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Thread: Baffle Width and BSC

  1. #31
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    Thank you Ian and once again, EarlK...

    Ian, I think I am getting what you're saying. Currently I have some 8cubic ft enclosures in storage that will be used as preliminary enclosures for the bass. In regard to the tops, I guess that is where I will start experimenting with different sizes etc, especially after I get my mic and can make quality observations with actual data on my end. I'm trying to learn a bit more about measurements as well as looking at the testing techniques etc, Troels does on his site as per EarlKs suggestions.

    - I don't see the existing bass cabinet being the end game, and would likely build a more sufficient bass enclosure when I finalize things.

    - Should have considered a sonotube attached to a baffle as being a quicker, more adaptable way to experiment with a Mid enclosure during testing, as I have no test boxes really at this point.

    EarlK, I went back and found the comment. It was in "assuming the pricing isn't a bait and switch". It's in the past. I was eager to try them (12BR70), but it is what it is. I'm going to look at crossover components this week and see what kind of prices I get for building them. Using an electronic cross on the bass sounds like it'll definitely save me some $.

    - What wattage resistors and what gauge coils should I be looking at getting?

    - I just looked and they have 4.7mH but not 4.8mH... close enough? I only know Solen, PE, and Parts Connexion for sources of parts.

    - Is it best to use just cheap caps for now? Electrolytic? Or go with some Solen films?

    Thanks again... More often than not I get cold feet about stepping into a project but thanks to you folk and some silent, albeit generous members, I've got little excuse to take the plunge. Many thanks, and hope everyone has a good day! Much appreciated.

  2. #32
    Senior Member RMC's Avatar
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    Since you're at design/testing phase no need to spend a lot for experiments:

    RE wattage resistors, 10W Lynk metal oxide should suffice (Solen)

    RE gauge coils, i posted elsewhere David Weems' recommendations for coils:

    For inductances from .1 to .32 mH, use 24 ga wire. For .33 to .51 mH, use 22 ga wire. For .60 to 1.28 mH, use 20 ga wire. For 1.4 to 4.3 mH, use 18 ga wire. "Avoid using wire of smaller diameter than that listed for a choke if possible." (p. 175).

    RE they have 4.7mH but not 4.8mH, check qcomponents.ca, maybe they have 4.8mH ?

    RE use just cheap caps for now? Solen has a lineup of yellow color 160V 5% tolerance polyester caps, bought a bunch for a small project and measured half dozen sample to see how good/close. They were at 3% tolerance! better than spec and similar to some more expensive black ones (don't remember the black models number but they have 250V, 400V or 630V).

    Again its for preliminary and testing no need to overspend at this phase, later you'll be spending enough dough

  3. #33
    Senior Member Ian Mackenzie's Avatar
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    Hi Morton

    I had a look at your previous posts on the 2251J (pro driver).

    There are some consumer variations of this driver.

    Based on the pro driver specs below using a simple simulation the sealed enclosure and the ported BB4 enclosure are very compact

    If you are using the 2245H woofer you can operate to up to the 4345 crossover point without an issues. Notions of the 2245 not being accurate in the 100-250 hertz region are a myth once room boundary interference is addressed in your Drive Rack.

    In this situation you will find a critically damped sealed enclosure quite satisfactory and the easiest to implement. You can use a LR 12 dB or LR 24 dB or 3rd order BW network on the high pass and low pass active crossover. Some manual adjustments of each crossover slope will yield a good phase null at the crossover point (280-350 hertz) with your spl test equipment and the integration will be seamless.

    Vb 6 litres plus volume of the driver say 7 litres or 0.25 cu ft3
    Fb 152 hertz
    F3 236 hertz
    Loose filled with fibre glass (not tightly packed)

    http://www.audioheritage.org/vbullet...hp?17040-2251J

    If you are looking at a full active crossover l suggest a 2nd order BW low pass electrical filter @800-1000 hertz on the 2251J, and a 3rd order BW on the horn as a starting points.

    Pad back the horn with 6.2 R series and a 6.2 R shunt fixed LPad to reduce noise from the horn. This will also act to protect your compression driver from clicks and pops.

