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Thread: Power Amps for JBL 4675C

  1. #16
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    Quote Originally Posted by baldrick View Post
    I had 4 If these, running them with 2x2,4kw.

    if you are going to use them as subs their average effiency is more like 96db, and If you want to be flat down to 22hz, you will need aprox 6db EQ. So suddenly you are down to like 90db, and therefore you need power.

    of course it will work with 300w but If you want to use it for What itís meant for, you will want more.

    Crown iTech will work great!
    Are you mistaking what speakers we're talking about? The 4675C (uses the 4648A LF cabinet, 2360 horn/2446HF driver. Who said anything about using them as subs?

    The 4648A box is vented at 40Hz. Anyone trying to pump it much below that is foolish. It is 10dB down by 35Hz even JBL recommends a high-pass at 40Hz (12dB/Octave). So no, 22Hz is out of the question as is a 6dB boost (below 40Hz though one can put in a mild boost near the vent frequency to flatten it out there (3dB down is at 45Hz). JBL once recommended it with the 5234/5235 crossovers.

    I don't know where you people make this stuff up

    I've worked with countless 4675s (hundreds for sure, possibly over a thousand). It isn't a subwoofer and it is decent down to about 40Hz. If you want a subwoofer, get a subwoofer (one of the 4645 variants if you want to keep it in the cinema family that would have mated up with the 4675 though by the time the "C" came around, it would have likely been the 4645C...using the 2242 driver). Then, you can bring out the big gun amps though in a household, probably still don't need anything too terrifying.

  2. #17
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by baldrick View Post
    I had 4 If these, running them with 2x2,4kw.

    if you are going to use them as subs their average effiency is more like 96db, and If you want to be flat down to 22hz, you will need aprox 6db EQ. So suddenly you are down to like 90db, and therefore you need power.

    of course it will work with 300w but If you want to use it for What it’s meant for, you will want more.

    Crown iTech will work great!
    Slightly off topic, but probably worth considering. Let’s say you have a pair of speakers with a one meter sensitivity rating of 90dB/watt/meter. A pair of them in a typical living room will require <10 watts to play at about 95 dB at 3m which is a typical moderately loud playback level and scenario. If you want 10dB of headroom you’ll want about 100 watts per channel. Kilowatts? If you want to hurt yourself I guess.


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  3. #18
    Senior Member baldrick's Avatar
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    Quote Originally Posted by sguttag View Post
    Are you mistaking what speakers we're talking about? The 4675C (uses the 4648A LF cabinet, 2360 horn/2446HF driver. Who said anything about using them as subs?

    The 4648A box is vented at 40Hz. Anyone trying to pump it much below that is foolish. It is 10dB down by 35Hz even JBL recommends a high-pass at 40Hz (12dB/Octave). So no, 22Hz is out of the question as is a 6dB boost (below 40Hz though one can put in a mild boost near the vent frequency to flatten it out there (3dB down is at 45Hz). JBL once recommended it with the 5234/5235 crossovers.

    I don't know where you people make this stuff up

    I've worked with countless 4675s (hundreds for sure, possibly over a thousand). It isn't a subwoofer and it is decent down to about 40Hz. If you want a subwoofer, get a subwoofer (one of the 4645 variants if you want to keep it in the cinema family that would have mated up with the 4675 though by the time the "C" came around, it would have likely been the 4645C...using the 2242 driver). Then, you can bring out the big gun amps though in a household, probably still don't need anything too terrifying.
    Sorry, I misread 4645C With 4675C

    BTW: I've also had 4675C. My oppinion is that's it hard to make it sound OK without a lot of EQ and prefarably biamp/triamp (and also extra tweeter). Whetere the woofers are 2226 or 2035 they need quite a bit of Power to shine.

  4. #19
    Senior Member martin_wu99's Avatar
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    Quote Originally Posted by sguttag View Post
    Small correction, the 4675C is only a 100 dB 1w/1m sensitivity. Still, not needing anything in a high powered amp for home use.

    How far away are you going to be seated and how loud do you want it to get? At about 10-feet away, you could hit 115dB with 300-watts (using the passive crossover). If you crossover at 500Hz, you'll find that you'll only need have of that power for the LF section...and we're talking about 115dB...the stuff that hearing loss is made from. And I'm also using power for pink noise, not actual program material.

    Before you remove the passive crossover from the circuit, use your existing power and ask yourself if it gets loud enough. I suspect that the answer will be "yes" with most any sized amplifier you put on it, unless you are really into VERY loud music (rock or even the cannon blast in the 1812 Overture, but for that, I'd recommend a subwoofer).

