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DIY cab project...

Discussion in 'Amps and Cabs [BG]' started by Joe Martin, Mar 23, 2005.


  1. Joe Martin

    Joe Martin

    Mar 23, 2005
    Frederick, MD
    First off, hello everyone, I'm kinda new to talkbass here, but read the site alot. My name is Joe (duh), and the reason I am making this thread is because I am about to embark on my own DIY cab building project. I am only 16 (thought you all might like to know that) but I am serious about doing this. I have been playing bass for a little over 5 years. In my school we have to do a graduation project to graduate, and I have decided to use that as an excuse to build my own cab :p .

    I have already read alot on the internet and here about building your own cabs, but that is no where near enough to do it with. I am curious to know if there are any books that I should check out and read to get myself started on the basics and ideas behind loudspeaker design etc etc.

    We have to have mentors to do this project (lucky for me), so I have already enlisted the help of a good family friend that happens to be a construction/carpenter dude, and my calc teacher to help me with any complex math that I am sure I will come across while doing this. I'm gonna see if this awesome local bass dudes knows anything and wants to help aswell. But it couldn't hurt to have a couple of seasoned bassists helping out too, so if any one here knows a good bit about this kind of stuff feel free to IM/email me, or just let me know your contact info so I may enquire you about certain topics at a later period in time. I'd greatly appreciate that.

    Also, if there are any computer programs that you all know of that may assist in the design phase of the project, that would be extremely helpful aswell.

    Thanks again to everyone for any and all help.

    ~Joe
     
  2. Passinwind

    Passinwind I Know Nothing Supporting Member

  3. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Joe, there are several TB'ers who know a lot about cab building. In the past the "IM/Email me" approach hasn't worked terribly well. Generally you're better off asking specific questions here on the forum and letting the guys jum in with related info. This way, everyone benefits and we all learn as we go.
     
  4. basspro2

    basspro2 I'm seeing Gorillas...

    Apr 6, 2002
    Northbridge, Mass
    I believe if you get on the Eminence Speaker site you can download a small program for cab building , Then if you want to buy the full program on CD you can.
     
  5. Joe Martin

    Joe Martin

    Mar 23, 2005
    Frederick, MD
    Alright, I'll keep it all in this topic then, my project topic. =P

    Okay first things have to come first. I need to decide what speakers I am actually going to use in the cab before I can do anything correct?

    From what I have seen, most people use the Pro Series and/or American Original series speakers from eminence. Those all look nice but I am considering using the Legend BP102 speakers instead. Eminence claims they are made specifically for bass guitar, and they have a very nice FS, and an enormous Xmax for a 10. The only thing I can see wrong with them is that they are not very effecient drivers.

    This is measured in SPL.

    Legend BP102 - 200Wrms (200Hz)91.8 (300Hz)90.5 (400Hz)91.0 (500Hz)89.3 (600Hz)88.2 (700Hz)89.0 (800Hz)90.8 (900Hz)92.0 (1000hz)92.5 (1500Hz)92.5 (2000Hz)92.5

    Is it just me or does that seem a little low? Though with enough power I'm sure these thigns would kick some major booty.

    Also I'm getting the crossover to go with, and they comes with power ratings on it. I have never dealt with a crossover before, so does the power rating on it mean how much juice you can push through it without burning it up? Right now I'm thinking a 3x10 cab + tweet, so I will need a 2-way correct?




    While we're on the subject of materials, what is the best kind of wood to use? Looked like most people used voidless birch ply. Should I be good with that?
     
  6. SirPoonga

    SirPoonga

    Jan 18, 2005
    WinISD, great program.
    Many kits out there
    www.billfitzmaurice.com

    www.partsexpress.com has a util for their speakers, you plug int he part no and it spits out dimmensions.

    Building a bass cab isn't that hard, especially when using winisd. Plug in specs for the driver, it spits out dimensions :)
    If you want a tweeter (like avatar cabients) then you need to build a crossover. Many resources on that too. Then it's just adding damping material, picking out a good wood (like plywood or mdf). If you want to get fancy and put in cary handles, corner protectors, outside carpet, etc...

    Another place you will want to check out is www.diyaudio.com. You could spend weeks just reading here.

    A good driver to use is eminence, avatar has the best price on those.

    If you look at Bill Fitz's Tuba24 or DR250a (which he uses for his bass) he has a list of cheap and good drivers to use when you buy the plans.
     
