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

[Pete Schumacher]

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

I cannot argue with your thought Pete. It makes sense, and is fair and balanced when you give a good explanation WHY you took the road you did. Like I said it is frustrating when a post its made that comes across like I did thing WG thing and it is the best thing that has ever happened since the movie Titanic. I think it helps people much better understand now just "hey, it's good", but why and how the strengths offset the trade-offs in these applications. It's sharing the knowledge, and feels a lot less like a marketing plug for Vapor's next big thing at risk of de-railing like the other conversation did. So again, thanks.

The Bellies. They will CRANK. for sure, and play to the upper 20's in room. I should see if I can dig up the 100dB 1/m distortion measurements I took...... No promises, that was 2 computers ago..... I could always re-take I guess. But that dosen's matter. What DOES is I think I would have a ton of build on them except the D8.8 went from $90/ea to $220/ea...... When I originally built them, the sheer value of the end product was flat out out-doing myself. I think that is why they were so well accepted. Now with the 8.8 at $220/ea. They are about what should be expected for a $650 investment between drivers and crossover.......Depressing.

Back to these though... Have a name? It is a very nice build and I am anxious to see what the end measurements end up like, I still think the driver choices are perfect and this may be the first real home/pro bridge that works.

lol @ the tags

I've been wanting to do a project utilizing the PE .75 cf cabinet. That was the criteria for the baffle. I also wanted the biggest woofer I could fit onto that baffle, and an 8" woofer was the only choice. That's the main reason for this build.

Besides, I promised to document a build using the RS28 in a guide mated to an 8" woofer, originally the RS225. But the pairing of the RS28 and the RS225 has already been done a couple times. That's the main reason I approached this build this way. Besides that, I wanted to evaluate the performance of this woofer for other projects, and this seems like a great way to get an impression of its ability to deliver the goods. Tom's a great guy too, and having a project that uses his skills in machining a baffle is a way to perhaps send a bit of work his way if anyone else wants to build this thing.

No ideas on a name yet. I'd be up for suggestions from the gang for that.

And I do have high hopes for the end result. Both drivers are very well executed, at least from the objective measurements. It should make for a pretty convincing monitor. Only time will tell if it has that "magic" I'm looking for.

[Erich H]

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

Pete,

I was curious why you went with the neo model versus the ferrite?

Oddly enough I made up some test boxes a few weeks ago for a very similar speaker, but one used the Eminence Beta-8 and the other used the B&C 8FG51 because we were worried about that dip around 1200hz or so. But we never bought one to double check that dip.

The only problem is that PE only had one of the FG51's in stock and I think they were only expecting another pair in mid December. So we were going to go a different way if they were that hard to come by.

Did your choice for the neo model have anything to do with availability, or was it mostly due to weight savings? Did you by any chance test out some of the FaitalPro models?

[mzisserson]

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

"The Marksmen" - I think what you are targeting takes some skill...Hitting this bulls-eye is not the easiest... Like when you head to the gun range and you see the real shooters pulling in their targets with the middle carved out vs. the occasional shooters who's targets look more like swiss cheese. Lets not forget that the simplistic-ish x-over is coming from the WG as well. See. There. I gave you an advantage.

[Pete Schumacher]

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

Pete,

I was curious why you went with the neo model versus the ferrite?

Oddly enough I made up some test boxes a few weeks ago for a very similar speaker, but one used the Eminence Beta-8 and the other used the B&C 8FG51 because we were worried about that dip around 1200hz or so. But we never bought one to double check that dip.

The only problem is that PE only had one of the FG51's in stock and I think they were only expecting another pair in mid December. So we were going to go a different way if they were that hard to come by.

Did your choice for the neo model have anything to do with availability, or was it mostly due to weight savings? Did you by any chance test out some of the FaitalPro models?

Based on how the two model in that .75cf cabinet, I chose the Neo version. Turns out that they were the last pair PE had in stock. I thought about the FG though.

Once on the baffle, the dip beyond 1KHz seemed to fill in well enough, at least to the point where a 1KHz crossover point to the tweeter was possible.

[lorenmjones]

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

It looks like the ferrite version is new. It is the only ferrite version of the BG series woofers (the 12" and 15" BG woofers don't have a corresponding FG version. Perhaps supply will increase as time goes along.

Pete,

I was curious why you went with the neo model versus the ferrite?

