First of all, welcome to AudioHolics … whether you're an audiophile or an audioholic
. Before I say anything further, I've never heard of your speakers before, much less actually listened to them. So keep that in mind.
First, a few questions: Are these speakers new? Or, have you had them a while? Because they are bi-polar monitors, their location in your room is quite important. How far away from the wall behind them do you have them? Are they out into the room a good distance, or are they close to the wall behind them? Your comments about their spacious sound suggest you've done that.
I looked online for a review of these speakers that includes decent measurements. I did find
a review in Stereophile of The One speaker, not the 1+1. It may be good enough to tell us something about how full-range their 3" driver is, even if it isn't the bi-polar version with 2 drivers. I don't think it's too much to guess that The One and the 1+1 speakers share the same drivers and have similar passive radiator cabinet tuning.
The 1+1 speaker cabinets have passive radiators which work essentially the same as a ported bass reflex cabinet. They are not a sealed box design. However, you may be right that there is something not quite right with their bass response that could lead to your difficulty in blending them to your subs. John Atkinson (the Stereophile measurements guy) had this to say:
Please note that John Atkinson's loudspeaker measurements are good, but he often understates things in an effort to avoid annoying a potential advertiser. I always find myself wishing I had a lawyer to help interpret his language. But I do think he's agreeing with your observation about the 1+1's bass response.
Here is Figure 3 from the review. The red trace is the response of the passive radiator and the blue trace is the bass from the 3" driver. The black trace is the overall response.
View attachment 62031
To me, the most obvious flaw I see is the elevated & ragged treble response, especially above 1,000 Hz. That 3" driver may be a good mid-range driver, but it isn't a good tweeter. That may very well be the overall brightness that you hear. I can't predict exactly how that might vary in a bi-polar design using two of those drivers, but I think the brightness will still be there.
John Atkinson said this about the treble response
In addition to the bright sound, the small diameter drivers start beaming their sound instead of widely dispersing it. Atkinson said:
Here is Figure 4 that compares speaker output on-axis (0 degrees, see the scale on the right side) to various degrees off-axis, as high as ±90 degrees. Note how there is wide dispersion at all off-axis angles up to a peak at about 3,000 to 4,000 Hz. But higher than that, off-axis dispersion drops off considerably. No 3" driver can avoid doing that. That's what smaller tweeters are for.
View attachment 62033
If those were my speakers, I'd start looking for good quality 2-way or even 3-way monitors. There are plenty of those commercially available. What price range are you considering?
I don't think this matters. But, as I mentioned above, it is possible that these 1+1 speakers can't go low enough to work well with your subwoofers.
There is no clear cut single answer to this question. It depends on a lot of factors – where the walls are relative to your speakers as well as you the listener. You have to go through some trial & error with speaker placement, listener placement, and sub-to-speaker crossover frequency.
If you don't have speaker design experience, I would avoid designing your own monitors. There's a long learning curve to do this well. The same goes for DIY wood working tools & wood working experience. However, there are a lot of very good quality DIY speaker kits where all the design work has been done by someone experienced at it.
