DrWho

Chris, what are the dimensions of your the 15" ports into the horn? I think somewhere you mentioned a 10:1 compression ratio? I've been going through your hornresp data and think I found a few bugs. For the 15" woofer section, you have the VTC chamber values set to 0. This turns off the effects of the throat port (Ap1 and Lp), which you have set to 46.2 and 10.5.....which is actually a relatively long narrow throat opening. You also are modelling 4 drivers in parallel, but I think you mentioned only using two 15" drivers (The ME1 value should be 2P, not 4P). And is the free volume of air between the K402 and your enclosure really 8cubic feet? I would expect to see a rear chamber volume closer to 5cu ft (144L) I think you should be using the following values: ME1 = 2P Vrc = 144 Vtc = 4500 Atc = 590 (average length of 7.63cm to the port) Ap1 = 178 Lp = 2.20 (3/4" + 1/8") Do these values correlate to what you built? Also, is the first conical length of 10.16cm going to the center of the port opening, or to the edge closest to the throat? Pictures of horns always create optical illusions so it's hard to tell from a picture. Is the K402 really only 18" long? The reason I'm digging into the details is to try and understand why the measured response is so drastically different from the predicted response. Or to look at it another way, I'd like to understand why the predicted and and measured results are so different. I've gotten much closer with these adjustments, and along the way I noticed some crazy coupling effects between the LF and HF units. Have you noticed that the Power2 result changes when adjusting the amplifier power sent to Driver 1? You have to crank the voltage on Amplifier 2 and cut the voltage on Amplifier 1 to simulate driving only a single driver - and then the results look very similar to what you're measuring. Likewise, you can raise the output impedance of Amplifier 1 and look at Displacement 1 to get an idea of how much the woofer section moves the tweeter diaphragm. Attached are pictures showing what I'm simulating. It's pretty close to your measurements except for the behavior below 300Hz. I think that's because the aperture of the horn doesn't meet the assumptions hornresp is using in its model....I've frequently seen the bottom octave in hornresp not line up to the real world. This seems consistent with what I've seen in the past. And I think your extra output right around 300Hz is due to the directivity of the horn.

Impulse response and frequency response are the same thing....especially when talking about devices like amplifiers. Any "hall of mirrors" effect is happening at the speed of light, and the distances here are very short. There is no way I the world that the "propagation delay" of the electrical energy is an audible facet here. We design circuits all the time where that matters, so it's not like we don't know how to deal with it. The magnitude of the effect is way smaller than the random vibrations of the molecules in your circuits. There is the whole TIM subject, which could be thought of as a "slow feedback" circuit, but that doesn't behave like "reflections" - which is what I think is implied by the mirror analogy. TIM is more like someone trying to keep their head still while balancing on one leg on a chair sitting on a ball. If the ball moves too quickly, then their head is going to move slightly to maintain balance....even if the ball is moved just as quickly back to its starting location. The head movement is the distortion added to the output. There's probably a million things wrong with the analogy so don't take it too far, but it has very little to do with how quickly the ball position gets transmitted through the chair and person's leg. It has to do with how far/fast the person's body can react to the stimulus. An older slower person's head will move further than a young fast kid.

Perhaps, but there are circuit components that change behavior with temperature. Music isn't a constant level signal, so the dynamic bits in music can be affected by thermal hysteresis. There can be other time domain factors too, like temporary bias shifts on AC coupled stages. Sure, on average over a long time they settle down, but music isn't necessarily symmetric for short periods of time. Speaking in generalities, feedback systems are not immune to these behaviors, but to discuss them in detail would require a very specific analysis of each circuit topology independently. All I'm trying to say is that "time smear" could very likely be referring to something real. Due to the complex technical nature of the subject, I wouldn't be surprised if an audiophile attributed sonic artifacts to the wrong thing.

Doesn't the Race software provide the ability to save/recall settings from a file? It's been a while since I've opened the Race software...

