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

[PWR RYD]

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

Hi Pete.
Can you explain the guide profile in a little more detail? I would like to try my hand at making them myself with a similar technique as TN Allen. Please explain (or better yet a drawing) the 120 degree throat angle. I think I know but want to make sure. How tight is the throat diameter to the OD of the dome's surround? Do you have a rule of thumb for width, depth, boost frequency? Thanks!

[RABrown]

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

Pete, that wave guide built into the baffle is very cool. Where would I look to find out how to make one like that? Has there been a thread here I just can't find?

Thanks,
Rick

[Pete Schumacher]

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

Yes Pete, I understand what a crossover does. Just never heard anyone refer to what it is doing as EQ-ing. With all the razzle-dazzle DSP's and active becoming more popular, I was unsure exactly what you were getting at.

Again, there is this approach like a waveguide is the end-all be-all and the best thing to ever happen to a tweeter. Everyone talks of the obvious advantages, no one ever speaks openly about the disadvantages because as you know when you get them wrong, they can be VERY wrong. It is not ALL upside to a waveguide. It would be nice to see some fair and balanced design around one instead of response measurements and "ta-dah" this is the best. I'll get off it now, this still looks very interesting. Good luck.

It's all fine and good for you to pooh-pooh the whole waveguide thing Mike. I get it, you need convincing. My suggestion is to get one of Dave Pellegrene's guides for a tweeter of your choice that you're familiar with, and give it a try. I know you trust your ears. What better way to see what all the hoopla is about than to hear for yourself? You keep talking about the downside to guides, but you've yet to identify any specific downside. I for one am curious about what you consider to be a downside. There's also a downside to using a tweeter on a flat baffle, most notably diffraction ripple and the loss of acoustic alignment with the woofer. Why not kill two birds with one stone? This is as good a place as any to identify what you consider a shortcoming. Please, let's discuss the subject. I know that others might be interested in all the pros and cons to any approach, as they all involve compromises of one sort or another.

And no one is saying "look at the measurements. Ta dah, it's the best." I only posted those measurements so that you could see that your impression that off axis response rolls off the highs wasn't quite correct. It might be for some waveguides, but this particular profile doesn't do that.

[Pete Schumacher]

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

Pete, that wave guide built into the baffle is very cool. Where would I look to find out how to make one like that? Has there been a thread here I just can't find?

Thanks,
Rick

Tom Jones (takitaj) did those on his CNC. He'd be happy to cut a pair for you too. Send him a PM.

[Pete Schumacher]

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

Hi Pete.
Can you explain the guide profile in a little more detail? I would like to try my hand at making them myself with a similar technique as TN Allen. Please explain (or better yet a drawing) the 120 degree throat angle. I think I know but want to make sure. How tight is the throat diameter to the OD of the dome's surround? Do you have a rule of thumb for width, depth, boost frequency? Thanks!

The exit angle of 90 degrees describes the angle of the throat opening. If you were to draw a line perpendicular to the tweeter at the center of the guide, the wall would be at a 45 degree angle initially.

From there, the shape curves away at a pretty much circular profile. I initially wanted a 4" radius for the curvature, but Tom made it smaller to better fit the baffle. I don't know exactly what the profile looks like, but Tom has the drawing.

The diameter of the opening is the same as the opening of the RS28 flange, 1.625". The tweeter is just mounted to the back of the guide, flange and all.

[jhollander]

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

Three part article here that may help

http://sound.westhost.com/articles/waveguides1.htm

[mzisserson]

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

It's all fine and good for you to pooh-pooh the whole waveguide thing Mike. I get it, you need convincing. My suggestion is to get one of Dave Pellegrene's guides for a tweeter of your choice that you're familiar with, and give it a try. I know you trust your ears. What better way to see what all the hoopla is about than to hear for yourself? You keep talking about the downside to guides, but you've yet to identify any specific downside. I for one am curious about what you consider to be a downside. There's also a downside to using a tweeter on a flat baffle, most notably diffraction ripple and the loss of acoustic alignment with the woofer. Why not kill two birds with one stone? This is as good a place as any to identify what you consider a shortcoming. Please, let's discuss the subject. I know that others might be interested in all the pros and cons to any approach, as they all involve compromises of one sort or another.

