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Size of enclosure behind midrange drivers infinity rsb speaker cabinets?

jefferylhenr

jefferylhenr

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I am building a new set of cabinets using all the drivers, crossovers etc from a set of vintage infinity RSb speakers. Does anyone know the volume of the enclosure behind the midrange driver? I am starting with scratch and don't have an actual example to work from. Also, since everything will be new and suggestions for improvements?
 
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The mid enclosure is a heavy fiberboard tube 5.25" ID which is glued sealed from front to back (9"). It feels pretty thick like .25 or .375 wall thickness. It also acts as a brace between the front baffle and rear panel. I have a pair of rsb cabinets I am planning to install Qb drivers in so if you need any more dimensional data let me know.
 

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TomBig58 said:
It also acts as a brace between the front baffle and rear panel. I have a pair of rsb cabinets I am planning to install Qb drivers in so if you need any more dimensional data let me know.
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That's some clever engineering there.

Regarding the installation of Qb drivers into RSb cabs, I believe the original enclosure volumes are slightly different. Planning any changes?
 
The cabs are about the same H x W but the RSb cabs are shallower by 1-1.5". I was not going to make any changes at all. Now I see the RSb cabs are losing the volume of that mid tube as well. The Qb mid drivers are self enclosed. It's all kind of experimental at this point, planning to do one at a time for comparison. Mounting the mid drivers will be a challenge, I will need to make some kind of transition plate. When I dig into it I will share pics.

FYI the Crescendo series does the same thing with the mid enclosure, front to back glued in solid.
 
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swechsler said:
Actually, now that you mention it, I think the Kappa 8s did the same thing with their midbass and polydome.
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The Kappa 8s & 9s do have sealed tubes front to back for the polydomes. Not sure about the polygraphs, haven’t pulled one of those out yet to see. I’ll have to check the K9s since I have them out in the shop right now doing a recap.
 
That makes total sense that it also functions as a brace. I couldn’t tell from the other images that I had access to. Thank you for the info. Btw, how dense was the dampening material? Same as the rest of the cabinet? I ask because the materiel inside the rs5000 enclosure is very dense. There is some fairly inexpensive 6 inch pvc pipe available and assume that I will need to shorten it a bit to offset for the larger volume? Will also need to the enlarge the cabinet a bit to make up for that same volume difference of the outside diameter. There are nice somewhat rounded end caps I can use to seal on the backside and then add a small piece to attach at the back.
https://www.homedepot.com/p/NDS-6-in-PVC-Drain-Cap-6P06/100126604
[URL]https://www.homedepot.com/p/VPC-6-in-x-24-in-PVC-SDR-35-Riser-Pipe-6006-2/202564459
[/URL]
 
The tube was packed pretty tight with normal white polyfill. The main enclosure wasn't packed so tight. Some construction ideas:

I think you should do the tube the full depth to take advantage of the cabinet bracing. I don't think I would be worried about the diameter volume difference but a pro speaker guy might think otherwise. If you are worried about overall volume ( diameter x depth)cut some MDF circles and glue the crap out of them stacked in the back of the tube to close up the volume. I thought PVC too but concrete form sonotube is some pretty tough cardboard material and easier to work with. Treated with shellac or something I think it would work as good and a little better matched with the wood adhesives you are already using.

I wasn't sure where to get it in a 6" diameter but here it is. It's 12 ft long though.....

https://www.menards.com/main/buildi...-concrete-form/tu10120001/p-1444442810252.htm
 
The polygraphs are sealed tubes front to back just like the polydomes. They are cardboard tube very much like the sonotube.
 
