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Cabinet tuning.Advice needed

Discussion in 'Amps and Cabs [BG]' started by Magneto, Jan 27, 2005.


  1. I'm adding 2x15" Eminence drivers to an older Fender Bassman cabinet. Will be rebuilding the interior to suit, and so far have approx 4.5-5.0 cu-in volume for each driver. This falls within the driver's recommended enclosure sizes.
    Drivers will be separated by an interior baffle, and wired individually, basically working as separate cabs. If one should fail, I can always "limp home" on a single 8 ohm driver.
    I will be using round ports for tuning.
    Question: How does one figure out what frequency would be best to tune the port to? I have all the information about the speakers, I have the box's internal volume, so basically I need to figure out what frequency I want the box tuned to, and then I can use my speaker design software (or formulas) for calculating the port sizes and depths, correct? I've done alot of research and reading, but I'm missing something.

    p.s. Would tuning to 40hz be about right for a 4 string? Since my cab dimensions are not flexible, I'm probably going to be limited to what I can do here, right?

    I would appreciate any help or info that can help me figure this out..
    Thank you..
    Mag...
     
  2. random_id

    random_id

    Jan 17, 2005
    go to http://www.pvconsultants.com/audio/frdgroup.htm

    Download Unibox. This program works with Excel and can help calculate ideal volumes and ports for speakers. I have used Unibox and the other software on the FRD Group to build both home speakers, and a cabinet with a 15" and a piezo. I put the piezo on a switch, but I always leave it on.

    Enter all of your speaker data and look at the corresponding graphs. One thing to watch out is the xmax of the speaker. This is the amount the voice coil moves in and out before bottoming out, or worse. It also determines the amount of watts you can thump into your speaker. Normally you can increase the xmax by 15% or so without doing any harm. Emininece, however, does rate their xmax very very conservitive.
    It basically becomes a juggling act, between power handling and low frequency. The lower the overall tuning, generally the less power it will handle.
    When I built my cab, I went with a sealed design. I know, this is crazy in bass world, but the difference in frequency it saved me was minimal, but it greatly increased the power handling.

    One other thing...I asked similar questions on diyaudio.com and I got the response that most of the energy of "the bass sound" actually comes from higher harmonics. So, with a four string, you really don't have to have it get 40Hz to sound great. Most of the sound/energy is comming from higher frequencies. Check out the thread DIYaudio

    Good luck...my cab has brought me nothing but pure bass-bliss.
     
  3. Thank you for replying with the information. I think it will be a big help.
    I'm using a pair of Eminence Delta 15s. I believe you used one of the Gammas in your box?
    I'm interested in hearing more about your sealed box, and I'll read that thread you supplied. Do you think there's an advantage with your box's design?
    I'm also considering a piezo tweeter for this rig. Could you tell me which make/model you used, and how you wired it?

    My biggest concern is building efficiency into my box. My box dimensions are somewhat already defined for me, so I just need to get the most out of this, as is.

    Mag...
     
  4. Rhythmalism

    Rhythmalism

    Sep 25, 2004
    http://www.linearteam.org/winisd.html
    Another program.

    If you don't have the qts, fs, and vas specs for your woofers, that program might already have your woofer in the list....

    And 40 hz would be a wonderful frequency, it'll nail the low E string. Many cab manufacturers go closer to 60hz, only to squeeze more output from their speakers or get a smaller box...
     
  5. Thanks for the info. I already have WinISD, been experimenting with it this evening. It has the parameters for my chosen drivers, plus I already have all that info.
    My biggest problem is all the conversions! I think I have everything on paper, then I find the program wants liters and cu mm instead of inches or feet. haha.. I have to x out of the program and go converting.
    I don't have Excel, so I guess the Unibox is out of the question for now.
    I need more info on the relationship between the size of the box and the frequency it can be tuned to. I really just need a setting that will be a good balance for bass guitar. I'm not looking for "super-box", but if I happen to stumble across it, I wouldn't be upset, ya know?

    Mag...
     
  6. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    In WinISD just double click on the liters/ whatever and it will convert to cubic inches/cubic feet/acres/whatever. As a last resort read the instructions.
     