    Crossover Primer

    Depending on your horn some specific response shaping maybe required. That can be addressed once you assemble your initial mid/ high frequency enclosure.

    Below are some screen dumps of some measurements you might expect.
    These are indicative voltage drives and driver response measurements showing in phase and phase reversal of the woofer & midrange. Such measurements can quite readily be made with REW and implemented with your drive rack. Greg Timber’s is an advocate of REW and has made reference to REW in some of his LHF posts.

    A point to note and a misnomer is that a loudspeaker driver on a baffle is not going to behave like a text book driver on a IEC test baffle under laboratory conditions. Therefore your Drive Rack text book filters will need some editing or application of PEQ filters to the raw driver response before application of your crossover filters.

    In the passive crossover world response shaping can now be incorporated into the crossover filter design with powerful Cad tools or by making trial and error adjustments to the crossover values.

    Good luck with your project

    If you get stuck or need a sounding board for ideas we are here to assist where we can
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  4. #34
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    Thank you RMC and Ian! Much appreciated.

    I suppose there are quite a few different ways to skin a cat as they say... Active vs Passive has always been something I wrestle with. Doing either right is not cheap. I suppose the one aspect of the passive crossover network that appeals to me, is that I don't have any unnecessary ADAC going on in my system.


    RMC - Thanks, I get what you're saying. I spent time last night looking over Troels' site and some forums. I had initially started to price out coils based on his suggestions of 0.8-1.0mm for mids, and 0.8-0.5mm for highs. As to whether or not that is a hard and fast rule, your answer suggests there are different schools of thinking? As you say, its for testing purposes, so I suppose building a network for that vs implementing a proper finalized one will differ in execution. Changing the awg used tho would affect the resistance and tuning tho, no?

    - I haven't found a source for a 4.8mH either yet... still working on it. I found a post about Giskard's charge coupled crossover. Heather had bought some and they weren't cheap. I have a friend who may be able to take a wind off of a bigger inductor for me and measure them at work, but it may be a bigger ask than just buying some pricier coils. Seems like they have a purpose around here, so if I didn't use them in my final network, I may be able to recoup some expense?

    - Solen seems like the most obvious source for components in Canada, dunno if worth ordering stuff from PE or getting it all at Solen. PartsConnexion doesn't seem to carry the lower gauge inductors like Solen, so it kind of leaves it down to the big 2 so far.


    Ian - I have wrestled with a few different approaches to the 2251J and how I would address it. Todallin uses a 2.5 way approach, and part of his appeal is a lack of high pass on the woofer - he made it sound like something to consider. I don't know if there would be merit in testing fully active, as my limited understanding has me thinking its not as simple as translating the electrical active settings into a passive network. Maybe that's part of what you're trying to convey, maybe I am totally Wrong.

    - Playing in WinISD a bit yesterday I kept getting results that looked best and smoothest in similar sized enclosures to the 7L size you suggested so feel I was headed in the right direction, so... I APOLOGIZE for the next point... I was trying to find a good primer and used some forum arguments elsewhere to make sense of this.

    - What is the effect of a bigger impedance peak on the lower or upper end if using a ported enclosure. Its the relationship between Fs of the driver and enclosure tuning, yes? Would this alone indicate how it's damped?

    - Or is being critically damped solely influenced by cabinet size? As it goes up, the system Q goes down, and makes it more damped, yes?? OR due to how everything is related, both this and my previous point indicative of the same? If I change cabinet size, the impedance curve changes IIRC... so maybe I just answered my own question.

    - I am not saying that the 2245 wouldn't go to 290hz or wherever it was crossed, but like the idea of trying both to see what they sound like. Especially if going active, it would be easy enough to try, no?

    - Should my TS be coming from the before or after power test? http://www.audioheritage.org/vbullet...hp?17040-2251J WinISD always says theres issues with my TS inputs when it tries to qualify the driver.



    ***The schematic EarlK posted shows a 2123 in the graphic, but presume the 2251J's impedance is taken into consideration in the filter section? Apologies for missing that in my last post.

