Adding weight to passive radiators...feedback

[Hifigogo]

I've got a pair of Forte 1's that I have upgraded with the Crite's crossovers and titanium tweeters. The speakers sound wonderful mated with a NOS Valves restored Fisher 500c...a hugely fun listen in many ways.
I'm thinking about is adding 2.5oz of weight to the passive radiators, and I would appreciate some feedback from those who have done it. I've read a few posts about the procedure, but I haven't seen a lot of feedback about how it sounds, and if there could be the possibility any long term damage to the passives given the added weight.

 

[moray james]

Hey there: I am the guy who started this modification idea for Klipsch with passive radiators. This is how passive radiators are tuned you vary the weight up or down to set the desired resonant frequency up or down. This is exactly the same as changing the length of a reflex vent longer or shorter which shifts the tuning frequency. So if you have a set of Chorus which have baffle thickness length vents (3/4") you can lower the system tuning by installing 7" vent tubes.
With a pre existing factory passive you need to be mindful of the peak to peak travel capacity of the PRU (passive radiator unit). That is why I limit the weight to 2.5 ounces. What re tuning does is just that you are setting a new and in this case a lower system resonant point for the loudspeaker. Result is deeper (lower frequency) bass extension. This is not a magic knob you turn and magically the bass lowers there is not unlimited range available. Both the woofer and the existing passive must be considered as they set the limits of what you can and cannot do. In the case of the Quartet, Forte, Forte ll (larger passive) and Chorus ll I chose to limit the added weight to a 2.5 ounces. This shift in weight results in a marked improvement in bass extension with no noticeable evidence of the passive being over driven at any levels that I have played at.
Why don't you invest the short amount of time necessary and install some weights and listen for yourself. This mod can be done in less than an hours time and the cost is not a factor. Decide for yourself if you like the change or not the mod is just as easy to reverse should you change your mind or simply want to return the speaker back to a stock factory tuning. The question here is not whether or not the mod works because this is a simple mechanical adjustment the question is do you like your speaker balance with or without the change and you are the one who must determine that yourself. moray james.

 

[Stan man]

Adjusting passive radiators with weights like putty, or clay is absolutely essential for any speaker that uses them. More often than not, they are not fine tuned at all at factories . The change in sound can be a revelation.

 

[Species 8472]

The suspension of the passive was not designed to carry an extra 2.5 ounces. Maybe on a new passive it would work, but on a 30 yo speaker your just asking do damage something that is getting harder to find suitable replacements. If you need more bass add a sub. Personally I find the bass even out of my Hereseys to be sufficient.

 

[moray james]

The suspension of the passive was not designed to carry an extra 2.5 ounces. Maybe on a new passive it would work, but on a 30 yo speaker your just asking do damage something that is getting harder to find suitable replacements. If you need more bass add a sub. Personally I find the bass even out of my Hereseys to be sufficient.

it has been some years since I first did this and I have had no issues on any of the Klipsch passive units that I have modified. In reality there is not very much very low bass content in music. I have never once noticed any distress of the passive and I do play loud electronic music with deep bass content from time to time. You are of course free to decide for yourself. Personally I am not fond of adding subs to full range loudspeakers. moray james.

 

[DEFTECHY]

The suspension of the passive was not designed to carry an extra 2.5 ounces. Maybe on a new passive it would work, but on a 30 yo speaker your just asking do damage something that is getting harder to find suitable replacements. If you need more bass add a sub. Personally I find the bass even out of my Hereseys to be sufficient.

i highly doubt 2oz of weight will do any harm to the robust passive/spider assembly of a klipsch passive... thats kind of like saying you cant add some bolt on performance items to a 30+ year old muscle car because it wasnt "designed" to have an extra 25 or 50 horsepower. simply untrue, most things are over engineered to allow for time & abuse & even upgrades, including speakers. manufacturers know full well that some people will turn the bass knob up more than others, or use loudness bttons, or run more power to them than what they are "rated" for etc etc. i have fortes & chorus2 & am planning to try the added weight on the passive, if i dont like it or it doesnt make any improvement i will simply remove it... but it wont harm anything.

& if you find heresey bass "sufficient" you either A- have never heard real quality bass or B- are easily amused. no offense intended, but the heresey is notorious for lacking bass, the vast majority of people say they are probably at the bottom of the list for bass output. i have owned hereseys before & while they sound good for mid/highs, they are like a ghetto blaster for real low bass frequencies... listen to some fortes that have the same size woofer or chorus, or the horn loaded belles or k-horns, or any of the dual woofer models like epics, KLF or KG series, they have real bass reaching down to almost subwoofer levels.

 

[Species 8472]

Ahh the old car analogy, somehow makes it all true.

Horsepower? are you talking about amplifiers or speaker sensitivity?
Suspension analogies would more correctly be compared to cornering. Tell me does a car handle better on good roads with the driver alone or when loaded to maximum gross vehicle weight?

