No compromises front loaded double 18” cab

Luke Robinson

Luke Robinson

Freshman
Jul 6, 2011
87
2
8
Philadelphia PA
www.audio-gods.com
I am looking to start a new Subwoofer project. I am considering a major line array purchase, but I can’t bring myself to spend the money that most companies are asking for subs.


First a short background. I have a decent amount of experience building Speaker cabinets. So far I am deploying 20 wedges, and a dozen single 18s as well as some older designs of a double 18 cab with a lot of success. My wood working skills are advanced, I actually went to college for furniture design and construction before I decided to pursue a career in live sound reinforcement. I have leaned a lot through trial and error, but I am (of coarse) still learning every day.


Enough about me, Lets move on to the project.


I am looking to build the best front loaded double 18 that I can. Budget is not my largest concern. I have a wholesale account with the local company that supplies baltic birch plywood, and I get great pricing on drivers, so I should be able to keep it reasonable. I am not scared by the pricing of B&C, and Faital Pro’s top of the line drivers, but I am not stuck on using the most expensive driver on the market either if it is not the best one for the job. On the same note Light weight speakers are nice, but this box is no doubt going to be big and heavy, so a few extra pounds for a ferrite magnet wont make or break me.


I am looking at front loaded for two reasons. When deployed in mass I feel like it gives me the greatest opportunity for directional arrays (correct me If I am wrong). Second, quite frankly I think that they will just be a heck of a lot easier to build.


Here is my list of priorities in defending order



  1. Loud and Proud: Tight and punchy bass!
  2. Stackability: I want to be able to stack the array on top of them when Flying the array is not practical. I am defiantly looking at using PTFE (teflon) strips on the bottom with grooves fro stacking.
  3. Truck Pack friendly: To me this means a rectangular box not a trapezoid, that has dimensions that add up to just short of 90” when packed side by side in at least one direction, bonus points for 2 directions.
  4. Portability: How am I going to attach wheels?
  5. What I am not concerned with is getting all the way down to 30hz Most of my work is bands, not EDM so I am perfectly fine with great performance from say 40-95 hz
  6. Price: To say it is of no concern would be a lie, after all I am trying to save money not buying a commercial sub.


So far I am looking at what the big boys over at Clair are using (if its good enough for them…) and I am thinking of a similar design to the BT-218. I am not above using jut about the same dimensions as them, and a similar port in the middle, If it aint broke….


The reason I am coming here is that I know there are a bunch of smart folks with many more years of experience than myself that may be able to add to my idea. I have recently purchased the eminence cab designer software but I am having trouble getting it up and running on Parallels, and i have not figured out quite what i should be doing with it any way.


Thanks in advance for any advice that you can give me.


Luke
 
Re: No compromises front loaded double 18” cab

The biggest part people always screw up is the port. Clair's BT218 has a very clever port design and there's a lot more going on in their than you'd imagine. I borrowed a few of their tricks with my subs. Get the port tuning right, and you'll have a great box. It seems that the standard double 18 size is 45x22.5x30. Ultra truck pack friendly. Oh, and getting to 30hz makes all the difference, even with rock and roll.



Evan
 
Re: No compromises front loaded double 18” cab

Luke Robinson said:
I am looking to start a new Subwoofer project. I am considering a major line array purchase, but I can’t bring myself to spend the money that most companies are asking for subs.


First a short background. I have a decent amount of experience building Speaker cabinets. So far I am deploying 20 wedges, and a dozen single 18s as well as some older designs of a double 18 cab with a lot of success. My wood working skills are advanced, I actually went to college for furniture design and construction before I decided to pursue a career in live sound reinforcement. I have leaned a lot through trial and error, but I am (of coarse) still learning every day.


Enough about me, Lets move on to the project.


I am looking to build the best front loaded double 18 that I can. Budget is not my largest concern. I have a wholesale account with the local company that supplies baltic birch plywood, and I get great pricing on drivers, so I should be able to keep it reasonable. I am not scared by the pricing of B&C, and Faital Pro’s top of the line drivers, but I am not stuck on using the most expensive driver on the market either if it is not the best one for the job. On the same note Light weight speakers are nice, but this box is no doubt going to be big and heavy, so a few extra pounds for a ferrite magnet wont make or break me.


I am looking at front loaded for two reasons. When deployed in mass I feel like it gives me the greatest opportunity for directional arrays (correct me If I am wrong). Second, quite frankly I think that they will just be a heck of a lot easier to build.


