:13 pm »
When I added a ribbon (Foster Leaf Tweeter) I simply used a ¼µƒd polystyrene cap @6dB/octave, but had to invert the phase of the tweeter to achieve a seamless result.

I had considered working with a phase compensating network but decided I didn't need it after inverting the tweeter phase and liking what I heard.

If the fullrange is producing up to and above your highest audible frequency, there should be no need for an additional Super tweeter, however, if it does not, try to bring the tweeter in at the frequency of -3dB mid roll-off and you should have near zero cancellation.

When I tested myself at college on the AF generator into the Foster ribbon/leaf I could hear 24K with my Right ear and 21.5K with the Left ear, but I was only 23 and hadn't yet enjoyed a world record for Bass competition, nor found my love for target shooting.

- I'm more than twice that now and strain to hear maybe 18K.
 
If I could go back I'd trade all that bass competition and shooting fun for my hearing back to even 20K!

-----------------

Now, I do not see how off-axis firing of the tweeter up or to the rear will help.

Not only does it seem counter-productive by causing phase anomalies and cancellation, how is one supposed to hear what one is evidently missing from the top octave if so high a frequency, which tends toward beaming, isn't directed toward the ear, as is the full range driver?

Perhaps the benefit of the rearward-firing tweeter is to add presence through room ambiance, but I fail to see how that layout would provide the fill needed for ~12KHz & above.

-----------------

I fully favor forward firing and fancy the fusion of Foster and Fostex for fidicinal festivity, from frolicking folk or fusion fantastique to fugue fortissimo!  :eyebrows:

Danny Richie

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Re: Will a ribbon help or ruin single driver sound?
« Reply #43 on: 25 Apr 2010, 01:14 pm »
RennoVattio,

It is actually just the opposite.

It is when the tweeter is forward facing that you get phase anomalies and cancellation.

I will try to set something up and take measured responses for you guys as soon as I can so you can see what is happening.

roymail

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Re: Will a ribbon help or ruin single driver sound?
« Reply #44 on: 25 Apr 2010, 09:42 pm »
Bob Brines once recommended using a rear mounted FT17H to augment a 167e if needed.  I'm sure he's tried it both ways.

RennoVattio

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Re: Will a ribbon help or ruin single driver sound?
« Reply #45 on: 26 Apr 2010, 01:02 am »
RennoVattio,

It is actually just the opposite.

It is when the tweeter is forward facing that you get phase anomalies and cancellation.

I will try to set something up and take measured responses for you guys as soon as I can so you can see what is happening.

Against what would the tweeter supposedly be canceling?

In my post I mentioned the tweeter should be brought in above the full-range driver's response curve where it is -3dB as it is on it's way to zero response. How would the tweeter cancel against something not there?  :scratch:

And as far as phase at the crossover point, I mentioned I had to reverse phase the tweeter to produce a smooth transition, probably due to the inductive reactance of the full-range coil having a phase opposite to that of the capacitive reactance of the crossover capacitor, but instead of building a phase compensating network I was happy with the reverse-phase wiring correction and never have had issue with any instrumentation having a smeared top end response due to that phase inversion.

Danny Richie

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Re: Will a ribbon help or ruin single driver sound?
« Reply #46 on: 26 Apr 2010, 01:56 am »
Quote
Against what would the tweeter supposedly be canceling?

In my post I mentioned the tweeter should be brought in above the full-range driver's response curve where it is -3dB as it is on it's way to zero response. How would the tweeter cancel against something not there? 


It will be out of phase with the woofers response at some point and at some wavelength and most often than not cancellation will be in more than one area.

Keep in mind that a 10kHz wavelength is only 1.3" long. 20kHz is only about .65" long. So just a slight movement one way or another with either driver can easily cause cancellation.

You will get coupling and a 6db gain in one area and a 15db dip in another.

In the vertical off axis you will get huge peaks and dips all over the place giving you a very uneven in room response.

RennoVattio

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Re: Will a ribbon help or ruin single driver sound?
« Reply #47 on: 26 Apr 2010, 04:35 am »


It will be out of phase with the woofers response at some point and at some wavelength and most often than not cancellation will be in more than one area.

Keep in mind that a 10kHz wavelength is only 1.3" long. 20kHz is only about .65" long. So just a slight movement one way or another with either driver can easily cause cancellation.

You will get coupling and a 6db gain in one area and a 15db dip in another.

In the vertical off axis you will get huge peaks and dips all over the place giving you a very uneven in room response.

I guess I'm not saying it well or being clear enough, I would not add a supertweeter if there is still decent response from the lower frequency driver.
 I would only use the supertweeter to supplement the top end which is missing and absent from the full-range, and utilize so small a cap in value that it disallowed anything below that frequency.

 - Perhaps you're pointing out the possible cancellation below the high pass frequency, and is well taken thus requiring a much steeper slope crossover including phase compensation, however mine seem to not need these patches.

So, to answer the original question, add a ribbon so high in frequency that all it does is supplement the full range adding only those frequencies which are missing from the lower frequency driver, utilizing the best sounding crossover to your ears.