Distance adds propagation delay, which in turn affects the phase coherency between the port and driver. If you're too far away, then you can actually get a small dip in response just above the tuning frequency. Hornresp actually has a method for calculating this effect. I suppose directly behind the driver motivates higher frequencies to fire straight through the port. Making the ports smaller is beneficial in this regard. You also want to avoid the internal port mouth to be sitting in the middle of an internal standing wave (since this will couple that resonance out of the box). I'd argue there should be damping material inside the cabinet anyway. I've been using the cheap $20 polyfill pillows from walmart with great success. You can easily see it clean up the frequency response, and the pillow casing makes it easy to mount it in the right location. Just knock some staples through the system.

How many cycles do you have it set to? The default 15? That would explain why the plot looks weird to me - this is the first time I've seen this, but it's totally something I've wanted for a while. I've been manually doing this for a long time now. So cool. http://www.hometheatershack.com/forums/rew-forum/99673-feature-request-frequency-dependent-windowing.html Btw, have you made any xover plots? (Three plots total showing the individual response of each driver and the summed response together). I'm analyzing your data more closely and I'm noticing a "dip/spike" right around 500Hz'ish. I've seen this a lot when the delays aren't perfectly matched. What was your method for measuring the delay? Were you using the results calculated by REW? Or maybe it's a dip that wasn't corrected in the LF system? You can see the phase response bumps a bit there too.

Btw, what is "psy octave smoothing"? It looks like I'm on a really old version of REW....

Oh my, I wasn't thinking of putting the ports in the horn. I was thinking they could go in the side of the cabinet surrounding the horn. It'd be pretty easy to plug any holes you made, or you could just rebuild the entire enclosure for way cheaper than buying a new K402. Do you think there is an advantage to putting the ports in the horn? I would expect the acoustic loading of the K402 to be nearly negligible below ~60Hz or so (for the same reason the driver excursion unloads so quickly). And for the same air velocity reasons, I'm not sure we want that much port chuffing in the horn? (The port would be much worse than the driver itself). Btw, have you seen this thread on a cardoid 15" driver solution? http://www.avsforum.com/forum/155-diy-speakers-subs/1764913-forward-radiation-sickness-big-waveguide-cardioid.html There's a camp that doesn't like this approach because you're throwing energy away to accomplish the directivity, but I wonder if the port couldn't be tuned (flared) in such a way as to have more control over the cardoid pattern. I think it'd be interesting to extend polar control below the horn cutoff. I believe EAW is doing this in their Anya cabinets - and it's really as "simple" as putting a hole somewhere in the side/rear of the cabinet. The hard part is knowing how to design those holes. I guess I'm just intrigued by the possibility of a full range system with "perfectly" controlled polar response....and you're showing potential here of doing that with a simple 2-way speaker. I've been looking for a better speaker setup for the sanctuary at my church and this strikes me as a potentially very cost effective solution. I haven't moved forward on it because the size/weight of the matching bass bin has been prohibitive.

