C-Note excursion

[JoeC]

Although I've listened to music most of my life, I'm a bit of a noob when it comes to speakers. I did get a pair of these C-Note speakers and after the build I really liked the way they did sound but after about 2 months I began to notice some distortion on the left channel, it only got worse and then the right channel started to distort shortly after the left channel got funky. After several discussions with the nice folks at P.E. (my apologies to P.E. if I got irate) it turned out the I blew out my woofers from over excursion. This led me to a search as to why or how I got that over excursion. I've listened to a few systems in my life time at home and in my car, never blew out a speaker in 40 yrs.

Before I built my C-Note speakers I read up and checked out a multiple source of reviews and on line forms. This is where I may have run into trouble. From post #76 on the Audio Science Review of these speakers Chris P. made a recommendation of adding damping material. I also installed a 5/8 support dowel to add from side to side.

My question is.... will adding a support inside and dampening (I used 3/4 denim insulation but just on the back wall only) change the cabinets frequency below that of the woofer frequency and cause excessive excursion from my woofer? I read at some other places that cabinet tuning can affect the speakers excursion. I'm basically trying to determine the cause of my blow-out so I do not let that happen again. This is my first experience with diy speakers.

About my system: running audio from my pc via usb to a Topping D30 DAC and connected a Modular Component Systems 3225 receiver rated at 27w per channel. The receiver and speakers are on my desk at an arms length.

Thank you for taking the time to read this long post! I hope I worded everything correctly and provided you enough info.
I did buy a new set of woofers and they do sound great again.

Edit: the port tube was left at the recommended 7.5"

[Kornbread]

Generally speaking, adding damping reduces port output because it reduces the intended internal resonances <or something like that. For an experiment, try using Unibox (it is simple to use freeware so give it a try) both with and without damping. A small dowel rod did not change the tuning much, but add enough bracing, and the volume will change enough to throw off tuning.
Odd that 27watts of raw power would kill a dsa135. Doesn't sound right.

[LOUT]

I don't think that would change excursion in a significant enough way (it could change the tuning/shape a little bit and may avoid some distortions, but that's about it...I don't think it'll meaningfully change the overall excursion much).
I was going to recommend that limiting yourself to a [email protected] amplifier might be a good plan if you have a tendancy to crank it, but it sounds like you're already using an amp with modest power (maybe the amp has really good transient response?).
It might be possible to find/lookup your amp or DAC's input impedance and add a tiny capacitor in-line/series with it to give a protective HighPass to the signal going through...saving any speakers from excessive bass and excursion. You can alternatively add a HighPass to the speaker itself, but this will be a lot more expensive parts-wise since it'll require a much larger capacitor and probably a pretty large inductor added to the woofer's XO (maybe just a parallel pair of ~500uf Capacitor and 8ohm resistor added to the speaker wire/input?).

FIrst, check if either the reciever or amp have a built-in setting for "small speaker" or bass-limiting that could do the same thing.

IF the current Cnote's are damaged from over-excursion, I don't think there's anything you can do to fix them aside from replacing the damaged woofers and taking steps to prevent it from happening again.

Might be some extra steps you can do to double check that the woofers are damaged from over-excursion first though...just to make sure.
Could end up lucky and it's really something loose inside, rattling...or a lose solder on a crossover part, or something nearby giving an ugly vibration (sorry if this is redundant and you've already thoroughly checked everything and found it definitely IS the woofer voicecoil rubbing after getting damaged/bent).

[LOUT]

Would it be possible for you to explain a bit more (more details?) about how you and the PE staff member concluded that the distortion was most likely damaged woofers from over-excursion?

[jhollander]

You will get distortion from over driving an amp that could cook the voice coil. If this is a vintage amp might be worthwhile getting it checked out.

[billfitzmaurice]

My question is.... will adding a support inside and dampening ...change the cabinets frequency below that of the woofer frequency and cause excessive excursion from my woofer?

No. The effect on tuning is nil, the effect on Q is slight.

