My Sub-Low Reflex Project

Furthering my research I decided to give other woofers that are known for their extended low frequency response a try.

I’m using the Beyma as the benchmark for the driver will need to match or exceed its performance in terms of SPL. Once that happens I’ll compare the volume displacement amongst the two. With all the drivers wattage configured to get 1000 watts per driver, efficiency will be the deciding factor.

The Acoupower offers a –3 dB at 23.73 Hertz, which is excellent. Unfortunately, at 1000 watts per driver, it only delivers 126 dB.

Next, is the Ciare 18.00 SW. It offers a – 3 dB at 24.85 Hertz. But, 127 decibels is no better than the Acoupower.

Moving right along is the McCauley 6174. I personally like this driver after hearing how low it can go. It offers a – 3dB at 26.85 Hertz. Still lower than Beyma which is 27.4 Hz. But, it falls short at 130 dB whereas, the Beyma is 132 decibels.





Cone displacement is not even my concern after viewing the outcome. However, if you would like to see the results just look below.







The Beyma is the most efficient.


Edited by Elliot Thompson - 10 September 2008 at 11:05pm

Here is a nice 21-inch woofer shootout.

This test was rather interesting for nearly all of them met or exceeded the Beyma.

I didn’t even bother adding Precision devices for they are not available in the States.

The candidates are:

B&C 21 NW 160
Eighteen Sound 21 LW 1400
Madison Executioner X 21
P Audio SD 21

The B&C was only 1 dB short (131 dB) of matching the Beyma (132 dB). So, it is a good candidate. There is only one problem. The box is too big for this driver to handle, which is clear once it offered – 2 dB from 80 Hertz to 40 Hertz in the Normalised Gain chart.


If I just looked at the Maximum Acoustic Power I would’ve said the Eighteen Sound is the winner offer 133 decibels. However, looking at the Normalised Gain and, seeing –3 dB from 67.8 Hertz to 36.7 Hz, it is obvious this driver is struggling to reach 29 Hertz before collapsing.


The Madison offered 129 decibels and, still requires a bigger box than what I can offer. It offers + 3.5 dB from 39.4 – 38 Hertz. I don’t mind having + 1.2 dB in Normalised Gain. A +3.5 dB gain means the box is going to ring like a bell from 39.4 – 38 Hertz.

The P Audio just fails in this cabinet period. It offers 135 dB from 107 Hertz and up. The – 3dB point is 103 Hertz and continues to decline. Whoever designed this woofer was aiming for horn usage. Possibly a nice HD 21 Kick Bin.






Just a few more woofers to try before investing in some Beyma 21 L50s.


Edited by Elliot Thompson - 11 September 2008 at 12:14am

Elliot Thompson wrote: Here is a nice 21-inch woofer shootout. This test was rather interesting for nearly all of them met or exceeded the Beyma. I didn’t even bother adding Precision devices for they are not available in the States. The candidates are: B&C 21 NW 160 Eighteen Sound 21 LW 1400 Madison Executioner X 21 P Audio SD 21

No precision devices? or turbosound?

Precision Devices and Void is probably the only driver that is scarce in the States.

It didn't fair well in my box either. As you can see, it goes into compression from 34.7 - 55.6 Hertz in the Maximum Acoustic Power chart in addition to declining to - 3dB from 81.3 - 38.7 Hertz in the Normalised Amplitude Response.

I would need to raise the tuning frequency to have a constant 133 dB across the frequency bandwidth, which would beat the Beyma by 1 dB. The only problem is the current tuning leaves the PD 2150 offering a - 3dB at 29.23 Hertz whereas, the Beyma is 27.4 Hz

So this driver won't go low enough for my needs.





As you can see I am very particular when it comes to speaker performance. I’m pretty particular period.

