Smartq Driver

[Recaredo Latreche]

Mostsubwoofers on the market are horrendously inefficient. Many need extreme power amplifiers to overcome this problem. Many are impressed at first with subwoofers which use kilowatts of power, thinking they must have extreme output. In reality, our sensibly powered and intelligently designed subwoofers will achieve the same output (if not more) with greater accuracy and less cost.

Please note: When this article was written we were selling Linkwitz Transform (LT) subwoofer kits. These are now discontinued. We recommend our Custom Install subwoofers as they are a superior range.

The first maximum excursion plot is for a case with corner frequency of 20 Hz and Q value of 0.7. We can see the excursion utilization at 20 Hz is only 75%. At 30 Hz, it is only 40% whereas at 40 Hz, it drops to only 25%. The important implication here is that at 30 Hz, the amp will begin to clip when the excursion reaches only 5mm. That means the listener will begin to hear the clipping distortion from the amplifier when the driver is still within a fairly linear excursion range. At 40 Hz, the amp will begin to clip when the excursion reaches 3 mm. A lot of subwoofer builders have ignored this important issue. The secret of getting more output does not end with a driver with high excursion capability. As shown here, the excursion plots determine how well the excursion capability is realistically realized.

Fig 1.0 -Excursion plot - Q = 0.7

The above chart shows the excursion plot for a typical sealed subwoofer. It shows how the excursion capability of the driver is not well used.

The next big question is how much excursion we should set as our design goal when we select the proper amplifier and enclosure size? As we have explained earlier, in order to prevent the driver from bottoming out during amplifier clipping, we need to leave an adequate excursion margin as headroom. I recommend at least 40% of the mechanical maximum excursion limit as excursion headroom. For sealed subs, one can adjust enclosure size to limit the maximum excursion. However, one should not overdo it such that the Q value becomes larger than 1.3. Without violating this rule, a smaller enclosure will have higher excursion headroom. For Infinite Baffle and Dipole users, the only way to control the excursion headroom is amplifier power selection (to match the BL and Vas of the driver).

Below is the excursion plot of a sub where the enclosure is too small, so that the Q value becomes too high. The result is an excursion hot-spot, along with reduced low frequency output. This indicates that the enclosure is too small.

The smallest enclosure size one should use depends on the driver parameters. It is best to simulate the driver in the intended box using a box design software package that provides excursion plots. Avoid enclosure sizes that produce a plot as shown above. An enclosure that produces a plot like the one above will result in frequent bottoming of the woofer, without satisfactory low bass performance.

We all once in a while turn up the volume just a bit too high. Adequate excursion headroom can prevent the driver from bottoming out, even when the amplifier goes into clipping. To increase excursion headroom, we can reduce the enclosure size. In the case of an existing enclosure, we can place blocks of wood inside the enclosure.

Servo subs become even more appealing if we add the flexible control of bass extension for the bass roll-off corner frequency and its Q value. For our A370 amps ordered with the LT add-on circuit board and our DS350 kit (now replaced with our CI range), the bass extension controls have 3 frequency settings (14 Hz, 20 Hz, 28 Hz) and 3 damping control setting (low, medium, and high which correspond to Q=0.9, Q=0.7, and Q=0.5, respectively). This allows for a sub with a low Q frequency response curve out of a small box. Those who like to tweak their systems for best results can experiment with these frequency and damping controls. Those who are building their first subwoofer would also have the chance to compare a variety of combinations of damping and corner frequency, given them a level of hands-on experience that usually only comes with several completed sub designs. And last but not least, the bass extension controls provide the opportunity to trade bass extension for maximum SPL, allowing one to play louder using the 28 Hz setting.

In the following discussion, we will see how adjusting enclosure size, moving mass, and amp size change the frequency response and excursion plot of a sealed box subwoofer. And finally, we will give an example of how to achieve better excursion utilization.

Increasing box size (that results in less stiffness) by itself will move the stiffness controlled region up while reducing box size does the opposite. This is why conventional wisdom says a larger box gives better bass extension. The extreme case is the so-called "Infinite Baffle" (or IB) sub configurations which don't use a box at all.

