m00n Posted March 3, 2003 Share Posted March 3, 2003 So, I have read about tuning ports on speakers and what not. How does putting a hole in a subs box or tube affect the sound and frequencies? And can I stick a tuning port in my RSWs and get lower frequencies? Or can I take appart my RSW-15 and make a SVS killer out of the parts in it? Quote Link to comment Share on other sites More sharing options...
mmiles Posted March 3, 2003 Share Posted March 3, 2003 I'm way out of my league here but... If you look at specs only there is no direct relationship to how low a driver will go based on size. I've seen 12", 15" and even the jumbo 18" woofers have a similar bottom end freq. response on paper. My feeling is this (please keep in mind this is not based on any physics principles here). It's all about moving air... period. That "punch" you here in your RSW-15 is a freq. range that is more common to music and most HT, say arouond 30 - 45 Hz while the chest pounding rumble you want in an explosion while watching U-571 or while Vin Diesil is skiing down the slope in XXX is much lower say 20/22 - 25 Hz. Therefore the design and size of the enclosure and how it matches the driver, and amp if a it's a powered sub, is crucial to the affect the speaker manufacturer is trying to obtain. I have listened to the RSW 10 and RSW 12 and I would love to try a RSW-15 and still might try to pick up a used one but at the price of some subs like the SVS 2039pc+ (little brother to the CS Ultra) it was not a good HT value IMO at $1250.00 since I bought a "B" stock SVS 2039pc+ shipped to my door for $787.00. If you are a music buff and plan to listen to DVD-A and SACD material in the future the Klipsch may be worth the extra $463. One more tip. If you plan on going with single or dual SVS Ultra's I'd buy the Crown K1. The amp is cleaner, quicker (better slew rate) and can manage the bottom end a bit better (damping factor) than the Samson. Or better yet go to www.chucklevins.com and buy the K2 for $1195.00 You may have to email them for a quote. This is not the technical explaination that you were looking for but as a listener and a SVS owner it might help. Regards, Mike Quote Link to comment Share on other sites More sharing options...
Dustin B Posted March 3, 2003 Share Posted March 3, 2003 http://www.danmarx.org/audioinnovation/theories.html Give that a read, may help your understanding a little. No you can't put a port in an RSW. It already has one with the passive radiator. This will help with your understanding on that point: http://www.stryke.com/prfaq.htm Like I said in your other post. The RSW series is tuned much higher than SVS subs. That is what gives it the punch and the lack of extension. If you wanted you could try and add some weight to the PR on the RSW to lower it's tuning point, but that's dangerous since you don't know how much is on it and how much it can handle. Quote Link to comment Share on other sites More sharing options...
m00n Posted March 3, 2003 Author Share Posted March 3, 2003 A passive radiator is a driver right? If so, what is the difference betten a regular driver and a passive radiator? Sorry if this is explained in your links, I have not had a chance to read them yet. Quote Link to comment Share on other sites More sharing options...
jstanton8 Posted March 3, 2003 Share Posted March 3, 2003 The passive radiator has no driver/motor. In essence it is "powered" by the driver in the sub (the one with the motor/magnet/wires & stuff)...that's why it's called a "passive" radiator. It simply replaces a port or vent... Quote Link to comment Share on other sites More sharing options...
dblue Posted March 3, 2003 Share Posted March 3, 2003 Moon, If you were to take apart your RSW, you would see that the passive radiator is just that...passive. It has no power going to it, and moves with the air flow created by the powered driver. It's like a port, but no air (or very little) actually leaves or enters the cabinet. Think if it as a sort of bellow. Quote Link to comment Share on other sites More sharing options...
dblue Posted March 3, 2003 Share Posted March 3, 2003 Oops, Jstanton and I replied at the same time, looks like he answered before I did. Quote Link to comment Share on other sites More sharing options...
