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

[PWR RYD]

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

I own and listen to several different commercial amps and DIY amps. My ClassDaudio 500 wpc amp sounds best when I want to crank any speaker I own. But at normal listening levels my DIY KT88 push-pull sounds the best and at low volumes my KT88 SET amp sounds much better than the rest. As some people at DIY Iowa heard though, the SET amp just doesn't cut it in a larger room at a normal level. It plain runs out of head room and that ruins the listening experience. Sorry for the OT Pete.

[Pete Schumacher]

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

I own and listen to several different commercial amps and DIY amps. My ClassDaudio 500 wpc amp sounds best when I want to crank any speaker I own. But at normal listening levels my DIY KT88 push-pull sounds the best and at low volumes my KT88 SET amp sounds much better than the rest. As some people at DIY Iowa heard though, the SET amp just doesn't cut it in a larger room at a normal level. It plain runs out of head room and that ruins the listening experience. Sorry for the OT Pete.

Hey, I brought up the KT88. So your post is hardly OT. I agree with everything you said. I am so looking forward to getting a 250W amp on these things in the near future. That should be the real deal on determining what these monitors can do.

I've had them playing all day, and they just keep sounding better and better. I've become quite impressed with the musical quality of the woofer overall. I've got the port tuning the cabinet to 40Hz right now which may not quite be optimal, but on material that has some good bass, they seem to deliver plenty of punch. F6 is 39Hz according to the models, and F3 is 59Hz. Raising the tuning to 50Hz will move F3 to 48Hz but F6 will move up to 42Hz. That might give a little more punch overall. I'll probably cut the port in half this weekend to see what the higher tuning does.

[Greggo]

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

Any ballpark on what it would take to put this together? Drivers, crossover and cabinets from PE, CNC baffle from Tom Jones?... just asking as I was about to pull the trigger on a JBL powered monitor for my home studio and I got the nagging feeling that I might have more fun and get better sound by looking at something like The Marksmen. I am not ready for a full DIY project, yet, for my main stereo system, so something that is close to a packaged kit that I could get by with minimal skill on my part is very appealing. Any rough estimate of completion date and ballpark price? I would be very interested, especially if you feel these can easily get by without subs in the mix.

Regards,

Greg Jensen

[Jeff B.]

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

This is the first time I have read thru this thread and I wanted to thank Pete for an excellent project and for giving such great explanations of the virtues of using a waveguide on the tweeter. Waveguides have become "the thing" these days because constant directivity and minimal diffraction really are important advantages if you are looking to improve the overall power response of the speaker system.

A couple of comments - referring to different things brought up along the way, most of which were answered well by Pete, but I thought I would add that -

Waveguides do not produce any time domain distortion. The response is still minimum phase.

Waveguides don't produce diffraction effects within the guide. They do increase acoustic impedance, but that's not the same thing.

For what it's worth, many of those tiny ripples in the frequency response are caused by the air the wave-front of the sound is passing through as well as tiny movements in the mic / boom. (I have seen comparisons using a typical mic on a stand and boom vs. a very secure rig to hold the mic, the differences in how smooth the response was, was worth noting).

And the off-axis dip in Dave's response data may be due to the dome's diameter. As you move off axis you move into a region where frequencies from the edge of the dome and from the tip of the dome may become out of phase and create a null. Many tweeters will do this.

Again, nice project.

Jeff B.

[Face]

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

Waveguides do not produce any time domain distortion. The response is still minimum phase.

Waveguides don't produce diffraction effects within the guide. They do increase acoustic impedance, but that's not the same thing.

Earl Geddes would disagree, scroll down halfway and look for the mention of HOMs: http://dagogo.com/an-interview-with-...-of-gedlee-llc

I don't know if I totally agree with his theory, but do find that horns that have smooth transitions(such as SEOS) don't have "horn honk" and don't sound unnatural like PA or large circular horns can.

