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Thread: JBL e120 in midbass horn application

  1. #1
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    JBL e120 in midbass horn application

    Hi,

    I am planning to build a "proper" midbass horn to cover 100 to 500hz to replace my current 80Hz Edgar straight Horn (a compromised design). Efficiency goal is AT LEAST 103db, to match my other horns. The new midbass horn will have a 12" driver, full 100hz mouth area, and possibly 4:1 or 3:1 compression, flare shape not determined yet but most likely -- straight tractrix.

    Question:

    I have a pair of working JBL e120-8 drivers. Are these good in the above application or should I consider a better candidate (used or new)? What I mean by "good" is actually the best available for my application. If anyone tried e120-8 for "no compormise" midbass or compared it to other JBL models, TAD, Presicion Devices, etc.

    Thanks,
    Herman

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    I am planning basically the same as you are, but havn't built a horn yet.

    The E120 have a very light cone. It might break.

    Go for a 15" driver with a high BL instead, the horn will be shorter. Consider JBL 2220, 2227 and PD154. Include horn upper frequency dropoff in your filter design. 15" is better than 12" if 500 is your upper frequency.

    Make simulations in Hornresp and post them here.

    Lots of informations in http://www.audioasylum.com/cgi/etv.mpl?forum=hug

    Best regards

    Mårten

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    not 15" woofer

    Marten,

    I currently have an Edgar midbass with 15" EV driver. For whatever reasons, I am not happy with them. Maybe it's the 15", maybe not, maybe the horn itself. I do not believe any 15" can play music good with good resolution above 500Hz. And I plan to use 6db filters so practically the woofer will be audible to well above 1kHz.

    Maximum is 12" but 10" or 8" is also on the table. Even large compression drivers, still not ruled out. I am not interested in making the horn shorter, I am interested in making a proper, no compromise midbass horn 100-500 Hz.

    Regards,
    Herman

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    Senior Member Lee in Montreal's Avatar
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    Hi Herman. Isn't the e120 driver more suited for guitar, with its aluminum dome, and therefore designed to reach much higher frequencies than what you need (especially cut at 6db/octave)? Can you replace the aluminum dome with a felt one, or perhaps recone it as a 2202?

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    Here's a secret

    Quote Originally Posted by Lee in Montreal View Post
    Hi Herman. Isn't the e120 driver more suited for guitar, with its aluminum dome, and therefore designed to reach much higher frequencies than what you need (especially cut at 6db/octave)? Can you replace the aluminum dome with a felt one, or perhaps recone it as a 2202?
    I will be removing the alum dome completely. It will be replaced with a big phase plug to reduce the on axis beaming.

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    Because of this the 6 db/octave low pass filter will work very well and predictably, to integrate with my midrange horn.

    Herman

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    I believe you are right Herman. 12" will work better than 15" reaching 500 Hz. Ill do some simulations later in the week. The horns will be placed on floor away from any walls (2pi)?

    Will you replace the dustcap with a phase plug, attaching the phase plug to the cone?

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    phase plug

    the horns will sit on the floor. I will try to get them as far away from the walls as possible, not sure the exact distance yet.
    The phase plug does not attach to the cone, rather to the pole piece (part of the frame assembly). So the phase plug is static, like the speaker frame and horn enclosure.

    Herman

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    Senior Member ivica's Avatar
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    Quote Originally Posted by Herman Chigrin View Post
    I will be removing the alum dome completely. It will be replaced with a big phase plug to reduce the on axis beaming.

    Attachment 55408

    Because of this the 6 db/octave low pass filter will work very well and predictably, to integrate with my midrange horn.

    Herman
    Take care about E120, because it's voice coil length is shorter ( I think in order to enlarge 2'nd harmonic, to 'improve' guitar sound, or to say: music "production") then 2202 (which is much more liner,and i think better for music "reproduction").
    I have no idea about the membrane strength concerning its 'loading' because of 'phase plug' applied.

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    http://www.audioheritage.org/vbullet...l=1#post320687

    Figure 2C. E120 has an "equal height coil and gap". This is what Ivica is talking about I believe. In a horn the cone will not move much. Maybe not a problem?

