Hi all, Just wondering if anyone has come across this issue. i bought a used yorkville nx750p powered loudspeaker (15” B &C Neodymium woofer) and during a gig the woofer starts to bottom out and you can hear the voice coil clack as it hits the magnet. This happens well into the party and before that it is able to produce good bass with no audible distortion so it seems to be a thermal problem. Im not over driving the speaker. When it starts bottoming I enable the 90hz high pass filter on the speaker and it plays normal and can get by. Since I only have this single speaker I borrow my cousins which is a 750p series 2. His cabinet is much newer and and some small differences but the biggest is it has a ceramic woofer instead, I’m not sure if it came like that or someone swapped out the woofer. His speaker can keep on going strong with no issue. He bought his used and told me the store changed to ceramic as the neo woofers we’re failing.
Just use the high pass filter until you can get it repaired or replaced. Nobody is likely to notice.
Yes I think that’s going to be the best option just to run high passed. Most likely the woofer would be the problem.
The replaced bad woofers were no doubt damaged by all the bottoming out.
There could be a design problem, it's probably not the woofer's fault.
There could be a design problem, it's probably not the woofer's fault.
All of the B&C woofers I have tested have the suspension limit excursion before the voice coil former makes contact with the back plate.
You can easily verify this by pushing the cone in, the surround suspension should be fully extended, and stop movement before you will hear the ticking sound of the voice coil former touching the back plate.
My estimate would be the suspension will limit at ~14mm one way excursion, 28mm peak to peak.
That said, as a voice coil heats, it may expand and "clack" at high excursions when it starts to rock.
When it cools down, that noise may not be present.
If the program material has very compressed (or clipped) low frequency, the average level may be as much as four times that of typical music. This can heat the voice coil, causing it's impedance to double, the amplifier will put out half the power it would if the voice coil was cool.
Clipping before the amp may sound like "bottoming out", you may be clipping your mixer input or output.
Have you verified the clip or limit lights on the NX750p have not illuminated when you heard the noise?
Some dance music has less dynamic range than a sine wave below 100Hz, ~3dB crest factor, compared to 12dB above, 8 times more average power in the low end. Easy to fry speakers with that even without clipping.
That's part of the reason why dedicated high power subwoofers are used for the bottom octaves.
The neo driver used in the 750p only weighs ~4.7 kg (10.36 lb).
The spec sheet lists the 750p-2 as the same weight as the 750p, a ceramic woofer would add considerable weight, so unlikely Yorkville has changed the driver in production.
The 750p-2 has more power than the 750p, so will clip at a slightly higher volume, as well as running cooler, less heat in the cabinet interior.
A ceramic magnet of the same strength will have ~double the thermal mass, so will take longer to heat up than a neo magnet. The store may have changed the drivers out to higher power (cheaper) drivers.
Art
You need a sub, 15" PA speakers like this really aren't very good at producing low bass.. as you are finding out.
One good 15" sub with a pair of 8" or 10" tops will produce much better sound.
One good 15" sub with a pair of 8" or 10" tops will produce much better sound.
I think I was bouncing off the limit light during the gig and when the clacking started I think the clip light did come on.
When I first bought the speaker I opened it up to have a look and saw how tiny the motor was and thought someone swapped in a mid bass driver, but looking up the part number it was indeed the intended driver. I’m pretty sure it was an ex-rental speaker and it must of been put through a lot of abuse. I was wondering if the neo could of lost motor strength for all the times it was driven hard.
For larger events I will use a sub or two (yorkville ls700p).
With low crest factor music, that may be enough to burn a woofer.
The voice coil will burn up on a B&C woofer long before the neodymium neodymium alloy with terbium and dysprosium magnet will loose strength, as the working temperature is around 240C, comparable to ferrite magnet formulations. Paper burns ~233C (Fahrenheit 451).
That said, the voice coil former may have slightly bubbled from heat in prior abuse, and at high excursions will rub, while still working OK > 100Hz.
At any rate, the woofer looks like a 15NDL76, which has about half the excursion (-6dB) and 1/3 the power handling of B&C's subwoofer drivers.
Top cabinets are not subwoofers 😉
I was just testing out the speaker earlier and had one of my subs (yorkville ls700p) connected to it via the link out, so no external crossover. With the top set full range and sub off it really does pound and gets loud and I don’t hear any vc rub. I didn’t play for too long so I don’t know the exact time time it would take to break down, but at my last gig I’m pretty sure it acted up after 5 hours. I don’t mind running it highpassed if I’m going to use the sub.
On another note this sub doesn’t seem to hit the low frequencies and sounds as if it rolls off around 50hz. It does boom though but it would be nice if it could dig a little bit deeper. Turning off the sub and setting the top back to full range I can hear some deeper bass. I am going to connect my active cross over and equalizer to see if I can boost the low end a bit. This is a 6th order bandpass and seems to have two peaks around 60 and 100hz. An idea that came to mind was to re-use all the components and make a new ported box to get some more low end at the expense of the extra db the bandpass gave. Problems I could foresee is what is the t/s parameters as I can’t find anything online and does the amplifier have any filtering below the cutoff frequency that may interfere with the response of a bass reflex design. I think the driver is either RCF or eminence 350 watt 4 ohm.
On another note this sub doesn’t seem to hit the low frequencies and sounds as if it rolls off around 50hz. It does boom though but it would be nice if it could dig a little bit deeper. Turning off the sub and setting the top back to full range I can hear some deeper bass. I am going to connect my active cross over and equalizer to see if I can boost the low end a bit. This is a 6th order bandpass and seems to have two peaks around 60 and 100hz. An idea that came to mind was to re-use all the components and make a new ported box to get some more low end at the expense of the extra db the bandpass gave. Problems I could foresee is what is the t/s parameters as I can’t find anything online and does the amplifier have any filtering below the cutoff frequency that may interfere with the response of a bass reflex design. I think the driver is either RCF or eminence 350 watt 4 ohm.
Yeah.. I find most Yorkville subs are voiced more for boom than extension, although I really like the PS15s as it sounds like it produces much more lowend extension than the specs would suggest.
You likely won't have much luck EQing the LS700p as the box tuning dominates output response.
You likely won't have much luck EQing the LS700p as the box tuning dominates output response.
The specs pretty much confirm it won't work for the change you want:
Since it is ~-6dB at 45Hz (gone..) the HP is also likely set there.
The 10" Fs probably around 45Hz, and not much excursion, probably in the 6mm Xmax range.
If you want to DIY a decent bass reflex, look for larger drivers, higher power and Xmax (>12mm), and an Fs ~ the Fb (box tuning frequency) you'd like.