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Thread: 4 way with 2242/2245, 251J, 435Be, 045Be, help with crossovers.

  1. #1
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    4 way with 2242/2245, 251J, 435Be, 045Be, help with crossovers.

    Hello, a little while back I posted this thread
    http://www.audioheritage.org/vbullet...eater-speakers

    I got some great advice, but I just confused myself trying to work with too many drivers. Now I am settled (well….. please do suggest if you’d go with the 2242 or 2245…)

    Other than the 18 I’m definitely using two of the 251J midbass drivers, a 435Be beryllium in an H9800 horn and an 045Be beryllium super tweeter.

    For music it’ll be just these and for movies I’ll be adding 18” Ultimax woofers. This isn’t super important.

    So basically I got all of the drivers and the crossovers from three SK2-3300s. Cabinets are gone and not by me. I’m trying to figure out how to work these drivers together. If I use the stock 3300 crossovers then one of the 10” midbasses would only play up to 150hz. That wouldn’t make sense with the 2242/2245 covering the bottom end.

    So, do I go with 12 channels (LCR 4 channels each) of amplification and DSP and run it completely active?

    Or do I run the 435Be and 045Be on the passive crossover and run the 2242/2245 and 251Js active? This would give passive protection to the two most expensive drivers in the speaker. One fear I have of going active is a mistake happening and sending full range sound to the 435 and 045. In this scenario I would need 9 channels of amplification and technically 6 of DSP if I just send a full signal to the passive crossovers. I could run the 18s to 200-300hz, the 10s up to 850 hz where the passive crossovers would take over and high pass to the 435 at 850 hz.

    Thoughts? Not only looking for suggestions on which 18 you’d go with, but also looking for suggestions on crossover/DSP. For now only looking at the minidsp 2x4HD. What else out there would give good performance without breaking the bank? I have a Dayton DSP-408, but I’d like the lower noise floor. So for now the plan is to pick up 2 or 3 minidsps unless someone has a better suggestion.

    Lastly, suggestions on crossover point for the 2242/2245 to the 251Js? Would you go
    as high as 300 hz?

    Dan

  2. #2
    Senior Member HCSGuy's Avatar
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    Very cool - youíve got quite a library of drivers to play with

    I think I read it right that you have everything except enclosures to build SK2-3300ís. I would start there - get something working and see if you like anything about it. I have no experience with 251jís or the SK2-3300ís, so I canít say what size the enclosure should be, or where to tune it, but I would start by running and impedance sweep on the 251ís in free air and see if they their Fs is where it should be, and how close they match. I would also try a vertical arrangement of the drivers for the L/R speakers to see if it helps at all with imaging.

    The 251ís should be able to play down to 70 or 80hz, so you can put a subwoofer driver beneath them - I think youíre asking for trouble putting crossovers at 300hz and 850hz. If it was me, I would simplify everywhere I could - first Iíd build the SK2-3300ís, and if I didnít like that, Iíd get a pair of 1500-ALís, which would let you clone a pair of K2-S9800ís.

    As far as woofer drivers go, 2245 is good, but it really needs a big enclosure, larger than most of us are willing to live with. Given some EQ and a HP cut on it, it can sound good. 2242 was never considered a HiFi woofer - it was really designed to play strong to 30-35hz in theater subs, and take a lot of abuse.

    I donít know if this helps or not, but the two pieces of advice I would give would be:
    1. Simplify wherever possible - itís alot easier to get a good sounding 2-way than it is a 4-way.
    2. Whenever possible, build on something someone else has done - if you can clone a factory JBL speaker and then copy Greg Timbersí passive crossover design, youíll be miles ahead of doing it yourself.

    Have fun!
    Last edited by Mr. Widget; 05-01-2022 at 01:36 PM.
    That the internet contains a blog documenting your life does not constitute proof that your existence is valid. Sorry.

  3. #3
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    Quote Originally Posted by saabracer23 View Post
    Hello, a little while back I posted this thread
    http://www.audioheritage.org/vbullet...eater-speakers

    I got some great advice, but I just confused myself trying to work with too many drivers. Now I am settled (well….. please do suggest if you’d go with the 2242 or 2245…)

    Other than the 18 I’m definitely using two of the 251J midbass drivers, a 435Be beryllium in an H9800 horn and an 045Be beryllium super tweeter.

    For music it’ll be just these and for movies I’ll be adding 18” Ultimax woofers. This isn’t super important.

    So basically I got all of the drivers and the crossovers from three SK2-3300s. Cabinets are gone and not by me. I’m trying to figure out how to work these drivers together. If I use the stock 3300 crossovers then one of the 10” midbasses would only play up to 150hz. That wouldn’t make sense with the 2242/2245 covering the bottom end.

