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Thread: Power Amps for JBL 4675C

  1. #1
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    Question Power Amps for JBL 4675C

    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

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    There is nothing special about "PA" amps. In fact, home amps tend to be more esoteric in nature, when it comes to sound. In the professional world, reliability, serviceability, speed of installation/replacement are key factors in the design (and, of course, cost).

    The 4675C was a staple of the cinema industry (and its lower suffix letters) for decades. It has been driven by most every brand of amplifiers you can think of. If there is a particular amplifier brand you like, use it. A good amp is a good amp. Its intended market should not be a factor in your choice other than your personal ease of use and potential noise (including noise for cooling...in professional areas, often ambient noise is not an issue and again, in the name of reliability, they may be noisier than anything destined for the home market). Since you want to bi-amp, you'll need 4 channels of whatever you seek.

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    sguttag, thanks for your opinion! Great to know these speakers arent too selective when it comes to amp choice. Just one more question: How much power do I need to get the best out of the speakers? Ive heard people say that even at low levels you can make great use of a 300W+ amp. Is that true or a waste of money?

    BMWCCA, I could spend about 1000€, so 500€ for each amp and I want to buy used gear.

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    Those are quite efficient speakers 101dB 1w/1m. Personally, I don't think you need a big amp at all for normal listening levels. Many cinemas drove them with 50W-100W. For the home, I couldn't imagine driving them with anything near 300W.

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    Quote Originally Posted by sguttag View Post
    For the home, I couldn't imagine driving them with anything near 300W.
    What, you can’t imagine 125 dB at a meter?


    Widget

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    Senior Member martin_wu99's Avatar
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    Quote Originally Posted by sguttag View Post
    Those are quite efficient speakers 101dB 1w/1m. Personally, I don't think you need a big amp at all for normal listening levels. Many cinemas drove them with 50W-100W. For the home, I couldn't imagine driving them with anything near 300W.
    I think even 300W is not so enough for two 15'' woofers,not to mention 50W-100W
    46 lover

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    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.

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    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

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    I wasn't implying that you shouldn't biamp the speaker at all. Just noting for your testing, you can use the passive crossover to get a "feel" for how loud that speaker will get with a given amount of power.

    I don't know if Martin was kidding or just doesn't understand how power works. The number of 15" drivers has no bearing on how much power a speaker system needs. If his argument is that more power is lost in the voice coils of a given driver, I'd argue that the air you are moving with the extra cone area wins that argument. There was a time when power wasn't cheap/easy to come by. And, unfortunately, the rooms/auditoriums were big back then too. The solution was larger/more drivers to increase the efficiency of the system (an an Altec A4 is more efficient than an A5, for instance).

    I'm not one of those that believes you get any sonic benefit to having an abundance of extra power available. You figure out how loud you need a system to be and size appropriately for that. Increasing power is a diminishing returns proposition since for each 3dB of more volume, you need double the power. The difference in cost between a 100 and a 200-watt amp is normally pretty small, the difference between a 500 and 1000-watt amp is normally significant. Both get you the same improvement...just 3dB in final output SPL.

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    Senior Member Mctwins'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
    Hallo!

    I would go with an amplifier rated at 1200Watts for those spekers. Reason, it is very power hungry bass and you need that. The cross-over will handle the power.

    My twin brother have Cinema screens with 3 crowns amps MAi5000 in bi-amp mode and it's sounds fantastic in home enviroment. Low as in high dB level.

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    Quote Originally Posted by Mctwins View Post
    Hallo!

    I would go with an amplifier rated at 1200Watts for those spekers. Reason, it is very power hungry bass and you need that. The cross-over will handle the power.

    My twin brother have Cinema screens with 3 crowns amps MAi5000 in bi-amp mode and it's sounds fantastic in home enviroment. Low as in high dB level.
    How do you come up with "power hungry?" It is just the opposite! It is quite power efficient. 100dB with 1-watt at 1 meter. It needs more power than a horn loaded system but as far as bass-reflex goes, it is pretty much up there.

    At 1200-watts, you'd get up to what? 115dB at 3m? And that is just on the bass. Adding in the HF, it would be closer to 118dB. Why not just take an ice pick to one's ears and be done with it?

    Anyway...again, I suggest taking whatever amplifier you have, give them a try and get a feel for how loud they go in your listening environment with your music and decide how much power you need from there.

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    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.

  14. #14
    Senior Member baldrick's Avatar
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    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!

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    I'd could probably make the argument that most amplifiers are designed as fixed-gain devices with just input attenuation (sensitivity) controls. As such, you are going to get whatever noise in the input stage amplified by the capability of the amplifier. It is probably easier to keep the noise down on a lower wattage amplifier than a higher one. Additionally, in order to achieve the higher power, which often translates into higher voltage required at the output terminals, the amp must have higher rail voltages...which consumes more power from your outlet...for no good reason other than to have that hefty reserve (that you won't use).

    For me, it is all about the math (and the practicality) of each situation. You size a system for the environment that it is working in. Unless there is a good reason to over-spec the amp, money could be better spent elsewhere. I suspect, if you were to put a meter on it, you'd find that you were using less than a watt for most of what you are listening to and only on some transients would you need more power. And even then, unless you like it at hearing damage loud, you wouldn't need that much.

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