SDA SRS drivers popping at high volume

F1nut

heiney9 wrote:

Guys....it's one of two things as mentioned.

1. Bad drivers, for whatever reason. Prior damage or old age.

2. Over driving the mid-bass drivers with either to low a frequency and not enough power or using too much processing and loudness or just plain clipping the low signal. When it starts to flutter (w/o poping) you've reached the excursion limit of the driver or the ability for the amp to control the driver(s). Regardless of how much power said amp produces.

This is really not that hard of a concept, only a few things can cause this. Watts are not watts and this is a prime example of there being what should be enough power but obviously there is some characteristic of said amps that causes the loss of control of the drivers.

The cabinet volume on the big SDA's is very large and throw the passive radiator into the mix which has to work off the cabinet volume and the pressure created by the mid-bass drivers and you can see why this is happening. PR designs not only need a fair amount of power they typically need an amp that can really control the drivers, there's a lot going on in that big cabinet. It's a matter of all these seperate issues accumulating to cause a problem. No offense to anyone's gear but it has it's limitations regardless of how much power it puts out. You can't look at one dimension and assume that just because the rated output is **** watts that it will perform well at it's limits.

I will also reiterate that if the driver has been damaged at one time, it will continue to pop until it's replaced. They don't magically reset or fix themseleves over time.

H9

Very good!!!

I'll also add that any speaker can be made to "pop", so one shouldn't think that this can only happen with SDA's.

ND13

heiney9 wrote:

the ability for the amp to control the driver(s).

Explain how the amp controls the drivers.....or better yet, what components of the amp do so. I'm not trying to be a smartass, I'd just like to know. I'm assuming that my PSound does this quite well, seeing that I haven't had this issue(20 year old, 1st gen SRS 2s), even when playing some bass heavy contemporary jazz at, what I'd assume was, over 100dbs. I need to get a SPL meter. How much do they cost?

reeltrouble1

I got one Noel, I dunno I might let it go for say 150.00???













RS--30.00 bucks or so will getter done.:)

H9, Its all good info my man.

RT1

heiney9

ND13 wrote:

Explain how the amp controls the drivers.....or better yet, what components of the amp do so. I'm not trying to be a smartass, I'd just like to know. I'm assuming that my PSound does this quite well, seeing that I haven't had this issue(20 year old, 1st gen SRS 2s), even when playing some bass heavy contemporary jazz at, what I'd assume was, over 100dbs. I need to get a SPL meter. How much do they cost?

Ted’s gonna have a field day with this post……:D

First off all I am not an electrical engineer, not even close. I can’t say what specific components in a particular amp or how they are designed will affect the interaction with any speaker let alone more than one model. The biggest indicator of how well a SYSTEM can control the speaker drivers is term called Damping Factor. This spec may show up on your spec sheet, it may not. A couple things to keep in mind is don’t get too wrapped up in the number; just know that the higher number is more ideal.

Also realize that the damping factor of the whole SYSTEM is the key, not just the amplifier rating and the manufacturer’s published number. Because both amplifier and speaker are reacting infinitely based on the changing amplitude and frequency of the signal, system damping factor is the key to controlling drivers. Speaker cables play a roll in the SYSTEM damping as well (anybody remember the discussions about the Polk speaker cable)

http://www.polkaudio.com/forums/showthread.php?t=19047&highlight=Polk+cobra+speaker+cable

Many look at manufacturer damping factor numbers and say they mean nothing. The number on paper may not be a great indicator, but the concept of damping is very real and is a major reason why some amps perform better than others. I would think a very robust power supply, simple straight forward design, high quality components; also my guess is amps that are designed and capable of driving very low impedance loads will perform better in this area.

Damping Factor
Technically, the damping factor of a system refers to the ratio of nominal loudspeaker impedance to the total impedance driving it (amplifier and speaker cable). In practice, damping is the ability of the amplifier to control speaker motion once signal has stopped. A high damping factor means that the amplifier's impedance can absorb the electricity generated by speaker coil motion, stopping the speaker's vibration.

Other points:

