18rbx100 review

[neil Fernandes]

first thread on the forum.

i neep help in choosing the right drivers for my subwoofer project. earlier i was almost set on 4 x 18tbx100 but i found a good deal on 18rbx100 (i think they have 4 new but opened/returned) and i can get about 6-7 for the price of 4 tbx. i don't need 6-7 but it saves me money and 4 tbx was really a stretched budget.

I'm mostly a weekend warrior and have been using 12"/15" tops for most of my events for upto 100 people. for bigger gigs i usually rent. but i feel that its time to add dedicated lows to my inventory.

I'm looking at single 18's from 30ish to 100.

what do you experts suggest, should i go ahead with rbx or buy once,cry once with tbx?

also while I'm at it, i was thinking about making 2 different boxes. 1) 4 single 18 - to be used at most of my smaller gigs 2) 4 of Art's Keystone for my bigger events and swap drivers depending on the need.

 

[Bennett Prescott]

Re: 18rbx100 review

Hi Neil,

The 18TBX100 is one of our best-selling subwoofers, and well proven having been on the market for the better part of two decades in one incarnation or another. It has a strong motor and a nice stiff suspension that can take a lot of abuse. The 18RBX100 has a similar goal, but takes advantage of all we've learned in the intervening years about longer throw suspensions and making a better loudspeaker while optimizing for cost. Its magnetic circuit is nearly as strong but considerably smaller (and therefore less expensive) thanks to modern computer modeling. It's designed to perform well in a compact cabinet and emphasizes excursion over power handling, we find Xvar to be the limiting factor in most designs today.

In short, I think the 18RBX100 could be an excellent match for your single 18" application. If you need more performance I doubt the 18TBX100 will be a big step up, probably you'd want to consider the 18TBW100 or 18SW100.

 

[neil Fernandes]

Re: 18rbx100 review

Thanks Bennett. Looks like I have just placed an order for 4 18rbx100.

The website recommends a 4.94 cubic feet box with 40hz recommended tuning. Is it possible to tune lower and make the box slightly bigger without loosing much output?

I really don't know what's the best for me, to opt for a box tuned lower or go for the output. I know I have the option to make 2 demo boxes and see what I like but any help here will be greatly appreciated.

I prefer the box to be a low profile therefore I'm planning to go with 4 triangular corner ports, instead of one port at the bottom. But that is secondary.
Also if anyone has a plan in hand or a link, please post it here.

Lastly, will this driver work in Art's Keystone. Again a keystone is not a priority now and will be a few months before I actually go ahead with this.

 

[neil Fernandes]

Re: 18rbx100 review

ok, my first attempt with Winisd. not sure if the below data is correct and also not sure if this is the right way to do it.

first, i entered driver parameters and then i simply entered the volume and port tuning frequency. so this is what i got -

