can someone explain passive radiators to me? (1 Viewer)

[Patrick Sun]

It bowls me over to think anyone here would spend $2000 on a subwoofer project of small enclosure size (unless they had a seriously big room to fill).

 

[Brian Bunge]

Well, not in the DIY forum, but they sure do in the Speaker and Subwoofer forum!
Brian

 

[John E Janowitz]

Thy, check out the PR FAQ on my site. I just did an update to it and plan to do another one shortly with some images to illustrate things a little better:
http://www.stryke.com/prfaq.htm
As far as your comments:
The problem is not the PR design itself, it is your implementation. In trying to get more output from a small driver, you will end up using smaller PR's with lower mass, and higher tuning frequencies. There are several issues you run into that cause this sound you don't like.
First, the higher tuning frequency. In a properly designed PR system you have a low tuning frequency, say 20Hz or so. At the tuning frequency you get a rise in group delay. The region of this rise is typically where people tend to think the bass sounds "sloppy". However, how "sloppy" the bass tends to sound is directly related to the relationship between the level of group delay in ms, and the wavelength of the frequency. If you are at a high frequency where the wavelength is short, and have high group delay, this will be audible. However, if you are at a lower frequency and have the same level of group delay, this will not be audible. Group delay of 20ms at 20Hz will not cause any audible effects, however group delay of 20ms at 50Hz may. If you're using smaller drivers and smaller PR's, you no doubt have a higher tuning frequency and will have to deal with this issue.
The next issue is related directly to the size and tuning of the PR's. PR's do have a "notch" in output that occurs at the free air resonance of the PR. This notch causes the rolloff to be steeper than that of a ported system. When using a PR with high mass, this is not much of an issue. For example with the Power15, the Fp on the Pr's is about 3.5Hz, so the rolloff below the 20Hz tuning frequency isn't much sharper than with a port. However, if you tune a small system to say 40Hz with a low mass PR, the Fp will be much higher, and your response will drop like a rock below that tuning frequency. This also attributes to the "PR sound" that some people don't like.
As others have said, PR's are harder to work with than ports. People often choose woofers that are not designed to be used with PR systems. They do not pick proper tuning frequencies. Most commercial designs are extremely compromised based on budget constraints. The most basic PR's would have $15 or so in materials cost compared to $.25 for a 4" diameter port, etc.
In general if you don't think PR systems can sound good, then you haven't heard one that was properly designed.
John

 

[Thy Luc]

--In general if you don't think PR systems can sound good, --then you haven't heard one that was properly designed.

I didn't say they didn't sound good, I said I didn't
like the sonic personality of PR's, regardless of
implementation. Subjective debates are never won,
a person can argue why they like them until they are
blue in the face, then I come along and say I don't
like the sound for music, but I like them for HT
and gaming - hehehe

Do they use PR's in prosound?

 

[Jack Gilvey]

Ahh, nevermind.

 

[Dan Hine]

Do they use PR's in prosound?

I haven't been around Pro sound as much as other guys here but from what I've seen, no. PR's are not really found in pro sound. But they don't have to be for a number of reasons.

* As stated earlier, PR's are used often because of the desire to have a small reflex design. But having a small enclosure limits the amount of porting you can do. Very few pro sound applications have space as a concern. All I can think of are trade show and corporate meetings, and even then you usually have plenty of room. I've done a lot of audio work for trade shows/corporate meetings and have only once not had room for 2 dual 18" sub enclosures.

* Going along with the above about not having room for sufficient porting, most pro applications are not looking for maximum extension, rather maximum output. Therefore a higher tuning frequency is quite alright. In which case, even in your smaller pro sound subs you can still save $$ and use a port since a higher tuning frequency is OK if not preferred.

* Maybe it's just me, but if someone said my bass was "sloppy" I would take that to mean "didn't sound good."


Regards,

Dan Hine

 

[Jack Gilvey]

* Maybe it's just me, but if someone said my bass was "sloppy" I would take that to mean "didn't sound good."

It's just you.
(LOL. Hehe.)

