Looking for Electro Voice Sentry III Speaker Port Length

[jorb]

Looking for Electro Voice Sentry III Port Length?
Thanks,

 

[totem]

jorb
Looking for Electro Voice Sentry III Port Length?

jorb
The EV Sentry III series I port length is 10 inch's, front baffle to rear of port
for both of the 2 ports.

Front baffle to inside rear of cabinet is 18"

Can't recall are you building cabinets or modifying?

 

[jorb]

Back in the early 80's I worked for a wood door manufacture.
They always had some nicked up doors laying around.
I thought those wood doors, being 1 7/8" thick would make great speaker cabinets.
I knew the EV Sentry III's had a really nice bass sound.
So I built a pair using solid core wood doors.
A solid core wood door is really not solid wood all the way through.
A solid core door, is like saw dust mixed in glue then sandwiched between 2 sheets of 1/8" veneer.
The only solid wood in a solid core door is the 2'' rails around the outside edges, for the hinges and door knob strike.

Back then, I talked to a EV engineer and he gave me the port sizes and the cabinet volume for the B15, 815-9062 Sentry III woofer.
I then bought a pair of replacement Sentry III woofers from the EV engineer.
When I finished the cabinets the woofers had a really nice sound, all you heard was the woofer.
I think it was do to the thickness of the cabinet material.
I sold the cabinets in 1989.

Right now, I'm trying build another pair but I only could remember the cabinet volume.
I called EV and this is what they sent me.

Box Volume (gross) = 7.25 ft3
Box Volume (net) = 6.93 ft3

Vent #1 opening = 4" H x 7 7/8" W (used in both normal and step down modes)
Vent #2 opening = 5" H x 7 7/8" W (used in normal mode, covered in step down mode)

Vent length (both) = 8 1/4"

815-9062 (TS parameters)
fs = 40 Hz
Qts = .380
Vas = 6.8 ft3
Xmax = .25 in

Everything looks correct but the Vent length seems to me to be shorter than I remember.
So I post this question on Audiokarma. "Looking for Electro Voice Sentry III Speaker Port Length"

EV made 2 different types of Sentry III cabinets, Series 1 and Series 2
I'm thinking the above port/vent dimensions might be for the Series 2 cabinets.
The EV engineer back in the early 80's may have given me the dimensions for the Series 1 cabinets.
The volume between the two cabinets would not change because they use the same woofer.
I think both cabinets Front baffle ports heights are the same at 4" & 5" inches.

On Your EV Sentry III series I
What is the width and height dimensions of the Front baffle port openings?
What is the width and height dimensions inside the ports?

 

[totem]

jorb

On Your EV Sentry III series I
What is the width and height dimensions of the Front baffle opening?
What is the width and height dimensions inside the ports?

As I recall the series I and II visually are quite different and very noticeable
when looking inside from the rear.

Front baffle [inset] 25.5" wide 19.25" high

Width of port [inside] 7" height 4.5"

 

[jwrauch]

I will be interested to see how these turn out. I've always thought a Century III build would be a cool project. I have most of the components, just not the exact woofers. JOHN

 

[jorb]

As I recall the series I and II visually are quite different and very noticeable
when looking inside from the rear.

Front baffle [inset] 25.5" wide 19.25" high

Width of port [inside] 7" height 4.5"

Sorry about the misunderstanding.
What I meant to say was:
What is the width and height dimensions of the 2 Front baffle port openings?
What is the inside height dimension of the lower port ?
To better understand what dimensions I need check out thie below picture.


A. Front baffle ports opening Width (both of the 2 ports)
B. Inside, ports Width (both of the 2 ports)
C. Inside, ports total Height (both of the 2 ports)
D. Front baffle bottom port opening Height
E. Front baffle top port opening Height
F. Ports divider Height
G. Front baffle bottom port, top of opening to cabinet floor Height

You told me in previous post the port length is 10 inch's, front baffle to rear of port for both of the 2 ports.

