Of Ripoles and Dipoles

[oneoldude]

I am considering building a folded dipole woofer for my Dipole panel. And I mean woofer not subwoofer. I am thinking of a bandwidth of perhaps 150 Hz to 40 or 50 Hz where the folded dipole runs out of steam. If I want more bass I will cut in my SB Subs from there. Unfortunately, I have not been able to find much discussion re: Folded Dipoles/Ripoles.

It seems that a Ripole is nothing more than a slightly squeezed folded dipole similar to the one SL introduced with his Pheonix system many years ago http://www.linkwitzlab.com/woofer.htm. Please correct me if I am wrong.

The Ripoles can be made a bit smaller than the standard folded dipole, but what is the consequence? Indeed, what is the difference is reproduced sound between a Ripole, Folded Dipole and an H or N Frame Dipole?

I don't know the answers, so I hope there will be contributions from people with experience with these different systems.

So what are the practical differences in these designs? Are there significant advantages/disadvantages between them? And most importantly, how do they sound? Is there a difference between them in they way they reproduce music? Which is better or worse and why?

Thanks

[gainphile]

At 150hz down, both H, N, W Frame dipole, and also 'Ripole' are acoustically small. So the polar response in free-space will be dipoles.

There might be differences in quarterwave resonance frequency as consequence of cavity depth and width.

Even in extreme example like narrowly folded sub, the resonance is 300+hz which is very useful

[oneoldude]

Yes, that is one of the things that interests me. With such a narrow slot, you might be able to use it at higher frequencies than a dipole facing you. Of course you must watch for the resonance peak and deal with that too.

But how do they sound?

I have heard they have stored energy issues due to the air in the box acting like a capacitor. Often that sort of talk is merely theorizing rather than listening. If they sound good they are really ideal as dipoles. At least down to where they run out of Xmax.

I am building some in the not too distant future (I hope). If and when I do, I will report here. But it would be nice to get a conversation going from people who have already done it and can fairly describe what they hear.

[gainphile]

Yes, that is one of the things that interests me. With such a narrow slot, you might be able to use it at higher frequencies than a dipole facing you. Of course you must watch for the resonance peak and deal with that too.

But how do they sound?

I have heard they have stored energy issues due to the air in the box acting like a capacitor. Often that sort of talk is merely theorizing rather than listening. If they sound good they are really ideal as dipoles. At least down to where they run out of Xmax.

I am building some in the not too distant future (I hope). If and when I do, I will report here. But it would be nice to get a conversation going from people who have already done it and can fairly describe what they hear.

Having built Slot, N, H, and W- frame I think they all sounds the same when equalised to the same target frequency. But W-frame is most impressive as you can see the subs pumping very hard, yet there's no vibration on the whole structure! It's also the hardest to build.

The air loading on the slot might actually beneficial as it lowe Fs but I see no strong evidence to suggest it's a major benefit. For sure my W-frame is very clean when crossed at 120hz, and I'm now running them 100hz LR4.


What *is* different is the simple baffle. They sounded the best but can't really reach 20-30hz with good SPL. It think it's down to the perfect dipolar alignment with the other drivers (with the other, you have some sort of offset). Also on high SPL you can see the top baffle vibrate violently.

[oneoldude]

BTW, in my prior post I neglected to say that I like your blog very much. I even have it bookmarked to revisit it from time to time. Good work! Kudos!

By simple baffle I guess you mean a simple flat baffle with the woofer directly facing you. And in that instance, the top of the flat baffle may vibrate wildly.

You say the simple baffle sounds best. How is it different. What is it about the sound you like better? What is it about the folded variety that sounds less tasty?

Thanks

[gainphile]

Thanks not much happening there lately though. I miss the days when I had spare time and high AUD$ rate

The simple baffle just sound cleaner and 'more coherent' to me. Yes they are just simple plank of wood and look like this: