Speaker's natural resonance versus tuning frequency?

Discussion in 'Amps and Cabs [BG]' started by Magneto, Feb 5, 2005.

  1. This is something that I'm curious about. How does the resonant frequency affect the tuning frequency of a cabinet?
    Should one try to tune the cab closer to that frequency?
    If so, how important is this compared to trying to get a better overall even frequency response and better group delay?

    I've been experimenting with WinISD pro alpha, trying different alignments. The speaker I've been using for these tests is the Eminence Kappa Pro LF-2 (15").


  2. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA

    this is definitely a bgavin/billfitzmaurice question
  3. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Once upon a time reflex boxes were almost always tuned to the driver fs, but Theile/Small discovered that this wasn't the best practice. Now it's done only when all the rest of the driver parameters also indicate that it's the correct tuning frequency for optimum performance.
  4. The Clap

    The Clap

    Jan 5, 2004
    Scottsdale, AZ
    You can tune a box to different frequencies for a variety of reasons, don't feel that it needs to correspond to the speaker's published fs if that's not what's going to work best for your application.
  5. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    The Thiele-Small parameters are abstractions of more fundamental parameters such as cone mass, spring constant, and so forth. The particular combination fs = sqrt(k/m) is not a hard rule for how to design the cabinet. Since you are using WinISD Pro Alpha, you just need to look at the curves, and decide whether you think the speaker will sound good. Of equal importance is keeping an eye on the Maximum Power curve to make sure you are not designing a cab that will bottom out.

    Worth checking out is the Eminence 151311, sold by Madisound. A real bargain on a good driver. I just bought one, and will be building the cabinet Real Soon Now.
  6. billfitzmaurice: Thank you for your explanation. Are you saying that this isn't as important as optimizing other areas first? Is it something you would strive for if possible? Is there advantages of tuning the cab to the driver's fs?

    fdeck: Thanks for your reply. I was especially interested in the 151311 driver you were talking about. I downloaded a PDF spec sheet, but I'm wondering if it has all the needed T-S data for WinISD pro. I entered what I could, and my first impressions were good.
    It appears to be something like a Delta Pro LF , if there was such a model. Might make a good bass guitar driver. Wish I could find more info. Nothing at the Eminence site. I wonder if it's made for Madisound?

  7. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    In theory you'll get the highest efficiency if the fs andf fb are identical but again that's only if all the other parameters work with that scenario as well. In most cases fs=fb is only feasible if the box size is 'perfect', and a deviation from that, usually smaller, results in tuning the fb to well below fs for best result.
  8. The easiest way to find this, is in the SBB4 column of my spread sheet. By design, SBB4 is Fb=Fs. Look for the tuning and cabinet volume that works for you. Build it, install it, and rock.
  9. Hi, thanks for helping. I'm having fun with your spreadsheet. There is so much information in there.
    I've just been figuring out some of the differences between the alignments. I did notice earlier today that the SBB4 alignment has the cab tuned at Fs. The beta version of WinISD used a default QB3 alignment. So I guess I'm learning as I go.

    I'm still deciding on which drivers to buy. I'm seriously leaning towards the Eminence Kappa Pro LF2s, but I'm concerned about their upper frequency range and how fast it falls off. Simply trying to use a tweeter, crossed over at 3.5k would leave a pretty large hole in the freq range. The bottom end would still work fairly well in the cab size I'm considering.

    I want to thank those of you who continue to help in my numerous posts. Hope I'm not pushing too much. I value your opinions and advice, and I think I'll be able to accomplish alot with it.

  10. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Since I live in Madison, I went to Madisound to pick it up. While I was there, I asked the guy about this driver -- he says it is in regular production at Eminence, but not in typical catalogs. So it may be a Madisound exclusive, but they have sold it for years. The guy said it was definitely not a closeout or surplus item. I have one, and it is a nice cast frame driver, well packaged.

    The spec sheet is complete except that the inductance is not given. That's not too important for predicting the low frequency response. A lot of the T/S parameters are interrelated, so if you supply the bare minimum needed, WinISD will compute the rest.

    I am going to start by trying a rather small box -- 47 liters with a 43 Hz port. My expectation is that this will result in the "tight" sound favored by jazz upright players, but with good efficiency and reasonable portability. The guy at Madisound thought that a more typical box size for electric bass would be in the ballpark of 3 cubic feet.

    In terms of amplifiers, I will start with my GK MB150E combo and see if the system is loud enough. It is going to be for gigs where the MB150E is a bit underpowered by itself, e.g., big-bands. If I decide that I still need more power, then I have my eye on an ART SLA-1 power amp, fed by my outboard preamp.

    This is somewhat of an experiment. Most jazz players think that 15's in general are too boomy. But it may be because all commercial 15 cabinets are too big for upright bass use.
  11. Petebass


    Dec 22, 2002
    QLD Australia
    Imagine for a second you're talking to 4 top class chefs. Each will have their own idea as to how to make the best Pasta sauce. The end result is always quite good, but how they get there can be different. They all taste like pasta sauce but they all taste slightly different.

    That is in effect 4 different alignments of pasta sauce, and speaker designing is very similar. Each of the pioneers of speaker design had their own philosophy. Generally speaking:-

    SBB4 yields a very good transient response (low group delay). Compared to other alignments, the box is largish and the F3 is higher. But it's the "fastest" resonse of the vented enclosures. The only thing faster is a sealed enclosure.

    QB3 has a slightly smaller box size than SBB4, but it's tuned higher. It also gives a lower F3. QB3 also comes in handy when you get a speaker with a QTS that's lower than 0.2 because the design tables for the other alignments don't go that low.