And no one is saying "look at the measurements. Ta dah, it's the best." I only posted those measurements so that you could see that your impression that off axis response rolls off the highs wasn't quite correct. It might be for some waveguides, but this particular profile doesn't do that.

Where's BF's dead horse beating icon when you need one.

Yes, compromises of one or another and there are many issues with a standard flush mounted tweeter. I certainly will be the first to admit that and the first to admit that shallow throat guides have gained popularity commercially as well as DIY.

In a regular room, is the controlled directivity a real advantage? to do it properly you would have to control down to 200Hz-300Hz, and what you gain in directivity, you lose in power response which can cause beaming, or horns to appear bright and have a very localized sweet spot. I am not surprised they do well in trade show halls and in auditoriums, but in a regular room I am unsure the single point measurement dictating controlled driectivity is worth it. I would like to see measurements 6', 9', 12' away as well. I would also like to see a measurement directly on axis because it can show a rising top where the dome is directional in some cases I have seen.

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.

I will give you boosting the low end because crossing to an 8, that's what is needed. Yet I STILL do not understand this trend of crossing tweeters over as low as possible.

Time alignment is kind of a meh argument. 1) It is easily fixed electrically 2) There is no guarantee your horn is going to line up with the exact acoustical center of your woofer. You also end up poking the center to center WAY out.

Your distortion plot has no assignment of volume/method. Makes it hard to tell how real it is. No Jab, just stating what I see. Also you have THD, but not broken down. I would like to see what the dominate order is, and where the 4th/5th orders sit.

I am unsure it is a shortcoming, rather a means to an end. I also think that people get very excited about it because it has a "cool" factor. Not everyone can afford to have baffles milled, and Dave p's guides are not for every tweeter. Some work better than others. I have played with horns, but found the benefits best left to the pro world and large venues. I have an experiment in controlled directivivity I am working on now and it is not a WG. We will see if I am all wet soon enough, which it will not be the first time.

I am not trying to have a witch hunt against horn loaded tweeters. I just want the truth. And instead of seeing "WOWIE ZOWIE THIS PROFILE IS THE BEST THING SINCE BOSE 901's!!!!" It would be nice to see, for once, someone state here this is why I thought a WG is good for this particular application, here is why, and here is how I am minimizing the sacrifices made by using a WG. I think a humble approach to why would educate much better. Ribbons are just as bad. People forget, quickly, how they are only most effective over a small window. The benefit is they do just about EVERYTHING better than a dome in every other manner. No free lunch there either. It is frustrating to see people gather enough information about WG's to be dangerous and their road can get dark, quickly. There are a handful of WG "experts" here. You are one, Dave TN allan, a couple of others, but that is about it. Sometimes, a standard tweeter may be in order so why mislead and come across like there is zero downside to waveguiding?

[Pete Schumacher]

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

Three part article here that may help
http://sound.westhost.com/articles/waveguides1.htm

The difference here is that this guide isn't a constant directivity type. It's not conical.

[Pete Schumacher]

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

Where's BF's dead horse beating icon when you need one.

Yes, compromises of one or another and there are many issues with a standard flush mounted tweeter. I certainly will be the first to admit that and the first to admit that shallow throat guides have gained popularity commercially as well as DIY.

In a regular room, is the controlled directivity a real advantage? to do it properly you would have to control down to 200Hz-300Hz, and what you gain in directivity, you lose in power response which can cause beaming, or horns to appear bright and have a very localized sweet spot. I am not surprised they do well in trade show halls and in auditoriums, but in a regular room I am unsure the single point measurement dictating controlled driectivity is worth it. I would like to see measurements 6', 9', 12' away as well. I would also like to see a measurement directly on axis because it can show a rising top where the dome is directional in some cases I have seen.

