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Eminence 8 beta

Discussion in 'Amps and Cabs [BG]' started by TonH, Jun 18, 2019.

  1. Jun 18, 2019 #1
    TonH

    TonH

    Jan 26, 2011
    The Netherlands
    In the rehearsal room of my band there is an old Ampeg B2-48 bass combo (4x8 inch speakers). I use that combo so I don't have to take my own amps and cabs. The sound is oke but could be better. During its life someone replaced the orignal speakers with Eminence bèta's but the ports are not adapted to these speakers. I want to calculate a good port length (with WinISD) for this combo. But then I need the correct parameters/spec's of the speaker.
    It is an older version of the Eminence beta (green sticker on the back of the magnet), not the one on the Eminence website.

    I searched the internet but couldn't find the specs. Does anyone regonize this speaker?
    And are the spec's the same of the new bèta's?

    20190617_193600.jpg

    Thanks!
     
  2. Jun 18, 2019 #2
    TonH

    TonH

    Jan 26, 2011
    The Netherlands
    Problem solved! I wrote an email to Eminence and within 15 minutes I recieved an answer. The Beta 8 on the picture has the same characteristics as the Beta 8A on the Eminence website. Excellent customer service!:):hyper::bassist:
     
    pie_man_25 and wave rider like this.
  3. Jun 19, 2019 #3
    4Mal

    4Mal Gold Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    Yep. The Eminence folks give good service.
     
    BassmanPaul and TonH like this.
  4. Jun 19, 2019 #4
    BogeyBass

    BogeyBass Inactive

    Sep 14, 2010
    I thought the Ampeg 4x8 combo was sealed.

    Fs of the beta8 is limited to 65hz

    It would be horrid to tune higher
    To obtain a typical Butterworth/Quasi Butterworth alignment.

    Rule of thumb and typical alignment will tune 10/12 hz above or below speaker Fs

    Tuning above or below 10hz from 65hz is absolutely horrible either way.

    A negative 3dB or 6dB bass shelf will tune below Fs. Close you'll ever get to a 40hz to 50hz reflex point. Which is what bass cabinet should be. Not sure if the Ampeg cabinet volume supports a bass shelf alignment. Be funny as heck if they actually did that.

    Probably confirm the Fb or tune of that cab. If it's around 55 to 50 hz that's about as low as it gets

    I thought Ampeg just used a larger sealed application for 8" drivers. Which is a more feasible design.

    Best bet is to remove the dense pointless sound board lining and just fully line the cabinet with poly fill batten sheets. Call it a day

    Definitely not trying be negative the original Eminence driver in that cab be similar to a alpha 8 the beta8 is a significant upgrade.

    If the cab is well sealed and lined with better material that's about the most you could improve.

    If the did tune it to 65hz might explain why it don't work well. Simply lower tuning 12hz below driver Fs. Low as it gets
     
    Last edited: Jun 19, 2019
    TonH likes this.
  5. Jun 19, 2019 #5
    TonH

    TonH

    Jan 26, 2011
    The Netherlands
    Thank you for your comprehensive answer, I will take that into account.
    BTW the B2 and SVT48 both are ported.

    For your information: I have an original B2-48 combo and SVT48HE at home that I use for gigs. But I don't take them to the rehearsal room, there I use the B2 that belongs to the owner of that space. So I don't want to spent a lot of money on that one, but if I can improve the sound with some tinkering, that would be fine.

    The original B2 and SVT48HE have speakers branded SLM Electronics part# 86-127-08. They feature a polypropylene cone and butyl rubber surrounds what you would find in a HIFI-speaker. The are only rated 50 Watt RMS each.

    Here is a picture of my SVT48HE:
    [​IMG]

    [​IMG]
    Spec's of this cab:
    1995 SVT48HE

    4 - 8" cones with 2 in. voice coils and 30 oz. magnets

    Dome tweeter

    RMS handling - 200 watts
    Program mat'l - 400 watts

    Freq Resp. (-3 dB) 60 - 20 KHz
    Usable Low Freq (-10 dB) 50 Hz

    Nominal Impedance 8 ohms

    Sensitivity 98 dB
    Maximum SPL 121 dB

    Crossover 5 KHz

    Dimensions 24 by 20.5 by 16 inches

    70 lbs.
     
    Last edited: Jun 19, 2019
  6. Jun 19, 2019 #6
    TonH

    TonH

    Jan 26, 2011
    The Netherlands
    Last edited: Jun 19, 2019
  7. Jun 19, 2019 #7
    TonH

    TonH

    Jan 26, 2011
    The Netherlands
    Anyway the ports of the B2 and SVT48 consist of 2 part, a plastic mounting ring and a paper cylinder:

    20190619_185210.jpg
    20190619_185222.jpg

    The length of the port consisting of paper and plastic ring is about 8.1 cm. The port consisting of the plastic ring alone is 2.55 cm long.
    The (inside) volume of the cab is 77 liter.

    So with WinISD I could make a comparison between the 2 different port lengths in a cab with 4 Eminence beta 8's.

    Here is screenshot of the comparison:
    Diff port length B2 Eminence beta 8a.jpg
    The thick green line is with a port length of 2.55cm. The thin green line is with a port of 8.1cm.
    A port of 8.1cm would be a tuning frequency of 48 Hz, not appropiate for the beta 8.
    By leaving out the paper part of the port, just the plastic ring as a port, the tuning frequency is 63 Hz.

    You can see that the smaller port result in a better performance for 55 to 200 Hz.

    So a quick and cheap mod, (removing the paper part) wil improve the sound of the B2 combo with Eminence beta 8a's.
     
  8. Jun 19, 2019 #8
    BogeyBass

    BogeyBass Inactive

    Sep 14, 2010
    Oh krap that's right the poly cones.

    I've only seen one of these combos ever and it too had paper cone replacements. One blown driver. Smaller magnet Eminence

    In a model using a somewhat typical quasi Butterworth. Yes the response graph appears to have better performance.

    Can be misleading depending on drivers with high Fs cause source material is usually electronic bass and fundamental is around 41 hz for standard E.

    So yes you could raise port tuning to obtain more Butterworth alignment.
    And then judge yourself how it feels as a player with such a higher tuning.

    Luckily it's easy to change the tuning.

    Try high tune. If you like it all good.

    If not it's gonna be similar to what I was assuming ampeg might have done or what I'd try to do. Is push tuning low as possible.

    Those pretty graphs definitely give insight to the system and give warnings if Q is too high. Otherwise very misleading to many and accounts for the general behavior of smaller high tuned cabinets.
    Cause bass appears to be better.

    Reflex point reduces cone movement. Then unloads below the reflex and causes massive cone travel. High tune can look good on the screen. But not realize it's causing bass frequencies to unload. And restricted cone movement in the fundamental for bass.

    Definitely try it. If it feels spongy or powerhandling gets worse. Go back to lower tuning.

    Likewise could plug the ports see if you like it sealed
     
    TonH likes this.
  9. Jun 19, 2019 #9
    BogeyBass

    BogeyBass Inactive

    Sep 14, 2010
    Otherwise ironically those ports work out perfectly and tune pretty good to the 65hz Fs of those drivers.

    Which technically is good alignment
     
    TonH likes this.