[TABLE="width: 503"]
[TR]
[TD]Volume[/TD]
[TD="align: right"]4.9c[/TD]
[TD][/TD]
[TD="colspan: 3"] 6cuft[/TD]
[TD][/TD]
[TD="colspan: 3"] 7cuft[/TD]
[TD][/TD]
[TD="colspan: 3"] 8cuft[/TD]
[/TR]
[TR]
[TD]Tuning[/TD]
[TD] 40[/TD]
[TD][/TD]
[TD] 35[/TD]
[TD] 37[/TD]
[TD] 40[/TD]
[TD][/TD]
[TD] 35[/TD]
[TD] 37[/TD]
[TD] 40[/TD]
[TD][/TD]
[TD] 35[/TD]
[TD] 37[/TD]
[TD] 40[/TD]
[/TR]
[TR]
[TD]30Hz[/TD]
[TD="align: right"]-11[/TD]
[TD][/TD]
[TD="align: right"]-7.7[/TD]
[TD="align: right"]-8.6[/TD]
[TD="align: right"]-10[/TD]
[TD][/TD]
[TD="align: right"]-6.9[/TD]
[TD="align: right"]-8.0[/TD]
[TD="align: right"]-10[/TD]
[TD][/TD]
[TD="align: right"]-6.3[/TD]
[TD="align: right"]-7.6[/TD]
[TD="align: right"]-9.7[/TD]
[/TR]
[TR]
[TD]35Hz[/TD]
[TD="align: right"]-6.5[/TD]
[TD][/TD]
[TD="align: right"]-4.3[/TD]
[TD="align: right"]-4.5[/TD]
[TD="align: right"]-5.5[/TD]
[TD][/TD]
[TD="align: right"]-3.2[/TD]
[TD="align: right"]-3.5[/TD]
[TD="align: right"]-4.7[/TD]
[TD][/TD]
[TD="align: right"]-2.4[/TD]
[TD="align: right"]-2.7[/TD]
[TD="align: right"]-4.1[/TD]
[/TR]
[TR]
[TD]40Hz[/TD]
[TD="align: right"]-3.5[/TD]
[TD][/TD]
[TD="align: right"]-2.8[/TD]
[TD="align: right"]-2.4[/TD]
[TD="align: right"]-2.3[/TD]
[TD][/TD]
[TD="align: right"]-2.0[/TD]
[TD="align: right"]-1.4[/TD]
[TD="align: right"]-1.2[/TD]
[TD][/TD]
[TD="align: right"]-1.1[/TD]
[TD="align: right"]-0.7[/TD]
[TD="align: right"]-0.4[/TD]
[/TR]
[TR]
[TD]45Hz[/TD]
[TD="align: right"]-1.9[/TD]
[TD][/TD]
[TD="align: right"]-2.2[/TD]
[TD="align: right"]-1.6[/TD]
[TD="align: right"]-0.8[/TD]
[TD][/TD]
[TD="align: right"]-1.6[/TD]
[TD="align: right"]-1.0[/TD]
[TD="align: right"]0[/TD]
[TD][/TD]
[TD="align: right"]-1.2[/TD]
[TD="align: right"]-0.5[/TD]
[TD="align: right"]0.6[/TD]
[/TR]
[TR]
[TD]50Hz[/TD]
[TD="align: right"]-1.1[/TD]
[TD][/TD]
[TD="align: right"]-1.8[/TD]
[TD="align: right"]-1.3[/TD]
[TD="align: right"]-0.4[/TD]
[TD][/TD]
[TD="align: right"]-1.5[/TD]
[TD="align: right"]-0.9[/TD]
[TD="align: right"]0.1[/TD]
[TD][/TD]
[TD="align: right"]-1.3[/TD]
[TD="align: right"]-0.6[/TD]
[TD="align: right"]0.5[/TD]
[/TR]
[TR]
[TD]60Hz[/TD]
[TD="align: right"]-0.5[/TD]
[TD][/TD]
[TD="align: right"]-1.4[/TD]
[TD="align: right"]-0.9[/TD]
[TD="align: right"]-0.2[/TD]
[TD][/TD]
[TD="align: right"]-1.3[/TD]
[TD="align: right"]-0.8[/TD]
[TD="align: right"]0[/TD]
[TD][/TD]
[TD="align: right"]-1.2[/TD]
[TD="align: right"]-0.8[/TD]
[TD="align: right"]0[/TD]
[/TR]
[TR]
[TD]70Hz[/TD]
[TD="align: right"]-0.2[/TD]
[TD][/TD]
[TD="align: right"]-1.0[/TD]
[TD="align: right"]-0.7[/TD]
[TD="align: right"]-0.1[/TD]
[TD][/TD]
[TD="align: right"]-1.0[/TD]
[TD="align: right"]-0.7[/TD]
[TD="align: right"]-0.1[/TD]
[TD][/TD]
[TD="align: right"]-1.0[/TD]
[TD="align: right"]-0.7[/TD]
[TD="align: right"]-0.1[/TD]
[/TR]
[TR]
[TD]80Hz[/TD]
[TD="align: right"]0.6[/TD]
[TD][/TD]
[TD="align: right"]-0.6[/TD]
[TD="align: right"]-0.4[/TD]
[TD="align: right"]0[/TD]
[TD][/TD]
[TD="align: right"]-0.7[/TD]
[TD="align: right"]-0.4[/TD]
[TD="align: right"]-0.1[/TD]
[TD][/TD]
[TD="align: right"]-0.7[/TD]
[TD="align: right"]-0.5[/TD]
[TD="align: right"]-0.1[/TD]
[/TR]
[TR]
[TD]90Hz[/TD]
[TD="align: right"]0.3[/TD]
[TD][/TD]
[TD="align: right"]-0.3[/TD]
[TD="align: right"]-0.1[/TD]
[TD="align: right"]0.1[/TD]
[TD][/TD]
[TD="align: right"]-0.4[/TD]
[TD="align: right"]-0.2[/TD]
[TD="align: right"]0[/TD]
[TD][/TD]
[TD="align: right"]-0.5[/TD]
[TD="align: right"]-0.2[/TD]
[TD="align: right"]0[/TD]
[/TR]
[TR]
[TD]100Hz[/TD]
[TD="align: right"]0.4[/TD]
[TD][/TD]
[TD="align: right"]0[/TD]
[TD="align: right"]0[/TD]
[TD="align: right"]0.3[/TD]
[TD][/TD]
[TD="align: right"]-0.1[/TD]
[TD="align: right"]0[/TD]
[TD="align: right"]0.2[/TD]
[TD][/TD]
[TD="align: right"]-0.2[/TD]
[TD="align: right"]-0.1[/TD]
[TD="align: right"]-0.1[/TD]
[/TR]
[/TABLE]
i have not added any filters at the moment cos im still figuring out. But, is this a good start?