Do you think Klipsch engineers miscalculated the cabinet volume or missed the proper weight for the passive to tune the box correctly? ALK did a terrific write up on how he made a crossover of his own design the first generation forte and found the box (at least his) was tuned correctly.

https://community.klipsch.com/index...ping-a-network-for-the-forte/#comment-1168913

And now bring in the KG series. the KG4 and the forte 1 has the same diameter passive and the difference is not the weight of the drone but rather how stiff the spider and surround is.

Go ahead glue anything you want on your passives it only makes mine more valuable.

btw, I got fortes and forte 2s and a couple pair of scalas and some KP 301s for when I really want to piss of the neighbors.

 

[moray james]

 

[DEFTECHY]

Ahh the old car analogy, somehow makes it all true.

Horsepower? are you talking about amplifiers or speaker sensitivity?
Suspension analogies would more correctly be compared to cornering. Tell me does a car handle better on good roads with the driver alone or when loaded to maximum gross vehicle weight?

Do you think Klipsch engineers miscalculated the cabinet volume or missed the proper weight for the passive to tune the box correctly? ALK did a terrific write up on how he made a crossover of his own design the first generation forte and found the box (at least his) was tuned correctly.

the analogy was very general, wasnt trying to compare a certain component of a car vs a home speaker. it was a reply to your comment that it wasnt "designed" for extra weight, any part of a car wasn't "designed" for extra weight or power, etc etc, but it can be improved without causing any harm, to a point of course.

your weight analogy is way off, because if you want to get all technical, then tell me how many cars are designed with a perfect weight distribution for "cornering?" just adding a bunch of weight willy nilly to max gross vehicle weight would be stupid & probably hurt performance, however adding the "right" amount of weight in the "right" places will greatly improve the cars handling & cornering abilities... just like adding a little weight to the passive (or extending ports some) will retune the bass a few hz lower. simple physics.

so as for klipsch engineers miscalculating, moray james never suggested that, they built the speakers to a certain design with compromises in certain areas to meet their cost of production vs performance goals... just like any car manfacturer builds a car to meet certain design goals & limitations... you cant make a production car (or speaker) be perfect in every way (unless its an exotic expensive sports car) but you can improve on the stock design with aftermarket performance upgrades or even changing the original design somewhat. thats what aftermareket parts like stiffer springs/shocks & bigger brakes/sway bars are all about (cornering/handling), same for bolt on engine upgrades to add power or changing the original engineering of the engine all together with internal parts like cams & porting heads & higher compression etc etc... i own a 1970's GM musclecar, its engine was made & "designed" to have about 250 horsepower, i completely changed the internals & external parts to now make almost 600hp but i still use the stock engine block that has been proven to handle the added power... did GM engineers "miscalculate" the engine tuning or "proper parts"?? no, it was designed to meet a purpose & make a profit to sell to the masses. same applies to klipsch speakers in this example.

your statements are way off base about what klipsch engineered or what can be done to speakers or any product for that matter... based on that logic the entire aftermarket industry for any product is a farse or gimmick & the original products design is the best it can ever be... sorry to break it to ya but original designs can almost always be improved on. thats like saying the titanium tweeters aren't any better than the stock tweeters... did klipsch engineers miscalculate how they built their tweeters? no, but they sure can be improved on. same with the caps they use in crossovers & cheap foam they put inside the cabinets, or the volti wood horns vs stock 400 & 401 horns etc etc etc. engineers are very smart people but they are almost always limited to what the higher ups & bean counters decide they can actually do.

the KG series & others i mentioned were simply examples of speakers with better bass than the heresey, that you said the bass was sufficient on... my opinion & many others is that heresey bass is not sufficient & leaves a lot to be desired.

& i wont glue anything to the passive untill i verify it makes a worthwhile difference... ever heard of tape, or non permanent rubber cement? sorry but yours still have the same value as mine...

& if we're comparing the speakers we have for some reason, btw, i got forte ii, 2 pair of chorus ii, a couple pair of K-horns & have had fortes, 3 pair of kg 5.5, epic cf-4, cf-3, a few RF series & heresy as well as many other models of klipsch & other brands, & i still say without a doubt the heresy had the least amount of bass by far.

sorry if my comments or analogies struck a nerve, was just replying to how you suggested heresy bass was sufficient & that adding 2.5oz of weight will damage the passive... it will not.

 

[Species 8472]

There are always tradeoffs. Lengthening ports or weighting the passive reduces woofer efficiency. This normally means the mids and highs are elevated. Klipsch are regarded my many to be bright enough already. How is reducing the woofer output beneficial? Why does Moray have the only Hereseys that can make bass?

 

[Gazdatronik]

I would agree with the elder statesman's post before mine. When you change a port length or passive radiator's resonance point, where the woofer begins to roll off in the high frequencies can be changed, sometimes with undesirable results. As for why the manufacturer doesn't just add more mass beyond the specified point that it leaves the factory, this is usually the reason.

Its fun experimenting with, for sure, but for the most part the designers understand the application in which the component is being used.
If more low bass is desired, my only recipe is to move more air, which I would trust better to an array of large woofers than my mains.

