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

[davepellegrene]

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

Pete,
Gonna be trying to copy this in similar way to Troels Quattro with MLTL loaded woofer. One question for you or Dave is whether or not the RS28A will work on the Pellegrene waveguide or is it just for the RS28F

The guide for the RS28F will not work on the A version. The F version has the throat reduced to 1-3/16" which boosts the top end and holds a more uniform directivity pattern as you go off axis. The A version did not like the throat reduced over the surround. It was causing a cancellation around 12 kHz. I have a pic of both domes side by side and the F version is quite a bit taller then the A version. I can't seem to find it at the moment.
I could make a guide up for the A version if you like either in an 8" round or 5x8 elliptical. I have the A version here so I could test it.
Dave

[buzzforb]

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

Dave,
Thank you for the info. I appreciate it as well as the offer. Perhaps for the sake of semi-uniformity, I should have tou make the round one for the 28A. Ill have to decide based upon Pete's input.

Pete,
Have I read that you prefer the A over the F? Here are two tapered options. ONe 33" length, the other 39". Both within the scale of the Quattro with the 33" one being slightly smaller. Both look good, but both have the same llarge secondary impedance spike. Dont know how much of an issue that will be, crossover wise. ALso, not real sure how having the tweeter/waveguide combo in the TL path-length will affect performance.

Mathcad - 8bg51 - 33 Inch Tapered.pdfMathcad - 8bg51-39 Inch Tapered.pdf

[Pete Schumacher]

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

Dave,
Thank you for the info. I appreciate it as well as the offer. Perhaps for the sake of semi-uniformity, I should have tou make the round one for the 28A. Ill have to decide based upon Pete's input.

Pete,
Have I read that you prefer the A over the F? Here are two tapered options. ONe 33" length, the other 39". Both within the scale of the Quattro with the 33" one being slightly smaller. Both look good, but both have the same llarge secondary impedance spike. Dont know how much of an issue that will be, crossover wise. ALso, not real sure how having the tweeter/waveguide combo in the TL path-length will affect performance.

[ATTACH]42288[/ATTACH][ATTACH]42289[/ATTACH]

Nothing you can really do about the upper frequency impedance peak other than compensate for it in the crossover with some HUGE component values (12mH, 400uF, 8 Ohm series connected) shunted across the woofer terminals. The lower peak is no big deal.

Thanks for the plots. They look to be better than the ML-TQWT up in the midrange.

I do like the A version better than the F, but that's a purely personal observation. While the F is more extended, it's also a tad too "polite" for me. The A version seems to have a touch more bite to it, a quality I rather like.

I'm sure Tom Jones (takitaj) could replicate the guide onto a larger baffle for you if you wanted to duplicate the build and crossover into a tower.

[buzzforb]

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

How detrimental to the response do yo think a fold would be? I want the baffle to be Walnut, so I may have to get Dave, to make some of the waveguides for it. I do not have the ability to wrap a shape like that in veneer. I will see if I can work on the impedance peak. IF you had an 8" that could cross higher, wouldnt this be beneficial in that it would cover more of the vocal range. Some 8"s could do close to 2K with 90 degree directivity

[Pete Schumacher]

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

How detrimental to the response do yo think a fold would be? I want the baffle to be Walnut, so I may have to get Dave, to make some of the waveguides for it. I do not have the ability to wrap a shape like that in veneer. I will see if I can work on the impedance peak. IF you had an 8" that could cross higher, wouldnt this be beneficial in that it would cover more of the vocal range. Some 8"s could do close to 2K with 90 degree directivity

I can't imagine a fold being too problematic really.

Tom could machine the entire baffle from solid walnut, including the guide. He could start with 1" thick walnut, cut the woofer hole and then use that piece to glue to the back of the baffle to cut the waveguide. Dave's guide would certainly work, but they would require a different crossover since I doubt he could duplicate the exact profile Tom put into this particular baffle. If you've got measuring gear, then there's no problem going with a different guide.

As for being able to cross higher, I can't see any reason to. Vocals with the setup I have now are superb. The tweeter covers the range to 1KHz with ease. In fact, its distortion is about 10dB lower than the woofer at 1KHz (-60dB vs. -50dB). Vocal range is mostly below 1KHz anyway. The consonants are much higher up than even 2KHz, and a smooth crossover takes care of the hand off.

[jonasz]

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

About the A vs F debate, my feeling is that a harddome and a softdome should "load" a wg in different ways. The A is pistonic up to about 30k while the F gradually goes from pistonic to only the outer edge of the dome moving at higher frequencies. This got to influence at least the higher frequencies in one way or another? Is a harddome or a softdome, or maybe even a ringradiator, to prefer in a wg?

Oh, and another question:
I know PE claims the F version to be able to cross REALLY low, shouldn't the A version be able to do the same? I mean they ARE the same tweeters apart from the domes, or?