    So, do I go with 12 channels (LCR 4 channels each) of amplification and DSP and run it completely active?

    Or do I run the 435Be and 045Be on the passive crossover and run the 2242/2245 and 251Js active? This would give passive protection to the two most expensive drivers in the speaker. One fear I have of going active is a mistake happening and sending full range sound to the 435 and 045. In this scenario I would need 9 channels of amplification and technically 6 of DSP if I just send a full signal to the passive crossovers. I could run the 18s to 200-300hz, the 10s up to 850 hz where the passive crossovers would take over and high pass to the 435 at 850 hz.

    Thoughts? Not only looking for suggestions on which 18 you’d go with, but also looking for suggestions on crossover/DSP. For now only looking at the minidsp 2x4HD. What else out there would give good performance without breaking the bank? I have a Dayton DSP-408, but I’d like the lower noise floor. So for now the plan is to pick up 2 or 3 minidsps unless someone has a better suggestion.

    Lastly, suggestions on crossover point for the 2242/2245 to the 251Js? Would you go
    as high as 300 hz?

    Dan

    Hi Dan,

    If I have understood your questions and your aim correctly the short answer is go full active and use two 2251J drivers and crossover between 50-80 hertz to your sub woofer.

    In more detail. Why go full active? This will allow you flexibility in getting the sub woofer - 251J crossover and the 251J -0435/ horn crossovers right including including the horn EQ and driver level matching.

    You have four challenges I that have outline below that need to be considered and dealt with separately.
    This can be accomplished with a suitable active crossover / processor.

    Its quite a list.
    Obtain the right subwoofer - LCR crossover blending. (see my explanation below on 251J single or dual configurations)
    Obtaining the right 251J LCR -0435/ 9800 horn crossover blending.
    Obtaining the 0435/ 9800 horn EQ for the correct tonal balance
    Obtaining the right level matching of the sub woofer and LCR for the best overall tonal balance.


    In more detail:
    The 9800 horn is acoustically different to the specific horn used in the SK2-3300 that the SK2-3300 crossover was designed for.
    By this I refer to the cut off frequency of the horn and the EQ response shaping of both horns is different.
    The level matching with the SK2-3300 crossover will also not be right.


    To your opening remarks on the 2nd 251 woofer please refer to the SK2 - 3300 tech performance link below.

    https://www.yumpu.com/en/document/re...-jbl-synthesis

    SK2 - 3300 Design:
    The response graph in the link using the two 251J drivers was done with an over damped bass reflex enclosure tuned around 45 hertz. This would look like a really drooping bass response from 120 hertz down a 50 hertz with a single driver. JBL used the 2nd 251J driver as a fill or helper driver below 100 hertz to level the response and provide significantly increase power handling in the 50-80 hertz region. You will note in the listening window response the 50 hertz lower limit is about -6 db down from the mid band with the test conditions used. In a listening room thr response below 100 hertz would be more level. its a case of interpreting these curves appropriately.


    JBL has applied this approach in the JBL 4435 and the DD67000 systems. A 1st order low pass passive filter shuts down the helper woofer. Its quite an effective solution.

    Why am I bring this up?
    The choice of using either one or two 2251j drivers in each of your LCR will dictate the crossover point to your sub woofer and will also impact on how you can use the LCR system.

    To explain further why this is?

    With the two 251LJ drivers in an enclosure as prescribed by JBL they will just cut it for normal music but will have no bass content below 50 hz. They just won't.
    If you decided to use a single 251J per LCR enclosure the response will be limited to about 68 hertz in a 10L enclosure tuned to 65 hertz. This tuning would be un-useable for music without support from a sub woofer. Ergo the acoustic output below 100 hertz from a single 251J based LCR will be significantly reduced compared to the two 251J based LCR enclosure mentioned above.

    Oh Really?
    You might challenge this reasoning if you have owned a ten inch bookshelf system. The answer lies in the detail.

    Not all ten inch drives are the same. The 2251J has a free air resonance of about 60 hertz. A typical ten inch woofer using in a bookshelf loudspeaker has a much lower free air resonance and different driver electrical and mechanical parameters. The 2251J is not a general purpose hifi woofer. Its won't work below 70 hertz if used as hifi woofer. It's a variant of the drivers used in JBL's Pro PA Array systems that have high power handle and can be utilised in compact enclosure over a defined bandwidth. A ten inch hifi woofer in a compact bookshelf design will typically go down to 50 hertz but with reduced sensitivity of around 86-87db. The applications are black and white but your not to know because this is diy okay. JBL has shoe horned the 251J to work in a LCR with some enclosure tuning tricks and by using one 251J as a bass helper woofer. Its as simple as that.

    Lets now link this back Back to the Big Picture.
    These enclosure and driver configuration choices will then also define the crossover point to your sub woofer.

