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Author Topic: Back to Speakers... Again! (Dirt Cheap Open Baffle Speaker Project)  (Read 17364 times)

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DaveBSC

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Re: Back to Speakers... Again! (Dirt Cheap Open Baffle Speaker Project)
« Reply #20 on: February 10, 2014, 04:52:31 AM »
Quote from: purrin on February 10, 2014, 12:16:59 AM
Pretty much. The problem with OB speakers is bass roll off depending upon the drivers used. The wide baffles help to extend that. The 15" Betas have a Fs of 35Hz and fairly high Qts. I think I'm getting extension down to 40Hz. Everything, x-overs, EQ, etc. so far has been done by ear, so I'm not totally sure about that. I'm hoping not to have to resort to a sub. I do know that I have quite a lot of headroom to probably squeeze another 5-10Hz of bass extension using EQ.

What do you think of doing a half open speaker ala something like the NOLA Viper? To me, having an open baffle design go well below 100Hz just seems unnecessary, being that all bass is omni directional, and most of what you're hearing is actually reflections as opposed to direct sound. A sealed or ported box would give you a lot more extension than not, and there are considerable advantages to a bipolar design of two opposing woofers in phase with each other.

As for size, I generally (very generally) prefer 12" woofers to anything else, I think they are the best middle ground between fast 8" or 10" woofers that struggle with deep bass extension and SPL without considerable xmax that makes them start to go out of control, or huge woofers that can often sound too slow without servo control, or otherwise sacrifice deep extension in order to not move too much and keep up. Two 12" woofers in a box are hard to beat. It's what Eggleston uses in the Andra, and they get 18Hz at -3dB, and that puppy can keep up with anything you throw at it.

The Lotus Granada is one of the more interesting full open designs that I've seen, but when I've heard it at shows it wasn't perfect, particularly in the treble region. It costs TOTL Venture money, and the Ventures definitely have it beat. Looks cool though.







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zerodeefex

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Re: Back to Speakers... Again! (Dirt Cheap Open Baffle Speaker Project)
« Reply #21 on: February 10, 2014, 04:59:37 AM »
wtfbbq rack are you using? Looks like a bunch of ikea lacks cut down and stuck together.


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Re: Back to Speakers... Again! (Dirt Cheap Open Baffle Speaker Project)
« Reply #22 on: February 10, 2014, 05:04:36 AM »
Quote from: zerodeefex on February 10, 2014, 04:59:37 AM
wtfbbq rack are you using? Looks like a bunch of ikea lacks cut down and stuck together.

Lol, good eye.
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Donald North

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Re: Back to Speakers... Again! (Dirt Cheap Open Baffle Speaker Project)
« Reply #23 on: February 10, 2014, 05:21:53 AM »
Congrats Purrin for building a dipole speaker system! I'm really glad you tried the concept and are enjoying the performance.

@DaveBSC: In my opinion the most benefit from dipole (OB) speakers is in the bass because you get a lot less room mode excitation. Dipoles have a directivity index of 4.8dB, which means for the same on-axis SPL as a box speaker, you're radiating 4.8dB less power into the room. With proper room placement you attain a much smoother frequency response in room at the listening position without the need for room EQ.

With dipole woofers, it's all about air volume displacement. Multiple 10 or 12 inch woofers are good. So is a pistonic 15 or 18 inch woofer.
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Re: Back to Speakers... Again! (Dirt Cheap Open Baffle Speaker Project)
« Reply #24 on: February 10, 2014, 05:38:59 AM »
Really cool! Looking forward to more details, design, etc.

Quote from: purrin on February 10, 2014, 12:07:43 AM
Dang, don't give me any ideas. I could might draw something like that on the boards.

Let me know if you need any help.
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Donald North

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Re: Back to Speakers... Again! (Dirt Cheap Open Baffle Speaker Project)
« Reply #25 on: February 10, 2014, 07:46:24 AM »
Quote from: purrin on February 10, 2014, 04:04:25 AM
The consideration for the Moth driver was to run them from a 3-6 watt tube amp (guess which ones) using one capacitor only. I hate passive x-over components. All they do is destroy the sound. But in this case, I was willing to make a compromise - a very small one. Because I was only using one cap, the best I was going to get was a 1st order 6db electrical roll-off. That's not very much roll-off at all to protect the Moth driver from over-excursion (always an issue with OB), so I wanted to make sure I could run the Moth driver as low as possible before crossing over to the woofers.

