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Speedy's SBD - InDIYana'15 Micro 3-way

Thu Apr 23, 2015 5:30 pm

Image20150417_130910 by gospeedlimitracer, on Flickr

SBD - either Stupid & Bad Design or Small but DANG.

WARNING: As this project sits, don't build it. I will over the coming month correspond on here my measurements and tweaks to get it sounding better.

Right now, mostly the former, especially after hearing some amazing speakers there.

Very humbling to be in the presence of so much brain power and gifted people. Not only their love and passion for speakers, but their willingness to freely give information and help anyone including a guy just getting started like me improve. I only hope one day I can give back to this community.

I will add xover info, box info, more pictures and graphs probably late tonight, if not Friday.

The SBD was entered into the InDIYana 2015 micro 3-way bookshelf competition. I will tell how it went below; This and the next posts are documenting the build. They were written as I created the speakers.

The rules for the 3-way (as my head understood them):
The interior volume must NOT be greater than 0.5 ft^3. This includes: port(s), drivers, internal braces, cabling, etc.
The drivers may not regularly cost more than 200 for all 6; this would include passive radiators if used.
The drivers may not by a buyout; UNLESS it is still going to be regularly available; the regular price must be used in the price calculation; not the sale price nor the buyout price.
Design must be repeatable, so the drivers must be available for purchase.
No IBs
All drivers must fit in the baffle, and the baffle may not be taller than the woofer cabinet (tweeter cannot stick out the top on a steeek)
Xover: go nuts; but it must be either inside or attached to the cabinet. it cannot be an outboard xover case.

Even though it was not a requirement, I thought I needed to make my pair compatible with a 6 ohm amp, so I can actually test them with the amp I have here without letting out its magic smoke. This would be a great excuse to get a new amp, but, I don't roll that way intentionally.

Box Design:

After a lot of newbie ponderings (many hours) and modeling in bassbox (another many hours; then back to newbie ponderings and back to bassbox); I decided on 'The Silky' Dayton Audio's DC28F-8 tweeter, Tymphany's 5.25" FSL-0512R01-08 for Midrange, and Dayton Audio RS180S-8 7" Woofer.

I ended up with a sealed compartment for the mid, and a simple vented enclosure for the woofer. As I only had .5ft^3 to work with, I planned to make the mid enclosure out of 1/2" BB, and used 3/4" on the rest.

The next challenge; getting a port that is too long to fit front or rear firing to work. I probably could have just built a bent port, but with time of the essence, I created a downward firing port, and made sure my feet gave well-over 0.5" worth of room to hopefully let the air and sound dissipate out into the room without chuffing or muffling of the sound.

Crossover Design:
ImageSBD-v1 Crossover by gospeedlimitracer, on Flickr

ImageSBD-v1 Phase by gospeedlimitracer, on Flickr
Phase seems to line up well, especially at the x-over points.

ImageSBD-v1 Impedance by gospeedlimitracer, on Flickr
System Impedance in yellow.
Aside from one spot that hits 4.3 ohm (around 6.7 kHz) I exceeded my goal, as the rest of the dips only hit around 6 ohm; Which I hear is acceptable for an 8 ohm system?

ImageSBD-v1 NAR by gospeedlimitracer, on Flickr
Here is the normalized amplitude response. It is horrid looking, and NOW I know what most of that means.

Not knowing any better (and I still don't yet), this is a complete parallel design, all second-order: High pass at 2k, mid 500 to 2.2k, low at 450. With the sim, even with the overlap/underlap the overall spl was nearly straight until about 5k, where it went nuts. Getting this system mic'd and analyzed will show what is really going on here.

The 7" was chosen to try and get sub 50 Hz sound; it is a three-way after all. We will see how I stack up!

After reading it looked like pegboard was the way to go for these. Got myself a piece to use for the next 10 or so projects. Soldered it away like the design, and tried to place the inductors out of phase. 4 per board so the lowest value inductors are in-phase and about as far apart as I could make them.

Yes, I did double up on my resistors. I was reassured that 1 would be sufficient, but I like to play it safe, and I did not do the calculations on W, Hz, and reduction of watts per frequency the day I was ordering my x-over parts. It does make a TON of sense that the higher frequencies use less power.

Here is testing the xover IB style.
Image20150309_233448 by gospeedlimitracer, on Flickr
On 30 Watts, it sounds GREAT, though, I have to admit the bass is lacking big time, I am thinking at this point it is partially due to the lack of a cabinet.
Last edited by SpeedRacer on Fri Apr 24, 2015 7:50 pm, edited 2 times in total.
Topic Author
Posts: 5
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Re: Speedy's SBD - InDIYana'15 Micro 3-way

Thu Apr 23, 2015 5:30 pm

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Topic Author
Posts: 5
Joined: Wed Apr 22, 2015 11:56 am

Re: Speedy's SBD - InDIYana'15 Micro 3-way

Thu Apr 23, 2015 5:30 pm

I had hooked them up to my amp at home briefly before I left for Indiana, but was not able to listen much, or to tweak. It had clear sound (still hardly any bass), but when cranked up to -5, the mid was starting to distort and the woofer was just starting to shine.

At InDIYana'15 on Friday, I was able to test them out. And the great crew there helped in saying the mid and even the tweeter needed some more dampening, I probably also need some BSC in there too, I will know more once I get a Mic and analyze these. I will hopefully test in about a week from now.

Since I had doubled up on the resistors, all I had to do to get some instant better sound was to cut one out. So I did, and competition day, they sounded A LOT better. There were still many builds that sounded better, but for my first shot, I am excited to learn more and dive in to more!

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