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Thread: Building an Enclosure Around a D.A.S D-401 2395 Clone

  1. #61
    Senior Member RMC's Avatar
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    Hi Robert,

    I doubt 2226 could make a worthwhile sub. The only way to know for sure is to try it in speaker design software. But in any case you would be a lot more in sub territory with 2242 or 2245... I'm not familiar with that UREI preamp so I can't comment on that. 80 hz could be a valid x-over frequency for your sub.

    Richard

  2. #62
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    Perhaps another tit bit of advice

    Before getting too carried away with a flat response attempt to consider the real impact of room gain and baffle step.

    Ignoring these issues can leave a crater in your midbass response while an attempt to win a flat response on paper can lead to bass bloom with inherent room gain.

    For example a 24 inch front baffle width will have a baffle step shelf in the response around 190 Hz with 3-6 Db shelving of the bass response depending on the location of the woofer on the baffle.

    Jbl typically use a larger than calculated series inductor on the woofer low pass filter to off set this effect with a low pass filter.

    Room gain is un predictable but normally courts below 150 Hz and I'd dependant on the woofer location on the baffle and distance from room boundary ie the wall floor junction.

    Proximity to the floor adds 6 Db room gain, proximity to floor and wall adds 12 Db room gain and proximity to a room corner/ floor adds up to 18 Db of room gain.

    Most bass reflex box simulator assume the baffle is suspended in free space.

    One way of evaluating your box response with the above effects is to try and measure your box outside on the drive way using a test set from the likes of Parts Express at 2 metres with the box on the surface of your drive well clear of any structures

    Expect to see some dips and peaks.

    Then start to move the box closer to a rear wall

    You will notice the bass response change

    By locating the box at a distance to the rear wall equivalent to your listening room you will have some idea on the impact of room gain

    Every box is different as is every box turning

    Subtle adjustment of the port tuning frequency can help smooth the bass response

    FYI Jbl did this with their statement systems andvis the difference between an arm chair diy project and a commercial hi end loudspeaker

    Room modes in small rooms also impact on the bass responses

    But the point here is don't look at your box response simulation in isolation

    Some experimenting will yield a much better sound in your room

    if you intend to use a Db drive rack much of this can be compensated with parametric equalisation.

  3. #63
    Senior Member ivica's Avatar
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    Quote Originally Posted by Ian Mackenzie View Post
    Perhaps another tit bit of advice

    ....For example a 24 inch front baffle width will have a baffle step shelf in the response around 190 Hz with 3-6 Db shelving of the bass response depending on the location of the woofer on the baffle.


    .......
    Hi Iam,

    Interesting explanation. I have never seen such behaviours on any JBL data, nor any forum presentations.
    Can You show us such results.

    regards
    ivica

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    Hi Invica,


    It's nothing new

    Room gain is talked about more often

    Baffle diffraction is acoustic theory

    Do a google

    It's a case of being able to measure it under the right conditions

    I use LMS which is very accurate at low frequencies

    MLS is not so good at lower frequencies

    The challenge is working out a measurement procedure.

    That is why you first need to remove all other influences like small room modes

    Jbl build it into the crossover

    Look at the voltage drives (see below the woofer voltage drive starts just above 100Hz)

    You probably won't see it done this way anymore as they fired the one guy smart enough to get it right.

    Depending on the system the voltage drives start to attenuate at frequencies far below the crossover point

    In a multi way system it's easier to deal with.

    The impact of room gain also needs to be weighed up

    If you have access to proper modelling software is quite obvious that what happens on a real baffle in a real room is quite different from a T/L calculated response.

    You can predict with diffraction modelling

    An analogy is tidal movement

    There are waves on the surface from room interference.

