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Calling bgavin....

Discussion in 'Amps and Cabs [BG]' started by Bigwan, Jan 9, 2003.


  1. Bigwan

    Bigwan

    Feb 22, 2002
    Ballymena (hey)
    Hi bgavin (and anyone else who's interested!).

    Some time ago you helped me out with the design of a couple of bass cabs using Eminence Kappa 15 LFs. I haven't quite got them finished yet (soon though! Can't wait!) and I've already started to plan my next project...

    I want to build a cab suitable for standalone operation based on the Bergie HT322... ie 1x12", 2x10" and horn. At the minute I'm considering using an Eminence Delta 12 LF (8 ohm, in a 2.65 cu. ft. enclosure), 2x Beta 10s (16 ohm, each in separate 1.5 cu. ft. enclosures) and an APT:80 tweeter with px2:3k5 cab ready crossover (running the Betas and tweeter with the crossover and the Delta 12 LF full range in parallel to produce a 4 ohm cab...).

    Do you think this is workable/useable? Any help/criticism would be greatly appreciated!

    Cheers

    Ian
     
  2. The Delta 12LF has the tightest response in 2.3 cubic feet, tuned at 45 Hz. This will be fine for a 4-banger, but not acceptable at high power going below 43 Hz. You didn't mentioned being a 5-stringer or not. A larger cab will get you a tiny bit more bass extension, but at the cost of MUCH higher group delays (read: mud).

    I would not match this driver with a Beta 10, but instead with a B102 10". The sensitivity is virtually identical for the B102 and the Delta, so they will cross over smoothly. A pair of Beta 10 has much more output, and will produce a big hump centered at 100 Hz. The Delta 12 will sound wimpy by comparision because it is not as loud.

    The Delta is a fairly high Qts (0.42) driver, so tuning is going to be more critical. The Beta is also a very high Qts driver, and requires a very large cabinet to achieve any bottom, so I'm speculating the Delta + Beta combination will sound thin in the bottom.

    The B102 doesn't have anything below 100 Hz, so I'd consider using the pxb3:3k5 3-way, non-cabinet-ready crossover. The down side is, this crossover does not have the tweeter attentuator control, and would make the entire system 8 ohms.

    If you run the Delta and B102 in parallel, you will have a 4-ohm system, where the B102 contributes very little to the sound below 100 Hz. But, the tuning for the B102 is also 45 Hz in 0.6 cubic feet for the tightest bass. It will be safe to run the B102 with a 4-string bass. Running parallel will boost the mids by +3dB above 100 Hz because both drivers are contributing to the output. The Delta will eventually roll off as the frequency increases, and only the B102 will contribute until the tweeter cuts in. IMO, the B102 is also a better quality driver than the Beta.

    The 10" driver will start beaming (becoming directional) around 1100 Hz, even though it will respond well far higher than that. By 1600 Hz, 45-degree off-axis response will be -6dB down, which is significant beaming. Crossing over to the tweeter at 3500 Hz will restore some of off-axis response, but there will be an off-axis 'hole' between 1600 and 3500 Hz where the B102 is directional. If the cab is facing straight toward the audience, I doubt it will be missed. These are harmonics, not fundamentals, so I think beaming above 1600 Hz is splitting hairs for bass.
     
  3. Bigwan

    Bigwan

    Feb 22, 2002
    Ballymena (hey)
    Hi bgavin

    thanks for the help...

    I have one other question - what is the most suitable Eminence 10" driver for use in a 2x10, 3x10, 4x10, 6x10 or 8x10 format...

    Many thanks again

    Ian
     
  4. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    Now I'm curious. The Delta 12LF is rated at 500w electrical with 4.8mm Xmax and 29mm XMech.

    How much can it take at 31hz before it takes damage?

    I'm about convinced that flat to 30hz is not going to happen for me. I can live with less low end but it's silly for me to build a box that I will fry.

    How do commercial manufacturers deal with this; tune the box at Fs and hope they don't blow too many drivers on low notes? Tune the box low and live with mud?
     
  5. Bigwan: most suitable for what? Lows, Highs, Loudness, Size?

    At 32 Hz, the Delta 12LF is good for 26 watts before it exceeds Xmax. In a vented SBB4 alignment, it will take the full 300 watts and remain under the 29mm Xmech, but will be well in distortion after it passes Xmax.

    Vented cabinets unload rapidly below the tuning frequency, and I would not operate it below 45 Hz at anything more than modest power. You will have to watch the cones and listen carefully below 45 Hz.

    Low tuning does not by itself generate mud. Lengthy group delays or sloppy cone control is the cause of mud. Group delay hits maximum at the tuning frequency, so a box tuned lower than the lowest operating frequency is less prone to mud, as a general rule. Efficiency is paired with Fs, and the lower down Fs goes, the less efficient is the driver. Also, a smaller port can be used without fear of chuffing because the tuning frequency is never reached. My subs are tuned at 20 Hz, but I only have 4-string basses that hit low E. However, my DBX 120a synth does get down to 26 Hz when I enable it.

