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DIY Cab suitable for Eminence.

Discussion in 'Amps and Cabs [BG]' started by flacko, Feb 6, 2002.

  1. flacko


    Dec 6, 2001
    Surrey , UK
    Have read the threads on roll-your-own cabinets and decided to give it a go. I have used bgavin's spreadsheet http://www.ofgb.org/reference/Musicians Reference.xls along with http://www.kbapps.com/audiodesign/calculators/index.htm and http://xsspl.tripod.com/Audio/KeeleBox.htm to calculate a ported enclosure for an Eminence KAPPA-15LF. I chose this speaker as it looked a good choice from gavinb's spreadsheet and I have found one for a reasonable price . I have got slightly different figures for cabinet sizes and port dimensions from the 2 URL's : I intend to go with gavinb's s/sheet figures and construct a port 5.35 inch dia. in a 5.23 cu. ft. box @ 20.84 in (W) x 33.73 (H) x 12.88 (D). I play a 4 string Precision. I currently do not own a bass amp.

    Some questions :

    What technical data should I look for when choosing a mid-range driver to go with the woofer. Can anybody recommend a suitable one (ideally Eminence to match the woofer ?). I intend to mount this in a sealed enclosure above the woofer's ported enclosure and in it's own sub-chamber. I had considered a speaker up to 7kHz could be suitable.

    What resources exist for designing a crossover or, preferably, can they be purchased off the shelf. I am not technical.

    What minimum wattage of amp would I need to drive the above driver configuration in a small venue (40 ft x 40ft room size say) and be in balance with unamplified drums.

    Thanks - I've got to say that this site conatins the best info on speaker building I have found and far outshines some of the speaker makers attempts at building "tips".
  2. There are many "alignment" possibilities in vented boxes, and this accounts for the variations you find between programs. The one in my spread sheet is the DB Keane pocket calculator formula lifted from one of my books by David Weems. The formula used in the WinISD program is slightly different. The DBK formula is for maximum low frequency extension (F3), and the WinISD formula is for the flattest response, but the F3 isn't quite as low as the DBK formula.

    You can reduce the 5.3 cubic feet down to about 4 cubic feet by stuffing the cabinet with 4 to 6 pounds of Fiber Fill. The trick part is, you must keep the area around the internal port opening free of the stuffing material. A good rule of thumb is 1 diameter open space all around the port opening. If your port diamter is 3", you should have no walls or stuffing closer than 3" to the port opening in all directions. Use open weave nylon netting stretched tightly and secured one diameter away from end of the port. This will restrain the stuffing and keep it from getting too close, or coming out the port.

    I've never found the port length calculators to be anywhere close to accurate. Start with a too-long port and make it shorter. I have a 14" cutoff saw that works fast, but a hacksaw will do. You can tune the box with a computer soundcard, power amp, and a software signal generator. An inexpensive digital volt meter and a few cheap Radio Shack power dissipating resistors are required.

    The Eminence Legend B102 is a 10" mid-bass driver with a whizzer cone that has a response to 7,000 Hz. Put it into 0.31 cubic feet sealed with 1/2 pound Fiber Fill stuffing from any fabric store, and you will have your midrange. Look for the Eminence crossover #PXB2-500 at www.partsexpress.com. The Kappa 15LF is good to 2,500 Hz before it rolls off, so you have a lot of margin for your crossover point. If cost is an issue, you might consider using a piezo tweeter instead of a driver and crossover, as this would be much less expensive and less construction.

    The Kappa 15LF will be a very good match for a 4-string bass. It is optimum when tuned at 39 Hz and will provide optimum damping for your open low E string.

    [ edit ]

    It looks like the Kappa 15LF will take 350 watts maximum before overexcursion sets in. You will need a single port with 11cm minimum diameter, and about 4.25cm long. Any smaller diameter and the vent velocity will be too high, and you will get port noise.
  3. flacko


    Dec 6, 2001
    Surrey , UK
    Thanks a lot for the info.