[Pete Schumacher]

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

Any ballpark on what it would take to put this together? Drivers, crossover and cabinets from PE, CNC baffle from Tom Jones?... just asking as I was about to pull the trigger on a JBL powered monitor for my home studio and I got the nagging feeling that I might have more fun and get better sound by looking at something like The Marksmen. I am not ready for a full DIY project, yet, for my main stereo system, so something that is close to a packaged kit that I could get by with minimal skill on my part is very appealing. Any rough estimate of completion date and ballpark price? I would be very interested, especially if you feel these can easily get by without subs in the mix.

Regards,

Greg Jensen

I was listening to a few tracks with some deep bass over the weekend (organ music) and was surprised what they were able to do. While the theoretical F3 is around 58Hz right now, the F6 at 38Hz with the 40Hz enclosure tuning seems to compliment the room well enough to support satisfactory levels of bass for most music. Depending on your room, you may find these can get by without subs.

I'm about ready to call the crossover done as the overall balance seems to meet my expectations. I'll probably begin to disassemble the setup after the weekend to get the baffle painted. After that, I'll get some final pictures of it posted along with a full set of off axis plots, as well as a high powered sweep (100dB).

I just added up a shopping cart with the parts I'm using and it comes to $778.08. That doesn't include stuffing, mounting screws, wire or solder. Tom's baffles would add in the neighborhood of $100/pr, but you'd better get that price from him to be absolutely sure. If you can work a soldering iron, have a 2 3/8" hole saw for a hand held drill to cut the port hole, these would be pretty simple to assemble. The baffle would need some final sanding and a few applications of sanding sealer in between sanding sessions of 320 grit, which then would allow you to apply a rattle can paint finish.

I can probably put a kit together for you and save you a few bucks. Send me a PM.

[Pete Schumacher]

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

This is the first time I have read thru this thread and I wanted to thank Pete for an excellent project and for giving such great explanations of the virtues of using a waveguide on the tweeter. Waveguides have become "the thing" these days because constant directivity and minimal diffraction really are important advantages if you are looking to improve the overall power response of the speaker system.

A couple of comments - referring to different things brought up along the way, most of which were answered well by Pete, but I thought I would add that -

Waveguides do not produce any time domain distortion. The response is still minimum phase.

Waveguides don't produce diffraction effects within the guide. They do increase acoustic impedance, but that's not the same thing.

For what it's worth, many of those tiny ripples in the frequency response are caused by the air the wave-front of the sound is passing through as well as tiny movements in the mic / boom. (I have seen comparisons using a typical mic on a stand and boom vs. a very secure rig to hold the mic, the differences in how smooth the response was, was worth noting).

And the off-axis dip in Dave's response data may be due to the dome's diameter. As you move off axis you move into a region where frequencies from the edge of the dome and from the tip of the dome may become out of phase and create a null. Many tweeters will do this.

Again, nice project.

Jeff B.

Earl Geddes would disagree, scroll down halfway and look for the mention of HOMs: http://dagogo.com/an-interview-with-...-of-gedlee-llc

I don't know if I totally agree with his theory, but do find that horns that have smooth transitions(such as SEOS) don't have "horn honk" and don't sound unnatural like PA or large circular horns can.

Thanks for joining in Jeff! You too Face.

While HOMs may be an issue with compression drivers and long throats, this kind of guide simply doesn't work that way. I like to think of it as diffraction control, not acoustic loading, though there may be some of that in play. The throat is so large that I haven't been able to see anything but minuscule effects on the impedance of the RS28. The guide simply doesn't add any appreciable loading to the diaphragm. The opening doesn't impinge on any of the moving parts of the tweeter, neither the surround nor the dome itself, so there's effectively no compression chamber.

[mzisserson]

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

Thanks for joining in Jeff! You too Face.

While HOMs may be an issue with compression drivers and long throats, this kind of guide simply doesn't work that way. I like to think of it as diffraction control, not acoustic loading, though there may be some of that in play. The throat is so large that I haven't been able to see anything but minuscule effects on the impedance of the RS28. The guide simply doesn't add any appreciable loading to the diaphragm. The opening doesn't impinge on any of the moving parts of the tweeter, neither the surround nor the dome itself, so there's effectively no compression chamber.

