Power Amps for JBL 4675C

[gameuno]

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 :D).

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

Thank you very much in advance :)

[sguttag]

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.

[BMWCCA]

What's your budget?? :dont-know:

[gameuno]

sguttag, thanks for your opinion! :D 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.

[sguttag]

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.

[Mr. Widget]

For the home, I couldn't imagine driving them with anything near 300W.What, you can’t imagine 125 dB at a meter?:D


Widget

[martin_wu99]

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:blink:

[sguttag]

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.

[gameuno]

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 :D

martin_wu99, even at relatively low listening levels? What would be the use of high wattage then? Im irritated :confused:

[sguttag]

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.

[Mctwins]

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 :D).

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.

[sguttag]

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.

[gameuno]

Mctwins, power hungry even at low db? Then im even more confused. :confused: :D

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. :D

[baldrick]

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!

[sguttag]

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.

[sguttag]

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!

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 :confused:

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.

[Mr. Widget]

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.


Widget

[baldrick]

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 :confused:

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.

[martin_wu99]

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.

[martin_wu99]

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 :D

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

[baldrick]

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.


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 also… 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.

[sguttag]

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.

[martin_wu99]

Mctwins, power hungry even at low db? Then im even more confused. :confused: :D

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. :D
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.

[martin_wu99]

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:crying:

[Mr. Widget]

BTW,i find it is very hard to convince somebody on the network:crying: 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. :banghead:


Widget

[Robh3606]

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:)

[gameuno]

Yes, sguttag, besser = better. I am German and besser is the german translation, I am sorry. :D
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 :D

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

[Ian Mackenzie]

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 :D).

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. It’s 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 don’t 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 what’s 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.

[sguttag]

I would be circumspect about using a Pro Active crossover at this point. They invariably don’t 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).

[martin_wu99]

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 also… 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 :D

[gameuno]

martin_wu99, I am curious, what do you mean by "dynamics and others"? Can I find evidence for that? :D

[Mctwins]

http://www.jblpro.com/ProductAttachments/JBL_TechNote_DangerLowPower.pdf

[martin_wu99]

martin_wu99, I am curious, what do you mean by "dynamics and others"? Can I find evidence for that? :D
Dynamic Compression,it is measurable if you have some instruments

[Mr. Widget]

Dynamic Compression,it is measurable if you have some instrumentsDynamic Compression as I know it relates to loudspeakers. Dynamic Compression is the condition where a loudspeaker’s sensitivity is reduced after the the voicecoil heats during higher output playback. Essentially the speaker will not respond as it did when the voicecoil was cool limiting the output level on higher energy peaks. Typically lower quality speakers exhibit this more than better designs where cooling techniques are built into the drivers along with the use of better materials.

Dynamic headroom on the other hand usually refers to an amplifier’s power supply’s ability to provide short term peak current in excess of the steady state current required for its rated output.


Widget

[sguttag]

Mr. Widget is on target.

The JBL document linked to by Mctwins is correct. But did you all read it? The overall emphasis on it is to not run an amplifier into clipping. That is absolutely true. I know that nothing I've written on this (and any other thread) has advocated or suggested it is okay to run an amp into clipping (or other high-distortion).

However, if you are interpreting the document to mean to have an absurd amount of power reserve that you never use, you'd be mistaken. If you have an amplifier that delivers a clean 100w (wide-band, not just 1KHz) and you are not driving up to 100w, even on peaks, there is no good reason to go bigger on the amplifier except for ego or mysterious perceived improvements. The document even states that it presumes that for a given speaker that you want to get all of the SPL it has to give and thus bases its power suggesting on that. Playing a 4675C at its full SPL potential in a typical household situation borders on absurdity.

There is a finite amount of level that a recording is going to give and it can't go above. There is a comfortable/desired listening level for the person that is selecting the equipment. With these two and the speaker's sensitivity, one can figure out how much amplifier is really needed.

