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

[Pete Schumacher]

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

Pete earlier in the thread you said you got the last pair of the BC woofers,
was P/E just out of stock and will they be available in the near future?

They were just the last of the current stock. If you go to the 8BG51 page at PE, it says they'll have more next week.

http://www.parts-express.com/bc-8bg51-8-neodymium-woofer--294-696

[69FireBird]

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

these look like a good speaker will they be for sale here?

[Pete Schumacher]

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

these look like a good speaker will they be for sale here?

Everything will be available from PE, except the baffle. The drivers, cabinets, ports, binding posts, crossover components, screws, stuffing, all of it will be constructed using PE components.

I'm sure that takitaj would be happy to replicate the baffle for anyone who wants one. PM him if you're really interested.

Once I'm happy with the result, I'll be posting the full schematic so that anyone can build it.

But if you wanted it as a kit, I'd be happy to put all the parts together for you for a good price.

It's been up and playing for a couple hours now. My wife has taken the sweet spot for some listening. So far, the woofers are impressing me with their ability to clearly play the mids. The tweeter is very familiar to me as I use it in my main speakers (Byzantium), but this waveguide so far seems to mate pretty well with it.

[Pete Schumacher]

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

Cool speaker project Pete and an excellent name!

Mzisserson coined that after I told him that I hadn't thought of a name. I liked it from the moment I saw it. Thanks Mike!

And thanks for the compliment Craig. I'll see if I can bring it to the next DIY as I'm sure it will be finished by then.

[Pete Schumacher]

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

Here's the crossover I've been listening to. So far, I don't know if I'd change anything. Vocals, male and female, are smooth, stay centered, don't jump forward or retreat from the plane of the speakers.

After another dozen hours or so, after I'm certain the woofers are fully broken in, I may revisit.

The resistor I'm using is actually 5.1 Ohm

[mzisserson]

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

Here's the crossover I've been listening to. So far, I don't know if I'd change anything. Vocals, male and female, are smooth, stay centered, don't jump forward or retreat from the plane of the speakers.

After another dozen hours or so, after I'm certain the woofers are fully broken in, I may revisit.

The resistor I'm using is actually 5.1 Ohm

Pete, they look pretty darn good! Have you cranked em' up yet? That is one of the litmus? I would like to see a 1m, 100dB FQ/Distortion measurement of them. Glad to hear about the woofer. That thing has had my eyeball for a while like I said... Just too many projects and not enough time. I was thinking of a TMWW with it, tower. Large enough and sensitave enough kill it, but small enough to still have some WAF...

[Pete Schumacher]

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

Pete, they look pretty darn good! Have you cranked em' up yet? That is one of the litmus? I would like to see a 1m, 100dB FQ/Distortion measurement of them. Glad to hear about the woofer. That thing has had my eyeball for a while like I said... Just too many projects and not enough time. I was thinking of a TMWW with it, tower. Large enough and sensitave enough kill it, but small enough to still have some WAF...

I don't have an absolute SPL measuring capability. What I can do is drive them with about 20W and see what happens. That should be real close to 100dB @ 1m.

[mzisserson]

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

I don't have an absolute SPL measuring capability. What I can do is drive them with about 20W and see what happens. That should be real close to 100dB @ 1m.

DO IT. lol It is the fun thing about about having a speaker like this. :D

[davepellegrene]

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

When I did my dipole design with the B&C 8BG51 crossed to the AC AST2560 I tested the max capabilities with my QSC GX3 which is 300 watts per channel. Although I was crossing to a sub at 250 Hz I started to run out of amp first. This was in my living room which is 25x27 with 11' ceilings. It was the first time in a home environment that I thought it was to loud for my ears. I could not detect any distortion and ran the amp up to 8 out of 10 for a short time then backed it back down pretty quickly. Knowing my Mini Statements while do about 106 dbs in that room and these surpassed them without any problems.

Dave

[mzisserson]

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

When I did my dipole design with the B&C 8BG51 crossed to the AC AST2560 I tested the max capabilities with my QSC GX3 which is 300 watts per channel. Although I was crossing to a sub at 250 Hz I started to run out of amp first. This was in my living room which is 25x27 with 11' ceilings. It was the first time in a home environment that I thought it was to loud for my ears. I could not detect any distortion and ran the amp up to 8 out of 10 for a short time then backed it back down pretty quickly. Knowing my Mini Statements while do about 106 dbs in that room and these surpassed them without any problems.

