- Thread Starter
- #41
And you think I'm crazy!So that system is using 12 of those SB Acoustics drivers, the room is not more than maybe 12-15m^2
And you think I'm crazy!So that system is using 12 of those SB Acoustics drivers, the room is not more than maybe 12-15m^2
And you think I'm crazy!
Really nice finish on those cabs. But you know, SB makes those drivers in black, too.No shallow mount driver is perfect, typically struggling with assymetric BL etc, but the SB acoustics one is a decent driver as long as you use enough of them. It's popular in shallow bass towers here in Norway.
Here is a video featuring yours truly assembling and tuning a bass tower with those drivers (from around 1:05).
Really nice finish on those cabs. But you know, SB makes those drivers in black, too.
Also curious, what's the cabinet volume per driver? One of the neat things about these drivers is that they play pretty well in tiny cabinet volumes. I've used them in as little as ~6L per driver!
@mcdn I haven't spent much time to understand what you are trying to compare here, but a quick simulation implies that the Purifi can do 3dB more than the SB Acoustics at 20hz before reaching its excursion limit, while according to your table you need 28 Purifi drivers to achieve the same as 4 SB Acoustics drivers.
That does not seem to compute (at all).
That's what I thought, but the Purifi is a spectacularly insensitive driver at 20Hz: 67dB from the Purifi data sheet, and confirmed by hificompass measurements. The SB is 78dB sensitive at 20Hz, confirmed by AudioXpress measurements, so requires ~4x fewer drivers to reach the same SPL on that basis alone.
I am not understanding what you are doing.That's what I thought, but the Purifi is a spectacularly insensitive driver at 20Hz: 67dB from the Purifi data sheet, and confirmed by hificompass measurements. The SB is 78dB sensitive at 20Hz, confirmed by AudioXpress measurements, so requires ~4x fewer drivers to reach the same SPL on that basis alone.
I haven't considered power or excursion at all, because the second half of the table uses the measured SPL to extrapolate driver numbers to achieve 110dB in-room under the measurement conditions. By definition this means each driver would be performing as measured in that scenario. Of course you can use fewer purifi drivers to get to 110dB @ 20Hz as they have huge excursion, but the distortion would be bad for the money you paid, and the amps would be huge.
There may also be a formula error with the sheet, but I suspect it's more a case of accumulated error across various approximate fields, plus a slightly nonlinear relationship between voltage and SPL for the Purifi at 20Hz.
Whether it's 4x or 7x the drivers, I was still very surprised, and happily expect to be shown I'm wrong! I'll publish a link to the actual excel sheet when I get a chance.
Yeah, that LaVoce WAN102.50LD looks like another solid choice, and very shallow. Some of the pro-sound drivers with neo magnets high efficiency, and lower excursion are quite shallow and will work really well in sealed with DSP.If I may add the Lavoce to the equation merely for fun
In a well-damped 20l sealed box I simulated 87.7dB at 20Hz at 90W using one driver. This will get to 50.6% of the linear xmax (I guess that would mean literally no distortion in real-life)
When driven to 100% of linear xmax (approx. 350W) it will yield 93.6dB at 20Hz
90W
View attachment 394644
View attachment 394645
350W
View attachment 394646
View attachment 394647
Of course, this is always true (although the SB spec is low according to Vance Dickason, he measured more like 330cm^2).SPL is just about moving air, so excursion vs cone area. The Purifi has a 360cm^2 cone area, while the SB Acoustics is presented to have a 312cm^2 cone area.
I think you are looking for a set of THD vs. SPL vs. frequency contours.Of course, this is always true (although the SB spec is low according to Vance Dickason, he measured more like 330cm^2).
What I'm looking at is something a bit different, which is SPL achievable for a given distortion level. In this case we can't use Xmax in our simulations. Since distortion and excursion are so closely related, let's invent a new parameter Xdist(f,d), which represents the maximum excursion a driver can achieve at frequency f and distortion < d. Whether it's sensible or not, I've chosen f=20 and d=10.
Of course, this is always true (although the SB spec is low according to Vance Dickason, he measured more like 330cm^2).
What I'm looking at is something a bit different, which is SPL achievable for a given distortion level. In this case we can't use Xmax in our simulations. Since distortion and excursion are so closely related, let's invent a new parameter Xdist(f,d), which represents the maximum excursion a driver can achieve at frequency f and distortion < d. Whether it's sensible or not, I've chosen f=20 and d=10.
@sigbergaudio thank you for continuing to discuss this. I think the phrase "knows just enough to be dangerous" applies to me. The way I was thinking about the issue and using the published measurements does indeed lead to absurd results. My approach is overcomplicated, and this is compounded by the difficulties in comparing measurements between reviewers.But that is typically what Xmax is. While not standardised, the Xmax typically implies the maximum excursion while keeping a linear response - where the definition of linear may differ from manufacturer from manufacturer. But for instance 10% THD is a common figure.