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

[Pete Schumacher]

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

I'm anxiously waiting for you to hook them up to something powerful... :D

I'm with you about the missing "live"-feeling in speakers, most hifispeakers are more than . I wonder why, is it brutal BL-force some drivers have or is it a nice sounding coloration that gives that feeling of live music?

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.

[davepellegrene]

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

I also noticed how much more realistic drums where on my dipole speaker with the B&C. Just tapping the driver with your finger it has more of a drum head sound to it. I figured it had more to do with the stiffer surround and suspension. I also noticed comparing it through A/B testing against my black box speakers that they did have more realistic drum sound but there where other instruments that I thought they did not reproduce as well as my black box speakers. Unfortunately I can remember what they were.
As I mentioned before the B&C as a dipole crossed to the sub at 200 Hz would take all my 300 watt pro amp could give it. It'll be interesting what you find in a sealed box with as much baffle step you have on them.

Dave

[Pete Schumacher]

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

I also noticed how much more realistic drums where on my dipole speaker with the B&C. Just tapping the driver with your finger it has more of a drum head sound to it. I figured it had more to do with the stiffer surround and suspension. I also noticed comparing it through A/B testing against my black box speakers that they did have more realistic drum sound but there where other instruments that I thought they did not reproduce as well as my black box speakers. Unfortunately I can remember what they were.
As I mentioned before the B&C as a dipole crossed to the sub at 200 Hz would take all my 300 watt pro amp could give it. It'll be interesting what you find in a sealed box with as much baffle step you have on them.

Dave

It's not just drums, although they are what has really stuck out. Voices, sax, guitars (acoustic and electric) are very vibrant and quite realistic sounding. So far, I'm very impressed with the quality of audio I'm hearing from this woofer. I look forward to getting other folk's impressions, as we all know how biased I am for my own creations . . . :o

[henry218]

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

this is becoming more and more interesting, i was noticing about how pro woofers seems to have better sounds for instrument than the typical hifi drivers, and i kept coming back to their parameters with high BL and Qms and low Qes.

is this the reasons??? but having the Qms so high, wouldnt it be best to use the drivers in louder SPL? as it needs more current to move the cones?? or is it the suppressions from the motor gives it a better control movements?

[Pete Schumacher]

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

this is becoming more and more interesting, i was noticing about how pro woofers seems to have better sounds for instrument than the typical hifi drivers, and i kept coming back to their parameters with high BL and Qms and low Qes.

is this the reasons??? but having the Qms so high, wouldnt it be best to use the drivers in louder SPL? as it needs more current to move the cones?? or is it the suppressions from the motor gives it a better control movements?

Who knows? As the woofer coil moves out of the gap, the dominant factor for Qts becomes Qms I believe. If that's the case, as you crank up the volume, the low frequencies could tend to become more pronounced due to excursion raising Qts. I'm not sure, just speculating.

Higher Qms means less damping in the suspension, and that may or may not be a good thing. Again, I just don't know. Low damping would lead me to believe that for very small signal changes, the easier to move cone would respond better to those low level signals . . .

Once I really get some power to these things, perhaps that will become more obvious. As it is now, the KT88 doesn't really stress the woofers at all. But so far, they're very engaging speakers at normal listening levels ([email protected], 85dB at the listening position with the pair going).

[henry218]

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

Higher Qms means less damping in the suspension, and that may or may not be a good thing. Again, I just don't know. Low damping would lead me to believe that for very small signal changes, the easier to move cone would respond better to those low level signals . . .

allright, my logic was backwards before, i thought the qms is the resistance of the suspension. i got it now, thanks

pete, ive been meaning to try 8" for midbass, thank you for posting this

cheers
henry

[davepellegrene]

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

I just realized I was using the B&C 8ndl51. It looks to be a slight step down from the 8bg51.

Dave

[Erich H]

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

Not sure it's a step down, just a side step depending for what you're after or need.

Forum member MTG90 made up a speaker last year that used the 8PS21 and it works out very well and can handle just about anything you can throw at it. It was designed to be used with a subwoofer and the overall weight of the speaker wasn't a big concern. A few months ago we were going to work on a speaker that could be used without a subwoofer, but the FG51 wasn't easy to come by so we started looking at other models. In general, I think they're all nice woofers, just made for different applications.




Last year I worked on a waveguide that would fit the RS28, but didn't know how much abuse that tweeter could handle alongside a pro woofer. They're made almost like smaller compression drivers, so maybe they would be okay even at high volumes. I'll be anxious to see what Pete thinks of it after he pumps some more power through them.

[Paul K.]

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

I apologize for interrupting your thread, Pete, but just want to know if you received the two emails I sent you on Thanksgiving day? If not I'll re-send them.
Thanks,
Paul

[buzzforb]

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

[Pete Schumacher]

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

Not sure it's a step down, just a side step depending for what you're after or need.

Forum member MTG90 made up a speaker last year that used the 8PS21 and it works out very well and can handle just about anything you can throw at it. It was designed to be used with a subwoofer and the overall weight of the speaker wasn't a big concern. A few months ago we were going to work on a speaker that could be used without a subwoofer, but the FG51 wasn't easy to come by so we started looking at other models. In general, I think they're all nice woofers, just made for different applications.

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Last year I worked on a waveguide that would fit the RS28, but didn't know how much abuse that tweeter could handle alongside a pro woofer. They're made almost like smaller compression drivers, so maybe they would be okay even at high volumes. I'll be anxious to see what Pete thinks of it after he pumps some more power through them.

When you look at the transfer function of the tweeter crossover, and see that it's down 20dB at 1KHz relative to the upper frequency range, I really think that this tweeter could easily keep up with the woofer in almost any application. For home listening, you'd be into serious hearing damage if you were to actually get 100W of music power into this tweeter. When you think about it, you'd need a 1000W amp driving these monitors to begin to even approach sending that much power into the tweeter with music as the signal. I'd be more worried about slamming the woofer VC into the back plate than roasting the tweeter.

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

I'm pretty sure that Dave's WGs will allow either RS28 to work just fine. I was able to switch back and forth between the A and F in the MiniByzy build with slight mods to the crossover.

And I like the idea of converting this into a tower build. The Qts with the crossover accounted for would actually let this woofer work quite well in a tapered transmission line.

[buzzforb]

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

Here is rough draft using roughly the same dimensions as Troels Quattro.

[Pete Schumacher]

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

Run that through Martin's spreadsheet again, but try a tapered TL instead.

Here's what I got using the old worksheet. Total line volume is 1.07 cubic feet.

[buzzforb]

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

First one was modeled as a expanding MLTL. What benefits do you expect from the tapered? Beneficial impedance response? Only thing ugly about the expanding is nasty spike of second impednace hump.

[Pete Schumacher]

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

First one was modeled as a expanding MLTL. What benefits do you expect from the tapered? Beneficial impedance response? Only thing ugly about the expanding is nasty spike of second impednace hump.

I don't know if there's any benefit other than the simplicity of the construction. I just like tapered lines I guess. The stuffing seems to offer more midrange control with the tapered TL, at least that's what it seems like to me. I'm just curious if the newer spreadsheets get the same results as my very old versions.

When I think about the 1cf Dayton MTM cabinet, I can see a folded line inside, with the woofer under the tweeter, centered on the front baffle, and the terminus on the bottom of the back panel using a simple 3" diameter opening or 6.8 sq inch slot.