 

[Peter Morris]

Re: 18rbx100 review

ok, my first attempt with Winisd. not sure if the below data is correct and also not sure if this is the right way to do it.

first, i entered driver parameters and then i simply entered the volume and port tuning frequency. so this is what i got -

[TABLE="width: 503"]
[TR]
[TD]Volume
[/TD]
[TD="align: right"]4.9c
[/TD]
[TD][/TD]
[TD="colspan: 3"] 6cuft
[/TD]
[TD][/TD]
[TD="colspan: 3"] 7cuft
[/TD]
[TD][/TD]
[TD="colspan: 3"] 8cuft
[/TD]
[/TR]
[TR]
[TD]Tuning
[/TD]
[TD] 40
[/TD]
[TD][/TD]
[TD] 35
[/TD]
[TD] 37
[/TD]
[TD] 40
[/TD]
[TD][/TD]
[TD] 35
[/TD]
[TD] 37
[/TD]
[TD] 40
[/TD]
[TD][/TD]
[TD] 35
[/TD]
[TD] 37
[/TD]
[TD] 40
[/TD]
[/TR]
[TR]
[TD]30Hz
[/TD]
[TD="align: right"]-11
[/TD]
[TD][/TD]
[TD="align: right"]-7.7
[/TD]
[TD="align: right"]-8.6
[/TD]
[TD="align: right"]-10
[/TD]
[TD][/TD]
[TD="align: right"]-6.9
[/TD]
[TD="align: right"]-8.0
[/TD]
[TD="align: right"]-10
[/TD]
[TD][/TD]
[TD="align: right"]-6.3
[/TD]
[TD="align: right"]-7.6
[/TD]
[TD="align: right"]-9.7
[/TD]
[/TR]
[TR]
[TD]35Hz
[/TD]
[TD="align: right"]-6.5
[/TD]
[TD][/TD]
[TD="align: right"]-4.3
[/TD]
[TD="align: right"]-4.5
[/TD]
[TD="align: right"]-5.5
[/TD]
[TD][/TD]
[TD="align: right"]-3.2
[/TD]
[TD="align: right"]-3.5
[/TD]
[TD="align: right"]-4.7
[/TD]
[TD][/TD]
[TD="align: right"]-2.4
[/TD]
[TD="align: right"]-2.7
[/TD]
[TD="align: right"]-4.1
[/TD]
[/TR]
[TR]
[TD]40Hz
[/TD]
[TD="align: right"]-3.5
[/TD]
[TD][/TD]
[TD="align: right"]-2.8
[/TD]
[TD="align: right"]-2.4
[/TD]
[TD="align: right"]-2.3
[/TD]
[TD][/TD]
[TD="align: right"]-2.0
[/TD]
[TD="align: right"]-1.4
[/TD]
[TD="align: right"]-1.2
[/TD]
[TD][/TD]
[TD="align: right"]-1.1
[/TD]
[TD="align: right"]-0.7
[/TD]
[TD="align: right"]-0.4
[/TD]
[/TR]
[TR]
[TD]45Hz
[/TD]
[TD="align: right"]-1.9
[/TD]
[TD][/TD]
[TD="align: right"]-2.2
[/TD]
[TD="align: right"]-1.6
[/TD]
[TD="align: right"]-0.8
[/TD]
[TD][/TD]
[TD="align: right"]-1.6
[/TD]
[TD="align: right"]-1.0
[/TD]
[TD="align: right"][/TD]
[TD][/TD]
[TD="align: right"]-1.2
[/TD]
[TD="align: right"]-0.5
[/TD]
[TD="align: right"]0.6
[/TD]
[/TR]
[TR]
[TD]50Hz
[/TD]
[TD="align: right"]-1.1
[/TD]
[TD][/TD]
[TD="align: right"]-1.8
[/TD]
[TD="align: right"]-1.3
