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Cab volume confusion: Eminence Delta15

Discussion in 'Amps and Cabs [BG]' started by Rockin John, Feb 10, 2003.


  1. When I posted a thread on the subject some while ago, there was much consternation about me housing this driver in a (approx) 110 Ltr cab. WinISD returns 556.8 Ltr @33Hz. By frigging the Vent figures I can achieve .215mm circular vent x 19mm long giving a .06 match (green).

    Now, Eminence's WWW recommends housing this driver in a vented enclosure, between 106 Ltr and 177 Ltr = 3.75 to 6.65 cu ft. I don't understand TS parameters, but the ones on WinISD and the Eminence WWW seem to be the same, other than power handling: 300 Watts for my driver; 400 for the latest model.

    It's clear from WinISD that I'm not going to get a flat plot with Eminence's recommended cab volumes. I'm OK with that. But I'm now confused. I've cut the wood for a 110 Ltr box according to what Eminence told me to do. They also told me to cut a 160mm vent x 19 wood thickness (not yet done). I'm now playing a 5 string so I'd appreciate help with reworking the the cab dimensions and some explanation abotu what's going on.

    Thanks V much.

    John
     
  2. TRU

    TRU

    Apr 12, 2002
    Northern Europe
    By default WinISD gives you the box size that gives ideally flat response. As you can see, the size of such box is not realistic. The box size that Eminence recommends is a compromise between box size and responce. I'd go with it.

    And a vent with 0.215mm cross-section is not going to work. You'll need at least 100mm and preferably more. Such vent needs to be _long_ to achieve 33Hz tuning. Welcome to the joyful world of cabinet design! ;)
     
  3. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    I have hear the rule of thumb mentioned that your port diameter should be at least a 1/3 of your driver diameter to control chuffing (too much wind trying to pass the port at tuning frequency). One solution to using a port that is too small in diameter is to tune the box below your lowest note, so that you never really get to the tuning frequency and so it isn't such an issue with port velocity.

    I'd say build it as Eminence said and if you don't like the sound with a 5 string, sell it, learn from it, and build your next one differently. You'll eventually end up with something you want to keep.
     
  4. Hello, guys, and thanks.

    First off, although I'm an electronics techie, I'm a cab design novice. Whatever I say, therefore, will almost certainly be naive!

    Clearly, the approach by Eminence will not yield a flat reaponse: they obviously know that, too!! Following from that, I guess, Eminence must have decided that the response of the Delta15 in that volume is quite acceptable. As you say WinISD gives a flat response, it is possible to generate non-flat responses by messing with the parameters.

    Also, guys on these boards figure that theoretically ideal cabs do not usually make good sounding cabs: smaller than ideal boxes usually sound punchier and tight. That leads me to wonder how the Delta in their box would sound. Further, I have used this driver in a cab that I estimate is about 80 or 90 Ltrs and it sounds fine with plenty of punch. It is, admittedly, sadly lacking at low B.

    If theroetically ideal responses are what's reguired, the cab deficiency could made good to some degree by turning up the bass control on the preamp a bit!. Likewise, as the heavier strings travel further when struck, their output tends to be higher so offsetting cab deficiencies once again.

    Where all that leads me, I'm not sure, so do you think I can trust WinISD to give me the correct figures? Or should I build as Eminence say and just use it?

    John
     
  5. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    I'll step off the deep end here, hoping that Joris or BGavin will give me yet another lesson ...

    I don't think that the width of the string pass will do much for you. I suspect if you were to look at the area under the curve of 35hz vs 350hz you'd probably find that the 350hz signal had more area under it and was hence "bigger". Also, the electronics in your bass may not be quite so flat at low frequencies either. I'd say at best case, it's a break even deal.

    The only problem with adjusting the EQ/power is that I don't think WinSD deals with excursion; once the cone tries to travel farther than the length of the voice coil (XMax), it will stop acting in a linear/predictable manner and distort or try and self-destruct in some cases. As far as "tight" sounding bass, one of the big issues there is how well the motor (magnet structure) controls the cone; this is reflected in Qts (low is better control).

    The Eminence makes lots of drivers for different applications, and this one is not the top of their line. The Xmax is 2.7mm which means that it won't go very far before distorting; usually a low Xmax means it's more suited for PA use where it deals with a mix instead of big low waveforms from a bass guitar. For example, a lot of the 15's used by Avatar have almost twice the excursion, and my 12" JBL subs have about 5x as much. The Qts is pretty high at .49 so the cone will not stop/start quite as cleanly as one with a bigger magnet and tighter suspension (although that's also about like my JBL's ).