I guess you can justify]nothing but upside that way. :p

Sure, there may be less ill effects because it is a good design, but they will still be there. Minimum effect is still and effect and from Dave's testing you can see how small issues in alignment/geometry can have a negitave effect on the end result. It does not mean the downside out-weighs the benefits it provides in this application because like I said, it seems like a smart decision for this application to get a dome to keep up with a high output 8" woofer. It also likely will sound very good (save the brick wall at 15K). I think your meaurements are pretty solid and paint the picture of a good, high-output speaker also capeable of good fidelity. Those two often do not go hand in hand.

I am still waiting for the high output sweeps....

[Pete Schumacher]

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

I guess you can justify]nothing but upside that way. :p

Sure, there may be less ill effects because it is a good design, but they will still be there. Minimum effect is still and effect and from Dave's testing you can see how small issues in alignment/geometry can have a negitave effect on the end result. It does not mean the downside out-weighs the benefits it provides in this application because like I said, it seems like a smart decision for this application to get a dome to keep up with a high output 8" woofer. It also likely will sound very good (save the brick wall at 15K). I think your meaurements are pretty solid and paint the picture of a good, high-output speaker also capeable of good fidelity. Those two often do not go hand in hand.

I am still waiting for the high output sweeps....

In all fairness, Dave's results showing a significant effect on Fs are due to the geometry of his guide. He's created a sort of compression chamber with that tweeter by bringing the throat opening over the moving parts of the dome. The sweeps I've run with this geometry have no effect on Fs. I'll run a couple of impedance sweeps later tonight on the tweeter in and out of the guide and post the results. I did that with the slightly larger guide that DanP made a couple years ago. The results of that comparison are what I base the "minuscule" comment on. The only difference I saw between in/out was as slight modification of the "Q" of the impedance peak, but the center frequency was unaltered.

And the "brick wall" is more a function of the tweeter itself than of the guide. The RS28F response was extended to 20KHz in the earlier example from the MiniByzy thread.

[davepellegrene]

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

Actually I've only had the Impedance issue with the ND25. All other tweeters I've tested with the reduced throat has had no effect on the Fs of the tweeter.
Here is the RS28F with the faceplate attached.


This is in my 8" guide with a 1" throat


Dave

[Pete Schumacher]

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

Well, I guess I won't pile on by posting an almost identical set of plots.

Thanks for that Dave

[PWR RYD]

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

Thanks Pete, Dave, and everyone else for sharing! Great info. My Dad and I have been mentally and raw sketching a simple way to DIY fab simple and repeatable waveguides.

[Pete Schumacher]

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

I should have a Wells Audio amplifier this weekend to play around with. It's a very high quality 120W/ch amplifier that I'll use to run a few high powered sweeps to see what happens to distortion. I'll also try and figure out a good way to do a series of sweeps at regular power increments to test compression. Could be fun!

[mzisserson]

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

Actually I've only had the Impedance issue with the ND25. All other tweeters I've tested with the reduced throat has had no effect on the Fs of the tweeter.
Here is the RS28F with the faceplate attached.


This is in my 8" guide with a 1" throat


Dave

I see a difference Dave... Wait, *cleans glasses*, nope spaghetti sauce. Looks identical to me.

[davepellegrene]

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

I see a difference Dave... Wait, *cleans glasses*, nope spaghetti sauce. Looks identical to me.

I do believe now that it is important to compare the impedance graph's of the tweeter with faceplate vs removed with a guide installed. On the ss 3004 it showed a double hump which told me that when removing the faceplate broke the seal to the rear cup. Once I sealed the guide to the cup it fixed the problem. Without taking the impedance measurements I would have not figured that out. I now need to figure out why the impedance is higher with the guide on the ND25. I'm going to test it with a guide that fits around the outside of the surround instead of over it to see if that is the issue. It may just have been that I didn't have the guide seated on the tweeter properly. When testing I use double sided tape and zip ties to hold everything together temporarily for easy switching.

I'm also going to do a test with the RS28A comparing the guide fitting around the surround using a 2-9/16" throat vs a guide over the surround with a 1-1/16" throat. I know the smaller throat will boost the upper frequencies but what I want to see is if it's at the expense of boost in the lower frequencies. I had thought when I first started testing guides the bottom end boost was the same for both guides. I need to double check this.

Dave