The interpretation of Q value is as follows. After we find the intersection of the blue and green dashed lines, we will assume the coordinate of the intersection point is (x,y). The coordinate x gives the corner frequency. The coordinate y gives a db value. The Q value determines the multiplicative factor of subwoofer output relative to the y value at frequency x. A Q value smaller (larger) than 1 means output at frequency x will be less (higher) than y. In our example the Q value is 0.7, therefore the subwoofer output is 3db down from y. Generally speaking, a larger box and/or lighter cone results in lower Q value. However, it is generally recognized that the Q value is important to make the bass sound more musical. As a result, there are a lot of ideas floating around on why Q value is important and how to change or control it, which will not be elaborated here.

The most important aspect of an LT-based sub (or servo sub) is what enclosure size should be used because as we have emphasized in these subs, we would like to more precisely control the maximum excursion and leave enough excursion margin in case of amp clipping. As shown in below, the nice characteristic about using smaller enclosure and a larger amplifier is that it actually gets higher excursion utilization.

In the above plot, the red line is the original plot, a 75L sealed sub driven by a 250WRMS amp. The orange plot is the same driver in a 54L sealed box driven by a 350WRMS amp. As one can see, the difference below 10 Hz is very minor and we can call it a wash. However, above 20 Hz, the brown curve has higher excursion, meaning higher SPL output. This improvement in terms of output is the key motivation to use an LT or servo-based subwoofer provided that the issue of higher corner frequency in smaller enclosures can be resolved (as it is by LT and servo designs).

Yes, we understand. It is indeed frustrating when the USB 3.0 hub is not recognized by your computer. Everything is hooked up, but there is error message popping up, "USB Device Not Recognized". Or even worse, there is nothing. The USB hub is simply not detected at all.

But please don't panic. All of atolla USB hubs have gone through multi-layers of inspection before shipping and we have the belief that your hub won't break that easy. Browse on, it is likely that any of the below troubleshooting steps will wake the hub up to work correctly.

As the USB 3.0 port is the most common port in today's computer, all motherboard manufacturers will provide an integrated USB 3.0 driver with it. If your laptop is running a Windows Version later than Windows 8, Windows also will provide auto installation for USB 3.0 driver via Windows Update.

Does your SD card reader fail to work when you insert an SD card to it? Why does this happen? How to fix this issue? In this post, MiniTool shows you 5 solutions to SD card reader not working.

Windows 10 is quite an excellent Windows operating system and many Windows users have chosen to upgrade their system to Windows 10. However, lots of users reported their SD card reader not working on Windows 10.

For most computer issues, you can try restarting your computer to see if the issue has been fixed successfully. So, when running into SD card reader not working on Windows 10, you can try restarting your computer first.

Before restarting your computer, disconnect the external card reader if you are using it to read your SD card and then reconnect it after restarting. See if your SD card reader can work well. If not, you can try the following solutions.

After learning about the possible factors that lead to SD card reader stopped working on laptop, you can try the following solutions one by one when the built-in SD card reader or the external SD card reader is not working.

Apart from the incompatibility between the older reader and the current operating system, the incompatibility between memory card format and the older reader can also lead to SD card reader not working.

Some older memory card reader is unable to recognize the SDHC and SDXC memory card format. Is your SD card reader too old? If yes, you may need to buy a new one and make sure it is compatible with the SDHC or SDXC format or your current operating system (Windows 10).

Excluding the above factors, you should check whether the USB cable leads to SD card reader not working if you are using the external SD card reader. To do that, you just need to try to replace the current USB cable with a different one.

Then, check if the SD card gets corrupted. If you unplugged SD card while the card was being read, leading to a loss of electrical power to the card, the card may be corrupted. To repair the corrupted, you can read the post Fix Corrupted SD Card with Professional SD Card Repair Tools.

Here I would like to show you how to change drive letter to SD card with MiniTool Partition Wizard. Apart from this function, this program can also help you restore partition on SD card, format 256GB micro SD card to FAT32, and erase an SD card with ease.

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