I haven't done the calculations for this scenario, but I suspect I could have gotten away with no baffle or just a 1-2" lip around the Moth driver if I wanted to crossover at 200-300Hz.

You'll need a much larger baffle than a 2" lip around the Moth driver to go down to 200-300Hz without roll-off. The size in your photos looks good.

For high-pass filter on the full-range driver, try using a series cap on the input of the amp powering it. You'll need to calculate the value depending on desired corner frequency and amplifier input impedance. In my experience this will provide a more predictable and desirable filter with the added benefit of more dynamic range from the amp itself.
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zerodeefex

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Re: Back to Speakers... Again! (Dirt Cheap Open Baffle Speaker Project)
« Reply #26 on: February 10, 2014, 05:06:06 PM »
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Armaegis

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Re: Back to Speakers... Again! (Dirt Cheap Open Baffle Speaker Project)
« Reply #27 on: February 10, 2014, 05:47:37 PM »
Oh that looks fantastic! I seem to recall reading that was a direction they were considering with Ti Kan's CBT36.
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Not sure if I like stuffing one hole or both holes. Tending toward one hole since both holes seems kinda ghey ~Purrin

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Re: Back to Speakers... Again! (Dirt Cheap Open Baffle Speaker Project)
« Reply #28 on: February 10, 2014, 07:11:08 PM »
Quote from: DaveBSC on February 10, 2014, 04:52:31 AM
What do you think of doing a half open speaker ala something like the NOLA Viper? To me, having an open baffle design go well below 100Hz just seems unnecessary, being that all bass is omni directional, and most of what you're hearing is actually reflections as opposed to direct sound.

I know... lots of old schoolers think OB bass is a waste of power - and indeed it is. To follow up on what Donald said on OB bass, the directionality of OB bass is actually not omni-directional, but rather in a figure eight pattern with the rear facing radiation in opposite phase to the front. In theory, we are actually reducing some of the initial side reflections from the wall.

I'll post of pic of the behinds. You'll see that I've actually implemented a partial U-frame with irregular patterns in the back. This should provide a slight hypercardioid radiation pattern. From other speakers, I know the significant room nodes (27, 44, 66, and 88), and I found out with OB that the magnitude of the 44 and 88 nodes were halved. (For some reason, the node at 66Hz wasn't mitigated.) In addition, I found that two nulls around 60 and 74, which I could never really fill before regardless of how much +EQ I applied were easily correctable.

Finally, despite the massive power waste, I like sharp and fast setting impulse response of OB. Everything in box (or even stuffed U frame) seems to have its impulse response dampened or settling time extended.
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DaveBSC

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Re: Back to Speakers... Again! (Dirt Cheap Open Baffle Speaker Project)
« Reply #29 on: February 10, 2014, 07:16:43 PM »
Quote from: Donald North on February 10, 2014, 05:21:53 AM
@DaveBSC: In my opinion the most benefit from dipole (OB) speakers is in the bass because you get a lot less room mode excitation. Dipoles have a directivity index of 4.8dB, which means for the same on-axis SPL as a box speaker, you're radiating 4.8dB less power into the room. With proper room placement you attain a much smoother frequency response in room at the listening position without the need for room EQ.

With dipole woofers, it's all about air volume displacement. Multiple 10 or 12 inch woofers are good. So is a pistonic 15 or 18 inch woofer.

Interesting, though it's worth noting that the majority of commercial fully OB designs (as far as I'm aware) use some form of active EQ, so you end up with room EQ anyway. There's also arguably more of a need for room treatments with dipoles and OB designs in particular than with traditional box speakers, and especially compared to FR enclosures or constant directivity horn types. FR enclosures for example should need little more than bass traps.

The typical treatments I see with traditional dipoles like ESLs or planars or OBs is to try to "black hole" the wall behind the speakers with absorption, though I've found that diffusers can actually be more effective, though trickier, as you want some reflection, just not right away. Linkwitz argues for >6ms IIRC, but I've heard other designers recommend >10ms. The other option is to pull your dipoles 6+ feet away from the wall, but of course that's often not practical.
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