[/TD]
[TD="align: right"]-0.4
[/TD]
[TD][/TD]
[TD="align: right"]-1.5
[/TD]
[TD="align: right"]-0.9
[/TD]
[TD="align: right"]0.1
[/TD]
[TD][/TD]
[TD="align: right"]-1.3
[/TD]
[TD="align: right"]-0.6
[/TD]
[TD="align: right"]0.5
[/TD]
[/TR]
[TR]
[TD]60Hz
[/TD]
[TD="align: right"]-0.5
[/TD]
[TD][/TD]
[TD="align: right"]-1.4
[/TD]
[TD="align: right"]-0.9
[/TD]
[TD="align: right"]-0.2
[/TD]
[TD][/TD]
[TD="align: right"]-1.3
[/TD]
[TD="align: right"]-0.8
[/TD]
[TD="align: right"][/TD]
[TD][/TD]
[TD="align: right"]-1.2
[/TD]
[TD="align: right"]-0.8
[/TD]
[TD="align: right"][/TD]
[/TR]
[TR]
[TD]70Hz
[/TD]
[TD="align: right"]-0.2
[/TD]
[TD][/TD]
[TD="align: right"]-1.0
[/TD]
[TD="align: right"]-0.7
[/TD]
[TD="align: right"]-0.1
[/TD]
[TD][/TD]
[TD="align: right"]-1.0
[/TD]
[TD="align: right"]-0.7
[/TD]
[TD="align: right"]-0.1
[/TD]
[TD][/TD]
[TD="align: right"]-1.0
[/TD]
[TD="align: right"]-0.7
[/TD]
[TD="align: right"]-0.1
[/TD]
[/TR]
[TR]
[TD]80Hz
[/TD]
[TD="align: right"]0.6
[/TD]
[TD][/TD]
[TD="align: right"]-0.6
[/TD]
[TD="align: right"]-0.4
[/TD]
[TD="align: right"][/TD]
[TD][/TD]
[TD="align: right"]-0.7
[/TD]
[TD="align: right"]-0.4
[/TD]
[TD="align: right"]-0.1
[/TD]
[TD][/TD]
[TD="align: right"]-0.7
[/TD]
[TD="align: right"]-0.5
[/TD]
[TD="align: right"]-0.1
[/TD]
[/TR]
[TR]
[TD]90Hz
[/TD]
[TD="align: right"]0.3
[/TD]
[TD][/TD]
[TD="align: right"]-0.3
[/TD]
[TD="align: right"]-0.1
[/TD]
[TD="align: right"]0.1
[/TD]
[TD][/TD]
[TD="align: right"]-0.4
[/TD]
[TD="align: right"]-0.2
[/TD]
[TD="align: right"][/TD]
[TD][/TD]
[TD="align: right"]-0.5
[/TD]
[TD="align: right"]-0.2
[/TD]
[TD="align: right"][/TD]
[/TR]
[TR]
[TD]100Hz
[/TD]
[TD="align: right"]0.4
[/TD]
[TD][/TD]
[TD="align: right"][/TD]
[TD="align: right"][/TD]
[TD="align: right"]0.3
[/TD]
[TD][/TD]
[TD="align: right"]-0.1
[/TD]
[TD="align: right"][/TD]
[TD="align: right"]0.2
[/TD]
[TD][/TD]
[TD="align: right"]-0.2
[/TD]
[TD="align: right"]-0.1
[/TD]
[TD="align: right"]-0.1
[/TD]
[/TR]
[/TABLE]
i have not added any filters at the moment cos im still figuring out. But, is this a good start?

You also have to look at cone excursion - B&C's recommended box allows 2000W without any Xmax issues above 30Hz.

