Thoughts on Passive bass Radiators
- Thread starter fomoco69
- Start date
TerryO
Super Member
That youtube video was posted by Steve Kephart, the Car Audio expert and all around good guy.
It's too bad that a "cone" wasn't shown on the video. The Parthenon could really push air. Dan had it at one of our DIY Meets a few years ago. It's a fascinating machine to see, even when it's not being used. Shades of the Bass List!
Dave, thanks for the link!
Best Regards,
TerryO
Pix
That is terrible. Please send me those Polk's and I will properly dispose of them.
AngelRa
Active Member
Today, took my Velodyne V-810B (10" PR) which was in my daughter's room. Placed in my listening room with 2 Yamaha MSP5 active monitors which sound tight and punchy. As I expected, the sub produced slow bass. Same happened years ago with my Klipsh SW10.
The Klipsh SW10 got fixed by replacing the radiator with a plate with a flared tuned port on it. I am doing the same to the Velodyne. Will post findings.
The Klipsh SW10 got fixed by replacing the radiator with a plate with a flared tuned port on it. I am doing the same to the Velodyne. Will post findings.
kfa888
Addicted Member
Huh? the passive makes it slow? Don't think so as it is tuned by weight to a frequency. Maybe the driver is slow. Maybe you need to move the sub closer or mess with phase. Subs always take a lot more work to integrate than people think. My point is to drop a sub in a room and call it slow is not fair IMHO.
I like passives on some speakers. I'd listen to these...
Listen to these every day in my office...
I like passives on some speakers. I'd listen to these...
Listen to these every day in my office...
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TerryO
Super Member
Dave,
I'm not sure what the chances are that the problem is related to slow bass or even sub bass.
Bill Poletti and I did extensive research some years ago that indicated that the actual problem was often due to fast treble, with the mids acting as an acoustic fulcrum.
Unfortunately, while I was typing the last paragraphs of the White Paper covering this research, there was evidently a malfunction in a gift that Lee Neidow had recently sent me. This malfunction somehow caused my hard drive to crash in a rather spectacular manner, with flames shooting out through the floppy drive slot!
Sorry to say, all that research came to naught, although Lee's thoughtful "gift" has continued to work accurately.
Best Regards,
TerryO
AngelRa
Active Member
What I mean with slow is that if you listen to the same music in a good sub or headphones the bass starts/stops sharply, while with this sub it overruns. An annoying persistence.
Went outside in the cold and finished the plate with the port. Did not computed anything yet. I used a port tube that was laying in my closet. It is 2-1/2" ID x 8-1/2" L Flared. Been listening to music for about 3 hours. So far is good. Also, it was a breeze to setup and get nice bass. Very happy with results.
The best thing is that if I later change my mind it is 100% reversible.
Went outside in the cold and finished the plate with the port. Did not computed anything yet. I used a port tube that was laying in my closet. It is 2-1/2" ID x 8-1/2" L Flared. Been listening to music for about 3 hours. So far is good. Also, it was a breeze to setup and get nice bass. Very happy with results.
The best thing is that if I later change my mind it is 100% reversible.
guiller
Toscaninichus Australis
My PR speakers don't show any signs of slowness. I play mainly classical music. The passive woofer gets visually activated very rarely, usually when the bass drum plays at forte or fortissimo intensity levels (i.e., in Stravinsky's Rite of Spring). Those are sharp, short-time bursts and the PR reproduces them in a way that I judge indistinguishable from the live orchestral sound. This is my experience on this point.
I would wager that the overrun you were hearing was your room, not your speaker. The speaker produces the sound and the room keeps it alive.
Went outside in the cold and finished the plate with the port. Did not computed anything yet. I used a port tube that was laying in my closet. It is 2-1/2" ID x 8-1/2" L Flared. Been listening to music for about 3 hours. So far is good. Also, it was a breeze to setup and get nice bass. Very happy with results.
As Dave allluded, you probably tuned the sub to a higher frequency so you're not energizing the low bass modes of your room anymore. It makes the bass sound "faster" but you'd probably be better served with some room treatment. Then you would have the low bass and the "fast" sound. Best of both worlds.
TerryO
Super Member
What I mean with slow is that if you listen to the same music in a good sub or headphones the bass starts/stops sharply, while with this sub it overruns. An annoying persistence.
Went outside in the cold and finished the plate with the port. Did not computed anything yet. I used a port tube that was laying in my closet. It is 2-1/2" ID x 8-1/2" L Flared. Been listening to music for about 3 hours. So far is good. Also, it was a breeze to setup and get nice bass. Very happy with results.
The best thing is that if I later change my mind it is 100% reversible.
It's a good thing it's reversible. Why in the world didn't you take the time to figure out what you tuned the box to? Most box design software will allow you to play with the parameters. Depending on the volume of the enclosure, you may have created using that vent, an enclosure tuned somewhere in the 40's or a bit more.
I'd carefully listen to what people like Ray and Dave are trying to tell you, they actually know what they're talking about.