I read at some other places that cabinet tuning can affect the speakers excursion.

It does. Model the speaker and it's obvious how.

I'm basically trying to determine the cause of my blow-out so I do not let that happen again.

It's simply too much power, usually below the pass band where the speaker should be used. This is where modeling is invaluable, as it will show excursion at any power level, and if you need to high pass the amp to prevent having too much power below the speaker pass band.

You will get distortion from over driving an amp that could cook the voice coil.

High distortion/clipping will create excess high frequency harmonic content that can over-power a tweeter, but it won't bother a woofer. However, when pushed into clipping an amp can put out far more than its rated power, and that can cook a woofer.

[fpitas]

If it was really over excursion, it almost has to be what Bill alluded to: too much power below the port tuning frequency. The cone is unsupported and will move violently.

[wogg]

Also, that should have been super obvious at the time of damage. I've slapped woofers against the pole piece on a number of occasions, and it was a loud holy crap! kind of moment.

More devious is overheating, but I'd be surprised if your amp was capable of reaching the thermal limits of the woofer. Unless... the amp has a problem with DC offset or an oscillation. An oscillation usually kills tweeters though, so that seems unlikely too. And a DC offset should be obvious when you power the amp up, the cones would bias out one direction or the other.

[djg]

You might want to add a subwoofer to your system to handle the lower frequencies. I run all my smaller 2 way desktop speakers with a sub. I can suggest a very nice PE unit that I use.

[Kornbread]

Also, that should have been super obvious at the time of damage. I've slapped woofers against the pole piece on a number of occasions, and it was a loud holy crap! kind of moment.

More devious is overheating, but I'd be surprised if your amp was capable of reaching the thermal limits of the woofer. Unless... the amp has a problem with DC offset or an oscillation. An oscillation usually kills tweeters though, so that seems unlikely too. And a DC offset should be obvious when you power the amp up, the cones would bias out one direction or the other.

The rs225 bottom with a very obvious and loud 'blat'. Sounds terrible as you jump up and head to the volume control, but I cannot distinguish when the sd215a-88 bottom. The rs is supposed to have the better motor but the cheaper sd has a bumped back plate. If the dsa135 has a bumped back plate, maybe it is being driven too hard without the listener knowing?

... but with 27 watts?

[billfitzmaurice]

If the bumped back plate is deep enough to prevent the coil from bottoming out even at xlim then the only issue from over-excursion would be high THD, which wouldn't cause damage to the driver, though your ears would suffer from the bad sound.

[Kornbread]

What's the volume and tuning on the c-note?

[981CS]

I tried running my C-notes with a vintage 30WPC Technics receiver and that was not enough power for those speakers. They aren't really all that efficient and if you want to get good bass out of them, you need to give them more power.


(I typically use that same receiver for Overnight Sensations TM's and it does a fantastic job with those).


But when I gave them a full 85WPC, the C-Notes not only sounded better, but seemed more effortless doing so.

[LOUT]

An amp that can push a pair of 8ohm speakers with 25-30watts should be able to have the Cnotes blasting around 95db. I'm also pretty sure pushing them farther will increase distortion beyond 10% (though deep+loud bass below 40-45hz will distort them earlier).
I'm guessing the Technics amp might not be giving a full/clean 30watts/each at 8ohms?...or maybe that particular amp loses some low-end (maybe moreso at higher volumes, if that's a thing).
I wonder if "vintage" could also be part of it, maybe aging capacitors lower in uF value or something else is rolling off bass?
Do the OvernightSensations sound about the same from both amps, or do they also sound deeper when moved over to your 85watt amp?

[981CS]

To be clear, the receiver is not the issue. The CNotes take some grunt to pronounce solid bass notes (with dynamics) and lower powered receivers typically aren't up to the task, even at moderate levels. The speakers scale with power and they tend to reward better receivers. I've always been impressed how a $100 speaker can sound so good with better equipment.

