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Tweaking my Avatar B410

Discussion in 'Amps and Cabs [BG]' started by DakotaBass, May 7, 2002.

  1. Hey gang,

    Long time listener, first time caller.
    I just got my new Avatar 4X10 last week and it sounds great for the price! Very clear and punchy.

    I took some measurements on it and plugged the numbers into WinISD. It looks like the internal volume is somewhere between 2.8 and 3 cubic feet, and there are 2 ports, each 3.75" with basically no length. According to WinISD this would put the tuned frequency at about 80 Hz.

    If I increased the length of the ports to 5", this would lower the tuned frequency to around 54 Hz. My questions are: How would this affect the overall sound of the cab? If I did this, is there an increased risk of damaging the speakers?
  2. PICK


    Jan 27, 2002
    Sydney, Australia
    If it were my cab i would leave it alone.
    If you like the sound why start messing with it??
    If you dont like it, find something you do like and buy that insted.
  3. Ok, here's the thing: I'm an engineer and I pretty much live by the motto "If it ain't broke, it doesn't have enough features".

    It sounds good now, but if I can make it sound even better for $2 worth of porting tubes I'll try it, but I don't want to risk damaging the speakers.
  4. Quadzilla

    Quadzilla Supporting Member

    Hi there Dakota,

    By all means, do this and get back to us on the results. I'm sure that if you call Dave (at Avatar), he will send you the tubes for nothing or next to it. He is the eaisiest guy that I have ever dealt with. I for one am VERY interested to see what you come up with. PLEASE let me know what you find out.

    Thanks much,
  5. Don't trust WinISD an inch as far as correctly calling your tuning frequency.

    You have an engineering background, so put it to good use and test the box yourself. You will need a power resistor, 25w in the 200 ~ 1000 ohm range. A DVOM, a freeware signal generator you can get from my web site, a computer sound card, and a power amp.

    The setup is to put the power resistor in series with your cab to create a constant voltage output from the power amp. Plot an impedance graph and find the lowest voltage point between the two peaks. This is the tuning frequency, and the cone movement will almost NIL (invisible) at this frequency. The two impedance peaks are the upper and lower resonances present in all vented cabs.

    Don't guess at tuning your cab: you will screw it up. Since you've been inside the cab, please post exactly which drivers are used.
  6. Quadzilla

    Quadzilla Supporting Member

    The drivers are as follows (I have the same cab):
    4 - 10" Eminence Delta's (pressed basket)
    1 - 150 watt Fostex (also known as Foster) horn.
  7. I will definitely try what bgavin suggested. All I have for a power amp is an SWR 350. I think this should work as long as I keep the source voltage constant across frequency, right?

    After I determine the tuned frequency, how do I know if that is the frequency the cab should be tuned to? If it isn't right, how do I determine what it should be?
  8. You're between the rock and that hard place. The optimum tuning for a Delta 10 is around 80 Hz.

    You can download the Delta 10 WinISD file from my site. It's a ways in, so you'll have to dig:

    Link to Delta 10 Vented

    Look for the "Delta 10 Vented" file.

    This WinISD file is the optimum setting for this driver. Set WinISD for 4 drivers and increase the box volume to what you measured for your cabinet. Subtract 4 x 0.12 cubic feet (0.48 cubic) feet for the driver displacement.

    Play with changing the box tuning frequency and watch what it does to your GAIN graph.


    I sent an email to Avatar Speakers, and it continues to bounce, so I can't reach the designer to see what he is using.

    I suspect he probably has the cab tuned at 80 Hz and is working on the concept of most bassists having never heard the fundamental reproduced accurately. If so, the 2nd harmonic of low E is... you guessed it, 82 Hz. This puts the frequency right into the optimum flat range of the Delta 10 driver. The fundamental just falls off the face of the earth and is ignored.

    The downside is, the cab is exposed to damage from any fundamental below 80 Hz at a high power setting. The cab unloads the drivers below the tuning point, which is the same as them flopping around in free air, or in an open back cabinet.

    You might call the designer and see if you can pin him down on the tuning frequency. Surely he must have some engineering behind this.. I doubt they are just building boxes and tossing in drivers at random.
  9. BillyB_from_LZ


    Sep 7, 2000
    Have you tried the cabinet in a band setting yet?

    Even if it is tuned to a frequency higher than one that would scores points with your bass buds, what counts is how it sounds on stage. Low end eats amplifier power and can create mud. A cabinet that rolls off a little higher can have more punch and actually sound better on stage.

    Forget the numbers and listen to what your ears (bandmates and audience) tell you.

    As for measuring the tuning frequency, I've had good luck with just using the sound card on my laptop with no interposing power amp. A 1K ohm resistor in series with the load helps minimize the loading effect on my soundcard and allows for some decent results.

    Have fun!!!!
  10. Quadzilla

    Quadzilla Supporting Member

    I emailed Dave from Avatar ( sales@avatarspeakers.com ) and sent him a link to this thread. I hopeful that he will respond. He is typically very responsive.

  11. BillyB_from_LZ


    Sep 7, 2000
    Hey Bruce,

    I read what you wrote about about speakers being unloaded below the tuning frequency and I just don't buy it.