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.

I will give you boosting the low end because crossing to an 8, that's what is needed. Yet I STILL do not understand this trend of crossing tweeters over as low as possible.

Time alignment is kind of a meh argument. 1) It is easily fixed electrically 2) There is no guarantee your horn is going to line up with the exact acoustical center of your woofer. You also end up poking the center to center WAY out.

Your distortion plot has no assignment of volume/method. Makes it hard to tell how real it is. No Jab, just stating what I see. Also you have THD, but not broken down. I would like to see what the dominate order is, and where the 4th/5th orders sit.

I am unsure it is a shortcoming, rather a means to an end. I also think that people get very excited about it because it has a "cool" factor. Not everyone can afford to have baffles milled, and Dave p's guides are not for every tweeter. Some work better than others. I have played with horns, but found the benefits best left to the pro world and large venues. I have an experiment in controlled directivivity I am working on now and it is not a WG. We will see if I am all wet soon enough, which it will not be the first time.

I am not trying to have a witch hunt against horn loaded tweeters. I just want the truth. And instead of seeing "WOWIE ZOWIE THIS PROFILE IS THE BEST THING SINCE BOSE 901's!!!!" It would be nice to see, for once, someone state here this is why I thought a WG is good for this particular application, here is why, and here is how I am minimizing the sacrifices made by using a WG. I think a humble approach to why would educate much better. Ribbons are just as bad. People forget, quickly, how they are only most effective over a small window. The benefit is they do just about EVERYTHING better than a dome in every other manner. No free lunch there either. It is frustrating to see people gather enough information about WG's to be dangerous and their road can get dark, quickly. There are a handful of WG "experts" here. You are one, Dave TN allan, a couple of others, but that is about it. Sometimes, a standard tweeter may be in order so why mislead and come across like there is zero downside to waveguiding?

I've never said there was zero downside to waveguide loading a tweeter. There are energy storage issues of course. On flat baffles, it's called edge diffraction. The guide just changes where it occurs, that's all. The use of large roundovers on flat baffles takes care of edge diffraction energy storage, with the advantage to the large roundovers compared to a guide.

In this case, crossing to an 8" woofer is the main reason this tweeter is in a guide. The use of the guide fixes many of the worst shortcomings of trying to do it with a tweeter on a flat baffle: High stress levels of the tweeter crossing low to the woofer; off axis issues due to the mismatch of a large woofer and a small tweeter; the large acoustic offset difference between a large woofer and a flush mount tweeter.

While the offset can be corrected in the crossover, not having to do so opens up other possibilities for what kind of transfer function might work best. Aligning the acoustic centers isn't a panacea, but there's nothing wrong with attempting to do so, whether by building a sloped baffle or using a waveguide to get them closer. And with the lower XO point, CTC matters less. At 1KHz, the wavelength is about 12". The tweeter and woofer center are well inside that dimension.

While there are tweeters that could cross at 1200Hz, like where this one will, this implementation will be able to handle much higher SPL requirements, which might come in handy if someone likes to crank it up once in a while and not worry about a tweeter that is begging for mercy.

For example, here's that same guide as above, with a 10W input level (measured) resulting in output SPL of about 97dB. The lowest distortion is at the crossover point, the place where stress is normally maximum for a tweeter on a flat baffle.



In the case of the RS28, most of the distortion is 2nd harmonic. 5th harmonic is below -60dB, 3rd is below-50dB. Objectively speaking, this is a very high performing high frequency transducer. The guide improves those numbers, especially lower in its operating range of 1100Hz - 20KHz.

Not everyone is going to want to spend money to have someone mill a baffle. So what? Not everyone is going to buy a Scan Beryllium tweeter either. That's not the point here. This is for someone who may have an interest in doing something along the lines of this particular build. Heck, they may even want to build it as-is for no other reason than to see what all the hoopla is about. The baffle and tweeter together will still cost less than a more expensive tweeter, like for example, that Scan Illuminator, or an Aurum Cantus Aerostriction tweeter. Isn't there enough room in the DIY world for different approaches to a problem?

