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Change woofer in very compact 18” sub

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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2019 at 2:11pm
Originally posted by Tonskulus Tonskulus wrote:

Originally posted by Elliot Thompson Elliot Thompson wrote:

Originally posted by Tonskulus Tonskulus wrote:


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 loaded and cubo 15 extended which I have tested with these. 

Otherwise good drivers and I do like the sound they make. 





It could be the box is tuned too high. That is the only time I have seen woofers loosing control.

Best Regards,

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..





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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JonB67 Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2019 at 2:16pm
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.


Edited by JonB67 - 11 July 2019 at 2:16pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tonskulus Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2019 at 5:30pm
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 :)






Edited by Tonskulus - 11 July 2019 at 5:33pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2019 at 11:57pm
Originally posted by Tonskulus Tonskulus wrote:



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 :)






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.

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Elliot Thompson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 12 July 2019 at 2:30pm
Originally posted by serioussound serioussound wrote:

I have some rcf l18 851 kn laying around would they play good in these cabs for example
No, the L18 851 requires a large box.

Originally posted by Elliot Thompson Elliot Thompson wrote:

You do not have enough power to drive modern day woofers properly.

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.


Edited by Conanski - 12 July 2019 at 2:35pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 13 July 2019 at 6:01am
Originally posted by Conanski Conanski wrote:

Originally posted by serioussound serioussound wrote:

I have some rcf l18 851 kn laying around would they play good in these cabs for example
No, the L18 851 requires a large box.

Originally posted by Elliot Thompson Elliot Thompson wrote:

You do not have enough power to drive modern day woofers properly.

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.


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,





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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 13 July 2019 at 6:22pm
Originally posted by Elliot Thompson Elliot Thompson wrote:


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.



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.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 15 July 2019 at 7:50am
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.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 16 July 2019 at 12:28am
Originally posted by Elliot Thompson Elliot Thompson wrote:

The percentage you do not subscribe to is higher than you might imagine.
I think I am lucky, the operators and DJs I work with are pretty sensible and respectful but I know that isn't always the case.

Originally posted by Elliot Thompson Elliot Thompson wrote:

It usually boils down to not having enough woofers/amplifiers to get the job done in which, SPL is all that matters.
Totally agree.
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