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

[BeeTL]

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

That looks like a variation of the new JBL M2 waveguide. Missing the vertical nodes to match the horizontal.

Nice!

http://www.jblpro.com/press/Jan13/JBL_M2.html

[Erich H]

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

I think a real contender for ultimate home theatre DIY speaker would be an MTM with B&C 8BG51 and RS28A on a custom SEOS 10 (throat cut to be shallow/zero, mounting plate).

The picture I posted on the last page with the SEOS-10 is actually a MTM design, I just covered the upper portion of the box.

[ryanbouma]

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

Pete, nice work here.

I've got a similar speaker half built. Been so busy with renovations around the house I can't seem to finish it. Then a rat went looking for some warmth in my shop while I was gone for work and had one of the tweeters for lunch. Also a couple of mid cones. He's dead now. And I have a replacement tweeter. Hopefully I'll find time to finish my project.

Even though I rarely log in anymore, I'm following along

[buzzforb]

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

I think the M2 resemblance is just light reflections and not physical shape...? Anyways, I don't get the SEOS 6 or 8 when Pete seems to be on to a good woofer and crossover point from 1-1.2 kHz. To maintain boost and pattern control down to that point you need the SEOS 10. Maybe a little boost from the SEOS 8, but definitely not good pattern control down that low (though maybe there is a real difference in this area between domes and compression drivers as I have only seen measurements of the latter in these SEOS guides...).

I think a real contender for ultimate home theatre DIY speaker would be an MTM with B&C 8BG51 and RS28A on a custom SEOS 10 (throat cut to be shallow/zero, mounting plate). Even better yet, a fairly large MTM tower with ML-TL on the woofers at slightly different tuning in separate chambers. If the woofer runs out of steam before the tweeter in waveguide, then double down on the woofers, do a little more baffle step compensation in the crossover so that you have a bit stronger bass, couple that with the ML-TL and a tweeter that definitely has a wave guide big enough to provide support well down into the danger zone... you get the idea. Not taking anything away from Pete's MT design here, which I am personally very interested in.

But the waveguide dilemma seems to still be a very real thing for those of us not wanting to do the pro compression driver route. Between CNC baffles and cutting up existing designs it still seems like a bit of a mess. I like what Mr Pellegrene is doing, and hoping that he can cover more ground and find favor with those still compelled to look elsewhere as his prices seem reasonable and quality seems good. Even better yet, knowing that the RS28A works well down to a certain point and that DIY crowd is very interested in waveguides...when will PE offer an integrated tweeter waveguide design that is designed to mount/work perfectly together? To me that is the frustrating part... that the makers of good dome tweeters aren't getting involved in mating them to good waveguides in an optimal fashion.

Regards,

Greg Jensen

Dave is doing a large guide for the efficient Audax tweeter. Looks very comparable'll e to the SEOS stuff so far. I will be getting the Be version from Transducer Labs, which is projected to be 95dB and will send them his way. Both will offer a real alternative to those who do not like compression drivers. The other option is the TPL150, which is a little above my price point at the moment.

[300Z]

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

Both will offer a real alternative to those who do not like compression drivers.

What is it that you guys don't like about newer compression drivers?

[Greggo]

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

buzzforb,

Thanks for that... I have been following Dave and his work with the Audax tweeter, but I am not so sure a bigger guide is the way to go with that tweeter since it seems to want a crossover around 1.4k at the lowest due to its high fs. I have been thinking about how nice that might match up with the 8 inch Audax aerogel mid at that frequency, but that demands a 3-way design given that the 8 inch Audax mid also has a very high fs in relative terms. I am keeping an eye on this as a possible home reference project with servo subs. But in the case of the RS28A and Pete's project here in particular, the goal was to match up with the B&C woofer around 1-1.2 which the RS28A seems to handle quite nicely. My only concern with this design, and this is not based on any skills or experience, just reading and forming opinions, is that there is little natural pattern control of the woofer that low and perhaps inconsistent pattern control form such a small waveguide at that point as well.

300Z,

I will be honest and say that I am fairly certain roughly 50% of my audio bias is perception driven and not based on anything real, measurable or otherwise, and I have always felt that even the better compression drivers in decent horns/waveguides sound a bit rough around the edges for lack of a better term. If I had a large room or if I was determined to have a big home theatre with crazy SPL capability, maybe I would be more open, but I just have the expectation that a dome tweeter would be smoother and more resolving of fine detail, so since I can't help but expect it, that is what I tend to hear. Out of fairness, I have only heard a few and one was exceptional (Audio Kinesis Jazz Module), but I seem to gravitate more to what Pete has done here. Even my own suggestion of an MTM with SEOS 10 in the middle is more of a speaker than I would probably take on for myself.