You can use a bigger box and tune it lower but that will do 2 things - reduce efficiency and power handling. With an 8 cu ft box tuned at 35Hz you will hit Xmax at 1350 watts instead of 2000 watts i.e. you will have about 2dB less output above 50Hz than the recommended box. You just have to pick the compromise that suits your needs

 

[neil Fernandes]

Re: 18rbx100 review

thanks peter, i think i understood what you said and this is what i got -

[TABLE="width: 832"]
[TR]
[TD="class: xl66, width: 64"]Vol[/TD]
[TD="class: xl66, width: 64"]Tun[/TD]
[TD="class: xl66, width: 64"]power[/TD]
[TD="class: xl66, width: 64"]30[/TD]
[TD="class: xl66, width: 64"]35[/TD]
[TD="class: xl66, width: 64"]40[/TD]
[TD="class: xl66, width: 64"]45[/TD]
[TD="class: xl66, width: 64"]50[/TD]
[TD="class: xl66, width: 64"]60[/TD]
[TD="class: xl66, width: 64"]70[/TD]
[TD="class: xl66, width: 64"]80[/TD]
[TD="class: xl66, width: 64"]90[/TD]
[TD="class: xl66, width: 64"]100[/TD]
[/TR]
[TR]
[TD="class: xl65"]8[/TD]
[TD="class: xl65"]35[/TD]
[TD="class: xl65"]800W[/TD]
[TD="class: xl65"]119[/TD]
[TD="class: xl65"]122.7[/TD]
[TD="class: xl65"]123.9[/TD]
[TD="class: xl65"]123.9[/TD]
[TD="class: xl65"]123.9[/TD]
[TD="class: xl65"]123.9[/TD]
[TD="class: xl65"]124.2[/TD]
[TD="class: xl65"]124.5[/TD]
[TD="class: xl65"]124.7[/TD]
[TD="class: xl65"]125[/TD]
[/TR]
[TR]
[TD="class: xl65"]4.944[/TD]
[TD="class: xl65"]40[/TD]
[TD="class: xl65"]1000W[/TD]
[TD="class: xl65"]115.2[/TD]
[TD="class: xl65"]119.6[/TD]
[TD="class: xl65"]122.6[/TD]
[TD="class: xl65"]124.2[/TD]
[TD="class: xl65"]125[/TD]
[TD="class: xl65"]125.7[/TD]
[TD="class: xl65"]126[/TD]
[TD="class: xl65"]126.2[/TD]
[TD="class: xl65"]126.4[/TD]
[TD="class: xl65"]126.6[/TD]
[/TR]
[/TABLE]

on 8cuft i got max excursion of 9.950mm at 48.57hz and
on 4.9 i got max excursion of 9.23mm at 58.44hz

so if i do plan to go with 8cuft, is an excursion of 9.950mm (just 0.05mm from limit) going to cause problems?

 

[Peter Morris]

Re: 18rbx100 review

thanks peter, i think i understood what you said and this is what i got -

[TABLE="width: 832"]
[TR]
[TD="class: xl66, width: 64"]Vol
[/TD]
[TD="class: xl66, width: 64"]Tun
[/TD]
[TD="class: xl66, width: 64"]power
[/TD]
[TD="class: xl66, width: 64"]30
[/TD]
[TD="class: xl66, width: 64"]35
[/TD]
[TD="class: xl66, width: 64"]40
[/TD]
[TD="class: xl66, width: 64"]45
[/TD]
[TD="class: xl66, width: 64"]50
[/TD]
[TD="class: xl66, width: 64"]60
[/TD]
[TD="class: xl66, width: 64"]70
[/TD]
[TD="class: xl66, width: 64"]80
[/TD]
[TD="class: xl66, width: 64"]90
[/TD]
[TD="class: xl66, width: 64"]100
[/TD]
[/TR]
[TR]
[TD="class: xl65"]8
[/TD]
[TD="class: xl65"]35
[/TD]
[TD="class: xl65"]800W
[/TD]
[TD="class: xl65"]119
[/TD]
[TD="class: xl65"]122.7
[/TD]
[TD="class: xl65"]123.9
[/TD]
[TD="class: xl65"]123.9
[/TD]
[TD="class: xl65"]123.9
[/TD]
[TD="class: xl65"]123.9
[/TD]
[TD="class: xl65"]124.2
[/TD]
[TD="class: xl65"]124.5
[/TD]
[TD="class: xl65"]124.7
[/TD]
[TD="class: xl65"]125
[/TD]
[/TR]
[TR]
[TD="class: xl65"]4.944
[/TD]
[TD="class: xl65"]40
[/TD]
[TD="class: xl65"]1000W
[/TD]
[TD="class: xl65"]115.2
[/TD]
[TD="class: xl65"]119.6
[/TD]
[TD="class: xl65"]122.6
[/TD]
[TD="class: xl65"]124.2
[/TD]
[TD="class: xl65"]125
[/TD]
[TD="class: xl65"]125.7
[/TD]
[TD="class: xl65"]126
[/TD]
[TD="class: xl65"]126.2
[/TD]
[TD="class: xl65"]126.4
[/TD]
[TD="class: xl65"]126.6
[/TD]
[/TR]
[/TABLE]

