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

[Greggo]

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

Great info here in this thread! I am following closely and very interested, both short term on The Marksmen for my home studio and long term on an ambitious DIY project of my own design or at least my own requirements for design.

I do see nothing but upside with a waveguide, but only because I have heard a few and know that I don't miss the super spatial imaging that seems to work best with 180 degree waveguides and narrow cabinets. I think proper waveguide designs, dipole, narrow flat baffle and wide flat baffle all have their own signature when it comes to image rendition and perhaps some other distinctive traits to the direct sound as well. Since I know that I am OK, or better than OK with the way waveguide based speakers image in a room, everything else seems superior to me: Physical alignment with mid or midbass, lower distortion at crossover, lower crossover point in general (I personally think the best speakers, regardless of 2, 3, or 4 way design... have a crossover point somewhere between 800 and 1,800 Hx and whatever that point is, the next transducer up in frequency should be a waveguide tweeter).... What I am still trying to understand, however, is just how important directivity at crossover frequency is between cone and dome with waveguide. In the Marksmen for example, it seems like there is no way the waveguide holds any real directivity control down to 1,200 Hz and that the woofer probably doesn't start to have any significant directivity until around 1,400-1,600 Hz, so I am interested in seeing the polars as well as hearing more from Pete about how this design comes together.

The thing that I am most excited about when it comes to constant narrow directivity designs is that this type of speaker does the best job of minimizing the impact of the room. This means a lot to me as I have had some recent disappointments between room sounds now that I have a more modest house and have to deal with a more practical mixed purpose room that has the speakers closer to boundaries and I have few if any options for proper room treatment. I think the role that your room plays in your listening experience is the most under rated factor for most folks.

Pete, thanks for the PM exchange and I am looking forward to seeing some pics of your finished project.

Have any of you considered using miniDSP to manage sub, woofer, waveguide.. and then a passive crossover between a waveguide and a ribbon at 8-12 kHz to play to the strengths of each? I am thinking about a reference project at some point in a year or two that would involve a pair of servo driven 8 inch subs, an 8 inch midbass like the Audax aerogel, an 8x5 waveguide with maybe a transducer labs tweeter running 1-16 kHz and an AC aerostriction tweeter running 12 kHz and up... any thoughts?

Regards,

Greg Jensne

[69FireBird]

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

the reason i asked is because the vapor audio whihc you work for pete was selling the last speakers you posted about and so i was curious if this would be the same or what. i like these because the cabinets ar enot that ugly, but i am worried about not having real bass?

[johnnyrichards]

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

The gods know I should stay out, but even the most cynical asswhole can see this is (currently) a pure DIY build, Firebird.

[Pete Schumacher]

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

Great info here in this thread! I am following closely and very interested, both short term on The Marksmen for my home studio and long term on an ambitious DIY project of my own design or at least my own requirements for design.

I do see nothing but upside with a waveguide, but only because I have heard a few and know that I don't miss the super spatial imaging that seems to work best with 180 degree waveguides and narrow cabinets. I think proper waveguide designs, dipole, narrow flat baffle and wide flat baffle all have their own signature when it comes to image rendition and perhaps some other distinctive traits to the direct sound as well. Since I know that I am OK, or better than OK with the way waveguide based speakers image in a room, everything else seems superior to me: Physical alignment with mid or midbass, lower distortion at crossover, lower crossover point in general (I personally think the best speakers, regardless of 2, 3, or 4 way design... have a crossover point somewhere between 800 and 1,800 Hx and whatever that point is, the next transducer up in frequency should be a waveguide tweeter).... What I am still trying to understand, however, is just how important directivity at crossover frequency is between cone and dome with waveguide. In the Marksmen for example, it seems like there is no way the waveguide holds any real directivity control down to 1,200 Hz and that the woofer probably doesn't start to have any significant directivity until around 1,400-1,600 Hz, so I am interested in seeing the polars as well as hearing more from Pete about how this design comes together.

The thing that I am most excited about when it comes to constant narrow directivity designs is that this type of speaker does the best job of minimizing the impact of the room. This means a lot to me as I have had some recent disappointments between room sounds now that I have a more modest house and have to deal with a more practical mixed purpose room that has the speakers closer to boundaries and I have few if any options for proper room treatment. I think the role that your room plays in your listening experience is the most under rated factor for most folks.