Regards,

Greg Jensen

[Pete Schumacher]

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

buzzforb,

Thanks for that... I have been following Dave and his work with the Audax tweeter, but I am not so sure a bigger guide is the way to go with that tweeter since it seems to want a crossover around 1.4k at the lowest due to its high fs. I have been thinking about how nice that might match up with the 8 inch Audax aerogel mid at that frequency, but that demands a 3-way design given that the 8 inch Audax mid also has a very high fs in relative terms. I am keeping an eye on this as a possible home reference project with servo subs. But in the case of the RS28A and Pete's project here in particular, the goal was to match up with the B&C woofer around 1-1.2 which the RS28A seems to handle quite nicely. My only concern with this design, and this is not based on any skills or experience, just reading and forming opinions, is that there is little natural pattern control of the woofer that low and perhaps inconsistent pattern control form such a small waveguide at that point as well.

300Z,

I will be honest and say that I am fairly certain roughly 50% of my audio bias is perception driven and not based on anything real, measurable or otherwise, and I have always felt that even the better compression drivers in decent horns/waveguides sound a bit rough around the edges for lack of a better term. If I had a large room or if I was determined to have a big home theatre with crazy SPL capability, maybe I would be more open, but I just have the expectation that a dome tweeter would be smoother and more resolving of fine detail, so since I can't help but expect it, that is what I tend to hear. Out of fairness, I have only heard a few and one was exceptional (Audio Kinesis Jazz Module), but I seem to gravitate more to what Pete has done here. Even my own suggestion of an MTM with SEOS 10 in the middle is more of a speaker than I would probably take on for myself.

Regards,

Greg Jensen

You can be sure that I'll get a full set of off axis measurements with this guide before I call it completely done. I think I've settled on the crossover that seems to offer the most natural delivery across the spectrum. 1KHz LR4 seems to be where these two drivers and this guide seem to want to settle.

As for off axis performance examples of the RS28, when the guide was an inch wider, the control and uniformity was impressive. I don't think this one will have any trouble based on what I've measured so far.

[Greggo]

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

Pete,

Looking forward to it and nothing but props to you on this cool project. I guess all my reading on Geddes work and speaker projects needs to be tempered a bit. I just got it drilled into my head that waveguides need to be 10, 12, 15 inches in diameter to do justice to matching woofers of the same size. And according to Geddes, at least 10-12 inches in diameter to have real pattern control down to 1.2 kHz, though I do get the impression that he has pushed his crossover point lower over the years for speaker models of same size woofer and wg but I am not 100% sure... I am still curious about learning more about a few things:

1) What is narrow constant directivity versus just constant directivity? At what point is it "narrow" and thus further mitigate room reflections? And do most experienced designers agree that at some point a waveguide design offers serious benefits in a typical small domestic room? Where walls, windows, tv screens and furniture leave little options for speaker placement ideals in terms of distance (and thus time) to first and second reflections.

2) Why do some designers insist or at least recommend that the waveguide diameter match the cone diameter of the driver it crosses over to?

3) Many folks report, and maybe you agree with this or maybe it is just coincidence with this particular project, that the lower you cross the better things seem to sound (going from 2k down to 1.6 down to 1.2 down to 1k down to 800-900 Hertz) so long as the waveguide is still doing a good job at the crossover frequency. So I wonder if what we hear regarding stereo image is mostly influenced in the 800-3,200 Hz range and having that come from one driver as much as possible makes for a more accurate and stable stereo image??? And does the waveguide tweeter just being able to cover the range more important than covering the range with consistent narrow directivity? Maybe the consistent narrow directivity is more important as we approach 2k and less important as we approach 1k?

All just food for thought, at least for me…maybe an annoying snack of "been there done that" for the rest of you guys.

Regards,

Greg Jensen

[Greggo]

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

deleted…double post...

[Pete Schumacher]

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

When you look at the design in this thread, the woofer cone and guide happen to be the same diameter. So the criteria of WG and woofer needing to be the same diameter has been met thus far.