I couldn't live without the air it provides, and I love my music too much to suffocate it.  :wink:

roymail

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Re: Will a ribbon help or ruin single driver sound?
« Reply #48 on: 26 Apr 2010, 12:10 pm »
What would be a good cut-off frequency for a tweeter added to a full range driver like the 167e?  I'm thinking single cap...  :?

SET Man

Re: Will a ribbon help or ruin single driver sound?
« Reply #49 on: 26 Apr 2010, 04:19 pm »
What would be a good cut-off frequency for a tweeter added to a full range driver like the 167e?  I'm thinking single cap...  :?

Hey!

   I'm using 0.47uf with my FT17H and 167E. :D Depend on how you are going to mount it and your room. You might want to try 0.68uf and 0.33uf also. With these the cut off is pretty high but it sound fine in my system.

Take care,
Buddy :thumb:

Danny Richie

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Re: Will a ribbon help or ruin single driver sound?
« Reply #50 on: 26 Apr 2010, 04:24 pm »
I took some measurements for you guys and will try to get them posted later today as time permits.

roymail

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Re: Will a ribbon help or ruin single driver sound?
« Reply #51 on: 26 Apr 2010, 06:45 pm »
Thanks, Danny... much appreciated.  :thumb:

BobM

Re: Will a ribbon help or ruin single driver sound?
« Reply #52 on: 26 Apr 2010, 07:32 pm »
I've heard a few "supertweeters" that were external to the speakers we tested them on. In every case they seemed to add that extra sparkle and top end livliness and increased soundstaging. But in every case it also sounded a bit disjointed and artificial, losing location specificity. It did improve when we tried to keep them close to the existing tweeter, but just placing them on top of a cabinet did not work very well to my ears.

I would expect that issue to be componded with a single driver speaker, where the single point source is a good part of what it's all about. So make sure you can mount it close to the original driver if you're going to give it a shot.

roymail

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Re: Will a ribbon help or ruin single driver sound?
« Reply #53 on: 26 Apr 2010, 08:19 pm »
... or on the rear of the cab.

Danny Richie

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Re: Will a ribbon help or ruin single driver sound?
« Reply #54 on: 26 Apr 2010, 08:47 pm »
Okay I set some stuff up and took measurements.

To some degree this is the best possible scenario as I used a small diameter 3" full range TB driver (good sounding too) and an Aurium Cantus ribbon tweeter.

The full range driver was mounted at the top of the box so the acoustic centers are pretty close. Please note!, that with a larger diameter full range driver, and with more distance between the acoustic centers, the effects that you see can be MUCH worse.

The first one is an individual response of the full range woofer and the tweeter (setting on top). The tweeter has a single 1uF cap on it and a resistor. I picked a 1uF cap as it is a commonly used value for adding these tweeters. A larger cap value lets it play down lower and the cancellation effects go lower in range. A smaller value can have less detriment effects but it can still have a detrimental effect in some areas. The effects in the top two octaves are about the same. There is no getting around these effects. If you don't hear them then you are simply not hearing them, but they are still there.

See woofer and tweeter individual responses.



The TB woofer has good top end extension but really lacks detail levels of a lighter weight diaphragm tweeter. The fact that everything it does is a compromise as it is having to play the short wavelengths and the really long ones at the same time makes matters worse. So I can see someone thinking that adding the tweeter up top might help it out.

Also keep in mind that I was able to move the tweeter around to find the best possible alignment and keep them in phase over a wide of a range as possible using my measurement system. In other words, I can make it as perfect in phase as possible. You must also remember though that just because it is in phase at the crossover point or at any given point does not mean that it will be in phase over a wide range or over the whole spectrum.

Also, just because you have a full range driver and no crossover does not mean that you have no shift in phase. The inductive reactance of the voice coil will cause a shift in phase just like any other small inductor.

So here the two are lined up as good as they can get and as perfect to being in phase as possible.



So from 3kHz on up they are still in what I'd call an "in phase" relationship and of coarse the lower they play the more the phase rotation, and at some point it passes 90 degrees and starts going the other way and decreasing output.

Note also that even with a 1uF cap on the tweeter, it still plays quiet low. Even though it is well down in output, it can still cause some cancellation.

Also, a full range driver with less output in the top octave will not couple as much with the tweeter and will not give you as much gain as this particular 3" full range driver that plays well to 20kHz. However, the cancellation effects will still be the same.

Now here is where it gets interesting and it is the measurements that follow that shows just how fragile this relationship is.

Here is the exact same setup, distance, etc, but the tweeter is moved back only 1 inch.



What a mess....

Now we have a coupling effect at 20kHz and some gain.

At about 18.5kHz we have nearly no gain.

From 9kHz to 17kHz we have an in phase relationship and getting gain.

From 5kHz to 9kHz we are in an out of phase range and getting cancellation.

From about 6.8kHa to about 15kHz we have about a 15db swing in response.

From 2kHz to 5kHz we are now in phase again getting some gain again.

