First time speaker build.

[DanielDsouza]

I've recently acquired a pair of 3 way speakers used by 2 generations in my family and hold sentimental value, Unfortunately the boxes are falling apart and there is no way to save them. Since it was not a calculated box, I needed to know the enclosure size and port dimensions for a BR enclosure that I plan to make. The current woofers are Phillips AD12100 W8, as for the other drivers they may need to be replaced. I have tried to work on Winisd for hours but can't seem to figure it out. Size is not a constraint.
Thanks in advance.

 

[roger2]

Hi Daniel, welcome to AK

Those boxes look good to me. In what way are they falling apart?

Were these speakers designed by a known manufacturer, if so who and what model number are the speakers? Or were they DIY? If they were a commercial design, you can assume that the boxes and porting are decent-to-good. At least better than what you could do unless you have some very accurate Thiele/Small parameters for the woofers and working knowledge of one of the box calculating programs. So if they were made by a reputable speaker company, and the boxes truly need to be replaced, you could simply copy them, or if you change dimensions, keep the same cubic volume and venting. Cabinet volume is determined by the woofers, not the other drivers.

As for the other drivers, if you change them to something else you will lose a lot because the crossover (assuming it was designed by a reputable manufacturer) was custom tailored to the parameters of those three drivers. Not just the crossover points, but also the padding (level adjustments) for the mid and tweeter to match them to each other and to the woofer.

Speakers appear simple, but they are deceivingly complex, especially the crossover and padding that match the drivers acoustically. And although people hack DIY speakers all the time, and routinely report wondrous results, 99.9% of that is expectation bias, i.e. people hearing what they expected to hear before they even started on their project. A lot can go wrong with "mods". Sorry if this isn't the information you were seeking, lol.

 

[DanielDsouza]

Thank you Roger2 for the welcome and your prompt response.

These boxes were built by my grandfather in the 70's and they were without any calculations. They were just built according to eyeballing other enclosures at that time.
The material used was ply wood which is now seperating and has layers falling off, puffed and the bottom has begun to disintegrate. It was initially a sealed enclosure but hard to drive and then a port was cut out and left as it is.Also the crossover was a locally designed one which was the only one available at that time.

The current box dimensions are 31.5", 18", 14" (L B and depth) and made of 3/4 inch Ply and the port diameter is 2.5" and is just a hole cut into the front baffle.

I scoured the internet for the parameters and what I found for the Phillips AD12100 W8 are-

Thiel Small Parameters AD12100/W8

Fs 23Hz
Re 6,8ohm
Qes 0,298
Qms 2,153
Qts 0,262
Vas 258,3 ltr
Mms 61,4 g
Xmax 5mm

Since I need to make new boxes before the current ones fall apart completely, I just wanted to make sure I try to achieve the most that I possibly can from them with a bass reflex box.

 

[trinhsman]

Thank you Roger2 for the welcome and your prompt response.

These boxes were built by my grandfather in the 70's and they were without any calculations. They were just built according to eyeballing other enclosures at that time.
The material used was ply wood which is now seperating and has layers falling off, puffed and the bottom has begun to disintegrate. It was initially a sealed enclosure but hard to drive and then a port was cut out and left as it is.Also the crossover was a locally designed one which was the only one available at that time.

The current box dimensions are 31.5", 18", 14" (L B and depth) and made of 3/4 inch Ply and the port diameter is 2.5" and is just a hole cut into the front baffle.

I scoured the internet for the parameters and what I found for the Phillips AD12100 W8 are-

Thiel Small Parameters AD12100/W8

Fs 23Hz
Re 6,8ohm
Qes 0,298
Qms 2,153
Qts 0,262
Vas 258,3 ltr
Mms 61,4 g
Xmax 5mm

Since I need to make new boxes before the current ones fall apart completely, I just wanted to make sure I try to achieve the most that I possibly can from them with a bass reflex box.

Reach out to AK member @GordonW. He can get very busy, but IMHO he’s one of the best. He’s done work for me and I trust his ideas very much.

 

[GordonW]

The size of the original enclosure was actually quite appropriate for that driver (about 3.2 cubic feet or 90 liters or so).

The only tuning difference I would have done, is instead of a plain hole of 2.5 inch- which was tuning a bit higher frequency than needed (it needs to be tuned at about 36Hz, and the 2.5 inch hole in a 3/4" thick baffle was about 39Hz)- I would use a 4" diameter pipe, about 5" long as a vent. That should maximize port efficiency (large enough diameter for proper energy propagation, compared to the too- small original vent which was losing some of the energy behind the driver), and result in an f3 of about 37Hz. If you are planning to use them near a wall behind them, you can probably lower that port frequency a bit (use a 6" long 4" diameter vent instead), and get a little more effective bass extension out of them.

BTW: I don't know what that midrange driver is, without seeing the rear of the frame- but that tweeter is a Philips AD11600 or something very similar. If those work, they are worthy of retaining. They're probably the same type tweeter as was used in the Georgia Tech Audio Lab speakers, designed by Dr. Wm. Marshall Leach. They did quite a good job.

Regards,
Gordon.

 

[Nat]

When you say 'current woofer', was the original replaced? If the other drivers and the box are now being replaced, what is left of the original sentimental favorite?
Not trying to be negative, but if the other drivers are shot, you might as well just design a new speaker. But if you can use all, or most, of the drivers, then doing the project as a tribute makes more sense, and you can probably come up with something that looks almost original, which would be nice.
Where you could really do some good work is making sure that the crossover is recapped and possibly redesigned. It was fairly common just to use off the shelf crossovers back then, which limit the performance of the system. Matching the crossover frequencies and slopes to the specific driver could be a real improvement.

 

[DanielDsouza]

Thank you trinhsman and Gordon for your suggestions, I will go with what you suggsted while building the new cabinets, the midrange is a brand called Bolton, I will check the tweeter model when I open the boxes again.

Thank you Nat, The woofer is the one they installed in the 70's for and all the drivers are still working , its only the box that is falling apart, I will also be changing to a more modern crossover.

 

[Nat]

Oh good - it occurred to me, after I posted, that if the caps in the crossover had dried up, you might think that the midranges and tweeters were bad, even if they weren't. But that is not an issue.

 

[rothwellaudio]

Thank you Roger2 for the welcome and your prompt response.

These boxes were built by my grandfather in the 70's and they were without any calculations. They were just built according to eyeballing other enclosures at that time.
The material used was ply wood which is now seperating and has layers falling off, puffed and the bottom has begun to disintegrate. It was initially a sealed enclosure but hard to drive and then a port was cut out and left as it is.Also the crossover was a locally designed one which was the only one available at that time.

The current box dimensions are 31.5", 18", 14" (L B and depth) and made of 3/4 inch Ply and the port diameter is 2.5" and is just a hole cut into the front baffle.

I scoured the internet for the parameters and what I found for the Phillips AD12100 W8 are-

Thiel Small Parameters AD12100/W8

Fs 23Hz
Re 6,8ohm
Qes 0,298
Qms 2,153
Qts 0,262
Vas 258,3 ltr
Mms 61,4 g
Xmax 5mm

Since I need to make new boxes before the current ones fall apart completely, I just wanted to make sure I try to achieve the most that I possibly can from them with a bass reflex box.

Just plug those T/S values into the calculator on this page http://www.mh-audio.nl/Calculators/BRH.html

 

[DanielDsouza]

Finally