Dave

That is the issue with high volume tests. It is easy to run out of amp. I know Pete is rocking that 500W pc, he shodul be able to get some 100dB sweeps out of it.

[Pete Schumacher]

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

That is the issue with high volume tests. It is easy to run out of amp. I know Pete is rocking that 500W pc, he shodul be able to get some 100dB sweeps out of it.

The only problem with that is that the 500W PC is in the TV room and it's difficult to get another speaker connected for any kind of testing. I may wait to do this until I can get it over to Ryan's and put it on his 250W B.M.C. Integrated amp. It has a power meter on the front so we can get a true 20W RMS sine sweep.

I've reduced the 4.7mH inductor on the woofer to 4mH. The balance top to bottom seems to be a little better now. I'm doing my listening at this point with a KT88 push pull that has about 25W/ch available. I did a couple of sweeps with it, but the power supply on it seems to drag a little when the signal gets between 100 and 200Hz causing a distortion spike. The supply may need a few more caps to stiffen the rails. But otherwise, the distortion levels are similar to the 97dB MiniByzy sweep, with a distortion minimum near 1000Hz.



It's definitely a nice 8" woofer.

[mzisserson]

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

I've reduced the 4.7mH inductor on the woofer to 4mH. The balance top to bottom seems to be a little better now. I'm doing my listening at this point with a KT88 push pull that has about 25W/ch available. I did a couple of sweeps with it, but the power supply on it seems to drag a little when the signal gets between 100 and 200Hz causing a distortion spike. The supply may need a few more caps to stiffen the rails. But otherwise, the distortion levels are similar to the 97dB MiniByzy sweep, with a distortion minimum near 1000Hz.



It's definitely a nice 8" woofer.

That may not be a function of the amp. What does you Z and phase look like? It is a tube amp after all and you are subject to matich with output transformers. It still looks pretty good. I guess we will see when you get it on a beefier amp. What does the THD look like for the system?

[Pete Schumacher]

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

That may not be a function of the amp. What does you Z and phase look like? It is a tube amp after all and you are subject to matich with output transformers. It still looks pretty good. I guess we will see when you get it on a beefier amp. What does the THD look like for the system?

The system THD is the bottom red line. As you can see, from 700Hz on up, it's below -50dB, which is probably around the same THD as the amp itself, around .3%. And if you look at the close mic for the woofer in blue, you can see that it's below -40dB (1%) from around 60Hz on up. That curve was taken with about 10W input. The wiggles down lower in frequency are room related, so that's why I also added the close mic for the woofer.

I'm pretty sure the issue between 100 and 200Hz is power supply related. That happens to be at the same frequency as the filter caps being charged by the full wave rectifier. I've done plenty of simulations of amplifiers and when you sync the power output frequency with the power rectifiers, you are putting maximum stress on the power supply. The impedance at that frequency, while it is the system low point, is still above 5 Ohm, with phase between 30 and -30 degrees. Backing off the volume knob just a touch completely fixes the issue. That plot above is with 10W instead of 20W and as you can see from the close mic measurement, the woofer distortion is quite good.

[mzisserson]

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

The system THD is the bottom red line. As you can see, from 700Hz on up, it's below -50dB, which is probably around the same THD as the amp itself, around .3%. And if you look at the close mic for the woofer in blue, you can see that it's below -40dB (1%) from around 60Hz on up. That curve was taken with about 10W input. The wiggles down lower in frequency are room related, so that's why I also added the close mic for the woofer.

I'm pretty sure the issue between 100 and 200Hz is power supply related. That happens to be at the same frequency as the filter caps being charged by the full wave rectifier. I've done plenty of simulations of amplifiers and when you sync the power output frequency with the power rectifiers, you are putting maximum stress on the power supply. The impedance at that frequency, while it is the system low point, is still above 5 Ohm, with phase between 30 and -30 degrees. Backing off the volume knob just a touch completely fixes the issue. That plot above is with 10W instead of 20W and as you can see from the close mic measurement, the woofer distortion is quite good.

Fair enough. Thanks for the clarity.

[Pete Schumacher]

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

Fair enough. Thanks for the clarity.

You're welcome.

I'm real curios myself to get a higher powered sweep on them, but I really need to use a solid state amp to be sure. The low end control of a SS amp is crucial to getting an accurate picture.

I've got a little DTA100a I could pop in there, just not sure about its capabilities. I've listened to it and the KT88, and for normal listening, the KT88 is simply better sounding.