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

[Jeff B.]

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

I had to cancel last minute. My new boat was being delivered to my house Friday evening just before the ice/ snow storm so I had to be there to shoehorn it through my garage door when it arrived. Being 5 hours away in good weather there was no way I was going to be able to make it.

I'd really like to hear your method. Do you think you will have a right up soon? I don't want to bother you because I'm sure you have more emails to answer then you want to already.

Dave

I DO get a lot of emails ;) But it's more the holidays and the family coming from out of town that will keep me from working on it right away. Hopefully, after the first of the year things will settle down and I will be able to pull the paper together. (Stereophile could learn a lot from this too, their method of presenting spliced data always give an incorrect response curve. JA admits that, but doesn't do anything to fix it. )
Jeff

[Pete Schumacher]

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

Curious if you ever got close to exceeding xmax during your jam session? 6.5mm. Like the idea of a Tapered TL
Is there enough inductance in the crossover to wire two of these in parallel with a RE of 5.1?

There are a few tracks where I have no doubt crested the Xmax limit, but it does so very gracefully. I've not heard any signs of overt distress. "Nevermind" from Infected Mushroom's Army of Mushrooms has prodigious bass levels and causes a lot of movement on that woofer. Another CD that digs really deep repeatedly is Yello's "Touch." The bass performance of this woofer is really excellent.

As they stand right now, I've probably got about .4 Ohm series resistance (I removed the second inductor on the woofer). Using an air core inductor with a pair in parallel would keep the total impedance at right around 4 Ohm according to sims I've done in PCD. Currently, there are a total of 7 components in the crossover.

The dip Dave mentioned in the response seems room related. I took a measurement from .5m and only saw a slight indication that a dip was forming.

[Pete Schumacher]

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

OK, here's the latest update with the current crossover and a set of distortion plots showing the lousy noise floor in my room.

blue is 2nd harmonic, green is 3rd.

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

I wonder which would fill a big room or be heard outside from inside. This or the Tempest build.

[Jeff B.]

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

I wonder which would fill a big room or be heard outside from inside. This or the Tempest build.

The Tempest has a 12" pro-woofer and 98 dB sensitivity. It can play REALLY loud.

[Pete Schumacher]

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

I wonder which would fill a big room or be heard outside from inside. This or the Tempest build.

A little anecdotal evidence . . . I had that Infinite Mushroom song going the other day for my daughter's boyfriend. The 120W amp was self limiting, meaning it was probably clipping often enough to cause it to shut off momentarily. There was no hint of strain on the speakers, and they were shaking the floor quite a bit. No doubt these can be heard outside when playing inside. And they'd have no problem filling a large room with clean sound and a proper power amp to deliver the peaks. In my 18' x 15' living room, they'll crest 105dB average levels at the listening position with this 120W amp, louder than I would normally listen for extended periods for sure.

[davepellegrene]

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

OK, here's the latest update with the current crossover and a set of distortion plots showing the lousy noise floor in my room.

blue is 2nd harmonic, green is 3rd.

[ATTACH=CONFIG]43415[/ATTACH][ATTACH=CONFIG]43416[/ATTACH]

[ATTACH=CONFIG]43417[/ATTACH]

What distance and SPL do you take you distortion measurements? I guess what I'm asking at roughly what SPL do you see it start to rise?

I use to take distortion measurements at lower volume with a close mic distance. I've changed to about one meter and I run the volume up higher. I think it gives more realistic measurements.

Dave

[davepellegrene]

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

The Tempest has a 12" pro-woofer and 98 dB sensitivity. It can play REALLY loud.

How do they do full range? Ok without a sub?

Dave

[Erich H]

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

I wonder which would fill a big room or be heard outside from inside. This or the Tempest build.

I'm sure both could handle that and sound great doing it. But the 2 models are quite different. 8" pro woofers get loud. 12" pro woofers get really.....really loud.

[Pete Schumacher]

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

I'm sure both could handle that and sound great doing it. But the 2 models are quite different. 8" pro woofers get loud. 12" pro woofers get really.....really loud.

The biggest difference between the two builds would be that the 12" version would play as loud as the 8" version using only 1/10th the power.

This one does reach below 40Hz in-room, so a sub would be optional for most music.

[Pete Schumacher]

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

What distance and SPL do you take you distortion measurements? I guess what I'm asking at roughly what SPL do you see it start to rise?

I use to take distortion measurements at lower volume with a close mic distance. I've changed to about one meter and I run the volume up higher. I think it gives more realistic measurements.

Dave

That's a 90dB reading at 1m. It rises with more power in a fairly linear fashion. I posted that earlier with a series of plots at 5dB increments.

Distortion only started hitting 1% when I was hitting it with approximately 20W input levels.

All of this will be revisited after everything is finished. Ryan's got a room that has a 30dB noise floor, so I'll be able to get some very nice distortion readings at 1m and not have to do them close mic. These plots should only look better in the quieter environment.

[Jeff B.]

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

How do they do full range? Ok without a sub?

Dave

That was one of my requirements - that they could be used full-range. The Tempests reach to the mid 40's, I believe the port is tuned to 42 Hz. In room they are good to about 40Hz before falling-off quickly. If you want that last octave then you will still need a sub. The Tempest is an over-achiever. It is a very good speaker, better than I was expecting. I could live with a pair as my mains for a long time.

[[email protected]]

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

Pete, on the above graphs, the woofer appears to roll off substantially by around 100. Am I looking at it correctly? Should I withhold judgment until after your visit to Ryan's?

[Pete Schumacher]

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

Pete, on the above graphs, the woofer appears to roll off substantially by around 100. Am I looking at it correctly? Should I withhold judgment until after your visit to Ryan's?

That low end response is very position dependent. Have a look at an earlier measurement.

[Pete Schumacher]

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

So I've been playing around with the 2D CNC program and spent a while calculating a series of concentric circles at regular cut depths to arrive at this. Instead of adding another section to the back of the baffle to make the guide deep, I just kept it at 1".

Why? I want to see what a 1" deep guide will do! I know it won't have the boost down low that the deeper guide does but the shallower guide should offer a little better top end and enough "gain" down low to continue to enable the 1100Hz crossover point. I may cut these next week and begin some testing. And being 1" thick, it will be a lot easier to make and finish these things. No seam in the guide throat is a benefit for sure. These are also designed to bolt right on to the PE 10x17 .75cf TM cabinet. At least if anyone is interested in doing this I'll be able to make them the baffles!