Time to cut my losses on this project?

Hello everyone, I started a thread about this project several weeks ago, and the responses were very helpful, thanks. I'll try to be as concise as possible to present my dilemma.
This is my first scratch build. The goal was to create a pair of speakers with minimum 94db sensitivity using a coax driver, to pair with an Alan Eaton SET45 amp, which is the epitome of "flea watt" at <2 wpc.
I ended up choosing the Radian 5210, a 10" coax with a very good reputation. Even though it looked anemic below 100hz, even 150, I thought with proper port sizing and fill I could get it to work and be pretty solid from 50hz and up, and since I use a sub I wasn't worried about these being bass monsters.

I've worked very hard on this project, all the while thinking that the satisfactory response curve was there to be found, if only I could dial things in and measure them well. Yesterday I did another round of measurements, as I'm getting more competent with REW and wanted to start clean and really see what's happening with these speakers.

Below I've posted the latest results, showing impedance and T/S parameters, and also the results of my summed port (compensated -6.4db) and nearfield woofer. The overall speaker consists of the Radian 5210 coax in a 3ft/cu box, with a 4" port tuned to 42hz. The problem is the rolloff starting at 170hz, eventually losing about 7db from 60 hz down. I don't know of any way to compensate for this without a correction network that would attenuate the woofer response above 80 hz, which means I'd lose 6-8db in sensitivity (woofer is 96db sens), and a catastrophic loss of 16db +/- for the tweeter, which is 105db. I guess it's basically a baffle step correction, but I don't have the headroom to lose that much.

I realized yesterday that this probably just isn't going to work, because you can't get blood from a stone, and that driver just doesn't want to go low, and it was my rookie mistake to think that I could trick the system by tuning the box and port to prop up the response below 100hz.

So I'm asking the community, am I correct in my assessment, or is there something I'm missing? I'd rather start over and cut my losses than keep beating my head against the wall.

Thanks in advance,
Bryan
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These are near field measurements right? So this is not baffle step you’re seeing. Bad alignment sure, as the impedance curve is not what you’d expect either.

Tune it to 70-90Hz, maybe a tad higher. You could consider a small enough closed box. You are on subs, so you’ve got everything up to 100Hz covered anyway. This driver isn’t meant to go low.
 
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You might do better with box size & port tuned to 54 hz instead of 40. Hardly any driver with fs over 25 will do 40, and tuning lower trades off what you can hear. If you ever connect to a more powerful amp there is a danger of xmax violation with too low tuning. Big series capacitor and parallel inductor required to filter off below fs.
Put some bricks or sandbags in there to cut volume and cover the port with something smaller. Like a plastic pipe floor flange with the right size pipe of correct length glued in it. Maybe the 150 to 54 crash won't be so steep.
 
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How do you plan to use the speaker? I'm working on something similar at the moment using the Beta 10 co-ax that also starts rolling off pretty high, but intend to use the speaker relatively close to the front wall (in audiophile terms), so that compensates for some of the roll-off. With the speaker cone about 24 inches from the front wall, the speaker has good in-room response down to 40 Hz (-4 dB at the listening position). You may want to do some in-room measurements/listening to see if yours is better than it looks in your current measurements.

This is the modeled response. I didn't bother trying to measure the quasi-anechoic response, since I was mostly interested in how it interacts with the room and whether it would do what I wanted. Overall it does. Power handling is sacrificed for the low-end extension and gradual roll-off, but for my application that was a reasonable trade-off.

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My test box is smaller than the one recommended by Eminence, but the tuning and general response trend is similar.
https://www.parts-express.com/pedocs/more-info/290-502--eminence-beta-10cx-cabinet-design.pdf

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Looks like baffle step to me. With a very narrow front baffle, the baffle step is going to be in that range. You can model that in Visaton Boxsim or other programs that include baffle step. 1. Add a very wide baffle. Go with 24 - 36". 2. If you want a narrow baffle, and high efficiency, the best way to battle baffle step in my opinion is to add a second woofer and cross it in at the baffle step frequency. This give exactly the 6 dB boost you need at the low end. Software is so good, it is getting easier to accurately predict full system responses before buying and building anything. VituixCAD or Visaton Boxsim are both free and youTube has videos explaining how to use them.
 