    Most home speakers are in the 80s-90s in sensitivity. Yours will be nearly 10dB more sensitive than that. 10dB in amplifier power is huge (9dB being 8 times so using rough numbers, if you think a typical home speaker needs 250-watts of power to hit your happy spot of level...these will need less than 35-watts.
    It is totally two things!high power amp doesn't mean high sound presure level,you need not have to turn your amp at big volume when at home,but you must let 4675 works in the best state,we call it power reserve, in order to make full use of 4675.
    46 lover

  5. #20
    Senior Member martin_wu99's Avatar
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    Quote Originally Posted by gameuno View Post
    sguttag, I understand what you mean. Just one thing: I dont want to biamp for more db, but for besser sound quality because of less distortion without the passive crossover. Following your argumentation, I surely wont need that much power. Good thing, that definetly equals less money to spend

    martin_wu99, even at relatively low listening levels? What would be the use of high wattage then? Im irritated
    What does "besser" "irritated" mean?
    To be frank,don't driver your truck with a lawn mower engine
    46 lover

  6. #21
    Senior Member baldrick's Avatar
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    Quote Originally Posted by Mr. Widget View Post
    Slightly off topic, but probably worth considering. Letís say you have a pair of speakers with a one meter sensitivity rating of 90dB/watt/meter. A pair of them in a typical living room will require <10 watts to play at about 95 dB at 3m which is a typical moderately loud playback level and scenario. If you want 10dB of headroom youíll want about 100 watts per channel. Kilowatts? If you want to hurt yourself I guess.
    For lot of use you might be correct, but I mean, if you buy a pair of 4645 and only power them with 100watt, you have probably bought the wrong sub And if you think of it... a sub like Array 1500 have a built in 1kw amp, why should you use 1/10 of this with 2242?

    For everyday music playback, 100w would be enough, but used for higher SPL and/or hometheater, it will be too litle. And alsoÖ my experince is very often a high power amp will have better Control than a smaller Power amp. Crown iTech is great for sub duty, but maybe not the correct choice for a speaker like 4675 used in a home enviroment.

  7. #22
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    besser = better
    irritated = annoyed or possibly upset.

    Whereas people come from all over the globe, there probably isn't a need to dive into one's broken use of a language when the intent seems self-explanatory based on context. Naturally, I'm fortunate that this forum uses English as its language (it is the one that I'm best at, though far from perfect despite a lifetime of usage).

    "don't driver your truck with a lawn mower engine"

    That is a poor analogy. The truck weighs a lot and a lawnmower engine doesn't have the horsepower to drive it. In the case of the speaker, the sensitivity tells us how hard it is to drive. Compared to the typical home speaker, the 4675 is much easier to drive and needs less power to achieve the same level as less-efficient speakers.

    To keep with your car analogy, you don't drop a Formula 1 engine into your car you drive to work on normal roads. You can, I suppose, but you'd never take advantage of it...you'd just have to pay for it.

    "
    a sub like Array 1500 have a built in 1kw amp, why should you use 1/10 of this with 2242"

    It all depends on the usage and desired SPL. The 2242 portion allows a particular frequency response with a given cabinet and based on those two factors plus room size and desired SPL, you get to amplifier size needed to achieve those. If a room is 3-4m long and one is listening to music, you just don't need that much power.

    Keeping with analogies, if your needs are that you are going to drink 2-cups of water in any meal, there is no good reason to get a full 1-gallon jug each time.

    "
    but used for higher SPL and/or hometheater, it will be too litle[sic]"

    Ah ha! Now you have changed the equation a bit. We've moved from music speakers (left/right) to home theatre subwoofer. Rather than just an augmentation to a normal speaker, the cinema subwoofer is its own channel with a potential 10dB more level. So now, the potential for the subwoofer is to play at about 112dBc (presuming reference level volume is set) in the pass band (120Hz and below). Coming off of that will be whatever room-gain you have and boundary conditions that might put the subwoofer in a more efficient circumstance. But yes, if the need was for a cinema-subwoofer, I would indeed go up on power. And, true to form, for my own home theatre were we built SUB 18 clones (a little larger) I'm indeed providing them with thousands of watts. In fact, despite being in the USA (normally 120VAC), that amp will be powered by 240VAC (home power) to keep the current down and avoid tripping any circuit protection (plus that balances out the power to the panel well). The 2269 is relatively inefficient driver but it plays quite deep and handles lots of power. I have two of them in the system for a room that is about 4m deep. They will be on the floor, in a baffle wall and near the sidewalls of the room.

    "my experince [sic] is very often a high power amp will have better Control than a smaller Power amp"

    Our experiences are not the same.




  8. #23
    Senior Member martin_wu99's Avatar
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    Quote Originally Posted by gameuno View Post
    Mctwins, power hungry even at low db? Then im even more confused.

