URGENT: Speaker design help needed! Altec content!

ICTWoody

No longer a junior member
Hey gurus.

You might remember those DIY Altecs I picked up a few months back.They had Altec. 414-16c’s and some Goodman’s parts in them. Well I’m about to have some new front and rear baffles CNC cut. I had sent the cut path to my vendor and dropped off the plywood... but I just realized I didn’t even think about a port!

Short request is I need to know what to add to my cut for porting? I know they need it... specs of the build are:

Cabinets: OD’s are 24x30x15. 3/4” ply. ~ 5cu/ft
Woofer: Altec. 414-16C’s (original)
Horn: Emilar EH800
Compression Drivers: 802-16G
Networks: JE Labs network as used in the 802/414/32/614 builds
Will be damped with OC703 on the back, bottom and one side like my 614’s

Here is the schematic of the front view. I’d prefer the aesthetic of a front port like the 614 cabinet that is just 3/4” deep and a rounded rectangle. But I’m open to whatever would be best for cabinet tuning.

Thanks!

- Woody

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Thermionics

Post Whore In Training
Would the standard 7x2" slot as used on the 614 cabinet work here? I'm not as familiar with the 414-16c driver.
 

je2a3

Senior Member
FWIW, my Altec 753C cabinet is roughly 30” x 21.5” x 14.5” and has a 7” x 2” vent. I’ve also repurposed a pair of Altec Madrid cabinets that housed 15” biflexes by replacing the front baffle with a 414 cut out + 7” x 2” vent.
 

ICTWoody

No longer a junior member
Would the standard 7x2" slot as used on the 614 cabinet work here? I'm not as familiar with the 414-16c driver.

Perhaps... but these are about 1.5 cu/ft bigger than 614's... so I wasn't sure what is acceptable?

I don't really understand "cabinet tuning"... that's why I was reaching out. I might just move forward with having the front baffles cut without a port and worry about porting from the bottom. It would be clean looking that way.

- Woody
 

Audionut

Next Round Is On Me
I bottom slot ported my 604E cabinets and am quite happy. You could tube port and tune to your liking by adjusting the tube length?
The 614 has a 7x2 port, 612 has a 7 3/4x3 port. If you are set on a slotted port I’d start with the 7x2 and increase as needed. There are also port size calculators.
 

ICTWoody

No longer a junior member
I bottom slot ported my 604E cabinets and am quite happy. You could tube port and tune to your liking by adjusting the tube length?
The 614 has a 7x2 port, 612 has a 7 3/4x3 port. If you are set on a slotted port I’d start with the 7x2 and increase as needed. There are also port size calculators.

How do you know what frequency to tune the box to?

- Woody
 

John Frum

Secret Society Member
I was able to find T/S parameters for the 414-8C, and I'd have to assume that the 16C is similar.

Basically, tuning is going to be a compromise. The lower you tune, the lower down your "knee" is going to be (which you want), but the lower your output is going to be from roughly 200 Hz until that knee. If you tune higher, you get flatter response and better power handling (which you want), but the rolloff is going to start sooner.

A 2" x 6" hole in the cabinet with rounded corners is going to get you tuned to about 40 Hz. That'll net you a knee at about 45 Hz, an F6 of 37 Hz, and about a 3 db dip centered around 75 Hz.

A 2" x 10" hole in the cabinet with rounded corners is going to get you tuned to about 48 Hz. The knee moves up to about 54 Hz , the F6 goes up to about 42 Hz. The results of the pre-knee "dip" are mitigated substantially, and you're going to get a nice little 3 db boost right in the "chest thumping" frequencies. Casual listening might give the impression of more bass than the lower-tuned cabinet, even though the lower-tuned cabinet will have about a 6 db advantage on everything below 40 Hz.

If it were me, I'd probably split the difference.

All simulations run in BassBox Pro.
 

mhardy6647

Señor Member
At the risk of sounding like I know and understand far more than I actually do :confused: :o -- and without offering any concrete guidance :tongue: -- I have heard it said that vintage drivers (woofers) like the Altecs, designed in a pre-TSP universe, don't necessarily play by the same rules that we expect of woofers in 2020 AD. Empirically, it could be argued that the spectrum of appropriate enclosure designs for, say, a 515B may not (heh, here comes a TSP pun!) align with expectations based on T/S parameters. This is not to say that the drivers are disobedient unto T/S -- but it should be borne in mind that T/S parameters do arise from a model.

1601986976523.png

Now, mind you, I have deliberately backpedaled and vigorously weasel worded the above, but I still felt it was worthy of mention. 🧐

Oh, and YMMV. ;)
 

ICTWoody

No longer a junior member
If it were me, I'd probably split the difference.

So what you're saying is a 2"x8" hole in the cabinet with rounded corners is a good starting place? Cool.

I've told the vendor to move forward with the baffles, I'm going to port in the bottom.

I like the slot ports cause that is what Altec did a lot, but should I consider using PVC round port tubes so they could be friction fit and changed easy if we need to adjust?

I really think I'm overthinking this and I should just use a 2"x8" hole and call it good.

- Woody
 
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