Also, it takes a lot more power for bass notes than it does to hit a certain db point at 1khz. When people say the Cnotes lack bass, I always assume they aren't feeding them enough power. I actually think they are quite good in that regards given the box and 5" woofer.

[JoeC]

Thanks for all of your answers. I'll try my best to answer all questions

Odd that 27watts of raw power would kill a dsa135. Doesn't sound right.

Makes no sense to me either!

FIrst, check if either the reciever or amp have a built-in setting for "small speaker" or bass-limiting that could do the same thing.
IF the current Cnote's are damaged from over-excursion, I don't think there's anything you can do to fix them aside from replacing the damaged woofers and taking steps to prevent it from happening again.

Yes... my receiver does have a button labled "Loudness" and another one called "Subsonic Filter". Of course I have the loudness on and the sub filter off

Could end up lucky and it's really something loose inside, rattling...or a lose solder on a crossover part, or something nearby giving an ugly vibration

I've removed the speaker and inspected it thoroughly with an led light and a strong magnifying glass. The spider looks o.k. I can't see anything that would indicate a rip or a tear, the surrounds look good too. I'm using a circuit board I bought from a third party on ebay. I'll post a pic.





When I first heard some distortion on the left side, I removed those green connectors for the speaker wires and soldered the wires directly to the board and I also added the .22 mfd cap mod. It made no difference, and after a couple days the right side went distorted too. P.E. informed me that because I used this board, I'll get no warranty. I've already spent way too much on these C-Notes to invest any more on any more caps or resistors.

Would it be possible for you to explain a bit more (more details?) about how you and the PE staff member concluded that the distortion was most likely damaged woofers from over-excursion?

Not sure what you want? I can make a video but the speakers wildly jump in and out at no bass and very low volume from the receiver. The new speakers barely move at all.

Also, that should have been super obvious at the time of damage. I've slapped woofers against the pole piece on a number of occasions, and it was a loud holy crap! kind of moment.

I do not think it slaps, just makes a rumbling kinda noise anytime the is a low frequency, and excessive vibration. The is no burnt smell and when I ohm'd out the coil I got 7 ohms reading on my digital meter.

You might want to add a subwoofer to your system to handle the lower frequencies. I run all my smaller 2 way desktop speakers with a sub. I can suggest a very nice PE unit that I use.

I really do not have a lot of space for a sub... and everybody states that the bass on these speakers are so great, you should not need to add a sub.

maybe it is being driven too hard without the listener knowing?

Might be possible? I am over 60 yrs old but one would think that this would be very obvious. My Mrs. would have said something.

What's the volume and tuning on the c-note?

I'll have to go to the P.E. web page and see if those specs are listed. But not getting those specs?
https://www.parts-express.com/C-Note...inets-300-7140

I tried running my C-notes with a vintage 30WPC Technics receiver and that was not enough power for those speakers. They aren't really all that efficient and if you want to get good bass out of them, you need to give them more power.

I like the way this vintage receiver sounds, but I do have a Technics SA EX140 receiver rated at 100w per channel. I hooked it up and did try that with the new speakers to see if there was any difference. The MCS receiver sounds way better.
I can connect these bad speakers up and upload a video if you want to see how they look. I may be wrong here that is why I'm posting this thread, but it seems to me that either the spiders or the surrounds (or both) "stretched" out? is that possible and how often does that happen? Keep in mind that these are $30. 5" woofers

[Kornbread]

Cannot find the writeup on the c-note design. From add copy, it looks like an 11x9.5x7.5" box. With 1/2" walls, it should be ~.31ft³/8.8L volume, and the op states 7.5"/19cm x 1.38"/3.5cm port.
Curious as to why PE would not warranty a woofer because of an aftermarket crossover? From the pics, it looks like all Dayton parts, and after all, this is diy where many of us build our own crossovers from scratch.

Unibox says tuning is 40hz using a 7.5"x1.38" port, in a .31ft³/8.8L box. Seems a bit low, but let's roll with it.
Anyhow, @27watts, yeah, if you like listening to edm, I could see a problem.