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Apr 04 2014

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Jensen 1071 Addendum (for Bats)

Do you like bats? Keep them as pets, maybe?
Do they like to listen to your music?
Here is an idea that you may wish to implement for the sake of your pet bats.
Or even for the sake of Yourself, if you come to think about it.

The Jensen 1071 covers very nicely the whole range of frequencies that I ** CAN ** hear.
But what about the frequencies that I can ***NOT*** hear?
Would it not be nice if you had the reassurance that those frequencies are simply “also there”? Just for the sake of it ?  Sounds like heresy ?

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Heresy, is that what you are thinking?

Not necessarily.

Come now, agreed. You can NOT hear a separate, single sine wave tone, that ranges within the 20 kHz to 40 kHz region. That is a fact. Especially if you are older than 4 years old.  It is a fact which I shall not even try to contest at this point.

But there is a “small caveat” to the aforementioned.

You *** ARE *** actually able to hear the small little differences in sound, the “coloration” of the high frequencies, a coloration that takes place, if the music material, signal, if you will, is impaired by a limited “slew rate”, or slope rise/fall time, or lack of quickness of change within your music transients, as represented by your speaker system.
Especially those transients, pieces of your music material, that contain lavish amounts of high frequency content. If your speakers do not faithfully convey, pass on, those ultra high order frequency harmonics that are contained within your music material, can not convey the “transients”, then this will result with you hearing a “coloration” or an “unnaturalness” of your music. The lack of those higher order frequencies simply translates to transient slopes that are not as steep as they should be.

How is this so ?  Simple.  Your music is not a trivial sine wave. If we were to listen to sine waves – OK, you are right, I rest my case. Fully agreed. There is no chance of hearing anything above 20 KHz.  But … listening to sine waves is very boring. I have yet to meet an audiophile that listens to a frequency generator, and not to music.  I much prefer listening to music, rather than to frequency generators.

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But this “normal music content” DOES contain very steep edges in some places of the graph.

Or … or even a much simpler case: a signal consisting of three sine waves, a superposition of a base frequency, it’s third harmonic, and then it’s fifth harmonic. Such material resembles a square wave. If you do not believe me – simply throw such a superposition on the screen of your oscillograph.

The thing is, that superpositions of a base frequency with it’s natural higher order harmonic frequencies actually may result in close to vertical edges within the signal that you are listening to.
Lets assume that your base frequency is F1 = 8 kHz.
Three times eight gives you the value of your third harmonic: F3 = 21 kHz.
Five times eight gives you the value of your fifth harmonic: F5 = 40 kHz.

OK, OK, … Instead of sending you off to your oscillograph, I shall make life easy for you. Look at the following picture, depicting three graphs, sourced from a very interesting article about the Fourier Transform of the Square Wave … a subject, which is very much related to what I am talking about here. So in your spare time, please browse through this following link:

http://electronics.stackexchange.com/questions/13591/what-is-the-function-of-a-fourier-series

fourier

What you see in the picture above is three signals, consisting of “overlapped” frequencies.

The “widest” frequency on top, a single “sine wave” – is the base frequency F1 (the one with the single top hump).  But on this upper graph, you also see a smaller, “third harmonic” frequency, F3, which is superimposed upon the base frequency. How do I know that it is the “third” harmonic ? Easy. Simply count the number of top humps on it.

What you see in color red is the result of this superposition. The red line, which is the sum of the two frequencies F1 and F3, starts to resemble a … square wave. It is hugely imperfect on that upper picture, but the “first impression” of a square wave is already there.

Now check out the middle graph. On that Humpty-Dumpty mediocre square wave from the top graph, we superimpose yet another frequency, additional harmonic, mainly the 5-th harmonic, F5. Now, do you see what happened? The red line starts to resemble more closely the “ideal” square wave. It is still a long shot, but the resemblance is much better.

Please note how the leading and trailing edge of this “square wave” becomes more and more steep, as we gradually add the higher harmonic frequencies.

On the bottom graph, we add yet another harmonic, the 7th harmonic, F7.  Now you see that the sum of all these signals, as represented by the red line, is “almost” an “ideal” square wave.

But there is a vast difference between “ALMOST” and “IDEAL”.