    I have tried to do my best at formatting, any suggestions on how to improve my posts are welcomed.

  5. #35
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    Ya know mortron you're getting way ahead of yourself when you start talking about passive component values and their suppliers.


    The values you see ( within my postings ) are not written in stone and are subject to change ( from your up-coming measurements ).


    If you want something wriiten in stone then build a bona-fide 4345 ( it's all sussed out ) .


    Apart from that, you should be focusing on building//obtaining test boxes and baffles and then making measurements of your drivers in various combos ( using your newly acquired test mic ).


    Once you start seeing some actual FR results ( plus impedance curves ) from your testing , everything ( in the passive sims I've posted-to-date ) is going to change ( I can guarantee that ).


    The WinISD results ( showing available LF ) from that miniscule 7L mid cabinet are just science fiction ( assuming best case room loading ). You'll realize this once you start measuring things .
    - Box size matters, as does baffle size, for LF performance. Those lessons are there, posted within TG's threads for you to pick up on.



    One example; my ( .65cu' ) test box is only slightly larger than the size that Troels used for his 10" mid enclosure ( which was 18 Litres ).
    - I displayed an actual measurement of one of my 2123H working within a ported ( .65 cu' ) test box that's tuned to 100hz . That was a few posts back. Here it is again .
    - It's the black trace ( & it's rolling off below 300hz ).
    - The brown trace is a sim of the 2251j using JBL's measurements ( which are taken using a very large sealed box, something like 8 cu' ). It goes low due to the size of the baffle and volume of the box .


    - Current talk about 4.7mH versus 4.8mH is completely beside the point if you are going to biamp ( because C1 + L1 aren't used when biamping )
    - Look//review the HiPass ( C1 + L1 ) components within the midrange section of the following Xsim simulation. They're not in circuit because this circuit was setup for biamping !
    - If you were to go passive ( and then lower your crossover point into the 200hz area ) you'd end up needing something like 90uF ( for C1 ) and 7.2mH ( for L1 ) .



    - Also, that black trace is very much a representation of how Todd runs his 10" 2251 mids. It should be obvious as to why he says there's no benefit adding any LC components to get extra roll-off ( when the small box and tiny baffle do all the necessary LF roll-off ) .
    - His approach ( small box // small baffle ) is all fine and dandy as long as one is happy sticking with the high-ish crossover point. Clearly, if one wants more LF out of the 10 incher then one needs to place that 10" driver within a larger baffle. I've already displayed some traces of Troels work showing the effects of two different baffle sizes and what LF extension can be gained.



    My small test box combined with it's small baffle size only supports the amount of LF seen above ( that's it // that's all // no matter what WinISD might suggest ).

    Real world measurements always trump simulations . So once you get your mic // make some measurements and post them here.


    In your other thread about choosing a mid I displayed 3, Xsim ( sims ) showing the FR effect of 3 different JBL 10" mids filtered through Giskard's 4345 equivalent mid filter ( each of the 3 mids was adjusted for level by the variable Lpad of that circuit ).
    - I used JBL's FR graphs as well as JBL's published impedance graphs for the sims. I think its obvious that these 3 midrangers are more or less interchangeable within that circuit ( no matter the drivers impedance ).




    Once you start posting some real response captures of your drivers ( made with your test mic ) , I'll return my attention to this thread.

    Till Then!


  6. #36
    Senior Member Ian Mackenzie's Avatar
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    Hi Earl,

    That’s a lot of great information.

    Morton is only just starting out and it may take him a while to get up to speed with the finer and important points you have raised.

    To summarise it down:

    1. Draft up a representative test enclosure for your proposed mid/ high frequency array.
    2. Load the drivers
    3. Make some initial measurements after becoming familiar with your measurement kit
    4. After some validation and interpretation of your measurements draft out your proposed crossover points
    5. Implementation initially with the Driverack.
    6. Measure and audition the test enclosure
    7. Make adjustments and re measure and audition
    8. Decide on an active or passive crossover


    There is a tendency with most diy loudspeaker builders to want to perfect the design before attempting construction. This is a short cut but can lead to long term dissatisfaction with your loudspeaker.