    Many times I've used both an Acme B2 (tuned in the low 30s) and an EV TL606 (tuned to 55 Hz) simultaneously and while the woofers from the B2 are banging against the grille, the EVM 15B is happy as a clam.

    Seems to contradict your theory.

    I'll have to go back in my archives and find Thiele's original paper on this subject to see if he offers any insight.
  12. Quadzilla

    Quadzilla Supporting Member

    Hi Fred, thanks for your email...We take what the computer says, and what
    Eminence says, then we take trial and error and end up with the porting we
    like...Players are welcome to tweak and experiment with their cab porting to
    get different results. Thanks for the input Fred...Take Care...Dave

    Well, there you have it. Not sure what application Dave is using to do his cab sizes, drivers, porting etc, but at least he is using something.....
  13. BillyB_from_LZ


    Sep 7, 2000
    Dave sells the Eminence software on his website. Click on the speaker components link (or whatever it's called).

    Like Dave says, it's what sounds good that matters not what the model shows as far as an expected response. We have an old saying at work..."One test is worth one thousand expert opinions"

    I recently ordered a pair of Compact115s and am looking forward to them showing up on my doorstep.
  14. Sorry you don't buy it, but I'll save you the trouble of digging. Check out the technical publications from JBL and others. They all spell it out point blank about operating below the tuning frequency.

    [ edit ]

    I'm home now, so I can plug in the links now.

    See Page 2 of the JBL Enclosure Guide

    Link to MTX Vented Disadvantage

    Link to Advantage of Vented Enclosures

    I can list many others if you like, but they all make the same statement: cone unloading occurs below the tuning frequency and this exposes the driver to damage.
  15. Jon Burnet

    Jon Burnet

    Jan 21, 2001
    Memphis, TN
    bgavin can you post on the gs 112 jump post? please.
  16. monkeyfinger

    monkeyfinger Moderator Staff Member Supporting Member

    Why would you spend the money on a top-end cab only to re-engineer it? Is the sound not to your liking, or are you driven by specs? If you don't like the way the cab sounds, buy another cab. I know this sounds a little harsh, but the guy who designed the cab spent a long time engineering it. Now you want to redesign it because some software says so?
  17. OK, I tried bgavin's method of measuring the tuned frequency of my Avatar B410. I found an impedance peak at 44 Hz, another at 98 Hz, and an impedance null at 59 Hz. This means the cab is tuned to 59 Hz, right? This is quite a bit different from what WinISD calculated (80 Hz).

    If I added length to the ports, this should lower the tuned frequency. It seems that as far as potential damage to the speakers, shouldn't it be safe to at least try this to see what it sounds like?

    To answer some previous questions, yes I have played the cab with a live band in a medium-size church in rehearsal. It sounded good. It cut through the mix very well, and pretty much shook the building. I'm not unhappy with the sound, (quite the contrary), but I am curious as to how different porting and tuning affect the sound of a cab.
  18. Make each port 4.5" long, including the baffle board depth. That should take you down to 41 Hz.

    The box will begin to unload 1/2 octave below the tuning frequency, or about 31 Hz.

    Verify your tuning point as the motion of the cone being almost undetectable. The ideal method is using a sound level meter 1/2" from the cone and measuring for the least loudness. This should agree with your electric measurement. Often there is a very broad trough at the bottom, so calling the tuning point is somewhat difficult. The SPL meter (Radio Shack $40) will help you find it.

    This lower tuning will protect your drivers better at high power, but it is a long way from the optimum 75 Hz for the Delta 10.
  19. BillyB_from_LZ


    Sep 7, 2000
    Thanks Bruce,

    I looked at the links that you provided...

    If what you write is true, then none of the JBL's would be suitable for use with a 5 string bass or a 4 string tuned to Eb as either's lowest frequency is below 40 Hz.

    I'll dig out Thiele's article and see what he had to say about it.
  20. True. I dearly love JBL drivers, but they are designed to be very loud and don't go down very low at all in vented boxes. The bass drivers are ideal for 2nd harmonic and higher production.

    The optimum vented tunings are:

    E110 - 68 Hz
    E120 - 124 Hz
    E130 - 75 Hz
    E140 - 66 Hz
    E145 - 51 Hz (most suitable)
    E155 - 54 Hz

    The optimum tunings are also in pretty small boxes. You can enlarge the box considerably and use an extended bass shelf (EBS) lower tuning to get lower response. This results in really sloppy group delay numbers and the drivers sound flabby.

    The amusing part is, the E110 lead speaker is the most suitable for electric bass at very low power because it goes down the lowest of all the JBL. However, it is unsuitable in the practical sense because it won't handle any real power due to its tiny Xmax. I use E110s as the highs in my bi-amped rig.

    Even though the efficiency bandwidth product indicates a vented box, I'd run the E145 in a sealed box, Qtc=0.577. The reponse for the low fundamental is about the same: awful. A sealed box will prevent the cone unloading and subsequent damage that happens in a live environment with lots of applied power. The sealed box also offers much better punch and transient response than an EBS alignment.

    The Avatar guys would like this, as the JBL E-series response is almost exactly the same as the Delta 10 used in the Avatar cabs.

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