    But the baffle, and the baffle location in the room have an overriding influence over the level and balance the sea (sound level in the bass, mid bass and mid range)

    It's the underlying influence of the voicing of bass and mid bass region

    Narrow tower loudspeakers use dual woofer in many cases for this reason (or slice of 3-6 db sensitivity)
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  5. #65
    Senior Member ivica's Avatar
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    Quote Originally Posted by Ian Mackenzie View Post
    Hi Invica,


    It's nothing new

    Room gain is talked about more often

    Baffle diffraction is acoustic theory

    Do a google

    It's a case of being able to measure it under the right conditions

    I use LMS which is very accurate at low frequencies

    MLS is not so good at lower frequencies

    The challenge is working out a measurement procedure.

    That is why you first need to remove all other influences like small room modes

    Jbl build it into the crossover

    Look at the voltage drives (see below the woofer voltage drive starts just above 100Hz)

    You probably won't see it done this way anymore as they fired the one guy smart enough to get it right.

    Depending on the system the voltage drives start to attenuate at frequencies far below the crossover point

    In a multi way system it's easier to deal with.

    The impact of room gain also needs to be weighed up

    If you have access to proper modelling software is quite obvious that what happens on a real baffle in a real room is quite different from a T/L calculated response.

    You can predict with diffraction modelling

    An analogy is tidal movement

    There are waves on the surface from room interference.

    But the baffle, and the baffle location in the room have an overriding influence over the level and balance the sea (sound level in the bass, mid bass and mid range)

    It's the underlying influence of the voicing of bass and mid bass region

    Narrow tower loudspeakers use dual woofer in many cases for this reason (or slice of 3-6 db sensitivity)
    Hi Ian,

    not to argue with You and known theory, but such baffle step can be very difficult to see on almost any JBL data presentation.
    Just to remember that all 43xx speakers are "book shelf" speakers, so it is expected to 'radiate in to 2pi space', so baffle is expected to be very
    large. Just to remember that most of the JBL data for 22xx (15") drivers are shown under 2pi 'surroundings' using about 250Lit close box.
    Here on the Forum it can be seen a photo of "on the roof measurements' procedure.
    Due to the drivers size its directivity changes so the amount of sound energy is emitted in the smaller angular space, and due to the cone flection, less moving mass is loaded to the BL force, and some large peak can be seen on the most drivers responses (over 1kHz). If we are talking about driver internal inductive part of internal impedance, I think it become 'active' almost over 0.5kHz ( 1mH in 0.5kHz is about 3.2 Ohms) not on 100~200 Hz.

    Here I do not want to elaborate the influence of the other surfaces , room standing waves, reverberations, etc...just I want to see mentioned baffle-step in the mentioned 'book shelf surrounding', on some real measurements data or graph. I am totally aware that real in the room response of the speaker would very, very different then the "pure 2pi case".

    regards
    ivica

  6. #66
    Senior Member RMC's Avatar
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    Hi Ian, (And Robert)

    I couldn't pass on this one (your post # 62). With all due respect, I don't know where you are getting some of that info, but mine is identified below.

    "Before getting too carried away with a flat response attempt to consider the real impact of room gain and baffle step." Agreed. If a sub was placed in the middle of a room (away from boundaries) and on a pedestal, base or stand, its unlikely one would get the 6 db room gain from boundary (since not real half-space).

    "Room gain is un predictable but normally courts below 150 Hz and I'd dependant on the woofer location on the baffle and distance from room boundary ie the wall floor junction." More or less agreed because room gain is somewhat predictable. Electro-Voice states, in the System Positioning section, that "... the audible location of a subwoofer operating at a sufficiently low crossover frequency (below about 150 hz) will not be particularly evident." (Data sheet, PI218L, Low-Frequency Sound reinforcement System, 1994, P.3) I understand from this that 150 hz, you also mentioned, is the point where bass frequencies start to get omnidirectional, and therefore more difficult to locate, plus can benefit from room boundary placement gain instead of "wrapping around" the box as "diffraction loss"...