 

[Anthony_Gomez]

Hey Jack, can you send me all your SLOPPY PR's....I can put them to use....I only like sloppy bass at my place

 

[Greg Monfort]

>I haven't been around Pro sound as much as other guys here but from what I've seen, no. PR's are not really found in pro sound.
====
Uh, the grandaddy of high SPL/low distortion subs, and though it's over 15yrs old still the reference by which other point source sub performance is compared, is the prosound dual 18" PR ServoDrive Contrabass.

You're right though, except for certain special effects, prosound box subs are BW limited high efficiency designs tuned to 35-45hz depending on the application, so large dia/short tube vents work fine.

GM

 

[Jack Gilvey]

John, I just realized your link was for the Lambda PR FAQ revised and posted on your site. This is the best such document and I'm glad to see it's back.
http://www.stryke.com/prfaq.htm
An important quote from it if I may:

Also, many people have said that they have not heard a passive radiator system that they like. Keep in mind, most commercial passive radiator systems on the market are not ideal, and are made with extreme compromises. It is very difficult for a large commercial company to produce an ideal passive radiator system because of budget constraints. These commercial systems are not a good indicator of what can be achieved with a DIY PR system, or with one of our subwoofers.

The Lambda/Stryke PR's come the closest to an ideal reflex alignment than the older "woofers without magnets" that many form their "judgements" from. Closer to ideal reflex than is likely possible with ports, actually.

 

[Will Orth]

RE: Jack Gilvey
quote:

--------------------------------------------------------------------------------
Well I messed with passive radiators years back and if you make a good box from the get go you are ahead of the game, I look at passive radiators as a band aid, make a great enclosure and you wont need to mess with those things,
--------------------------------------------------------------------------------

Well if you make a well designed sub enclosure you wont need a passive radiator, "box" could mean 1-2-3-4-5-6-7 orders with many ported designs "box" WAS JUST A
'TERM' there are many ways to make a box , I have made about 2000 on the conservitive side most bass-sub boxes.

hope that clears up your Quote...

Will

 

[Jack Gilvey]

Well if you make a well designed sub enclosure you wont need a passive radiator, "box" could mean 1-2-3-4-5-6-7 orders with many ported designs "box" WAS JUST A
'TERM' there are many ways to make a box , I have made about 2000 on the conservitive side most bass-sub boxes.

I still don't get it, sorry. So "well-designed" could mean ported, but not PR? If a PR is a "band-aid", how is a port not one? (Have patience with me, I haven't built anywhere near 2000 subs).

 

[ThomasW]

I'm going to drop in here with a quick IMO......
Having built a 'few' subs in my lifetime too, my experiences are as follows:
The absolute best sound quality comes from IB subs.
Properly designed and built sealed or ported subs offer the next best level of sound quality.
PR's offer good bass, but do not provide the best overall transient response, when compared to a properly designed and built sealed or ported unit. (I'll qualify that by saying no, I've not had the pleasure of hearing a ServoDrive ContraBass unit )
Over the years I've built several PR based subs, including one of the more famous PR based cubes, (this unit was built to the designers exact specs). I then put an identical driver in an optimized ported design. Those that heard and compared the two designs under identical operating conditions (same room/same placement/same equipment) thought that the ported version offered better overall sonic quality/bass definition. Understand it's not that the PR based design sounded bad, it's that the ported version simply sounded better.
Anyway my $.02. It combined with an additional $2.85 is enough to buy a Grande Latte' at most Starbucks
Regards
Thomas

 

[Jack Gilvey]

Anyway my $.02. It combined with an additional $2.85 is enough to buy a Grande Latte' at most Starbucks

Well, it's worth a helluva lot more than that given that you've got the relevant experience to speak from. I have to say, though, that my dipole bests my IB in quality (certainly not in extension) using the same driver(s). These are the only two examples of each that I've heard, though.

 

[Thy Luc]

--dual 18" PR ServoDrive Contrabass.

apples/oranges.

You can't compare a direct drive PR system with a
standard PR and call it the same thing - LOL
There is a huge difference between the two.