1. Damping varies with frequency. Some manufacturers publish a damping curve for their amps.
2. The effects of damping are most apparent at low frequencies, in the range of the woofer's resonance. Well damped speakers sound "tighter" in the low end. Low damping factors result in mushy or indistinct bass.
3. Speakers connected in series or parallel will experience the same damping factor from the amp. Impedance determines damping factor, not speaker wiring.
4. Higher impedance speakers increase system damping factor.
5. The damping factors you see published as amp specs are for the amp only, not referenced to an entire system. Higher is better, and you'll often see quite high numbers, 200, 300, even 3000 or higher.
6. System damping factors over 10 are generally acceptable. The higher the better.
7. For the tweaky among you, here's how to calculate a system's damping factor: First, calculate the output impedance of the amp into, say, an 8 ohm speaker (use the nominal impedance of whatever speaker you are using for your own calculations), and a 100 foot 12 gauge speaker cable. Let's also say we have an amp with a published damping factor of 3000. Since damping factor is the ratio of speaker impedance to amp output impedance, you can work backwards, dividing 8 by 3000, giving us .0027 ohms amp output impedance. You must also consider the impedance of the speaker cable; 12 gauge wire is in the range of .0016 ohms/foot (cable catalogs sometimes publish this spec). For a 50 foot speaker cable, you've got 100 "feet" of impedance (50' out, 50' back) giving a total cable impedance of around .16 ohms (note this is much higher than the amp's impedance - one reason larger speaker wire is better for long runs!). This makes the total output impedance .1627 - pretty low. The system damping factor will then be 8 ohms divided by .1627, resulting in a very good score of 49.

Damping Factor: This is a quantity which defines how quickly the amplifier can stop a reproduced frequency such as a bass note. The higher the damping factor, the better the amp will control the woofer and help reduce overhang distortion (again to a point). The damping factor of an amplifier is mostly dependent on the output impedance of the power amplifier and the ability of the power supply which feeds the power amp.

The damping factor in an electrical circuit gives the ratio of the impedances of two electronic devices, the load impedance Zload (input impedance) and the source impedance Zsource (output impedance).

For audio power amplifiers this source impedance Zsource (also: output impedance) is generally smaller than 0.1 Ω (ohms), and can be seen from the point of view of the loudspeaker as a near short-circuit. This will very rapidly absorb any unwanted currents induced by the mechanical resonance of the speaker's voice coil, acting as a very effective 'brake' on the speaker (just as a short circuit across the terminals of a generator will make it very hard to turn), thus keeping it under control.

Note that modern amplifiers, employing relatively high levels of negative feedback, generally exhibit extremely low output impedances - one of the many consequences of using feedback. Thus "damping factor" figures in themselves do not tell you very much about the quality of a system, and given the controversy that has surrounded the topic of feedback for many years, may actually be seen as a mark of poor quality, if excessively high, for those who subscribe to the view that high levels of feedback are a bad thing.

Incidentally, maintaining a good damping factor is why decent quality (that is, very low resistance) speaker cables are part of every good system, as cable resistance adds to the source impedance. However, this subject brings its own controversies; in general the most gains are made for a modest increase in outlay over the very cheapest of cabling - beyond that is where the controversy lies.

Well there you have it..........and the last paragraph is very interesting about speaker cable. Another positive to using high quality cable.

Anyone else who has anything to add, please do.

H9

Dennis Gardner

My head hurts................must be my brain's low damping factor to so much info in the morning.

reeltrouble1

Heiny acutally LIVES at a Holiday Inn Express.

The larger the driver the harder it is to control.

RT1

heiney9

reeltrouble1 wrote:

The larger the driver the harder it is to control.

RT1

This is true, but with a PR design you have all that internal cabinet pressure to deal with and that can play havoc with the many individual drivers. The idea with Polk (with their PR design) is to make several smaller drivers produce the sound of a larger surface area driver with out having many of the drawbacks of a larger driver. So yes, specifically speaking a smaller driver is easier to control than a bigger driver. But in the case of mutiple drivers in a large cabinet with a large PR you can definetly have some physical control issues. Each driver is NOT independent of the other. They are designed to work together (with the exception of the SDA drivers).

Also keep in mind damping factor is not THE reason the drivers are poping, it's just one small factor, over driving the amp is the major contributor here. Noel specifically asked what controls the drivers, so I tried to lay it out as straight forward as possible.

H9

P.s. Don't you just love this hobby

Zen Dragon

Wow! Great information on damping there Heiney. (where's my coffee)

Vikashp: Concur you should stop doing that to your SDA's. The drivers are way extending and you will damage them if you continue if they aren't already. When fed a hard deep bass note the SDA's drop below 2 ohms impedance during that note, which is drawing a momentary large burst from your amplifier, which sends many a strong amp into a momentary clip.
2 questions.
- What are you feeding the Acurus with?
- At what clock position is your volume knob?

reeltrouble1

yes, I do, I also have a very large driver.

It is not damp here today, it is dry, my driver is not damped.

However, the SDA drivers still move air along with all the other drivers in the cabinet meaning they are coupled, fluidly working together.

Polk Paul ism "Nothing like big watts on a large radiating surface".

The speakers in this thread are still popping.

You need three nuns. Two to watch and make sure one nun gets none.

Same reason you need three ducks, well almost.

Totally sealed cabinets require more damping energy. flip flop off axis

Drivers need linearity.