    "Proximity to the floor adds 6 Db room gain, proximity to floor and wall adds 12 Db room gain and proximity to a room corner/ floor adds up to 18 Db of room gain." Two of these numbers appear to be wrong. First, floor OR wall placement does provide half-space (2 Pi) environment that leads to 6 db room gain, but one has to mention compared to full-space (4 Pi, or free space) environment. Again, from the same E-V data sheet mentioned above, in the same System Positioning section on P.3: "Floor location provides the acoustic half-space environment associated with the 6.1% system efficiency noted in the Specifications sections." Moreover adds: "Location at a floor-wall junction (acoustic quarter space) doubles efficiency (a 3-db increase in acoustic power level)..." That is compared to floor location only. Then further adds: "Corner placement (acoustic eighth space) doubles efficiency again..." Which I understand means another 3 db increase compared to floor-wall location. So, if I count correctly, it would be 6 db gain from full-space to half-space, then 3 db gain from half-space to quarter space, and finally another 3 db gain from quarter space to eighth space, for a total of 12 db of possible room gain from speaker placement. Not exactly the same numbers as yours.

    "Most bass reflex box simulator assume the baffle is suspended in free space." I think this statement is questionable. John Eargle (JBL) writes "The data calculated from the thiele/Small parameters refers only to the LF performance of the system ... Further, the analysis assumes that the loudspeakers will be locating adjacent to a single reflective boundary, such as the ground, or a wall." (Handbook of Sound System Design, ELAR, 1989, P. 106). And in the Low-Frequency Systems and Enclosures chapter, section Thiele-Small parameters, of his "Loudspeaker Handbook", Chapman & Hall, 1997, P. 58, John Eargle makes it even more clear, if it wasn't enough: "Modeling of the system's response functions assumes that the enclosure is mounted in a large wall (a so called 2 Pi, or half-space, boundary condition)." My understanding is that any software using T/S model should therefore assume 2 Pi boundary condition of use, not free space.

    "One way of evaluating your box response with the above effects is to try and measure your box outside on the drive way using a test set from the likes of Parts Express at 2 metres with the box on the surface of your drive well clear of any structures" "Then start to move the box closer to a rear wall. You will notice the bass response change. By locating the box at a distance to the rear wall equivalent to your listening room you will have some idea on the impact of room gain" Bass wise, to me this is half-space front wave radiation, as inside a room, however with no reflections from walls and/or ceiling since there are none in that setup... Moving closer to a rear wall as you say, leads to quarter space radiation, as inside a room, however again with no wall and ceiling reflections in your setup. You can also get "some idea on the impact of room gain" by doing the same inside, but with reflections...

    "But the point here is don't look at your box response simulation in isolation. Some experimenting will yield a much better sound in your room." Mostly agreed. Speaker placement experimentation MAY lead to better sounding, not automatically much better, since there are always constraints in a room.

    "if you intend to use a Db drive rack much of this can be compensated with parametric equalisation." In my post # 59 I did suggest parametric EQ relief but on the driver's mid-bass rising response: "Adjustable Parametric EQ on the "agressive or offensive" mid-bass level is another interesting alternative..." Whereas your suggestion seems to be for the low end. Regards,

    Richard

  7. #67
    Senior Member ivica's Avatar
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    Mutual coupling as a model

    Quote Originally Posted by RMC View Post
    Hi Ian, (And Robert)

    I couldn't pass on this one (your post # 62). With all due respect, I don't know where you are getting some of that info, but mine is identified below.

    "Before getting too carried away with a flat response attempt to consider the real impact of room gain and baffle step." Agreed. If a sub was placed in the middle of a room (away from boundaries) and on a pedestal, base or stand, its unlikely one would get the 6 db room gain from boundary (since not real half-space).

    "Room gain is un predictable but normally courts below 150 Hz and I'd dependant on the woofer location on the baffle and distance from room boundary ie the wall floor junction." More or less agreed because room gain is somewhat predictable. Electro-Voice states, in the System Positioning section, that "... the audible location of a subwoofer operating at a sufficiently low crossover frequency (below about 150 hz) will not be particularly evident." (Data sheet, PI218L, Low-Frequency Sound reinforcement System, 1994, P.3) I understand from this that 150 hz, you also mentioned, is the point where bass frequencies start to get omnidirectional, and therefore more difficult to locate, plus can benefit from room boundary placement gain instead of "wrapping around" the box as "diffraction loss"...