on 8cuft i got max excursion of 9.950mm at 48.57hz and
on 4.9 i got max excursion of 9.23mm at 58.44hz

so if i do plan to go with 8cuft, is an excursion of 9.950mm (just 0.05mm from limit) going to cause problems?

No that will not be a problem, this 18 is good for 13mm (Xvar) before it becomes an issue. Most of the low frequency energy you need will be around 60Hz-80Hz out of your sub. Often people look to go down lower than they really need so its really a matter of deciding weather you need more output between 60Hz- 80Hz or more LF extension.

The thing you don't want is to select an alignment that will sound boom-y or slow (like car audio where SPL is every thing). These types of alignment will have a rise in the output at the lowest frequencies.

http://www.bcspeakers.com/resources/faq-frequently-asked-questions/

 

[Art Welter]

Re: 18rbx100 review

thanks peter, i think i understood what you said and this is what i got -


on 8cuft i got max excursion of 9.950mm at 48.57hz and
on 4.9 i got max excursion of 9.23mm at 58.44hz

so if i do plan to go with 8cuft, is an excursion of 9.950mm (just 0.05mm from limit) going to cause problems?

Neil,

The "problem" with exceeding Xmax (maximum linear excursion) or Xvar is the non-linear behavior of the driver when pushed beyond, it simply distorts badly, and odd- order distortion starts to rear it's non-musical head. Xlim (or Xmech) is the mechanical limit where if driven harder, the driver parts may break- either the voice coil hammers on the back plate (clackety clack, crunch), the surround or spider(s) rips, or the cone buckles or rips. In the usual smallish BR box, the driver voice coil will usually burn up first, larger BR boxes may experience Xlim problems before Pmax (power thermal burnout) occurs.

If you start looking at the excursion curve, you will notice that minimum excursion is at Fb, and maximum excursion for a BR cabinet is about 1/3 octave above that, and below Fb, excursion increases rapidly- below Fb the speaker will "flap", with the (usual) 24 dB per octave drop in output below FB you should protect it with a steep HP a few Hz below Fb.

The 18RBX100 will work in the Keystone design, but the 6 dB (or so) gain it provides comes with increased pressure loading. Although the SPL will be greater per a given excursion, distortion also will be higher for a given excursion. My concern is the lighter, curvilinear cone of the 18rbx100 compared to the heavier, stiffer conical cones of the 18TBX100 or 18SW115 may result in greater distortion and possible buckling if driven to (or past) Xvar (which is 13mm). BL (magnetic strength) is also less, so may be somewhat self limiting, it probably will burn up if pushed too hard in the Keystone. The single Keystone is 13.24 cubic feet net, but probably would be very close in output to a pair of the BR in a similar net volume using twice the power.

The TBX100 has an Xlim of 28.5mm (57 peak to peak), the 18SW115 30mm (60mm p to p), but the 18RBX100 does not list an Xlim, though if consistent with the others should be at least 20mm, perhaps Bennett could confirm that figure.

Art

 

[neil Fernandes]

Re: 18rbx100 review

Thankyou Peter and Art.

i have finally made up my mind and going with tuning and box size as suggested by B&C.

also going with 4 corner ports 12 X 12 X 16.7 cm and 22cm long, do you guys think this is ok? or should i go with a single rectangular port at the bottom. (i only have theoretical knowledge about ports and need a suggestion from someone with practical knowledge).

Also a question about paint - what to use when there is no duratex, warnex, lineX or any other brand of speaker paint or bedliner paint available?