  7. :eek: Oops! Thanks a bunch for that tip. I looked for this in the options, didn't find it, didn't think I could change it, etc.. Much easier now.

    I'm now consider the tuned ports for the cabs. I am leaning towards using 2 round tubes (per speaker), instead of slotted ports. This way I could do some fine tuning later if needed. I've been looking at many of the commercial cabs to see how they are ported. Many are slotted, and this confuses me. How does Avatar use the same cab for different speakers, using the same port dimensions? Wouldn't these requirements change between the Deltas and Kappa Pros, Neos, etc??
    Any recommendations for choosing port type, location, etc??

    Thanks for all of the help. I'm actually getting somewhere now.

    Mag...
     
  8. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Slot pots have the advantage of also serving as braces. Many manufacturers use the same box dimensions for a variety of driver configurations to minimize box SKUs; whether they actually get properly tuned to the driver that ends up inside of them is a good question.
    A pair of Delta 15's isn't the best choice. A single Delta 15LF in the same size box would provide better extension and equivalent output, while combining it with an Alpha 8MR crossed over at 800 to 1kHz would give far better highs than any ten incher.
     
  9. Bill, thanks for the help. I'm curious as to why you would say a single Delta 15LF would provide "equivalent output" compared to two regular Deltas. Is it the LF's extended Xmax? There's not that much difference in costs between the two, and cost is a major concern here. I need to get a cab up and running for a new band that I'm working in. I have an amp, no cabinet, and this is the cheapest route I can take for now. If finances weren't a major concern, I would either buy prebuilt, or custom build cabinets using higher-quality drivers.
    Can't afford anything more than perhaps a piezo tweeter.So basically I'm going with 2x15s, in a sturdy, large Fender cabinet, and I'm going to TRY to get them to sound as good as I can, considering.

    The Delta reg specs show the freq response to go higher than the LF model. If using only the large drivers, this would help, wouldn't it?
    I look forward to hearing from you again, or you can PM me .

    Mag...
     
  10. random_id

    random_id

    Jan 17, 2005
    As for the piezo, I got the 270-011 from PartsExpress.com. I wired it parallel with the 15” with a 20-ohm/10 watt resistor. There is a link at partsexpress that details the reason that the resistor is needed. I also hooked mine with a simple SPDT (center off) switch. I hooked up another resistor with the idea that I could switch the tweeter between off, 20-ohm, and 40 ohm. However, the difference between the 20 and 40 ohm settings are barely noticeable, I should have tried something more like 20 and 80 ohms.

    As for going with the sealed design, I just kept playing around with box sizes and looking at the frequency response and power handling. In the end, the frequency response wasn’t that drastically different between a sealed and ported design for the Gamma 15” that I was using. Sure, I could have made a box twice as big with a port, but I wanted the speaker to be small. I forget the actual dimensions, but it’s something like 21” X 21” X 21” (actually, the dimensions aren’t all the same, but you get the idea).
     
  11. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    The difference between the Delta 15 and Delta 15 LF is mostly in the xmax, and it's a huge difference. Nearly double the xmax in the LF means it can provide the low frequency output of two Delta 15's. By using a single driver instead of two in the same size box it will work better. Model it yourself and you'll see.

    Instead of making the box into 2 separate chambers use panel to panel shelf bracing to beef up the box, with 6" holes in the shelves to allow the rig to breath.

    Going directly from any 15 to a piezo isn't the best idea. A direct radiating 15 has falling off-axis response above 1kHz or so, leaving a two octave response hole until the piezo kicks in. While the on-axis response of the Delta is good to 4kHz it's a moot point if you only get that response within a ten degree radiation pattern.

    You're much better off sticking an Alpha 8 MR in the hole formerly occupied by the uppermost 15 and crossing over with an Eminence PXB2-800 crossover. Above it you can add a piezo if you want response to extend above 4kHz, though you'll need two to match the rest of the system's sensitivity. But with the money you saved on using one woofer instead of two you essentially get the midrange, crossover and tweeters for free.
     
  12. Use a slot port only when you don't have enough baffle board area for a round port. The end result is the same, but a slot port is a whole lot more difficult to build, then correctly tune.

