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Thread: 30 Hz -300 Hz? Please help a noob

  1. #1
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    30 Hz -300 Hz? Please help a noob

    Gentleman,

    As can be inferred from the subject title, I am looking for a solution for the 30 Hz to 300 Hz frequency range. I am completely ignorant about any design issues in this frequency range, hence my post. Please, let me first describe where I am now with my design.

    I have a horn with average sensitivity of 106 dB/1w/1m, low distortion, and controlled directivity in the remainder of the audio frequency range. Examining the horn response, it would be possible to cross-over as low as 220 Hz, but for better distortion the preferred minimal cross-over point is about 250 Hz.

    It is my understanding that a good practice would be to split the lower frequencies between two drivers/speakers, e.g., 20 Hz-60 Hz, and 60 Hz – 300 Hz; unfortunately, for the time being and a foreseeable future, space is at premium.

    It is my further understanding that producing lower frequencies with reasonable sound pressure level (SPL) is a matter of moving lot of air, which translates to large (15” or 18”) woofers. Following that logic would appear that it would be preferable to acquire an 18” woofer with reasonable sensitivity. However, will such a woofer make it to 300 Hz without breakups? On the other hand, would a 15” provide low distortion at the lower frequencies? Would two 15” woofers be better? However, will they not require bigger cabinet? As you can see, I need help.

    I understand that the ultimate solution is a matter of compromises. My main criteria are low distortion, good transient response, peak SPL about 110 dB. I am willing to compromise on the lowest frequencies, if necessary, as I listen mostly to classical music.

    I can do rather sophisticated frequency shaping and steep filtering as a result of using digital signal processing. Wood working is not a problem, but design of a cabinet is.

    Based on the foregoing, if you are still reading, could you help?

    Thank you,

    M

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    RIP 2013 Rolf's Avatar
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    Hi. In my opinion the 15" 2235H would be a good solution. Also the 2245H, but that is an 18". Needs more space. About the cabinet, I let the more learned than I climb in.
    It's really all about music.
    Rolf

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    Super Moderator yggdrasil's Avatar
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    Look at http://www.linearteam.dk/ and download one of the WinISD's.

    As Rolf said the 2235H is a very good 15" alternative, which JBL has used up to 1K in the 4430 monitor. The 2245H was used to 290Hz in the 4345 monitor. Both these woofers are able to play very low, given enough box.

    The 15"'s 2225H, 2226H and 18"'s 2240H, 2241H have higher efficiency at the cost of the lowest octave.

    You will (a lot) more than 110dB max SPL with all of these drivers.

    I can provide you with driver files and / or T/S parameters if you choose to download the pro-version.
    Johnny Haugen Sørgård

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    Obviously... not a golfer grumpy's Avatar
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    Hi M,

    What are your desired cabinet size constraints?
    Biamping with line-level crossovers?
    Room placement options?
    Multiple subs OK?
    Any home theater aspirations?
    Are used drivers OK?
    Preference for sealed vs. ported?
    Bass horn might be an option, but size and/or construction complexity can be
    limitations.

    Ability to EQ opens up the option for smaller cabinets.

    There are a number of cabinet designs available (15", dual 15", 18", ...) that
    might suit your requirements. Steer us a bit closer to your target

    -grumpy

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    Thank you all very much for your time to reply.

    yggdrasil,

    I apprecitate your generous offer and will take you up on it, if I am forced to go the way of designing the cabinet myself. However, as I indicated, I do nut understand all the issues and would, therfore, prefer to build something proven.

    grumpy,

    Here are the answers, as best as I can manage with my meager knowledge.

    What are your desired cabinet size constraints?

    I believe that the maximum is about 10 cubic feet.

    Biamping with line-level crossovers?

    Biamping with DSP based cross-overs.

    Room placement options?

    I do not quite understand this question. My understanding was, that given the hight cross-over, I will build two and position each of them with the corresponding horn.

    Multiple subs OK?

    See above.

    Any home theater aspirations?

    I am afraid that I do not understand the question. I just listen to stereo, whether the source is CD or DVD.

    Are used drivers OK?

    Certainly, I believe that I can obtain the above-mentioned 2245.

    Preference for sealed vs. ported?

    This is one of the issues I need help with. My understanding is that sealed has inherently better transient response while ported will go lower, but the ultimate result is (as usually) an implementation issue.

    Bass horn might be an option, but size and/or construction complexity can be
    limitations.

    No, at present time, the size of such a bass horn rules it out.

    Steer us a bit closer to your target

    I would love to, but, as I admittede, this is an unchartered territory for me, and I do not know how to be more specific. Perhaps, if you do not get tired of me, we will get there during the course of discussion.

    Thank you again for all the help.

    M

  6. #6
    Obviously... not a golfer grumpy's Avatar
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    I believe you've patiently answered all of my questions

    30-300Hz
    (not really subwoofers, but bass drivers integrated with a mid-bass capable horn)
    <=10ft3 each
    biamped
    positioned with horns (2)
    music only (no boom boom effects)
    old drivers are OK.

    ported vs. sealed?
    existing/documented cab designs?

    My thoughts would lean toward a pair of 15" 2235H in each box (not hard to find)
    of 8.5ft3@30Hz to 9ft3@20Hz tuning, depending on preferences. Going big
    would give you room to experiment, as taking volume away is easy

    Suggest getting other inputs and checking reference material before cutting wood.
    I'm sure you'll get other experiences and inputs (that totally contradict my suggestion).

    The plans available here for subs would probably not suit your application, but there are
    construction plans and guides for quality-built boxes.

    -grumpy

  7. #7
    Super Moderator yggdrasil's Avatar
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    Just a thought:

    A couple of these would solve your problems. http://cgi.ebay.com/JBL-USA-Professi...QQcmdZViewItem
    Johnny Haugen Sørgård

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    Hello
    What kind of horn and driver are you going to cross into at the 250/300 hz range. Most drivers designed to operate at that low of a crossover frequency do not offer extended high end response.
    Are you planning on a two way or three way system.

    Mike Caldwell

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    Thank you again for your suggestions.

    Mike, I have a prototype of Unity, which has been re-designed for lower frequency cut-off.

    M

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    Obviously... not a golfer grumpy's Avatar
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    grumpy,

    I have the original drivers as depicted in the second link you posted. However, the horn has been re-designed using Dr. Geddes' waveguide mated to L'Cleah's end flare and extended in length to 1/4 wavelenght at 200 Hz.

    So, now you understand that I need something really nice to complement the Unity. ;-)

    M

  12. #12
    Obviously... not a golfer grumpy's Avatar
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    Me thinks you will need to expect some experimentation and failure to find what
    suits you best. Myself, I wouldn't worry about the lowest octave too much and
    concentrate on matching/complementing the horn. I've never heard a Unity designed
    horn setup ... interesting concept -grumpy

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