Oddly enough I made up some test boxes a few weeks ago for a very similar speaker, but one used the Eminence Beta-8 and the other used the B&C 8FG51 because we were worried about that dip around 1200hz or so. But we never bought one to double check that dip.

The only problem is that PE only had one of the FG51's in stock and I think they were only expecting another pair in mid December. So we were going to go a different way if they were that hard to come by.

Did your choice for the neo model have anything to do with availability, or was it mostly due to weight savings? Did you by any chance test out some of the FaitalPro models?

[Navy Guy]

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

Have you seen The Princess Bride before? How about The Inconceivables?

[davepellegrene]

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

There is also the diffraction artifacts of the horn in the time domain. You can see it in Dave P's measurements as the ripple like-immediate change in output vs. fq. It's a trade off. Like you say. EVERY horn has them.

Mike, can you show me or explain what you mean? I know that on axis with a round waveguide there are a couple dips in the on axis measurements between 5-10 kHz that go away by 20 - 30 degrees off axis but I don't believe this is what you are referring to.

Is this in the FR plot or the Impulse?

By the way nice job Pete! As usual.

Dave

[mzisserson]

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

Mike, can you show me or explain what you mean? I know that on axis with a round waveguide there are a couple dips in the on axis measurements between 5-10 kHz that go away by 20 - 30 degrees off axis but I don't believe this is what you are referring to.

Is this in the FR plot or the Impulse?

By the way nice job Pete! As usual.

Dave

The best place you can see it is in the polar. While the FR looks very smooth for the most part, even through 5-10K range they do not look unreasonable. You can see the rapid changes in energy. From what I have measured in the WG's I have played with it is attributed to diffraction inside the throat and bell of the WG itself.

Please don' take my earlier ranting and raving as an attempt to discount the merits of using WG's, specially since the community is lucky to have folks like yourself who are untangling the black art of proportions and geometries to make them very effective. I have reached the point where I like to know why people are making the design choices they make, really, that's all. I find that more interesting than the end result most times.

[Pete Schumacher]

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

The best place you can see it is in the polar. While the FR looks very smooth for the most part, even through 5-10K range they do not look unreasonable. You can see the rapid changes in energy. From what I have measured in the WG's I have played with it is attributed to diffraction inside the throat and bell of the WG itself.

Please don' take my earlier ranting and raving as an attempt to discount the merits of using WG's, specially since the community is lucky to have folks like yourself who are untangling the black art of proportions and geometries to make them very effective. I have reached the point where I like to know why people are making the design choices they make, really, that's all. I find that more interesting than the end result most times.

Now I'm confused. If you could grab one of Dave's polar plots and identify the areas of those rapid changes in energy, it would go a long way towards clarifying what you mean.

For example, here's one he recently posted of the ND25FN-4 in a guide. Looking at the top half of the picture, all I see is a very consistent frequency response as you move off axis (excepting the dip at 15000Hz).

[davepellegrene]

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

The best place you can see it is in the polar. While the FR looks very smooth for the most part, even through 5-10K range they do not look unreasonable. You can see the rapid changes in energy. From what I have measured in the WG's I have played with it is attributed to diffraction inside the throat and bell of the WG itself.


Please don' take my earlier ranting and raving as an attempt to discount the merits of using WG's, specially since the community is lucky to have folks like yourself who are untangling the black art of proportions and geometries to make them very effective. I have reached the point where I like to know why people are making the design choices they make, really, that's all. I find that more interesting than the end result most times.

I just wasn't sure what you where referring to. I didn't feel you where discounting my work.
In the short time I've been working with waveguides I'm getting pretty good manipulating the response. The thing I'm fighting with the most is what's the best or right choice. The bigger and deeper the guide the more bottom end boost but also the quicker the top end rolls off. Shallow the guide up and you get less bottom end boost but you also get less top end roll off. The shallower guides are what I've been focusing on the most. You get the advantage of less baffle diffraction plus a more level off axis response. On average I like to see from on axis to 90 degrees off axis a drop at 1-2 kHz, depending on the cut off of the guide, of 12 to15 dbs and at 10 kHz a drop off of about 20 to 22 kHz. Above that it just depends on the tweeter and throat iteration.
So when you go off axis with a waveguide it will lower the spl level on the bottom end along with the top end.
It seems to work best to toe in a waveguide loaded speaker so they are either pointing at you or crossing just in front of you at the listening position. By doing this when You are standing in front of say your right speaker from the same distance back as your listening position the left speaker is pointing at you which is farther away then the right. The right speaker is pointing away from you so it is lower in SPL. If done right the image will stay centrally located. With my black box speakers this works pretty well. Although the sweet spot is only about a foot wide to get optimal imaging it stays in the center as I walk off axis it's just not pin point. I do a lot of listening from my work bench which is on the back wall in line with my right speaker so it works well for me.
Waveguides also work well in small lively rooms because they reduce first reflections off the side walls which are known to smear imaging. I think this is what you are seeing in the polars. A waveguide narrows the dispersion directing the energy forward creating a narrow polar plot.