Then finally below 2kHz we are back out of phase and even though the tweeter is well down in output by then, it is still reducing output levels slightly in that range.

Keep in mind that this was a movement of only 1 inch. It can get much worse.

Now in the next graph you can give you an idea of what the in room response might look like as the vertical off axis causes more of a wide band cancellation effect.

The first measurement is on axis with the tweeter moved back up so that they are in phase again over as wide of a range as possible. It is the Red line. Next the mic is moved up 4 inches. That is 4 inches from 1 meter away. See Orange line. Lastly the mic is moved up 4 more inches, See Yellow line.



Now with just a very small movement of the mic we see a total swing of nearly 20bd from about 9.5khz to 15kHz.

Now just image how much worse this would be with a larger diameter driver (much worse).

This is why I recommend facing the tweeter to the rear or facing it up. You still get the same added air, and space to imaging, but without the adverse effects to the on axis response.

Does this make sense now?

kyrill

Re: Will a ribbon help or ruin single driver sound?
« Reply #55 on: 2 May 2010, 05:08 pm »
ok
do not really believe yr brain is susceptible to linear logic
you may well stop hearing 12khz and up, but you may hear at the same time much higher than that. Say you stop hearing at 12 khz
but dynamic differences between for instance 14khz and 15khz can be perceived.

I found this by accident in my younger years when I played with a sinus tone generator in a technical audio repair lab
i stopped hearing (then) at 17khz,which I accepted, in my (also then) unshaken  belief in "sensicial" logic. The tone generator was "steered" ( erghh my English)with a rotary knob.
in the area beyond my hearing threshold of 17 khz, i turned the knob swiftly clockwise<-->counter clockwise and i heard changing peeping tones.As soon as the knob was steady I could not hear a thing. Curiously I played a bit more "nuanced" and it depended  on how fast (or how slow for not hearing) i turned it up and down
I listened with a Stax electrostatic head phone

So it suggested my brain/ear does not hear or neglect a too high freq, but dynamic differences between those by itself "unhearable" single non dynamic tones, can be perceived
« Last Edit: 2 May 2010, 08:30 pm by kyrill »

chadh

Re: Will a ribbon help or ruin single driver sound?
« Reply #56 on: 2 May 2010, 08:37 pm »

At AK Fest yesterday I had the chance to hear the Parker Audio Excalibur: http://www.parkeraudio.net/excalibur.htm.

It uses a 10" driver running without a low-pass filter of any kind.  The Heil Air Motion Transformer is used at the high end, with a simple first-order filter.

They sounded pretty good, at least on the simple, sparsely arranged material I heard them playing most of the time.

Chad

SET Man

Re: Will a ribbon help or ruin single driver sound?
« Reply #57 on: 2 May 2010, 11:16 pm »
Hey!

    Danny, that for the measurement. It is very interesting. :D

    I actually tried this out with my system. I've always have my horn tweeter Fostex FT17H xovering it very high with just one 0.47uf cap facing forward.

     So, I tried facing backward and connecting them both same polarity and reversed polarity with the main drivers. But I have to say that I still preferred them facing forward.

    Don't get me wrong here. I'm not trying to pull your legs or anything. And I really appreciated see the measurements you've made. I'm just sharing my finding with my system. I guess it is just happened that all the dips and peaks with the tweeters facing forward in my system fall in the right place for me.

     BTW... my tweeters are actually mounted about 0.75" back from the main drivers baffle.

Take care,
Buddy :thumb:

RennoVattio

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Re: Will a ribbon help or ruin single driver sound?
« Reply #58 on: 3 May 2010, 02:31 am »
Danny,

Try a mid with severe roll-off ~12kHz and a ¼µƒd cap on a forward-firing leaf tweeter, reverse the tweeter phase, then run your sweeps.

My ears are pickier than most people I know, but they like this.

Danny Richie

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Re: Will a ribbon help or ruin single driver sound?
« Reply #59 on: 3 May 2010, 05:00 am »
Quote
Danny,

Try a mid with severe roll-off ~12kHz and a ¼µƒd cap on a forward-firing leaf tweeter, reverse the tweeter phase, then run your sweeps.

My ears are pickier than most people I know, but they like this.

My ears are pretty picky too and I have yet to find a full range type driver that will do it for me with or without a tweeter added.

Here is another full range driver that I have on hand. This one is more typical in that it is rolled off on the top octave plus it has some break up in its upper range.

I used a ribbon tweeter on top of it also.

I also reduce the cap on the tweeter to a .56uF value.

Here are individual driver measurements:



Here it is with the drivers as much in phase and lined up as I can get it:



Getting them to both sum is not easy and can only be achieved for one point in space. In any other direction they can be out of phase and causing cancellation.

Now here it is with the tweeter moved back 1 inch:



Since the woofer is only a 3 inch woofer right at the top of the box then it is not near as bad as a larger diameter woofer with the tweeter much further away.

It still caused a 10db swing though.

Here it is with the tweeter moved forward 1 inch (now almost even with the front baffle).



Now we are looking at a 20db swing.

Moving the microphone up or down causes a similar effect.