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

[Navy Guy]

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

I had fun too.

The RS28A is a great dome tweeter, despite it's lack of extension above 15KHz.

Pete, you might want to check your soundcard or settings on your measurement gear. Based on the measurements from Zaph's website on the RS28A, it extends out past 20 kHz. I noticed you are using HolmImpulse. I have had measurement issues with HolmImpulse before, rolling off the measurements too early. It used to do it around 15-16 kHz. I have to keep playing with my settings to get it to work, but I measured the RS28A out to about 18khz matching Zaph's data pretty close (minus diffraction issues). I think I am still having some issues with my setup though, and it's likely that it does extend all the way out to 20 kHz or higher.

Here is his measurement:

[Pete Schumacher]

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

Pete, you might want to check your soundcard or settings on your measurement gear. Based on the measurements from Zaph's website on the RS28A, it extends out past 20 kHz. I noticed you are using HolmImpulse. I have had measurement issues with HolmImpulse before, rolling off the measurements too early. It used to do it around 15-16 kHz. I have to keep playing with my settings to get it to work, but I measured the RS28A out to about 18khz matching Zaph's data pretty close (minus diffraction issues). I think I am still having some issues with my setup though, and it's likely that it does extend all the way out to 20 kHz or higher.

Here is his measurement:[ATTACH=CONFIG]42704[/ATTACH]

When I mention the lack of extension, it's the drop off at 15KHz that I'm referring too. Compared to the RS28F, that 6dB dip is quite substantial.

The measurements I'm getting also include the guide which does have an impact above that point. But I'll have another look at Holm and compare it to ARTA.

[Navy Guy]

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

When I mention the lack of extension, it's the drop off at 15KHz that I'm referring too. Compared to the RS28F, that 6dB dip is quite substantial.

The measurements I'm getting also include the guide which does have an impact above that point. But I'll have another look at Holm and compare it to ARTA.

I forgot about the guide. That is probably what is causing it. I just noticed yours look like they rolled off completely at around 15khz, and since I had been having that, I thought that might be it.

[BeeTL]

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

Pete,

Has anyone ever attempted to mount the RS28 in a horn like the B&C ME15?

[Pete Schumacher]

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

Pete,

Has anyone ever attempted to mount the RS28 in a horn like the B&C ME15?

I don't recall any experiments in that direction. I don't know if the A version would work or not. The flange of the tweeter would probably have to come off in order to mount it to that particular horn, and the flange/mesh has the phase plug on it.

Might be fun to try it out.

[BeeTL]

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

Might be fun to try it out.

My thoughts exactly...

Do you have any direct links to photos of how you mount the RS28 to the waveguide?

The search function here is not so fun.

[Pete Schumacher]

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

My thoughts exactly...

Do you have any direct links to photos of how you mount the RS28 to the waveguide?

The search function here is not so fun.

Since the RS28 has a 4.125" flange, it won't fit onto the back of that horn you linked. The back of the waveguide baffle is just a flat panel. I hold up the tweeter and adjust it by looking at the front and centering it in the throat. My wife then took a sharpie and located the mounting holes. I then drilled some pilot holes and used those to drive screws through the back of the flange to hold the tweeter down.

Here's the back of the baffle before locating the mounting holes. I wound up trimming an inch off the top of the back section so that it would fit into the enclosure.

[Erich H]

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

Pete,

Has anyone ever attempted to mount the RS28 in a horn like the B&C ME15?

That model would not work well with the RS28. You really need a larger opening for a smoother transition into the throat of the horn. The problem is that by the time you widen that throat enough, you'll end up removing so much of the horn that all you'll be left with is a rectangular opening. You should look at a circular or elliptical waveguide.

[BeeTL]

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

What if you made an 1/8" adapter plate out of ABS, ply, or aluminum?

Bolt the plate to the horn, then bolt the RS28 to the plate?

The opening in the plate could be slightly larger than the perimeter of the dome to accommodate the lip.

Of course, then it would work with any 1" plate-style horn.

[Pete Schumacher]

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

What if you made an 1/8" adapter plate out of ABS, ply, or aluminum?

Bolt the plate to the horn, then bolt the RS28 to the plate?

The opening in the plate could be slightly larger than the perimeter of the dome to accommodate the lip.

Of course, then it would work with any 1" plate-style horn.