    Resources: paper curves on the internet are insightful but not to be used as a baseline for your design unless you only want a short cut design.
    REW is a free download with lots on support. You only need a Minidsp mic for about $100
    Dayton sell a great loudspeaker measurement kit- see Dayton Audio.

    Making useable measurements, particularly below 300 hertz will take some learning and a number of attempts with various techniques. Don’t rush this as your end result will not be necessarily as good as it could be.

    Use your Drive rack to help craft your crossover design as passive crossover design is quite difficult.
    This is because there are calculations and the drivers interact with the passive components. Once you are happy with the drive rack crossover a passive crossover is a little easier to organise by using the active voltage drives.

    Take your time and enjoy the journey

  7. #37
    Senior Member Ian Mackenzie's Avatar
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    Thumbs down

    Quote Originally Posted by mortron View Post
    Thank you RMC and Ian! Much appreciated.

    I suppose there are quite a few different ways to skin a cat as they say... Active vs Passive has always been something I wrestle with. Doing either right is not cheap. I suppose the one aspect of the passive crossover network that appeals to me, is that I don't have any unnecessary ADAC going on in my system.


    RMC - Thanks, I get what you're saying. I spent time last night looking over Troels' site and some forums. I had initially started to price out coils based on his suggestions of 0.8-1.0mm for mids, and 0.8-0.5mm for highs. As to whether or not that is a hard and fast rule, your answer suggests there are different schools of thinking? As you say, its for testing purposes, so I suppose building a network for that vs implementing a proper finalized one will differ in execution. Changing the awg used tho would affect the resistance and tuning tho, no?


    Ian - I have wrestled with a few different approaches to the 2251J and how I would address it. Todallin uses a 2.5 way approach, and part of his appeal is a lack of high pass on the woofer - he made it sound like something to consider. I don't know if there would be merit in testing fully active, as my limited understanding has me thinking its not as simple as translating the electrical active settings into a passive network. Maybe that's part of what you're trying to convey, maybe I am totally Wrong.

    - Playing in WinISD a bit yesterday I kept getting results that looked best and smoothest in similar sized enclosures to the 7L size you suggested so feel I was headed in the right direction, so... I APOLOGIZE for the next point... I was trying to find a good primer and used some forum arguments elsewhere to make sense of this.

    - What is the effect of a bigger impedance peak on the lower or upper end if using a ported enclosure. Its the relationship between Fs of the driver and enclosure tuning, yes? Would this alone indicate how it's damped?

    - Or is being critically damped solely influenced by cabinet size? As it goes up, the system Q goes down, and makes it more damped, yes?? OR due to how everything is related, both this and my previous point indicative of the same? If I change cabinet size, the impedance curve changes IIRC... so maybe I just answered my own question.

    - I am not saying that the 2245 wouldn't go to 290hz or wherever it was crossed, but like the idea of trying both to see what they sound like. Especially if going active, it would be easy enough to try, no?

    - Should my TS be coming from the before or after power test? http://www.audioheritage.org/vbullet...hp?17040-2251J WinISD always says theres issues with my TS inputs when it tries to qualify the driver.

    Hi Morton,

    I will try and address your questions:

    1. You are correct there are a number of diy ways to address setting up your 2251 J pro drivers.

    It comes down to your skills, your expectations and complexity.

    In diy you can do whatever you like. However if you have expectations of the project being comparable to a Jbl monitor or some favourable feedback from your HIFi friends a bit more work is required.

    At this point you are at the cross roads of building out a proven design, an adaptation with similar but not identical drivers or your own home brew.

    All can work out if you follow some basic steps and do not over think the design at the outset.

    2. You are right going active can be a cut and paste of another design or text book sloped but you risk loosing the tonal balance and coherence that these drivers are truly capable of. That said with some measurements on hand they can guide you to what’s required.