Tubes Rule



RT1

F1nut

Let's not forget HIGH current, which has no relation to low tide.

danger boy

what's the difference between a high current amp and one that is not high current?

thehaens@cox.net

danger boy wrote:

what's the difference between a high current amp and one that is not high current?

That is a good question, I know the carver has a Voltage and Current Load on the speaker outputs.

I have yet to see an amplifier that boasts an advertising campaign of being low current....

From what the BK Manual says "High Current amps are designed with large amounts of capacitive power. The amp will remain stable even at very low impedance nominally at 4 Ohms w/ dips below 1 Ohm..."

Scott

heiney9

danger boy wrote:

what's the difference between a high current amp and one that is not high current?

Short and simple here's a basic statement about what makes an amp a high current amp.

A good power supply is extremely important, and can be one of the major factors which distinguishes the quality of two amplifiers that have the same specified output. The main components in a power supply are the power transformer, rectifiers, and some large capacitors. If the power supply is inadequate, then distortion will result when high power demands are made, such as during loud passages in the music. Whereas one amplifier rated at 100 watts per channel may "clip" (go into high distortion) at just over 100 watts, a different 100 watt per channel amplifier with a better power supply may give much more than 100 watts, at low distortion, for short bursts (a kettle drum thud in a musical passage, or a gunshot in movie, for example). Well built power supplies not only provide noise free electrical power to the amplifier parts, but are capable of delivering high voltage and high current. You will see why this is important in the section on speakers.

I'm tired and that's the best explanation I can give right now.

H9

F1nut

A high current amp is what I have. A not so high current amp is what these guys that keep popping drivers have.

heiney9

F1nut wrote:

A high current amp is what I have. A not so high current amp is what these guys that keep popping drivers have.

...

reeltrouble1

F1nut wrote:

Let's not forget HIGH current, which has no relation to low tide.

Oh yes, if you have high current outflow in conjuction with a low tide you get a deeper wider cut.

Therefore it follows that low current outflow with a high draw pull results in popping and the occasional clipped line.

Quite simple actually.

High currrent amplifiers supply sufficient electron flow down the pipe as it is pulled by the speakers, the lower the impedence the more flow is called for. Voltage supplies the pressure to the flow. When the flow cannot keep with the demand the amplifier heats up and cuts or "clip" the wave.

RT1

BobMcG

heiney9 wrote:

...if the driver has been damaged at one time, it will continue to pop until it's replaced. They don't magically reset or fix themseleves over time.H9

HEY! Now that's not fair! :eek:

Who came up with that rule???:mad:

vikashp

That popping sound was when pushing the speakers very hard with the bass cranked all the way. In regular listening they never pop like that even at pretty loud levels. I don't have an SPL meter to measure with. I added a pair of 10" Velodynes a while back to get the deep bass I wanted at higher listening levels.

btw. I am a web developer and developed a site that mashes Google Maps and eBay. It was even mentioned in the Wall Street Journal. I just realized it can be used to find Polk speakers within driving range since shipping these can be a killer.

It's mapBid at http://www.mapbid.com

F1nut

That popping sound was when pushing the speakers very hard with the bass cranked all the way.

Well, what did you expect??? You do that to any speaker and you'll have the same problem. Tone controls and EQ's should be banned and anyone caught using them should have their gear taken away.

Loud & Clear

lol. We're back to taking people's equipment away from them again. I'd missed that. I find that to be absolutely charming.

heiney9

A gear "time out"

Tour2ma

Lately folks have been getting creative with the sound uploads...

I listened a few times and that sounds mechanical to me, like one (or more) MW's cone has torn away from VC assembly. Ignore them giving you the raspberries and just after mid-point of the video you can clearly hear a tap-tap (or click-click) that's tell-tale. I think to a certain extent the sealed design employing a PR ameliorates the tapping at lower volumes by cushioning the faulty driver.

And the raspberries sound is very similar to when Rob Zombie killed one of my CA's woofer a while ago. Same kind of "buzz" at volume. Difference was that with their open baffle design, while the noise lessened at reduced levels, it could not go away completely.

My .02 worth...

joeparaski

F1nut wrote:

Well, what did you expect??? You do that to any speaker and you'll have the same problem. Tone controls and EQ's should be banned and anyone caught using them should have their gear taken away.

I nominate myself as the person having the most excessive tone control system on this forum......if anyone can outdo my excessiveness I'd like to know about it.

Joe (master of the separates) Albanese

heiney9

joeparaski wrote:

I nominate myself as the person having the most excessive tone control system on this forum......if anyone can outdo my excessiveness I'd like to know about it.

Joe (master of the separates) Albanese

I think you need a gear "time out".......JK .

danger boy

a person should get an electrical shock every time they touch the bass or treble control.. Zzzzzzzzzzzzzzzzaaaapppppppp!