    Cross-over looks good , hope its available here in the UK. Is it waterproof I wonder :)

    I notice the wattage of the B102 is 200 compared to the 400 for the 15LF. Does this matter? Also I still have concerns about the power I would need to drive the cabinet - I keep reading about cabinet efficiency problems in these threads. I play with an unamplified drummer in small venues. What sort of minimum amplifier watt rating should I be thinking of using to drive the proposed cabinet.

    Tuning the cabinet - now you have me worried! This is certainly beyond my ken at the moment although I think this old dog may have to learn a new trick. I had hoped to just follow exactly the generated port dimensions for the cabinet size : not good enough? Can it be done by ear (stupid question probably I know). What will happen if the port dimensions are slightly inaccurate - will I hear the difference or do you loose the advantages of building your own cab. Certainly building a sealed box would result in too larger cab for me to lug around and is inappropriate for this driver I am sure.

    Incidentally , you give suggested port dia. in your s/sheet but no port length for that dia. or have I missed something.
  4. ThunderStik

    ThunderStik Guest

    Jun 25, 2001
    Claremore OK.
    I will take a stab, I dont think the wattage difference will be a problem as the "10" will only be getting the power for the highs via the crossover. The 15 will recieve the bulk of the power as lower f's require more power to generate. This i would call fairly efficient cab, myself I would use something in the area of a 500 watt head at least. I believe your cab would be an 8 ohm cab so you will need to find a head that can supply at least 350-500 watts at an 8 ohm load but thats just me. You can use lesser powered heads but you wont have the nuts when you need it (headroom). All your worst fears about tuning a cab are correct, If its not tuned properly you will loose the advantage of having a ported cab. The reason for no port lengths is the the length depends on the driver and the volume of the box. The diameter is given so you dont get "chuffing" or power compressions inside the box---really it will sound like wheezing through the port , so you need a large enough port area to keep the air speed in the port tube down low enough to avoid making your cab sound like it has asthma.
  5. You will need 350 watts of clean power to drive the Kappa 15LF to maximum output. I'd think an SWR 750 would do just fine and would leave you with extra headroom. A 500 watt amp would leave you nearly 50% in reserve. The high end (or piezo tweeter) will draw very little power compared to the 15".

    You cannot tune by ear. Perhaps by eye, the cone motion is the least (almost completely still) at the tuning frequency. Borrow a meter and a friend who can use it. Don't go to all the work of building it, and not tuning it. It is easy to do.

    I sized the port at 11cm with a 4.25cm length which will keep the port velocity below 0.010 Mach. I doubt you will hear anything from this port, as you'd have to be at absolute maximum wattage, low E, and playing by yourself. You will feel the breeze from the port, though. Don't fart in front of your amp, cuz it will blow right out into the audience.

    [ edit ]

    The Kappa 15LF isn't suitable for electric bass in a sealed cabinet. The size is only 2.27 cubic feet, but it is down -10dB (half as loud) at low E.
  6. ThunderStik

    ThunderStik Guest

    Jun 25, 2001
    Claremore OK.
    bgavin, is mach .01 the number to keep under?
  7. ESP-LTD


    Sep 9, 2001

    Is there any Eminence driver other than a 15" Kilomax that would do a reasonable job for a 5 string?

    I thought the 15 Delta LFA looked "not bad".
  8. Thiele specified 0.0045 Mach as the number that will give no audible port noise. This is a big port that needs lots of duct length. The size of it adjusts the internal volume of the cabinet, so as the duct gets longer, the cabinet volume shrinks. In short, it's a pain in the butt.

    Keeping under 10% MACH (0.010) won't be heard, especially in a live environment. Both of my 1x15 subs run at 0.010 and they are fine.

    The vent velocity rises rapidly as the frequency approaches the tuning frequency. If you are tuned at 39 Hz, and your lowest note is 41 Hz, you will approach maximum velocity, but never reach it. Robert Bullock's DOS BOXMODEL program shows a nice picture of this.