[Pete Schumacher]

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

About the A vs F debate, my feeling is that a harddome and a softdome should "load" a wg in different ways. The A is pistonic up to about 30k while the F gradually goes from pistonic to only the outer edge of the dome moving at higher frequencies. This got to influence at least the higher frequencies in one way or another? Is a harddome or a softdome, or maybe even a ringradiator, to prefer in a wg?

Oh, and another question:
I know PE claims the F version to be able to cross REALLY low, shouldn't the A version be able to do the same? I mean they ARE the same tweeters apart from the domes, or?

In this particular guide geometry I was able to get both the A and F versions working pretty much equally well. The difference between this guide and the one you heard in my living room, and Dave's guide for the F, is that these two guides simply continue the profile of the flange of the tweeter, which is the same for both versions of the tweeter. The F version is more extended on top and it was in the guide too, but just a little.

This is the response for the F version you heard.



This one is with the A version.

[davepellegrene]

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

I found the pics.



The A version also has a small piece of plastic on the inside of the screen for a phase plug. The F version doesn't have one. This is probably the reason for the A version not working in the reduced throat size. I remove the faceplate in order to connect the guide directly to the tweeter.



Dave

[lorenmjones]

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

I don't know about the influence of Qms or BL etc, but I will jump on the bandwagon as saying that I think I definitely enjoy the sound of pro style drivers in home applications. I think it is mostly related to dynamics. The pro drivers generally are higher sensitivity and have higher power handling therefore they have much greater dynamic capability. I think that this plays out not only in the absence of power compression when used at home levels but that there could also be some influence due to reduced demand on the amplifier. Just a 6 db difference in sensitivity costs 4x the amp power and it seems possible to me that if the amp is operating further within it's performance envelope (as opposed to closer to the its limits) that it may be more linear and dynamic as well. I'm not an engineer though, just spitballing here.

I do agree that drums sound phenomenal and I think voices are really great too. Frankly I haven't found the pro drivers in my system to be lacking for much, but I haven't listened to the Scans, Accutons, Seas Excels etc to compare.

You may be on to something there. The rated RMS power for the RS225 compared to the B&C is 1:3. The ability of the B&C to shed heat might have something to do with that "live" sound. Maybe less thermal compression? The other BIG difference between the RS225 and B&C is the Qms number: 1.44 vs. 12.3. I believe the higher Qms means that it's just plain easier to push the cone around by the motor. The B&C moving mass is slightly higher, but it does have 33% more motor force.

[buzzforb]

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

It has been suggested that the MMS/BL ratio is a good indicator of speed in a driver, but seems that it is hard not to consider Qms. LeCleach has shown that transonductance amps can improve the performance of horn loaded compression drivers, especially lower in frequency. After this build, I will start my PCD build.....assuming I am not satisfied fully with this one. This speaker will most likely end up at my brothers house who has a slightly smaller room, hence the 8" drivers.

One naggging question, Pete. Part of the reason for impedance spike is box size wanted by these drivers. Since you are crossing so low, would a 10" with similar specs and large box size needs be a reasonable thought. It would have no issue crossing at similar point, but I am not sure how it would pair acoustically with the much smaller waveguide. I had looked into 8" drivers for a 3 way PCD, but this was simply to cross in the 1.8-2K region. I have sent emails to both Dave and TOm about waveguide options. Dave said he should have not trouble replicating your chosen profile, so just waiting to hear from Tom. Thanks for the help.

[Pete Schumacher]

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

It has been suggested that the MMS/BL ratio is a good indicator of speed in a driver, but seems that it is hard not to consider Qms. LeCleach has shown that transonductance amps can improve the performance of horn loaded compression drivers, especially lower in frequency. After this build, I will start my PCD build.....assuming I am not satisfied fully with this one. This speaker will most likely end up at my brothers house who has a slightly smaller room, hence the 8" drivers.

One naggging question, Pete. Part of the reason for impedance spike is box size wanted by these drivers. Since you are crossing so low, would a 10" with similar specs and large box size needs be a reasonable thought. It would have no issue crossing at similar point, but I am not sure how it would pair acoustically with the much smaller waveguide. I had looked into 8" drivers for a 3 way PCD, but this was simply to cross in the 1.8-2K region. I have sent emails to both Dave and TOm about waveguide options. Dave said he should have not trouble replicating your chosen profile, so just waiting to hear from Tom. Thanks for the help.

The only way to get a smaller upper frequency impedance peak is to use a driver with a much lower Qts than this one. The size of the peak isn't really related to the box size as much as it is to the driver parameters themselves.

I see no reason that a 10" woofer couldn't be used with this tweeter/guide combo, as long as the sensitivity matches up. The RS28 would really be limited to woofers with no more than about 94dB/2.83V sensitivity at low frequencies. Any higher and the tweeter just wouldn't be able to properly keep up.

