The JPG - A tribute to my dad's DIY work

[wogg]

I've wanted to get this design on paper for a while. My dad did a pair of large 15" 3 ways when he was young, and I grew up with them as inspiration to get into speaker building my whole life. They were designed with tools at the time, which were basically text book 2nd order crossovers and adjustable L-Pads on the tweeter and mid to bring the levels in. I have no idea what drivers he used, I do know that it was a 15" woofer, and a paper dome mid and tweeter. The design was set on it's side, with vertically oriented mid and tweeter next to the woofer. He originally did it ported, but didn't like the sound so he sealed them up. I'm pretty sure he didn't have the correct port calculations though, based on us building boxes later in my teens.

He passed away in 2015, just before I learned all these sweet DIY crossover design tools. So this design is a tribute to his work in the 70's, I'll call the JPG Tribute. Also, since I don't have a purpose or place for speakers this size the design will remain theoretical for me. All Dayton drivers designed using their FRD / ZMA files, processed with response modeler to add baffle and diffraction signatures processed to minimum phase. The acoustic offsets, particularly the Z offset is guestimated, so some minor adjustments are likely if these end up in real life by anyone.

Drivers:
DC380-8 15" woofer
RS52FN-8 dome mid
RST28F-4 tweeter

Design aesthetic: The originals had an inset baffle with a classic tweed fabric covered grill, so I'm doing that here as well. He actually used particle board, and stained and poly coated it for a deep color with the fine chips of the particle board visible through the stain. Looked pretty good, but this would be nice in a BB ply as well.



Woofer Alignment:
The volume was dictated by my estimated size of the originals, a solid 5.8 cu ft. That puts a a vented alignment tuned to 23Hz with a 4" x 7.7" port in line for the DC380-8 woofer with an F3 of 30Hz. Sealing the port yields a low box Q of 0.48 with an F3 of 52.

Vented


Vented Vs Sealed


In my opinion, either would work well. The DC380-8 does run out of Xmax a bit though, so a full 100W and 110dB of output will get you some over-exertion.

[wogg]

Crossover Design:
All FRD files were processed with their position on the baffle, though the inset was not considered. I played with 2nd order electrical filters, targeting around an LR4 acoustic roll off. Didn't quite nail it, since this works without an inverted mid as you would expect for LR4. Regardless this shows a sim of within +- 3dB with a bit of a reverse null, though not super deep.

Crossover points landed around 600Hz and 4.5kHz.


For the woofer, I saw a large breakup peak in the response that was tamed with a parallel notch cap on the woofer coil. Since the notch cap ended up fairly large at 2uF, I added some series resistance to avoid very low capacitive loads at supersonic frequencies.


With the sensitivity of the woofer, I didn't have to pad the mid and tweeter too hard so the mid has just a little series resistance both before and after the network.


Likewise, the tweeter is a simple 2nd order with a single pad resistor.

[wogg]

The system impedance ends up approximately 8 ohm nominal, but dips into 4 ohm territory as you reach high frequencies. This shouldn't be a big deal for amplifiers though, as the vast majority of your power is spent down low.


If my dad were around I think he'd dig these suckers. Sadly, my parents were living in condo's later in life so the originals had to go long ago due to the space needed to place them, and the irritation that resulted with the neighbors due to a pair of rocking 15" woofers.

Even though I won't be building these, the design is here for anyone to give it a shot. Thanks for checking it out!

[Geoff Millar]

A really nice idea to build a tribute to your father, and the design looks pretty cool too!

Geoff

[Harvylogan]

Very cool!

[Serenitynow]

These may be just what I've been looking for.

I've never built a DIY speaker before, but I really want to do so for my under construction basement room.

I had decided to build Paul Carmody's Tarkus until I saw this.

I'm really confused by the crossover schematics however. Is there a possibility of showing a more simplified version so that a beginner could understand ?

Also, a Bill of Materials for the crossover components would be super..

Can these be oriented vertically instead of horizontally with no loss of performance? I'm considering 3 of these to go behind an acoustically transparent projector screen.

Thanks.
TK

[wogg]

Thanks! Honestly I wouldn't expect these to compete with the Tarkus directly, Carmody's design is built and tested with measurement data while these are simulated from Dayton's test data. But I would love to see these in reality.

Here's the schematic drawn up in Xsim, much easier to follow.

I haven't had a chance to run these values against available parts to lock in the BOM and get a full cost. I did increase the series element in the woofer notch from 4 to 10 ohms here, lightens the load a little up top while keeping the breakup down just fine.

As for orientation, horizontal as designed is preferred due to the horizontal dispersion lobing that will occur at the crossover frequencies. Horizontally, you'll get the lobing at the woofer to mid transition, around 500-600Hz but the mid to tweeter transition remains smooth.

Here's the PCD sim horizontal all angle chart.


If you place them vertically, this vertical plot becomes your horizontal plot.

We have less lobing at the woofer to mid transition, but that mid to tweeter region is all over the place. Generally, you want the lobing in the vertical axis, because as you move listening positions around the room the vertical height is generally about the same.

Note about these: this is PCD's estimation based on XYZ settings and phasing, as well as estimated driver directivity based on radiating diameter. Real life, the dispersion is not entirely controlled by piston size, so there's some fudge factor in here.

[Serenitynow]

Thanks for the simplified schematic. That is easier to follow.

The rest of your post will take me some time to understand ( I'm a NOOB ), but I'll read it several times and try to figure it out.. I think I understand the lobing part,, the rest is fairly new to me tho.

Thanks again.

[Wolf]

Not sure the mid will play that low, but otherwise this looks like a solid sim.
I hope someone does build it!
Wolf

[wogg]

Thanks Wolf!

I think you're probably right, crossing from a 15" woofer to a 2" dome mid is a stretch, it will probably be the first to complain as the volume gets pushed. I wish there were more 3" domes around to meet that particular design requirement.

[Serenitynow]

Thanks Wolf!

I think you're probably right, crossing from a 15" woofer to a 2" dome mid is a stretch, it will probably be the first to complain as the volume gets pushed. I wish there were more 3" domes around to meet that particular design requirement.

Does it HAVE to be a dome mid ?
There are lots of 3" mids that will play the range you have.

[wogg]

Does it HAVE to be a dome mid ?
There are lots of 3" mids that will play the range you have.

Technically, of course not. But... the goal was to match the originals aesthetically with modern available drivers so I stuck to an available dome mid.

[Serenitynow]

I completely understand your reason !

[4thtry]

Nice design. Thanks for sharing. I bet the BR version could really belt out the deep bass! You mentioned that the mid and tweeter were vertically oriented. How was this accomplished? Did the originals use custom, angled mounting rings of some type?

[jtheisen521]

SB just released a new 2.5” mid to their Satoti line. Looks pretty robust but of course it’s pricey. May be worth look though as I think it will be the mid that will make or break this design. It’s available in Wisconsin Sent from my iPhone using Tapatalk