Pete, thanks for the PM exchange and I am looking forward to seeing some pics of your finished project.

Have any of you considered using miniDSP to manage sub, woofer, waveguide.. and then a passive crossover between a waveguide and a ribbon at 8-12 kHz to play to the strengths of each? I am thinking about a reference project at some point in a year or two that would involve a pair of servo driven 8 inch subs, an 8 inch midbass like the Audax aerogel, an 8x5 waveguide with maybe a transducer labs tweeter running 1-16 kHz and an AC aerostriction tweeter running 12 kHz and up... any thoughts?

Regards,

Greg Jensne

Adding a super tweeter is certainly an option, but I don't know if limiting it to the top octave would really add any benefit. The ASTs and ribbons add a lot of liveliness when crossed around 3000Hz. Not utilizing what they have to offer in that range seems to be a waste of their best qualities. Were I to use an AMT, I'd probably go with one of the larger AC units in a shallow guide. They're already good to 1000Hz without a guide so there's no real need for any boost, just a measure of control. The Beyma TPL150H is one WG loaded AMT that has those excellent qualities missing in dome tweeters. I'm pretty confident that the AC units would offer similar qualities at a little lower price. And if you're going with a T-labs tweeter, I doubt you'd need to augment the top octave at all. We're using one in an 8" wide, 2" deep guide similar to this one and it offers smooth response to 20KHz. It's a very nice dome tweeter.

Based on previous work with a similar guide, this tweeter and guide combo seems to match well with the directivity of an 8" woofer through the crossover range. If you look back at the off axis plots I posted earlier in the thread, you can see that the response stays quite smooth as you go off axis with a consistent drop in level across the spectrum from about 600Hz and up. This would indicate that a 45 degree "crossfire" setup would work very well, which will help limit the effects of boundary conditions (first reflection) as well as widen the sweet spot. I anticipate a very similar result with this setup and should be doing a more thorough set of measurements this weekend.

[Pete Schumacher]

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

the reason i asked is because the vapor audio whihc you work for pete was selling the last speakers you posted about and so i was curious if this would be the same or what. i like these because the cabinets ar enot that ugly, but i am worried about not having real bass?

The gods know I should stay out, but even the most cynical asswhole can see this is (currently) a pure DIY build, Firebird.

The previous build used a cabinet construction that was beyond the abilities of most DIY'ers, so the resulting crossover work would be almost useless to post since it is so critically matched to the enclosure. This build intentionally uses a cabinet that is available to everyone, or can be easily fabricated by most any DIY'er. The only part not available would be the baffle, but takitaj has already told me that he'll make an identical set for anyone who asks. That was the whole reason for this project; to make a build that mirrored the MiniByzy build in function without the need to construct such a difficult cabinet.

As to whether there's enough bass, that's a tough question to answer since "enough" is so personal. This B&C woofer seems to do just fine in the current enclosure and box tuning. F10 is around 30Hz, F6 in the upper 30s, and F3 in the mid 50s. Put them in a typical listening room like my living room (15x18), and there's real bass to below 40Hz, which covers most of the musical spectrum. It doesn't have the extension of the Vifa NE225W, but it does offer an easier load as well as higher sensitivity, a reasonable tradeoff.

While it's not the cheapest project with a shopping cart price of about $708/pr for everything but the baffle, it should provide a robust build that offers high output with low distortion that could easily be augmented by a nice sub and offer HT SPL (>110dB).

[69FireBird]

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

I am ok with building weird stuff i have some friends we all do so stupid ugly box shapes should not matter I just came here to build speakers if people tallking about them are not talking about them that means they are what? hiding stuff?

johnnyrichards asswhole? you

[Pete Schumacher]

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

I am ok with building weird stuff i have some friends we all do so stupid ugly box shapes should not matter I just came here to build speakers if people tallking about them are not talking about them that means they are what? hiding stuff?

It's all out in the open here 69Firebird. Everything. I've already posted the XO and the mod I made to it. There will be more data later this week too.