Here is my list of priorities in defending order



  1. Loud and Proud: Tight and punchy bass!
  2. Stackability: I want to be able to stack the array on top of them when Flying the array is not practical. I am defiantly looking at using PTFE (teflon) strips on the bottom with grooves fro stacking.
  3. Truck Pack friendly: To me this means a rectangular box not a trapezoid, that has dimensions that add up to just short of 90” when packed side by side in at least one direction, bonus points for 2 directions.
  4. Portability: How am I going to attach wheels?
  5. What I am not concerned with is getting all the way down to 30hz Most of my work is bands, not EDM so I am perfectly fine with great performance from say 40-95 hz
  6. Price: To say it is of no concern would be a lie, after all I am trying to save money not buying a commercial sub.


So far I am looking at what the big boys over at Clair are using (if its good enough for them…) and I am thinking of a similar design to the BT-218. I am not above using jut about the same dimensions as them, and a similar port in the middle, If it aint broke….


The reason I am coming here is that I know there are a bunch of smart folks with many more years of experience than myself that may be able to add to my idea. I have recently purchased the eminence cab designer software but I am having trouble getting it up and running on Parallels, and i have not figured out quite what i should be doing with it any way.


Thanks in advance for any advice that you can give me.


Luke
Click to expand...

I have built exactly what you are describing. The latestversion uses two of these: http://www.eighteensound.it/PRODUCTS/Products/ProdID/58/CatID/8#.VF2U-Wkbrq4
Its dimension are : 550 mm wide, 1220 mm high, 750 mm deep. It hasa large curved centre port to minimize turbulence. It sounds great, plays solidto 40Hz and is -6dB at about 30Hz. It’s easy to transport and truck packs well.The original design is about 15 years old but it has been so successful anduseful that the only thing need was a driver upgrade.
I will take some pictures if anyone is interested …
 
Re: No compromises front loaded double 18” cab

Hey Luke,

When you say "no compromises" you make me nervous. That generally means someone is making compromises they are not aware of.

That said, I agree with Evan that many sub designs can't push enough air through the port, and are tuned too low. At the end of the day you're going to have to build a cabinet anyway in order to find out where your tuning frequency ends up, if everything was true to simulation life would be a lot easier. The good designers are good because they have built a lot of bad cabinets and learned to modify expectations and simulations to meet reality.
 
Re: No compromises front loaded double 18” cab

Thanks for all of the replays, I will be carful to try and get the right port size. I think to try and hone in on this a bit Maybe I should try and select a driver. I am either Looking at B&C or Faital Pro. Bennett nows you chance to sell me! In B&C I would guess that means either the 18TBW100 or the 18SW115. Or in Faital the 18HW1070, or the 18XL1600. What if anything does any one think of these, and does anyone have a reason that one might work better than another?

All things being the same, the price of the 18TBW100 is a little more attractive, if we are splitting hairs at the differences besides weight I would probably look in that direction. The 18SW115 asks for a smaller box size according to the web sight at first glance. that could help if it is the case.

I just came cross a deal on some really heavy duty perforated sheet metal for the grills, I bought enough to make around 20 subs. I also linked up with a guy that builds fiberglass resin pools, and is interested in sound, and really jazzed about the idea of coating my subs. I know this is something that other manufacturers have done, It should make the boxes even more ridged and tough than bed liner. of corse I know Bracing is key and Will make sure to adequately brace the cabinets as well.
 
Re: No compromises front loaded double 18” cab

Peter Morris said:
Here is another suggestion - needs a lot more bracing than shown in the plans however.

http://www.eighteensound.it/Portals/0/EnclosuresKits/18sound_18_dual_subwoofer_kit.pdf
Click to expand...

Wow I really dig that port design, it is really easy to build, and requires 4 of the same part and just a plain rectangle in the middle. Nice! I might want to play with the dimensions of the box a bit for truck pack reasons, but I think that the port shape might be the winner.

thanks,
Luke
 
Re: No compromises front loaded double 18” cab

Luke,

There's also the 18SW100, which is kind of in between the 18TBW100 and 18SW115 in terms of price. It is better performance than the 18TBW100, as well, and would do well in a smaller box too. Personally I would spend the few extra bucks there to upgrade to neodymium.
 
Re: No compromises front loaded double 18” cab

Luke Robinson said:
Wow I really dig that port design, it is really easy to build, and requires 4 of the same part and just a plain rectangle in the middle. Nice! I might want to play with the dimensions of the box a bit for truck pack reasons, but I think that the port shape might be the winner.

thanks,
Luke
Click to expand...

As a rough comparison - there are the drivers that have been discussed at their rated program power. The box is about 160L in each case tuned to 32 to 36 Hz depending on the particular driver.

