RSS315HF-4 as the anchor of a 3-way???

[Pete Schumacher]

Re: RSS315HF-4 as the anchor of a 3-way???

Scan Speak Revelator 15W for a mid! This is going to be something. I'm not sure if you or other people agree, but after I extensively tested and compared the RS180S-8 and the Usher 8945P with various types of measurements, including my own HD sweeps, and with many filters (including C-E high order filter for the RS180S, recently), I'm now a firm believer of the importance of low tall order harmonics between 500 Hz - 1.5 kHz. I believe that this is because my ear (or our ear?) is very sensitive to the range of 1.5 kHz - 7.5 kHz in which the tall order harmonics arise from fundamentals between 500 Hz - 1.5 kHz.

By the way, I'm now using the 8945P up to 2.3 kHz with a LR acoustic 2nd order filter (w/ a couple of notch filters) and hearing no adverse effects of its 1.2 kHz dip and 3 kHz node on its non-filtered response.

Jay

Yeah, when I was offered a deal on the Scan by DoubleTap, I HAD to figure out a way to get it to play with the RSS315. I'm curious to see how that damped 3rd order approach will work. The transfer function throughout the bass looks real flat by adding the cap.

I will definitely use the Usher in upcoming projects. Paul K's Marcato's were amazing to say the least. He and Dan did a great job integrating the BG tweet into the system.

[Jeff B.]

Re: RSS315HF-4 as the anchor of a 3-way???

Thanks for the tip. Now, the question is what a tube vs a true open back does to the response into the room. I want to use the mid down to the 200Hz XO point. Does the 3dB hold down to that frequency? It seems like a tall order. And I really don't want to push the RSS315 much higher in frequency.

I don't know if you can get down to 200Hz without some tube length.

[Jeff B.]

Re: RSS315HF-4 as the anchor of a 3-way???

Pot plant?????? :eek:

But in all seriousness, the reason for that shape is more than just looks. The aerodynamic shape will allow the qualities of the drivers to reach the listener with less turbulence and therefore, greater clarity.

Wow, that's brilliant! Why didn't I think of that? :rolleyes:

[Pete Schumacher]

Re: RSS315HF-4 as the anchor of a 3-way???

I don't know if you can get down to 200Hz without some tube length.

The tube would be a straight shot from behind the mid to the rear baffle, about 20". Is that enough???

[jkim]

Re: RSS315HF-4 as the anchor of a 3-way???

Pete, this is just a guess, but it's interesting how you got phase perfectly aligned between mid and tweeter with only a 15 dB/oct electrical slope for the mid if the two drivers are time-aligned on the baffle. It might still be possible depending on the drivers' natural rolloffs (w/ the mid slightly off-axis), but I'd double check on the drivers' modeled responses especially at top ends (up to 40 kHz - 50 kHz) for proper rolloffs that were used for HBT phase extraction.

Also, why not LR acoustic 2nd order filters for mid and tweeter if they are time-aligned? The RS28A or F is perfectly suited for this application with its proper Q rolloff, thus having plenty of power handling if crossed at 2.3 k to 2.5 kHz. With respect to linear excursion, it will produce about the same output as the case with your current LR4 filter between 1 k - 2 kHz where the max excursion occurs. This is because any LR2 filter for a tweeter in reality has a slightly steeper slope than the theoretical target below 1 kHz. This still gives excellent phase tracking because of the natural low-end rolloff of any real-world midwoofers---consider how the Duelund 3-way filters work ;). I believe the same filter topology as Zaph used for the XT25 in his ZD5 (single series cap and shunt RL) will work nicely. Impedance flattening LCR may or may not be needed.

[Jeff B.]

Re: RSS315HF-4 as the anchor of a 3-way???

The tube would be a straight shot from behind the mid to the rear baffle, about 20". Is that enough???

If the tube is large enough in diameter to not restrict the output of the driver then it will behave like a U-Frame, however, it will also have some line resonance effects too. For the purpose of determining the extension you can use my diffraction simulator in dipole mode and model the baffle width as twice the tube length. This should give you the frequency of the dipole peak and the subsequent roll-off below that. It will put you in the ballpark.