    Link to DOS BoxModel on my Site

    To use the KAPPA 15LF.SES file, you have to rename it to BOXMODEL.SES in the directory where DOSBM.EXE runs. This program is a bit klunky to use, but works very well. The only bug in the program that I am aware of, is comparing the SPL of two drivers that have different sensitivity ratings. The program displays them wrong, relative to each other.

    ESP-LTD, download my spread sheet and sort the DRIVERS tab by the "USE" column. I have drivers color coded for 4 and 5-string suitability. My absolute favorite so far is the Adire Maelstrom 18" in 5.0 cubic feet, tuned around 25 Hz. It will hit 92 SPL with 1w/1m, which is awfully good for a real sub.
  9. flacko


    Dec 6, 2001
    Surrey , UK
    I’ve been away reading up on cabinet design - Loudspeakers for Musicians - Vivian Capel, Great Sound Stereo Speaker Manual - David Weems and Eminence Enclosure Design. I’ve now got a little more idea of what the cab design gurus on this site are talking about! I have come across a cabinet design I would like to go ahead with but I am concerned about its shape. It is a cabinet with a total gross volume of 162 litres containing a Kappa 15LF tuned to 39Hz in a 153litre reflex sub-enclosure. Another sealed sub-enclosure (11" x 13") is in the top right corner of the reflex cab containing the Legend B102. This sealed box extends into the main cabinet approx. 8in. The overall cab size is worked to golden ratio but does the resulting non-simple box shape of the reflex cab, caused by the insertion of the sealed cab in the top right corner, affect the volume requirements of the reflex cab at all or I can I go ahead with the standard volume/tuning freq. design calculations on winISD. My design and the one in the Eminence book for 15+10 bass cab are similar but my reflex enclosure is slightly larger. Any help would be greatly appreciated.

    Also, once the cab is built, I am afraid of knacking the 15LF speaker by putting a low frequency through it. Should I be concerned about this, and if so should I consider an Infra-sonic filter of some type or is there a better method. Do amps usually have low frequency filtering on them to stop you blowing speakers. Would the lows on a 5string bass cause the 15LF to fail? Incidentally I intend to take up bgavin’s recommendation of PXB2-500 crossover.
  10. Don't forget Vance Dickason "The Loudspeaker Design Cookbook". This is essential reading. Weems is excellent, and I've had his books since 1978. Dickason translates the Thiele-Small theory into usable material for the reader.

    Don't be. Low bass cabs don't suffer from shape induced problems like HiFi cabs do. Build your cab for portability and function. The Golden Rectangle is great for pleasing the eye and reducing internal high frequency reflections... but not necessary for grunt bass gear.

    Optimum for the 15LF is 148 liters. The correct subchamber internal volume for the B102 is 8.78 liter. Add 7 liters for the 15LF driver displacement and a little more for your bracing material. Then add 13.5 liters for the volume occupied by the subchamber (19mm walls). This is 168.5 liters gross internal volume without compensating for the bracing material.

    You can make your enclosure acoustically smaller by about 30% by adding 3.56 kg of fiber fill stuffing to your cabinet. Get this at any fabric store. You can reduce the total volume of your enclosure by 34 liters using this trick. You must rig some open wave nylon netting around the internal port opening to prevent the fiber fill from blocking the port. Stuff the enclosure with the fiber fill and distribute uniformly. The port must have 1 diameter distance between the opening and the wall. Turn it 90 degress if necessary, or use two ports.

    You can reduce the size of the B102 subchamber from 8.78 liter to 6.75 liter using the fiber fill trick. The ratio is 117 grams of fiber fill per liter. I'm converting from US to metric, so bear with me if I screw up the math. The fiber fill ratio is 1.5 pound of fiber fill per cubic foot of enclosure volume.

    Everybody should be concerned because infrasonics will trash speakers quickly. Yours is tuned at 39 Hz, which means it will unload quickly below this frequency. Cone movement will be almost at a stand still at 39 Hz (D#) and will increase rapidly as you move down toward low B. If you are a 5-string player and have a thing for open low B, you need to watch the cone movement and listen for farting.

