My First DIY Speaker - Mini Bass Array Module (Teaser)

[mattlong8]

Greetings fellow Bass-Heads,

I just couldn't wait any longer so here are a couple of pics of my first DIY Speaker project.
I'll be doing an extensive write up as well as posting plans after AES/BAF.








Please don't post links to this on other forums just yet.

-Matt

[mattlong8]

Vb = 3.3ft^3
Fb = 33Hz
Width=17"
Height=20"(plus feet)
depth= 24"
Driver Lab-12

[mattlong8]

Here is a few more images:

Transfer function with filter settings from WinISD

Cabinet rear with acrylic cover to show the guts and for smoke turbulence testing.
In this prototype version I didn't make an internal flare and did not cover the expanding foam void filler.

Clay molded "plug" for the external flare

Port mold__________________________________^

[ßart West-VL.]

Mysterious...
You've got my attention!

[mattlong8]

Here are some measurements I took in my garage (read very echoic) with a 50ohms sense resistor for impedance and A DBX reference mic for the frequency response both using a macbook pro, presonus 1818, a demo of smaart 7. Pink is impedance, blue is on axis in the ground plane at about 2 feet, and green is on axis at the mid point between the woofer and the port 16" away.

The large ripples in the freq. response are mirrored 1 octave up so I assume they are standing waves/room modes.
The impedance plot puts the Fb between 33 and 34, So great success there especially considering I made the port by hand and I was expecting it to be off by a much larger margin. I wonder what the response would look like with out room gain but that's hard for me to get as I live near the freeway in San Francisco.
Please post any comments, questions, and suggestions. I've been in the sound biz for a while, but this is my first build.

[Etocynned]

Cool to see this methodical approach.
Nice work.

[mattlong8]

The port for Prototype B is coming along.

[mattlong8]

Doh! Wrong link in last post. Here are the images

[weltersys]

Originally Posted by mattlong8

Here are some measurements I took in my garage (read very echoic) with a 50ohms sense resistor for impedance and A DBX reference mic for the frequency response both using a macbook pro, presonus 1818, a demo of smaart 7. Pink is impedance, blue is on axis in the ground plane at about 2 feet, and green is on axis at the mid point between the woofer and the port 16" away.

The large ripples in the freq. response are mirrored 1 octave up so I assume they are standing waves/room modes.

Matt,

Interesting that your cabinet seems to have a more pronounced port resonance than my Lab 2x12" box:
FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter Systems

My outdoor (mic on ground 2 meters from cabinet front) plot below with yours for comparison. Other than the port resonance, response looks very similar.

Why did you make the cabinet front arced?

Art

[mattlong8]

Hi Art,
I'm really glad you chimed in and shared your results in this thread for comparison. The results are very interesting. I'll take some time comparing these results with our design dimensions as I'm sure there is some valuable insight there. My initial thoughts are that your ports are greater than a 1/4 wavelength apart for 290Hz-350Hz so the response should vary with distance in that range. My ports are just inside a 1/4 wavelength apart (center to center) for 300 so the resonance effects are couple probably coupling.

In this prototype I didn't install an internal flare due to time constraints and there is a sharp edge at the top inside of the port. I suspect the turbulence coming from this would tend to excite any resonances greatly. I really need an outdoor measurement to get a better idea of whats going on, but I'm pretty close to completing the second prototype and I live in a very noisy area so that will have to wait.

The curved baffle came from my thoughts on making a medium-large array out of small cabinets. My concern is that increased low end from clustering would drown out the frequencies near the top of the subs band. One of of balancing this would be to increase the baffle area of the array to increase the directionality of the top end and level the response a bit towards the audience. I thought that perhaps using an arc instead of a plane would give me the area I needed with out increasing the size of the box. So when arrayed the arcs could align by angling adjacent in. This would also reduce the distance between the woofer radiating surface and might add to the coupling of the higher frequencies. I started modeling it in sketchup and really became attached to the look of the stacks. Then I did some math and it appeared that the effects I was hoping for would probably be negligible =(. But it still had a unique attractive appearance so I figured I would try it out.

I have run horn loaded subs like the TH-115 and the Bassmaxx Trip angled in with the mouths together and was pleased with the sound so my hopes are it won't make things worse. The setup with 6 per side ground stacked 2x3 with the mains on top will really stand out from all the other system in my area; I'm pretty excited about it.

-Matt