    There still seems to be a huge debate about the influence of wattage on the bass at low volume.
    Guess I should just read more and more, maybe somewhen I will come to a sure conclusion.

    sguttag, I fully understand what you are saying, and I am sure you are getting annoyed by this thread.
    IMO,you'd better find a amp with 500W/ch/8ohm for your 4675C HT,if you want Hifi,bi-amp it with 500W/ch/8ohm solid amp and a several watts single-ended class A tube amp,it is amazing!there are some examples in Chinese audiophiles who play 4675C.

    Whatever,others favorite is not yours,try as many amps as you can,untill you find one which satisfy you.
    I drive my 4628b with SAE P500 (500W/ch/8ohm) in my fifteen square meters room.
    46 lover

  9. #24
    Senior Member martin_wu99's Avatar
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    Quote Originally Posted by sguttag View Post
    besser = better
    irritated = annoyed or possibly upset.

    Whereas people come from all over the globe, there probably isn't a need to dive into one's broken use of a language when the intent seems self-explanatory based on context. Naturally, I'm fortunate that this forum uses English as its language (it is the one that I'm best at, though far from perfect despite a lifetime of usage).

    "don't driver your truck with a lawn mower engine"

    That is a poor analogy. The truck weighs a lot and a lawnmower engine doesn't have the horsepower to drive it. In the case of the speaker, the sensitivity tells us how hard it is to drive. Compared to the typical home speaker, the 4675 is much easier to drive and needs less power to achieve the same level as less-efficient speakers.

    To keep with your car analogy, you don't drop a Formula 1 engine into your car you drive to work on normal roads. You can, I suppose, but you'd never take advantage of it...you'd just have to pay for it.

    "
    a sub like Array 1500 have a built in 1kw amp, why should you use 1/10 of this with 2242"

    It all depends on the usage and desired SPL. The 2242 portion allows a particular frequency response with a given cabinet and based on those two factors plus room size and desired SPL, you get to amplifier size needed to achieve those. If a room is 3-4m long and one is listening to music, you just don't need that much power.

    Keeping with analogies, if your needs are that you are going to drink 2-cups of water in any meal, there is no good reason to get a full 1-gallon jug each time.

    "
    but used for higher SPL and/or hometheater, it will be too litle[sic]"

    Ah ha! Now you have changed the equation a bit. We've moved from music speakers (left/right) to home theatre subwoofer. Rather than just an augmentation to a normal speaker, the cinema subwoofer is its own channel with a potential 10dB more level. So now, the potential for the subwoofer is to play at about 112dBc (presuming reference level volume is set) in the pass band (120Hz and below). Coming off of that will be whatever room-gain you have and boundary conditions that might put the subwoofer in a more efficient circumstance. But yes, if the need was for a cinema-subwoofer, I would indeed go up on power. And, true to form, for my own home theatre were we built SUB 18 clones (a little larger) I'm indeed providing them with thousands of watts. In fact, despite being in the USA (normally 120VAC), that amp will be powered by 240VAC (home power) to keep the current down and avoid tripping any circuit protection (plus that balances out the power to the panel well). The 2269 is relatively inefficient driver but it plays quite deep and handles lots of power. I have two of them in the system for a room that is about 4m deep. They will be on the floor, in a baffle wall and near the sidewalls of the room.

    "my experince [sic] is very often a high power amp will have better Control than a smaller Power amp"

    Are experiences are not the same.



    Never mind,i don't understand that two words indeed,and i want to make the discussion light.
    Whether or not a poor analogy,it is not very hard to find some cases that driving 4675 amps for pro and home use.
    Again,audiophile is very personalized,there is not a standard answer for such question.
    BTW,i find it is very hard to convince somebody on the network
    46 lover

  10. #25
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by martin_wu99 View Post

    BTW,i find it is very hard to convince somebody on the network
    Don't feel bad... it is very hard to change people's opinions through any means of discussion. It's human nature I suppose.

    To objectively look at a problem with the mind of a scientist is one thing, but this goes against our nature at least for the vast majority of us.


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  11. #26
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    FWIW I always power systems based on my max SPL number which for me is 115db clean with no amplifier headroom in the consideration. Just use speaker sensitivity and listening distance to determine how much power I need. Yeah you can throw a kilowatt at a system but why waste the money on that much power if you simply don't need it? Subs with EQ however loose much of their headroom in the EQ. So with a common JBL alignment of +6db at box tuning you just chopped your available power to 1/4 of the rated amp power.

    Rob
    "I could be arguing in my spare time"

  12. #27
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    Yes, sguttag, besser = better. I am German and besser is the german translation, I am sorry.
    For now I have made the conclusion that your argument makes sense.