Looks like standard baffle step loss of 6dB to me. Increase the lowpass inductor until flat, and attenuate the tweeter until it matches.
It's a nearfield woofer measurement, so this can't be baffle related right? And my 1meter measurement is gated so not much good below 400hz.
These are near field measurements right? So this is not baffle step you’re seeing. Bad alignment sure, as the impedance curve is not what you’d expect either.

Tune it to 70-90Hz, maybe a tad higher. You could consider a small enough closed box. You are on subs, so you’ve got everything up to 100Hz covered anyway. This driver isn’t meant to go low.
I think this is very good advice. I was really hoping to squeeze the impossible out of this driver, but you're absolutely right, it's not meant to go low, originally designed as a stage monitor or small PA driver, and I think the recommended box volume is 30L/1 cubic foot. I can put a false bottom in the cabinet and move it around a bit and see how it goes. Thank you Mark.
How do you plan to use the speaker? I'm working on something similar at the moment using the Beta 10 co-ax that also starts rolling off pretty high, but intend to use the speaker relatively close to the front wall (in audiophile terms), so that compensates for some of the roll-off. With the speaker cone about 24 inches from the front wall, the speaker has good in-room response down to 40 Hz (-4 dB at the listening position). You may want to do some in-room measurements/listening to see if yours is better than it looks in your current measurements.

This is the modeled response. I didn't bother trying to measure the quasi-anechoic response, since I was mostly interested in how it interacts with the room and whether it would do what I wanted. Overall it does. Power handling is sacrificed for the low-end extension and gradual roll-off, but for my application that was a reasonable trade-off.

View attachment 1212070

My test box is smaller than the one recommended by Eminence, but the tuning and general response trend is similar.
https://www.parts-express.com/pedocs/more-info/290-502--eminence-beta-10cx-cabinet-design.pdf

View attachment 1212072
Thanks Matt. I'd be using these paired with a 45 SET amp, super low wpc (2). Your numbers look pretty similar except your speaker has a Much bigger Vb. Interesting you're getting such a boost from the room, I measured in room at 1m and did get a bit of a boost but not enough to make me relax!
 
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You might do better with box size & port tuned to 54 hz instead of 40. Hardly any driver with fs over 25 will do 40, and tuning lower trades off what you can hear. If you ever connect to a more powerful amp there is a danger of xmax violation with too low tuning. Big series capacitor and parallel inductor required to filter off below fs.
Put some bricks or sandbags in there to cut volume and cover the port with something smaller. Like a plastic pipe floor flange with the right size pipe of correct length glued in it. Maybe the 150 to 54 crash won't be so steep.
Right now the naked 4" port hole is tuned to 50hz. I'll start there and add the false bottom as I mentioned above, and work my way up to 70 or even higher tuning as suggested by Mark. I've got a REL T7x and it does a great job filling in, pretty seamless in my current setup, so this just might work out.
 
I made some sims assuming 3 Ohm total series resistance (amp output plus cables connectors etc.) and result is -6dB step in bass response, very similar to your measurements. Its caused by alignment and driver properties, not baffle step (nearfield measurements).
If tuning frequency is raised to 48-50 Hz with current box than bass step is reduced to -3dB which should be acceptable.
To make flat response, you'll have to go with even higher tuning, but also smaller box.
 
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Thanks a lot Davor, I'm still learning the ropes with REW and VCAD, so doing those sims for me would be a day's work. This is reassuring, I'll start with 50hz tuning and cut (fill) the box from 3 to 2 cu ft, and see what happens. I'll keep going til I get pretty flat, I need all the sensitivity I can get for this amp, and I'll already have losses from the damping but I may be able to reduce that if the resonances are more tame with different tuning.
 
I have a speaker driver with a rated Fs of 88 Hz and I think it has nice sounding bass. My box is tuned to 82 Hz, pretty close to the actual Fs of the driver. My enclosure is a lot smaller also, less than the Vas of the driver. In my experience, tuning too low can cause a dip in the mid and upper bass. And the mid and upper bass notes are present in most music, so it will be very noticable. Pro drivers with stiff suspension port very well in my experience, just not super low.
 
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Well I'm about to go out to the barn and make some mods to the cabinet, shrinking the volume to 2cf/60L. The Vas for this driver is only 26L and the Fs is 67 hz. Sounds like I need to start at 62hz, which would be just a 10cm/4" hole through the double plywood baffle of my test box, 3.6cm.
If I'm using a 56L box with a Vas of 26L, what kind of problems am I creating?
 
