Bass Module for SBA-741 - and other small speakers
Copyright 2019 © Troels Gravesen

   Go to on this page:
DRIVER   CABINET    MEASUREMENTS  KIT   GO TO SBA-741 WEBSITE

The bass module here is designed for the SBA-741 speaker, but it suitable for a wide range of "6+1"s, like:


Check intro page for all 6+1s.

Why a woofer and not a subwoofer? A subwoofer is really meant to assist in the 20-40 Hz range, maybe up to 60 Hz, but that's it and what smaller speakers need is really some help in the mid-bass to middle-bass are, 40-160 Hz, where most 6-7" drivers fail to deliver the punch and dynamics needed to assist the illusion of live music. 95-150 cm^2 (5-7" drivers) membrane area simply cannot move enough air.

We can't all have ~150 litre cabinets with 15" bass driver, but we can have some of the goodies from smaller designs by choosing the right drivers. Good bass is about membrane area and efficiency - and an amplifier delivering the necessary amperes. As such, there are no sonic attributes linked to bass, it's all about moving as much air as possible - and moving it fast. And we can have most of it at reasonable price from using PA drivers and plate-amps.

Had a mail recently where the writer had a friend stating PA drivers cannot be used for hifi. Nothing could be further from the truth. I still claim my The Loudspeaker is more hifi than any other speaker I've made, but it takes 300 litres.

Scanning the Faital portfolio for smaller bass drivers my eyes caught this 10" variant and from this  potent 600 watt bass driver and a plate-amp we can make smaller stand-mounts into something better. And if we use a 1st order high-pass filter for the stand-mount as suggested here, even more so.
The 10RS350 features a rubber surround, not that common in PA world, but much like my beloved BMS 12N630.

From 40 litres volume we get -3 dB @ 40 Hz, not bad at all, but given the high power handling of the Faital driver, we can boost the low-end some additional dB to go louder and deeper. We do that in programming the Hypex FA251 plate-amp/DSP. On top of this we place the driver some 8 cm from the floor taking advantage of room-gain. Out on the floor we get +3dB room-gain over a wide frequency range and a theoretical -6dB @ 30 Hz. Not bad for a small speaker with fairly high efficiency.

Example of the simplest set-up: You have a 6+1 and build the bass module. Install the Hypex software B and connect the Hypex input via a wire from the speaker terminals. Find some bass-heavy source material and adjust the bass to suit your taste and room conditions. That's all it takes.

I'm sure I'll have the question whether this or that bass driver can replace the Faital. I cannot tell, so please do not ask.

Basics:
Bass module with 10" bass driver driven by Hypex FA251 plate-amp/DSP.
Dimensions: 34 x 40 x 50 cm, WxDxH.
System sensitivity: NA
Impedance: 8 Ohm.
Point of crossover: Default 80 Hz, 2nd order or your choice.
Power handling: 600 watts. Please also read: http://www.troelsgravesen.dk/power-handling.htm, and remember any burned driver is a misused driver.

Useful links:
http://www.troelsgravesen.dk/tips.htm

DRIVER
BACK TO INDEX    


Click image to view large.

Download specs:  FAITAL 10RS350-8

This phenomenal bass driver is available from LEAN, UK for 95 £, equal to 108 EUR!



HYPEX SOFTWARE

This is not a subwoofer, but a bass driver having Fs = 40 Hz. This may seem a bit high, but capable of handling 600 watts we can make it do the lows with the help of the Hypex DSP programming.
Check this out for installing software on the Hypex module:  http://www.troelsgravesen.dk/Hypex-FUSION_FA252.htm (FA251 works the same way as FA252).
And just to make this clear: You do not need more power than the FA251 can deliver.

Three softwares, A, B and C,  each with three presets have been made and comes on a memory stick with the kit.

Software A: Low-level input via balanced or SE cable from pre-amplifier with and without 1st order high-pass filter before power amplifier. Read here. Adding the 1st order filter to your power amp driving the main speakers, seriously increase power handling.
Software B: High-level input from speakers cables and without 1st order high-pass filter before power amplifier.
Software C: High-level input from speakers cables and with 1st order filter before power amplifier.

Preset 1-2-3 for software A and B
Preset 1: Low-pass LR2 @ 80 Hz, high-pass LR2 @ 20 Hz, total gain 19 dB*.
Preset 2: Low-pass LR2 @ 80 Hz, high-pass LR2 @ 20 Hz, bass boost 4 dB @ 40 Hz, total gain 19 dB.
Preset 3: Low-pass LR2 @ 80 Hz, high-pass LR2 @ 20 Hz, bass boost 8 dB @ 40 Hz, total gain 19 dB.

