Tl806 ported cab with different speaker

[GAStan]

Looking into this I learned much of the technology and approach has changed since I dabbled in it, not surprising considering its been a bit over 40 years... All I can find is calculators or ads, not the formulas to do the actual calculations longhand. Such is the state of today's 'net.

I was hoping @solderhead would stop by, he's MUCH more knowledgeable about this than I.

[didit]

If i enter the evm12l speaker specifications the program gives me a suggested cabinet volume that is much bigger than the tl806 too.

With these EVM12L parameters as input:

• Vas = 82.9 lts
• fs = 55 Hz
• Qts = 0.232
• D = 9.8 in

that tool computes:

Dimensions

• Vb = 0.47 ft3 = 13.36 lts = L x W x H
• f3 = 122.81 Hz
• fb = 66 Hz
• Dv = 4 in = 10 cm
• Lv = 13.19 in = 32.33 cm

Eyeball quick review suggests it's close ballpark for an 806 cabinet. The vent can take various shapes, just preserve volume with length. The tool doubtless renders circular tubes for simplicity. How did you conclude this was a desirable path? Earlier in your thread a suggestion was offered of a poor match up -- round peg vs square hole. Experience and the tool's calculations support that. The popular Dumble design single 12" oval open back maybe?

Best ..

[Mikante]

14lts for the cabinet volume won t even be big enough for the speaker only.
I don t remember why it gave me a 80 liters box the first time i used the program, probably i mistyped some of the evm12l values.
Anyway, i don t know about the oval open back, thank you for the suggestion, i will take a look into it.
I maybe have the chance to get my hands on an eminence em12 which is a clone of the evm12l, same specification apart from the 1.27mm Xmax, i understand a speaker with any lower value in this area will benefit less of the ported design. The jensen tornado has even less Xmax.

[didit]

14lts for the cabinet volume won t even be big enough for the speaker only.

That page's "result" presentation is somewhat misleading. One needs to dimension HxWxL of the outside of cabinet with the computed volume plus the space for the speaker, the full volume of the port plus all of the materials that make up the enclosure (panels/braces/etc). That is, our 14 litres is all the remaining internal open space within once all is subtracted.

I maybe have the chance to get my hands on an eminence em12 which is a clone of the evm12l, same specification apart from the 1.27mm Xmax

That'll be way closer. Doubtless an 806 based design could be tweaked around minor differences, or even simply left as is. The EM12N spec shows an Xmax of 2.2mm, which is closer even to EV's 3.3mm. I've yet to listen to one but reviews have been generally positive. After a few duds and several years of effort, Eminence seems to have worked out how to use neomagnetics for their motors.

..

[nuke]

interesting thread, as I have a pair of Altec ER-12 speakers stashed away I should do something with.

The T/S params are a little different than EV12L, but it is a similar cast-frame heavy duty speaker.

[Mikante]

14lts for the cabinet volume won t even be big enough for the speaker only.

That page's "result" presentation is somewhat misleading. One needs to dimension HxWxL of the outside of cabinet with the computed volume plus the space for the speaker, the full volume of the port plus all of the materials that make up the enclosure (panels/braces/etc). That is, our 14 litres is all the remaining internal open space within once all is subtracted.

I maybe have the chance to get my hands on an eminence em12 which is a clone of the evm12l, same specification apart from the 1.27mm Xmax

That'll be way closer. Doubtless an 806 based design could be tweaked around minor differences, or even simply left as is. The EM12N spec shows an Xmax of 2.2mm, which is closer even to EV's 3.3mm. I've yet to listen to one but reviews have been generally positive. After a few duds and several years of effort, Eminence seems to have worked out how to use neomagnetics for their motors.

..

I didn t know that 14 liters had to be the the empty space inside the box, good to know.
Opinions about the em12 are very positive indeed but there isn t much talking about the neo version. I should dig more into it, sure a cabinet with that one would be easier to carry around.

[Mikante]

interesting thread, as I have a pair of Altec ER-12 speakers stashed away I should do something with.

The T/S params are a little different than EV12L, but it is a similar cast-frame heavy duty speaker.

Altec ER-12 TS params.jpg

The Xmax value showes the fisical ability of the speaker to push air back and forth. Lower frequencies need more escursion to be pushed at the same volume of the higher frequencies. The ported cabinet is all about that, air coming out the vents carrying out the lower frequencies information. A speaker with such a low Xmax will not be able to push a lot of air out of the vents and for what i ve just learned, the bass would sound dull and unfocused and probably not even in the desired cabinet low tuning plan.

[nuke]

I'll have to go pull them out, it is possible they're ER-12L or ER-12S. I got them in a 1965 Pro Reverb, they had so much excursion that the cones were hard slapping the baffle board all the time.

Someone had lightly modded the amp in the late 70's. I restored the amp back to its original circuit, left the 1970 50-watt Bassman output transformer, and put in a pair of Alltone 1250's. It sounds killer good.

Here's where I got the T/S params:

http://alteclansingunofficial.nlenet.ne ... Small.html

Great resource for Altec speakers.

[solderhead]

The Xmax value showes the fisical ability of the speaker to push air back and forth. Lower frequencies need more escursion to be pushed at the same volume of the higher frequencies. The ported cabinet is all about that, air coming out the vents carrying out the lower frequencies information. A speaker with such a low Xmax will not be able to push a lot of air out of the vents and for what i ve just learned, the bass would sound dull and unfocused and probably not even in the desired cabinet low tuning plan.

X and Xmax are different parameters.

X tells us the actual displacement of the speaker, while Xmax tells us the physical excursion limitations of the speaker -- Xmax is not linearly related to how much air is being moved as the relationship between displacement and air movement is a function of frquency, which is always changing in a loudspeaker. Xmax doesn't tell us how much air is being moved, it's actually the Thiele-Small formula that tells us that. What Xmax really tells us is how far the cone assembly can be displaced before it seizes.

It may seem counter intuitive, but at the box/port tuning frequency, the speaker and the air in the cabinet form a resonant circuit, such that the port produces the air movement and the speaker isn't moving much if at all -- X (linear excursion) is related to air movement when you're well above the box frequency, and it gets smaller as you approach the tuning frequency where X reaches a nadir value as the port becomes responsible for moving the air, not the driver. Then, if you exceed (below) the lower limit frequency of the box, X rises exponentially ... until you exceed the excursion limit of the driver. When X exceeds Xmax the cone freezes, killing the speaker. That's the main hazard that you have to deal with when replacing a driver in a T-S cabinet with a driver that the cab wasn't designed around. The driver bottoms and displacement increases exponentially. Because the increase in excursion is exponential you don't have much warning before you waste your driver.

[cdemike]

Really interesting thread. I'm curious how Mikante's cab turned out. I've been flirting with the idea of trying to tune a 2x12 to a frequency matching that of a closed 4x12 with some heavy-magnet Greenbacks (I'm sure I'll be the first to try to blaze that trail...).