[Audio Mark]

After searching and calculating the best choose I find is:

DaytonAudio ND90-8 with:
f3 = 80.9 Hz
fb = 97.02 Hz


You may think why not the ND91-8, I will answer you because it score:
f3 = 107.95 Hz
fb = 94.02 Hz

Am I right ? If not please explain

P.S. Box volume is 2 lts. And I will use passive radiator, so maybe it will change my choose.

[srb]

I know you're working within the limitations of a 2 liter enclosure, but 81.4dB is pretty low sensitivity.  If you were willing to spend more on the drivers you might be able to get a driver with better sensitivity.

The FaitalPRO 4FE32 4" would work in a 2 liter space and has a sensitivity of 91dB.  The difference between 91dB and 81.4dB is a power ratio of > 9X.

If your TPA-3110 is the Dayton KAB-215, the specs are THD: 0.07% @ 8 ohms, 10W, 1kHz.  They don't give specs at lower frequencies or maximum power, but relative THD can often be very high at bass frequencies and maximum power.

A higher sensitivity driver might make a big difference in sound quality and headroom with a relatively low power amplifier.

Steve

[S Clark]

The Dayton driver will get about 20 Hz lower, but srb is right in that it will be so inefficient that it wont matter with the power you are providing.  His recommendation is about as good as you are likely to get. 
You want high efficiency, low bass, and a small box... pick two of three. 

[JLM]

The Dayton driver will get about 20 Hz lower, but srb is right in that it will be so inefficient that it wont matter with the power you are providing.  His recommendation is about as good as you are likely to get. 
You want high efficiency, low bass, and a small box... pick two of three.

Realistically (in the cheap and cheerful world) pick one out of three.  Sorry for those pesky laws of physics to kick in.

[Audio Mark]

I know you're working within the limitations of a 2 liter enclosure, but 81.4dB is pretty low sensitivity.  If you were willing to spend more on the drivers you might be able to get a driver with better sensitivity.

The FaitalPRO 4FE32 4" would work in a 2 liter space and has a sensitivity of 91dB.  The difference between 91dB and 81.4dB is a power ratio of > 9X.

If your TPA-3110 is the Dayton KAB-215, the specs are THD: 0.07% @ 8 ohms, 10W, 1kHz.  They don't give specs at lower frequencies or maximum power, but relative THD can often be very high at bass frequencies and maximum power.

A higher sensitivity driver might make a big difference in sound quality and headroom with a relatively low power amplifier.

Steve

Thank you for reply.

Amp I'm using is ( http://store3.sure-electronics.com/2-x-15-watt-class-d-audio-amplifier-board-tpa3110 )
So you want to say, that these daytonaudio with 81db is much more quieter than faitalpro with 91db?
But what you can say about that faitalpro fb is only 141 hz and f3 is 121 hz and like I imagine there will be no bass compared to daytonaudio ? Please explain for me.

[S Clark]

The amp you list is 15w/c at 10% distortion, and that's probably at 1 KHz only.  It probably puts out a clean 7 or 8 watts.  With drivers that are only around 80 dB/1w/1m you won't get enough volume regardless of how much bass it could produce if properly driven.  Now if you had, say, around 50 clean watts to work with, it might work fine and provide deeper bass.  SRB was suggesting a driver that is more suitable to the limitations of your amp and the tiny box size.   
Honestly, you are just too limited by the box that you've described.  Have you thought about just starting from scratch?  I think you'd be much happier with the outcome. 
But it's your dollars, and your project. 

[Audio Mark]

The amp you list is 15w/c at 10% distortion, and that's probably at 1 KHz only.  It probably puts out a clean 7 or 8 watts.  With drivers that are only around 80 dB/1w/1m you won't get enough volume regardless of how much bass it could produce if properly driven.  Now if you had, say, around 50 clean watts to work with, it might work fine and provide deeper bass.  SRB was suggesting a driver that is more suitable to the limitations of your amp and the tiny box size.   
Honestly, you are just too limited by the box that you've described.  Have you thought about just starting from scratch?  I think you'd be much happier with the outcome. 
But it's your dollars, and your project.

Ok, thank you. I will try to improve something. Stay tuned

1) And one more question is: for example, box volume is 10lts and I want to fit there two speakers without any walls just clear 10lts box. And its count like one speaker have 5lts and another have 5lts or one have 10lts and another have 10 lts too ? If they both work in one 10lts box. I hope you understand me correctly.

2) If I will add some foam inside box and add passive radiator? This will improve overall box volume and bass response.

[JLM]

1.)  Yes

2.)  The passive radiator is sized to replace the proper port size (based on the selected driver).  Foam can absorb sound to make the cabinet acoustically appear to be bigger and reduce echo, but nearly all foam has almost zero acoustic effectiveness (especially for bass frequencies). 

[Audio Mark]

1.)  Yes

2.)  The passive radiator is sized to replace the proper port size (based on the selected driver).  Foam can absorb sound to make the cabinet acoustically appear to be bigger and reduce echo, but nearly all foam has almost zero acoustic effectiveness (especially for bass frequencies).