m00n Posted March 3, 2003 Author Share Posted March 3, 2003 So does the passive radiator produce sound? I kinda understand that a port will allow air to flow in and out of an encloser, but what is it about the radiator that achieves the same affect. Looking at it, it looks to me as though it's another speaker without the magnet and all that. Seems to me all it would do is move back and forth with no air coming in or out of the box Quote Link to comment Share on other sites More sharing options...
jstanton8 Posted March 3, 2003 Share Posted March 3, 2003 The way I look at it, it moves air like a driver EXCEPT that it is powered by the air that WOULD'VE been coming out of a vent IF a vent would have been there...that's why it's used instead of a vent/port. Quote Link to comment Share on other sites More sharing options...
formica Posted March 3, 2003 Share Posted March 3, 2003 ---------------- On 3/3/2003 1:03:33 PM m00n wrote: So does the passive radiator produce sound? I kinda understand that a port will allow air to flow in and out of an encloser, but what is it about the radiator that achieves the same affect. Looking at it, it looks to me as though it's another speaker without the magnet and all that. Seems to me all it would do is move back and forth with no air coming in or out of the box ---------------- Actually the speaker, PR and the vent all move air to create sound... so in a way the all act similarly. In a very "summarized" way, the speaker's tuning frequency is defined by it's motor/cone, the PR by it's mass, and the port by it's length. The fact from where the air originates from isn't the defining factor of the performance. It's then up to the designer to try to match and adjust these characteristics to create the desired frequency response curve. Notice I said DESIRED frequency response curve, as many subs which people find "musical" aren't actually flat, but have an increased output in the midbass region. It's the punch people refer too... although not necessarily accurate. I believe (personal opinion here) that a good sub is good for both music or HT. Later... Rob B Quote Link to comment Share on other sites More sharing options...
TheEAR Posted March 3, 2003 Share Posted March 3, 2003 Moon, If you stick a port in the RSW series subs the port will ruin the performance.Since the front "woofer" is not a woofer but a passive radiator(no motor structure,the cone has added weight and this weight "tunes" the PR). Sure you could use the RSW15 woofer in a BIG sonotube or cabinet with vents,providing you can change the amp built in EQ.The performance would improve down low,no doubt about this. But the question is,are you ready to make a GIANT TOILET PAPER roll out of your good looking RSW15? LOL PR's and ports do not like each other.The PR needs to ne sealed with the woofer,as it uses the pressure created by the woofer to move and produce sound.A port would lower the pressure in a BIG way and render the PR almost worthless. To me a well designed sub using PR's can sound as clean as a sealed design.Ported always bring audible air rushing out of ports noise at very high SPL below 20Hz.A few very large ports and with proper flaring can for the most part take care of these shortcomings. Quote Link to comment Share on other sites More sharing options...
m00n Posted March 3, 2003 Author Share Posted March 3, 2003 Well I don't think I would turn my RSW-15 into a TP roll . It was more hypethitical than anything. So, I really do like the punch of the RSW-12 and 15. However, I keep hearing people talk about how much lower the SVS can go. Would adding a single SVS Ultra to my RSW-12 and 15 be a good 3-way? Or even finding a good DIY plan where the sub is tuned down low. Or you even mentioned that they add weight to the passive radiator to tune it right? Can a guy like myself add weight to my PR to tune my RSW-15 down, or is that just asking for trouble? Quote Link to comment Share on other sites More sharing options...
Dustin B Posted March 3, 2003 Share Posted March 3, 2003 That's just asking for trouble. Please read the Stryke PR FAQ. It will answer all your questions. There are some group delay rises associated with a PR. A PR just can't respond as fast as the slug of air in a port (that's right, air doesn't flow through the port, a slug of air vibrates back and forth). If both are well done I doubt you could tell the difference, but part of being well done is getting the tuning frequency low enough that the associated rise in group delay is with inaudible frequencies. Now the Ears beloved Aerial SW12 is underported and will have the port noise problems down low. As long as the air speed stays below 17m/s in a striaght port (like it does in my DIY Tempest) and below ~25m/s with a flared port you won't experience compression and/or port noise. Also remember that PRs have excursion limits and can create problems like port compression when they are asked to travel farther than they can linearly. Quote Link to comment Share on other sites More sharing options...