    "Proximity to the floor adds 6 Db room gain, proximity to floor and wall adds 12 Db room gain and proximity to a room corner/ floor adds up to 18 Db of room gain." Two of these numbers appear to be wrong. First, floor OR wall placement does provide half-space (2 Pi) environment that leads to 6 db room gain, but one has to mention compared to full-space (4 Pi, or free space) environment. Again, from the same E-V data sheet mentioned above, in the same System Positioning section on P.3: "Floor location provides the acoustic half-space environment associated with the 6.1% system efficiency noted in the Specifications sections." Moreover adds: "Location at a floor-wall junction (acoustic quarter space) doubles efficiency (a 3-db increase in acoustic power level)..." That is compared to floor location only. Then further adds: "Corner placement (acoustic eighth space) doubles efficiency again..." Which I understand means another 3 db increase compared to floor-wall location. So, if I count correctly, it would be 6 db gain from full-space to half-space, then 3 db gain from half-space to quarter space, and finally another 3 db gain from quarter space to eighth space, for a total of 12 db of possible room gain from speaker placement. Not exactly the same numbers as yours.

    "Most bass reflex box simulator assume the baffle is suspended in free space." I think this statement is questionable. John Eargle (JBL) writes "The data calculated from the thiele/Small parameters refers only to the LF performance of the system ... Further, the analysis assumes that the loudspeakers will be locating adjacent to a single reflective boundary, such as the ground, or a wall." (Handbook of Sound System Design, ELAR, 1989, P. 106). And in the Low-Frequency Systems and Enclosures chapter, section Thiele-Small parameters, of his "Loudspeaker Handbook", Chapman & Hall, 1997, P. 58, John Eargle makes it even more clear, if it wasn't enough: "Modeling of the system's response functions assumes that the enclosure is mounted in a large wall (a so called 2 Pi, or half-space, boundary condition)." My understanding is that any software using T/S model should therefore assume 2 Pi boundary condition of use, not free space.

    "One way of evaluating your box response with the above effects is to try and measure your box outside on the drive way using a test set from the likes of Parts Express at 2 metres with the box on the surface of your drive well clear of any structures" "Then start to move the box closer to a rear wall. You will notice the bass response change. By locating the box at a distance to the rear wall equivalent to your listening room you will have some idea on the impact of room gain" Bass wise, to me this is half-space front wave radiation, as inside a room, however with no reflections from walls and/or ceiling since there are none in that setup... Moving closer to a rear wall as you say, leads to quarter space radiation, as inside a room, however again with no wall and ceiling reflections in your setup. You can also get "some idea on the impact of room gain" by doing the same inside, but with reflections...

    "But the point here is don't look at your box response simulation in isolation. Some experimenting will yield a much better sound in your room." Mostly agreed. Speaker placement experimentation MAY lead to better sounding, not automatically much better, since there are always constraints in a room.

    "if you intend to use a Db drive rack much of this can be compensated with parametric equalisation." In my post # 59 I did suggest parametric EQ relief but on the driver's mid-bass rising response: "Adjustable Parametric EQ on the "agressive or offensive" mid-bass level is another interesting alternative..." Whereas your suggestion seems to be for the low end. Regards,

    Richard

    Hi Richard,

    Generally speaking if we have TWO sources of sound (working together) very near each other, and producing the sound in the same frequency region, but independent each other (example each producing noise) we can expect the +3dB rise in the sound level, but if they are reproducing the same sound source (correlated sound) then the rise would be +6dB. Such behavior can be seen in the:

    http://www.zainea.com/mutualcoupling.htm
    http://www.audioheritage.org/vbullet...l=1#post399606

    so if the distance between the sources is LESS then 0.5 Lambda (Lambda=345/f), or better to say LESS then 0.25*Lambda we can expect the rise in the response of MORE THEN +3dB, but not more then +6dB.