[Ian Mackenzie]

It’s about context and relate what is relevant to the OPs application.

You don’t have enough data from the OP on his max spl required so speculation is not going to provide a conclusion. In the document exceptions 1 and 2 are useful.

Looking at it on a practical level most home users have no idea they are at the onset of clipping an amplifier unless the amplifier has accurate metering of the power output. But clipping will damage a loudspeaker and or the amplifier where the peak output voltage approaches or exceeds the supply rails. The result is a flattening of the sine wave towards a square wave.

On a simplic level of the OP is using the system or hifi and he sits 2 -3 meters from the loudspeakers it’s not difficult to calculate how much power is required.

Back to the original post concerning how to improve the system if the loudspeaker is relatively sensitive which it is the first watt is the most important for the hifi user.

[gameuno]

I agree, that the document has no justifiaction for running a 600W+ amp in my situation.

My room is 3*4,5m, so for example 300W are definetly going to be enough. Bigger amps just arent needed, but I will take the damping factor of the amps into account, since that seems to have an impact on sound quality. (Getting the membranes to stop at the right time?)

Id rather focus on improving sound quality with - as Ian says - EQ and DSP, maybe room correction. Now that I have found out that it wont be necessary to spend as much money as I can on amp, I might considering using a sub or woofer at the opposite site of the room, to get rid of room modes.

I am aware of the theory behind this and I also know that I will have to take measurements and be very careful if I want a good result, but at least one can dream. :D

[sguttag]

My room is 3*4,5m

And the 2360/2446 horn/driver are about a meter deep on their own so you are down to just 3.5m for listening...but wait, you probably have some comfy recliners or a sofa so take another meter off and down to 3.5m from horn to listening position. So what are we up to? 39W for 105dBc (playing pink noise). But yeah, if you want 115dBc (out of just one speaker) break out the 400W amp...unless you only wanted 115dBc from the pair, in which case your 300W amp will be MORE than adequate! :bouncy:

I don't know what music you are listening to or how loud you like it but I strongly suspect that Ian is correct...that first watt will be what you are using for 99% of the time. Gute Nacht

[Ian Mackenzie]

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).

I think it comes down to the expectations of the OP.

http://www.jblpro.com/pub/obsolete/23606566.pdf

Looking at the curves in this document the OP can obtain the best overall response in the listening window with some REW measurements. That could be just toe in of the system carefully or some form of EQ if absolutely nec.

Hi fi being what it is not everyone is going to like converting an analogue signal from an analogue source to digital and then back to analogue.

This system is already a very low distortion design so any degradation of the signal is best avoided.

I would first get the best response in the listening window without EQ by adjusting the toe in.

The top end can be easily modified with some passive EQ added in the passive network.

Then start looking at the bass by way of a sub. Once the right balance is obtained options for improvement to the resolving power can be considered . This might include better crossover capacitors, a better power amp and preamp or design of a very high resolution analogue active crossover network and a small class A power amplifier for the horn.

The reasoning for an analogue active network is that with such a sensitive loudspeaker your line level signal is going to be tiny. An analogue active crossover is going to be quieter and offer better very low level resolution than a digital dsp network under these conditions.

[sguttag]

The OP said he already had M500 series crossovers...which are analog. I would agree that these speakers normally need very little in the way of EQ and I've always gone for a minimalist approach. I'm not a fan (through actual usage) of the passive crossover that is part of the 4675C so the use of an active crossover, for that speaker, is encouraged. In fact, that is the speaker that THX started with back in early 80s and designed their crossover (used in cinemas) around. A L-R 24 with appropriate CD horn boost and time-alignment.

[Ian Mackenzie]

Yes he did.

But we here have categorically proved (quite a while back) the M500 series are not strictly speaking a hifi unit in direct comparison to other devices. A pa active crossover in the pa or theatre business has always got a lot of benefits however when the focus is on hifi it has to be done on a better level.

An active crossover will tighten up the bass a bit but can badly corrupt the fidelity of the rest of the sound.