WMcD Posted March 3, 2003 Share Posted March 3, 2003 If you don't mind me being pedantic: We're talking about the world of bass drivers as direct radiators. 1) Let's start with the driver in free air. It doesn't move much air. This is because when the diaphragm moves forward (looking from the front) it creates a small pressure in front, which is good. However, the back of diaphragm moves back (looking from the rear) to create a small, relative vacuum. The vacuum at the back ruins the pressure at the front because the front pressure runs around the edge of the speaker to fill the vacuum, rather than being radiated. This is most pronounced at low bass frequencies. 1.1) Of course the situation is reversed when the diaphragm moves backwards, looking from the front. Essentially, the diaphragm moves, but it is just pumping air around the side of the driver, rather than creating a high and low pressure in front of the diaphragm in time to the music. 1.2) This is an active radiator. It is called such because the permanent magnet and coil of wire in the voice coil (an electromagnet, like the coil of wire around the nail connected to a battery in grade school science) make up a motor to move the diaphragm. 2) The easiest solution to the pressure and vacuum problem is to enclose the back of the driver in a box. That is called an acoustic suspension. The Heresy works like this, as do the classic AR speakers. The volume of the box creates a spring effect (the acoustic suspension) and thus the resonant frequency of the system increases. However, now the box contains the pressure and vacuum off the back of the driver. It just doesn't get out anywhere. 3) Particularly in the bass frequencies, bigger is better. You want an efficent radiator or pump. So you could do better in a sealed box with a bigger driver. On the other hand, there is all this potential to use the back of the diaphragm as a radiator. 4) The pressure / vacuum issue can be described as the pressure off the front of the diaphragm being "out of phase" with the pressure off the back. So we could use the pressure off the back if, somehow, we could reverse its phase again, to be "in phase". 5) Unfortunately, there is no easy way to take the pressure and vacuum off the back of the diaphragm and reverse its phase at all frequencies. But we would settle for a solution which works at the low bass, where we need a bigger, effective radiator. 6) Happily, there is such a device, called a Helmholtz resonator, a type of filter with a peak. That is made up of a mass and a spring. In the bass reflex, ported design we add the mass of air trapped in a pipe connecting the box to the outside air. We still have the spring of the box. 7) It is counterintuitive that the box still acts as a spring when the port provides some where for the air to escape. None the less it does. It has to drive the mass of air in the pipe. Mass resists being moved. 8) You have to take a fuzzy look at what is going on. The back of diaphragm is pumping air into cabinet, which pressurizes. Then the pressure has to force a mass of air down the pipe. And back and forth. 8.1) My favorite analogy for the system is a paddle board toy. That is the thing with a paddle and a ball (mass) on a rubber band (sping). It doesn't work out too well because the rubber band gets relaxed (non stretched) and is not a spring. None the less, at low amplitudes you can move the paddle up and down at a resonant frequency and the ball (mass of air in the pipe) moves out of phase with the paddle motion. Try it if you can. 8.2) You see what is going on here, at frequency around resonance, the mass is moving out of phase with what is driving it. So we have a resonator which reverses phase. 9) At the risk of over explaining, that means that the ported box can take the energy off the back of the diaphragm, and reverse it back into phase with the front of the diaphragm. So, by magic, we have a second radiator, at low bass frequencies. Two is better than one. The second radiator is the air coming out of the port. 10) The same principle applies to a passive radiator (a big diaphragm which has no electro magnet innards). It is like the mass of air in the port. However, it has a bigger radiating surface. It works well to move air. Again it is a bit counter intuitive. You'd think it would always move in phase with the back of the active radiator, but no. It is again, like the paddle ball mass. 11) The Helmholtz resonators work over a narrow frequency range to give some boost. So you have to make some critical design choices. Obviously you want this narrow reinforcement just at where the bass response of the main speaker is falling off. You can't avoid the roll of of the system, but you can postpone it (in lowering frequency) by giving a boost (from the resonator being in phase) just before everything goes to heck. Gil Quote Link to comment Share on other sites More sharing options...