    We can assume flat surface near the sound source as ideal reflecting surface (as a sound mirror), and that the sound source is not-directional (Omnidirectional) and IF THE DISTANCE BETWEEN THE SOURCE AND THE SURFACE IS LESS THEN 0.25*Lambda (or better 0.15*Lambda) then we can expect almost +6dB in rise in the sound level, because in such citcumstances such sound source and the surface behave as TWO correlated sound source that are near (twice the distance the sound source from the surface) each other.
    If another surface is prezent perpendicular to the previous one, then (again imagine as another mirror) the sustem would behave as 4 (four) corelated sources working together, so another +6dB in the sound level can be expected, so totally +12dB, but again the surfaces are assumed to be less then about 0.15*Lambda from the sound source. If the distances from the surfaces are larger then mentioned, total rise would 'only' +6dB.

    Asumming another perpendicular surface to the previously mentoned two, would give another +6dB rise in the sound level, as in such case it would behaves as 8 (eight) corelated sound sources, so totaly +18dB in the sound level, but again sound source has to be about less then 0.15*Lambda from any of the surfaces. As an example for f=170Hz (or less) Lambda=2m (or more), so the distance has to be less then 30cm from the surface(s). If the distances are larger then total gain would be reduced from +18dB to about +9dB (fot some specific frequency even less).
    The whole scene would become more complicated if the directivity of the sound source is assumed. Not to mention that when the sound frequency rises, the infuence of the surface 'reflectivity' would become factor of influence, but for relayvely low frequency, and usual surface characteristics in our home, previously mentioned model can be assumed.
    I would say that if we put the speaker relatively away (say about 1m) from the wall or the flore (ceiling) in the almost bookshelf arrangement then I would expect to get almost predicted LF response, and if we want to enhace LF section (but to be aware of the irregularities) then we can move the speaker near the flore arrangement. A lot of experiments has to be done to find out the best possible compromose.
    In the previously mentioned, other in-the-room effects (multiple reflections, standing waves, reverberations,...etc) are not considered.

    regards
    ivica

  8. #68
    Senior Member RMC's Avatar
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    Hi Robert,

    Re your post where you mentioned hoping not to have to use a series resistor with the woofer, and my post where I said I was not a fan of using a series resistor on a woofer. While looking for something else in my audio library (searching for A and finding B as often happens...) , here's what I found in Bullock On Boxes, 1991, P. 7, in the Design Box, examples # 2 and three, where additional resistance with woofer is covered.

    (Talking about a cut-off frequency reduction with increased box size), here's what Bullock says in example # 2: "... which can be reduced even more by adding a resistor in series with the driver. This will increase Qts and reduce F3. In my opinion, added resistance tends to degrade other aspects of performance, so do not use it unless you must. Your own ears are best judge of the results, however." In example # 3 he uses a driver with a Qts of 0.28, adds resistance to it, and concludes "Thus, a resistor of 2/3 ohms in series with the driver will raise Qts to 0.32." A 14% increase.

    The point here is that driver Qts is an important number (like Fs and Vas) in determining an enclosure's characteristics. Tampering with Qts (as a side-effect of wanting to reduce mid-bass rising response with a resistor) also means different box design parameter... The parametric EQ or small bass bump ideas have more appeal to me.

    One more time, searching for A and finding A and B this time!, I came across Electro-Voice's equation for vent length tuning (Lv) on the 1993 spec sheet of 15" driver EVX-150A (P.4). I gave it a try with YOUR box numbers plugged-in to see. The vent length result is 1.09347" (or 1.1") which is still in the range of 1 to 1 1/4" mentioned before...

    Richard

  9. #69
    Senior Member ivica's Avatar
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    Quote Originally Posted by RMC View Post
    Hi Robert,

    Re your post where you mentioned hoping not to have to use a series resistor with the woofer, and my post where I said I was not a fan of using a series resistor on a woofer. While looking for something else in my audio library (searching for A and finding B as often happens...) , here's what I found in Bullock On Boxes, 1991, P. 7, in the Design Box, examples # 2 and three, where additional resistance with woofer is covered.

