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A Neat Iota Alpha Inspired Speaker, the Zetas
I recently saw a thread on DIY Audio about the Neat Iota Alpha speakers. They are kind of a neat concept, and I thought they looked really cool. I am planning on building something that resembles them, but much bigger. I plan to use the HIVI RT1.3WE tweeter, the MAC-04 as a mid, and a down firing Dayton Audio SD215A-88 8" driver. I think I have a design where I can start sealed and go ported by drilling holes in a divider and adding a port. It looks like the lower rectancle is .7 cubic feet, which would give me a F3 of 55hz sealed, and if I opened it up to the top I would have 1 cubic foot tuned to 30hz for an F3 of 33 hz. The only reason I am thinking of going sealed, is that I am worried I may get a bit of a peak in the response due to basically slot loading the woofer in down firing position.
Comments
Here is the predicted low end response of the sealed and ported versions. Also, the speaker is 10x10"x33" tall. I hope to start cutting wood in the next couple of weeks.
Depends on how much the cabinet is elevated off the floor, but since it would be open to all sides I doubt it would take much elevation to minimize any "loading". Always a hard decision between sealed and ported, but you can always stuff a port.
I got all of my wood cut and started assembling the first one tonight.
Got the 2 upper drivers routered today.
I got the cabinets assembled today. I need to sand them and then start taking measurements. Because of the size of these it was hard to get a port bigger than 2" in the way i wanted it. If it chuffs too much I will have to go to 3" with an elbow.
I got the cabinets built and ready for measurements. Ran impedance sweeps and nothing weird showed up with the down firing woofer. The feet will be machined aluminum eventually, and not sure about finish yet.
Well, after doing a bunch of measurements and a bunch of crossover sims, I don't think that this design will be something I will be happy about. There is a ton of diffraction on the midrange, and I don't think I can make something I will be happy with. I may build a more conventional 3-way with these instead. I think I am gong to call this one a failure and move on.
Other than the top, one side, and front baffle, the mid/treble are open? I'd wager with a sawzall and some felt you could make a huge difference.
I am not sure what you are suggesting.. Can you elaborate?
Here are my nearfield and far field measurements.
I have a feeling that in order to get the look I am going for, the diffraction is just too much for me to compromise.
If you bring the woofer in at 300-350, I don't see the low-end droop as an issue.
If you remove the smoothing, you might be able to identify the causal distance from the midrange. Rounding the edges will help.
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Oh- and I noticed something...
The woofer is the 8" SD215A-88, not the SD270A-88 as that is the 10". The 215 should easily play high enough to meet at 350, but the down-firing orientation may prevent it contrast to a normal front firing orientation.
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That was a typo on the woofer. You are correct, it is the 8 ". The 8, even though it is down firing is smooth to around 500hz. I can design a crossover around the droop, but my part could was getting higher than I wanted. I will put the rest of my measurements up later and see what everyone thinks.
In the originals, since the drivers are side by side, they are offset horizontally in the baffle. If you were to somehow plug the holes (or glue on another board in front) and recut them off center that would make the diffraction effect from each side different and thus less pronounced overall.
I know gluing on a new baffle board might be dicy due to the dimensions. But could also glue on a piece down the front lower half to match up better.
I am pretty sure centering the drivers and not rounding the edges is a major contributor. I originally modeled them in CAD with offset drivers and did not like the look. I think I am going to start over with a more standard tower and use a chamfered design like I have done in the past. I think these drivers will play well together if I start off with a better design. I won't be too upset, I got this sheet of MDF off of the Menards bargain rack for $20.
Chop the top section off with the table saw and make em bookshelf stands with integrated sub?
I would put a round over or bevel on it and see how much it improves. So close, won't hurt to try it.
My 2cents:
Possibly move the woofer from down firing to forward- with woofer 1/3rd up from base, no need for the feet. Then the crossover frequency to mid will be easier to match.
Haven't had much free time lately so I just pop in here form time to time, so ... I probably missed something, or a lot of something. One of the pics looked like the mid/tweet were open on two sides on the back. Guess that's not the case?
No, they are sealed within the cabinet.
I drew up a design that I will be shooting for next. These will be 40" tall. I will up the volume of the SD215A to 1.5 cubic foot and should allow a sub 30hz f3.
The facets are visually more appealing also...
Yep, 29Hz in 1.5ft^3. That is what makes the SD215 a high bang for buck. Used to be just $29.
Good solid cheap woofers still exist with the SD line.
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I think I will like this design a lot more. I like to try weird designs, but more times than not, there is a reason they are not popular. I will be hopefully cutting wood again later this week.
Surprise surprise I like the looks of the faceted design.