    "Optimal Flat" is what the old WinISD used because it has the lowest F3 of them all. It also has the largest box size and the poorest group delay calcs.

    Now lets say you make you own pasta sauce at home. You might base it on one of the other chef's recipies but you may want to use less salt than he did.

    Here's the beauty of it. Use a standard alignment as a place to start. If it pans out that WinISD pro gives you a series of perfect looking graphs for that alighment, then go for it. But if you want to try and change the recipe a bit, that's not out of the question. Keep running WinISD projects until you find a tradeoff between freq response, Bix size, and power handling that you're happy with.

    But for all this modelling and designing, no amount of fiddling will tell you how the speaker actually sounds. Speaker design does nothing to account for the speaker's own "colour" or "taste", especially in the frequencies from the low mids upwards. You might get perfect design that still sounds like junk if that's how the speaker "sounds".
  12. PeteBass: Man, thank you for your explanation. My tired brain can make sense of that. I'll keep experimenting with my sauce. Need to order my tomatoes tomorrow. Gotta get a cab up and running.

    fdeck: Thanks for getting back to me. I'll do some more testing tonight with that 151311. Might be something I could work with. If not, I'll go with the Kappa Pro LF2 15s.
    Good luck with your project. Let me know how it works out for you, because it sounds very interesting.

  13. Well.. after alot of consideration, I ordered two Kappa Pro15 LF-2s today. I'll keep crunchin' the numbers to see what works best for the cab volume size they are going into.

    fdeck: By the way, I got some extra T-S data specs from Eminence on those 151311s. Might be helpful for you.

    01-SPEC 151311
    02-PART # 151311
    03-MODEL # 1525F8037

    05-RE OHMS 5.62 13-FS HZ 40.35
    06-LE MH .68 14-MMS GMS 52.98
    07-QM 4.80 15-CMS mm/N .2937
    08-QE .350 16-RMS NS/M 2.7959
    09-QT .330 17-VAS LTRS 302.47
    10-XMAX MM 1.80 18-SD SCM 856.34
    11-BL TM 14.59 19-EBP 113.7
    12-EFF % 5.40 20-SPL dB 99.3

  14. ESP-LTD


    Sep 9, 2001
    Looks like a very nice driver. You might want to pair that with something that has some highs, because they run out about 1500hz, and might be a little 'dark' for a lot of things (or you might just love them as-is and make a lot of walls shake).
  15. I'll try them as-is for now, with the option to add a tweeter in the near future if needed.
    I realize I'd be leaving a frequency hole between about 1500-3500 hz, but I can always rebuild these into custom cabinets with crossovers at a later date.

    As far as group delay goes with the various alignments I'm trying, I'm still a bit foggy when it comes to what to make of that graph. All of the alignments (except sealed box) have a pretty high spike at the lower frequencies. Is it better to have a high spike that falls off rapidly instead of a spike that gradually reduces?
    How important is this compared to lower tuning freq and F3?
    Well maybe someone can steer me back onto the road with this one.

  16. The LF-2 is a nice driver. Put one into 2.6 cubic feet (net), tune at 35 Hz, rock 'n roll.

    Skip the tweeter. Mate it to an Alpha 6 instead, cross over at 800 Hz. Eminence makes a crossover for you at 800 Hz.

  17. bgavin: Thanks for this idea. Man, 2.6 cu-ft sure is a small box, but all WinISD data points to an enclosure this size for the kappa pro15 lf-2.

    That Alpha 6 you are talking about is an "open-back" speaker, right? So it would require an isolated area in the enclosure?
    The Alpha 8MR wouldn't, but then again it does not have the higher range as the 6 has.

    If you happen back by this thread, is there a formula for calculating the driver volume displacement of a woofer? I know the 15 LF-2s are gonna eat up some volume and I need to take this into account. Thanks..

  18. I keep displacement volumes in my spreadsheet. Eminence doesn't publish that many, so I've whined and pleaded to get a few from their tech support.

    You can take an average and make a good guess from a range of 15" drivers. Sort the spread sheet by the driver size, then the displacement columns. I have provided averaging formulas in the top section so you can change the ranges after sorting, to get an average. Or, just look at it. That is easier.

    Remember to account for internal bracing in your volume displacement calculations. This becomes substantial when you do 100% cleating of all joints (I do). I also use an X-Y-Z internal brace that occupies volume.

    The Alpha 6 requires a subchamber, or you will blow its brains out. The volume is tiny, but has to be subtracted from the internal volume.
  19. andruca


    Mar 31, 2004
    Madrid (Spain)
    Man, am I learning a lot with this thread! Wow! Thanks so much, guys!

  20. Thor

    Thor Moderator Staff Member Gold Supporting Member

    Mag, I am buliding the following project published by Len Moskowitz

    Compact Bass Speaker Article

    This uses a Peerless 10" speaker at 4 ohms, and Len
    addresses and compromises on all the same issues
    you are working on including internal volume.

    I sent him a SASE and got a reprint of the article showing the graphs and the rolloffs of the woofer and midrange he chose to match it to.

    I acquired the drivers from Madisound as well, ( nice people, btw, very helpful ) and as soon as the weather warms, I will be building the box.

    I found the article interesting as a specialty project.
    I am going to run this box with an Ampeg B2R, which may be a bit big. Len runs 2 boxes presented at 8ohms final with
    an AMP bh420 iirc.

    Hope that reference can give you additional insight. Len published it in a speaker design magazine about 10 years ago.