    3. As an example: Your project playbook

    3.1 You measure the 2251J on the baffle and there are a few wrinkles in the response and a slight rise and peak at 4khertz. At 150 hertz you can see the sealed enclosure resonant frequency in the impedance. Ideally you want to attenuate the signal by at least 10 dB at this frequency to improve power displacement x max and undue interaction with a passive high pass network. This suggests a crossover point of 250-300 hertz with a slope of 12 dB per octave. The LR filters give a flat summation with the electrical phase reversed unlike Butterworth 12 dB filters which do not sum flat. For diy purposes the LR filters are easier to work with.

    3.2 Your measurements indicate you want the 4khertz peak attenuated by 20 dB at this frequency to avoid it effecting the upper midrange response. This suggest a 12 dB per octave crossover slope at 1000-1200 hertz. Again the LR filters are preferable for diy purposes.

    So you connect up your Drive Rack and trial the above crossover settings by test measurements and auditions. The response curve closely matches the acoustic slopes you are looking for on both low and high pass filters. There is a small amount of ripple in the pass band and do you some modelling in a diffraction calculator and come up with a revised baffle dimensions and driver cut out locations for asymmetrical layout.

    You fabricate another test baffle and re test with improvement in the response.

    4. The magnitude of the impedance peak in not a big deal. The location of that peak relative to your lower crossover point is something to consider when working out the crossover. In an ideal situation a seal .5 box tuning is said to be critically damped. But for the purposes of a mid range sealed back chamber who’s main purpose is to prevent rear sound ways cancelling like an open baffle loudspeaker.
    So anything from 0.7 to 0.5 cuft that is practical to fabricate is fine. The driver low end roll off will flatten out but this will be swamped by the 12 dB high pass midrange crossover. So it’s not something to dwell on. In terms of audible performance attributes you want good dynamic output not limited by driver X max, smooth pass band response and very low distortion.

    Yes you can try a ported enclosure. There are a few caveats.

    1. Can the driver deliver enough output in the crossover region to match the woofer?
    2. Unwanted rear back waves may reflect back through the port towards the listener.
    3. The crossover point if in proximity to the impedance peaks will make design of a passive crossover very difficult. Try it and judge for your self.
    If you were using a 12” or 15” mid bass driver it would be more appropriate.

    5. Repeat this process for the woofer. You are best to place the woofer on your driveway and the mic 2 metres from the baffling the driveway. Place the mid/high frequency array on top of the woofer enclosure.

    The woofer response below 100 hertz may have some bumps due to nearby solid objects. Your measurements show the woofer has a relatively flat response up to 1khertz but the off axis response is quite narrow.

    *Later on you an EQ out the room interaction to obtain a crisp well defined low and mid bass from the woofer.

    You plug in your Drive Rack and use a 300 hertz LR crossover filter and measure the response. The response somewhat steeper than you expected. This is due to the significant inductance of the motor.

    6. Crossover testing.
    You then plug in the midrange high frequency array with the same settings. With the drivers connected out of phase the crossover region has 2 dB hump. This could be due to mutual coupling of the drivers. So you adjust the woofer response slightly from 300 hertz to 280 hertz and re test thd measurements. The response is now flat. You put the drivers in electrical phase to confirm the phase null at the crossover point which is a uniform - 20 dB null.

    The woofer and mid first cut crossover is now completed. Note the woofer will behave differently in your room due to room boundaries.

    This is a road map of what your journey might look like. Some other things might crop up. But the key is run the entire exercise and see where you get to. Try and avoid getting bogged down in perfection at the expense of loosing sight of the overall project.

    People get hung up on perfectly smooth curves. Most curved published are smoothed or touched up. They are magazine curves. What’s important is any tilt or broad unevenness in the response of each driver and the system response overall. If your subjective assessment tells you something is wrong do some measurements of both channels and impedance. Look for any odd bumps, peaks or dips.

    Critical to the tonal balance will be setting the driver levels. I recommend 1/2 octave smoothing to assess the levels overall. Then nearfield high resolution level tests of each driver so both left and right channel match very closely. This will payoff in your listening enjoyment immensely.

    All loudspeakers are compromises in one way or another. With any luck most of the compromises will not impact on your subjective enjoyment!

    https://m.youtube.com/watch?v=_ov5fvCHmxo
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