I have found it sounds best not to push the tweeter to low even if it hasn't reached the cut off of the guide yet. If the mid/ woofer holds its directivity high enough not to have to push the tweeter to low seems to work best for me.

Are waveguides better then putting a tweeter on a flat baffle. I couldn't answer that because I have not done a direct comparison. I don't think you can fairly do this because the crossover point won't be the same.

Dave

[davepellegrene]

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

Now I'm confused. If you could grab one of Dave's polar plots and identify the areas of those rapid changes in energy, it would go a long way towards clarifying what you mean.

For example, here's one he recently posted of the ND25FN-4 in a guide. Looking at the top half of the picture, all I see is a very consistent frequency response as you move off axis (excepting the dip at 15000Hz).

That's a perfect example of what I was explaining in post #55. That guide has a 1" throat. 12.5 kHz is about a 1" wave.
That dip could very well go away in an elliptical guide or with a slight throat adjustment.

Dave

[Pete Schumacher]

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

So Dave, how deep does the guide have to be for you to notice the top octave drop off?

[davepellegrene]

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

So Dave, how deep does the guide have to be for you to notice the top octave drop off?

It's a gradual drop off the deeper you go. Basically look at the dome through the waveguide off axis. When you can no longer see it the top octave starts to roll off. By reducing the throat size to the size of the dome this will boost the upper octaves which will make the top end hold up longer off axis.

This is the Flat baffle vs waveguide on the tweeter/ waveguide you posted above. By reducing the throat size you can see the boost up to the throat size. This tweeter works well in a guide.


The dip at 15 kHz is in the flat baffle measurements as well. It's at 12.5 kHz and a little farther off axis. Sometimes they go away with a guide but usually whatever happens above the guide boost is amplified.


Dave

[mzisserson]

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

Now I'm confused. If you could grab one of Dave's polar plots and identify the areas of those rapid changes in energy, it would go a long way towards clarifying what you mean.

For example, here's one he recently posted of the ND25FN-4 in a guide. Looking at the top half of the picture, all I see is a very consistent frequency response as you move off axis (excepting the dip at 15000Hz).

All of the ripples in response. +/-1 to 2db or so. Then the polars look choppy as well. There are arguments to the audibility, I would even go as far as to say it does not effect tonality since the response is pretty flat. However after this sound leave the guide, These interference and reflections seem to ultimately effect imaging. I cite this on Jeff B. paper on imaging being similar to fractals. In many ways the spatial sound coming out of a waveguilde is much like shot-gun bb's vs a smooth lobe. On a flay baffle, you end up with reflections, and worse, edge diffraction, however it is occurring across a much wider plane and much of it gets dispersed vs. directed. I believe this is why any wave guide s typically have a real hard time imaging or "filling" a soundstage. The roll-off off-axis as well (let's leave the 15K dip out of it) is indicative of a rapidly falling power response. Continuing on the fractal theme, if the acoustic energies of the HF information is being diminished, you not only can lose the soundtage width and depth, but also placement. I say this because there is information that exists everyday above 20K that interacts with what we hear. This is recorded on Mics, this is also captured on media. Furthermore, spatial queues and resolution queues like a vinyl tip of a drumstick tapping a ride cymbal, or the valves of a sax often have extreme HF info attached to them that may not always be directly heard, but when reproduced by a speaker, aids your ears and mind in painting the picture of the music. It is similar why people have trouble understanding what they hear when people talk as they lose their ability to hear the HF information, the consonant queues in normal speech get lost. The good thing the WG's do in exchange for this sacrifice is eliminate the room. Toole's book talks a lot about interactions in room. Is this really good? In certain rooms yes. Big venues, absolutely. But what about your box? Your living room or listening room that is not the size of a hotel conference room or auditorium? These are all aspects of ANY design, WG or not seldom discussed because it is in many ways very grey. I also think it is why there are two distinct schools of thought on home loudspeaker design where on one hand you have controlled directivity, on the other as smooth and broad of power response as possible. Both have advantages and disadvantages. I also think that if I dig back through mounds of books and the intrwebs I could make an argument for both. Dave mentions better imaging in reflective rooms. I agree. If you put a speaker with good power response in a highly reflective room you end up turning the room into a horn with the very refraction that started this whole conversation, except in the room itself. Most rooms are not highly reflective. And in tool's book he discusses that averaging by the ear/mind makes up for a great deal of "issues" such as floor/ceiling bounce. We do not hear like a mic.