    Avatar uses the same cab and tuning for a variety of drivers. Looking at the T/S data, there is no specific match. Therefore, the box is a generic size that fits with other cabs in their line (read: marketable). IMO, the Avatar is a sturdy cab that is reasonably priced, but not engineered to a specific driver.

    If you are interested in an engineered solution, start with my spread sheet. The price is right (free), and the data will help you make a sound choice. You can sort it for size, tuning frequency, F3 (cutoff), and so forth. If you are looking for maximum tight bass, use the SBB4 alignment.
     
  13. random_id: Thanks for that piezo information. I'm not sure if I'm going with a piezo yet, but it's an option. I might have a few more questions for you. Perhaps I could PM you?

    billfitzmaurice: You've been a big help, and the ideas you've presented are very interesting. At this time, I might be going with better speakers (Kappa pros), as I can get them for basically the same price as the Deltas I was considering. I see what you mean about the piezo and crossover freq problem. What a about a piezo horn mid/tweeter? freq response of 1,800-30,000.. Parts express has one #280-062
    Would this help fill the blanks if I did go with the 2x15 arrangement?
    The reason I like the separated cab chambers is that in case one speaker would fail during a gig, I could easily go with one 15 (running 8 ohms of course), and it should perform reasonably well without the extra dead cab space. The ply separator baffle would also add extra support without eating up too much cab volume. This is a fairly large cab. Measures 40h x 30w x 17 d.

    bgavin: I've got your spread sheet, but I don't have Excel. Might find a viewer at the microsoft site, I'm not sure.
    I'll look it over. Thanks for the info on the ports. I'm just now getting WinISD beta dialed in, and I have tons of data to go over before I buy or build.

    Thanks for all the help. Any more ideas or suggestions are always welcomed...

    Mag...
     
  14. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Don't use a piezo to 1.8kHz. Piezos sound good above 3.5kHz, like crud below that.

    If you're running two 15's in parallel it's most unlikely you could damage one and not the other. Parachutes are best carried in pairs; it's not a requirement for drivers.

    A Kappa Pro 15 will outdo a Delta 15, but not a Delta 15LF. A Kappa Pro LF is about equal to a Delta LF. Model them, see for yourself.

    You seem fixated on the idea that 2 drivers will work better than one. From a finite cabinet volume the opposite is true more often than not. Going back to Leo Fender and before manufacturers have stuffed too many drivers into too small boxes for them to work properly. Leo can be forgiven, he didn't have WinISD. You do. Use it wisely.
     
  15. Bill,

    Thanks for the advice with the tweeter/mid.. At this time I don't have definate plans to use a tweeter at all.

    I'm not so much worried about damaging one or both of the speakers, but more concerned with ending up with the "bad apple" that fails because of quality issues or the likes. Years ago I never gave this a second thought. These days I don't trust squat.

    Man, you're right. I am fixated on the 2 x 15 cab scenario. If I were custom building a new cab, I'd most definately consider going with a smaller cab, using a crossover with one of those Alpha 8MRs, or going with a 1x15 cab and 2x10 cab combos. 20 years ago, This cab originally had 4x12 speakers, in the angled-in enclosure. Never sounded right, so I thought I was a genius when I tore all that out, and rebuilt it for 2-15s, never giving a thought about what I was doing. Played live with it for 3 years and it sounded "ok".. Ok isn't great, but it should work for me until I can buy or build something better.

    What are your opinions of the Kappa Pro 15LF's?? These offer the extended xmax also, and I can get a decent deal on these. Do you still think the Delta Pro 15 LF's would be better?

    I need to do some modeling and research.. Thanks again. you've been a big help..

    Mag...
     
  16. random_id

    random_id

    Jan 17, 2005
    And yes, by all means, consider some other tweeter/mid options. I slapped the piezo in mine because of two reasons: 1. Man, are they cheap 2. Nothings easier than a one component crossover.

    I figure there are plenty of people out there playing with a single 15, or 12, without any tweeter. In my situation, I haven't noticed any off-axis response differences. However, my rig sits in the same corner of my house all the time (my days of playing out are long gone :crying: ). Also, any recording I do comes from the line out of my amp.