Between the “almost” and “ideal” is the difference, and the difference consists of all rest of the harmonics, of all the MISSING harmonic frequencies.

So, now you might ask:  Well, how many are still missing, actually ?

The answer is: INFINITY.

If you were to strive to achieve an IDEAL square wave, you would actually have to provide for an infinite bandwidth, with no end.  You would have to add an infinite number of higher harmonic frequencies.

So, now you get the picture ?  If your loudspeaker system is not capable of conveying the ultra high frequency content of at least up to 40 kHz, or better yet, even MORE,  the “coloration” of your base F1 frequency, and the “way” it “sounds”, will be just a “bit different”.  It will be lacking the “steepness” of those square wave edges, that it NEEDS to faithfully represent from time to time.  And it is this tiny “bit of a difference” that is simply speaking just not good enough. Without the 40 kHz (at least!), your musical “square wave” response shall rather resemble the top graph, and not the bottom one. It will be … slow and sluggish, without the air, without the details.

As with any audio project, the moment that you think that you have just “finished” it … that is more often than not the moment, when you come up with “yet another wild idea”.  A Modification. like a ribbon ultra-high-frequency-tweeter.

Something for the Bats.  The ribbon tweeters …

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I purchased, after thinking about this subject for some time, some extra transducers, especially for my pet bats.

Just as before, I purchased them at www.audiotransducers.com, and they arrived promptly, before the Englishman in New York was able to pronounce: “Chrząszcz brzmi w trzcinie”.

You may ask: why “ribbon”? Well, the thing is, the mass of the ribbon is very very small. This actually translates into very low THD distortion, especially in the higher frequency ranges. At the same time, they have a very high efficiency, in the order of 95 to 100 dB, some models even more. If we make a crossover for the such very high frequencies that I am considering to obtain here, the signal at the end of the cross-over may actually turn out to be very weak.  So this pairs well with the high efficiency of the ribbon as such.  Actually, there might even be a need to attenuate them slightly, but having said that, we know how to build the (probably) best, non inductive resistor in the world, so that is absolutely a non issue here.

Below are some new photos of these new ultra ribbon tweeters. They are already in action. My listening test is ongoing.  All the bats are sitting in the living room and enjoying Sting with his Englishman in New York thing …

And I herewith confirm: YES, there is an audible difference in the way the sound … sounds. The whole upper deck has received a whole bucket load of more “air” …  Ok, this is just a preliminary first, crude, out-of-the-box “lets listen to how it sounds” setup, very much temporary, with small little support matchboxes acting as ultratweeter stands, and crocodile jumpers as hookup cable. Not to mention the very crude crossover to accompany them.

But the effect, the ** AIR ** ,  is ** THERE **.

OK, so this is just a crude setup, a yet another work-in-progress. A long way to go, from this crude temporary setup, to the final boxed version, with a good piece of wooden box, varnish, crossover, phase relationships, measurements and stuff, but the initial impressions are positive.

Oh, and B.T.W.   If you have the option to select between various different versions of these ribbon tweeters, my advice is: rather go for the “shorter but wider” ribbon option.   I chose this particular model, the Fountek Neo CD 2.0, because it was readily available in the black color, which, considering the color scheme of my existing setup, was an important feature to me.

If I have had the choice of black within the X series, without extensive waiting time, I would probably go for the Fountek Neo X 3.0, the Fountek Neo X 2.0, or even the Fountek Neo X 1.0.

Why ?  The reason is as follows: if you look into the specs of those ribbons, you shall notice that they are actually of a slightly different construction. They are “wider” (eg.: 12mm instead of 8mm) an at the same time, they are “shorter” (eg.: 80, 60 or 40 mm, instead of 120 mm).

This results in a much less directional behaviour of the sound energy emission pattern, when you consider the VERTICAL axis of sound propagation.   In simple words:  They will sound similarly, independent of if you are sitting or standing.   With the ultra long ribbon, such as the 120 mm one … there is a perceptible difference in the intensity of the sound, as a function of wherever you are standing or sitting.  But having said all that, let’s not be too picky. The difference is there. The sound is better. The angle of vertical tilt / directional positioning of the additional ultra high frequency ribbon tweeter box can be optimized.  No problem.

Cheers,

zjj_wwa.

 

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