First, let me be sure we are talking about the same thing. In my designs a U-frame is basically an open ended tube with a driver mounted at one end. If you want it to operate as a quasi-cardioid the tube must ne damped (or stuffed) correctly to reduce the quarter wave resonance and to achieve the correct delay. Quasi-cardioid frequency range will typically be from Dc to a frequency 1/2 octave, or a little more, below the quarter wave resonance. If undamped the U-frame will operate as a dipole at low frequency (well below the 1/4 wave resonance).
Details can be found here NaO U-frame
Details can be found here NaO U-frame
Cardioid vs. dipole question
John, what's your position on a dipole vs. quasi-cardioid now? I seem to recall you saying something to the effect that you're not so enamored of cardioid. I ask because I've had two 10" XLS drivers on the shelf for several years and am thinking of building a pair of subs with them. I've always liked the idea of cardioid woofers.
Dave
John, what's your position on a dipole vs. quasi-cardioid now? I seem to recall you saying something to the effect that you're not so enamored of cardioid. I ask because I've had two 10" XLS drivers on the shelf for several years and am thinking of building a pair of subs with them. I've always liked the idea of cardioid woofers.
Dave
I have built cardioid subs based on a combination of a monopole and dipole sub. I couldnt find an advantage of cardioid compared to monopole in the <100hz region.
I have also built cardioid tops using a damped u frame, which works quite well.
I have also built cardioid tops using a damped u frame, which works quite well.
Hi Dave,
I don't check in very often these days. I still like the quais-cardioid, damped u-frame woofer but there are +/- compared to a dipole woofer. Given the same overall effective separation, correctly damped the U will be about 6dB more efficient than the dipole. But getting the damping right is an issue, particularly without measurements. Both radiate the same acoustic power, about 4.7dB less than a monopole at the same SPL. The Room modes aren't that much of an issue to me. I looked at both and the best I can conclude is that they are different and each behave differently as you change placement and orientation. Lastly, the dipoles lack the ability to pressurize a room. Whether you view that as a + or a - depends on what you are after I guess. Over all I would say that for woofers the dipole is just a lot simpler to build and for that you give up efficiency. But remember, I'm olt talking about below 100 Hz here.
I don't check in very often these days. I still like the quais-cardioid, damped u-frame woofer but there are +/- compared to a dipole woofer. Given the same overall effective separation, correctly damped the U will be about 6dB more efficient than the dipole. But getting the damping right is an issue, particularly without measurements. Both radiate the same acoustic power, about 4.7dB less than a monopole at the same SPL. The Room modes aren't that much of an issue to me. I looked at both and the best I can conclude is that they are different and each behave differently as you change placement and orientation. Lastly, the dipoles lack the ability to pressurize a room. Whether you view that as a + or a - depends on what you are after I guess. Over all I would say that for woofers the dipole is just a lot simpler to build and for that you give up efficiency. But remember, I'm olt talking about below 100 Hz here.
I'm clearly biased towards super-cardioid bass due to good experiences in several houses and flat apartments. It is possible to get better response with dipole but it's not very likely and easy. Super...hyper-cardioid is quite insensitive to source location though cannot eliminate lowest axial room mode if room has massive & reflective rear wall. Weakest features of cardioid in practice are low efficiency (leaking box) and required volume (dipole+boxed combination). In many cases front wall and corner reflections boost mid-bass with dipoles, but this gain is not available with cardioid. Fortunately weak front reflections improve integration of bass and mid-range.
I wouldn't consider damped U-frame (with solid side walls) because cardioid band is too narrow. Whole bass range should be super...hyper-cardioid in order to make valid selection of source type. Without adequate damping it's just a bad dipole.
I wouldn't consider damped U-frame (with solid side walls) because cardioid band is too narrow. Whole bass range should be super...hyper-cardioid in order to make valid selection of source type. Without adequate damping it's just a bad dipole.
I've been planning to build a U-frame. From what I've heard, it's difficult to get it right, but it seems nobody's ever documented and shared the optimization on the basis of clean far-field measurements with sufficient frequency resolution. I'm very curious how well an optimized U-frame performs, especially in comparison with a box with side-vents.
I would make U-frame with leaking (=resistive) side walls to reduce problems due to solid transmission line. Leakage should help tuning because damping alone doesn't have to do everything. Partial side port may also extend usable frequency range until upper bass. "Cardioid bass" is worthless without cardioid upper bass, imo.
Cardioid pattern close to near field is valuable in practice. Otherwise front wall and corners may boost rear port signal.
Cardioid pattern close to near field is valuable in practice. Otherwise front wall and corners may boost rear port signal.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.