3-Way/Side-Firing Woofer - Measurements for XO Design

[jhollander]

Re: 3-Way/Side-Firing Woofer - Measurements for XO Design

Robert, OK thanks. The offsets make physical sense if the tweeter is below the mid.

If all the drivers are measured from the same point you, did you use the measured phase?

I will not use offsets if the time of flight is already in the measurements.

[Robert Dunn]

Re: 3-Way/Side-Firing Woofer - Measurements for XO Design

Robert I assume the tweeter was measured on the tweeter axis so the 0,0,0 is OK. Now if the woofer and mid were measured on the mid axis why isn’t the X, Y offset the same for the mid and woofer?

Did you derive the z offset for the mid? The +.35 inches means the acoustic center of the mid is forward of the tweeter in PCD.

No, all measurements are on the mid driver axis. The mid driver acoustic center is 0.35" behind the tweeter but, since all measurements were on mid axis, the tweeter is 0.35" in front of the mid. I came to this value using the impulse delay in MLS measurements between the drivers and a bit ..of geometry. It may be off a bit but should be close enough.

[Robert Dunn]

Re: 3-Way/Side-Firing Woofer - Measurements for XO Design

Sure and your sim graph if possible. There are some very talented people here who might have suggestions. I'm not necessarily one of them, but am curious what made you give up on this.

I'll post the additional stuff when I get a chance. Primary reason for giving up is parts cost. I see no way to get the capacitor values under control -- see the xo when I post it. I think it would be cheaper to use a plate amp for the woofer. But maybe someone smarter than I will have a solution.

[jhollander]

Re: 3-Way/Side-Firing Woofer - Measurements for XO Design

Robert I assume the tweeter was measured on the tweeter axis so the 0,0,0 is OK. Now if the woofer and mid were measured on the mid axis why isn’t the X, Y offset the same for the mid and woofer?

Did you derive the z offset for the mid? The +.35 inches means the acoustic center of the mid is forward of the tweeter in PCD.

[jhollander]

Re: 3-Way/Side-Firing Woofer - Measurements for XO Design

Sure and your sim graph if possible. There are some very talented people here who might have suggestions. I'm not necessarily one of them, but am curious what made you give up on this.

[Robert Dunn]

Re: 3-Way/Side-Firing Woofer - Measurements for XO Design

Last attachment.

Woofer SPL.txt

Would you like to see the xo that I have so far?

[Robert Dunn]

Re: 3-Way/Side-Firing Woofer - Measurements for XO Design

Maybe post some FRDs, ZMAs, and the offsets.

Sure. I'll have to post the last one in a separate message (limit of 5 attachments).

SPL measurements were at 1m on mid axis. Tweeter xyz = 0, -5.25", +0.35". Woofer = +5", -18", -7.25".


Attachments:
Mid Imp.txt Mid SPL.txt Tweeter Imp.txt Tweeter SPL.txt Woofer Imp.txt

[jhollander]

Re: 3-Way/Side-Firing Woofer - Measurements for XO Design

Maybe post some FRDs, ZMAs, and the offsets.

[Face]

Re: 3-Way/Side-Firing Woofer - Measurements for XO Design

A 4ohm woofer would cut down on the inductor size.

[Robert Dunn]

Re: 3-Way/Side-Firing Woofer - Measurements for XO Design

Sadly, I think this project has reached a full stop. It's time to cut the losses and treat this as a learning experience.

After XO simulations, it's clearly not possible to design a passive XO that will have both reasonably flat SPL through the woofer/mid XO band AND maintain a reasonable minimum impedance. Well, that's not exactly true -- it can be done but the inductors become very large and the capacitor values are simply insane. Driving the woofer with a plate amp appears to be much cheaper than passive XO parts.

Anyway, I think that I now understand why we see so few passive 3-way designs.

Thanks to all for encouragement and suggestions. If anyone wants to see sample XO schematics, SPL or impedance curves, etc., let me know and I'll happily share.

[Robert Dunn]

Re: 3-Way/Side-Firing Woofer - Measurements for XO Design

My opinion is to splice the woofer near field with the woofer far field measured on the tweeter axis and skip the offsets if using PCD.

That's essentially what I did for the posted curves, only I used the mid instead of the tweeter as the reference.

I’m not sure how you could derive a z and x offset if you were to measure the woofer on axis, splice the near field then rotate in PCD, save frd, etc.

I think something rational could be done, maybe measure at 1m on woofer axis, adjust SPL to account for additional distance of woofer to 1m on mid axis. But, for the moment, I'm going to work with the on-mid-axis measurement, work up an xo, and see how that measures/sounds.

I would also consider raising the woofer up and measure outside to see if I could get some measurements below my x-o point.

I do wish my equipment was portable but it's not. Not to mention that the box weighs 73lbs.

Thanks.

[jhollander]

Re: 3-Way/Side-Firing Woofer - Measurements for XO Design

My opinion is to splice the woofer near field with the woofer far field measured on the tweeter axis and skip the offsets if using PCD.