That's a possibility and should work. The big issue will be whether or not that aluminum dome is a proper match for the horn geometry without the phase plug in place. There will likely be a lot of response irregularities in the top octave. And with a horn that deep, you're just begging for the honky sound that horns can tend to bring.

I'd use one of Dave's guides for the RS28A before I'd try to adapt that horn.

[Erich H]

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

I can test the B&C horn, but I doubt it will be very good going from 1.5" down to 1", then back up again in that geometry. I have a few of those sitting around.

The waveguides I converted for the RS28 a few months ago were all elliptical like the one Pete used. I think that's the best way to go for this tweeter.

Pete, I got pretty good results just leaving the protective mesh over the dome. Did you remove it on yours? My throat diameter was a little smaller as well, but our results were similar, so it might not matter too much.

I've drilled out a SEOS-10, but haven't gotten around to testing it yet. 10" might look a little too wide over an 8" woofer, I'm not sure.

[Pete Schumacher]

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

I can test the B&C horn, but I doubt it will be very good going from 1.5" down to 1", then back up again in that geometry. I have a few of those sitting around.

The waveguides I converted for the RS28 a few months ago were all elliptical like the one Pete used. I think that's the best way to go for this tweeter.

Pete, I got pretty good results just leaving the protective mesh over the dome. Did you remove it on yours? My throat diameter was a little smaller as well, but our results were similar, so it might not matter too much.

I've drilled out a SEOS-10, but haven't gotten around to testing it yet. 10" might look a little too wide over an 8" woofer, I'm not sure.

I simply mounted the stock tweeter to the back of the guide, no mods to the tweeter at all. It's all there including the mesh and phase plug.

Which of your guides did you modify to accept the RS28?

[Erich H]

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

Pete, it sounds like we both mounted the tweeter the same way.

I modified quite a few different waveguides for testing. EOS-6, 8, and 10. OS-6, and the SEOS-10 and 12.

I've got a handful of other small models that I messed with, but nothing that seemed any better than the ones just mentioned.

I worked with both RS28's because their internal design is pretty close to the smaller compression drivers. Actually very similar to something like the B&C DE10. It was put on the back burner because I wasn't sure it could handle enough power to be used in a 2 way with 8's or 10's. But you and a couple others have mentioned that it should be just fine even in a fairly high powered speaker design.

[Pete Schumacher]

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

Pete, it sounds like we both mounted the tweeter the same way.

I modified quite a few different waveguides for testing. EOS-6, 8, and 10. OS-6, and the SEOS-10 and 12.

I've got a handful of other small models that I messed with, but nothing that seemed any better than the ones just mentioned.

I worked with both RS28's because their internal design is pretty close to the smaller compression drivers. Actually very similar to something like the B&C DE10. It was put on the back burner because I wasn't sure it could handle enough power to be used in a 2 way with 8's or 10's. But you and a couple others have mentioned that it should be just fine even in a fairly high powered speaker design.

When you consider the transfer function of the crossover and see that it's down about 20dB at the crossover point with the guide in place, and that music is heavily weighted to the region below 1000Hz, I can't imagine the RS28 having any trouble keeping up with these woofers in a home environment. If you're doing sound reinforcement/PA duty outdoors, the higher powered, higher sensitivity compression drivers would be in order.

I might have to try out the EOS 8. It should fit the PE baffle which would allow someone to simply modify the existing baffle instead of needing a CNC cut baffle. If you can recall, how did the stock tweeter do mounted to the back of the EOS? Didn't the mesh interfere with the opening, or did you have to modify the guide?

[Erich H]

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

The whole back end of the waveguide needed to be removed for the dome to fit in. Basically it looks just like yours from the front.

At first I removed just enough of the 1" throat for the mesh to clear it and sit flush. It didn't test smooth enough. Then I just bored out a 1.5" hole straight through the throat until it blended into the inner curves of the waveguide. But that usually meant that the throat was too deep (like a tunnel) and gave some bad responses. So I slowly ground it shorter until the response was better. In the end, no throat works the best for these types of dome tweeters.

The grill on the PE enclosure won't clear the EOS-8 if the waveguide isn't recessed. I do have some smaller models that I should look closer at that would probably fit okay. The EOS-6 might be a good choice because it wouldn't look out of place with a 6-7" woofer either. I did testing on that with the RS28 and it looks good but I probably removed more of the throat than needed. I should give that one another try this weekend if there's time.