You built the Fat Bellies using the more standard approach of a robust tweeter on a flat baffle mated to a quality 8" woofer. Not everyone is going to want to spend that kind of money on a woofer, so why exactly did you build it? I have a feeling your answer would be very similar to why I chose to pair this tweeter and woofer together with a guide.

[Pete Schumacher]

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

I finally got the baffle mounted into the cabinet, nice and sealed up. I'll add the port a little later. I remeasured the drivers at 1m, extracted minimum phase and adjusted the levels up to an appropriate SPL using Jeff B's response modeler. Based on the summed response, woofer is now slightly proud of the tweeter by 1cm using the point between the tweeter and woofer as the design axis. This woofer definitely has a rising response into the mids relative to the range below 200Hz, and that's where they get their high sensitivity rating. Add in baffle step, and the difference between the lows and highs is more like 10dB, not 6dB.

So with this new data, I plugged everything into PCD, and using a total of 7 components, came up with this system response.
This is with no gating and includes the room response, with 1/6th octave smoothing. Overall, looks pretty good to me, at least a good place to start.

Woofer XO is 4.7mH and 33uF.

Tweeter XO is 3.9uF in series with a parallel trap of .3mH, 5.6uF, and 6.5 Ohm, with a .5mH shunt across the tweeter terminals.

As you can see from the reverse null, tracking is good and the crossover point is right at 1000Hz, LR4.

Time to order some parts to build up the XO.

[foxfire3]

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

Pete, I must be missing something as it looks like the red and blue lines intersect around 1.2KHz.

Do you know what these baffles will cost?

Thanks...

[Pete Schumacher]

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

Pete, I must be missing something as it looks like the red and blue lines intersect around 1.2KHz.

Do you know what these baffles will cost?

Thanks...

They do cross at that point, but if you look at the reverse null, the center of it is right at 1KHz. The exact crossover point is probably 1200, but the region where both tweeter and woofer are contributing to the total is spread over an area centered at 1KHz.

I'm not sure what Tom will charge, but I'd imagine a pair for around $100 shipped.

Try doing that stop sign recess for the woofer on your own. Ick!

[lorenmjones]

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

Looking good Pete. That doesn't look bad at all. I'll be curious to hear how they sound, and how they sound at a fairly loud level compared to something using a hifi 8" woofer and a surface mounted dome tweeter crossing a little higher. They will certainly give up some LF extension to an 8" RS or Scan or Usher. I would be willing to bet though that for the rest of the range they would sound cleaner or more effortless at higher levels given the more efficient woofers and the way the horn loading helps the tweeter out on the bottom end. On the other hand I could be wrong...Have fun with them.

They do cross at that point, but if you look at the reverse null, the center of it is right at 1KHz. The exact crossover point is probably 1200, but the region where both tweeter and woofer are contributing to the total is spread over an area centered at 1KHz.

I'm not sure what Tom will charge, but I'd imagine a pair for around $100 shipped.

Try doing that stop sign recess for the woofer on your own. Ick!

[mzisserson]

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

You built the Fat Bellies using the more standard approach of a robust tweeter on a flat baffle mated to a quality 8" woofer. Not everyone is going to want to spend that kind of money on a woofer, so why exactly did you build it? I have a feeling your answer would be very similar to why I chose to pair this tweeter and woofer together with a guide.

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

[lorenmjones]

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

Well, I think there may have been other successful home/pro "bridge" projects that work. I would cite mdocodd's recent Celestion HT build documented in this thread

http://techtalk.parts-express.com/sh...ight=celestion

Another example would be the speakers in my sig which use all pro sound drivers. They sound very very good IMO. I would also think that many of the Vapor products would qualify as several of them use AE woofers and one of them uses the "pro" Beyma AMT. Not to mention the diysoundgroup products.

Depending on your design goals, I think it can make very good sense to use prosound drivers in a home hifi speakers.

this may be the first real home/pro bridge that works.