I’m not sure how you could derive a z and x offset if you were to measure the woofer on axis, splice the near field then rotate in PCD, save frd, etc.

I would also consider raising the woofer up and measure outside to see if I could get some measurements below my x-o point.

[Robert Dunn]

Re: 3-Way/Side-Firing Woofer - Measurements for XO Design

Here are NF/FF tagged curves for all three drivers in box. Woofer curve was taken on the mid axis.



Any thoughts?

[Robert Dunn]

Re: 3-Way/Side-Firing Woofer - Measurements for XO Design

Hi Robert. I'm keenly interested in your project, because it mimics what I am going through right now. I can give you advice based on my experience. But first some questions:

Can you provide us with a 1-2M SPL of your midrange in its acoustic cavity? We would want to see what it is willing to do before choosing a cross point frequency. Even NF of the mid will help.

The mid 1M curve below However, I did not take a NF measurement. Need to do that and splice to FF for sure since the FF is good only down to around 200Hz. I'll post that, hopefully later today.

Can you take your proto sub outdoors for ground plane measurements? If so, then measure at 1-2M distance. (Let us know if you need tips on the GP technique.) Take 4 curves, one for each face of the sub. This will give us an idea of the SPL with woofer and port summing, and show the performance for front- or side-firing. If your SW can average curves, then average the 4 curves and that will give us an idea of the performance in your room at the lower frequencies.

I wish that I had portable measurement equipment but, no, it's not practical. However, I think that my simulations so far are reasonably accurate. Here is a simulation in free space taken at the mid height, centered on each side.


Alternatively, here is a polar simulation for selected frequencies up to about 5kHz taken on the mid axis (front).



The polar graph suggests that things begin to become directional around the 320Hz curve. Of course, in-room is going to be quite different.

Do you have means to modify your test cabinet to move the woofer down low? You really don’t want the port opening too close to the woofer or you may get additional or louder pipe resonances. (A woofer firing 90° across the port opening is the worst case.) If the woofer is down low to the floor, then you would put the port up high. Or you could go to an elbow port like I have. The port opening is now high inside the cabinet, but the elbow exits out low. In this configuration, you can have the elbow exit any panel you want.

Gee, I hope I don't have to move the woofer. FWIW, the port does have a 90deg bend. The woofer and port NF curves (see first post) do show a summed anomaly around 440Hz but otherwise look ok to me.

Thanks.

[Robert Dunn]

Re: 3-Way/Side-Firing Woofer - Measurements for XO Design

Looks like a fun project. You're torn between:
1. keeping the woofer and mid close to each other for phase reasons, and
2. putting the woofer close to the floor for increased boundary augmentation (and also to minimized floor bounce issues.)


Hmmm... let me throw some ideas at you. You can dismiss them if you don't like 'em. It might already be too late for my suggestions because you said that you already have a protoype box built.


A. How about lowering the crossover point to 100Hz where the wavelengths are much longer (11.3 feet) and more omnidirectional.

B. Then you can physically locate the woofer lower in the cabinet to minimize the floor bounce problems, while still having the phase integrate reasonably well with the mid. (because of the longer wavelengths). Do some quick trogonometry and convince yourself that the path-length differences (and thus phase) of your woof & mid will be mitigated by going with an 11.3 foot wavelength.


Choosing 100Hz reduces the amount of midrange frequencies coming out of the side firing woofer, (At 250Hz, it may be more difficult to integrate the side firing woofer's output with the midrange driver's output. At 100Hz it will be easier.)

I would suggest a 3rd order or 4th order network on the woofer to simplify the acoustic/phase integration with the midrange driver. You may have to add a notch filter to the woofer's x-over network to make the response behave... but that's a small price to pay to overcome the other issues mentioned above.

Try splicing the NF and FF curves, import them into Jeff's PCD, and design a steep filter that only lets the woofer sing to 100 Hz. Be aware of the filter "Q" during this step... you don't want nasty peaking. (maybe a notch filter will help with this.)

Get the polarity (phase tracking) correct from woofer to mid, then keep the mid's polarity fixed and determine the tweeter's polarity for best integration with the mid. You can run hundreds of trials with Jeff's PCD before you attempt to build the crossover. Best of luck on this design.

I think you're right, I will need to keep the XO point low. But I also don't want to push it so low that the mid is stressed at higher SPL. 100Hz is probably too low.

I'm sure that I need to splice the NF & FF. The thing that I'm struggling with is, what FF curve to use? If I take the FF from the front on the mid axis, I'm both farther from the woofer and 90 deg off axis. While that seems right for the XO phasing, it seems wrong for the SPL being radiated into the room. If, on the other hand, I take the FF from the side, the curve will have a more accurate SPL in the higher frequencies but I lose the off-axis information that I need to integrate the drivers. Or that's what I keep telling myself.

The solution is, of course, higher order XO where FF accuracy will be less of an issue. OTOH, more expensive parts.

Thanks.