Finally got the Wells amp. I'll be hooking it up tonight and will see what an additional 100W available can do. :D

[buzzforb]

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

The 8NDL51 models nicely in comparison, with a much lower second peak. I will spend some more time playing with different woofers to see what I can come up with. Thanks for the help

[Pete Schumacher]

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

The 8NDL51 models nicely in comparison, with a much lower second peak. I will spend some more time playing with different woofers to see what I can come up with. Thanks for the help

I'm not sure what you mean by the second peak. Are you talking about the one at higher frequency above tuning, or below? The 8NDL51 will not have nearly as good extension as the 8BG51.

[Pete Schumacher]

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

Ok, I got the Wells Audio amplifier hooked up. It's a really nice piece of gear too. Fairly spartan looking with a nearly gratuitous AC voltmeter on the front panel. Hey, at least it lets you know what your line voltage is.

So I took a few sweeps just to see what the pair are capable of. Holy crap, does it get friggin loud. Best part is, the tweeter is the cleaner of the two at high volumes to levels that seriously hurt my ears during the sweeps. I forgot to bring over the SPL meter, but I know it's gotta be over 100dB on the loudest sweep I wanted to take. I'll wait to post it until I get a calibrated level.

So, after seeing how freakin' loud it played cleanly during the sweeps, I queued up some tunes. I went through a few easy ones, vocals, Chinese drums, Cosmic Hippo, typical voicing stuff. After being satisfied with the sound of the amp under these circumstances, I decided to go for the gusto and pound out some plain old, driving ROCK/METAL.

Rammstein, Ich Will. Mmmm . . . this is getting fun.

So I peruse the server looking for something I hadn't heard in a while. Alter Bridge . . . One Day Remains, Find the Real.

I start with the volume at -45, pretty loud in the seated position. Gotta be over 90dB, and I'm 3m away from each monitor. Well before the end of the song, the volume setting had moved up over 10dB. And I want it even louder. Basically, here's me during that song.



Wow, these pro woofers could easily get addictive!!!

The sound was HUGE, clean, defined. I couldn't believe how the vocalist stayed front and center, in between the speakers, not in front, not behind. Just right THERE. Didn't matter how loud it played, the sound stage was massive. Chest pounding. Exhilarating. Goosebumps!

I can't wait to get these in front of someone else. Ryan hasn't heard them yet, just me, my wife, and now one of my daughter's friends who stopped by to pick up an old console radio project. He sat and listened for a few minutes, and his first comment went something like, "those would make great bar monitors wouldn't they? I mean, I would never have guessed something so small could sound like that!" He's into drums, so the Chinese drums track really got his attention. After that, I played him some vocalists, and he sat completely still for the entire song.

They've turned out really good. After experiencing the Alter Bridge track, I've had the urge to rename them Jack Hammers. These might give Tarkus a run for the money. My expectations have been greatly exceeded now that I've got some real power to throw at them.

[mzisserson]

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

Ok, I got the Wells Audio amplifier hooked up. It's a really nice piece of gear too. Fairly spartan looking with a nearly gratuitous AC voltmeter on the front panel. Hey, at least it lets you know what your line voltage is.

So I took a few sweeps just to see what the pair are capable of. Holy crap, does it get friggin loud. Best part is, the tweeter is the cleaner of the two at high volumes to levels that seriously hurt my ears during the sweeps. I forgot to bring over the SPL meter, but I know it's gotta be over 100dB on the loudest sweep I wanted to take. I'll wait to post it until I get a calibrated level.

So, after seeing how freakin' loud it played cleanly during the sweeps, I queued up some tunes. I went through a few easy ones, vocals, Chinese drums, Cosmic Hippo, typical voicing stuff. After being satisfied with the sound of the amp under these circumstances, I decided to go for the gusto and pound out some plain old, driving ROCK/METAL.

Rammstein, Ich Will. Mmmm . . . this is getting fun.

So I peruse the server looking for something I hadn't heard in a while. Alter Bridge . . . One Day Remains, Find the Real.

I start with the volume at -45, pretty loud in the seated position. Gotta be over 90dB, and I'm 3m away from each monitor. Well before the end of the song, the volume setting had moved up over 10dB. And I want it even louder. Basically, here's me during that song.



Wow, these pro woofers could easily get addictive!!!

The sound was HUGE, clean, defined. I couldn't believe how the vocalist stayed front and center, in between the speakers, not in front, not behind. Just right THERE. Didn't matter how loud it played, the sound stage was massive. Chest pounding. Exhilarating. Goosebumps!

I can't wait to get these in front of someone else. Ryan hasn't heard them yet, just me, my wife, and now one of my daughter's friends who stopped by to pick up an old console radio project. He sat and listened for a few minutes, and his first comment went something like, "those would make great bar monitors wouldn't they? I mean, I would never have guessed something so small could sound like that!" He's into drums, so the Chinese drums track really got his attention. After that, I played him some vocalists, and he sat completely still for the entire song.

They've turned out really good. After experiencing the Alter Bridge track, I've had the urge to rename them Jack Hammers. These might give Tarkus a run for the money. My expectations have been greatly exceeded now that I've got some real power to throw at them.

But really....