Woofer Movement

[ninetynine]

What is considered abnormal as far as how much the woofer cone moves when music is playing. I am running some psb image 2b bookshelf speakers with a vintage technics receiver and sony cd player and my woofer seems to be bouncing back in and out noticably. Its even worst when tunning into radio stations. Its usually noticable with bass driven music especially ambient stuff like Brian Eno, it seems as though the woofer wants to jump out , i'm worried I might break my speakers. What is odd is that this does not happen when I use my psb's with my new Rotel RA-02 amplifier. To what degree is it considered normal for a woofer to bounce ? Also, can it be that it is the receiver that is causing this(maybe due to its age)? Thanks

[Florian]

Does the Woffer make a mechanical noise like its hitting something?
What can also be that the speaker gets just too low of information that the driver will try to play it but ofcourse cant and there you see the high excursion. Thats how i killed my first Infinity RS3 speakers with that cool the Great Mezani CD ;-)

Becarefull with tooo much excursion. A little jumping around is not a problem, but if it stretches nearly flat than "Houston we a problem" :D

[bjornb17]

that old technics receiver probably doesnt have any sort of subsonic filter to prevent over-excursion. i read somewhere ( i think on the axiom audio website) that these subsonic filters are essential since CDs contain lots of junk material below 10 or 20Hz, and that will cause your woofers to flop around uncontrollably.

Your new receiver probably has this filter, and that's why you dont see this happenining on that or any modern receiver.

[ninetynine]

that old technics receiver probably doesnt have any sort of subsonic filter to prevent over-excursion. i read somewhere ( i think on the axiom audio website) that these subsonic filters are essential since CDs contain lots of junk material below 10 or 20Hz, and that will cause your woofers to flop around uncontrollably.

Your new receiver probably has this filter, and that's why you dont see this happenining on that or any modern receiver.


That makes sense, but what about back in the days, people were replacing speakers often because of this? Isn't it the exact opposite because of the turntable dominating the market and the prevention of dropping a tone arm onto the vinyl ....?

[ninetynine]

Does the Woffer make a mechanical noise like its hitting something?
What can also be that the speaker gets just too low of information that the driver will try to play it but ofcourse cant and there you see the high excursion. Thats how i killed my first Infinity RS3 speakers with that cool the Great Mezani CD ;-)

Becarefull with tooo much excursion. A little jumping around is not a problem, but if it stretches nearly flat than "Houston we a problem" :D

It doesn't really make a noise or anything but it gets ugly when theres a lot going on in the track especially if there is a lot of bass. When I listen to the radio its worst especially when changing radio stations its very much like a unisolated turntable when you put the needle on the groove and the woofer jumps like mad.

[RGA]

Well the woofer has to move in order to push enough air -- bass at volume will make the woofer have a high excursion. Small woofers have higher excursion to push the same amount of air that a big woofer would have to move. This is often why small speakers can't play as loud because as volume goes up the woofer can no longer provide enough bass without failing and also why standmounts are often tougher to drive needing more power from amplifiers. In extreme cases when overdriven you can get what is called "doubling"(overloading) where the driver/amplifier is trying to hit the first base line and becomes to slow because ti is trying to push out and not fast enough to get back in to begin again(this is the real simple version). It happens more in car audio systems where you get that real boomy bass that sounds almost echoey. It may be a lack of power that results in this.

You will find often that people will go to a subwoofer(most of which are glorified woofers) which are 8, 10 or 12 inches in a box with a high powered amplifier to make up for what you did not get with your initial purchase of the standmount or floorstanding speaker. It's one thing to hit 40hz -- it's qquite another to have feeling kick you in the chest bass at 100db...and very few standmoutns and not as many floorstanders as i would like do this. Luckily I have heard some impressive inespensive Paradigm Subs which can make you feel like your bones are being crushed -- not that i've heard that from a symphony -- but from Movies it's cool.

[ninetynine]

is there any way of fixing this by opening up the receiver?

[Woochifer]

I suspect that there's some extraneous noise getting into the signal path that goes below the tuned port frequency on your speakers. With a ported speaker like the Image 2B, the cone movement is controlled by the back pressure that the vent creates. As the frequency goes lower, the cone movement actually decreases as the output closer to the tuned port frequency, and at that tuned frequency, all of the bass output goes through the port with none of it originating through the woofer.

