Jims 3 way speaker build

[jimbones]

All, Id be lying if I said i wasn't nervous about having a good outcome here. I have a finished cabinet and not sure of all my options at this point. I calculated the box volume many time to be sure I had enough volume. I made sure the port was sized appropriately and correct length. I appreciate everyones help hopefully we can get past what I thought was the easiest part of the project so so I can move on to the next step.

[jimbones]

Billet, I am not that optimistic with the results. I thought that the raw Fr of the woofer would go lower as well as the Port. This set up should be able to get to 35hz

[Billet]

That looks like a nice FR curve to build on. I'd add the midrange with a single cap (1st order electrical) and see how it looks.

[jimbones]

here are a set of measurements bypassing the XO.

[jimbones]

here are a set of measurements with the cabinet with stuffing and nearfield measurement and no gating at all coil changed from 5mh to 8.3mh

[rpb]

I made the assumption that it was measured on the tweeter axis. My bad. Either way, the breakup still exists. I think it should be notched to potentially improve sound quality.

[jimbones]

I have no stuffing in the box. I will add some (I actually have the lambs wool lol!)

[jimbones]

I measured the woofer on axis nearfield I'll do it again no gating and bypass the XO. If you see the impulse graph it shows the gating at 14 msec. I'll do it at 100msec.

[DeZZar]

I was of the understanding the woofer was on axis.....if the woofer was measured with the mic pointing at the mid point between tweeter and midrange it's little wonder. Perhaps Jim can confirm?

[rpb]

Factory measurements of woofer.​ There is a drop above 1k, but it comes back. Jims measurement was likely off axis if he measured on the tweeter axis, so his measurement was probably more like the red trace.

[DeZZar]

It can be 24db/oct electronically and still have a lesser of greater effect on the acoustic result. The measurement for the woofer, assuming its fine, shows that its response naturally falls off a cliff after 1k. So with a 7.5mh and 75uf in place its pretty easy to fully suppress everything from about 800hz up without any notch - again, all according to the files provided.

[DeZZar]

Based on the aligned sum (blue) of these measurements you're currently sitting at an f3 of around 46hz. I've assumed a 4" port diam...
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The measurement really shouldn't be taken with crossover parts in place at this stage - hard to tell what sort of effect they are having.

As you've started before your woofer is near the floor so I have no real way of knowing what sort of effect that's having on the measurements either (maybe none). I would apply 80-100ms gate time to see if there is much difference in what is showing.

I also don't know if you have or haven't included the acoustic stuffing required to try and tame the resonance issues. Just to state this very clearly once again - it will have a sizeable impact on the results!

You mentioned you've cut off some of the port length - is the above before or after that? Have you re-measured impedance now to confirm where the tuning lies? Optimum results for an SB34 in net 70L is around 32hz...


Here's an example of the sorts of results you should expect when measuring a ported system:

First up is the model for this woofer - its an SB WO24P-8 in a 37L (net) enclosure tuned to 28hz. Here is the expected magnitude:


Here's our measured impedance which shows the port tuning is right on the desired 28hz from the model
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And here are the measured frequency results...


In these results you can very clearly see the woofer response has a deep null right around the tuning frequency (28hz) - which is further confirmation of where the tuning has landed.

The ports contribution to the system response also starts to peak around the tuning frequency and its overall contribution is fairly narrow spanning roughly 1 octave overall before trailing off.

The aligned sum is very close to our predicted results. We can confirm an increase of 1db or so around 60-70hz and an f3 of 38hz (a little higher than predicted but this is a brand new woofer without break-in and so we expect the compliance to reduce along with the fs over time which should bring us a lot closer to predicted f3).

I'm just sharing this as an example of what you should be seeing in measurements which in turn gives you confidence your measurements are correct and can be relied on.


I suggest in your case....

- Replace any polyfill you intend to include to tame standing waves and other resonances
- Remove your crossover parts
- Re-measure the impedance with the shorter port
- Re-measure the woofer and port responses without crossover parts, with all stuffing and with new port length

[Chris Roemer]

From what I think I remember, on a vented box the driver and port are in "quadrature" (90*) at the tuning freq?, and the port phase is sliding w/respect to the driver output (rotating more out of phase) as you drop below Fb, which is what creates the -24dB/oct bottom-end rolloff associated w/a vented box. (A closed box rolls off at -12dB/oct going down.)

[rpb]

I have a suspicion, and a suggestion, and some questions too.

1 I'd add a cap for a tank filter centered on the peak at 4k. It shows up in both measurements, which leads me to the next suggestion.

2 I think the sound off the back of the woofer is bouncing directly off the back wall, and out the port. If you add an elbow, that should fix it, I think. The manufacturers data shows a peak there. The xo needs to knock it down as far as possible.

3 I would increase L1 to about 7 or 8 mH.

4 What gate setting did you use? It needs to be 100ms or so.

5 Other sims show the response dropping like a rock above 1k, but your measurement indicates that's not what is happening. I would suspect an issue with the files used. A second order filter should only drop at a rate of 12dB per octave, which is about what the close mic measurement shows. Both your sim, and DeZZars show a much steeper roll-off.

[jimbones]

attached are frd of woofer and port as well as snapshots. Does the impulse show the woofer phase is inverted?