    Look for a low Qts driver <= .370
    Look for a high Bl driver >= 18.0
    Look for a high BL:LE ratio
    Look for Fs <= lowest usable note

    Depending on the driver, the group delays may be severe or moderate. 25msec is just awful, and under 12msec is great. Sealed boxes are nearly perfect with only a few msec delay. This is why sealed boxes sound "tighter".

    A low Qts driver is usually a high quality (read: expensive) driver. One exception is the Magnum 15LF. JBL drivers are very low Qts, very high priced, and have big magnets and precision engineering. Low Qts drivers have better cone control, and this often goes hand-in-hand with a high BL number.

    Adire engineering has a good explanation of how transient response is directly related to the inductance of the voice coil. A lower inductance is a faster responding driver.

    The SBB4 vented alignments tune at the driver resonant frequency. This provides the lowest group delay numbers and tightest transients available in a vented box. This also requires a somewhat larger box and more rolloff, from a higher frequency. This is correctable with EQ, and is my personal alignment of choice.

    IMO, most manufaturers are simply trying to provide the loudest possible box, with the least amount of bass response short of the buyers complaining about it. Again, IMO fidelity takes a very far back seat to the ability to make lots of noise.

    FWIW, I like the Omega Pro 12 a whole lot more than the Delta 12LF. A better driver, all the way around. SBB4 alignment is tuned at 39 Hz in 1.23 cubic feet, less than 12msec delay at 31 Hz.


    Link to Omega Pro 12 Plot
     
  6. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho


    Because ... you will see excessive cone motion, and distortion as it passes Xmax?



    So, in fact the lowest notes are probably exceeding Xmax, and the user is probably just not noticing it until they get to Xmech or the voice coil catches fire?



    In reviewing the Eminence site, they suggest the Omega from 65-1.2k (although it has the best excursion and magnet structure). The Kappa Pro 12 has an Fs of 37; would that be a better 5 string choice than the Omega even though the excursion is 4.8?

    Can you point me in the right direction of tools that could show me cone excursion vs frequency for an SBB4 alignment?

    My ultimate goal is probably a pair of 8 ohm boxen, driven up to 275w max each (probably more like 200) that will not make a mess of the occasional note between 35-40 hz.

    (I saw a 4 0hm JBL 2226 recone last night on e-bay and almost snagged it.... I will probably regret that, but I've carried enough 15's).
     
  7. Bigwan

    Bigwan

    Feb 22, 2002
    Ballymena (hey)
    Hi again bgavin...

    My question was a little vague! What I'm really wanting to know is what 10" drivers will give me a loud, efficient cab that goes low enough to handle a drop D tuned 4-string and not need a 5 cubic foot box per driver? If I was to build 2 2x10s, a 4x10 or 6x10 cab with an HF horn, similar in dimension to the SWR Goliath series or Nick Epifani's cabs, what would be the best Eminence 10" driver to use to get a nice, tight, punchy sound that will cut through 2 Marshall half stacks and be efficient enough to do so using 500watts...

    Bear in mind that I think my first-production-run Ashdown ABM 1x10" combo loaded with a Celestion BG10T 150watt sounds good!

    Or do I have my head in the clouds again? ;)

    Cheers

    Ian
     
  8. Link to Omega Pro 12 Excursion

    The Omega Pro 12 driver exceeds Xmax in two areas. The first is below the tuning frequency. Note it does not reach Xmech (mechanical limits) until 25 Hz or thereabouts. The more important exceeding of Xmax is the 2nd impedance peak around 65 Hz. Note the excursion does not come close to Xmech at 65 Hz, even at full power. Distortion will be up, but damage won't be a problem.

    Other than the B102 model, I'm not much thrilled with commercial 10" driver offerings. The B102 is not suitable for use below 125 Hz due to the amount of rolloff it has. This driver is down -15dB at 41 Hz, which is pitiful bottom end, IMO. I expect the B102 to sound the same as the Delta 10 used in the Avatar boxes from 50 Hz and lower. Many players find this entirely suitable.

    The plot below shows how the Delta 10 responds in an EBS alignment used by the Avatar B410 compared to the SBB4 alignment used by the B102. The EBS alignment extends the bass response with a flat shelf, hence the EBS naming. Group delay is still moderate here, peaking at 11 msec at 65 Hz.

    A B102 is 35% more expensive than a Delta 10, which I would expect, as the B102 is a lot more driver.

    Link to Delta 10 - B102 Gain Plot


    If you tune the B102 and Delta at 65 Hz, in 1.08 cubic feet, the EBS performance is identical. The advantage to the B102 is the much higher frequency response, greater Xmax, better Qts, larger magnet, greater displacement, and higher BL factor.