Best Regards,
TerryO
AngelRa
Active Member
Computed the port tuning and is 33Hz, the original PR was tuned at 43Hz which hits the nerves of my room. It is evident that the original design was for maximum output, not accuracy.
My room was computer optimized using CARA software. 8 bass traps (8 Auralex LENDR, and 3 large panel traps that cover one entire wall), Auralex ceiling panels and diffusors, Sonex panels on some locations on the walls, heavy draperies around the projection screen and a plush rug over the carpet. I did everything I could to the room, the only way to improve on it is to change room since the dimensions are far from ideal. Even after all the bass traps it still have a dominant 40Hz mode.
So it is true my room makes the problem worst, and the sub was tuned right where it hurts the most. In this case I cannot pass judgment on the PR transient performance.
It is possible that increasing the weight from 140g to around 246g do the same effect, but this passive will not take any extra weight. This passive does not have a basket neither spider support, it is a flat piece of cardboard with foam surround and an elastic band to the opposite side of the box.
Next weekend I may take the plate amp out and add a SPDT switch to bypass the LPFs, that increases the transient performance.
My room was computer optimized using CARA software. 8 bass traps (8 Auralex LENDR, and 3 large panel traps that cover one entire wall), Auralex ceiling panels and diffusors, Sonex panels on some locations on the walls, heavy draperies around the projection screen and a plush rug over the carpet. I did everything I could to the room, the only way to improve on it is to change room since the dimensions are far from ideal. Even after all the bass traps it still have a dominant 40Hz mode.
So it is true my room makes the problem worst, and the sub was tuned right where it hurts the most. In this case I cannot pass judgment on the PR transient performance.
It is possible that increasing the weight from 140g to around 246g do the same effect, but this passive will not take any extra weight. This passive does not have a basket neither spider support, it is a flat piece of cardboard with foam surround and an elastic band to the opposite side of the box.
Next weekend I may take the plate amp out and add a SPDT switch to bypass the LPFs, that increases the transient performance.
TerryO
Super Member
You computed the port tuning and it was 33Hz? What was the volume of the inside of the box?
You also mention that the PR was tuned to 43Hz...with a rubber band? FWIW, they made PRs ("Floppers") like that over thirty years ago and they were junk then, I really didn't know that anything of that sort was still around.
I'll have to disagree with you at this point, your sub was not designed for maximum output, nor accuracy. It was designed "cheaply" and if your 43Hz figure is correct, it's not really even a subwoofer. My standmount monitors are tuned to almost exactly the same frequency and they use a single 6.5 inch mid-woofer!
You really do need to get a decent Subwoofer Driver with a quality Passive Radiator. Your present amp may actually work, although very nice ones are available at reasonable prices anymore.
My personal preference is the SOTA 12 inch Shiva-X with a 15 inch passive radiator from Exodus Audio. It has a good price, features an outstanding design and has a quality fit and finish. In fact, get two PRs as they can be placed on opposite sides from each other and you can then crank up the volume without the cabinet walking across the floor!
As for increasing the transient response by bypassing the filters, I wouldn't spend the money, nor the time on trying to fix what is a flawed design.
OTOH, why not? It's paid for and experimenting can be fun as well as educational, just don't expect too much.
Best Regards,
TerryO
AngelRa
Active Member
I expected more from a brand like Velodyne. You will be surprised, most of the subs in the market do not even reach 30Hz. They should not be called a subwoofer, instead something like "movie bass boom booster"
To compute the tuning I weighted the passive (since all of it is the moving mass) and used an online calculator. Same with the port, but instead used the diameter and length.
For me tinkering is the fun. Once working right...
, I keep on tinkering with something else.
AngelRa
Active Member
Yes you got it perfectly right. 1.174 cu ft (if I recall correctly).
SaSi
Seriously Illogical
I was toying with the idea of building two "subwoofers" for my KEF CS1 that only go decently down to 80-100Hz.
I examined sealed, vented, PR, and 4th order bandbass enclosures. Each has it's own benefits and properties.
I then started thinking of a 4th order bandpass enclosure with a PR. I haven't seen anything like that described anywhere. Taking the analogy that a PR enclosure is a variation of a vented enclosure, would a 4th order bandpass + a PR be a variation of a 6th order bandpass?
My thoughts may be silly but I happen to have 6 KEF B139 PRs and I am trying to find out something interesting to do with them. As I have a pair of Calindas and 104ab, the conventional way to use them has seems just so ... boring.
So I am thinking about some unconventional enclosure designs, including acoustic levers.
I examined sealed, vented, PR, and 4th order bandbass enclosures. Each has it's own benefits and properties.
I then started thinking of a 4th order bandpass enclosure with a PR. I haven't seen anything like that described anywhere. Taking the analogy that a PR enclosure is a variation of a vented enclosure, would a 4th order bandpass + a PR be a variation of a 6th order bandpass?
My thoughts may be silly but I happen to have 6 KEF B139 PRs and I am trying to find out something interesting to do with them. As I have a pair of Calindas and 104ab, the conventional way to use them has seems just so ... boring.
So I am thinking about some unconventional enclosure designs, including acoustic levers.