    Saying that high wattage brings better control over the woofers, even at low levels, does not make sense to me.
    What even does "control" mean in this case? There is no mathematical explanation that the high power is useful in my situation.
    This argument seems like something one would say to have a justification for the big 1kW amps that he wants at home, when in reality one just likes big numbers

    Tube amps on the other hand might be worth considering, but that will make things even more complicated.

  13. #28
    Senior Member Ian Mackenzie's Avatar
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    Quote Originally Posted by gameuno View Post
    Hello, this is my first post on this forum, hopefully you can help me

    I recently bought a pair of used JBL 4675C (https://www.jblpro.com/ProductAttachments/4675c.pdf) and right now they are hooked up to a Pionner A-757 integrated amp. Although I am very happy with the sounds my system is producing I think I can improve it even further.

    Id like to biamp and already got the JBL M553 active crossover to do so, but Id like to know what amps I should use. Of course I am going to remove the passive crossover from the speakers.

    The system is used for hi-fi porpuses and loudness is not important (unless I want the neighbours to kill me ).

    So what should I use and how much better will the sound get? PA-amps maybe?

    Thank you very much in advance

    If you google this Jbl system there is a lot of discussion on AV forums about hifi usage. This is a different purpose to home theatre. Itís a cinema loudspeaker but here are people out their using it for hifi at home .

    While the thread discussion has been around power amp selection if you are more concerned about quality as in HFi then consider the following. It would be helpful if you elaborate on your overall system such as your source and so on.

    You already have a good amp. More power will the sound louder and potentially for dynamic.
    Depending on your room size and listening position this may or may not be a consideration.

    It would be best if you provide more information on your room.

    How to get more quality out of this loudspeaker.

    REW is your friend. By measurements you will gain a better understanding of the performance about smooth amplitude response and frequency extension.

    Fast track this to improvements and you might add a suitable sub with A built in power amp or a separate power amp with dsp crossover and EQ like some of the Dayton Audio plate amps.

    You can invest in EQ with fancy hardware like DEQX Roomate. If your amp has a tape loop or HT bypass loop the EQ hardware can be inserted in the signal pathet that way.

    I would be circumspect about using a Pro Active crossover at this point. They invariably donít have sufficient flexibility to emulate the existing passive crossover networks and sound quality will be degraded.

    It also requires a fair bit to get your head around whatís really going on to make an active crossover work correctly.
    There are some okay dsp active crossovers that are one route to taking better control of the loudspeaker BUT it adds complexity to what you are doing and there is a big learning curve. Dayton have just released a basic dsp active crossover.

    As l said have a look at REW. In addition to a sub you might eventually add a super tweeter like a Fostex uhf driver but these can be used down to 5000 hertz in some cases.

    In the better Jbl consumer systems JBL basically add a sub and a super tweeter to improve the performance of the frequency extremes. That invariably leads to superior listening enjoyment.

    Bi amp or Tri amp when done carefully provides SOA performance.

  14. #29
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    Quote Originally Posted by Ian Mackenzie View Post

    I would be circumspect about using a Pro Active crossover at this point. They invariably donít have sufficient flexibility to emulate the existing passive crossover networks and sound quality will be degraded.
    My only comment there is that the passive crossover used in the 4675C was nothing special or particularly good. It was a token piece to make a passive system and it had to work for both the 4670 and the 4675 and did neither particularly well. Depending on the vintage of your 4675C, it would have the 4638TH LF cabinet or the 4648TH cabinet (different drivers and crossovers). While I'm no big fan of the M-series crossovers (never used them...I was using Rane crossovers during that era like the AC-22 and AC-23), I suspect it will do better than the passive that comes with this speaker. They have CD horn compensation and should hit the crossover points as well as the passive. I'd say with proper DSP based crossovers you could do better. That said, I've set up a ton of theatres with the 4675 with various electronic crossovers and the passive ones, the electronic ones generally came out better (less tuning, better sounding).

  15. #30
    Senior Member martin_wu99's Avatar
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    Quote Originally Posted by baldrick View Post
    For lot of use you might be correct, but I mean, if you buy a pair of 4645 and only power them with 100watt, you have probably bought the wrong sub And if you think of it... a sub like Array 1500 have a built in 1kw amp, why should you use 1/10 of this with 2242?

    For everyday music playback, 100w would be enough, but used for higher SPL and/or hometheater, it will be too litle. And alsoÖ my experince is very often a high power amp will have better Control than a smaller Power amp. Crown iTech is great for sub duty, but maybe not the correct choice for a speaker like 4675 used in a home enviroment.
    Sufficent power requirement is not only for bass control but for dynamic and others as well
    46 lover

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