 

[Art Welter]

Re: 18rbx100 review

Thankyou Peter and Art.

i have finally made up my mind and going with tuning and box size as suggested by B&C.

also going with 4 corner ports 12 X 12 X 16.7 cm and 22cm long, do you guys think this is ok? or should i go with a single rectangular port at the bottom. (i only have theoretical knowledge about ports and need a suggestion from someone with practical knowledge).

Also a question about paint - what to use when there is no duratex, warnex, lineX or any other brand of speaker paint or bedliner paint available?

I prefer triangular corner ports as they brace the cabinet well. The port volume sounds a bit on the small side, I found a fair amount of port compression using about 325 square cm with the BC18SW115, which only has a bit more excursion than the 18RBX100. The corner ports will tune a bit lower than a simulation with a round port would suggest.

Before using Duratex I had decent results mixing exterior latex house paint with about 25% or 33% latex floor varnish. The floor varnish reduced the tendency for the latex paint to stick between cabinets when they sat in the hot sun, and they did not scuff as badly. Also found that "lamp black" only as the coloring agent (for black) was the way to go, many of the designer black colors seem to have have some blue tint in, which does not match real black.

 

[Uwe Riemer]

Re: 18rbx100 review

Thankyou Peter and Art.

i have finally made up my mind and going with tuning and box size as suggested by B&C.

also going with 4 corner ports 12 X 12 X 16.7 cm and 22cm long, do you guys think this is ok? or should i go with a single rectangular port at the bottom. (i only have theoretical knowledge about ports and need a suggestion from someone with practical knowledge).

Also a question about paint - what to use when there is no duratex, warnex, lineX or any other brand of speaker paint or bedliner paint available?

While the advantage of the triangular port to strengthen the enclosure without additional wood is unquestionable, this port tuning is also the most
difficult to get right.
Most vented enclosure sim tools will get the round port about right, while the triangular port in the corner might be off quite a bit.
Also the triangular port will choke earlier than the round port for the same area.
Measuring the impedance at high power levels is crucial for this port shape IMO.

 

[neil Fernandes]

Re: 18rbx100 review

Yes Uwe, i'm aware of the pro\'s and cons of different kind of ports and the only con i can think of is the trial and error - until i get it right part.
i really want to go ahead with the triangle port but im willing to play safe if i can't get it right the first time.

Art, are you suggesting that i go with 325 square cm? if yes, how deep?
Thankyou once again for the paint advice, looks like i'll go ahead with that.

 

[Art Welter]

Re: 18rbx100 review

Yes Uwe, i'm aware of the pro\'s and cons of different kind of ports and the only con i can think of is the trial and error - until i get it right part.
i really want to go ahead with the triangle port but im willing to play safe if i can't get it right the first time.

Art, are you suggesting that i go with 325 square cm? if yes, how deep?
Thankyou once again for the paint advice, looks like i'll go ahead with that.

No, I'd go a bit larger than 325 square cm to minimize port compression. The depth is dependent upon the port area and Fb you have chosen.

The only problem with larger area ports is they require a deeper duct to tune as low, and the volume of the port reduces the volume of the enclosure, which reduces efficiency.

My sine wave tests indicated the 325 square cm port was loosing about 3 dB at full power, though with pink noise run up to just below amp clipping (around 2000 watts) the frequency response looked the same as at low volume. That said, the sine wave level I used for testing would burn up the speaker if used long term, so whether a larger port area is needed is hard to say.

I also used a round ring (a cutout from the 18" speaker hole) around the port interior entrance to reduce turbulence, which also effectively increases the port length a bit. Took several reductions in port length before I arrived at the tuning I had intended...

 

[neil Fernandes]

Re: 18rbx100 review

Art, i can't seem to figure it out.
firstly, i have taken all the parameters from WinISD (including the ones that were autocalculated, which are very close to the numbers on b&c website) and entered them on Bassbox pro.
the second picture i uploaded shows the internal volume (140L) and tuning (40Hz).

the third is where i have selected 1 triangular vent with a total area of 350sq cm and i get a port length of 29.45cm.
the fourth is where i have selected 4 triangular vents with port area of 350sq cm (i think this is the area per vent). but, here the lenght of the port is 172.4cm which is too long.


the port dimensions that i mentioned earlier were 12 X 12 X 16.97, which is a port area of 72.0376 sq cm/port.
72 X 4 ports = 288 sq cm for 4 ports.

so, the 325 sq cm you mentioned, is this the total area of all 4 vents or just 1? (i think it's for all 4 but i just need to clarify)


Finally (not pictured) i entered 4 triangular vents with Area (AV) : 90 sq cm and i got a port lenght : 36.87cm. is this correct?
if this is correct, then do you think that 4 X 90 = 360sqcm enough or should i go even bigger?

