URGENT: Speaker design help needed! Altec content!

mhardy6647

Señor Member
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?

... and there are always (and I am not being entirely facetious now, honest!) some quick and dirty port fine tuning options including at least two classics:

1) stuffing a (typically) round tube/cylinder type of port with straws (although those may be hard to find in 2020!).
2) ad hoc aperiodic damping by stuffing old socks, cotton batting, etc. in the port. Be creative!


The perfect is the enemy of the good.

🧐
 

Audionut

Next Round Is On Me
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
You can always add louvers for fine tuning.;)
 
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
Since we are compromising anyway, why not start with a 2” X 7” like in the 614? Speaking of which, has anyone modeled the 614 (3.2 cu ft, 0.75” x 2” x 7” rounded corner port) in Bassbox Pro?
 

John Frum

Secret Society Member
Since we are compromising anyway, why not start with a 2” X 7” like in the 614? Speaking of which, has anyone modeled the 614 (3.2 cu ft, 0.75” x 2” x 7” rounded corner port) in Bassbox Pro?

Next time just @ me. All speaker designs are compromises.

The difference between a 2" x 8" x 3/4" port and a 2" x 7" x 3/4" port in Woody's cabinets is a tuning frequency of 45 Hz vs. 43 Hz. This is hardly noticeable, and falls into the category of distinctions that will be swamped by cabinet damping and placement.

A 2" x 7" port is definitely on the spectrum I laid out of possible tuning schemes for Woody's cabinets, but tuning is dependent on both port dimensions and cabinet volume. Starting with a 2" x 7" on the basis of, I guess, being good enough for the 614, doesn't strike me as sound. Such a port tunes the 614 to about 54 Hz, but tunes the 5 cu. ft. cabinets to about 43 Hz. And that works fine, but getting there because you selected the port size based on the 614, rather than any understanding of cabinet tuning, is a happy accident.

If you're looking for a response like the 614, the alignment that's going to get you the closest in 5 cu. ft. cabinets is actually the 2" x 10" port that tunes them to 48 Hz. The curves are really similar, but the larger cabinets have better extension.
 
Next time just @ me. All speaker designs are compromises.

The difference between a 2" x 8" x 3/4" port and a 2" x 7" x 3/4" port in Woody's cabinets is a tuning frequency of 45 Hz vs. 43 Hz. This is hardly noticeable, and falls into the category of distinctions that will be swamped by cabinet damping and placement.

A 2" x 7" port is definitely on the spectrum I laid out of possible tuning schemes for Woody's cabinets, but tuning is dependent on both port dimensions and cabinet volume. Starting with a 2" x 7" on the basis of, I guess, being good enough for the 614, doesn't strike me as sound. Such a port tunes the 614 to about 54 Hz, but tunes the 5 cu. ft. cabinets to about 43 Hz. And that works fine, but getting there because you selected the port size based on the 614, rather than any understanding of cabinet tuning, is a happy accident.

If you're looking for a response like the 614, the alignment that's going to get you the closest in 5 cu. ft. cabinets is actually the 2" x 10" port that tunes them to 48 Hz. The curves are really similar, but the larger cabinets have better extension.

Thanks!

@John Frum could you model the Altec 614 vs. 9849 enclosures? They are both 3.2 cubic feet. The 614 uses a simple port, rectangular with rounded corners, 2” x 7” x 3/4”. The 9849 is the same dimensions (other than internal bracing and the horn/driver) with 2 x 3” dia x 6” d round ports. The actual ID is slightly smaller, but it seems in the Altec world the drivers tolerate a wide range of alignments.

Many thanks in advance,
R
 

John Frum

Secret Society Member
Thanks!

@John Frum could you model the Altec 614 vs. 9849 enclosures? They are both 3.2 cubic feet. The 614 uses a simple port, rectangular with rounded corners, 2” x 7” x 3/4”. The 9849 is the same dimensions (other than internal bracing and the horn/driver) with 2 x 3” dia x 6” d round ports. The actual ID is slightly smaller, but it seems in the Altec world the drivers tolerate a wide range of alignments.

