A Thiele or a ported cabinet taking Thiele-Small parameters into consideration acts more like an open back cabinet in regard to damping.
I have to take issue with this quote, as it is not entirely correct -
A ported enclosure actually exerts greater control on the speaker's cone at and above the resonant frequency of the driver/enclosure.
No, it doesn't.
View the speaker as a compressor. The cone is a diaphragm. The cone moves backwards into a sealed cabinet, internal pressure goes up slightly. Cone moves forwards in a sealed cabinet, internal pressure drops slightly.
Cut a hole in the enclosure, the compressed air is free to move in or out of the opening. Less damping even if the port is incredibly restrictive. A port will flow more than a seal, that's simple physics.
It's the same principles as applied to automotive mufflers. The trick with an automotive muffler is to achieve attenuation without backpressure. For our purposes we're interested in uncorking the muffler, amplification instead of attenuation.
respectfully, I disagree. At least in the case of ported cabinets. What you are describing is an open-back cab, in which case you are 100% correct.
What I failed to explain clearly is that at frequencies exceeding those of the ported enclosure's tuning frequency, the ported box exerts greater control over the cone of the speaker than a sealed box.
Watch two enclosures tuned to 50HZ, one sealed and one ported(and tuned to 50HZ). The ported enclosure's cone will appear to almost not move in comparison to the sealed enclosures cone. this is the effect of resonance and tuning on the speaker's cone.
What I was attempting to point out is that a ported enclosure's speaker will move MORE below the tuning frequency of the box - in this case the TL806 - which is about 75HZ. Above that frequency the TL806 will control the speaker better than the equivalent sealed box.
Btw - I'm not making this up, this is ancient Theile-Small tuned enclosure design stuff, with which I designed high output subwoofers professionally for a decade or so.
BobW wrote:Henry, that's a very cool looking cab! How do you like the tone?
Before the end user got it I put a WGS British lead 80 in the bottom hole and it sounded fantastic. The owner loves it too..... The cool thing about those old Fender cabinets is the center divider board so It's like having 2 separate cabinets.
FWIW a closed back cabinet acts like a single pole (6dB rolloff) high pass filter. A properly designed vented cabinet reacts like a 2 pole high pass filter (12dB roll-off). The advantage is a lower bass knee frequency (-3dB) but with a sharper cutoff.
You can tweak the size of the cabinet and the port tuning to achieve Butterworrh, Chebychev , 1dB dips, 3 dB dips and host of other responses.
Located in the St Croix River Valley- Afton, MN
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I have a question. I gather that the Theile TL806 plans are designed specifically for an EVM12L speaker. Will that cabinet as designed work with any other speakers that are available today ( I heard rumors that an Eminence Delta 12 might) or does the design have to be tweaked for the speakers you are using? How do you figure out how to tweak the cabinet for your speaker of choice if you don't have a Phd in Physics? I was thinking of trying a G12H65 or a Weber Ceramic Blue Dog in there.
pine wrote:I have a question. I gather that the Theile TL806 plans are designed specifically for an EVM12L speaker. Will that cabinet as designed work with any other speakers that are available today ( I heard rumors that an Eminence Delta 12 might) or does the design have to be tweaked for the speakers you are using? How do you figure out how to tweak the cabinet for your speaker of choice if you don't have a Phd in Physics? I was thinking of trying a G12H65 or a Weber Ceramic Blue Dog in there.
The Theile is a tuned port design, so that means the cabinet volume, port size and port depth are tuned to the parameters of the driver (cone compliance, mass and so forth). So you will definitely find some speakers do not work at all in those cabs. (WGS BL-80 for example resonates to the point of self destruction, so don't try this at home!) Ideally, you should take you physics degree and a tool like WinISD Pro (and the T-S parameters of the speaker you want to try, if available - thanks for nothing Celestion!) and tune the cab.
However, with the port cover off, I would describe the tuning as 'loose' and it seems to work with a variety of speakers. Without your physics degree, my advice is to try it and see.
"Let's face it, the non HRMs are easier to play, there, I've said it." - Gil Ayan... AND HE"S IN GOOD COMPANY!
I am using a 212 version of the 806 design for my steel guitar. Fortunately, I had a couple of NOS EV-12S speakers. Back in the day, I built a pair of them for PA mid's. I can't find the photo of it, but here is a crude drawing.
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So your 212 is just a double 806 but with a divider in the middle?
Did you compensate for the displacement of the divider board?
This has probably been stated before but what do those cabs do for the EVM 12L?
How do they sound?
I mean, does it tighten up the bass, make it punchy and how is the high end of it?
I have two EVM 12L's in an open back 2 x 12 (Lopo) it sounds alright but I know they could probably sound better.
The problem to me would with a double 806, that thing has to weigh a ton!
Probably as much as 1960 412.
[quote="glasman"]FWIW a closed back cabinet acts like a single pole (6dB rolloff) high pass filter. A properly designed vented cabinet reacts like a 2 pole high pass filter (12dB roll-off). The advantage is a lower bass knee frequency (-3dB) but with a sharper cutoff.
Unforntunately Glasman - you err by a factor of 2.......
A close cab rolls off by 2nd order - or 12 dB, whereas a BR rolls of as a 4th order or 24 dB.....
The shape of the rolloff around the knee is determined by the Q value of the alignment, the "filter" order sets the asymptote of the ultimate rolloff curve.
Modern loudspeaker theory and simulators, ca give quite accurate predictions of a design, provided the T/S parameters are accurate. Unfortunately a lot of the more popular guitar speakers don't have T/S parameters, and a lot of the few that have, are highly inaccurat and unreliable.
The open back cab's as shown, cannot be calculated as BRs - more like a "cut-and-try" job... but that doesn't mean they cannot sound good.
Structo, my cabinet is really 1/2 of the 806Q, 412 EV design, I think I have that builder plan, it will give you the spec's.
Sorry posted the wrong one, try again.
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That's nice Jaysg, I think using wood, and rear mounting the speakers, would make it a lot more portable. I do think that the rear, raised cleat serves a useful purpose, possibly forcing the sound waves more toward the outer ports.
If I were to build one to transport often, I think I would try 1/2 plywood, and dampen the thing with bedliner material.
When I built the originals, our PA had 13 cu ft bass bins,(TL405), with 18" EV proline drivers. I used EV HR9040 horns for the high freq. It seems we crossed over at 500 hz, and 1200 hz. It was a great R&R system, but when we later formed a country band with my wife's sisters, I downsized to 7 cu ft bass bins,(TL505), no mids, and the EV horns, crossed over at 1200 hz. The younger sister could almost break glasses with her voice.
One of the mid boxes went to a steel player we used for a while, when he blew his BW, and I didn't have a 15" to load into his Nash 1000. I brought a mid down for him to play through, and after the 2 week gig he told me to keep his pay, he just wanted the cabinet! When I started to attempt the pedal steel I cobbled another together from materials on hand, and it sounds great.
How do you like the tone?