 

[Bennett Prescott]

Re: 18rbx100 review

The TBX100 has an Xlim of 28.5mm (57 peak to peak), the 18SW115 30mm (60mm p to p), but the 18RBX100 does not list an Xlim, though if consistent with the others should be at least 20mm, perhaps Bennett could confirm that figure.

Hey Art, sorry for not following this thread more closely. The 18RBX100 has an Xmech limit of +/- 21mm (42mm peak to peak). In general it's not something to worry about, we design our motor structures and soft parts so that it is extremely difficult to reach Xmech with the available motor strength and compliance. I haven't seen a sign of mechanical bottoming on a coil in any B&C product, ever.

 

[David Morison]

Re: 18rbx100 review

Art, i can't seem to figure it out.
the third is where i have selected 1 triangular vent with a total area of 350sq cm and i get a port length of 29.45cm.
the fourth is where i have selected 4 triangular vents with port area of 350sq cm (i think this is the area per vent). but, here the lenght of the port is 172.4cm which is too long.

I see the Area (Av) text in your pic for 4 vents is blue - does that mean it's a link? If so, follow it - it'll probably explain whether that's assumed to be the area per vent OR the area of all the vents. If that's not a link, check the helpfile or user guide for the software.
Given the radical increase in length, I'm 99.9% sure that's the area per vent. Splitting the vent into 4 smaller parts totalling the same area would normally result in an increase in predicted length of perhaps 10-20%, not nearly 600%.

HTH,
David.

 

[Art Welter]

Re: 18rbx100 review

Art, i can't seem to figure it out.


The port dimensions that i mentioned earlier were 12 X 12 X 16.97, which is a port area of 72.0376 sq cm/port.
72 X 4 ports = 288 sq cm for 4 ports.

so, the 325 sq cm you mentioned, is this the total area of all 4 vents or just 1? (i think it's for all 4 but i just need to clarify)
Finally (not pictured) i entered 4 triangular vents with Area (AV) : 90 sq cm and i got a port lenght : 36.87cm. is this correct?
if this is correct, then do you think that 4 X 90 = 360sqcm enough or should i go even bigger?

The 325 sq cm port I used was a single square port, in a much larger cabinet. Since it exhibited some port compression, I suggested to go larger, but not 4 times larger, which obviously would occupy a lot of internal volume due to the longer length to tune low.

360 sq cm sounds like it should be adequate, though your cabinet volume at 140L is a bit over half the size I used, pretty small considering the Vas of the 18RBX100 has a larger Vas than the 18SW115 I used.

 

[Art Welter]

Re: 18rbx100 review

Hey Art, sorry for not following this thread more closely. The 18RBX100 has an Xmech limit of +/- 21mm (42mm peak to peak). In general it's not something to worry about, we design our motor structures and soft parts so that it is extremely difficult to reach Xmech with the available motor strength and compliance. I haven't seen a sign of mechanical bottoming on a coil in any B&C product, ever.

Considering that bottoming out a coil usually is "end of story", nice to hear none of the B&C woofers do that.
Glad to hear my Xmech guess was 1mm on the conservative side.

 

[neil Fernandes]

Re: 18rbx100 review

Thanks David and Art. Sorry for the delay in responding, i got busy over the weekend.

sorry about that question about the vent size, was just trying to make sure that i understand it correctly and i think i have

ok, moving to other questions -
which one is more closer to real performance for simulating a bass reflex in WinISD or BassBox?
the reason i ask this is because there is a slight difference (approximately 1db) between the fq. plot on WinISD and BassBox which i think is fine but the difference in cone excursion is almost 2mm. On winISD at 58.27hz it's 9.23mm and on BassBox at 59.76hz its 7.83mm.

 

[Jim McKeveny]

Re: 18rbx100 review

/... emphasizes excursion over power handling, we find Xvar to be the limiting factor in most designs today.

Today? It is a long-standing truth! Anyone fresh to LF/VLF loudspeakers should internalize this.

Bennet: Your wisdom and honesty do BNC proud.

P.S. I recall when they were "BBC Speakers"....