    I really think the more you play with the numbers in WinISD, the more clear these issues will be regarding what driver and how many. You also have to consider your amp. If you have a 500 watt head, then you really need to be carefull with the cabinet design. If you only have 150 watts or so, you probably don't have to be too carefull. Eminence drivers are really good stuff.
     
  17. I keep the Microsoft viewer in the same directory as the spread sheet. It's a freebie made available by Microsoft.
     
  18. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Kappa Pro has a lower Qts, and depending on box size it may or may not be a plus. Crunch them both in WinISD and see what looks better in terms of LF extension in your box. Then double the number of drivers without making the box larger and watch the average SPL go up while extension is lost. No such thing as a free lunch. As far as power is concerned, moot. If the speaker is rated at least one half of the amp's output it's enough.

    The angled in enclosure increased horizontal dispersion, but the box volume sacrificed made it a bad trade off as far as bass was concerned. The design was flawed, you didn't hurt anything by bagging it.
     
  19. bgavin: Thanks man.. I did get the viewer and have been looking over your spreadsheet. Good info .. thanks..

    billfitzmaurice: Thanks for getting back to me so quickly. Man, I'll be honest. I feel overwhelmed and lost. I do not really know what you mean by LF extension and SPL, or what I should be looking for. I am trying to learn, and I find this fascinating.
    I am having difficulty figuring out what the plot data in WinISD is showing me, and the relationship between the frequencies, db, etc.. I'm still not sure what I should be shooting for in the tuning frequency or cab volume. I have a bit of flexibility.
    For instance, for the Kappa Pro LF2 drivers, WinISD is presenting me with an initial 2.554 cu-in. cab volume and a tuning frequency of 45.82. Well, since my cab volume will be higher than that (approx. 4.0-4.5 cu-in), I don't understand what I'd be gaining or losing here.

    Before ordering my drivers, I need some advice as to which of the models I've been discussing will actually work best for bass guitar. I can see that xmax is important too, so the LF series of drivers can punch out more bass, but would they really be suited best for bass guitar or perhaps PA woofer-type setups? I won't be going with crossovers or tweeters for now, so would a driver that had a more extended range (Deltas 40-4000hz) be better than a 40-2500hz driver? I realize that most (if not all) 15" drivers don't produce highs very well at all, but I'm wondering how limited I would be going with a driver that tops out at 2500hz compared to a 4000hz upper end.
    My goal is to have a cabinet that is effecient and doesn't suck up a gob of watts without producing volume. I'd gladly sacrifice some low-end and power handling to achieve this, as I don't think I'll ever be overpowering the cab.

    Any more info is always welcomed, and I want to thank all of you for taking so much time to help.

    Mag...
     
  20. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    OK lets start here - run this speaker (or any speaker) through WinISD again. Just for kicks, change the tuning frequency to 200Hz, and have a look at what happens to the graph. Now change the tuning to 20Hz. Keep doing this until you get an idea of what happens to the frequency response when you tune either too high or too low.


    From my experience, adding more highs later on is not difficult or expensive. Correcting problems relating to distortion or lack of bottom end is a lot harder. I'd be worrying more about the speaker cone movement and lower end of the spectrum first.


    Which Delta's in particular were you looking at?. Bgavins spreadsheet makes reference at Delta a, b, Pro, Pro LF c, LFa, and Deltalites. Of these the Delta Pro 15 is the only one that's in the ballpark in terms of prefered cab size, and even then your 4cu.ft will probably be a bit too small.

    I always find Bgavins spreadsheet is a good place to start when your box diameter is already set. I sorted it for you and the following drivers are contenders for the 4.5 to 5 cu.ft range. I've left out the low efficiency sub type drivers and anything marked as being out of production:-

    Eminence Gamma 15
    Selenium WPU1507
    Lambda TD15-M
    Klipsch K-1546
    Klipsch K-1548
    Pyramid PW1572-US
    Eminence Magnum 15LF
    JBL M115-8A
    Madison Executioner 15

    Try running a few of these through WinISD and see if you start to develop any leanings towards one of them.