Change woofer in very compact 18” sub
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URL: https://forum.speakerplans.com/forum_posts.asp?TID=103983
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Topic: Change woofer in very compact 18” sub
Posted By: serioussound
Subject: Change woofer in very compact 18” sub
Date Posted: 10 July 2019 at 9:24pm
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I recently bought some very compact 18” subs really cheap. They are very small: 53cm wide 53cm deep 68cm height Is it even possible to make a 18” sub sound good that small? Woofer is RCF L 18 P540. These drivers dont handle so much power so I want to replace them. But with what? Is there any other 18” driver out there that plays good in such a small cab? I want to keep them because they are really handy and well built cabs. Maybe change baffle and put 15” in there? :/   |
Replies:
Posted By: Elliot Thompson
Date Posted: 11 July 2019 at 12:51am
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How much power are you feeding the RCF L 18 P540? You are using the old RCF series in which, the power was conservatively rated. The cabinet is fine for the RCF L 18 P540. However, if you are looking for lots of 50 Hz – 40 Hz, you may find yourself living on your equaliser.
If you cannot feed that driver anywhere from 1000 – 1300 watts RMS, you are just going to make matters worse swapping to a modern day woofer. A modern day woofer will need even more power to drive to optimum levels.
Best Regards, ------------- Elliot Thompson |
Posted By: serioussound
Date Posted: 11 July 2019 at 8:21am
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I drive them with EV P3000. I just thought with 350 w power rating and only 3” voicecoil I would be better of with a more modern driver?
Would a modern standard 18 fit in such a small cab?
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Posted By: Elliot Thompson
Date Posted: 11 July 2019 at 11:27am
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The EV P3000 offers 750
watts per channel @ 8 ohms. It is a good suggested match for the RCF L 18 P540 as, it delivers 2 times
the rating of the RCF L 18 P540. I own a good amount of RCF L 15
P540 woofers and, each driver will get anywhere from
1300 - 1500 watts RMS (4 times the rating of the RCF L 15 P540 ) of amplification power. So, you can feed the RCF L 18 P540
1000 watts – 1300 watts as they both were rated the same when the RCF L 18 P540 was in production. All the old RCF models were conservatively rated as they did not adopt the AES method of power rating.
The size of the voice coil and the xmax does not determine how much power a loudspeaker can handle in a reflex box. How the loudspeaker reacts in a reflex box (based on its TS Parameters) will determine its outcome in terms of performance.
Best Regards,
------------- Elliot Thompson |
Posted By: serioussound
Date Posted: 11 July 2019 at 11:36am
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Ok but just for interest is this a inflexible cab since its so small or can many modern drivers play good in such a small vab? I have some rcf l18 851 kn laying around would they play good in these cabs for example (they are not new drivers I know)
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Posted By: Tonskulus
Date Posted: 11 July 2019 at 11:44am
Yes, I have 15p540's too but they seem to go out of control around 1kW. Flapping, bottoming out no matter the high pass setting. Might be wrong enclosures tho, one dual manifold/reflex loaded and cubo 15 extended which I have tested with these. Or possibly uneven cone load.. who knows. Otherwise good drivers and I do like the sound they make. |
Elliot Thompson wrote:Posted By: Elliot Thompson
Date Posted: 11 July 2019 at 11:52am
The cabinet is not small. You do not have enough power to drive modern day woofers properly. Instead of worrying about switching loudspeakers, invest in a more powerful amplifier. You would be surprised how well those RCF L 18 P540 will perform if you fed them more power. This how it works. You always feed the loudspeaker more power than it is rated. The RCF L 18 P 540 is rated 350 watts. The RCF L 18 851 is rated 1000 watts. You have an EV P3000 amplifier that delivers 750 watts per channel @ 8 ohms. Which loudspeaker will be easier to drive on the EV P 3000? Best Regards, ------------- Elliot Thompson |
Posted By: serioussound
Date Posted: 11 July 2019 at 11:57am
| Some guys I talk to says that for bass you cannot compare the real watts of EV P 3000 with modern amplifiers... |
Posted By: Elliot Thompson
Date Posted: 11 July 2019 at 12:06pm
If you want to believe them, its up to you. Best Regards, ------------- Elliot Thompson |
Posted By: Elliot Thompson
Date Posted: 11 July 2019 at 12:23pm
It could be the box is tuned too high. That is the only time I have seen woofers loosing control. Best Regards, ------------- Elliot Thompson |
Posted By: Tonskulus
Date Posted: 11 July 2019 at 12:38pm
Might be.. dual 15 is 220 litres, tuned to 45Hz or so. Cubo 15 extended.. in this box these woofers can handle more power compared to dual 15. When cone bottoms (bangs), I can see cone moving around 10-15mm which is no where near the Xlim. Not sure whats going on there.. |
Posted By: midas303
Date Posted: 11 July 2019 at 1:22pm
| Just out of interest, it wouldn't be the guys who sold you the amps that told you they can't be compared to new amps would it? |
Posted By: Elliot Thompson
Date Posted: 11 July 2019 at 2:11pm
It may be the fs of the RCF L 15 P540 in the Cubo 15 Extended is around the resonant peak frequency of Cubo 15 Extended. This could lead to the driver unloading from the box and acting as if it is in free-air. Try sweeping (a slow sweep) a sine wave from 100 Hz to 40 Hz. If you approach 50 Hz - 40 Hz in which, you hear no sound however, the driver is moving erratically, that is the point the driver is unloading from the box. Best Regards, ------------- Elliot Thompson |
Posted By: JonB67
Date Posted: 11 July 2019 at 2:16pm
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My subs used to lose control and go all flappy when pushed but it was the old amp losing control, not the drivers. My modern matrix amp drives them much harder without any flappiness! Id try them on a different suitable amp before swapping out the drivers.
