What is the difference between Flexunits and the C-Quenze drivers?

The main difference is that C-Quenze uses a solid cast frame, opposed to the bolted together frame in Flexunits. All other materials used are of the same high quality. The cones used in the C-Quenze drivers, have been refined to a broader response with less pronounced breakups.

Why does Audiotechnology use Polypropylene cones?

There are always advantages and disadvantages when choosing a material for a product. 

In the world of transferring electrical signal into acoustic signal one must choose carefully. All materials have their own sound. Some at high frequencies and some at lower, some with a high Q breakup and other with lower.

Polypropylene is the material we find with the most neutral sound, among the materials known in the business. Paper cones, liked by many serious audiophiles, have a “crispy” sound with a lot of “edge”. But this “crispy” sound is really the sound of paper adding to the sound. All materials add to the sound. One of the worst is a magnesium cone. The break-up is very pronounced and the Q of the break-up is among the highest. The faults can naturally be annulled using notch filters, but these have to be with an equal high Q and therefore far from ideal. P/P adds little to the sound and with a low Q and therefore sound natural.

Some companies add a coating to paper cones, which helps damping of the high-Q break-ups and approaches the qualities of the P/P cone. Why not use a P/P cone then? Building and establishing the cone geometry and making a moving system with a good balance takes time. In house we have all the machinery for producing the tools for P/P cones. A nice tool for production costs around 7000 to 10000 US$. A paper cone tool costs almost 10 times the amount. If you do not hit the right geometry within the first couple of times, it will very fast become a costly affair. The P/P tools can be adjusted into hitting the right geometry and you therefore have much more attempts with a relative low cost. It is quite seldom one comes across a driver with paper cone and a nice useable frequency response. We believe P/P cones, all things taken into consideration, are the best.

What is the difference between Kapton and aluminum voice coils?

Kapton is a non-conductive material and is therefore not influenced by the eddy-current effect like aluminum, when situated in a magnetic gap.

In practice this means no mechanical brake and therefore a very high mechanical Q-factor and low Mechanical resistance.

Drivers with Kapton voice coil former often perform a more detailed midrange with higher dynamic and less coloration and distortion.

Due to the lack of mechanical brake, we do not recommend the use of Kapton drivers as bass driver, because if the x-max is exceeded there is nothing to prevent the driver from bottoming out. For sub woofer applications, please use drivers with aluminum voice coil formers.

For use in the drivers with 77 mm and 102 mm voice coils, we have made a hybrid between the two - the Kapton Alu system (KA system). It utilizes the advantages from both systems. When the driver is within it´s x-max, the voice coil works as a Kapton voice coil but if the driver exceeds x-max, it works like an aluminum voice coil, braking the cone.

Drivers with Kapton voice coil former, can have a tendency to a more pronounced break-up before roll off, because of the lack of mechanical brake.

What are the conditions of the measurements on your web site, with respect to baffle size?

The measurements are made in anechoic chamber in a infinity baffle at Half space distance.

Does Vas and fs change with usage or is this just a fairytale?

You once manufactured a pair of custom-defined drivers for me (that perform excellently by the way !!!!!! ).
When I fist installed them I broke them in, using a sweep generator at very low frequencies. I had the feeling that they slightly improved that way but I may also be waaaaaaay off.

You are not way off!! The suspensions change a lot over time.

When we measure a driver, it has been run in - not necessarily the drivers supplied to the customer, but at least the test driver made prior to the supplied drivers.

When we run in the drivers, it is done with a relatively high wobble sinus tone around the expected resonance frequency (fs) and for approximately 24 hours. We know that there are companies that only run in their drivers for 1 hour, before measuring Thiele/Small data (T/S data).

Our experience says, that the drivers change for weeks - even months, when playing, but the change after running for 24 hours, does not have any technical influence on the performance. An example:

After 24 hours of running a driver has reached an fs that is lower, a Vas that is higher and a Qts that is also lower than the original "cold" driver.

A simulation is made on the "run in" data and a nice frequency response curve is found. After ½ a year, the driver is taken out of the box that vas build according to the simulation program, and the T/S data are measured once again. We then find that fs and Qts has dropped further and the Vas is yet higher.      

But - the simulated frequency response curve, in the same box, does not change.

We hereby conclude that: When a driver has been run in for 24 hours, the changes of the T/S data, do not have influence on the performance of the bass output of the driver in cabinet.

You could also say: After 24 hours of running in a driver, there is a certain balance in the T/S parameters that stabilizes the bass performance of the driver in cabinet.