  7. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    You've spotted the efficiency problem. At 92dB each, 2 of them will yield a 400w cab with a 95dB sensitivity rating. That translates to a maximum SPL of 121dB. The obvious question here is wether or not that's going to be loud enough for you. The answer depends of course on what you're going to use it for.

    There's another problem with these drivers. They need a large cabinet. 62 Litres (2.19Cu.Ft.) for each one. So your 2x10 is going to be 124 litres, which isn't small. However, this size may be perfectly acceptable to you given that these little 10's do indeed go quite low. Tune the cab to 40Hz and you'll get a -3dB point of 39Hz - not bad!

    The third problem is the "Honest watts" rating. You say you've got WinISD. If you use the Pro version (which is available for download in Alpha testing version, but works very well), have a look at the Max Power graph. See the dip at about 58Hz. That's telling you that this 200w speaker will hit X-max at 75 watts at 58Hz. Now before you panic, most drivers have this problem. The ones that don't are both rare and expensive. Off the top of my head I can only name a few and none of them are 10's. Is this a problem? Again it depends on you and how much you rely on that 58Hz frequency. In practice the distortion created may not even be audible because it occurs at such a low frequency. Generally speaking low freq. distortion is harder to hear than mid and high freq. distortion. That's just the way our ears work.

    Yep you've got it covered. However, consider rolling your own crossover. It's not too hard or expensive, and will certainly get you extra points for your project. All we'll need is the nominal impedance and the resonant frequency of the tweeter, and we can calculate capacitor and inductor values quite easily.

    Ply is good. MDF is sonically better but it weighs more. Technically concrete is better again but you really do have to draw the line somewhere right? I draw my line at MDF. I'll use it on a cab that's either very small, or isn't going to be carted around much. I usually go for plywood.
     
  8. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    i'd be very cautious about going thru the expense of building a cab for such inefficiant drivers. typically, bass guitar cabs have sensitivity ratings of 100 - 106 dB, and that includes 1 speaker enclosures.

    as you probably know, every 3 dB drop in efficiency requires that you have twice the power to make up for it. that means with a cabinet that has an efficiency/sensitivity of 92 dB, you'd need eight times the wattage to be as loud as a cab with a efficiency/sensitivity of 101 dB.

    of course sensitivity doesnt tell the whole story, as it is typically measured at 1 Khz. A full response curve graph will give you a better idea of what to expect, but i cant imagine a driver with a sensitivity of 92 dB having just the right response curve to compete with a driver of 100 dB. ;)
     
  9. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    While I agree with you Ivanmike, I also take manufacturer's claimed sensitivities with a grain of salt. Now I'm not calling them liars, but I do think they add a couple of dB to their sensitivity specs sometimes. Raw speakers are a little more "honest".

    With current technology, the old rule still applies - Efficient, Low, Small, pick any 2. We're talking 10's (small) which go low, therefore we have to sacrifice some efficiency. Sometimes it's worth remembering that 10's for bass started with a fridge that held 8 of them. Personally I never gig with less than 4x10's. If I'm going to use less than that, I'll use a larger diameter speaker as well to take the lows.
     
  10. Many of those ambitious SPL specs are taken at high frequencies outside the usefull range. The example above might be measured at 1,000 Hz. Fat lot of good that does for a bass player.

    This exposes the Big Lie that so many manufacturers participate in. They claim the moon for specs, but never publish plots or measurement criteria to back them up.

    Building/testing season starts for me on April 1 (after a year of down time), and I'm preparing to build a herd of Bill Fitzmaurice's Tuba 36. I'll also borrow Aroarah's D410XLT when they are between shows, and get some accurate measurements under controlled conditions. I have every confidence there will be a huge difference between reality and marketing bullsh*t.
     
  11. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    By all means you always have to take SPL ratings with a very large bag of salt, if not two. This especially applies to bass. SPL ratings of both raw drivers and finished speakers invariably are averaged figures that seldom reflect what is actually going on below 100 Hz, and as far as bass is concerned that's where that action is. For instance, an EVM12L is rated at 101dB/watt. In a 2 cu ft cabinet tuned to 50Hz its actual sensitivity at 50Hz is 92dB. A Delta12LF rated at 98dB/watt will have 95dB sensitivity at 50 Hz in the same box. Plus, the Delta 12LF will have a response peak of 101dB/watt at 80 Hz, while the EVM is only putting out 94dB at 80 Hz. The EVM is decidedly superior only above 300Hz.

    Watts tell you nothing about the performance of a driver/speaker, and SPL ratings tell you next to nothing. The only definitive way to predict performance is with an SPL chart, and manufacturers are loath to provide those. No problem. Download WinISD and create your own; the program database has over a thousand drivers in there, including 95% of those used in bass cabs going back the last 20 years. Knowing what (model of Eminence 99% of the time) driver is in a cab along with the cabs dimensions gives you 90% of the information you need to predict what anyone's speaker is actually capable of, and the other 10% you can get from the manufacturers specs.
     
  12. Joe Martin

    Joe Martin

    Mar 23, 2005
    Frederick, MD
    Okay, sorry for the long wait here guys, and the info is much appreciated.

    Okay also, we have a set amount of time to do this project in. We can choose to do it over one term, or during summer break. I've choosen to do it this summer, I'm just "cheating" and getting some preliminary grounds on what I am gonna do. I like to know what it is before I do it. Anywho, since I'm doing it this summer, I think I may check out some of Bill's designs and toy with those just to get my feet wet in the subject.

    Okay, I got this whole WinISD thing going and I got all the specs in there and whatnot, but once I put the specs in I'm not exactly sure what to do, or what I'm looking at for that matter. It doesn't really do anything. I just put them in there... Is there somwthign special I have to do with them to get box dimensions out? After I get the cubic internal volume needed, can I toy with the dimensions as long as I retain the same internal volume?

    Something I did get out of that is that these speakers don't have a very large mid-range. The rolloff starts at about 2k, so should I toss in like a 6 or 4 inch mid speaker to fill that in, or would I be better going with one of the whizzer versions of that speaker and then a tweeter?


    Thanks again so much for all the help guys.
     
  13. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    What WinISD does is take the driver specs and spit out the box that works best with it. What you have to do then is decide whether the box size it gives you is in line with what you want. If so fine, if not you click on 'box' and put in the cubic volume you want to use, and change the tuning frequency till you get the response you want. If you can't get what you want try another driver.

    To simulate existing boxes do the same, as if you were building a cab with the driver in question, then alter the box size to the existing box and play around with the tuning frequency to see what is actually possible out of that driver/box size. Click on 'box shape' and then 'optimal' to figure dimensions. Keep in mind the box dimensions are all internal, less the volume taken by the driver(s) and ports, if any. Also note that if you're using two or more drivers they have to be vertically aligned for best results, so you often will have to flip the box.

    Predicting HF response is dicey, but assume that the driver isn't going to be worth much at all beyond 1 wavelength of the actual cone diameter, as irrespective of the on-axis response, what the manufacturers quote, the all important and seldom quoted off-axis response is what counts. That means (best case) a 15 is good to about 1kHz, a twelve to 1400 Hz, a ten to 1700 Hz. A whizzer does a lot better as the whizzer cone is about 3 inches across, good to perhaps 4500 Hz before beaming sets in. These figures assume a wide-band driver, and for drivers with especially low fs figures the frequency will be lower, sometimes by an octave or more.
     
  14. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    OK next step is to click on the "New Project" button located in the top left corner. The box that appears has a pull-down menu of speakers. Select the one you require for this project then click "Next". It's now just a matter of following the prompts:-

    Enter the number of drivers, then hit "next".

    Enter the enclosure type, then hit "next".

    The newer version now asks you to choose an alignment. If you're on the older version, it assumes the Optimal Flat alignment automatically.

    You're done. You should now see a frequency response graph, and a box that has several tabs:- Driver, box, Vents, plot etc.... The Box tab tells you the cab size and the tuning freq. If it's displaying litres and you prefere cu.ft, keep clicking on the unit measurement until you get the one you want.
     
  15. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    no argument here. of course the sensitivity is only a very narrow snapshot, i just imagine there's gotta be some drivers that are inherently higher output than others accross the spectrum. tone being equal (hah!) i'd try to pick the higher output driver if i was going to the trouble of rolling my own.
     
  16. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Actually the opposite is true. You generally get higher average sensitivity in a couple of ways. The easiest is to raise the fs by using less moving mass, and higher fs invariably leads to less bass extension. The other method is to increase the size of the magnet, which does raise sensitivity. It also raises Bl and lowers Qts, both of which lead to lessened bass response. The only mod that can seriously increase SPL without hurting bass response is to make the coil to polepiece clearance smaller, and that can lead to all sorts of alignment problems, as EV discovered with their SRO drivers of the late '60s that would suffer from coil rub if you looked at them the wrong way. There are actually very few drivers with average sensitivities of greater than 95dB that don't sacrifice bass extension, and those don't come cheap by any means. How much, you say? Well, if you have to ask...