(the L in boxplot is 30Hz)
 

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Peter Morris said:
As a rough comparison - there are the drivers that have been discussed at their rated program power. The box is about 160L in each case tuned to 32 to 36 Hz depending on the particular driver.

(the L in boxplot is 30Hz)
Click to expand...

The plots shown above seem to neglect excursion limits of the drivers in question, which makes them somewhat useless IMO.

Personally I own 18SW115 and 18SW100.
The SW100 is more efficent ( tuned slightly higher ) and therefore fits better to sub amps, I am willing to pay for.
IMO the SW115 needs an amp that can deliver about 3kW and these amps are rare and very expensive ( one of the reasons Danley chooses the 4Ohm version IMO ).
Since the SW100 is available ( about 2 years ), I have sold 24 drivers to befriended companies as upgrade into an existing design. None of the drivers failed so far.
I limit the power to 145V peak, which is of course useless information without knowing the enclosure design and high pass filter applied :razz:


Uwe
 
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Re: No compromises front loaded double 18” cab

Uwe Riemer said:
The plots shown above seem to neglect excursion limits of the drivers in question, which makes them somewhat useless IMO.

Personally I own 18SW115 and 18SW100.
The SW100 is more efficent ( tuned slightly higher ) and therefore fits better to sub amps, I am willing to pay for.
IMO the SW115 needs an amp that can deliver about 3kW and these amps are rare and very expensive ( one of the reasons Danley chooses the 4Ohm version IMO ).
Since the SW100 is available ( about 2 years ), I have sold 24 drivers to befriended companies as upgrade into an existing design. None of the drivers failed so far.
I limit the power to 145V peak, which is of course useless information without knowing the enclosure design and high pass filter applied :razz:


Uwe
Click to expand...

No, Xmax is included, its the green line. With this type of alignment Xmax is not an issue until about 30Hz. This was a "no compromise" design so if you have the amp power the 18SW115 and the 18NWL9000 are probably the best. The 115 goes a bit lower the 9000 a bit louder ... but they are all excellent! If there are some compromises Bennett's suggestion with 18TBW100 looks the best.
 
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Re: No compromises front loaded double 18” cab

Peter Morris said:
This was a "no compromise" design so if you have the amp power the 18SW115 and the 18NWL9000 are probably the best. The 115 goes a bit lower the 9000 a bit louder ... but they are all excellent!
Click to expand...

Peter,

Do you have Klippel Bl(x) and Kms(x) curves for this Eighteen sound product? While there are a number of pro woofers that purport to have similar excursion capabilities to B&C's split coil woofers, in my experience what distinguishes the B&C line is their exceptionally broad and flat Bl(x) curves and the symmetry of their Kms curves. Any number of drivers can wind a coil long enough to meet a nominal Xmax target, but B&C has taken this further to insure the BL product through the range where an underhung driver performs well is exceptionally well behaved.

JBL has similarly high quality linearity for their double coil woofers, based on the data I've seen, but their drivers are not readily available to the general public.

Personally I'm at the point where I essentially won't consider a low frequency driver where Klippel data is not available.
 
Re: No compromises front loaded double 18” cab

Phil Graham said:
Peter,

Do you have Klippel Bl(x) and Kms(x) curves for this Eighteen sound product? While there are a number of pro woofers that purport to have similar excursion capabilities to B&C's split coil woofers, in my experience what distinguishes the B&C line is their exceptionally broad and flat Bl(x) curves and the symmetry of their Kms curves. Any number of drivers can wind a coil long enough to meet a nominal Xmax target, but B&C has taken this further to insure the BL product through the range where an underhung driver performs well is exceptionally well behaved.

JBL has similarly high quality linearity for their double coil woofers, based on the data I've seen, but their drivers are not readily available to the general public.

Personally I'm at the point where I essentially won't consider a low frequency driver where Klippel data is not available.
Click to expand...

Hi Phil,

You have hit the nail on the head regarding Klippel etc. One of the biggest problems designing woofers with excursions in excess of 10mm is keeping them stable so there is no bias and they continue to return to centre so you can make use of the quoted Xmax. Drivers with higher Fs tend to be better (assuming the same Bl(x) curve).

I was discussing this with a friend last week who has measured many of these drivers … and they all struggle. As you said this is one of the things that the 18SW115 is very good at, I suspect slightly better than the18sound.

I generally can’t get B&C drivers in Oz at a reasonable price and used the 18sound, it is however very good driver. I do have some 21SW152 .... :)~:)~:smile: This new driver from 18sound does however look very good in this respect http://www.eighteensound.it/PRODUCTS/Products/CatID/2/ProdID=109

The other thing to note is that both of these have very largeVCs and minimal thermal compression compared to some of the other drivers.
 