[Pete Schumacher]

Re: RSS315HF-4 as the anchor of a 3-way???

Pete, this is just a guess, but it's interesting how you got phase perfectly aligned between mid and tweeter with only a 15 dB/oct electrical slope for the mid if the two drivers are time-aligned on the baffle. It might still be possible depending on the drivers' natural rolloffs (w/ the mid slightly off-axis), but I'd double check on the drivers' modeled responses especially at top ends (up to 40 kHz - 50 kHz) for proper rolloffs that were used for HBT phase extraction.

Also, why not LR acoustic 2nd order filters for mid and tweeter if they are time-aligned? The RS28A or F is perfectly suited for this application with its proper Q rolloff, thus having plenty of power handling if crossed at 2.3 k to 2.5 kHz. With respect to linear excursion, it will produce about the same output as the case with your current LR4 filter between 1 k - 2 kHz where the max excursion occurs. This is because any LR2 filter for a tweeter in reality has a slightly steeper slope than the theoretical target below 1 kHz. This still gives perfect phase tracking because of the natural low-end rolloff of any real-world midwoofers---consider how the Duelund 3-way filters work ;). I believe the same filter topology as Zaph used for the XT25 in his ZD5 (single series cap and shunt RL) will work nicely. Impedance flattening LCR may or may not be needed.

Interesting observation on the tweeter phase.

Jay, I do believe you've found a shortcoming in Jeff's tools. Perhaps we can prevail upon Jeff to extend the upper bounds of Response Modeler to more accurately portray phase up high. There is some phase error, and it will be worse for tweeters crossing high if the minimum phase isn't at least somewhat more accurate.

I resampled the tweeter FRD. Still got good, but not great phase match. However, slight mod to the mid slope and all came back.

I have thought about 2nd order LR2. It's not out of the realm of possibility by any means, though I am not sure if the baffle slope is quite enough to time align the mid and tweet.

Check out the modeled on-baffle response of the 15W. If I can't do LR2 acoustic with that, there's something wrong, eh?

[jkim]

Re: RSS315HF-4 as the anchor of a 3-way???

Interesting observation on the tweeter phase.

Jay, I do believe you've found a shortcoming in Jeff's tools. Perhaps we can prevail upon Jeff to extend the upper bounds of Response Modeler to more accurately portray phase up high. There is some phase error, and it will be worse for tweeters crossing high if the minimum phase isn't at least somewhat more accurate.

I resampled the tweeter FRD. Still got good, but not great phase match. However, slight mod to the mid slope and all came back.

About this issue take a look at my old post:

http://techtalk.parts-express.com/sh...97#post1542797

(Sorry, Jeff, I bring this up. Just to point this to Pete.)

I think Jeff's modeler is still accurate enough for most real-world designs. Maybe I'm too much perfectionistic :D By the way, have you remodeled the midrange FRD, too? Believe it or not, it also has some effect.

I have thought about 2nd order LR2. It's not out of the realm of possibility by any means, though I am not sure if the baffle slope is quite enough to time align the mid and tweet.

Check out the modeled on-baffle response of the 15W. If I can't do LR2 acoustic with that, there's something wrong, eh?

I still think it's perfectly feasible. The RS28A has a slightly recessed AC than other domes, and you can have a bit more distance between tweeter and mid with no issue.

Jay

[Pete Schumacher]

Re: RSS315HF-4 as the anchor of a 3-way???

About this issue take a look at my old post:

http://techtalk.parts-express.com/sh...97#post1542797

(Sorry, Jeff, I bring this up. Just to point this to Pete.)

I think Jeff's modeler is still accurate enough for most real-world designs. Maybe I'm too much perfectionistic :D By the way, have you remodeled the midrange FRD, too? Believe it or not, it also has some effect.



I still think it's perfectly feasible. The RS28A has a slightly recessed AC than other domes, and you can have a bit more distance between tweeter and mid with no issue.

