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Open Baffle Open Source: The Sound

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If you've been following along, I have been engaged in a fun and educational project involving building an active biamplified open baffle loudspeaker. They are modular, which will give me the option in the future to change out drivers. But for now I am using Eminence Alpha woofers, 2 per side, and the Dayton Audio PS-200 8 full range driver. The total cost of the speakers alone is around $1000. But, spoiler alert, if one is willing to do a little assembly, is not afraid of using things like a MiniDSP, laptop and microphone, one can set up a very high performance audio system for not a lot of money.

"Mike why are you doing this?" Well, I love to build things, I love to learn, and I love to share things that will bring more people into the hobby of listening to music as a "mindful" activity. That is why. 

The System

We need to talk about the system because, especially in this case, it is integrated more deeply with the speakers and I am guessing has much to do with the overall sound. The active speakers need a crossover, and the crossover I used was also the EQ, the DAC, and the volume control. For $300 it packs a lot of functionality and good sound into one package. My only modification to it was the addition of a linear power supply over the stock wall wart. Keeping it modest, I used an Auralic Mini streamer. The amps were 2 channel Pascal amplifiers Both rated at 200 watts, but one channel rated for lower current output. We used the lower current amp channels for the highs. Let me just say this about the Pascal amps, they are extremely good as stock. In my opinion they bested the NCore NC500 amps I have heard. They were more dynamic, ran way cooler, and never failed.

Dual 18" powered subs (One shown on the left) and the 2x 15" Eminence Alpha 15" drivers provided coverage from 170 hz on down. The Subs were crossed at 50hz and volume set at about 9 O'Clock. The Alphas played from 50 hz on up to 170Hz.


The 4 Eminence Alpha 15 woofers will play very solidly down into the 40 hz range with some of the best bass you've ever heard. Not quantity mind you, but quality. Actually quantity too if you stay above 40hz. Once you hear open baffle bass, you will understand. because there is no box behind the woofers, and they radiate into open space behind the speakers, there is no boxy or boomy sound. Again you really have to hear it to understand. The dipole radiation pattern created by dipole bass has less room interaction, and with the right woofers, it is truly amazing. 

At $100 each, and with some EQ, this driver is a solid high end audio driver.

Dayton PS 220 8 Full Range Driver

This is a really nice driver for it's price point. It's rising response curve demands EQ, and the MiniDSP did a great job with it's parametric EQ features. Once EQ'd properly using the UMIK microphone and Room EQ Wizard, it's high efficiency allows it to keep up with the Eminence woofers, and it's shallow profile cone makes the dispersion pattern of this 8" full range driver quite wide and even. I was shocked that I could stand, sit and walk around the room without the sound changing. 

On resolution, before I ran DIRAC room/speaker correction, I was going to say it wasn't the finest driver I've ever heard. AFTER running the DIRAC program and executing the filters however, the 8" full-range drivers came alive. Playing from 170hz on up they were open, coherant, imaged like crazy, with superb tones, and yes air galore. Again, this is one route of many. This is a single 8" driver getting a lot of help in the digital realm, and the results were low cost ($100 each, $300 or so for the MiniDSP) and I would guess that 98% of audiophiles would approve (there's always that 2%....)

Complex harmonics, short reverbs, any acoustic event where two tones were close in pitch but slightly different timings were rendered beautifully. This I consider an advantage of the full range driver. The very fine micro details that I have heard in some very nice multi-way speakers were a little veiled. Tonally however once the driver was EQ'd it was lovely. I have to wonder however if the veiled nature of the sound was also a shortcoming of the DAC (I soon found out it wasn't) . With the MiniDSP DDR 24 I had to use the built-in DAC since it did not have digital outputs. I also used the built in volume control, which was digital. That might explain why I had to turn the volume up just a bit to get the overall sound to open up. The new SHD version from MiniDSP offers a 32 bit volume control, better DACs, and a digital output for each channel in case one wants to use their own DAC. That may open up the sound further.

This is all well and good. But I didn't realize how incomplete the setup was until after I ran room correction.

Above: FR with no EQ on any drivers yet. 

Above: The left channel before and after EQ.

Above: The right channel before and after EQ only.

Above, Both Channels after Dirac 


Dirac room and speaker correction compensates for frequency and impulse response. Companies like Arcam and NAD incoproate DIRAC into their audio components. The process is pretty simple. You have your MiniDSP and a microphone connected to your laptop, and you start the DIRAC program up. It walks you through a series of steps of measuring your speakers at 9 different listening locations, then it creates the filters designed to compensate for frequency and phase response. This is much more powerful than just using the parametric EQ functions of the MiniDSP. I mean, not even in the same league.

Once I had all of the measurements, I clicked the "calclulate filters" button and after a few seconds, the screen displayed the predicted results of those filters. It looked impressive, but how would it sound?

I was not expecting much, but DIRAC absolutely opened up the speakers, to the point that they were punching way above their $1000 parts tag would suggest. The sound stage became enormous, clarity lept upward, and they just disappeared like a great imaging speaker does. They disappeared with scale too. I could turn it up with no stress or strain coming through the speakers. It was fun. Really fun.


You know I had to go there, and I did. I found placing DMT Qubes on the back panel of each driver opened them up oh so slightly more, but enough to warrant doing so. The biggest shocker was not a speaker tweak, but a power cord tweak. Jack Bybee sent me 4 of his new V2 iQSE's and instructed me to place them on the ends of my power cords. So I started with one on the cord feeding the power conditioner, usually this is the least effective place. Why? Because the power then has to flow through all of the power conditioning elements and benefits can be lost. Not so hear. More detail and way more low level information became present. This was most noticeable in the speaker's ability to disappear. With each subsequent V2 placement on the cord, resolution and clarity went up, and the speakers disappeared more. The V2's really allowed me to hear what these speakers were capable of, and it was astonishing. 


This project was so much fun, so educational, and it's actually taken an unexpected turn. No I will not be selling the kit, but I did provide a parts list in my first blog. If you wish to build it, I really encourage you to do so. It's an amazing speaker. Great for budding audiophiles who have mechanical abilities and are somewhat computer savvy. The performance would be good enough for 99% of the population, and they would never desire to upgrade. The looks, well, while a little modern and DIY, they could use some creative help perhaps. But that was never the point. The point was to build something that sounded good, and these sound great. I would put them up against any floorstander in the 3-5k price range. I would bet they image better, play louder, scale better, and have better (not necessarily lower) bass.

Regardless of their cost, these speakers engage me. They do need a sub to really get that convincing low end. But even without a sub, they have tone, holography, boxlessness and can play loud.

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