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Re: No compromises front loaded double 18” cab

Luke Robinson said:
  1. Stackability: I want to be able to stack the array on top of them when Flying the array is not practical. I am defiantly looking at using PTFE (teflon) strips on the bottom with grooves fro stacking
Click to expand...

Luke,

Teflon will be a poor choice for your runners, though I appreciate the intent of what you are aiming to do. PTFE is very expensive and has dreadful impact resistance.

More affordable, better performing alternatives include:

  • Ultrahigh molecular weight polyethylene (UHMW PE)
  • Polypropylene
  • Acrylonitrile Butadiene Styrene (ABS)

And a couple of more exotic plastics:

  • Kydex (a fancy PVC)
  • Delrin 300CP

---

Some pointers on box design:

  1. The prediction programs are based on math designed to simulate the small signal performance of vented boxes. They will let you enter big values for things like input power, but you should not assume that their models scale up to high power performance in a linear fashion.
  2. The port length prediction of these programs is rarely on point. Expect to have to make sawdust to confirm box tuning
  3. High performance modern woofers have been squarely out-performing the ports in boxes for more than five years now. Further extracting performance from vented boxes is now in the realm of fluid mechanics.
  4. One of the quickest way to make sure that your box is tuned how you intend is by looking at the impedance curve. Parts Express sells a nice affordable tool for doing impedance sweeps.
  5. People also look for the box tuning frequency by inputting tones to the driver and looking for the frequency where the cone moves the least. This is also a valid method, but has the potential caveat that the box's tuning frequency will tend to increase as the input level increase.
  6. Driver parameters change with increased power input. The most obvious of these changes in the increase in voice coil resistance as it heats up. As Re increases, Qe increases proportionately, which means that the driver has less electrical damping. The boxes overall response will change as a result. You can't assume the pretty flat line in your simulation program will match the boxes performance in the middle of long day out on a gig.
 
Re: No compromises front loaded double 18” cab

Phil Graham said:
Luke,

Teflon will be a poor choice for your runners, though I appreciate the intent of what you are aiming to do. PTFE is very expensive and has dreadful impact resistance.

More affordable, better performing alternatives include:

  • Ultrahigh molecular weight polyethylene (UHMW PE)
  • Polypropylene
  • Acrylonitrile Butadiene Styrene (ABS)

And a couple of more exotic plastics:

  • Kydex (a fancy PVC)
  • Delrin 300CP

---
Click to expand...

In general, UHMW is the preferred material for wear strips and glides where extended temperature ranges are not required, with nylon and Delrin (Acetal) as good alternates. UHMW is about half as expensive as nylon and Delrin, with somewhat lower tensile strength (nylon has high tensile strength and low impact resistance, Delrin is in between). All are available in black.
 
Re: No compromises front loaded double 18” cab

Phil Graham said:
Luke,

Teflon will be a poor choice for your runners, though I appreciate the intent of what you are aiming to do. PTFE is very expensive and has dreadful impact resistance.

More affordable, better performing alternatives include:

  • Ultrahigh molecular weight polyethylene (UHMW PE)
  • Polypropylene
  • Acrylonitrile Butadiene Styrene (ABS)

And a couple of more exotic plastics:

  • Kydex (a fancy PVC)
  • Delrin 300CP

---


Some pointers on box design:

  1. The prediction programs are based on math designed to simulate the small signal performance of vented boxes. They will let you enter big values for things like input power, but you should not assume that their models scale up to high power performance in a linear fashion.
  2. The port length prediction of these programs is rarely on point. Expect to have to make sawdust to confirm box tuning
  3. High performance modern woofers have been squarely out-performing the ports in boxes for more than five years now. Further extracting performance from vented boxes is now in the realm of fluid mechanics.
  4. One of the quickest way to make sure that your box is tuned how you intend is by looking at the impedance curve. Parts Express sells a nice affordable tool for doing impedance sweeps.
  5. People also look for the box tuning frequency by inputting tones to the driver and looking for the frequency where the cone moves the least. This is also a valid method, but has the potential caveat that the box's tuning frequency will tend to increase as the input level increase.
  6. Driver parameters change with increased power input. The most obvious of these changes in the increase in voice coil resistance as it heats up. As Re increases, Qe increases proportionately, which means that the driver has less electrical damping. The boxes overall response will change as a result. You can't assume the pretty flat line in your simulation program will match the boxes performance in the middle of long day out on a gig.
Click to expand...


FWIW, my subs I mention above use 6mm x 50mm black HDPE strips - cheap, seems to work fine, but perhaps a little slippery
 
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