    I guess what I'm getting at is this would make a decent floor monitor or PA main, but it just isn't high on my list for a bass guitar project. That being the case, I'd do what Eminence said and if it didn't make me smile, I'd sell it saying "just like Emiinence said to do it" and try again. All that being said, you may just love the sound; I used a couple of Altec PA 15's for a year or two in sealed boxen and was very happy with a 4 string. I've made a few cabs over the years and I think I found something to like in each of them. I guess I view making cabinets as successive approximations towards a goal, and no longer expect any single project to satisfy me completely.
     
  6. Rockbobmel

    Rockbobmel Supporting Member

    John, FWIW, If I were bulding a 15 box, I would copy a Sonic, or Peavey BX 115. The Peavey box is taller, wider, and shallower, but you could math it out so it shapes the way you want. The Peavey handles a B string (I use one at practice) extremely well, and all your notes are well defined and smooth.
    I'm sure you could find one in a store you could measure.
    Also, I found an interesting article on www.londonpower.com about "de-tuned boxes" meaning bigger than the figures say, so you get the most out of the speaker.
    But I really would check out the Peavey thing first.
    Good luck.
     
  7. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    Interesting article although a little short on detail.

    Basically, the box is 2x the normal size and has a "larger port size than is customary."

    "Our 112 is bigger than most 212s and has more bass output than the average 412."

    "Some "real" speaker designers will tell you this simply cannot be, but their thinking is founded on the constraints of traditional design. "


    I'm not a "real" speaker designer or even a gifted amateur, but I must admit that having read it I am still bound by the constraints of traditional design.
     
  8. Rockbobmel

    Rockbobmel Supporting Member

    I think Kevi's major point is that it will utilize any driver to it's maximum. Thus "non driver specific" theory. That way they can make only one cab for each config. Of course, we bass players want the portability of a brief case. Myself, I would opt for a smaller cab too. But not wanting to take a chance of a flubbed project, I would do the coycat thing.
    Also Parts Express's "Dayton" speakers come with box plans for that driver. My drummer/PA owner got the 18s, and the boxes are about a 4-10 size, but a little deeper.
     
  9. Your points are appreciated.

    I agree on the suitability of the Delta 15, although Eminence bill this driver as suitable for bass guitar. If I were starting afresh and were choosing an Eminence driver I would select the Kappa 15LF. Unfortunately I already have the Delta15. I was given the speaker and would like to use it if possible: money's short, presently, and £75 for the Kappa's too much at the moment.

    I never thought of cone excursion, to be honest.

    Perhaps I should just give up now. But.....I could build the cab as designedby Eminence then if ££ allows, buy a Kappa to put in it. Or is that naive, too?

    John
     
  10. Eminence bills this driver as a "woofer" and advises using it from 50 Hz and up. (Read: PA system).

    Put into a small box, the performance of this driver is awful. It gets a big hump at the 100 Hz area, so it will have the big boom that many players prefer. This is a taste issue, and up to the individual.

    The way to avoid the huge cabinet problem is by using isobaric construction.

    A clam shell isobaric configuration would let you cut the cabinet volume back to 164 liters tuned at 40 Hz as an SBB4 alignment.

    The downside is the cost and weight of the 2nd driver. The advantage is the reduced cabinet size, and the vastly improved group delay numbers. The Delta 15a in the WinISD alignment gives ghastly (25msec) group delay numbers.

    I have many of the Dayton drivers in my spread sheet. Several look very promising.
     
  11. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    For what it's worth, I've had some wierd and wonderful box designs pop out of WinISD, but especially with drivers that I have added to the database myself. Last night it tried to tell me that a 2x10 cab with P.Audio drivers should be 7 litres - not possible.......

    I then tried it again but with P.Audio drivers that were in the existing database and it spat out 125ltr - much better. But in comparing the specs to the P.Audio website, they were actually quite different? Who should I believe - P.Audio (who may cheat on their specs to sell more speakers), or WinISD (freeware and therefore worthy of caution)?
     
  12. I've put these Delta 15's in an old Kustom tuck and roll cab, and they did OK, for what it's worth.
     
  13. WinISD will let you do data entry in several different formats (metric, imperial, etc). If you get something really out of whack, go back and check each field (display parameters) and see if you are entering a Vas in liters, but the field is expecting Vas in cubic feet.

    As for accuracy, WinISD does not appear to work correctly for full power plots, but only for 1w/1m. Displacement and thermal limitations come into play under full power. As I understand it, T/S data is really accurate only at 1w/1m, but it does provide a very accurate apples-to-apples comparision model for the designer.
     