 

[Thy Luc]

--PR's offer good bass, but do not provide the best
--overall transient response

bingo!

 

[John E Janowitz]

ThomasW,

It's been awhile since we talked about that subwoofer. I know you were using 15" PR's but were they the 3 standard PR's, or the 2 high excursion PR's with adjustible mass? Either of them seemed to have some problems. With the standard PR's, the sub seemed very particular to placement. If not placed at proper distance from the backwall it seemed to have some cancelation at higher frequencies leading it to not sound quite right. If placed at the right distance from the wall, it wasn't an issue. The stiffer HEPR's were just too stiff to work as ideal PR's. The softer the suspension, the closer you get to an ideal port. The HEPR's were capable of the volume displacement needed, but because of the stiff suspension you lose some output efficiency at low frequencies, and group delay goes up a good deal.

The new 18" PR's are a better option. They have the softer suspension needed to keep the group delay down and increase efficiency. Also having them only on the sides and no PR on the back makes the cabinet less particular to placement.

John

 

[John E Janowitz]

Another reason many people do not think PR systems sound "tight" is because they aren't used to the low bass output. Most often the subwoofers that are described as the "tightest" sounding are the ones that have the low end output rolled off the most. One of Tom Nousaine's quotes that I love was "the bass was so tight that it got up and left the room" or something along those lines.

I actually did an experiment with somone listening once to a Thunder12 enclosure. The first time he listened to it, it was playing as it normally would. In the room it was relatively flat down to 20Hz. He thought it sounded very good in this way. Then I rolled off the low end response 6dB per octave starting at 50Hz. He listened again and asked what I did. He said it was so much tighter sounding now. All I did was take away a lot of the low output that he wasn't used to. Nothing else changed. The more low output you have, the "slower" people tend to describe the bass. Why? Because it is slower. The speed of bass is the frequency. A 50Hz tone has a much shorter wavelength, and plays much faster than a 20Hz tone. Roll off those slower low frequencies and to the ear it sounds "tighter or faster".

John

 

[Jack Gilvey]

apples/oranges.
You can't compare a direct drive PR system with a
standard PR and call it the same thing - LOL
There is a huge difference between the two.

LOL, indeed. Welcome to the forum, btw...you're very entertaining!
If you decide which PR's you've actually used, and in what alignments, please post them.

 

[ThomasW]

Hi John.....
Please understand I'm not trying to start a confict, just stating my personal opinion
The cube had the 3-15" PR's. It was set up in 2 rooms each with very different acoustical properities. Optimal room placement was determined with a labratory grade B&K 4133 using a Clio system. Both rooms have IB subs in them, (these are the standard by which we judge all subwoofer performance). The ported design was also located in the same rooms using the same measurement criteria.
There were levels of inner bass detail that could easily be heard with the IB's; and were audible to some extent with the ported design, that weren't audible with the PR based design.
People should understand that I'm not 'dissing' John's PR based designs. I'm just offering my opinion based on the above comparison. It may not necessarily be be a fair comparison although we tried to make it so. I certainly can't comment about what Tom Nousaine heard or didn't hear. He's paid to test subs, I'm not. One thing I do notice is that Nousaine never draws any comparisons between his huge IB sub and any other sub. For those that don't know Nousaine's IB contains 8 TC-Sounds 15" drivers.
Also people should know that the ported sub used is a Herculean effort = ~350lbs. It's massively braced, with a dual flared 6" diameter port and damped with 1/2" thick very expensive wool felt material. So IMO it took that level of construction; and that investment of time and $$$ to better the performance of the cube, using the same driver (Stryke HE-15).
So like I said the cube certainly isn't a poor sounding design. To the contrary, many rave about it's performance, and I've certainly never heard a better sounding PR based design.....
Jack,

I have to say, though, that my dipole bests my IB in quality (certainly not in extension) using the same driver(s). These are the only two examples of each that I've heard, though.

I've a dozen DPL-12"s on order, so I anxiously await their arrival for use in a new pure dipole project