    (Talking about a cut-off frequency reduction with increased box size), here's what Bullock says in example # 2: "... which can be reduced even more by adding a resistor in series with the driver. This will increase Qts and reduce F3. In my opinion, added resistance tends to degrade other aspects of performance, so do not use it unless you must. Your own ears are best judge of the results, however." In example # 3 he uses a driver with a Qts of 0.28, adds resistance to it, and concludes "Thus, a resistor of 2/3 ohms in series with the driver will raise Qts to 0.32." A 14% increase.

    The point here is that driver Qts is an important number (like Fs and Vas) in determining an enclosure's characteristics. Tampering with Qts (as a side-effect of wanting to reduce mid-bass rising response with a resistor) also means different box design parameter... The parametric EQ or small bass bump ideas have more appeal to me.

    One more time, searching for A and finding A and B this time!, I came across Electro-Voice's equation for vent length tuning (Lv) on the 1993 spec sheet of 15" driver EVX-150A (P.4). I gave it a try with YOUR box numbers plugged-in to see. The vent length result is 1.09347" (or 1.1") which is still in the range of 1 to 1 1/4" mentioned before...

    Richard
    i
    Hi Richard,

    the problem of using electronically assisted EQ has one problem, if driver as E145 is used.
    For the Vb=225 Lit, Fb=45Hz, and if You use hi-pass (12dB/oct) EQ where Q=1.5 at 35Hz, almost flat response can be get ( F3=40.5Hz, without EQ, F3=51Hz), but maximal cone displacement would limit max input power to about 60W instead of about 150W without EQ.

    regards
    ivica

  10. #70
    Senior Member RMC's Avatar
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    Hi Ivica,

    The parametric EQ suggested has NOTHING to do with the bass range. That suggestion was to correct, improve or reduce mid-bass rising response of E-145 instead of a series resistor. Please read my last posts again...

    Richard

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    Hi Invica,

    I understand your reference to Jbl test data.

    We are all able to express an opinion and that is good.

    But my view is the kind of Jbl designs here with a 15 inch woofer the term book shelf is "name sake ".

    They are floor standing loudspeakers.

    Most of the blue baffle designs talked about here are not book shelf or more appropriately sofit mounted in a forum members home.(1)

    Perhaps more pertinent is the fact that JBLs blue baffle monitors are sold out of Hifi retail shops to consumers. They are not building those into walls st home.

    (1) Baffle diffraction and its complex nature are at work as is boundary reinforcement.

    In some cases the impact of room boundary reinforcement offsets the baffle step.

    If you google baffle step out loudspeaker baffle diffraction there are some good references and spreadsheets to model the impact.

    It's a fact in contemporary loudspeaker design that baffle step compensation is a consideration as is room boundary reinforcement.(room gain)

    My comments concerning room gain encompass room boundary influences as the source can be a point anywhere in space meaning the room.

    This is a more difficult challenge in a two way design as you are trying to get one driver "the woofer" to behave a particular way. A 3 or 4 way system can purposely use a driver to overcome a particular issue.

    Jbl use a standardised measurement approach but they have varied the design of the vented systems over the years to "incorporate" the impact in a variety of listening rooms and enclosure locations.

    It not necessarily a good idea to take a manufacturers test results on face value.

    Unless your wife is comfortable with you digging up the back yard you are not going to be doing equivalent measurements.

    On bass reflex tuning no body doubts GT's approach to banana curve tuning of the statement systems.

    The next point is that in a pure diy design you are not using a Jbl engineered design that was empirically evaluated with several prototypes.

    Therefore what might appear good on paper can have a less than predictable results in reality. This was the point of my earlier posts.

    It really depends on how far you want to go with your own diy project.

    Any diy project is just that and it's a case of looking at what's in scope and within your means.

    I always find it useful to look at Jbl did with certain drivers in their system designs.

