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

[Pete Schumacher]

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

I've mentioned a couple times before that I would help get it mass produced if anyone wanted to help me make one up. I hadn't heard anything so I just started working on my own. But I'd be willing to help get a different one made up too.

I'm up for it Erich. What would you like from me in this endeavor?

The EOS8 looks like the best candidate to me, or maybe a 7"-7.5" diameter round guide. While elliptical allows for closer spacing, at 1000Hz, it's pretty simple to keep an 8" woofer within the 1 wavelength CTC distance. There's a BIG upside to a round guide: anyone with a circle jig can cut the recess to host the guide. Better yet, why not make the flange of the guide equal to a large number of 8" woofer flanges? That way you don't even have to change the circle jig to cut both recesses. :applause:

[300Z]

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

I would be interested in a set of 8" round waveguides if they had fit a Seas 27TDFC.

[Pete Schumacher]

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

I would be interested in a set of 8" round waveguides if they had fit a Seas 27TDFC.

I tried the previous guide with the 27TBFC/G and it worked quite well. Seems that the flange opening for the 27 series from SEAS is quite compatible with the opening for the RS28.

[Greggo]

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

I would be interested in a set of 8" round waveguides if they had fit a Seas 27TDFC.

with all due respect, why bother? Are there any measurements in any waveguide to suggest that the 27TDFC performs as well or better in this application than the RS28A? Dave Pellegrene has probably done more than anyone to sort through dome/guide combos that may or may not work better than others, and though I always like choices, the fact that there isn't a single optimized combo that works down to 1k and and measures as well as anything else above... That is what holds these projects back, starting from scratch every time.

I think the DIY community would benefit from one starting point, an optimized dome/guide combo that requires no cutting, sanding, special treatment, jig, mounting contortions or any kind of special effort and just works, and works very well, as is... Once that happens, and if it is successful, then folks could ask, is there still a higher performance level to be reached in finding a second optimized combo, maybe with an AMT or Be dome or something else. I know that no tweeter is perfect, but trying to solve for many of them instead of one starts to create compromises or complexities in a very rapid fashion. Just my two cents.

Regards,

Greg Jensen

[Pete Schumacher]

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

with all due respect, why bother? Are there any measurements in any waveguide to suggest that the 27TDFC performs as well or better in this application than the RS28A? Dave Pellegrene has probably done more than anyone to sort through dome/guide combos that may or may not work better than others, and though I always like choices, the fact that there isn't a single optimized combo that works down to 1k and and measures as well as anything else above... That is what holds these projects back, starting from scratch every time.

I think the DIY community would benefit from one starting point, an optimized dome/guide combo that requires no cutting, sanding, special treatment, jig, mounting contortions or any kind of special effort and just works, and works very well, as is... Once that happens, and if it is successful, then folks could ask, is there still a higher performance level to be reached in finding a second optimized combo, maybe with an AMT or Be dome or something else. I know that no tweeter is perfect, but trying to solve for many of them instead of one starts to create compromises or complexities in a very rapid fashion. Just my two cents.

Regards,

Greg Jensen

The 27TDFC will not reliably support a 1KHz XO point, but it will probably do 1500 pretty simply.



As you can see from Zaph's data on the TDFC, it cuts off just below 2000Hz, and a guide will not change that.

That said, the same 8" guide with the TDFC should work just fine to its own natural cutoff. The fact that the TDFC and TBFC both have the flat flange that slightly recesses the dome will help it work well. Off axis is usually very good with the on axis response showing perhaps a bit of top octave irregularity in a guide not purpose built for a particular dome.

But I'm with your Greggo, a purpose built guide to properly mate to the tweeter is key. Dave's got the adapter thing down pretty well allowing a particular guide profile to work with a variety of tweeters of similar size.