Dustin B Posted March 3, 2003 Share Posted March 3, 2003 Excellent post William. One of the best simple explanations of what's going on I've every read. Doubly so on the simple part since I get the feeling from your post that your knowledge level goes way over mine. Quote Link to comment Share on other sites More sharing options...
j-malotky Posted March 4, 2003 Share Posted March 4, 2003 Holy crap Gill. What a great post. That will get good old Moon thinking. I have a close friend who use to be an engineer at a reputable compeitors speaker company (won't mention names, but is is not BOSE). Anyhow, he has a bunch of one of a kind speakers at his home from the lab that never made it to production, or were "fixed" versions of production speakers. He tried once to explain to me how the porting design process worked.... Tried is the key word here. VERY COMPLICATED. Good luck in your Subwoofer discovery and quest Moon. JM Quote Link to comment Share on other sites More sharing options...
m00n Posted March 4, 2003 Author Share Posted March 4, 2003 ---------------- On 3/4/2003 12:31:31 AM j-malotky wrote: Holy crap Gill. What a great post. That will get good old Moon thinking. Good luck in your Subwoofer discovery and quest Moon. JM ---------------- Tell me about it. I read it about an hour ago and I am still thinking about it I really want to do a DIY sonatube sub. But I just don't know enough yet. Like what kind of driver is good for what kind of sub, what size the tube would need to be, etc.... I want something that can pick up where the RSW-12 and 15 leave off yet I want a very smooth transition. Oh and Gil... Yes, thank you for taking the time to reply with that in debth description. Admittadly most of it went over my head. But I think that is mostly because I was having a hard time visualizing what you were talking about. I will read it a few more times and I am sure it will sink in. Quote Link to comment Share on other sites More sharing options...
Dustin B Posted March 4, 2003 Share Posted March 4, 2003 You could also sell your two RSW subs and build a pair of sealed Tumults with Linkwitz Transform circuits, a nice EQ and a QSC PLX3402. With an appropriate LT circuit you can have extension to below 20hz and with the XBL^2 motors and a sealed allignment the sound will be amazing. Highly doubt you'd miss either RSW with those. And if you wanted more bass, just go to a less powerful amp, forget the LT circuit and buy 4 of Styrke's dual spider 18" passive radiators. Enclosures will need to be a little bigger, but a pair of Tumults in an appropriate passive radiator allignment will be scary. Quote Link to comment Share on other sites More sharing options...
formica Posted March 4, 2003 Share Posted March 4, 2003 Nice post Gil... reminds me of Physics 101... m00n, I think the key to understanding the port/PassiveRadiator is the flipping of the phase as Gil put it... ---------------- My favorite analogy for the system is a paddle board toy... at low amplitudes you can move the paddle up and down at a resonant frequency and the ball (mass of air in the pipe) moves out of phase with the paddle motion. Try it if you can. ---------------- So the energy of the port is added to the one produced by the woofer. Quote Link to comment Share on other sites More sharing options...
m00n Posted March 4, 2003 Author Share Posted March 4, 2003 ---------------- On 3/4/2003 8:42:40 AM Dustin B wrote: You could also sell your two RSW subs and build a pair of sealed Tumults with Linkwitz Transform circuits, a nice EQ and a QSC PLX3402. With an appropriate LT circuit you can have extension to below 20hz and with the XBL^2 motors and a sealed allignment the sound will be amazing. Highly doubt you'd miss either RSW with those. And if you wanted more bass, just go to a less powerful amp, forget the LT circuit and buy 4 of Styrke's dual spider 18" passive radiators. Enclosures will need to be a little bigger, but a pair of Tumults in an appropriate passive radiator allignment will be scary. ---------------- The Tumults, is that a brand or style of speaker. I did a search on google and at PartsExpress and didn't find anything. Quote Link to comment Share on other sites More sharing options...
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