DIY 2 Way With 4" Woofer Needed

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Kotter67

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Joined 2021
#1
I recently picked up these powered BT speakers from Amazon, model R28BTUS. They sport a 1” tweeter and 4” woofer. Didn’t need them, but for $25 what was I to do? Crossover is a 2.2uF cap on the tweeter. Drivers wired in series. They aren’t too bad with the ports stuffed, but they very likely can be improved.

The Overnight Sensations using the HIVI T20-8 and B4N design appears to be a very good fit to the unit’s .18cf (5.2L) cabinet. The OD of the B4N frame is .1” larger than the existing, might be able to sand out the difference. The hole for the tweeter will need a bit of enlargement, but that should be easy. Even the odd port looks pretty close to what is needed. Driver costs would be $23 per side, about as low as can be expected. I have good stash of crossover components, so I’m not that concerned about crossover cost.

Are there any other 2 way designs out there that use similarly sized (or somewhat smaller) drivers in about a 5L box that I should look at? Is there a full range driver that might fit with no modifications? The drivers can’t be surface mounted, the grill is flush to the front baffle and there would be no room.
 

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#2
The Sopranos is an open design from Jeff Bagby – uses the 4" SB Acoustics SB12NRX and the SB26STCN-04 which is a small flange 1” dome tweeter with coated textile dome, short waveguide, damped chamber, and a neo magnet. It turns out to be a very nice tweeter for the money. It works very well for systems with small baffles, tight driver spacing, and even low crossover points.

The cabinet measures 6.5” wide by 10.5” tall by 8” deep. It is made of ¾” MDF with an internal brace. The final volume is 4.7 liters or .17 cubic feet. Both drivers are centered horizontally on the baffle with a space of 3.8” between them.


Meniscus has info and parts.
 
#5
I'd try a better crossover first. This sort of thing works with 4 ohm bass and 6 ohm tweeter:

532776d1456062082-classic-monitor-designs-visaton-hw2-70-crossover-png


Order some pairs of 3-5W resistors too. About 2.2R and 3.9R to put in front of tweeter filter for level adjustment.

Measure your drivers;

591815d1484284062-visaton-alto-iii-morel-cat298-jpg


An 8 ohm bass (6 ohm dcr) might prefer 1.8mH and 6.8uF.

Couple that might fit. The second is a millimeter over.

MONACOR: SPM-116/8
Dayton Audio TCP115-8 4" Treated Paper Cone Midbass Woofer 8 Ohm
 
#7
@TubaV.

I have little idea, TBH. 😀

Your midbass has significant inductance and a serious looking peak around 5kHz. This rules out the old SB Eka crossover.

Eka - Sbacoustics

Whether the peak needs attention remains to be seen.

You might email Mike Chua for some of his Lark circuits:

Lark-XT (SB16PFC25-08 with Peerless XT25TG30-04) – AmpsLab

AmpsLab Speaker Projects

Although for the 8 ohm driver of this type, it might answer these questions.

Lojzek did a nice project with a 4 ohm bass:

Visaton-Monacor 2 way sealed simple loudspeaker build plans

No idea what you might run into with a fullranger as tweeter, but it's not a bad idea that I am trying myself.
 
#9
The W4-1052 should work and I have a pair of ND20TA-6 in the Amethyst which I could use in lieu of the FA. So far, the options are the Overnight Sensations ($50 driver cost with the HiVi tweeter) and the Amethyst ($100 driver cost- assuming use of TA driver).
 
#10
system7 said:
I'd try a better crossover first. This sort of thing works with 4 ohm bass and 6 ohm tweeter:



Order some pairs of 3-5W resistors too. About 2.2R and 3.9R to put in front of tweeter filter for level adjustment.

Measure your drivers;



An 8 ohm bass (6 ohm dcr) might prefer 1.8mH and 6.8uF.

Couple that might fit. The second is a millimeter over.

MONACOR: SPM-116/8
Dayton Audio TCP115-8 4" Treated Paper Cone Midbass Woofer 8 Ohm
Click to expand...

Sure, I could try this as an option. I am going to make a faceplate to fit the ND20TA-6 instead of this tweeter, which I am going to assume is the weak point of the existing arrangement. So that would leave a 4 ohm woofer and 6 ohm tweeter as the installed drivers. I do have a concern about the crossover posted, it says 3,000 Hz as the crossover point, but wouldn't this be too low for either the existing tweeter (which currently has a 2.2uF cap on it) or the ND20TA-6?
 
#12
The "Sopranos" have proven excellent sound quality.

Outer Diameter:
W4-1052 = 116mm under your consideration
SB12NRX = 123mm in Sopranos

The SB26STCN-04 tweeter has a small NdFeB motor which allows a modest 72mm diameter faceplate, which you can cut down to as small as a 50mm diameter faceplate.
 
#15
planet10 said:
How is that wired? It makes little sense.

Not a big 2-way guy, but that box size works for FF105wk and Alpair 6.2p full ranges

dave

dave
Click to expand...

I was wrong, the way it is wired threw me off, never seen it done like that. positive wire goes from amp to (+) woofer to 2.2uF to (+) tweeter. negative from amp is same, goes to (-) woofer then to (-) tweeter.

These full ranges should work.
 
#16
Boden said:
I would suggest to start measuring the current drivers first of all, and work from there. Get ARTA, REW, HOLM or whatever freeware and learn to measure the raw drivers in box.
Click to expand...

My initial intention was to drop in a proven design. But maybe I'll upgrade the tweeter to the ND20TA-6 which I already have on hand, make use of the existing 4" and either use a canned crossover crossed at 4000 Hz or develop the zma and frd files for a more customized crossover. I have the necessary tools, its just a matter of learning how to get good data and then coming up with a crossover that will work.
 
#17
LineSource said:
The "Sopranos" have proven excellent sound quality.

Outer Diameter:
W4-1052 = 116mm under your consideration
SB12NRX = 123mm in Sopranos

The SB26STCN-04 tweeter has a small NdFeB motor which allows a modest 72mm diameter faceplate, which you can cut down to as small as a 50mm diameter faceplate.
Click to expand...

The volume works, but the drivers are too large. The wide flange thickness on the SB unit also might not work due to the grille being solid particle board with cutouts for the drivers (like the old Smaller Advent) and sitting flush with the baffle. This particular model is not very forgiving as to modification to make things work.
 
#18
I still think a better crossover would help your cause here. A 4" 4 ohm midbass plus a balanced drive poly tweeter is hardly difficult. D

But have no idea if the built in amp is applying bafflestep bass boost.

Balanced drive tweeters work better than most on a single 2-3uF capacitor. Attenuation might be required, of course:

Audax TW010E1 10mm Polymer Tweeter Review – AmpsLab

I would be modelling it with similar flattish drivers, I take it you have established 4 ohm midbass and 8 ohm tweeter:

Software | Visaton

DTW 72 - 8 Ohm | Visaton

FRS 8 - 4 Ohm | Visaton

But Planet10 (Dave) has made an excellent suggestion with the Markaudio Alpair 6M, the current model AFAIK:

Markaudio Alpair-6M Gold 3.5" Fullrange Gen 2

Everything fits and enclosure works. I would have no trouble turning that into a two way using the existing tweeter, just for fun. 🙂
 
#19
Since you have the tools and are already aware of the existence of .frd and .zma files, why not get your feet wet? There is nothing to lose. This is DIY after all. For just a few bucks in x/o components and some time for designing the x/o, you might be able achieve major improvements.
 
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