The front baffle port openings dimensions are different than the inside cabinet port dimensions.
What dimensions would you use, inside port or front baffle port openings?

 

[jorb]

I will be interested to see how these turn out. I've always thought a Century III build would be a cool project. I have most of the components, just not the exact woofers. JOHN

To make a EV Sentry III woofer.
An EV15L or 15B frame may be re-coned with the DL15W cone kit.
Read this POST
This is the 2nd person that I heard say that.

 

[BobbyBluz]

The lower ports on my Sentry III's are plugged for use with the SEQ Equalizer.

 

[jorb]

The lower ports on my Sentry III's are plugged for use with the SEQ Equalizer.

I posted this on one of your recent threads.
You CAN use the SEQ on the Sentry 500's also.
You might be able to use one SEQ box for both the Sentry III's and 500's
What part of WI did you find the blonde Sentry III's

 

[totem]

jorb

See following, should clear things up.

A = 6" 15/16 for both

B= 8" 9/16

C= 13" 1/4

D= 6" 3/16

E= 4" 1/2

F= 3/4"

G= 7" 13/16

 

[BobbyBluz]

What part of WI did you find the blonde Sentry III's

They found me and were in Racine.

 

[jorb]

totem

Thanks for the info. And the precise measurements. I really appreciate it.
I have come to the conclusion that the port/vent measurements that
EV sent me are for the Sentry III series II cabinets.

The other thing that I realized is the front baffle 2 port opening measurements
are really only the true measurements that matter, not the internal port measurements.
In fact the 1 1/2" vertical space on the right side of the ports could be filled in 9 1/4 inches to the back.
And the 1 5/8" horizontal space along the bottom port could be filled in 9 1/4 inches to the back.
By filling in the spaces probably will tune the port better, in turn making the bass sound better.
Check out Drawing Below:
Fill in colored areas with a solid type of material (wood), so internal ports matches the front baffle port openings.


So all that is need is two rectangular port tubes,

Sentry III series I
Top port------ 4 1/2" H x 7" W x 10" L
Bottom port--- 6 1/4" H x 7" W x 10" L (I rounded off some of your measurements + or - 1/16 of a inch )

Sentry III series II
Top port------4" H x 7 7/8" W x 8 1/4" L
Bottom port---5" H x 7 7/8" W x 8 1/4" L

If you need any help that pertains to EV or anything electronic let me know.

Thanks Again,

 

[totem]

jorb

I see what you mean regarding the port opening size versus the right side wall
offset/difference.

I went back and found another interesting point that does somewhat relate
to your 8 1/4 depth series II figure.

The left wall of both ports is shared with the woofer enclosure being 10"
The tops and bottoms of both ports again 10"
But the Right walls of both ports are roughly 8 1/4"

So the ports are wider internally than their openings and 1 wall

is 1 3/4 shorter than the other 3.

Do you think it worth while to both fill in the width versus opening difference
and extend the right wall to equal the 10" figure?

I presume you are doing some acoustic tuning calculations regarding the
woofer performance.​

 

[jorb]

totem

Take look at the below picture.

Looking at the Top View drawing
Is A and B two different lengths?
They both should be 9 1/4 inches long on the inside or close to that.
When you add the front baffle thickness 3/4" you get 10" total port length. D
The ports should match the openings, from the front of the front baffle 10 inches into the cabinet.

I think when the cabinet maker made them,
It was easier for them to rout out the openings (woofer, ports, tweeter & L-pad hole) on the front baffle all at once.
They wanted to reproduce them the easiest way and never bothered to fill in the sides. (More work).
The EV prototype test cabinets ports, in the lab, were most diffidently the same dimensions 10 inches deep all the way into the cabinet.
To save production cost things get a little fudged.

I was told that when they were designing the Sentry III,
It was the first time that anyone used Thiele Small parameters to build a speaker.
So when they were trying to figure out the ports dimensions.
Below is what I was told how they did it.

