Moving not enough air. Adding membrane surface.

Hi people,

as it was my first try in DIY-Audio with small budget and mixed chances of success, I deceided to build rather small floorstanders, 2.5-ways driven fully active by chipamps. The drivers are two Gradient W130AL-8 for the midbass and a Peerless by Tymphany XT25TG30-04 ring radiator. Driven are the Chassis by three LM3886 chipamps.
I was really surprised, as the result of my efforts came out really nice, and it sounded, with the help of a subwoofer under 80Hz, for my uneducated ears, far better than expected.
As time went by, I noticed one thing which I didn't think of, when planning the speakers (because of a lack in experience): two 5.25" drivers with a linear max. of 2,6mm will not be moving really much air. Ok, they are loud (more than 50-60% is to loud) and they sound beautiful, but I cannot feel them. I realized this, when hearing such a mobile "boombox" (a bigger one ) and this thing made me feel the kicks of the upper bass in my stomach. Ok, I could build new speakers with 6.5 or 7" midbass, but a: expensive, b: no real tools (except of a router, which I got cheap from the supermarket), which means weeks of work.
As I saw my actual Gradient midbass drivers on sale for half the price, I deceided to cut my speakers open. I'm still far from done, but today I put the drivers back in the first box, and I'm really excited about how they might sound. I expect nothing, as always, but I hope for a little improvement. The two lower drivers will play from 80Hz to 600Hz, the upper one from 80Hz to 2200Hz.. The Speakers measure H: 1048mm x W: 190mm x D: 300mm.
At the moment I'm at putting a fourth LM3886 in the back of the speaker, and I'm thinking about class-D. 4 channels with each about 80W should do it. What do you think?
(before/ after)

best regards
Jochen
 

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Thats why I explained why I didn't build new speakers. Would 6 new speakers have been a possibility, I would have bought others. I also explained, that, in the case of new speakers, I would have chosen 6.5 or 7" midbasses. I bought these 5.25" because they were at a low price, but not cheap, and there was a building-report about it in the net. It was my first DIY try and I took proven constructions and modified them for my needs. Best chance not to fail completely.
 
A problem with any DIY speaker is you can't hear it how it sounds until you completed it, unless someone built it and showed to you.

In my opinion, if you put more of this midbasses to your speaker, they won't give the kick-feel more, just they would be louder. Of course this is similar to the kick-feel, but not the same.
 
Hi! yeah, according to datasheet the Gradient W130AL-8 woofer has cone area of 85cm2, xmax 2.6mm. This is 10x less surface area than average 15" driver has, while xmax is about third of typical 15" woofer.

From experience 12" woofers start to kick in home use, while 15" seems better, I'd say try equal one 15" driver volume displacement for proper kick. With maths from above you need 30 of those drivers, per side ;) perhaps less is fine, this is just to illustrate scale, kick and bass is about volume displacement.
 
And what about room acoustics or the match between main speakers and sub? For all I know you could have a deep null at 80-100Hz at your listening position, either due to standing waves or to phase mismatch between the systems. Both are very likely. Is this range (80-100Hz) missing everywhere in your room?
 
If you go for subwoofer and have main speakers you can do alot with placing.

Subwoofer profits +10db from corner placement. You get sound pressure for free. Can even be reinforced putting the driver faced to the corner leaving some cm at the sides with a plate of wood on it.

Crossing over I recommend 80 Hertz as you do not want to have problems with imaging. 80 Hertz was the frequency where I never experienced that the main speakers (satellites) change their sonic integrity. Cutting higher can be more difficult because you have to take care to adjust the phasing more precise.

You can measure the response and adjust with some EQ everything. (smartfone eq apps can be used)
 
The suggestion for a higher crossover point with two (stereo) subwoofers is to answer the quest of the OP.
He's already crossing at 80 Hz and it's not bringing him what he wants.
The subwoofers can move the air required for that kind of sensation. Place them close (enough) to the mains for best results.
Most active subwoofers can also do some phase manipulation.

Best scenario: use everything you've got and EQ the subs plus mains at these lower frequencies for optimum results. Measurement equipment and some time to learn the ropes required, the rewards are huge. Placement can help, but also look at how each woofer can contribute to the result, especially if there's something like floor bounce from main speakers, the subs might be used to level it out, fill that gap etc. Lots of work, big rewards. If you keep the bass Stereo and get it right you'll even be able to get a feel of envelopment from these lower notes.