Another thing is that the sound and performance of the drivers change for a long period of time. This is caused by softening of the moving parts and from small fractures in the glue joints, etc....

A speaker is like a good wine: It gets better with time.

What is your general rule for crossing over the midrange to a woofer?

What is your general rule for crossing over the midrange to a front or side firing woofer say 150Hz? Same thing 1 series coil on the woofer, and 1 series cap on the mid?

You are right about the one cap on the mid, but it seldom makes an ideal roll off. The roll off will often be disturbed, where the midrange has its resonance. It creates a phase shift that makes the amplitude rise at the resonance point. To avoid the amplitude rise, it is necessary to make an impedance compensation to take away the resonance peak. It is done with a coil, a cap and a resistor in series, placed parallel on the midrange. You can avoid the resistor by using a coil with a high internal resistance, which should be equivalent with the driver impedance. Once the impedance of the midrange is linear, the roll off will be like we would expect, a quasi 3rd order roll off.

The challenge now, is to make a mirror of the roll off of the midrange, on the woofer. The obvious solution is a 3rd order x-over which works in most cases, but sometimes a 1st order x-over will also do the job. You will sometimes experience a small phase failure between the two drivers. It can be caused by non linear time alignment which can be corrected by slightly changing the slope on the woofer roll off or by changing the offset between the drivers. you can also change the slope of the midrange by changing the damping of the midrange chamber. To check, if the slopes of the midrange and the woofer are mirrors, of one another and if the phase shift between them is minimal, you can alter the phase on one of the drivers (change about + and minus) The amplitude you should experience is a maximum suck out that should be symmetric and ending in a sharp conical point. The cross over point, the conical point and the -6 dB points, should all be at the same frequency............ the x-over point.

Would you please tell me the difference on Characteristics for the 18 H 52 17 06 SD and without SD

The question you ask is very comprehensive and can not be answered in few words. There are many advantages connected with the SD system. Among them we can mention the following:

  • A greater usable frequency range.
  • Greater thermal power handling.
  • Lower intermodulation distortion.
  • Linear rise time no matter where the voice coil is situated in the gap.
  • A more consistent impedance curve.
  • Much lower inductance of the voice coil.
  • Rise time is increased up to a factor 10
  • SD makes it possible to have both full bodied bass performance and fast clear midrange.

The frequency response curve of a 18 H 52 17 06 without SD looks like a driver with SD with a 0,82 mH inductor in series.

Do you have a brief explanation why the dome design is better than a stationary phase plug?

We do not use phase plugs, as the centre dome is an active part of the cone. As you know our voice coils are quite big and we would loose a considerable part of the cone area if we used a phase plug.

I wonder if you could clarify the power rating of your drivers?

Power rating is a interesting conception. Most data are given after the "old DIN norm" and does not make any sense today. Power handling was measured on sine wave tone bursts in certain frequencies and certain time domains.

With today´s recordings, the figures that come out have outgrown the DIN norm as music power is often lower than the continuous power handling because of the massive bass on some recordings. You are absolutely right, that it is not continuous Sine wave power ratings that we give, but if you read the power handling capabilities as "Maximum recommended amplifier size", it will come quite close regarding music power and the Nominal Power Handling.

What are the differences between P/P and Sandwich Cones?

Apart from appearance, the main difference is the stiffness of the Sandwich cones.

They weigh pretty much the same. The Sandwich cone drivers have a bell-mode, which is an energy build-up in the higher frequencies, where a woofer is seldom used. (2 KHz) The peak is no way near the bell mode Q of a metal cone due to the internal damping of the sandwich construction. The P/P cone drivers have more linear frequency response.

Biggest difference is probably in the sound. We have chosen to present the thoughts of a customer who has used drivers from Audiotechnology in the passed 10 years. He changed the twin P/P woofers of his latest project with sandwich cone drivers, without making changes in the x-over and the following was his impressions:

“After listening to the “new” speakers I was chocked, because I have never made any upgrade that delivered so much sound improvement.

The two first things I noticed was:

  • The bass was much more powerful, without dominating the total sound image.
  • The sound was much clearer.

Then after some more listing I observed:

  • My speakers can now play bass at low sound levels with the right authority.
  • The bass is more precise, detailed and goes deeper.
  • The midrange is also more detailed.
  • The sound stage is improved a lot.

After the upgrade I wanted to listen to some of my old CD’s and found that the upgrade reveals details in my CD collection I didn’t know existed.
This upgrade is simply stunning.”

Jacob, Brande.

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