Jay

The mid phase was actually already quite good.

I'll post the LR2 attempt a little later on.

[jkim]

Re: RSS315HF-4 as the anchor of a 3-way???

You're right, Pete. Out of curiosity, I compared the two methods using my SS 15W (8 ohm version) FRD.



First with a modeled response up to 20 kHz and "Quick Phase" in FRC (same as with Jeff's modeler), and the second with a response up to 50 kHz and "Precise Phase." No difference above 1.5 kHz. But note that this result is due to the 15W's nice rolloff between 10 k - 20 kHz. We might have a little different result with other drivers.

Jay

[jkim]

Re: RSS315HF-4 as the anchor of a 3-way???

Hmm... This is interesting. I knew this, but had to refresh memory. It turns out that the top end response of the midrange can also be important for accurate HBT phase calculation. Pete, looking at your modeled in-box response again, I realized that you have a fast rolloff above 10 kHz, but it stops at 20 kHz because that's what the SS data sheet shows which you must have traced. Looking at Zaph's SS 15W measurements, we see the rolloff pattern change above it. Assuming that Zaph's measurement is accurate up to 40 kHz, this means something. The 4531 must have the same uncoated cone as the 8531-K01---a bit different measured FRs between them must be due to sampling variance. Coated or uncoated, one thing clear to me is that you won't have the same smooth, fast rolloff above 20 kHz, which is quite common for many midwoofers even if they are a little off-axis, say, 10 to 15 degrees.

So, below is how this difference (responses modeled only to 20 kHz versus beyond it) can affect the HBT computation.



The responses used were from the SS 15W8530K00 (w/ coated cone) Zaph measured---the uncoated version has even higher a peak right above 20 kHz. The first one was modeled to have the same rolloff to 20 kHz as yours, and "Quick Phase" function in FRC was used for HBT. For the second one, I used Zaph's measurement up to 40 kHz, and "Precise Phase" was used for HBT (see the 2nd plot attached). Notice that the two responses are EXactly the same up to 18 kHz. Nevertheless, the result of HBT is a phase difference as large as 21 degrees at 3 kHz.

Jay

[Mr. Wizard]

Re: RSS315HF-4 as the anchor of a 3-way???

I thought the 15W was better as a midbass for a small 2-way than a dedicated midrange?

[Pete Schumacher]

Re: RSS315HF-4 as the anchor of a 3-way???

I thought the 15W was better as a midbass for a small 2-way than a dedicated midrange?

Releasing the bass duties from the 15W, inevitably cleans up an already excellent midrange presentation. The midwoofer has a bit low sensitivity as a mid, restricting its use somewhat. The 15M has 90dB/2.83V sensitivity, while the 15W is around 87dB.

The Revelator midwoofers are aptly named. They do have excellent bass performance, but what impresses me the most is the midrange performance. I doubt the 15W really gives up anything other than sensitivity to it's 15M sibling.

[Mr. Wizard]

Re: RSS315HF-4 as the anchor of a 3-way???

I see. The rating of 87dB/2.83V on a 4-ohm driver is quite low. Any concern for power compression and unstable voicing (impedance shift)? I suppose that 3dB gain Jeff was talking about will come in handy.

[Pete Schumacher]

Re: RSS315HF-4 as the anchor of a 3-way???

I see. The rating of 87dB/2.83V on a 4-ohm driver is quite low. Any concern for power compression and unstable voicing (impedance shift)? I suppose that 3dB gain Jeff was talking about will come in handy.

I don't really think compression will be a problem. It's not like these are being used to fill an auditorium. Further up the thread, I analyzed the power distribution of the drivers with the XO points I've chosen and concluded that even when driving a 500W amp to just short of clipping during music, I might be getting 30W RMS to the mid. The Revs are rated at 60W continuous. They should be fine.

I haven't given up on the idea of opening the back of the mid chamber to add some extra energy to the room, but moving the woofer up off the floor reduced sensitivity somewhat so that now the entire system is closer to 88dB/2.83V.