High efficiency active 2/3 way portable speaker

zaxder

Member
2015-03-12 4:05 pm
First of all, this is my first post, so please be kind to me. Also I’m from Denmark.

For a long time, I have thought about building a high efficiency portable speaker. The plan is to have it powered by a 12 Ah LiFePO4 battery, filtered and EQ by a ADAU 1701 DSP and driven by two small(ish) amps.

The goal is to have decent low end, good coverage + spl. I know this is the holy trio, which really isn’t possible to achieve, but yet here I am.

I’ve ordered the speakers already, but there is room for change. Sadly I learned about the new Faital Pro 12pr320 after I bought the drivers, but luckily they’re kind of similar. The drivers are as follows:

Midbass: RCF MB12N251
Mid: Faital pro 8fe200
Tweeter: B&C DE250
Horn: RCF HF101

The original idea was to do a 2.5 way consisting of 2x midbass crossed at around 1700 Hz to the tweeter, but since then I worried about it being too much to handle for the 12” RCF drivers. So since I got a good deal on the Faitals, I thought about doing a 3 way instead, which I think would blend better with the tweeter and the radiation pattern.

Sound quality is a concern, but I’m in no way an audiophile + the speaker is probably going to be used most often in noisy place and under the influence of beer.

Box will be ported and tuned at 45 Hz, around 70 liters or 120 liter depending on if I'll go with dual RCF midbass or not. According to WinISD that will give me a F3 of around 60 Hz, and with a bit of EQ I can get it down to 45 Hz, while still leaving me with a cone excursion under 5 mm if powered by 50 watt.


I’m sorry for the wall of text, but am I going in a completely wrong way, or does it sound like a decent plan?
I will appreciate any form of feedback.

- Alexander
 
The challenge is to get decent power to your (bass) speakers in a mobile/portable/battery powered setup.
Under powering makes to speaker bigger/ less portable then needed.
What amps are you going to use ?


You have 8ohm drivers (8fe200 might be 4ohm) and if you take a high power amp like the TPA3255 it is only putting out about 120W at 8ohm while you can get 480W at 2 ohm. (in PBTL)

Powering the RCF MB12N251 with 600w @8ohm might be possible (does anyone have a good solution?) but lower impedance drivers (and dual voice-coil; 1 amp/channel for each coil) are much easier to power.
Problem then is to find efficient drivers as there are not many low impedance PA drivers.

But the good and also the bad news is that this driver has only 4.8mm xmax so will reach its max excursion with a lot less power when used as a bass woofer. So it won't need much power as it won't put out much (low) bass. I would change this driver for one with more xmax and lower impedance and get 2 or more of them. (bass drivers) You can always leave half of bass/subwoofers at home if you don't need all the output. If you go with 4 you might also want to get 2 extra 8fe200's. (mids)


Any way I would go with a 2.1 (2 way passive xover tops with low level xover to mono sub/bass woofer(s)) setup as you get +6db (double output) and better SQ if the (sub/bass)woofer is on the floor/ground and separate boxes are easier to transport. A wall doubles the bass output again and a corner results in 8x the bass output. So where do you plan to use it?

A 12 Ah LiFePO4 (low voltage drop) battery is great, what voltage is it?
Keep in mind that even under full load the continues power consumption is only a fraction (less then 1/10th) of the peak power, so your battery will run for a long time. (if you use class D amps)
 

zaxder

Member
2015-03-12 4:05 pm
I see no reason why I would have to power my RCF speaker with 600 watts. I'm on battery so efficiency is a big part of the design, which is why I've chosen these speakers as well.

Bass has changes to putting my driver in a Cubo12 mod, which will make it drop to around 40 Hz with good sensitivity all the way up to 120-130 hz. Using a decent HP will allow it to withstand around 300 watts, although it will never see more than 80 watts max.

Next change of plan is putting the other MB12N251 in a sealed 30 liter enclosure and crossing over at around 120 hz all the way up to 1600 hz, from where to CD takes over.

Battery wise I've upgraded to a 20 Ah 12v LiFePO4 and amp is bassface db 4.3, which will be able to power the bass with around 90 watts and 25 watts to mid and tweeter. That should more than suffice.