DIY Port Tubes.

[Deleted]

I just ordered some Dayton Audio 8'' (DC200-8 8" Classic Woofer) woofers to replace the original woofers on my Fortura 8 AMT speakers.  The original woofers are paper with foam surrounds (the surrounds have been re-foamed once).  The paper cones are not stiff at all and to my ears have a sloppy response and prone to giving a slapping sound when pushed on hard hitting bass.  I am hopping the treated cone of the Dayton woofers along with rubber surrounds will improve the sound. 

I did a little investigation regarding matching enclosure volume with replacement woofers and it seems the Dayton Audio woofer I chose are the best match according to specs that I could find without spending several hundred dollars per woofer.

I am not knowledgeable about the technical details on enclosure size, proper porting, etc.  With that said based on a bit of research, from what I can tell I need to modify the existing port in my speaker to improve get the best out of the new woofers.  The ports on the Fortura 8 speakers are 2.5 inches in diameter by 3 inches deep.  I have been able to find info that would indicate that the ideal for the Dayton replacement woofers is a tube 2.5 inches by 7.75 inches deep.

Does anyone have suggestions or ideas on how to build a DIY tube?  I could not find any ready made tubes that would fit the original enclosures without having to drill out a larger opening for the existing ports, which I would rather not do.

[DYohn]

Assuming your math is correct, there are plenty of port tubes available, or simply use some PVC pipe cut to the right inside dimensions.

[Gary Cook]

It is the inside diameter (ID) of the port that is important, the outside diameter (OD) is less relevant being in the context of affecting the volume of the enclosure itself. You need to measure the OD of the existing port (knowing that the ID is 2.5") which will give you OD and then look for similar tube with that ID and OD.

Common PVC pipe is 2.445" ID and 2.875" OD, which may be the best fit. (I wish you guys would hurry up and go metric, it's so much easier, 62 mm ID and 73 mm OD)


Cheers
Gary

[Deleted]

Feb 15, 2014 15:53:39 GMT -5 Gary Cook said:

It is the inside diameter (ID) of the port that is important, the outside diameter (OD) is less relevant being in the context of affecting the volume of the enclosure itself. You need to measure the OD of the existing port (knowing that the ID is 2.5") which will give you OD and then look for similar tube with that ID and OD.

Common PVC pipe is 2.445" ID and 2.875" OD, which may be the best fit. (I wish you guys would hurry up and go metric, it's so much easier, 62 mm ID and 73 mm OD)


Cheers Gary

The OD of the existing port is 2.5 inches.  I did some searching on the internet and could not find PVC in 2.5 inch diameter.  I might try to find some kind of heavy cardboard tubing or cardboard product I could shape into the correct dimension.

[Gary Cook]

Feb 16, 2014 2:18:52 GMT -5 @joebbathehut said:

Feb 15, 2014 15:53:39 GMT -5 Gary Cook said:

It is the inside diameter (ID) of the port that is important, the outside diameter (OD) is less relevant being in the context of affecting the volume of the enclosure itself. You need to measure the OD of the existing port (knowing that the ID is 2.5") which will give you OD and then look for similar tube with that ID and OD.

Common PVC pipe is 2.445" ID and 2.875" OD, which may be the best fit. (I wish you guys would hurry up and go metric, it's so much easier, 62 mm ID and 73 mm OD)

The OD of the existing port is 2.5 inches.  I did some searching on the internet and could not find PVC in 2.5 inch diameter.  I might try to find some kind of heavy cardboard tubing or cardboard product I could shape into the correct dimension.

What's the wall thickness? It's the ID that's the most important, that's where the air flows.

For example 2" (51 mm) ID PVC tube has an OD of 2.375" (60 mm), so a layer of 1 mm thick tape around the outside will make it a tight fit in a 2.5" hole.


Cheers
Gary

[Deleted]

I was not clear. The hole (inner diameter) in the port is exactly 2.5 inches. The original port only goes 2.5 deep into the speaker as well. I just realized that if I extended the port to 7.75 it would only be about 1/2 inch from the back panel of the speaker enclosure as well as getting in the way of the crossover. I may not be able to set up the post hole to the ideal of the new woofers I am getting shipped soon.

These are not a picture of my actual Fortura 8 speakers, but this will give you an idea of what I am working with. 

[Gary Cook]

I have seen angled ports used. i.e.; they don't have to be straight.





