Another Sensitive OB Woofer Design

[gainphile]

Very intriguing. I'm always interested in "small but more SPL" dipoles (and cheap).

How does your 4x woofer work, and what is the function of the opening on the side? Any pics right from the side to show how the woofers are aligned?

Is this a smaller version of CS1's 4xalpha setup?

Very interesting.

[cuibono]

Thanks CLS and MJK for the comments!

MJK - At 30Hz, I could hear beating of the sine wave with the Alpha - and I think it shows in the NLD. I'm can't recall hearing it with the GWx4, but there was clearly large cone movement. Voltage was 5.66Vrms. Unfortunately, I can't measure displacement (although I could try it with a wedge micrometer), and I'm not sure I am driving them to Xmax - but considering the high NLD below 40Hz for both woofers, I consider them at their limit. But, like you've pointed out before, music isn't pure sine waves, and likely the limit for max spl is somewhere higher with music. In the past, I used to impress my room mates by playing very loud rock music - like really really loud, probably close to live levels - but at these levels, especially with rock, I just couldn't hear distortion - I don't know how to explain it really, but I assume my ears were probably being heavily distorted, preventing me from being able to judge stuff like that. All I can say is that they impressed all my rocker room-mates - and they didn't sound bass shy.

There has been some interesting research lately that has given rise to my opinion that below 45Hz, sealed subs work the same as OB - so the obvious choice for this area would be a couple of subs.

[cuibono]

Originally Posted by gainphile

How does your 4x woofer work, and what is the function of the opening on the side?

Magic! No, actually... Yes, the inspiration for the second back set of drivers was from seeing the CS1. The (kind of obvious) idea of using multiple amp I got from SL. I had recently been trying to do room treatments and find ways to diffuse/reflect/absorb things below 200Hz, and ultimately found nothing affected sound that low - so I had a good idea that having one baffle in front of another would not be a problem. I also initially tried mounting the woofers face to face (isobarically), but that didn't work at all. Keeping the midsection open is essential (it looks like). Essentially, the front baffle is transparent up to about 200-400Hz (except for about a 1.5dB loss). There is no special alignment of the woofers - they are basically two H-frames one in front of the other, just missing the inner wings. I'll take some more pictures when the sun returns to this part of the earth

[MJK]

Originally Posted by cuibono

At 30Hz, I could hear beating of the sine wave with the Alpha - and I think it shows in the NLD. I'm can't recall hearing it with the GWx4, but there was clearly large cone movement. Voltage was 5.66Vrms. Unfortunately, I can't measure displacement (although I could try it with a wedge micrometer), and I'm not sure I am driving them to Xmax - but considering the high NLD below 40Hz for both woofers, I consider them at their limit. But, like you've pointed out before, music isn't pure sine waves, and likely the limit for max spl is somewhere higher with music.

That was why I was a little curious. I have run my Goldwood 18" H frame system and before that my Alpha 15A OB system at very loud listening levels (even the Telarc 1812 CD) without seeing much deflection. So if you are seeing distortion at volume levels approaching Xmax, I started wondering how loud the system was playing. My listening is all acoustic music so electronic music and HT might place different demands on a speaker then my favorite jazz CDs.

You have an interesting concept that definitely warrants a little MathCad work to see what is possible.

[cuibono]

Originally Posted by MJK

That was why I was a little curious. I have run my Goldwood 18" H frame system and before that my Alpha 15A OB system at very loud listening levels (even the Telarc 1812 CD) without seeing much deflection. So if you are seeing distortion at volume levels approaching Xmax, I started wondering how loud the system was playing. My listening is all acoustic music so electronic music and HT might place different demands on a speaker then my favorite jazz CDs.

You have an interesting concept that definitely warrants a little MathCad work to see what is possible.

Thanks! I'm glad its got you interested.

I just edited my above post you're referring to - and like I said, at very loud levels, it becomes very difficult to judge NLD, possibly because the ear is overwhelmed.

[exurbia]

Another Sensitive OB Woofer Design

Awwww, that's so sweet

My OB's are big tough and manly, nothing sensitive about them.

Your typical Ocker.

[ra7]

I'm going to build my OB system soon. But I'm wondering how loud you need to play to need 4 woofers. I'm currently not unsatisfied with my full range driver in a folded voight pipe. Granted, I don't play very loud, it still gives me enough clean bass to be happy. Of course, it is by no means thundering, loud, scary. I've heard that. But wouldn't one of those big 15" thingies be enough for a home environment?

Also, what trade-offs do you have to make when you go to something like 4 woofers? More power, more amps maybe (you mention that). Does that not add to the quality (or lack thereof) of the sound?

I'm intrigued by your design and can only thank your and many others' efforts here for helping us understand better how these things work (not to mention saving us time and money).

[cuibono]

Hi ra, thanks for your comments! Sharing is a big part of all this.

Either of these designs can play loudly, although that is opinion ultimately. It depends on what kind of stuff you're listening to and how loudly. They will definitely play a good bit more loudly than a single full range driver.

I guess the only compromise I feel with the GWx4 is having to use a extra amp per side. More drivers usually means more complicated frequency response, crossover and enclosure build, but the above design doesn't really have these - in fact, building the baffles was pretty simple.

[fwater]

Dammit, somebody always beats me to it!

I bought a pair of the GW-210/8 a few years ago and messed around with a W frame with mixed but acceptable results. For a long time I figured that this arrangement was probably the best for low-end extension with these drivers, short of a very wide standard OB, and lost interest, finding it kinda a novelty.

I revisited these drivers armed with a little more knowledge, an inspiration from the ultra-exclusive "Whisper" (or the newer Helix http://legacyaudio.com/index.php?opt...=65&Itemid=195), and 8 of the 4 ohm versions. The results are surprising in the amount of output and extension (within reasonable expectations), and un-surprising insofar that the claims of the Whisper's arrangement and it's effect on bass are probably true. The sound is quite good and the low cost makes it very attractive for me to look deeper into this configuration.

I'm not the first to the plate, but I'll never be armed with hard numbers, either...

[navin]

Originally Posted by cuibono

For your enjoyment, here is another open baffle woofer I recently threw together.

From the pics what I see is 3 drivers facing in one direction and one driver facing in the other. Now unless the drivers are wired to compensate for this I am not sure how this works.

Maybe the angle the pictures are taken does not provide a complete view.

Any idea on what specs should the drivers be for this application? How does this system compare in Max SPL and F3 to a system using the same driver in a sealed/ported box? I would assume that a single driver in a sealed box would produce as much Max SPL as this combination of 4 right? What we are gaining is better quality of bass.

Also is the radiation pattern similar to that of an H frame? Can such a woofer be placed in the middle of a room or in a corner?

So many quyestions! :-)