 

[twiiii]

I don't read about using test equipment to confirm or verify any of the claims made. Its the same idea as rolling tubes for amplifiers or pre-amps. Claims claims and more claims with out measurements to confirm gains or losses. The correct tube can reduce distortion over old tubes by significant amounts, but which tubes. Add ing weight may lower the frequency but it also makes the cone more susceptible to ringing, slower rise time and exaggerated decay. It also changes the loading on the active woofer increasing the amount of modulation at the woofers lower limits increasing distortion further. So unless you have a very large anechoic chamber and proper test equipment leave your speakers alone. I realize we all have distortions we love in different forms. But if you want bass below 30 HZ you are going to have to look else where. especially if you want low distortion. And for folks who say there is no bass below 40 to 35 Hz you need to invest in a spectrum analyzer and see it for your self. You may not be able to hear it and your speakers more likely can't produce it, but its there.

 

[Joseph Jove]

I added the extra weight on my Chorus 2 passives two years ago. Since then I've only used my subwoofer a handful of times. I once used my sub all the time. Don't really need it any longer. As for "damage," none so far after two years of playing my system almost on a daily basis. No ringing either, perhaps because I've braced my cabinets (another Moray James recommendation). Those two upgrades have worked wonders. I don't feel the need to upgrade my tweeters or crossovers as of yet, but I'll probably do the crossovers soon do to age. My two cents.

 

[Hifigogo]

Thanks to all who responded to my query. I think I'll hold off on the mod for now. I moved the Forte's closer to the walls, (14" from the side and back walls) which has resulted in deeper bass. I also now have them facing straight foreword, no toe in...I changed their positions by about 2", and the overall improvement in bass and imaging was significant in a 17' by 30' room.

 

[J U Stone]

Hey there: I am the guy who started this modification idea for Klipsch with passive radiators. This is how passive radiators are tuned you vary the weight up or down to set the desired resonant frequency up or down. This is exactly the same as changing the length of a reflex vent longer or shorter which shifts the tuning frequency. So if you have a set of Chorus which have baffle thickness length vents (3/4") you can lower the system tuning by installing 7" vent tubes.
With a pre existing factory passive you need to be mindful of the peak to peak travel capacity of the PRU (passive radiator unit). That is why I limit the weight to 2.5 ounces. What re tuning does is just that you are setting a new and in this case a lower system resonant point for the loudspeaker. Result is deeper (lower frequency) bass extension. This is not a magic knob you turn and magically the bass lowers there is not unlimited range available. Both the woofer and the existing passive must be considered as they set the limits of what you can and cannot do. In the case of the Quartet, Forte, Forte ll (larger passive) and Chorus ll I chose to limit the added weight to a 2.5 ounces. This shift in weight results in a marked improvement in bass extension with no noticeable evidence of the passive being over driven at any levels that I have played at.
Why don't you invest the short amount of time necessary and install some weights and listen for yourself. This mod can be done in less than an hours time and the cost is not a factor. Decide for yourself if you like the change or not the mod is just as easy to reverse should you change your mind or simply want to return the speaker back to a stock factory tuning. The question here is not whether or not the mod works because this is a simple mechanical adjustment the question is do you like your speaker balance with or without the change and you are the one who must determine that yourself. moray james.

I have a pair of quartet. There is a large black heavy paper attachment on the inside back of the passive radiator. How do you recommend attaching the weight to that? And also what to do you recommend using to make the attachment?

 

[moray james]

I have used large flat steel washers which I layered up to get to the right weight. I use 3 - 4 small dots of epoxy to bond the disks together and the same to bond the disks in place on the passive. the fast setting epoxy is more than strong enough and if you ever want to remove it to return to stock tuning it is easy to take off with a small razor knife. Hope this helps. Please post your impression as I am sure others will be interested in your thoughts on this mod.

 

[J U Stone]

I have used large flat steel washers which I layered up to get to the right weight. I use 3 - 4 small dots of epoxy to bond the disks together and the same to bond the disks in place on the passive. the fast setting epoxy is more than strong enough and if you ever want to remove it to return to stock tuning it is easy to take off with a small razor knife. Hope this helps. Please post your impression as I am sure others will be interested in your thoughts on this mod.

I will do so thank you... i am considering beating a 2 oz lead sinker into shape ... ill let you know how that works out.

 

[851 SP3]

Fyi, the original weight, and glue it's embedded in, in the passive of the Forte II I am fooling with weighs 4 oz.

 

[moray james]

I would not use that much weight, I decided upon 2.5 ounces based upon passive motion with test tones. You cannot make the driver play lower than it can and adding more weight will make matters worse not better with that much weight you will not have any load on your woofer it will be free to resonate. A four ounce weight is going to get yo into trouble. Even if the driver could play low enough to drive the passive the passive itself does not have the necessary range of motion available.

 

[851 SP3]

To clarify, the weight was original to the unit, under the dust cap. It was attached to the front of the cone and covered by glue. It was not glued 'on'; the cone material peeled right off the backside of the weight. The 4oz measurement is the total of the weight and glue combined. The weight is 40 mm diameter, the glue (at its widest) is about 75 mm, and the total thickness is about 15 mm. I'll try and post a photo or two shortly.