[davepellegrene]

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

As far as the RS28 I think Pete has about the best set up you can get with the 8" diameter 2" deep guide. I think any deeper it creates more reflections off axis then it does good.
With the 2" deep guide you could rear mount the woofer and put the acoustical centers pretty close. Using a 7-1/4" cut out would fit quite a few 8" drivers. Adding a round over on the cut out would put it pretty close to the size of the 8" guide. Rear mounting would also make the B&C drivers easier to use.

Dave

[Erich H]

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

Pete, the EOS-8 is designed to easily surface mount if necessary. I think there are a lot of round waveguides already out there that can be cut down if anyone wanted to go that route, but I would still look into it. I personally think something just a little bit smaller than the EOS-8 might be the best way to go. It would still look fine over an 8" woofer, and it wouldn't look too out of place over 6" - 7" either.

Elliptical might make more sense even if it just means keeping the baffle height down. If you went with a 7.5" circular model and that B&C woofer, you would need a pretty tall enclosure. It's still worth looking into though, and I have quite a few different ones to experiment with.

There were plans to get this done for nearly a year now, so it will be great to get things rolling again. I shouldn't have put it on the back burner but things got pretty busy with the other projects.

[300Z]

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

with all due respect, why bother? Are there any measurements in any waveguide to suggest that the 27TDFC performs as well or better in this application than the RS28A?

I have used both the RS28A since they first came out and the 27TDFC about a year after that, and personally I prefer the sound of the 27TDFC. The RS28A is in a system paired with the RS180 that hardly gets any use lately. The 27TDFC is not in use at the moment either but I'm thinking about building a active system with it paired to a FailtalPro 6FE100 using a spare MiniDSP, I don't need the tweeter to play down to 1khz, anywhere from 1.5 to ~2khz should work just fine, I want matched constant directivity.
Ever since I got the B&C's back in 2008 the only change I have made to my setup was getting the JBL 2408H CD and never looked back but I need to build another system for another room, it's needs to be smaller and simpler and that's why I want to use the 27TDFC since I already have it.

Zaph has already tested the 27TDFC in a MCM waveguide and I may just end up going that way.


For what it's worth the response may be down at 1khz on the 27TDFC but distortion is lower from 1 to ~2.5khz.

[Pete Schumacher]

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

Pete, the EOS-8 is designed to easily surface mount if necessary. I think there are a lot of round waveguides already out there that can be cut down if anyone wanted to go that route, but I would still look into it. I personally think something just a little bit smaller than the EOS-8 might be the best way to go. It would still look fine over an 8" woofer, and it wouldn't look too out of place over 6" - 7" either.

Elliptical might make more sense even if it just means keeping the baffle height down. If you went with a 7.5" circular model and that B&C woofer, you would need a pretty tall enclosure. It's still worth looking into though, and I have quite a few different ones to experiment with.

There were plans to get this done for nearly a year now, so it will be great to get things rolling again. I shouldn't have put it on the back burner but things got pretty busy with the other projects.

Ideally, this particular woofer should be mounted to the back of this baffle in a shallow recess to better align it with the 2" deep guide. Doing that would allow a guide with an 8" flange to be mounted onto the front and not interfere with the woofer in any way. That combo would still fit on the 10 x 17 PE baffle, which happens to be a perfect enclosure volume for this particular woofer.

[Pete Schumacher]

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

I have used both the RS28A since they first came out and the 27TDFC about a year after that, and personally I prefer the sound of the 27TDFC. The RS28A is in a system paired with the RS180 that hardly gets any use lately. The 27TDFC is not in use at the moment either but I'm thinking about building a active system with it paired to a FailtalPro 6FE100 using a spare MiniDSP, I don't need the tweeter to play down to 1khz, anywhere from 1.5 to ~2khz should work just fine, I want matched constant directivity.
Ever since I got the B&C's back in 2008 the only change I have made to my setup was getting the JBL 2408H CD and never looked back but I need to build another system for another room, it's needs to be smaller and simpler and that's why I want to use the 27TDFC since I already have it.