What you've got here, in your original post, is essentially what's known as an extended bass shelf alignment. When coupled with some decent room gain the two can often cancel each other out, and you get something flattish, but there's a limit to how far you can take things.

I think the biggest issue here, at least from a subjective point of view, if you've got that far with these yet, is that there are going to be two bass loss phenomena at work. The first is the EBS alignment but the second is bafflestep losses. This has been mentioned before but shouldn't be ignored.

Your in-room measurements showed some boost but not enough for you to relax. It's possible that the boost was enough for the EBS alignment but when coupled with bafflestep losses this is what made things look poor .

The main problem here is that you've got a woofer with 96dB sensitivity when you were expecting that to yield a system sensitivity of 96dB. Unfortunately this isn't going to be as you will usually lose 3-4dB of that to bafflestep compensation (most find the full 6dB too much in room but this depends on room and speaker placement). Still a system with a real 92-93dB sensitivity is a lot more sensitive than the norm and will probably go surprisingly loud on a couple of watts.

In my opinion your first priority is to eliminate the EBS alignment because it will add to the subjective effect of bafflestep losses and make it harder to tune your crossover for the correct amount of bafflestep compensation to apply.

As you've got a subwoofer you don't even really need these to attempt bass anyway, although I'm not knocking the idea, it's just getting in the way at the moment.

You are already going this route anyway but reduce the cabinet volume and then raise the port tuning. At a guess you can probably get something that's flat down to about 100Hz whilst eliminating the bass shelf. Then you really need to do what wolf suggested in post 2, or something to that effect, until you've applied enough bafflestep compensation for things to measure roughly flat, or sound right, in room. Too little bafflestep compensation and things typically sound thin and fatiguing.
 
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5th Element - that was a really clear bit of information, thank you very much, and everyone else who's chimed in. When I put it all together I'm getting a lot more clarity.
I think I'm going to need to make dual 3" ports to get above 60 hz tuning, and I couldn't find my 3" hole saw so I'm off to the lumberyard tomorrow and will grab some 3" ABS too. Two 3" holes tunes me just over 80Hz with the double baffle, and I can move down from there.
Hopefully room gain will help make up for some of the baffle step losses, but if I have to add a circuit to bring down the upper bass/midrange, I'll just have to live with it and hope I can still retain enough sensitivity to make this little amp sing. I had a pair of Klipsch RP-600Ms here for a few weeks and tested them on the 45 and they were fine if not screaming loud. They're reportedly only 90db sens, so that's a good marker. My main speakers are a pair of Jeff Bagby's Auricles with a RAAL 70/20 and a Satori 6.5" MW, it's a shame they can't play loud enough for this amp, because they're lovely speakers.
 
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Did you consider a closed box and if so, why did you pick a vented alignment? I would choose a CB in a small enclosure.

The acoustic 2nd order highpass function created that way would be a perfect starting point for the lowpass setting on your sub, thus creating a clean X-over. It would be way better than what you will realize with a combo of ported enclosure tuned at -say- 60Hz and electronic highpass at 100Hz. I’m not stating a good crossover isn’t possible, you could pick a fitting B6-alignment (4th order acoustic plus 2nd order electric). But it is more complicated.

Besides, a closed box allows for better damping inside the enclosure and eliminating resonances from standing waves within. I mean, that driver at that price point deserves attention at that point.
 
Mark - I didn't consider a closed box, out of a combination of ignorance/inexperience, and the idea that I'd get extended bass with a ported system. But you make good points, and I'll measure it both ways.
My next step is to measure a bunch of different combinations - closed/vented, 45L/60L, port tunings from 50hz-80hz, various levels of damping.
It was a mistake on my part to think I could get a nice even response below 80 hz with these, and I was looking at two speaker makers who use this driver and seemed to figure out a way to get below 50hz: Coherent Audio and Live Act Audio in Germany. I've since figured out that Frank at Coherent is basically rebuilding this driver with different surrounds and who knows what else, and Live act is just stomping on the upper bass, mids, and treble to bring everything down, and ending up with 88db sensitivity. Brute force approach. I'm continuously surprised at how much BS there is in the commercial speaker world.
 
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