HT style 1x12 dimension question with regards to the back

HT style 1x12 dimension question with regards to the back

Postby Erbacher » Tue Jun 06, 2017 6:24 pm

Hey I'm building a 1x12 and am using the jbl chart dimensions which tunes the cab to 80hz...if you partially enclose the back of the cab, the reflections of sound cause the internal resonance of the cab to change...does anyone know the formula for adding a partial back with regard to dimension and this 80hz resonance? If I use the dimensions on the jbl chart and partially enclose the back of the cab at 1/3 of the total opening, how much shorter would the cab chamber need to be to still keep the 80hz resonance? It makes total sense why Garcia had his cab tuned to 80hz bc the low note on a standard tuned guitar is right around that...the total package being completed by cab resonance...no stone left unturned
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Re: HT style 1x12 dimension question with regards to the bac

Postby waldo041 » Tue Jun 06, 2017 6:38 pm

Image

Image

Image

Image

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Re: HT style 1x12 dimension question with regards to the bac

Postby Erbacher » Tue Jun 06, 2017 7:27 pm

Looking at my original post I should have clarified that my own personal cab will not have a partial enclosure and that my question was more of a "what if" type question...I have someone else wanting one of these made and they may not want the back to be totally open...but I guess I could just try to convince them that if they want the real thing it's supposed to be totally open!
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Re: HT style 1x12 dimension question with regards to the bac

Postby waldo041 » Tue Jun 06, 2017 8:15 pm

Erbacher wrote:Looking at my original post I should have clarified that my own personal cab will not have a partial enclosure and that my question was more of a "what if" type question...I have someone else wanting one of these made and they may not want the back to be totally open...but I guess I could just try to convince them that if they want the real thing it's supposed to be totally open!

No worries, I wasn't sure if you had known he used an almost entirely open cabinet. The 12" JBL's can handle the lower 80hz no problem, but you are onto something with the "tuning" of that 80hz.

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Re: HT style 1x12 dimension question with regards to the bac

Postby Erbacher » Tue Jun 06, 2017 8:38 pm

And thanks Waldo for all your expertise and help along the way
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Re: HT style 1x12 dimension question with regards to the bac

Postby Erbacher » Tue Jun 06, 2017 8:46 pm

It seems totally logical and I can almost hear Garcia asking or a conversation between he and Bear happening about the low E note being around 82hz and the logical next step is to create the cab to resonate at as close to that frequency as possible so when you go to that note or a multiple of that, you get the best possible sound via resonance...this is what the Egyptians were into and also builders of cathedrals back in the day so it makes sense and when I became curious about it today while building I started poking around and was like "of course" haha...this is yet another reason why the Grateful Dead are the greatest band ever and most recorded entity of all time...no stone left unturned while searching for the sound bc it's all relevant if you want the best sound you can get...you can't gloss over the details and expect the same results
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Re: HT style 1x12 dimension question with regards to the bac

Postby Erbacher » Tue Jun 06, 2017 11:00 pm

Ok so now I went back and looked at the dimensions of 14.4 inches 17.4 inches and 12.3 inches given by the jbl enclosure chart and I must have missed the portion of the chart which shows port dimensions (this must have been why Waldo put all those pics up haha don't I feel dumb)... so if the cab is open back this means the depth of the cab must be changed right? I know other sites on the net for building cabs say to have the length X widthX height=1728 but I'm having difficulty in figuring out what that means in Hz
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Re: HT style 1x12 dimension question with regards to the bac

Postby playingdead » Wed Jun 07, 2017 5:56 am

I'm certainly no expert, but it would seem to me that the dimensions of the cabinet (volume) is critically important in a sealed enclosure. The port size would be a way of "tuning" the enclosure to get the optimum response out of a conveniently sized cabinet. When you are dealing with an open backed cabinet, I would suspect that once it's "open" enough the dimensions and size of the opening cease to have much effect on how the speaker sounds, particularly from in front and at the sound pressure levels these speakers are usually driven at (with a microphone an inch away, no less). It would seem to be more about building the cabinet to be strong enough to support the heavy JBL speakers and hold the baffle.

Were the original wall of sound cabinets sealed? That's my memory of photos I've seen. I expect they came to the conclusion that Garcia's cabinet sounded best open in the back.
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Re: HT style 1x12 dimension question with regards to the bac

Postby ac4468 » Wed Jun 07, 2017 7:40 am

And not to complicate things but it's not just the size of the opening. In ported cabinets, the diameter, DEPTH of and number of ports as well as overall volume have an affect. I would tend to think that once the back is open a certain amount there's not a huge difference.
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Re: HT style 1x12 dimension question with regards to the bac

Postby playingdead » Wed Jun 07, 2017 9:00 am

Designing audio speakers, studio monitors, etc., it's about getting as accurate and flat a response as possible over the widest frequency range. Difficult to accomplish. Lots of engineering and measurements and waveform studying and analysis.

With guitar cabinets and speakers, it's about coloring the sound in a way that you find pleasing to your ears. If you plug an electric guitar straight into a recording desk and crank it up over studio monitors, it sounds awful ... bright and tinny ... not unlike Mr. Garcia's reviled 94-95 Bolt tone. So the cabinet dimensions, open or closed back, ports, speakers used, ohms they are run at, wattage they are played at, how the tubes and preamps are voiced, tone controls, etc. ... that's all modifying that thin, tinny electric guitar tone, beefing up certain frequencies, rolling off high end, fattening the notes and harmonics with distortion. Completely open palette of possibilities. A 6" oval coaxial speaker with a low wattage amplifier, as allegedly used by Jimmy Page early on in the studio, or the 32 Marshall heads and cabinets favored by Yngwie Malmsteen. It's whatever works for you.