HOWEVER, once you go below the tuned frequency, then the air pressure that dampens the cone movement above the tuned port frequency is no longer there. Pretty much any low frequency signal in the lower bass range will cause excessive driver movement unless you have a subsonic cutoff or rumble filter of some kind (this was commonplace on amps when turntables dominated, because surface noise on vinyl records frequently went deep into the lower frequencies). Obviously, whatever noise your receiver produces is below the tuned port frequency.

With the Image 2B's rated frequency response extending down to 49 Hz, the tuned frequency on those speakers is not especially low, and a lot of sounds on music and movie sources go well below that point. Also, it's conceivable that the noise causing the excessive driver movement is coming from some kind of electrical interference inside the receiver, especially if this does not occur with your Rotel amp. Keep in mind that any source with a fair amount of deep bass content will cause your woofers to move excessively, and anything with content that even goes below about the mid-50 Hz range will also cause excessive cone movement. That's plenty of sources that can account for that kind of cone movement.

I suggest that you plug the Rotel in again, and look carefully at the woofers with the levels playing identically to how you typically play the Technics receiver.

If the Rotel again does not show any excessive movement on the speakers, then maybe you should even try plugging a CD player into the Technics receiver and run the tape output into your Rotel to see if the excessive driver occurs with that connection as well. If it does, then you got a problem with the preamp section of the Technics receiver, if it does not, then you got a problem with the amp section. Either way, you got a decision as to whether or not to try fixing the receiver.


is there any way of fixing this by opening up the receiver?

Yes, but if you don't know what you're doing, then you could actually make the problem worse by poking around the inside, and give yourself a nice jolt in the process.

[ninetynine]

thanks for the insightful information! One thing I didn't understand , do you mean speakers that have a frequency response below 50hz will have less cone movement?
Also you said that the frequency response goes below the level of 50hz with movie and music sources but what about a speaker like the B&W DM601 S3 that has popular use for ht and 2channel and has a frequency response of 60Hz - 22kHz ± 3dB on reference axis? I also noticed that a speaker like paradigm goes from 42hz and the higher end models go into the 30hz. Correct me if im wrong, im just not sure if your saying if that below 50hz there will be more stress on the cone or if its the contrary. Basically what Im asking , does the frequency response of the speaker have an effect with the cone moving ?

[kfalls]

I believe what he means is with lower frequencies, say 20Hz, the woofer will move in and out less times (20) than with 60Hz (60). The number of times the cone moves in and out is the frequency. How far the cone moves would be the amplitude. You will see more cone excursion with an 85db tone than with a 75db tone.

[Woochifer]

thanks for the insightful information! One thing I didn't understand , do you mean speakers that have a frequency response below 50hz will have less cone movement?
Also you said that the frequency response goes below the level of 50hz with movie and music sources but what about a speaker like the B&W DM601 S3 that has popular use for ht and 2channel and has a frequency response of 60Hz - 22kHz ± 3dB on reference axis? I also noticed that a speaker like paradigm goes from 42hz and the higher end models go into the 30hz. Correct me if im wrong, im just not sure if your saying if that below 50hz there will be more stress on the cone or if its the contrary. Basically what Im asking , does the frequency response of the speaker have an effect with the cone moving ?

I think you're misreading what I posted. There's no magic to the 50 Hz point, it's simply what YOUR particular speakers are rated for. I was posting that since your speaker has a frequency response that goes down to about 49 Hz, the driver will move a LOT more below that point. This is because once you go below the tuned port frequency for your speaker, the driver will move uncontrollably due to the lack of back pressure that dampens the cone movement for sounds above the tuned frequency.

The port tuning occurs by matching the size of the port opening with the interior volume of the speaker cabinet. Different speakers have different tuned port frequencies depending on the size of the speaker and the type of frequency response curve the designers are aiming for. In general, a smaller speaker with a smaller port diameter will have a higher tuned port frequency. Depending on how the speaker was designed, you could put an identical driver into a different speaker cabinet, have deeper bass extension with LESS woofer movement in general. But, all of these box/port parameters have different effects on the tonal characteristics, so it becomes a matter of taste in how it all works out.

In a nutshell, here's how a ported speaker's woofer typically works:

For sounds above tuned port frequency - the driver will move with the audible sound, and the woofer movement will be controlled and dampened by the back pressure from the vent.

