2 Woofers in Parallel Config - 4 Options

[HiFiNutNut]

Can you please provide some links / info on matrix bracing?

Regards,
Bill

[sreten]

Originally posted by Svante

I wonder... How common is this in real life? You show simulations, but have you tried the corresponding thing with real systems? It seems to me that one would have to know quite a bit about the nonlinearities of the suspension in order to cancel it with an appropriate box volume.

*I mean, the simulations are probably correct, but I would imagine that they represent a special case where the nonlinearities of the suspension and air happens to cancel. I don't think that happens that often in real life.

Hi,

As far as I'm aware the phenomenon has been well known to
manafacturers for years, but its obviously not an easy thing to
ascertain for an amateur speaker builder.

As far as I'm aware it is part of the suspension design.

/sreten.

[sreten]

Originally posted by HiFiNutNut

Although 4 does not necessarily eliminate / reduce cabinet resonance / vibration, it does prevent cabinet rocking to some extent so I guess the MTM above would still see less movements. But this may be a small gain and I have to consider other factors.

With Option 4, let's presume the crossover is at 200Hz for my MTMWW speakers. The wave length of 200Hz is 1.7m. Let's assume the cabinet depth is 600mm, considering a monopole with a 4pi radiation pattern, the sound of the back woofer would come in 127 degree delay. At 100Hz 64 degree delay. Would this cause significant sonic problem?

Bill

Hi,

For front / back mounting you really also have to consider at
least the back wall if your talking significant cabinet depth.

But if its a concern side mount both drivers near the front.

/sreten.

[john k...]

(JPK) Svante, your points are well taken. The simulation are not intended to be taken as a way to correct for the NL distortion in a in a driver but rather to show that the common wisdom that push/pull always reduces even order distortion isn't necessarily true. Yes, a big box (or infinite baffle) reduces/eliminates the NL of the air spring allowing PP mounting to reduce even order driver realted HD, but big boxes and IBs aren’t typically convenient. In a dipole woofer PP can be a good thing, but the high excursion of dipole woofers means all distortion tends to be high to start with unless the driver is extremely linear up it excursion limits. It's not clear to me that reducing even order HD, leaving the discordious odd order HD unmasked is even a good thing.

However, with regard to the simulations, they were not a special case. Air spring nonlinearity is modeled through the thermodynamic properties of air. The driver was assumed to have a typical top hat (or bell shaped) variation in suspension compliance. Asymmetry of the suspension is just a simple center offset. And I just threw in somme numbers I thought might be represeititive of a real driver (Qts, Fs, Vas, etc). I did not introduce nonlinear BL in the simulation to date. Still, even order HD only results from asymmetries in the forces applied to the driver. So if there are asymmetries in the suspension or motor, the asymmetries of the air compliance will always contribute to increasing or decreasing those asymmetries depending on mounting. That doesn't mean it will cancel even order distortion from the motor or driver suspension, but it should mean that even order distortion will always be greater with one mounting configuration than the other. The devil is, as always, in the details. The bottom line for a DIY builder is that he is probably working blind here.

Now don't get me started on constrained layers.

[MBK]

I have done some measurements on my open baffle woofers recently (shallow U-frame, 7.5" deep, 24" wide). The results are surprising.

- In push pull at 100 Hz both 2nd and 3rd are elevated compared to same SPL of a single woofer measured in front (all at 8" distance to mic).

- If I raise the dual woofer SPL by 6 dB to get the same excursion that a single woofer would experience, the case worsens even more.

Unless something was clipping I have no ready explanation for this. Pictures below. "woofer-s" is a single woofer, "woofers" are both in push pull. The woofers are Vifa 10" with decent Xmax, according to calculations far from excursion limits at this SPL (100 dB at 8" doesn't translate to much at 1m reference distance).

When in push pull the woofers were wired in series - this is where I suspect the issue (inductance? back emf?).

[MBK]

push pull same SPL as single woofer

[MBK]

push pull same excursion as single woofer