So the passive crossover an often win subject to the caliber of the overall system.

Until now high performance active crossovers have been a rarity in consumer the hi fi audio market.

I will discuss this on my visit to LA and SF later this month.

[Robh3606]

The OP said he already had M500 series crossovers...which are analog.

The M552/553 come with a preset for both the 2380 and 2360 family of horns. These are approximations for each family so if you have the capability you may be able to do a superior passive comp depending on the driver horn combo. Certainly a good place to start though as they may work out just fine.

Rob:)

[Ian Mackenzie]

White Paper

http://www.jblpro.com/pub/cinema/2360b_wp.pdf

Thread on 2360 application with 2450 driver with DBX260

[gameuno]

I really wouldnt mind using a DSP, Im no analog-fanatic or anything like that. :) Since my source is going to be digital anyway, I could just put a DSP directly after that, which would give me pretty much no signal loss. Then I could go with a digital signal to a good DAC. I guess that would work best.

[Ian Mackenzie]

Okay well that works for you.

Once you start on this in your Man Cave you might want to tell your wife or girlfriend you are going to be pre occupied for quite a while.....Lol

[sguttag]

I think you're going to find that the 4675C doesn't need a bunch of fancy DSP. An L-R 24 crossover (3rd Order on the HF, 4th order on the LF will work best with that horn/driver on the HF) with the right delay on the LF and some CD horn boost and you are pretty much going to have a pretty flat response. In the cinema industry, there are a TON of analog crossovers for that speaker because it was so popular. If you like QSC, their MXa amplifiers had the XC-1 crossover, the EX amp had the XC-2 the current DCA (though CX will work) can use the XC-3 crossovers. The Series 1 amps had octal plugs and both QSC and a company called USL (now, recently, owned by QSC made their XTA series of octal plugs as well as a frame that took those octal plugin crossovers). One of the last vestiges of those crossovers that had the JBL 4675C in mind is the XTM-300 by USL (now QSC)
https://www.qsc.com/cinema/products/processing/usl-processors/usl-xtm-300a/

Component Engineering may even have some of their cards (fit a dbx 900 series frame, as I recall or the Genuine THX crossover/monitor (analog)). Those cards will be for the 4675C https://www.componentengineering.com/thx_crossover.html. There are a ton of the D1138 crossover/monitors on eBay at the moment, and they will work but they are EARLY dsp audio and you'd need the correct DOS program to configure it (yes, I said DOS). I would tend to stick with a good analog crossover myself unless the DSP is coming along for other uses.

[Mctwins]

If you are using the passive x-over there is no settings in dbx260 for EQ-ing.

In dbx260 there is settings for both 4675C-4LF and 4675C-8LF in bi-amp mode.

[Ian Mackenzie]

Might be able to get one on Ebay cheap

[Ian Mackenzie]

We have pretty well covered what can be done

Out of curiosity l am interested in what area the OP thinks it can be improved?

[gameuno]

Thanks, sguttag, Ill take a look at these amps. But why shouldnt I keep my JBL M553 as a crossover? I understand that a DSP-crossover might be better, but why these other analogs?

Well, Ian, honestly I dont have much experience with high end audio, so I cant exactly tell how much better the sound will get. I am 17 and Ive just recently gotten into all this stuff, but it is absolutely great. Anyway, as long as there is a scientific explanation, that something can make a noticable difference, Im ready to try it. :D

Thats why Ill try to time delay the woofers with a DSP, and obviously an active crossover also has advantages has big advantages over passive ones. Measuring the frequency response will also be done and corrected with EQ. Maybe even bass array-type of ideas... And of course more room treatment.

However, I am not really convinced by the arguments made for high wattage amps in hifi. Still Ill probably have to get an amp with at least 300W, because I cant find anything less powerful in pro audio. : ( Maybe 2 Bose 1800s?

[sguttag]

Go ahead and give the M553 a go. It will probably do fine. I've never worked with it.