"Logic, seems to me, is that they were actively tuned, from a calculated rough guess
and then by moving the stack left until the top port was tuned, then moving the stack up/back until the bottom port was tuned.
You could make a similar volume test-prototype-cabinet with an adjustable(similar volume) front/port panel to tune it...or if you were really good with CAD you could just draw it in and it would calculate box volume and port frequency for you."

As far as if it would make a difference if you filled in the side wall and bottom. (Blue Areas)
I say yes. It can't hurt anything, if it does just take it out.
You might have to take out woofer to do it though.

They must of learned how to adjust the ports better as the years went on
because this is how the Sentry III series II Ports look like.
Still has that space along the cabinet wall though, but not on the bottom.
A top port board, a divider port board, a bottom port board.

 

[totem]

Looking at the Top View drawing
Is A and B two different lengths?

Yes oddly enough, see pic #1 {upper port} showing bottom of port being longer than exterior/right wall of port.

Pic #2 shorter wall being 7 7/16" in length.

Pic#3 {lower port} taken from inside looking to the front showing the internal
brace and port opening, again this exterior/right wall is shorter and equal to the one in the upper port.

 

[jorb]

totem;

Took me a couple minutes to figure out what I was looking at.
This is what I was talking about how the cabinet maker was cutting corners.
They should have used a side wall board that was 1 13/16 inches wider.
Or at lease match the the port divider board length. 9 1/4"
They did that because you don't see it. Cheapos

Does not really matter if you slide in some pieces of wood to match the openings.
Check picture:

Is board A hanging past the side wall also?

If I designed those cabinets I would of extended the front, side wall board all the way to the back.
It would of made them stronger.
But it would have added weight.

The B board, at first I thought could be one solid piece of wood.
But decided it would be better to put legs under it, trying to not change the cabinet volume.
If you make the pieces of wood tight fitting, that might be all you need to keep them inplace.
Just curious if you have woofer out, what is the inside depth of the side wall board on the left side of the cabinet?

In below picture the internal cabinets ports match the openings.

 

[totem]

jorb

Is board A hanging past the side wall also?

Yes board A is longer than the side wall.

The side walls being short is a head scratcher since its a small matter to
change the original dimension during the build,
where as other port changes would need additional material and steps.

Originally the Sentry III was priced higher than the Altec 19's by $200 or so and when you look at the cabinet changes overall, streamlining construction was evident in the MKII,s albeit slight modifications to the ports were being made.

The port changes are very simple to make and I will be adding them in the near future thanks for the suggestion.

Just curious if you have woofer out, what is the inside depth of the side wall board on the left side of the cabinet?

I do not have the woofer out at the moment as I am playing around with an active crossover setup.

 

[BobbyBluz]

In regards to your active crossover I finally got my Sentry III's powered up two days ago. The EV SEQ runs the low direct and the high through the box. I was experimenting with some Ashly and Behringer active crossovers as well as the SEQ yesterday. I also tried a few different power amp combinations with BGW and Crest amps. The best sound by far came with the SEQ, BGW 750B on the bottom and BGW 250C on top. I spent a few hours experimenting, if you have a SEQ or can clone one I'd go with that. The other crossovers just didn't sound "right" no matter how I had them configured and that included flipping phasing on the highs. The Sentry III's are awesome speakers and with SEQ and port plugs there's no doubt they're doing 28hz on the low end.

 

[totem]

I agree larger SS on the bottom works well I have used Aragon and a Yamaha PC 2602M.

I presume you were Bi-amping when you were going active?
Otherwise the ST350 needs compensation being a constant directivety horn.

Never did find an EQ, the SEQ was the model spec'd but the D series I think was the same with the other models needing modification.

 

[BobbyBluz]

Yes, bi-amped. The BGW 750B & 250C pair well in bi-amp mode with the Sentry III's, at full gain for each the balance is just about perfect with the SEQ. When I get everything done I'll do a scan with my RTA and see what the actual response curve is.