This is venturing outside the realm of what I've played with, but I had a few thoughts on the phase plug: 1) The volume inside the "pyramid" created by the shape of the driver diaphragm reacts with the "port" of the throat opening to create a low pass filter. The bigger the volume and the smaller the hole, the lower in frequency the low pass occurs. You can see this in the hornresp model by adjusting VTC. You'll note the high frequency corner moves around. Start with an arbitrarily high VTC and you'll notice an early HF rolloff. As you decrease VTC, the HF rolloff happens higher and higher. Sometimes you you can get to a point where you hit the peak corner, and then it starts going down again. With the offset horns, you'll have a secondary reflection off the throat messing with the total phase seen at the port opening - I've always wondered if a "tapped horn" approach would be an effective solution to extend the HF bandwidth a bit further: Try to balance the reactance of the throat chamber to the "reactance" of the reflection. I wonder if Danley hasn't alluded to that in the past. 2) Roy talks about extending the horn through the phase plug. I'm not sure how much another 2" or so matters from the perspective of the bandwidth you're using, but with an offset throat you will have some phase misalignment between the two ends of the driver. (not talking about the offset from the throat of the K402, but the offset inside the "VTC" where one end of the driver is closer to the throat than the other side). Adding a ridge inside the throat to extend the path length of the close end of the driver will improve the phase coherency. There will always be some pathlength differences, so again this is about extending the HF bandwidth and its importance is relative to the bandwidth you need from each portion of the system. 3) At higher SPLs (although I think it applies to some extent at all SPLs), you're going to get more "port chuffing" due to the sharp transitions happening at the throat opening. Smoothing those out like a flared port will improve the laminar flow, and ultimately reduce distortion. You can see the woofer excursion increase quite a bit as you get below 60Hz, and the air velocity is going to follow a similar shape. One unfortunate thing about the synergy horn approach is that this air turbulence shares the same air that the HF information is travelling through. The air nonlinearity is definitely an exponential effect (so it gets exponentially less important as the SPL goes down). One of these days I'd like to get around to measuring the significance of this. I know it happens, I just don't know how bad it is. I know I've heard the effect when placing a classic port near a tweeter - it sounds very much like FMD, or adding a tremolo to the higher frequencies. Move the port away and the problem goes away. Along the lines of 3, have you considered porting the LF driver to reduce its low frequency excursion requirements? It sounds like the horn portion has all that freedom with the rear volume, so maybe you could add some port holes and reduce the LF excursion - you could even target the same bandwidth. With a properly sized port, you can add a lot of EQ without increasing driver excursion - and a good port can be made to be fairly linear too. Anyways, just thinking out loud since it seems you're interested in more experimentation. Ok, one more thought since you brought up the other direct radiating bass bins from Klipsch. I've done a ton of measurements of all sorts of box shapes and sizes and I always run into standing waves happening inside the box. I've also run into reflected energy inside the cabinet bouncing its way out through the port openings. With every design, adding a carefully placed pillow or two has dramatically improved the sound of every ported cabinet I've played with. Even with a sealed cabinet I've seen improvements, and I think that is due to energy leaking through the diaphragm of the driver. Although the sound is naturally attenuated a lot by the driver, you still see it show up in the measurements. I didn't start correlating this behavior until I started doing anechoic measurements. The room totally swamps the frequency response accuracy, but I don't think all frequency response aberrations have equal audibility. In other words, room acoustics induced dips/peaks sound different than internal cabinet resonances / reflections...and the latter is more annoying in my opinion. Btw, I'm not familiar with the SynTripP design. I see on Page 138 he's using a wooden phase plug: http://www.diyaudio.com/forums/multi-way/264485-syntripp-2-way-2-part-virtual-single-point-source-horn-14.html#post4523799 That's not quite what I had in mind for your application, but then I don't know all your dimensions either.

Very cool Chris. Will you be doing any experiments with phase plugs?

For the port, you could make a circular disc with the port in the middle and then install the whole assembly into the same place as the original passive radiators. This would give you a fully reversible mod should you ever find passives for sale in the future...

Could possibly be a software issue.....I've seen some sound card drivers that will automatically detect the program and apply an equalizer to the system. I prefer to turn off all that nonsense. Game modes, music modes, skype modes, etc... As far as your bandwidth concerns, reduced bandwidth will generally reduce HF extension. It should not affect the lower frequencies at all (unless it's a really bad codec). I've streamed Pandora over my phone in the car for a long time - the lower bandwidth modes of their codec never caused a tonal shift in the music. It just gets more mp3'ish sounding.

What I'm curious about is how much latency the system has and what levers Klipsch has provided to mitigate that.

Dennis has a point.... That distortion info from AE is showing amplitude modulation distortion. Frequency modulation distortion doesn't create harmonics - it changes the actual pitch of the music based on how fast the diaphragm is moving. Amplitude distortions can create frequency modulation effects, but at some point the size of the diaphragm and the bandwidth it's covering will dominate.....and there's nothing more you can do at that point unless you add more drivers, or hornload the system. Even then, you will have a finite amount of frequency modulation distortion - so really the bigger question is how much is too much?