Cheers
Gary

[garym]

Feb 16, 2014 2:50:31 GMT -5 @joebbathehut said:

I was not clear. The hole (inner diameter) in the port is exactly 2.5 inches. The original port only goes 2.5 deep into the speaker as well.

You should get WinISD and re-calculate the port size for that driver and that size box. 2.5" x 2.5" sounds small to me.

[Deleted]

Thanks for the suggestion.  There are online calculators for WinISD.  I played around with them and realize that I will need to measure the dimensions of the volume of my speakers "box" carefully.  I presume the dimensions for calculating the volume needs to be based on interior dimensions (i.e. the thickness of the walls should not be in the dimensions of the volume calculation).  The original ports are 2.5i inches in diameter by 2.5 inches (measured from the interior wall of the front of the speaker).  The speakers are about 40 years old and may have been designed before Theile-Small.

Based on WinISD calculations I tired, varying the Volume slightly, I may be looking to extend the 2.5 inch port length by 2-2.5 inches, depending on the target tuning frequency. 

According to a plate on the back of the speakers the low end frequency response is 40Hz.

I am still very noob on my understanding of enclosure design issues but am learning.

Feb 16, 2014 20:02:20 GMT -5 garym said:

Feb 16, 2014 2:50:31 GMT -5 @joebbathehut said:

I was not clear. The hole (inner diameter) in the port is exactly 2.5 inches. The original port only goes 2.5 deep into the speaker as well.

You should get WinISD and re-calculate the port size for that driver and that size box. 2.5" x 2.5" sounds small to me.

[Deleted]

Well I got my new 8"  Dayton Woofers today.  I certainly got them fast having ordered them on Saturday, 02/15/2014.  Compared to my speakers original woofers, they have smaller less heavy magnets.  They were only $25 each plus $10 shipping for a total of $60.  I did not buy theses specific Dayton woofers because of their price, but simply because they were the only Dayton woofers with an outer dimension of exactly 8" to precisely fit the existing woofer cutout.

I looked in the original cabinet interior after removing the original woofers and found that the ports should be easy to extend as soon as I find my solution for 2.5" inner diameter tubing of some sort.  I have looked into paper mailing tubes, mortar tubes for fireworks, and heck when I was shopping today I even looked at the possibility of using a Comet cleanser container (not the right diameter).  The original port is tube in my speakers are simple straight carrboard tubes.  Intend to modify them is such a way that I can undo my modifications easily in case I do not like the results.

I did decide to go ahead and install the new woofers until I do modify the port tubes.  (I also took measurements of the interior of my cabinet to double check my dimension for the volume calculation so I could re-do a calulation for the tube length.  I did correctly calculated the interior dimensions based on what I could tell was 3/4 inch cabinet walls).  I am debating whether I will try to tune the port for 35Hz or 40Hz.  A decal on the back of my speakers indicated a 40HZ low end frequecy response; however, the Dayton Woofer has a resonant frequency of 31Hz, so I may lean toward a 35Hz port tuning.

The Dayton Woofers are treated paper woofers, and the treatment seems to have made the cone adequately stiff.  The paper cones on the 40 year old woofers are worn and not stiff at all the spiders are very very loose.  I imagine this contributed to the somewhat sloppy low end I was haring in my speakers, included sometime getting a nasty slapping sound if I tried to drive them loud.

I have been listening to Led Zepplin II & IV with the new woofers and there is a surprising amount bass presence. especially on the drum solos.  A big improvement in that regard.  I am not so certain about the midrange, but I think I am just getting cleaner sound from the new woofers.  I am sure they will loosen up a bit in the initial hours of use.  The bass in not in your face but pleasing.  My intent on changing the woofers was see if I could improve the bass response in my speakers (enough so that I might forego the possibility of integrating a sub in my 2 channel setup.

I have noticed a difference in the power I need to drive my speakers now.  With my XDA-2 and 2 XPA-100s before the new woofers I was typically running -15 to -10db.  I am finding I needin -10 to -5db now.  It is possible I have changed the impedance of the speakers (the Daytons are rated as 8ohm, and I don't know what the old woofers are)..  The amps do not show any signs of struggling, and are only modestly warm.

[Gary Cook]

Have you tried 2.5" ID PVC tube?


Cheers
Gary

[Deleted]

I have tried getting 2.5 PVC tubing. I did some checking on the internet and a big box retailer (Menard's in the states) showed selling 2.5 PVC, but when I got to the store they have everything but 2.5". It must be an odd size. I am going to have to go to a smaller true plumbers supply store to try to get it. I won't be able to until Saturday.