Hi guys ...specifically for open baffle subwoofer driver, which is more important ???
High QTS ?? Or Low CMS? Or both?
Or a combination of high QTS and low CMS?
Or a combination of low QTS and high CMS?
Or...what is a reasonable combination of QTS and CMS for open baffle subwoofer drivers? (For 15" or 18" drivers)
I know this has been discussed few times, but it always feels like some degree of clarity is missing. So asking again, please bear with me guys...
And secondly BL also comes into picture which may effect the CMS ....
High QTS ?? Or Low CMS? Or both?
Or a combination of high QTS and low CMS?
Or a combination of low QTS and high CMS?
Or...what is a reasonable combination of QTS and CMS for open baffle subwoofer drivers? (For 15" or 18" drivers)
I know this has been discussed few times, but it always feels like some degree of clarity is missing. So asking again, please bear with me guys...
And secondly BL also comes into picture which may effect the CMS ....
You should aim for low enough (for your needs) Fs, suitably high Qts and sufficiently large cone diameter. Good examples are Acoustic Elegance Dipole units.
well....Fs will be around 30hz.
Popular opinion is that Qts around 0.7 and higher is preferred for open baffle.
But there is another argument saying CMS is more important that QTS for open baffles.
There im trying to get some clarity.
Popular opinion is that Qts around 0.7 and higher is preferred for open baffle.
But there is another argument saying CMS is more important that QTS for open baffles.
There im trying to get some clarity.
Cms is already defined by Fs. Fs depends on 2 variables, stiffness and mass. Cms is reciprocal of stiffness.
The thing with high Q resonance came from a dipole design here in the past, as far as I know. A side effect of the open baffle is that you lose bass as you go down in frequency. One thing you need to do is to equalise it. It was discovered in that one particular design that a rising response from a high resonance Q worked to advantage. So to answer your question a high Q isn't needed but it may help.
Its more about the Q of the driver when in use in the application and not the driver's TS parameters Qts value.
For example, if you will be using the driver in a closed box the Q value will be elevated above the Qts value depending on the ratio of Vbox/Vas (I forget the exact relationship). I am sure you are already well familiar with the relationship between Q and the time domain response, and frequency response around resonance. So assuming one wants the in-box Q to be in the range 0.5-0.8, you need Qts to be lower, e.g. 0.25-0.5.
In an open baffle, what you have is very similar to an infinitely large box in terms of the Q of the driver in the application (an open baffle). So using a driver with a Qts that is already around 0.7 is helpful. Lower Qts values only cause a slow and premature bass rolloff. Because the dipole cancellation is causing a 6dB/oct decrease in SPL in the bass region, this can be partially compensated by using a Qts that is even higher, e.g. up to 1.4 or so. Combined with the "first order HP like" response from the dipole cancellation you get something like a third order response, and for example a third order Butterworth filter is a first order HP filter combined with a second order HP filter with Q=1.0.
High Qts driver have gotten a bad rap, and used in the wrong way they are less than ideal. In an open baffle, they do have a place. One tangential side effect is that these drivers often tend to be cheaply made all around because a small magnet/motor is used to obtain the high Qts value. So shop carefully.
Also, Cms is not an important parameter for an open baffle. This is giving you exactly the same imformation as the Vas parameter:
Thiele/Small parameters - Wikipedia
Who cares what Vas is when the "box" in an OB system is infinitely large?