Never had the big truck nor any use for one. As to car audio, no interest. They can sound very, very good...but I have a listening room for that. I'd be safer driving drunk than listening to the stuff I love on a top notch car system. Talk about intoxicating and absolutely demanding one's total focus...that's what music does to me. Therefore, I'd need a designated driver if I had a first class car system. Actually, one of our vehicles has a Fosgate system with sub that just happened to be in a used vehicle I caught a good deal on. However, I listen to NPR pretty much exclusively for the reasons stated above. Dave Just to clarify, I wasn't talk about car audio.....I was talking about the relatively smaller cars I've used for hauling bigger speakers around. My version of car audio is the sound of the engine and wheels. I never have music in the car....unless I have passengers and then it's just a social expectation at that point.

Mike I'm gonna ask a question that's a little off-topic, but I'm interested in what you mean by this. Could you have listen to some of the videos on my channel (through headphones of course) and tell me if you hear any of what you describe? https://www.youtube.com/user/TerdFurg3zon I'm talking about if one made a properly sized bass horn....it'd be huge and long and deep. It literally would look like a cavern. All of the Klipsch stuff is designed to couple to the room's corner so the mouth's are small and a small percentage of the room. They also aren't really "subwoofers". Everything would grow 4x to be a proper sub, and that's when it would matter. So no, I don't hear it on your Youtube channel. I do hear your room modes and some flutter echo from parallel surfaces though Not to psych you out though because your recordings sound quite good as far as most room recordings I've heard. Were those mono recordings through a measurement mic?

I ended up going with the K48 over the TD15M after conducting a week of side by side comparisons in a cabinet similar to a Cornwall. Hurd was there the entire time too - it actually surprised us a ton because we were going to purchase a ton of those drivers for our setups. These were older versions of the TD15M (like so far back it was a different company name) and I think the problem was related to a known issue with the suspensions - the suppliers could never get it right. I think all of that has been remedied now so I'd like to give it another try sometime using the modern stuff. B&C makes some really good drivers too. I've only played with their 12" drivers, but I think they have 15" versions that'd work for horn loading. I forget the model number, but Eminence makes a driver similar to the K48 too....is it Kappa Pro 15LF? Or something like that. Although for horn loading you'll probably want something else. Speaking of which, I've always felt that the K33 was designed for the Khorn/Lascala and just happens to work well enough in a Cornwall....but really a Cornwall design is going to benefit from a driver optimized for a vented cabinet of that size. So really it's gonna be very application specific. Heck, even for Lascala versus Khorn - one might argue that it'd be worth the minor efficiency gains to go with a driver that doesn't dig as low.

Duhhh...did you see the size of my sub? Dave You Texans and all your big trucks....do you ever put them to use? P I've carried more system in my old FRS (a small sports car), and certainly more in my Subaru wagons over the years. Hurd came down one year from Canada with a sub that required removing the car doors to get in and out. Now that's dedication, haha.

