Do you dampen a Uframe?

[mrkennyk]

Do you need to add dampening to a Uframe?

Kenny

[AllenB]

I've just built a u frame but I don't know if it's the same kind of u frame as you.

[norman bates]

Hmm.

You mean the walls from vibration or filling it with fluff ?

[mrkennyk]

Filling the box. Tried using bonded poly to foam a tube(not blocking the back of the speaker), but was not sure if that is a correct application. There are little actual detailed build threads around and the published info is gray in regards to stuffing.

Kenny

[john k...]

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

[mrkennyk]

John K, thank you. I will reevaluate what I did.

Kenny

[dlr]

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

[Jag768]

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.

[dlr]

Thanks for the links. I'm going over the thread and some of the info at Merlijn Van Veen's site linked by weltersys. I have downloaded his spreadsheets to check out. Very interesting, it provides some additional perspectives.

Dave

[john k...]

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.