    As l said most of their home systems are empirical design iterations before these go into production

  12. #72
    Senior Member ivica's Avatar
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    JBL Bass Drivers Responses

    Quote Originally Posted by Ian Mackenzie View Post
    .......I understand your reference to Jbl test data.

    ...
    (1) Baffle diffraction and its complex nature are at work as is boundary reinforcement.
    In some cases the impact of room boundary reinforcement offsets the baffle step.
    If you google baffle step out loudspeaker baffle diffraction there are some good references and spreadsheets to model the impact.
    It's a fact in contemporary loudspeaker design that baffle step compensation is a consideration as is room boundary reinforcement.(room gain)
    My comments concerning room gain encompass room boundary influences as the source can be a point anywhere in space meaning the room.
    ......
    It not necessarily a good idea to take a manufacturers test results on face value.
    Unless your wife is comfortable with you digging up the back yard you are not going to be doing equivalent measurements.
    On bass reflex tuning no body doubts GT's approach to banana curve tuning of the statement systems.
    ....
    As l said most of their home systems are empirical design iterations before these go into production

    Hi Ian,

    Many thanks for the comments.
    Just to remember that our speakers are not usually in opens-pace hanged on the tree, but near the one large surface.
    I think that attached "Driver Stp Response" would give the best explanation.

    regards
    ivica
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    Hi Richard and Invica,

    Thank you both for the stimulating discussion.

    Half space, box simulations , ground plane measurements can be a bit of challenge to make sense of at the best of times

    I wrote the earlier post on the iphone at the airport gate lounge waiting for a flight.

    I hope it made sense.

    This is a simple link but l like it

    http://www.mh-audio.nl/Groundplane.asp

    In terms of references l use hard copy manuals for LEAP software, Bullock on Boxes and the Loudspeaker Cookbook.

    But Enclosure Shop can actually simulate a lot of this stuff but it take a long time to render.

    Unfortunately the scientist who wrote it died recently.

    I have an older version of Sound Easy but it a complicated package to use.

    I will post links to some interestingly online baffle diffraction simulator when l recover from the return flight.

    As you point out the JBL measurements are on a roof top (half space)

    Some also splice a ground plane measurement below 100 hertz.

    The rooftop (in the ground) approach gives a cleaner graph which some affectionately call magazine curves!

    Of late have been getting my hands dirty with some ground plane measurements outside.

    I will check out the E145 in Bass box with the amended Vas.

    Bassbox allows importing of room gain data and overlay on the box simulation.

    http://www.tolvan.com/edge/help.htm

    http://audio.claub.net/software/jbabgy/BDBS.html

  14. #74
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    Just to add some thoughts and information. I have been using an E-145 sub-woofer combination for years now and have been pleased with response. I originally started with Le-14 subs and changed over to B380 2235's under. I see some concern about baffle step but I would not worry all that much as between the choice of the crossover point, placement/boundary reinforcement and potential mutual coupling between drivers through the crossover it gets a bit complicated. If you are running active you can stagger the levels on the drivers as well to give an added measure of response tailoring not to mention slopes, delay and EQ in the digital domain. I am posting the simulations I used in Bass Box to build my boxes just for information.

    Rob
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  15. #75
    Senior Member ivica's Avatar
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    Quote Originally Posted by Robh3606 View Post
    Just to add some thoughts and information. I have been using an E-145 sub-woofer combination for years now and have been pleased with response. I originally started with Le-14 subs and changed over to B380 2235's under. I see some concern about baffle step but I would not worry all that much as between the choice of the crossover point, placement/boundary reinforcement and potential mutual coupling between drivers through the crossover it gets a bit complicated. If you are running active you can stagger the levels on the drivers as well to give an added measure of response tailoring not to mention slopes, delay and EQ in the digital domain. I am posting the simulations I used in Bass Box to build my boxes just for information.

    Rob
    Hi Rob,
    It seems to me thay on 2235 (B380) model, a kind of 'Active HP EQ Filter' is applied, while on E145 is without such 'help'

    regards
    ivica

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