$8.95 for two foot piece at Home Depot. I recalculated the volume and will cap it at 6.5 inches with birch plywood to offset the volume difference. Then cut another piece to extend behind the cap to the back of the cabinet as a brace piece. I have a 1 1/2 inch wood drill bit that can then drill numerous holes in the brace piece with the goal of maintaining the cabinet volume. I was able to find high quality 3/4 inch birch plywood at Home Depot as well for the cabinet. Using parts of the BBC design as well with a 1 1/2 thick inch front mounted baffle. I also hope that by coating the interior and exterior of the mid enclosure with a rubberized spray on materiel that it will significantly dampen reflections.
 
jefferylhenr said:
$8.95 for two foot piece at Home Depot. I recalculated the volume and will cap it at 6.5 inches with birch plywood to offset the volume difference. Then cut another piece to extend behind the cap to the back of the cabinet as a brace piece. I have a 1 1/2 inch wood drill bit that can then drill numerous holes in the brace piece with the goal of maintaining the cabinet volume. I was able to find high quality 3/4 inch birch plywood at Home Depot as well for the cabinet. Using parts of the BBC design as well with a 1 1/2 thick inch front mounted baffle. I also hope that by coating the interior and exterior of the mid enclosure with a rubberized spray on materiel that it will significantly dampen reflections.
Click to expand...

Just a thought but it will cost you another trip to HD, if you are using PVC.. Instead of a cap how about a coupling and use two pieces of pipe, one at the mid driver volume depth and the other to the back of the cabinet. You can glue/set a round piece of 1/2" or 3/4" in the cap before you glue in the front piece, cut to size front and back, and the whole brace assembly would be a lot stronger than gluing an extension onto the back of a cap.

Just thinking outside the box here.
 
I do like the idea of the coupler as you don’t have to cut the pvc exactly to length. You can slide the coupler for a snugg fit and then glue it in place on both ends.
 
Trying to keep the volume consistent with the original design. If the Thiele-Small Parameters were available for the infinity rsb drivers one could do the calculations. I have no idea if they were optimized originally or if compromises were leading the design. If one lays out the cabinet panels on a standard sheet of 4 x 8 it’s interesting how well they fit and so on...
 
jefferylhenr said:
If one lays out the cabinet panels on a standard sheet of 4 x 8 it’s interesting how well they fit and so on...
Click to expand...

Interesting theory. I have Quantum 5s, RSBs, RS5Bs and Kappa 6s and they are all within about an inch of each other across all three dimensions. One may be 1/2-3/4" taller but 1/2" shallower or narrower, etc.
 
Yes, that is the question. Was the volume optimized for the drivers, or cost of materials? I was hoping someone here would Have some insight on how to improve at minimum, the cabinet volume. Getting ready to do the final cuts on the cabinets.
 
jefferylhenr said:
Yes, that is the question. Was the volume optimized for the drivers, or cost of materials? I was hoping someone here would Have some insight on how to improve at minimum, the cabinet volume.
Click to expand...

Given the RSBs, RS5Bs and Kappa 6s all use a 10" woofer and the RSBs and RS5Bs use the 10" poly woofer seems there may be some correlation, maybe, possibly....
 
I just did a set of RSa's that may help with some questions if interested? Also if you want the carboard tube it's just a carpet tube . IDK if I would do PVC. Cardboard will never vibrate like a PVC pipe would.

 
Nice job and documentation. I bought a set of RSA’s new which I eventually needed to refoam when those parts weren’t easy to source. I sold them somewhere around 2010. They were great speakers but without a dedicated mid had their limitations. This era of infinity RS monitors regardless are well worth restoration and there is nothing like bringing them back to life. My project with the RSb’s is an effort to improve on the original design including new 3/4 inch Baltic birch cabinets, crossovers with jantzen capacitors and redesigned mid range enclosures. I am also copying the front baffle mounting and isolation from the BBC LS/3. Who knows what the result will be. I love the emit performance and want to see how far the mids can be improved. With the minimal butyl rubber surrounds and large magnets they should be outstanding. It’s a work in progress but I have done quite a bit of research including recalculating the volumes and resonances. The mid enclosures are two part with the back 3rd isolated with a layer of acrylic silicone. I also built 6 inch to zero heavily dampened cones that were rubberized and then covered with a heavy mâché made from fiber blue shop rags. The back side of the cone will be filled with 4 alternating layers of high density foam and cardboard fiber rings. The fronts of the cones will also be mâché. The exterior of the enclosure and the interior will be laminated with high density foam (high quality 3/8ths carpet pad). The idea is to maintain the original enclosure volume but do a better job of eliminating any back waves that might reflect back through the driver cone. upload_2020-2-3_19-33-39.jpeg
upload_2020-2-3_19-34-23.jpeg
 
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