Zaph has already tested the 27TDFC in a MCM waveguide and I may just end up going that way.
[ATTACH=CONFIG]42910[/ATTACH]

For what it's worth the response may be down at 1khz on the 27TDFC but distortion is lower from 1 to ~2.5khz.

That particular guide with the TDFC looks limited to about 1800Hz. And the top end control isn't quite as nice as it could be. Still, it's not terrible but it could use a more purpose built guide over the MCM version.

What you hear is the most important aspect. The differences in the way transducers present the signal are the most important feature of why a speaker sounds the way it does. Directivity is a distant second to 1st arrival. If you prefer the sound of the TDFC over the RS28, then by all means pursue something that uses it. But don't just settle for any old guide.

[300Z]

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

That particular guide with the TDFC looks limited to about 1800Hz. And the top end control isn't quite as nice as it could be. Still, it's not terrible but it could use a more purpose built guide over the MCM version.

What you hear is the most important aspect. The differences in the way transducers present the signal are the most important feature of why a speaker sounds the way it does. Directivity is a distant second to 1st arrival. If you prefer the sound of the TDFC over the RS28, then by all means pursue something that uses it. But don't just settle for any old guide.

You're right that MCM guide certainly isn't as good as it could be and that's why I'm hoping someone comes up with a better waveguide by the time I'm ready to start building that system in a couple of months.

[Pete Schumacher]

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

You're right that MCM guide certainly isn't as good as it could be and that's why I'm hoping someone comes up with a better waveguide by the time I'm ready to start building that system in a couple of months.

Send your tweeters to Dave Pellegrene. I'm sure he'd work with you to come up with a suitable guide. Plenty of folks like the TDFC/TDC and having a ready made guide that works might find an audience.

[markk]

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

Well, not in my experience. See the graphs below.

However, I have to say that, when pushing a tweeter that low, there is a lot of unit to unit variation. Not every TDFC and not every RS28F will go as low. You are pushing the limits. Individual testing is needed if you're pushing it this low. Including using any waveguide. You can't assume the WG will automatically lower distortion.

I have used both the RS28A since they first came out and the 27TDFC about a year after that, and personally I prefer the sound of the 27TDFC. The RS28A is in a system paired with the RS180 that hardly gets any use lately. The 27TDFC is not in use at the moment either but I'm thinking about building a active system with it paired to a FailtalPro 6FE100 using a spare MiniDSP, I don't need the tweeter to play down to 1khz, anywhere from 1.5 to ~2khz should work just fine, I want matched constant directivity.
Ever since I got the B&C's back in 2008 the only change I have made to my setup was getting the JBL 2408H CD and never looked back but I need to build another system for another room, it's needs to be smaller and simpler and that's why I want to use the 27TDFC since I already have it.

Zaph has already tested the 27TDFC in a MCM waveguide and I may just end up going that way.
[ATTACH=CONFIG]42910[/ATTACH]

For what it's worth the response may be down at 1khz on the 27TDFC but distortion is lower from 1 to ~2.5khz.

[Pete Schumacher]

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

Well, not in my experience. See the graphs below.

However, I have to say that, when pushing a tweeter that low, there is a lot of unit to unit variation. Not every TDFC and not every RS28F will go as low. You are pushing the limits. Individual testing is needed if you're pushing it this low. Including using any waveguide. You can't assume the WG will automatically lower distortion.

Here's the transfer function of the crossover I'm using with the RS28A in the guide Mark.



In any other implementation of this tweeter on a normal baffle, the effective crossover point for the tweeter is well above 2000Hz using this transfer function.

1KHz is no problem for the RS28 family in a guide like this. By the time a tweeter in this guide is getting the signal level you tested with at 1KHz, the overall output at 1KHz would be at least 15dB louder.

[buzzforb]

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

Pete, and others,
What is the general opinion, if any, on zobel networks?