    This rig will be very nice for a 4-string bass. It will give you about 96 SPL, or the same as an Acme B4-II cabinet. Remember the Acme is a 4x10 and moves more air than a single Kappa 15LF. The piston area of a 15" driver cone is about the same as (2.5) 10" drivers. You will probably need a second Kappa 15LF cabinet, without the B102 and crossover, if you play larger venues or have a loud guitar player. That will take you up to 99 or 102 SPL for the lows, depending on how you arrange your cabs.

    I've been trying to play using a single 1x15 sub and a 2x10 JBL bi-amp rig, but I've run out of gas in the lows. I've started taking my 2nd 1x15 sub so I can keep up. Mine are much, much worse, only 89 SPL so I have trouble keeping up. Using the second sub makes a ton of difference both in thump and keeping up with Mr. Loud.

    Always keep in mind that it might be cheaper in the long run to find a used D410-XLT, than buying all the parts and all the hassle of building your own. If this is a labor of love, go for it. If you are trying to save money, buy something instead because you get instant gratification and you can usually audition it first. Building is a LOT of work.
  11. flacko


    Dec 6, 2001
    Surrey , UK
    Well, like any fool, I've totally ignored your advice that cab. building is a lot of hard work and gone for it.

    Hmmm..... you're right, it is hard work but it's fun.

    I have the cabinet finished, covered and everything is ready for me to load the speakers, glue the back of the cab on, wire up the speakers and get the port length right.

    A couple of questions for the cab gurus here :

    I was going to use an 800Hz passive crossover in the cab but I have now ordered a Laney B1 which allows me to bi-amp with an active crossover in the amp of 150Hz. I would like to dispense with the Eminence passive crossover. Sounds sensible? If so , anybody want a psbx2-800 : going cheap.

    Also, I have a digital multimeter to tune the ports - I'm using 2 tubes at 3 inch dia. by 4.5 inch long and am gradually going to chop them down until I get the 39Hz I want. I was going to use bgavin's volt method but I cannot find a 100 Ohm 25 Watt power resisitor. I am now going to use either (or both) the current and impedance method and look for the 2 peaks/dips. If I use these methods how do I connect the meter - across the speaker output posts at the back of the amp or in line in one of the speaker cables. And I am right in thinking that, for a given cab size and port dia., shortening the ports will lower the resonant frequency?
  12. flacko


    Dec 6, 2001
    Surrey , UK
    I'm not sure what AMP or Current range to select on the multimeter either. In fact I'm stuck.
  13. Don't forget you can series / parallel lower wattage resistors to make up 100 Ohms @ 25 Watts.

    Take 4 of, 470 Ohm, 7 Watt or 11 Watt resistors and connect them in parallel. The total load is 117.5 Ohms at 4 x 7 = 28 Watts or 4 x 11 = 44 Watts. You then need to pad that setup to bring the total resistance down to 100 Ohms. Take a 680 Ohm resistor (4 or 11 Watts) and connect in parallel with the 4 x 470. You will have a 100 Ohm load that will handle at least 25 Watts.

  14. flacko


    Dec 6, 2001
    Surrey , UK
    Thanks a lot : a great help. Hadn't thought of that!

    I was hoping though to get out of using resistors and attempting to measure either the current or resistance for any given Hz using the multimeter. Is this possible and where would I connect the multimeter to take the readings. I will have the back on the cab at this point - can I take the readings across the amps speaker connections?
  15. Well, I dunno. Measuring resistance directly in a dynamic situation is really difficult. Measuring AC current is OK (meter goes in series with the speaker). By far the easiest is to measure the voltage drop across a resistor. You put the resistor network in series with the speaker then put the AC voltmeter in parallel with the resistor network.

    Assuming (hoping) the drive from the amp stays constant, altering the tuning will alter the voltage drop over the resistors. Now, I don't know how to tune a cab so I don't know what to look for as a response to altering the tube length. Bruce Gavin does and he'll doubtless help you there. But I've described the basic principle of measuring the voltage drop over (in this case) a bank of paralleled resistors.

  16. The 100 ohm value is not critical. Higher is OK, but will absorb more power to get the same loudness from the driver.

