look hereOK, I don't remember that one. Will have a look.
qts 1.26>0.58>0.30http://www.quarter-wave.com/OBs/OB_Design_Part_1.pdf
According to Beyma SM-118/N - 18" Woofer these drivers have an F2 of 42Hz which is a little higher than optimal but not a disaster (especially if a sub will be added). The linear Xmax of 7.25mm is also lower than ideal. You might want to consider 2 per channel, depending on your expectations.
If is a good price you can take them. If active and eq there will be no problem to go low. You will like the sound. I used in one setup two per side in plane narrow (50cm) baffle. Some 12" after then in a 4 way setup.
I believe SPL target should factor into the equation. Even with dual 15s a side it is not quite enough for me and I don't listen loud at all.
Whether it is low QTS and EQ or higher QTS and no eq the SPL limitation is present when OB is asked to push even a little bit. With low QTS you give away xmax quick and with high QTS it is rare to find a large XMAX driver so with both you are in the same boat in my opinion.
Maybe the best option if OB is you thing is to double up the number of drivers you think you need right away. The distributed load difference between 2 x 15s and 4 x 15s a side is significant. I use 6 x 15s a side with FS of the drivers at 42hz and I do get a slight roll off below 40hz after EQ but usable down to 25hz and I don't hear the stress that I heard with 2 x 15 a side.
For OB I like the presentation of less physical impact. It does not pressurize the room like sealed or ported.
Whether it is low QTS and EQ or higher QTS and no eq the SPL limitation is present when OB is asked to push even a little bit. With low QTS you give away xmax quick and with high QTS it is rare to find a large XMAX driver so with both you are in the same boat in my opinion.
Maybe the best option if OB is you thing is to double up the number of drivers you think you need right away. The distributed load difference between 2 x 15s and 4 x 15s a side is significant. I use 6 x 15s a side with FS of the drivers at 42hz and I do get a slight roll off below 40hz after EQ but usable down to 25hz and I don't hear the stress that I heard with 2 x 15 a side.
For OB I like the presentation of less physical impact. It does not pressurize the room like sealed or ported.
Why do you say that? X is constant for a given SPL and frequency. You can say that a low Qts driver will need more drive, and that may mean slightly higher distortion (BL modulation, thermal effects possibly), but you'll get lower group delay - which will make for better bass. Non-linearity won't be welcome if the driver has to handle mid-range too (IMD), I suppose.
Don't see the obsession with high Qts, unless there's an amplifier power limitation.
I guess the devil is in the details yes, so you are correct. For a given SPL with a driver on a baffle, for your consideration what happens with a driver 1.2 Qts vs a driver with a QTS of 0.3 QTS at say 30hz? More drive so all else being equal you are using up amplifier power. Since an amplifier has fixed output and is not unlimited, from a system perspective your using up potential. That said it does not take that much from an amplifier to push a driver to xmax in OB application so one could argue you don't need that much power from an amp so that is not a consideration.
From limited my experience I don't find there is much difference in usable output between a low QTS driver with higher xmax than driver with high QTS and lower xmax.
However this is off topic from my intended point which is:
I believe from a subjective perspective in my room, more drivers = better for OB presentation from a low frequency perspective. I've tried a number of drivers and each time when the # of drivers was increased, I've liked it better. I have no objective data for proof but whether it is lower distortion or radiation pattern or room loading the exact details don't matter when making a subjective assessment. Of course your room might be different than mine so take this for what it is. A subjective assessment
.Agreed about high QTS. Unless going passive I'd take the lower QTS driver. To me, they sounded better.
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is more relate to quality of the woofer not the hight qts....
look https://www.diyaudio.com/forums/sub...truct-stereo-pair-subwoofers.html#post5452253
Could be but there have been a number of reports of individuals swapping out there ae dipole drivers for lower qts drivers and have been more happy with the lower qts. I'd say the ae drivers are a quality driver but the dipole series does have higher qts. Also in the another ob thread I believe an individual went from the alpha 15a to the beta and was more happy with the beta which has almost half the qts rating. I don't have time to link the threads but they are on this forum someplace.
nothing wrong with that post ...we start play ob 15year ago thanks to mjk
In EU with 12x15" we play disco party