Luckily, people like Waldo have revealed the details to acquiring Mr. Garcia's vaunted tone. Follow the path.
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Re: HT style 1x12 dimension question with regards to the bac

Postby Erbacher » Fri Jun 09, 2017 10:15 am

Thanks for all the posts...to be really clear I have yet to see a post with exact dimensions of Jerry's cabs and from what I can see, it looks like they were all a little different...so this means that it either doesn't matter a huge amount or it was a work in progress to find the sweet spot...I recently read a post about how less wood gives a sweeter and more scooped type sound, so at least one person on this forum has had two cabs with different dimensions and the same speaker and can attest to what that does to the sound...from a mathmatical standpoint the dimensions of the cab all relate to a potential for a standing wave to exist if the cab has parallel walls, which is somewhat unavoidable unless the cab is made with geometry that tries to get around this...so from my perspective it's important to get a good grasp on the dimensions rather than making random choices based upon the fact that it's open backed...i.e it will still have an impact on the overall cab tone...so for now I am going with the 14.4 dimension bc that was the smaller dimension for the baffle given on the jbl chart for cab dimensions, and I'm using the golden mean ratio to find the cab depth...I don't know if Tracy wants to chime in here with his findings but I thought I would at least share what my philosophy is in choosing my dimensions...it could be that Jerry had his cabs made slightly different to get more/less mids over the years depending on his rig and what was going on with the electronics...wouldn't it be nice to just have the dimensions? I saw a post with Rick Turner talking about wall of sound dimensions being based upon the cube root of 2...
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Re: HT style 1x12 dimension question with regards to the bac

Postby kurt eye » Wed Jun 14, 2017 3:23 am

waldo041 wrote:Image

Image

Image

~waldo


I assume those are K-120s in Jerry's cabs? Interesting. I was under the impression that Jerry went from using D-120s straight to E-120s.
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Re: HT style 1x12 dimension question with regards to the bac

Postby Searing75 » Wed Jun 14, 2017 4:33 am

I believe he used K's from the early mid 70's until around 80? The K's have the best sound of the D,K, or E. IMHO.
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Re: HT style 1x12 dimension question with regards to the bac

Postby Erbacher » Sun Jun 25, 2017 2:08 pm

I ran across this on the gear page...a post by Steve Kimock relating to cab construction and talking to Jerry about it...Mar 4, 2014


"Quick Jerry Garcia story as relates to cab building and this thread. .
I did a bunch of speaker and cabinet related experimentation years ago, pretty nit-picky stuff, materials, dimensions, speaker mounting, lots of various baffle board minutia, every possible detail, just to see where it might take me.

I ran my entire program past Jerry, to see if he'd have anything to add, and at the end of my rap asked him "what are your requirements for a speaker cabinet?"
He said, and I quote: "It just has to be heavy enough to hold the speaker".

That's it. If it doesn't collapse under its own weight or fall over, and the speaker doesn't fall out, you're good to go.
The Hard Trucker's stuff back in the day was obviously overbuilt to withstand the constant rough handling of touring, but no more so than that. Just real solid, no BS construction.
The particulars of the design dimensions for the multiple 12 inch guitar cabs were just "Twin Reverb on its side without the chassis", extrapolated up to however many drivers tall the thing needed to be and deep enough to not fall over.
That's it.

So, no super secret fairy dust there. Just two Twins stacked sideways sturdy enough to hold a couple JBL's and deep enough not to fall over.

So yeah, you can build that yourself or have any decent local woodworker build it for you.
I have a beautiful 2x15 JBL guitar cab similarly constructed by my local woodworking guy, and it came in around 200 bucks for materials and labor.

Nothing wrong with that if you don't have the scratch for the Hard Trucker cab.
They are pricey."
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Re: HT style 1x12 dimension question with regards to the bac

Postby paulinnc » Wed Jul 05, 2017 7:07 pm

Erbacher wrote:I ran across this on the gear page...a post by Steve Kimock relating to cab construction and talking to Jerry about it...Mar 4, 2014


"Quick Jerry Garcia story as relates to cab building and this thread. .
I did a bunch of speaker and cabinet related experimentation years ago, pretty nit-picky stuff, materials, dimensions, speaker mounting, lots of various baffle board minutia, every possible detail, just to see where it might take me.

I ran my entire program past Jerry, to see if he'd have anything to add, and at the end of my rap asked him "what are your requirements for a speaker cabinet?"
He said, and I quote: "It just has to be heavy enough to hold the speaker".

That's it. If it doesn't collapse under its own weight or fall over, and the speaker doesn't fall out, you're good to go.
The Hard Trucker's stuff back in the day was obviously overbuilt to withstand the constant rough handling of touring, but no more so than that. Just real solid, no BS construction.
The particulars of the design dimensions for the multiple 12 inch guitar cabs were just "Twin Reverb on its side without the chassis", extrapolated up to however many drivers tall the thing needed to be and deep enough to not fall over.
That's it.

So, no super secret fairy dust there. Just two Twins stacked sideways sturdy enough to hold a couple JBL's and deep enough not to fall over.

So yeah, you can build that yourself or have any decent local woodworker build it for you.
I have a beautiful 2x15 JBL guitar cab similarly constructed by my local woodworking guy, and it came in around 200 bucks for materials and labor.

Nothing wrong with that if you don't have the scratch for the Hard Trucker cab.
They are pricey."


That's a great Kimock, Jerry story. I figured as much from looking at pictures of the cabs that there wasn't anything super special about them other than they were built to be strong.
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