I don't know what you think enough bass really means. Depends on the music you like I suppose. I had some Tool cranking last night to very satisfying levels and wasn't thinking to myself "these could use more bass." For an 8" 2-way, they are quite nice and I personally wouldn't mind keeping this pair for a long time.

[Pete Schumacher]

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

Well, I was unable to acquire the Wells Audio amp for the weekend, so I had to use the KT88 to do a power linearity set. 0dB is approximately 20W, and I dropped the level 5dB for each sweep. I'll do these again with higher power when I can get the amp here, probably early next week. I also did a set of off axis sweeps. I'll do a closer spaced set later on when I have a good protractor to set accurate angles.

Distortion lower in frequency is kind of iffy to say the least. Room effects greatly affect results. And as I go lower in power, the noise floor starts to really introduce error. But the levels are accurate at least over this 30dB range.

And as I suspected, the best response looks to be with these aimed to cross a couple feet in front of the listening position. Response extends to nearly 20KHz that way, smoothly.

[davepellegrene]

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

If I'm reading these right the distortion is about the same increasing with amplitude except on the bottom end of the tweeter?
Why are there no distortion lines on the second set of distortion measurements?

Are you taking these from your listening position with both speakers? If so do you have the speakers crossed in front of you then moving the mic position to get you off axis?I'm trying to understand why the top end is staying at the same spl on and off axis.

Sorry for all the questions!

Dave

[Pete Schumacher]

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

If I'm reading these right the distortion is about the same increasing with amplitude except on the bottom end of the tweeter?
Why are there no distortion lines on the second set of distortion measurements?

Are you taking these from your listening position with both speakers? If so do you have the speakers crossed in front of you then moving the mic position to get you off axis?I'm trying to understand why the top end is staying at the same spl on and off axis.

Sorry for all the questions!

Dave

I left the distortion off the lower power sweeps because the noise floor started interfering with the actual distortion measurement. You'll notice the sweep levels are hovering around the -40dB line on the graph, which is where the distortion levels were. The SPL and distortion got all jumbled together and you couldn't really make them out from one another. You can see the trend starting in the top traces. The highest power trace (blue) actually has the lowest distortion at 1KHz, partly due to the good separation from the noise floor of my living room. As I reduce the power level, you can see the noise floor starting to affect the distortion level, especially down lower in frequency (green).

The last chart is the off axis plot at the higher power setting.

These were all taken at 1m with only a single speaker playing.

[Pete Schumacher]

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

I had the parts, so I thought I'd try out a version of the crossover that incorporates a bit more baffle step compensation that better addresses the rising response of the woofer through the mids. So I added a couple of parts to the woofer circuit in the form of a parallel RL filter before the crossover. Overall, it adds a couple more dB baffle step. Here's the XO I'm going to listen to for a few days along with the difference between the earlier version and the new one.

[Pete Schumacher]

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

Some thoughts on the differences between the two versions of the crossover.

This latest with more BSC sounds a little richer, fuller in my living room. However, if someone was using them nearfield, or closer to walls or on a console, the version without the extra RL component on the woofer would be the way to go.

I just got finished listening to the Delicate Sound of Thunder, Pink Floyd's live concert. All I can say is I can't wait to get a much larger amplifier on these. They sound so live, so energetic, so uncompressed. Transients are delivered with a crispness that is startling. What a nice woofer!!!

[jonasz]

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

Interesting design Pete! Any subjective thoughts on the audible differences between this B&C, NE225 and RS225?

[Pete Schumacher]

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

Interesting design Pete! Any subjective thoughts on the audible differences between this B&C, NE225 and RS225?

Hey Jonasz,

I don't have much first hand experience with the RS225. I've heard it in a few designs as a dedicated woofer, but not as a midwoofer paired with a tweeter. Because of that, I can't really offer an A/B comparison with the B&C.

On the other hand, the NE225 does have the ability to dig deeper than the 8BG51. But for most music, it not noticeable. What is really getting my attention is how well the B&C seems to render drums. It's a very "live" sounding presentation. There's a certain effortlessness about it that's really cool. As I said before, I'm anxious to put some real power behind them to see what they're really capable of achieving.

I'll put these in the same room with the MiniByzy/Aurora soon enough and try an A/B comparison so that my auditory memory is much fresher.

[jonasz]

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?