    The intent of the resistor is to drop the bulk of the output voltage across the resistor. This keeps the amplifier operating in a constant-voltage mode. Your DVOM reads the voltage across the speaker terminals. The more stable the amplifier output voltage, the more accurate your reading.

    You will be shortening both your port tubes and coming UP in frequency. Starting with too-long tubes will put your tuning frequency lower than where it should be. It will RAISE as you shorten the port tubes.
  17. flacko


    Dec 6, 2001
    Surrey , UK
    Thanks guys. I used my multi-meter and read the ac volts. I could not see the peak/trough below the box frequency as I had started with too long a tube length and it was falling below the useable range of the driver. This was with 2 x 3 in. tubes at 4.5 in long.

    I decided to get the box frequency by sight and found that sticking a small square of sticky white paper tape onto the cone and shining a light on it showed easily when the cone's motion was at it's least. I chopped the tubes down .5 in. at a time until I got the 39Hz I was looking for.

    bgavin - I found with a fully stuffed cab (1 Lb per cu foot) that the resonant peaks were much less than without the stuffing : they altered the tuning by about 2 Hz. I prefered the sound from the tone generator without the fully stuffed cab so I went for a middle road of approx. 1.5 inch stuffing on the rear wall of the cab only (internal!).

    I have sealed the ports now into the cab and all that remains is to glue the back on.
  18. Stuffing a vented cab 1 pound per cubic foot is putting yourself into wildly variable territory. This technique is usually done with sealed boxes.

    But... if you are careful to use something like nylon open web netting, you can keep the area surrounding the vent tubes free of stuffing material. If the rest of the box is stuffed 1lb/foot, it will make the box acoustically larger. The trick is keeping the material away from the vent. It is strictly trial and error at this point.

    If you are a 4-string player, the 39 Hz tuning will protect your drivers but won't have quite the tendency to make port noise. The 39 Hz tuning is below your usable (4-string) range, which means the port will never develop maximum velocity. The group delay numbers are the worst at the tuning frequency, again this is below your range.

    I'm sure you will have a very punchy cab when you are all done. Please report back on the sound. It is always a revelation when a bassist hears a killer cab for the first time.

  19. flacko


    Dec 6, 2001
    Surrey , UK
    Yes - I constructed the open weave netting inside the reflex cab as you suggested to keep the stuffing one diameter clear of the ports in all directions. It did lower the tuning of the box but I found that the port output was not as great once the ports started to come into action (around 50 Hz ish). I tested this with a cigarrette paper stuck onto the cab front and hanging over the port. The stuffed cab got it flapping around a bit - the unstuffed cab damn near blew it across the room.

    The sealed box with the B102 in it did not sound at all good without stuffing.

    I found also that ensuring the reflex chamber was airtight made a great difference. At one point in testing I had the Speakon connector panel just screwed onto the back of the cab. When I also sealed it with vinyl tape the output difference was noticeable.

    The cab is constructed from 1 inch Baltic ply which I have re-inforced with some hardwood strips at random points on the inside panels. I don't think I'm losing much energy now through panel resonance. This made a small but noticeable difference to the "punch" of the Kappa 15LF.

    The cab is looking great - it should be finished this week and I'll borrow a digital camera and post some pics. I'll report on the final sound as well once my new bass amp is delivered.

    Your help has been invaluable. Thanks.
  20. Way cool.

    1" baltic ply... yikes! I suspect that probably weighs like my 3/4" MDF does... ghastly heavy. Each of my subs takes an entire 4x8 sheet of MDF, which weighs 98 pounds. Add driver, grille and hardware... and I move two of these things 3x weekly. In and Out of the truck...

    I can hardly wait to here the official review. There is a good reason for selective home-building, and you are going to hear it from the Kappa 15LF.

    I'm very curious to hear your opinion on the B102. My JBL E110 add a tremendous amount of "yellow" coloration to my rig and it is very noticeable running CD program material. The tone of the subs is fine, but I think the E110 are going to go, so I'm very interested in the B102.

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