For sounds closer to or right at the tuned port frequency - the driver movement will decrease as the frequencies go lower towards the tuned port frequency, until at the tuned frequency the driver movement stops altogether and all bass output goes through the port. (for your speakers, a test tone somewhere around 50-55 Hz will likely produce minimal or no woofer movement whatsoever)

For sound below the tuned port frequency - the driver basically "unloads" with uncontrolled movement because the dampening effect of the back pressure from the port is no longer present. As the frequencies go lower, the woofer will continue to move, but you will no longer hear anything as a result of that motion.

Basically, what you should concern yourself with is NOT how much the woofer moves, but whether the movement appears uncontrolled, floppy, and unmatched with any audible sounds. Drivers are designed to move quite a bit, and if you see a lot of action, but can hear the bass that accompanies it, there's not much of a problem provided you keep the volume reasonable. However, if you see a lot of movement with nothing audible, then there's a lot of bass sounds getting fed through the speakers that are below the tuned frequency. And that is somewhat of a concern, because the movement is uncontrolled.

[ninetynine]

wow great post, thank you for taking the time to write that. I'm a big fan of music in general I listen to everything you name it and I rarely meet audiophiles that like avant-garde or experimental music it seems as though they are stuck in jazz or classical only and dont get me wrong , i'm just as big of a fan of those genres but I enjoy experimental music especially ambient stuff where there is layers upon layers of sounds and "drones" which really digs deep into the bass region. The thing is , I cannot find a speaker that will compliment "complex" music and its hard to find an answer from anyone that doesn't listen to experimental music. It seems as though that my psb image 2b , (which are great speakers btw) had a hard time with "complex" music. Should I go with a speaker that has a frequency response that goes down to 30-40hz?

[Woochifer]

wow great post, thank you for taking the time to write that. I'm a big fan of music in general I listen to everything you name it and I rarely meet audiophiles that like avant-garde or experimental music it seems as though they are stuck in jazz or classical only and dont get me wrong , i'm just as big of a fan of those genres but I enjoy experimental music especially ambient stuff where there is layers upon layers of sounds and "drones" which really digs deep into the bass region. The thing is , I cannot find a speaker that will compliment "complex" music and its hard to find an answer from anyone that doesn't listen to experimental music. It seems as though that my psb image 2b , (which are great speakers btw) had a hard time with "complex" music. Should I go with a speaker that has a frequency response that goes down to 30-40hz?

Simpler and less expensive solution would be add a subwoofer and crossover the bass around 60 Hz. Your Image 2B just has a hard time with deep bass, because it was not designed to handle that kind of range. If the music is throwing drones that plunge below 30 Hz, that's a lot of information below the tuned port frequency of your speaker, and a lot of wasted and undampened driver movement. A subwoofer with the crossover set at around 60 Hz would keep the signal content above the tuned frequency, ensuring that all of the woofer movement stays within the range that's dampened by the port, and allow you to listen to the full range that's in your music.

[ninetynine]

I was thinking of a sub aswell, i'm not sure if an integrated Rotel RA-1062 takes a sub though...What about floor standing speakers, will that do the job? How much would a decent sub cost, prefferably small and not too pricy , any recommendations?

[Woochifer]

I was thinking of a sub aswell, i'm not sure if an integrated Rotel RA-1062 takes a sub though...What about floor standing speakers, will that do the job? How much would a decent sub cost, prefferably small and not too pricy , any recommendations?

A decent sub will cost a lot less than a pair of floorstanders with comparable performance. With your amp, you will need to use the speaker level crossover on the subwoofer to cutoff the outgoing bass going out to the speakers. Whatever sub you consider, you need to make sure that its crossover is capable of doing a high pass crossover using the speaker level connections.

[ninetynine]

I see, thanks for the advice, what do you think of the monitor audio b4 floorstanding ?

[ninetynine]

ah never mind the b4's actually i dont have space lol, also I think I will upgrade to a subwoofer much later but for now I have broken down my choices to these following speakers

Monitor Audio Bronze 2
Monitor Audio Silver 2
Paradigm Studio 20
B&W DM602 S3

the monitor audios go down to 30-40hz and the paradigm and b&w are about the same at 49hz. Will the monitor audios give me better lower bass response?