Many thanks in advance,
R

Based on your internal volume and port dimensions, the 614 is tuned to 54 Hz and the 9849 is tuned to 35 Hz. Very different presentations.

Traces generated using 414-8C T/S parameters. Yellow is 614. Red is 9849. Despite the lower output under 48 Hz, I'd likely prefer the punchier 614. Different drivers will yield different results.

Altec Boxes.JPG
 
Thanks @John Frum.

That makes perfect sense. The 614 was originally designed when the 414A was current. That driver has a rising response relative to the 414-8C and would benefit from the boost in the “chest lock” region. Add you noted this curve seems to be one the Altec driver likes. The 614 was also designed as a general purpose utility enclosure. It was used in a variety of environments and could use the boost to flatten things down to 50hz.

The 9849 was intended as a control room monitor. I can’t find it, but there is an Altec advertisement showing the 9849A soffit-mounted in in the control room. I would expect bass reinforcement from the near boundary mounting of the wall and ceiling. This would appear to complement to falling response below 200hz. In fact, the response below 200hz looks pretty much identical to my Yamaha NS-690 sealed monitors. I would expect both speakers to sound a bit lean in free space but to fatten up with some boundary reinforcement.

Would you be willing to run the 414A thrPugh the same simulation?

Thanks,
R
 

mhardy6647

Señor Member
I can’t find it, but there is an Altec advertisement showing the 9849A soffit-mounted in in the control room. I would expect bass reinforcement from the near boundary mounting of the wall and ceiling.
I took that as a challenge ;)

I failed, but I did find some cool old Altec ads, etc.

e.g.,

1602362021920.png

1602362067778.png
source: https://worldradiohistory.com/hd2/I...974-12-OCR-Page-0051.pdf#search="altec 9849a"
 

Anyone notice anything missing here?

You’ve provided me with another piece of the puzzle: we can infer from the first ad that the 9849A first came out in 1974.
 
Based on your internal volume and port dimensions, the 614 is tuned to 54 Hz and the 9849 is tuned to 35 Hz. Very different presentations.

Traces generated using 414-8C T/S parameters. Yellow is 614. Red is 9849. Despite the lower output under 48 Hz, I'd likely prefer the punchier 614. Different drivers will yield different results.

View attachment 28395
@John Frum I looked at the 9849A drawing again and scaled the port tubes at 2 x 3” ID x 5.5” L. I can infer what the response change would be but it would be interesting to see how minor port length tweaks will change response.
 
I would, but you'd have to rustle me up some T/S parameters. I don't have that one.
I Measured my 4 414A's and this is where they came in. if something looks off, let me know.

Driver 1 -
spl = 91.5
R(e) = 11.53
F(s) = 29.61hz
Q(ts) = .3457
Q(es) = .3816
Q(ms) = 3.675
L(e) = 1.256 mH 10k
M(ms) = 79.05 g
V(as) = 4.8 cf

Driver 2 -
spl = 93.33
R(e) = 11.68
F(s) = 26.24 hz
Q(ts) = .194
Q(es) = .213
Q(ms) = 2.141
L(e) = 1.107 mH 10k
M(ms) = 83.39 g
V(as) = 5.8 cf

Driver 3 -
spl = 90.94
R(e) = 12.05
F(s) = 26.92hz
Q(ts) = .22
Q(es) = .238
Q(ms) = 2.813
L(e) = 1.171 mH 10k
M(ms) = 132.4 g
V(as) = 3.5 cf

Driver 4 -
spl = 93.3
R(e) = 11.79
F(s) = 26.24 hz
Q(ts) = .2331
Q(es) = .2468
Q(ms) = 4.2
L(e) = 1.468 mH 10k
M(ms) = 72.5 g
V(as) = 6.6 cf
 
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