And to be clear, this is NOT a constant directivity exercise. It's merely "controlled" directivity via the use of the guide to improve both the low end performance of a tweeter with REAL low end response to below 800Hz, and to better match the off axis performance of an 8" woofer. Based on previous work with the RS28A/F and another 8" woofer, that goal seemed to be quite do-able. Originally, I wanted the guide to replicate the earlier version that was almost 8.5" wide. Experiments with that guide on a 10" wide baffle showed that the guide was controlling the tweeter output to 800Hz or so. (see below)



That guide was giving a boost to the tweeter output to below 1000Hz at 8.5" diameter. To cross at 1000Hz, you don't need to have boost that low, and this current guide seems to lose it's ability to control the tweeter output at around 1200Hz, which is a perfect point to achieve a 1000Hz XO frequency. The reason I know about where the guide loses control is based on the response of the RS28 sans guide, which extends to well below 1000Hz. When the guide stops adding boost, it's lost control. With a 10" or 12" guide on the RS28, I'd wager you could probably run the tweeter/guide combo almost to the tweeter cutoff near 600Hz.

Part of the reason the Geddes adherents might consider the cutoff points for guide dimensions could be due to the use of compression drivers that don't support the natural response that allows the guide to continue to control the output of the tweeter itself. You mention the Audax example, and the usable low frequency cutoff is not determined by the guide, but by the tweeter response itself. And while you could EQ the transfer function to squeeze a little more extension from the Audax/guide combo, there's really a diminishing benefit to doing so.

The ability of this particular tweeter to operate at a low cutoff frequency and maintain low distortion (lower than the woofer) certainly helps in the rendering of a clean program. Stereo imaging is a matter of spatial queues which are more easily identified at higher frequencies. I don't know if a capable tweeter WG combo will do a better job at 1KHz than an equally capable midwoofer. But there's no doubt in my mind that removing as much information as possible from a driver that's doing the heavy lifting below 200Hz will do nothing but improve intelligibility in the upper mids. For a high output 2-way, being able to have a tweeter effortlessly cross at 1KHz certainly seems to allow the woofer to better handle its duties.

[davepellegrene]

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

Thought I would post this here since it seems to fit in to the conversation. I was getting ready to redrill my 11x6x 3" deep guide out to 1-3/4" to test it with the Aura whisper and thought I might as well drill it out to 1-5/8" and see how it did with the RS28A. After drilling it is now 2" deep.

It seems to have held the top end up to 15 kHz before dropping off as compared to the flat baffle and has great bottom end extension.

0-90


I threw together a second order electrical circuit with a series LRC to flatten it out and roll it off on the bottom end.



Distortion at 95dbs at 1 meter



I think it looks really good. Possibly could cross around 800 Hz?

Dave

[Pete Schumacher]

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

800Hz no doubt.

Thanks for posting that Dave. It definitely ties in to what this thread is all about and seems to confirm my observations above.

[Greggo]

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

Interesting stuff. So it looks like there may be an advantage here to using a dome rather than compression driver, and that is that a dome seems to mate better at lower frequencies and allow a waveguide to provide better boost and pattern control. There is no doubt that the idea of achieving near optimal performance from guides in the 7-9 inch diameter range is much preferred to those in the 10-12 and larger, especially if one is dealing with 6-8 inch woofers rather than larger pro drivers... everything seems so much more baffle size friendly and WAF friendly at that point. I have to say, it would be great to see a few of you collaborate on the perfect guide for the RS28A, given performance/price/availability hitting such a sweet spot. I would definitely prefer to buy a waveguide rather than have to order a CNC'd baffle, though the latter does look nice.

Pete, when you mention the slightly larger guide you had worked with before, did you shrink this design down due to the baffle size of the PE cabinet, to get closer to woofer cone diameter, or other reasons ? And do you see any advantages to this approach versus an elliptical or super elliptical wave guide?

In an ideal world, and please don't anyone take any offense to this, it would be great to see PE commission Pete and Dave to develop a prototype and/or mold for the perfect guide for the RS28A, then take it for mass production and price reduction, giving you each a royalty on every unit sold. I would think a combo pack of two tweeters with two waveguides could sell for around $149.99 and would do very well.

Anyways, I am really liking this project and it might be a candidate for my eventual home reference system as well. Looking forward to more data and opinions.

Regards,

Greg Jensen

[Erich H]

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

In an ideal world, and please don't anyone take any offense to this, it would be great to see PE commission Pete and Dave to develop a prototype and/or mold for the perfect guide for the RS28A, then take it for mass production and price reduction, giving you each a royalty on every unit sold. I would think a combo pack of two tweeters with two waveguides could sell for around $149.99 and would do very well.

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.

[BeeTL]

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.

What would be involved in getting one mass produced?

Would you use the EOS-8 face outline as the template?

Having interchangable designs would be awesome for the tinkerer who doesn't want to build another cabinet each time he/she wants to try out a new driver.