    To be more specific if you plan to use only one 251J then you are looking at a full active low pass and high pass crossover point with single 2251J from 150-300 hz.

    If you opt for the two 2251J drivers in the above mentioned enclosure to can consider a range of crossover points to your sub woofer from 50 hz to 300 hz.
    If you opt for the single 2251J driver you crossover point will be limited to above 150 hertz. A crossover point below this 150 hertz will start to significantly limit the dynamic performance of the LCR system in terms of acoustic output and distortion in the 50 - 150 hertz region. You can experiment of course.

    As mentioned above a full active approach will enable you to navigate the crossover points and any required driver EQ. You won't be able to achieve a useable outcome with the 9800 horns without a lot of passive crossover and passive horn EQ engineering.

    As can be seen the response falls off sharply below 60 hertz. this is with the two 251J drivers running. if you decide to use only now 2251J driver.

    https://www.yumpu.com/en/document/re...-jbl-synthesis

    I hope this answers your questions. I'm surprised I could think this out while in day 2 of isolation.

    EDIT

    The passive filter low pass filter on the 251J helper woofer is similar to that used here. Just put the helper woofer network in parallel with the main 251J which is connected to one of your active channels
    http://www.audioheritage.org/vbullet...10640-SK2-1000

  4. #4
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    I have no experience with a 251J. But I have plenty of experience with the 2251J and ~300 Hz is about the ideal crossover point for that woofer, and is where JBL crossed them over in their 4-way monitor.

    This is the near field response for the 2251J in ~ 1/2 cu ft with a rear port. The port actually boost/flattens the response from just above 160 Hz as shown. This is in a 2.5-way system and the 2251J runs all the way down so you are seeing it's natural roll-off.

    As for the 2242/2245, I prefer the 2241H. It goes deeper in a smaller cabinet than the 2242, and almost as deep at the 2245, but with more "texture/vibrancy." Run all three drivers through WinISD for a chosen cabinet volume and convince yourself. Besides, unless you bi-amp, you would find that a single 2251J cannot keep up with a 2242H unless you horn-load it.


  5. #5
    Administrator Robh3606's Avatar
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    I don't understand the confusion. This speaker systems were made to be used as LRC with a sub. You are going to have a very hard time coming up a better use of these drivers beyond how JBL designed these speakers. All you need to do is clone the cabinets and your done.

    Rob
    "I could be arguing in my spare time"

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    Quote Originally Posted by Robh3606 View Post
    I don't understand the confusion. This speaker systems were made to be used as LRC with a sub. You are going to have a very hard time coming up a better use of these drivers beyond how JBL designed these speakers. All you need to do is clone the cabinets and your done.

    Rob
    Hi Rob,

    ďI donít see what all the blah is aboutĒ.

    Thatís a seniors statement from his rocking chair. Lol.

    Itís obvious to you but not the OP because youíve been there and done it numerous times.

    This is a learning curve. Itís taken you 20 years donít forget.

    You donít learn anything by blindly cloning it.

    I think Danís post raised some interesting points that will help other members.

    Dan is unaware or unfamiliar with how a driver specification can vary and impact on the choices in how a driver can be used. Nor is Dan familiar with the approach JBL used with the helper woofer. I donít think many LHS members would get that either?

    So it was an opportunity to work it through and expand on what it all means.
    That is why l went into it, what it means and the choices.

    These drivers are not out of the Parts Express catalogue under a hifi mid bass listing. On simulation they are nothing like that. No oneís done a simulation. I did. Nor has the spec on the sk2-3000 been posted until now. JBL donít out source hifi drivers for their top systems. They design in-house and how the LCR works is their secret unless you you have the skills to work it out.

    The horns not the same so this points to an active solution.

    These kind of posts come up because people donít understand.
    They come here for an understanding. Not to be told just go do this.

  7. #7
    Member sebackman's Avatar
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    045's

    Just a small note.

    The sensitivity of the 045's is way lower than most pro woofers and in the low 90's (87db 2,83V/1m, 4ohms, 15kHz). I ended up doing 3-way active as the difference between my woofers and the 045 was not solvable with a passive link between the driver and the UHF.

    The 1500AL used in the K2's are rather low sensitivity so with a horn on the 045 and the lower impedance it obviously works fine.

    With a higher sensitivity woofer it may be more difficult without an active setup as proposed above.

    Since you have all the drivers, the horns and the crossovers I agree that building a clone cabinet sounds like the most reasonable usage.

    However, with time available and a good measuring rig you can build pretty much what you want. Albeit rarely as good as a JBL factory speaker with the same components it will be fun, hopefully "good enough" and very rewarding to have build you own speakers.


    My 25 cents
    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

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