Best Regards,

Volume Displacement Comparison

If you haven’t read Rog’s notes in regards to Volume Displacement hear it is:

Originally Posted By Rog Mogale Vd: Displacement volume. Also something you catch from people with an appetite for drivers over 24”. Vd is Sd x xmax. It’s often overlooked but if moving lots of air at low frequencies is your game then you should know about it. I’ve put the parameter here after Sd and xmax because it ties in with both of these. Basically to make sound you need to move air, and the lower the frequency you are trying to reproduce the more air you will have to move for a given output. You can do this with larger cones, which will give you more Sd, or you can do it with smaller cones that move in and out more (have more xmax). So an 18” driver with an Sd of 1150 sq cm and an xmax of 5 mm can move 5750 cubic centimetres (cc) of air. Think of it like a big scoop that will hold 5750 cc of air and then get some one to throw that air at you very quickly and repeatedly, that’s a speaker. Now take a driver like the Precision Devices PD 1850, it has 11.25 mm of xmax and an Sd of 1150 sq cm. So its Vd would be 12,975 cc. Throwing 12,975 cc of air at someone is going to hurt a lot more than 5750 cc of air. Some of you will have noticed than 12,975 is over double 5750, now can you start to see why I rant on about drivers like the PD 1850. Comparing Vd figures is very useful for working out how much bass a driver can produce and is something most people don’t do.

It seems some brands use a two times method where some do not. Pretty much like the measurement of xmax. Some say plus minus while another will say one way. I’m going to use the two times method to prevent any confusion among the drivers.

Peavey Low Rider 18 = 2375 (4752 for two drivers) cc

Beyma 18 SW 1600ND = 2510 (5020 for two drivers) cc

Beyma 21 L50 = 3200 (6400 for two drivers) cc

Amplifier Tone Burst and Speaker Tolerance

With all old Crown amplifiers, there is a Maximum Power chart located in their instruction booklet. While many feel this graph is useless, I do not. It tells you how much wattage the speaker is getting with high dynamic material. Pulses can destroy a driver just as fast as a long-term continuous signal. The Maximum Power listed on a 4 ohm load is 3220 watts 1 KHz @ 0.05% THD and, 2310 watts 50 Hertz 0.05% THD. I’m going to use 3220 watts for the THD is very low and, at 1% THD it is highly possible 100 – 20 Hz will favour the 1 KHz analysis.

I’ve also added my Double Eighteens to compare. The Lavender line will be the Beyma G 550s I’m currently using and, used as a benchmark when I started the whole project.


I’m using Cone Displacement different than how Eminence Designer/Bass Box Pro suggest. With Cone Displacement, it measures the linear movement and darkens the offending line that exceeds its linearity. What I want to know is how much xmax is used before it approaches its xmech limit.

I will more than likely never feed each driver 1610 watts, but for the idiot who boosts the fader from 6 – full on my mixer, I need to know where the woofers will stand.





As we can see the Peavey has encountered some difficulty, and begins to go into compression dropping 1 dB from 134 – 133 decibels. The xmax is the highest amongst all three offering a peak of 16.6 mm @ 40.1 Hz.

Next, is the Beyma 18 SW 1600ND, which maintains its consistency, delivering 133 decibels from 27.9 – 100 Hz. The xmax peaks at 14.1 mm @ 38 Hz. With a one-way peak of 30 mm there is still ample amount of headroom.

We now look at the Beyma 21 L50. This driver still showing it’s class having no difficulty to handle the power. It delivers 134 decibels from 100 – 27.4 Hz in addition offering the lowest xmax out of the two contenders. The one-way xmech is 17.5 (or 35mm Peak to Peak) mm. Its highest peak receiving 1610 watts (3220 for two woofers) is 11.9 mm @ 41.6 Hertz.

The Beyma 18 SW 1600 ND has more leeway than the 21 L50 however we must take the Volume Displacement into consideration here.


Beyma 18 SW 1600ND = 2510 (5020 for two drivers) cc

Beyma 21 L50 = 3200 (6400 for two drivers) cc


The 21 L50 offers 690 cc over the 18 SW 1600ND. In addition to having the ability to deliver 134 decibels at 27.4 Hz whereas, the 18 SW 1600ND offers 133 decibels @ 27.9 Hertz.

So, the 21 L50 is the best choice for my Sub-Low Reflex cabinet.

I will now move on to the next stage, which will be cabinet construction.


Edited by Elliot Thompson - 12 September 2008 at 1:16pm

rich_gale wrote: if going for 18" id use the mccauley.  being based in the US i think this would be my first choice.  second would be to find that photo of some half completed bassmaxx's and work out the horn path.  drop the mccauleys into the bassmaxx's and enjoy:)

Since I've met David Lee at two Subwoofer Shootouts and have the utmost respect for the man, I wouldn't do that.

The McCauley was already tested in my box and offered too low of an output.

All the drivers I tested (With the exception of Precision Devices) are readily available in the States. So, I not importing nothing.

Best Regards,