5 lts per speaker?

[JLM]

Yes

[Audio Mark]

Maximum what I can get is ~8 lts in total (~4 lts per speaker) H*W*L = 15*12*45

If this box will work much better and will give better results I will use it.

[JLM]

Mark,

You're after the holy grail of speakers: high efficiency, full bass, small enclosure, low cost, and of course good sound quality from a single driver.  Sorry, but that hasn't been invented yet.  As for now there has never been a perfect speaker. 

Being as the enclosure is relatively small, why go 2-channel (stereo)?  You might be better served to look for one better driver that could be optimized to a 8 liter enclosure.  For instance my $99 USD Logitech UE Smart Radio (approximately 25 cm x 15 cm x 12 cm = 4.5 liters) is monophonic, has a 6 hour battery, one woofer/tweeter, fills my 600 cubic meter space with background music, provides clock/alarm functions, and can wirelessly access 12,000 internet music streams (unfortunately no longer sold but similar are). 

For enough money you can bend the laws of physics.  TBIsound.com sells the MD-1 (12 cm x 14 cm x 13 cm, single driver speaker, rated 35 - 18,000 Hz, 87 dB/w/m at 8 ohm efficiency, maximum 20 watt input, reportedly very placement flexible, weighs less than 0.5 kg, starting at $200 USD each).  I only vaguely know one person who has heard these remarkable speakers and was pleased with them, but TBI also offers more expensive, amazingly small/fast subwoofers and again a more expensive well respected amplifier. 

[S Clark]

Maximum what I can get is ~8 lts in total (~4 lts per speaker) H*W*L = 15*12*45

If this box will work much better and will give better results I will use it.

Seriously, you can't always get what you want (bass).  In that box (~4L), srb has told you it won't work, JLM has told you it won't work, I've told you it won't work.  You need a box nearly twice that size.  The box you describe is the same box that I got under the Christmas tree containing a bottle of scotch.  It's just too small!
Take a look at the plans for the GR-Research LGK speaker.  It's a three inch driver, and still takes twice the box you are describing.  http://gr-research.com/pdf/lgkbox.pdf
What you are asking for just isn't out there at any price that you might be willing to pay.  Save yourself the headache and money in the long run, and buy a set of Elacs, Pioneers, or one of Danny Richie's kits. 
Hope you end up with something that makes you happy. 

[JLM]

There's a good example of 2 small drivers with 2 passive radiators in a small cabinet for sale here on Audio Circle in the Trading Circle: Audience Clairaudient 2+2.  Not portable, not cheap, and not as small as you'd like, but it gives you another look at what you're realistically looking at for good quality sound.

You can always shove a pair of car speakers into a box to make noise.

[srb]

Not a recommendation, but an example of a 4" driver with a more efficient and expensive neodymium motor - the Tang Band W4-1879 full-range ($150) can play down to 55Hz with a respectable 87dB sensitivity.

What's the catch (besides the high price)?  It requires a 9 liter vented enclosure to do so.

Steve

[Audio Mark]

I think I will stop on (overnight sensation kit) I will separately buy 2 Hi-Vi B4N + 2 DA ND20FA-6 . Also crossover is already ready, don't need to calculate new one. And Hi-Vi B4N can reach f3 of 80Hz. What do you think?

Or it's will be better to use Visaton W100S-8 (f3 is 90Hz)

[wushuliu]

Markaudio chr70 is what you want.  But for two you will need more than 4 liter. 9 might work. No matter what what you will need more than 4liters. Revise your plan.

https://www.madisoundspeakerstore.com/approx-4-fullrange/markaudio-chr-70-champaigne-cone-4-full-range/

[Audio Mark]

Markaudio chr70 is what you want.  But for two you will need more than 4 liter. 9 might work. No matter what what you will need more than 4liters. Revise your plan.

https://www.madisoundspeakerstore.com/approx-4-fullrange/markaudio-chr-70-champaigne-cone-4-full-range/

After some research I stopped on CHR-70. But will they produce good bass in ~4L box. And in that price category (under 60 Eur) is there any better fullrange speaker with good sensitivity that will produce better bass?

Thank you.

[Audio Mark]

After some research I stopped on CHR-70. But will they produce good bass in ~4L box. And in that price category (under 60 Eur) is there any better fullrange speaker with good sensitivity that will produce better bass?

[wushuliu]

After some research I stopped on CHR-70. But will they produce good bass in ~4L box. And in that price category (under 60 Eur) is there any better fullrange speaker with good sensitivity that will produce better bass?

Thank you.

Oy. The link I provided gives you the info you need to determine if they will work or not. We can not do all the work for you!

If you really want to know more specifics I highly recommend asking at the Full Range thread at diyaudio.com. They have one of the most active diy full range forums around. You will find more detailed recommendations there. Good luck.

http://www.diyaudio.com/forums/full-range/