An old project, newly found, on a sad day

[Phil Graham]

I was cleaning out a hard drive Tuesday night and came across a project from 2012. At the time I was playing around with horn flares that were augmented with a resonator of sorts near the throat. The simulations looked interesting, so with the help of Loren Jones' excellent carpentry, we took the fourth iteration of that design and made sawdust.

The result was a single 18" in a 22.5" x 45" package, built around the B&C 18SW115. At the time, the 18SW115 was the best woofer widely available to the DIY audience. Today I would use the (upcoming) B&C 18DS115-4 instead. Sadly, we never had the opportunity to properly measure that enclosure in anger, under high power operation. Life is very different for both myself and Dr. Jones today, but I am hopeful that we can still get this project properly tested. Stay tuned on that.

Today is a musically impactful day for me, with unexpected suicide of Chris Cornell. My grandfather ran a company designing and installing paging equipment in Detroit's heyday. As a teenager I was already marginally competent with audio gear and building speakers. It was my discovery of Soundgarden's Superunknown, first on the radio in the high school cafeteria, and later as full record, was instrumental in expanding interests beyond electronics to the craft of micing and mixing music. I never had the talent or patience for the studio world, but I have more than fifteen years of moonlighting in live sound, including a five year stint as the technical columnist for FOH magazine. Superunknown had a tangible role in that for me, and it feels an appropriate date to release an old science experiment to the community.

The Google Drive link below has the Akabak files and Sketchup drawings for the version that we built. There were never formal CAD for the ASSY, but there's an outside possibility those could be generated at a later date:

https://drive.google.com/drive/folders/0BwZr3b_1ro5URHR3M2JWZGdCOFE?usp=sharing

 

[Loren Jones]

Thanks for the trip down memory lane Phil. I had a good time building this box. Thanks so much for designing it...I had planned to build a pair of simple ported boxes with mid level drivers but you made it much more interesting. I wish I'd had some measurement chops and gear and I would have measured this as well as comparing it to the RCF 21" vented boxes I had built (with your help) just prior to building this one. I would assume that this back loaded horn would have enough gain from the cabinet design to be in the same league as the vented 21" box but Phil could speak much more clearly to that than I could. I built it for the church's portable youth system. I had a bridged MA2400 for it and it seemed the sub had way more capability than the amp could exploit. I am no longer at that church but hope to get the sub back since my understanding is that it is not currently in use at all.

 

[Art Welter]

I was cleaning out a hard drive Tuesday night and came across a project from 2012. At the time I was playing around with horn flares that were augmented with a resonator of sorts near the throat. The simulations looked interesting, so with the help of Loren Jones' excellent carpentry, we took the fourth iteration of that design and made sawdust.

Today is a musically impactful day for me, with unexpected suicide of Chris Cornell.

Phil,

Loosing musically important figures is tough, especially to suicide.

Good to "hear" from you again, your post brought back memories of your 2009 "Resopump" design.
Your 2012 project shares some simillarities to Stipe Ergovic's 2010 CBe-18 Cyclops "tapped horn" design, though the Cyclops does not use the resonator chamber approach.

The symmetrical layouts use too many sheets of plywood in one cabinet for a given column length for this old man ;^).

Cheers,

Art

 

[Phil Graham]

Phil,

Loosing musically important figures is tough, especially to suicide.

Good to "hear" from you again, your post brought back memories of your 2009 "Resopump" design.
Your 2012 project shares some simillarities to Stipe Ergovic's 2010 CBe-18 Cyclops "tapped horn" design, though the Cyclops does not use the resonator chamber approach.

The symmetrical layouts use too many sheets of plywood in one cabinet for a given column length for this old man ;^).

Cheers,

Art

Art,

I'm always intrigued by your interest in naming projects. I have no such internal motivations. I had forgotten about that earlier project. 2009 was not a good time for me. The 2012 project I view as totally impractical from a DFM and cost standpoint. It was more to see if the underlying principle could fly.

Most of my interest in any sort of enclosure configuration is from the fluid mechanics side. The type of alignment is more or less inconsequential to me, as they all start to experience performance degradation in the transitional flow region.

 

[Kevin McDonough]

hey

Can I ask a little more about this design and the sound it would produce. Seems to me to almost be a "scoop", with the driver's front playing into free air and then the rear having a small chamber feeding into a horn path. The main obvious difference being that it splits into two symmetrical horn paths rather than a single one.

How would this compare to other alignments such as tapped or ported horns (or scoops), and what kinds of advantages would the symmetrical horn give compared to a single horn, more like what Art has posted in his wooden example.

k

 

[Art Welter]

Kevin,

In my "wooden" 2009 iteration of Phil's Resopump design using a LAB 10" (HL something or other, discontinued AFAIK), I found it to "sound" like a 6th order bandpass box, a narrow pass band followed by a rapid phase shift and upper "hole". Phil & Loren's 2012 design seems to functionally be the same, though eyeballing the path length the pass band would be around an octave lower.

In an outdoor A/B listening test with a tiny bass reflex box with a LAB 12 and the Resopump both equalized to the same response in a narrow bandpass, my subjective "take away" was the Resopump sounded "muddy", upright bass notes were hard to tell apart, a classic "one note wonder". That said, with bass that was mixed "boomy" and "drone like" (hip hop stuff), hard to tell much difference in sound, other than the greater "boom" factor of the Resopump, which leveraged the output of a 10" to near that of an 18" in a very compact package.

Having done several tapped horn designs, I find (if properly done) they sound more like a FLH (front loaded horn) than a 6th order bandpass. Since it has been something like 40 years since I have listened to a "scoop" with any interest, with a grain of salt I'd say they are kind of "in between" a TH and a 6th order bandpass.

That said, there are a myriad of designs that are all across the gamut of transmission lines, BLH, TH, Scoops, etc.
Every dog has it's own fleas...

Art

 

[Phil Graham]

hey
Can I ask a little more about this design and the sound it would produce.

All the files for this design can be found in the Google drive link in the first post, including the AkaBak lumped parameter models. So feel free to play with the design to your heart's content.

How would this compare to other alignments such as tapped or ported horns (or scoops), and what kinds of advantages would the symmetrical horn give compared to a single horn, more like what Art has posted in his wooden example.
k

I vaguely remember picking a split path for something related to folding, it is not material to the acoustic considerations. It certainly doesn't make the design simpler or cheaper to build. You could execute a version of the same thing with a single flared reactance.