They also indicate that as of present, there haven't been enough production horns tested. I'd like to see genuine representation from JBL, EAW, EV, Martin, Funktion-One, Klipsch, and Danley's DBH 218 on that list. Too much DIY. That's totally a fair point, but some of these other subs have been measured in other places...some even provided by the manufacturers. It doesn't take too much work to derive an apples to apples comparison most of the time (sure there are always caveats to that). I just find it interesting that the pro audio world is almost entirely direct radiating for the subwoofer portion of the systems. And the better line arrays look less and less like multiple horns too - and more like multiple direct radiators. I just wanted to point out that modern direct radiator design has come a long way. Granted, doppler distortion is a fixed entity for a given bandwidth and driver size - but it's not like this distortion magically goes away on a horn. It's just simply reduced by a lot. You can get that back by adding multiples. Speaking of multiples....I totally hear the arguments about price and limited wall power, etc... Most of these subwoofer shootouts are obsessed about SPL capability, and they pick a lot of source material that rumbles your butt. I totally get the fun of that, and even play around with that on occasion, but for me it's more about sound quality. Just because your drivers can dissipate a crap ton of heat doesn't mean you need to use the fully capability of the system. I bring that up to emphasize that multiple driver solutions are all about improving the sound quality. The room modes are just an incredibly dominant acoustic effect and no amount of "better subwoofer" will ever overcome that. We need subwoofer solutions that are immune to room modes - and to my knowledge there is only one such approach. Ironically it's the least implemented. The problem with talking about generalities is that not everyone enters with the same assumptions. This is why I like to focus on what would be the best of every world and use that in the comparison. Ultimately I'd posit that the best of the multiple direct radiator will outperform the best of the multiple horn setup. This is because horns of that size are part of the acoustic sound of the room - so now you've got all these caverns for the higher frequencies to bounce around in and make it sound like you're listening in a cave. But since we're kicking around the crazy ideas....one thing I'd like to try is a bifurcated tapped horn with mouth exits at the ideal locations for a dual zoned bass array. This reduces the number of drivers you need, and the mouths are small so high frequency cavernous effects don't happen. The hard part is keeping the recipe of what makes the Othorn measure so different from all other tapped horns.

What is the primary function of the room? Mostly movies?

What's this horn loaded sub you speak of Dave?

Ouch! That's a real bummer.

They didn't have Klippel back in the day when PWK put together that article....modern drivers are much more linear over a wider excursion range than they used to be. Much of PWK's measured results were demonstrating the lack of motor linearity in the older drivers. That's different than just straight up doppler distortion. The ironic thing is that fixing the driver linearity doesn't benefit the horn much because the horn itself starts limiting performance at the higher SPL's, and you don't notice any difference at the lower levels where everything is already linear...

Impulse response is generally better with the direct radiating systems - especially sealed cabinets. This is because the frequency response is flatter (freuqency response and impulse response are really two views of the same thing). With enough radiating surface area you can achieve the same (or better) modulation distortion with a direct radiator. It's really hard to get a horn to have the same transparency at low levels (with all the folds and reflections and resonances along the way). I'd suggest the hardest part about low frequency performance in a small room is the room acoustics. The dual zoned bass array is not only the best performing solution to that problem, but it's also the least invasive. Acoustic treatment takes up way more space and costs a lot more. What you're gaining with direct radiating drivers is that the cabinet can be way smaller for the same low frequency extension. Sure, you gotta throw some power at it, but amplifier power is cheap and is not a directly audible parameter. You need several acoustic sources to achieve the results of a dual zoned bass array anyway. It's simply easier to accomplish with several smaller cabinets. No way I'm going to fit 8 bass horns in one small room - let alone have the flexibility to place them in the ideal location. Small cabinets are easy to place properly, and then there's the benefit of each one increasing the total radiating area. Eight 15" drivers is equivalent to a single 15" horn with an 8:1 compression ratio....and that 8:1 compression ratio horn is gonna need to be really long to reach down to 20Hz. The numbers over at data-bass.com indicate that the direct radiating systems can certainly keep up with the horns....especially if you keep the total solution size as the constant variable.

Anyone ever take any measurements of adding foam inside the horn? I'd be really surprised if it affected the polar response - especially at lower frequencies. There's a lot of talk about how the wavefront in an exponential isn't actually planar, so in reality we get reflections due to the curvature of the wavefront - especially at higher frequencies. I wonder if the foam is helping attenuate some of that craziness? Looks like a simple low cost mod. I've done similar experiments with folded bass horns in the past to help clean up some of the standing waves at higher frequencies. I wonder what would happen if you did a similar thing to the khorn bass bin? Would that tighten things up there too? It wouldn't be very PWK like though because it would ultimately be reducing efficiency a bit...