  14. Well, Bruce, I'm not going to take you - the master - to task over speaker issues but I quote from Eminence WWW (looked up this morning) regarding the Delta 15:-

    "For all high power applications including bass guitar".

    Not making an issue of it, it's just what I read. I'm sure the Delta's not the best choice for BG for various reasons but they say the Delta is suitable. Anyway....

    Using WinISD I plotted the Delta 15 and the Kappa 15LF under identical cab conditions: 110Ltr; tune to 32Hz. The delta shows a (approx) 1.6dB hump @ 100Hz compared with the Kappa, a (approx) 5dB droop @ 35 Hz against the Kappa and is approx 5dB down @ 30 Hz. The Group Delay is very different between the two, but that statistic means nothing to me!!!

    I guess what I'm coming round to is that the Delta in the 110 Ltr cab is not theoretically ideal, as I understand the issue. Whether that makes a bad bass guitar cab is another matter, and is subjective, as Bruce says. Considering there's not so much difference between the two curves as I see it, I reckon it's worth building the 110Ltr for the Delta.

    So, could someone please guide me as to how I should design the ports to tune that cab at 32 Hz?

    Thanks.

    John
     
  15. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    Converting 111l to 3.91 cu ft, Perfect Box says:

    4" port 5.56" long
    or
    4.5" port 7.45" long
    or
    5" port 9.6" long

    Keep in mind that formulas can get you close but final tuning may require some fiddling. I found Parts Express has some adjustable ports for $15; there is probably something comparable on your side of the water.

    I reckon it's worth building the 110Ltr for the Delta.


    That's how it starts ... then you start buying parts "on sale" and in quantity ... then you get curious about those T-S parameters ... and the drivers start getting more expensive ... and then your standards get higher ... then you start measuring commercial cabs and wondering what they were thinking ...

    I look forward to your future posts about your projects. Let us know how you like it.
     
  16. Thanks.

    There is another avenue I could go down. I've found a supplier of boxes minus drivers. I can get a 110Ltr Bin fully finished, handles, corners, etc for £65. I'm very tempted.

    The tuning is a slot at the bottom of the box going the full width of the cab. Without exact dimensions I estimate the slot to be 560mm x 50mm. Before considering the cab I'd need to be sure I can tune it. Is ther any guidance, please, on how this might be done?

    Thanks.

    John
     
  17. flacko

    flacko

    Dec 6, 2001
    Surrey , UK
    Either Maplins or Wilmslow Audio will have whatever you want I'm sure. It's tricky getting flanged plastic port tubing over 110 mm dia though.

    Wilmslow Audio are especially helpfull. I ordered my Kappa 15LF and B102 drivers through them plus castors, handles etc.
     
  18. Here are some plots to visualize your question.

    Link to Delta - Kappa SPL in 110 Liters at 32 Hz

    Link to Delta - Kappa Group Delay in 110 Liters at 32 Hz

    The group delay is important, as this is a huge factor in what bassists perceive as "mud". Tuning down the Delta to 32 Hz moves the GD peak below the operating range.

    Cone excursion peaks at 70 Hz, at about 6mm under 300 watts input power. The Delta 15a has a 22mm maximum excursion before damage, so you apparently won't be over driving the cone at 300 watts in this box. You will be driving it into distortion at much less input power. The full 300 watts will incur distortion from 135 Hz and lower because the cone movement will exceed the 2.7mm maximum linear excursion (Xmax).

    A net internal volume of 110 L shows a vent diameter of 7.62 cm, and length of 6.56 cm. This is only a theoretical size, so I would start with a longer vent (plastic pipe) and cut it back. A DVOM for tuning is a must. Any computer sound card, a freeware tone generator, and a few resistors will be all you need to measure the tuning.
     
  19. OK Bruce, and thanks V much.

    The max power I can pump into 8 Ohms is a theoretical 117 Watts. And with the Delta in a (approx) 80 ltr cab at present, there's plenty of volume already and I'm running about 3/4 power. I suspect the SPL will be massively down @ B and E strings. Even so, I've used that setup (incl outdors) with no worries on the volume. So, the chances of driving the Delta past Xmax are reduced: is that sensible?

    Are there any thoughts on the pre-built cab I spoke about?

    John
     
  20. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    I believe the critical figure will be the surface are of the port; compute that and then you can compare it to one of the port sizes mentioned; for equivalent surface area, the length should be equal as well.

    My guess, is that you'll find it is actually a rather large port and tunes the box pretty high (50-80hz). The problem with ports like this is that tuning them is a construction job, and not just trimming a tube and sliding it in the hole again.

    On the upside, your resale value will be higher with a commercially built cab unless you are very handy with tools.