Home/Pro 8" 2-way: RS28A and B&C 8BG51

[Pete Schumacher]

This thread is to document a build using the RS28A in a waveguide teamed up with the B&C 8BG51 Neo motor pro-sound mid-woofer.

Tom Jones (takitaj) provided the baffle. He fashioned a waveguide to fit the opening of the RS28, 2" deep, 7" overall width, with a smooth curve that ends tangential to the baffle. I'm unsure yet as to how well it will work but I have high hopes. It follows fairly closely the profile of the larger guide made by DanP with a 3D printer a couple years back. That guide was wider, with a larger radius profile. This one features the same throat opening, and same depth. Exit angle is a bit smaller at about 90 degrees.

Tom's baffle is made to replace the baffle on the .75 cf TM Parts Express cabinet, using the same mounting screws, so it will be removable to allow mounting the tweeter onto the rear of the baffle.

I expect the baffle to be here tomorrow so hopefully I can get things mounted and start testing. I want to bring this to the KYDIY this weekend, so I probably won't have time to get any paint on the baffle. Hopefully, I'll have enough time to get a crossover built along with getting some voicing time in.

This will be an 8 Ohm system, and I'm guessing at around 87dB overall sensitivity after baffle step, with F3 about 47Hz, and should be able to produce over 110dB from 50Hz on up. Not too shabby for a stand mount monitor. I'm going to try a 2.5" port which will have 38m/s port velocity with 100W input. It's a compromise for sure, but the smaller port pushes the port resonance up above 1KHz. And for normal listening levels, port velocity will be low enough to not cause problems.

More to come as progress continues.

[lorenmjones]

Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

Looks like a very cool project Pete. Can't wait to see how it turns out.

This thread is to document a build using the RS28A in a waveguide teamed up with the B&C 8BG51 Neo motor pro-sound mid-woofer.

Tom Jones (takitaj) provided the baffle. He fashioned a waveguide to fit the opening of the RS28, 2" deep, 7" overall width, with a smooth curve that ends tangential to the baffle. I'm unsure yet as to how well it will work but I have high hopes. It follows fairly closely the profile of the larger guide made by DanP with a 3D printer a couple years back. That guide was wider, with a larger radius profile. This one features the same throat opening, exit angle (120 degrees) and same depth.

Tom's baffle is made to replace the baffle on the .75 cf TM Parts Express cabinet, using the same mounting screws, so it will be removable to allow mounting the tweeter onto the rear of the baffle.

I expect the baffle to be here tomorrow so hopefully I can get things mounted and start testing. I want to bring this to the KYDIY this weekend, so I probably won't have time to get any paint on the baffle. Hopefully, I'll have enough time to get a crossover built along with getting some voicing time in.

This will be an 8 Ohm system, and I'm guessing at around 87dB overall sensitivity after baffle step, with F3 about 47Hz, and should be able to produce over 110dB from 50Hz on up. Not too shabby for a stand mount monitor. I'm going to try a 2.5" port which will have 38m/s port velocity with 100W input. It's a compromise for sure, but the smaller port pushes the port resonance up above 1KHz. And for normal listening levels, port velocity will be low enough to not cause problems.

More to come as progress continues.

[ATTACH=CONFIG]41806[/ATTACH]

[Pete Schumacher]

Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

Ran a sweep of the 8BG51 nearfield, mic about 3" from the dust cap, just outside the front of the woofer flange. I'm guessing about 1W input. Ungated, no smoothing. This looks close to the manufacturer's data. Clean performance up to 1K. I hope the RS28A/guide can meet up with this without too much trouble.

[aarond]

Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

So what's the major "diameter" on that woofer?

[Pete Schumacher]

Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

So what's the major "diameter" on that woofer?

From the PE product page:

Overall Outside Diameter	8.8"
Baffle Cutout Diameter	7.4"
Depth	3.50"
Bolt Circle Diameter	8.3"

[aarond]

Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

Ha, I looked there but didn't scroll down to see it. I'm still not used to the (not so) new site format. I didn't see an "A" dimension in the description and assumed they left it out because of the odd shape.

So practically speaking it's the same OD as the RS225, which is what I was really wanting to know.

Following along, enjoying the ride.

[[email protected]]

Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

cool Pete. Eager to see how the WG works out.

[mzisserson]

Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

Pete, looks really interesting. I have been eyeballing that 8" BC for a while.

[Pete Schumacher]

Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

Well, getting this to KYDIY is going to be tough. The baffles need to be modified on the back side in order to fit into the cabinets. It'll take some creative router or table saw work but the mod shouldn't be more than time consuming.

In the meanwhile, I got the RS28A mounted and ran a sweep. I'm liking the looks of this guide. Should be a perfect match for the cutoff knee of the woofer.

[Pete Schumacher]

Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

Well I couldn't get the baffle all the way onto the enclosure, but it did fit well enough to get a measurement of both woofer and tweeter together without the dipole cancellation on the woofer. I really wanted to start on a crossover design.

So far,so good. 8 components yields this system response. LR4 at 1200Hz.

[jonasz]

Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

Pete, is this wg the same as the LOKI or is it slightly smaller? Speaking about the LOKI, is that design dead? :( I hope not!

[lorenmjones]

Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

That should be an excellent HT speaker for folks that want high output levels from a standmount form factor. I'm sure it will ne nice for music too, but reasonable sensitivity and extension in a standmount box with pretty high output levels is a nice combination.

Well I couldn't get the baffle all the way onto the enclosure, but it did fit well enough to get a measurement of both woofer and tweeter together without the dipole cancellation on the woofer. I really wanted to start on a crossover design.

So far,so good. 8 components yields this system response. LR4 at 1200Hz.



[ATTACH=CONFIG]41875[/ATTACH]

[Pete Schumacher]

Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

Pete, is this wg the same as the LOKI or is it slightly smaller? Speaking about the LOKI, is that design dead? :( I hope not!

L.O.K.I. will resume when the new reference drivers come out. The 8" composite cone should be around in February (or there about) according to Rory.

This particular guide is slightly smaller than the original and from the looks of it, doesn't extend quite as deep before cut off. Otherwise, it still produces the same smooth transfer function.

[JasonP]

Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

In the meanwhile, I got the RS28A mounted and ran a sweep. I'm liking the looks of this guide. Should be a perfect match for the cutoff knee of the woofer.

Distortion looks excellent all the way down to 1 khz, and that is impressive. Most of the response slope is nice and smooth, great work. I'm not sure I like that massive early roll-off though. I wonder how audible that will be in the end.

[Pete Schumacher]

Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

Distortion looks excellent all the way down to 1 khz, and that is impressive. Most of the response slope is nice and smooth, great work. I'm not sure I like that massive early roll-off though. I wonder how audible that will be in the end.

Good point. I'm not sure how much of it is really there. These were all far less than optimal measurement conditions. Once I get the baffle into the cabinet properly, I'll get a new set of data.

But it looks like this will not make it to KYDIY. Just not enough time. And now, my traveling partner has come down with a bad chest cold, so I'll likely be staying home to baby sit her. :(