    Very smart thing to attach a phase plug to the pole piece. What material will you use? Will yop glue it to the pole piece?

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    E120 chassis with 2220 cone question

    The e120 and 2202h have different magnet depth. So what happens if I re-cone e120 with 2202h cone?

    As far as the phase plug goes:
    If the e120 pole piece has a hole in the center I can mount the phase plug to the pole with a screw and a washer. The washer will be at the back of the magnet (covering the vent on the back, the screw will go through the pole piece exiting at the front and attaching to the phase plug.

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    Last edited by Herman Chigrin; 04-11-2012 at 01:59 PM. Reason: mistake

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    Senior Member jerv's Avatar
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    This is very interesting.
    I am also contemplating a midbass horn.
    How do you make the horn and phaseplug?

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    Loudspeaker Power Handling Vs. Efficiency. It might seem that plugging the vent is a bad idea. But if you turn the phase plug into a heatsink, it might improve the driver considerably. A phase plug made of aluminium will be quite heavy though. If you make a straight horn you will have natural convection in the horn as well.

    This is definately something I will try myself.

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    Sample of the phase plug horn

    http://www.funktion-one.com/products/resolution-3-sh/

    Look at the midrange section, it uses a 10" mid. The idea is to keep this concept but adapt to the 100Hz horn with 12" driver.

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    Also see this 15" midbass horn.
    http://www.funktion-one.com/products/ds15/

    my version would be something between the 10" and the 15". You guessed it, 12" midbass!!!


    Herman
    Last edited by Herman Chigrin; 04-12-2012 at 01:44 PM. Reason: addition

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    I have done some simulations using 2202, E120 and PD.121. They all perform very similar in a horn optimized by hornresp. What varies are the compression factors and horn lengths.

    I have used fs=68 to get the first acoustical impedance minimum at 100 Hz, making the horn useable from 100.

    Driver compression length
    E120 4.22:1 189 cm
    2202H 3.4:1 190 cm
    PD.121 5.17:1 203 cm

    The biggest problem with this kind of horn is the beaming. At 0 degrees the response rises 9 dB from 100 to 400 hz.

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    let's do this, looking for cooperation in Chicago

    Quote Originally Posted by more10 View Post
    I have done some simulations using 2202, E120 and PD.121. They all perform very similar in a horn optimized by hornresp. What varies are the compression factors and horn lengths.

    I have used fs=68 to get the first acoustical impedance minimum at 100 Hz, making the horn useable from 100.

    Driver compression length
    E120 4.22:1 189 cm
    2202H 3.4:1 190 cm
    PD.121 5.17:1 203 cm

    The biggest problem with this kind of horn is the beaming. At 0 degrees the response rises 9 dB from 100 to 400 hz.
    Thanks for the modeling! The phase plug will reduce this 9db beaming and diffuse the sound energy on axis, providing much more even coverage. This works well in my midrange horn, the picture of which was posted earlier. It must be noted that this phase plug must be big enough, close to the driver area at the plug's max cross section to "steer" the sound energy around the plug.
    Also, the dome (dust cap) must be removed so that effectively REDUSES the driver area and must be accounted for in the modeling. 80" is one long horn already! Also, because the plug is big, the horn throat and flare shape must be adjusted for the plug to maintain the proper flare rate/compression.
    By the way, which type of horn flare are you thinking about for this midbass thing?
    This is all just my theory but so far the phase plug seems very appropriate for this midbass project and everything is naturally falling in place. Although it is a tricky project, but very simple and elegant at the same time.
    Making the phase plug from aluminum is a very good idea and will promote very effective "active" cooling of the pole piece!

    here is another Funktion-One model, this one seems more symmetrical, perhaps easier to use as the "base" of the midbass build:
    http://www.funktion-one.com/dl/files/2113.jpg

    Maybe with a few changes, but the concept seems solid and I am motivated to give it a shot. I am looking for some cooperation on this project, I am in chicago. Will be happy to discuss this with anyone interested. I have an interesting (but tricky) idea on how to approach this so emial me: noviygera (at) gmail
    if interested.

    Herman

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