Zen Dragon

Now c'mon. They wouldn't put the knobs on there if you weren't supposed to play with them.
Actually the tone controls help to compensate for less than ideal acoustics of the room, or to make adjustments to recordings that are poorly mixed. You just have to use reason when using them. My treble and bass are usually near center, and if not are adjusted between -2 and +1. The problem occurs with the people maxing them on the plus side.
Take theirs away. I wanna keep mine.

heiney9

Zen Dragon wrote:

Now c'mon. They wouldn't put the knobs on there if you weren't supposed to play with them.
Actually the tone controls help to compensate for less than ideal acoustics of the room, or to make adjustments to recordings that are poorly mixed. You just have to use reason when using them. My treble and bass are usually near center, and if not are adjusted between -2 and +1. The problem occurs with the people maxing them on the plus side.
Take theirs away. I wanna keep mine.

Sorry Zen, I disagree. The tone controls and most equalizers are rudimentary and don't cover enough of a frequency range to effectively compensate for room issues or poor recordings. Only thing I can see is possibly using a bit of bass boost if you have smallish bookshelf speakers. This is just the way I see it and prefer it. Tone controls in my experience do more harm to the music than good (I haven't had tone controls on a pre-amp in about 20 years). Or to put it another way they rarely work to correct a problem. I'm a purist and I'll continue to be a purist. Of course to each their own.

H9

wire

heiney9 wrote:

The problem comes in when you are underpowering the speakers or are trying to produce a really low bass note at higher volume or when you have loudness switch on at higher volumes or bass boosted. Like I said before I ran into this alot when I sold them. It happened on all models and was usually younger kids trying to play Ac/Dc, etc. at ear bleeding levels with out having enough power.

You can usually get away with a mild pop a couple times but in these cases it sounds like the damage was done. It's a blown driver(s) plain and simple. A driver doesn't have to completely cease functioning in for it order to be blown. I'm not sure the best way to isolate the driver, obviously you don't want to turn it up so loud to reproduce the sound. Perhaps there are some measurements you can make across the drivers to see which one it is. Call Ken @ Polk CS and see if he has any suggestions for isolating the bad driver.

Your Acurus probably puts out enough power now, but the Denon may have caused the problem to begin with and once the damage is done there is no going back.

This is wrong also . Many years ago i had the same problem with my SDA 2b's . They where still under warrenty then , I had the same poping , I think it came from to much movement in the 6.5 driver . Back then i liked i loud and was running the 2b's with a Bryston 4b ( and still am ) , so all i did was replace the poping drivers and settled down on driving them so hard .
So i wasnt under powering my 2b's with a 4b . i heard his popping , wow , nothing like i had . I had a single pop once and awhile at high volumes , not yet clipping my bryston ( but coming close) .

Tour2ma

Point taken (correct me if I am wrong here, h9), but I don't think h9 is stating that given enough power an MW, or woofer, can't be damaged by being driven to its excursion limits. We all know that sub's can be driven to the point of "bottoming out".

What I read that he's saying is that the most common cause of these drivers' failing is underpowered amps driven to their limits, by lethal combinations of excessive volume and boosted bass. And when amps are exhausted, they lose control of the drivers' movement.

I can testify to the above. Many years ago I witnessed a naked AR 6's (if memory serves) woofer cone deform (almost appeared to be folding) when the deep synth note in ELP's "Lucky Man" hit it at serious volume. It made no noise when it did this, so it was not an excursion limitation (which sounds like a quick ****). The guy at the controls even repeated the track twice, before switching to a couple other speakers with more or less the same result. This took place in a then high-end, audio shop in Cleveland, Ohio. The amp was a McIntosh MC 2300. Funny thing was the guy turned out to be just another customer. Another customer with a pair of brass ones...

The only point of h9's with which I'd take issue, is placing any blame on engaging the good old "Loudness" circuit (do they even design these in anymore???). The designs I know of all boost low/ mid frequencies at low volume, but gradually diminish as the volume setting is increased. I know by the time my old Heathkit AA-15's volume knob reached 10 o'clock, switching the loudness in and out produced no discernable change.

That said, 2b's are not SRS's, which are the subject of this thread. In his testing of the SRS for his Stereo Review review, Julian Hersh exhausted his amp at over 1800 wpc applying tone bursts to the SRS's and had not yet reached the SRS's limit.

Now maybe if you had a model 40b...

heiney9

I saw his post Tour and I was going to respond but I was too tired. Yes, your analysis of what I said is dead correct and I stand by it. I was stating that it was ONE, if not the most common ways these things happen, not the only way.

I haven't used a loudness circuit in years. But my understanding is most are a simple mid and bass boost and it's present until one switches it off. Some manufacturers use a variable loudness control (knob) that can be trimmed down manually as the volume goes up. Anyways, it's a small issue that in the right situation can cause this problem.

H9