I just wasn't sure what you where referring to. I didn't feel you where discounting my work.
In the short time I've been working with waveguides I'm getting pretty good manipulating the response. The thing I'm fighting with the most is what's the best or right choice. The bigger and deeper the guide the more bottom end boost but also the quicker the top end rolls off. Shallow the guide up and you get less bottom end boost but you also get less top end roll off. The shallower guides are what I've been focusing on the most. You get the advantage of less baffle diffraction plus a more level off axis response. On average I like to see from on axis to 90 degrees off axis a drop at 1-2 kHz, depending on the cut off of the guide, of 12 to15 dbs and at 10 kHz a drop off of about 20 to 22 kHz. Above that it just depends on the tweeter and throat iteration.
So when you go off axis with a waveguide it will lower the spl level on the bottom end along with the top end.
It seems to work best to toe in a waveguide loaded speaker so they are either pointing at you or crossing just in front of you at the listening position. By doing this when You are standing in front of say your right speaker from the same distance back as your listening position the left speaker is pointing at you which is farther away then the right. The right speaker is pointing away from you so it is lower in SPL. If done right the image will stay centrally located. With my black box speakers this works pretty well. Although the sweet spot is only about a foot wide to get optimal imaging it stays in the center as I walk off axis it's just not pin point. I do a lot of listening from my work bench which is on the back wall in line with my right speaker so it works well for me.
Waveguides also work well in small lively rooms because they reduce first reflections off the side walls which are known to smear imaging. I think this is what you are seeing in the polars. A waveguide narrows the dispersion directing the energy forward creating a narrow polar plot.

I have found it sounds best not to push the tweeter to low even if it hasn't reached the cut off of the guide yet. If the mid/ woofer holds its directivity high enough not to have to push the tweeter to low seems to work best for me.

Are waveguides better then putting a tweeter on a flat baffle. I couldn't answer that because I have not done a direct comparison. I don't think you can fairly do this because the crossover point won't be the same.

Dave

As I said above, I do not think one is better than the other. I think some strides have been made in developing WG's to work better in specific applications which has made them much more feasible than the old option of just a bolt-on, patterned directivity horn. I just would hope that the trade off's as part of the design are understood and communicated as such as a learning lesson for DIY-ers new to the game, old to the game, and those who are already knowledgeable and just want to know. I am most interested in why people make the design choices they do. I find it interesting that everyone has their own thoughts and flavors. I have learn a lot too from it. I think all too often too people forget to "understand their customer". A speaker speaks to a human through the air, in a room. A little study into psycoacoustics, room acoustics, and just what the heck happens when the sound actually leaves the speaker as a music signal, not just a chirp 1m away at one point in space/time could help a lot of designers up their game and make the right choices like: To waveguide, ribbon, ribbon in a waveguide, small dome, large dome, heck even bi-pole, OB etc. I admit the only WG's I have played with are designing some pro gear and some of the early PE models. So who knows, maybe someday it will be time for a re-visit.

[Pete Schumacher]

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

I just don't see what you do there Mike. Have a look at Dave's flat baffle vs. guide on the same display.



There are no more "ripples" in the response with the guide than there are on the flat baffle.

And what tweeter doesn't lose off axis energy up high as you move off axis? The difference with the guide is that the entire band falls off more uniformly than it does without the guide. The advantage of that characteristic is that power response is actually smoother with the guide than without it, depending on the woofer you're crossing to. With the 8" woofer, the off axis response of a flat baffle tweeter system will show a gradual dip in the region of the crossover due to the woofer "beaming" while the tweeter doesn't, until much higher up in frequency. Some members here call it a "midrange mushroom cloud" power response, with an increased energy in the 2KHz - 8KHz region relative to the 800Hz-2000Hz range.

As for imaging and sound stage, I think the enclosure can have as much to do with that as the driver implementation. An enclosure that talks during the program just ruins the presentation.