If you have a vented 6+1 without using the high-pass filter you may stuff the vent with acoustilux to get an earlier roll-off and gain a little extra power handling by limiting the 6" bass driver from excessive excursion, but it doesn't prevent the voice coil from receiving the full low-end signal.

Preset 1-2-3 for software C:
Preset 1: Low-pass LR2 @ 80 Hz, high-pass LR2 @ 20 Hz, shelf + 3dB @ 80 Hz, shelf +6 dB @ 40 Hz, total gain 19 dB.
Preset 2: Low-pass LR2 @ 80 Hz, high-pass LR2 @ 20 Hz, bass boost 4 dB @ 40 Hz, shelf + 3dB @ 80 Hz, shelf +6 dB @ 40 Hz, total gain 19 dB.
Preset 3: Low-pass LR2 @ 80 Hz, high-pass LR2 @ 20 Hz, bass boost 8 dB @ 40 Hz, shelf + 3dB @ 80 Hz, shelf +6 dB @ 40 Hz, total gain 19 dB.

The gain can be adjusted via a potentiometer on the Hypex module. The input signal can be taken from either from a pre-amplifier or directly from speaker wires (high-level input, so no need for interconnects). When I use my EAR-861 power amplifier with 25 dB gain, I set the volume control to ~1200 to match either signal via LCR or high-level input from speaker cables.

The 20 Hz high-pass filter is meant for vinyl addicts and well, it does protect the bass driver some unintentional subsonic signals. I use the high-pass filter all the time.


One important thing when using program B and C with high-level input.
Each preset needs to know the kind of signal, here "Analogue SUB".

*

19 dB gain is basic Hypex gain when all attenuation controls are set to zero. I use this setting with the volume knob on the Hypex in the middle (minor click when it reach the middle). Obviously this can be adjusted to preferred level.



Click images to view large


CABINET
BACK TO INDEX


Cabinets are made from 20 mm Baltic birch and 20 mm HDF. Follow images below. Internal panels were added 4 mm bitumen pads and 8 mm felt. Two pieces of 30 x 50 cm acoustilux is placed at bass cabinet top. See images below.
Make holes in the two bracings as shown on images below, evenly distributed over the surface of the brace. Six in the horizontal brace and two in the vertical brace. Adjust diameter to you actual conditions.

I used 75 mm (71 mm ID) PVC pipe for the vents. In the kit below Ø7 cm ports are listed. Read about ports here.

You can obviously use this bass module principle for a wide range of smaller speakers and do not have to make a pyramid like this one specifically  made for SBA-741, but adjust the cabinet for whatever you may have on top. Any 38-42 litre cabinet made with the bass driver mounted as shown is suitable. You should not place the bass driver on the front or sides as you will loose room-gain and overall efficiency.

Please check all items here before writing: http://www.troelsgravesen.dk/tips.htm 


Workshop images

 


Gluing the bass cabinets.


Add upper bracing and bitumen pads.


Add felt before the middle brace in glued in place.


Preparing the Hypex compartment and fillets for bass panel.


Bass panel ready and to the right routed for bass driver, here the Faital 10RS350.
Add 2 pcs 25 x 50 cm acoustilux to top of bass cabinet.


Faital driver in place. Adjust feet to make the some 3-4 cm from cabinet to floor.
I made two 20 mm holes for ventilation of the Hypex cavity. The holes towards the front are for screws holding the bass panel.

 


MEASUREMENTS
BACK TO INDEX


Bass module ready for near-field measurements. Mic ~1 mm from cone.

Software A and B


Nearfield response of bass driver. Program A, LR2 @ 80 Hz. Preset 1, 2 and 3 (red/green/orange)
Nearfield response of ports, preset 1, 2 and 3 (blue/yellow/purple)
Level from ports corrected for relative area to bass driver.


Same as above but summed response from preset 1, 2 and 3. Red, green and orange respectively.


Software C


Above a presentation of how this works. The signal to the power amplifier is cut -3 dB @ 80 Hz, thus -6 dB @ 40 Hz, etc.
This signal profile is reversed in the Hypex programming to produce a flat signal before the bass low-pass section is added.


Nearfield response from 10RS350 and ports when using program C.


Summed response of driver and ports corrected for port dimensions relative to bass driver.

 


The volume knob on the FA251.


High-level input. No need for interconnects from pre-amplifier.



KIT only available with Hypex module
BACK TO INDEX

All kit and component prices may be subject to change and are always to be confirmed by Jantzen Audio Denmark.
You can buy the kit with or without the ports if you want to use standard 75 mm PVC ports.
You cannot buy the kit without the Hypex and software.
 

Download Complete Kit Sale Presentations (pdf file):

All technical questions to troels.gravesen@hotmail.com

All questions regarding purchase of kits, please mail Jantzen Audio at contact@jantzen-audio.com