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Posted By: Tonskulus
Date Posted: 11 July 2019 at 5:30pm
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Yes, I have tested different amps too (it was actually the first thing that came to my mind) which are excellent with my 18" hog-scoops, 18" reflex etc.. and giving good control for them. I also have small tops w/12" JBL 2206H's, those can take some serious punshment and not a single problem ever. No flapping, no bottoming like L15P540 does with same power levels.. I have four of them and was thinking to make some kick cabs with these.
Elliott thank you! Need to try that. So never tune the reflex to around Fs of the driver? I think you are right, it has to do something with those enclosures.. Sorry, ot :) |
Posted By: Elliot Thompson
Date Posted: 11 July 2019 at 11:57pm
It depends on the TS Parameters of the driver. The most important TS figures for a reflex design is the fs, Vas and, Qts. If your aim is 50 Hertz, in which, the driver offers an fs of 50 Hertz, you should not tune the box to 50 Hz for, you are creating a response curve that will be -3 dB @ 50 Hertz. The VAS may allow you to go lower at the expense of a larger enclosure even if the fs is higher than expected. If the cabinet is too small, you can forget about the VAS helping you to go lower despite what the fs states. I have not seen a measured much less a simulated response of the Cubo 15 Extended so, I cannot say where the roll-off point begins on such a design. However, from what little response curve I could find on the Cubo 15, such a design would create the havoc you are describing using the RCF L 15 P 540 in the Cubo 15 enclosure. Best Regards, ------------- Elliot Thompson |
Posted By: Conanski
Date Posted: 12 July 2019 at 2:30pm
I'm going to disagree with that for a couple reasons. A) it depends heavily on the program material in question, while a driver will generally handle more power with really dynamic music it could be in danger of failure at RMS levels with other genres. B) The difference between 750w and 1500w is 3dB which might just be enough to notice but this happens to be at the power compression end of the spectrum where voice coil heating tends to eat up most or all of that gain. So I'm of the opinion that the OP would be better off adding more cabs and powering them the same than adding more power to the existing cabs. I own some L18 851 loaded reflex subs.. dual 18 boxes actually, and at 1000w/driver I think they are fully powered, I'm actually afraid they are a bit overpowered for music genres with those long synth tones. The point I want to make though is that it takes 4 of these 18's to generate any appreciable amount of thump.. dynamic punch you can feel. A pair of reflex 18s can produce a good amount of bass but you're not going to get much kick drum punch.. that simply requires more air displacement, four 18's just starts to get into that zone. So how many of these compact subs do you have and what about the sound do you feel is lacking? They won't go super low by todays standards.. 40hz is probably where they should be high passed, and it's going to take a small wall of them to produce kick you can feel in large rooms or outdoors, so maybe your expectations are just too high.
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Posted By: Elliot Thompson
Date Posted: 13 July 2019 at 6:01am
When using a more powerful woofer in which the amplifier has difficulty to drive, the user will drive the amplifier harder in order to achieve the proper SPL. Unfortunately, the amplifier tends to clip under the given circumstances constantly in which, will lead to overheating the voice coil of the loudspeaker.
It is one thing to have headroom so you do not have to drive amplifier ragged and take advantage of the dynamics. It is another thing to not have enough volume in which, you will drive the amplifier harder until you reach the proper SPL. This is why many tend to use amplifiers that are 2 times the rated power to their loudspeakers. It will lead to achieving maximum output from the loudspeaker without clipping the amplifier during the process.
Best Regards, ------------- Elliot Thompson |
Posted By: Conanski
Date Posted: 13 July 2019 at 6:22pm
I see you point about having some headroom but I don't subscribe to the notion that a speaker "needs" a certain amount of power to sound good, in this case the OP has the drivers program rating which for all but the most dynamic material is fully powered. And your description is just another way of describing a muppet operator that pushes a system beyond it's capabilities, it is my experience that this type of operator will always push the system too hard and it doesn't matter how it's powered or what the systems overall capabilities are. We have to assume the OP is not such an operator since this is his rig afterall. |
Posted By: Elliot Thompson
Date Posted: 15 July 2019 at 7:50am
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The percentage you do not subscribe to is higher than you might imagine. It usually boils down to not having enough woofers/amplifiers to get the job done in which, SPL is all that matters. Best Regards, ------------- Elliot Thompson |
Posted By: Conanski
Date Posted: 16 July 2019 at 12:28am
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