Exploring high performance ferrite driver options

[Seth]

...I would be happy to be proven wrong I just thought I would share my theory as to why the response is so different...

I think you may be right about the rear chamber, or at least on the right path. Ultimately, it's half the rear chamber and half the horn area. Which, if you model an 18½" cab, would be the the result. Something else to take into consideration when looking at the resultant curve of a dual loaded cab is, unless you adjust the voltage to compensate, we're also comparing one cabs response at 1 watt to another cab at 2 Watts, which positively skews the dual loaded cab by 3dB cross the board. If you adjust the voltage, you'll see portions of the dual loaded cab that are actually less sensitive at one watt than that of the single loaded cab.

I'd personally prefer to compare multiples of single loaded cabs, which is the way most of us use them. 1, 2, 4...

That said, it seems to be one of those things that's like trying to not look at a naked lady or an automobile accident on the highway.

You got that right that is exactly what's going on here. In mind it seems that replacing the driver with a higher performer is the best way to get more out of 1 box. We are very lucky that there are drivers coming out like the prv 15sw2000 and SB audience rosso 15sw800 for under 250$, especially considering that the 4015lf seems to be discontinued. At least it's not available from any of the usual retailers.

I will say the 24 inch wide box is pretty much the perfect size for a sub. With the kappalites they are about as loud as a single 18 reflex and weigh a tad bit more, and they are about the size of a compact double 18. But then you get all this fun horn physics. By the time you have 4 boxes it gets funky pretty quick. Now with the prv driver it seems the t48s maximum output becomes more comparable to double 18 reflex. Bring 4 of those, a v plate and shove it into a wall or corner and now you're cooking. This would award you pretty much as much spl as one could possibly want or need for most applications, dubstep included. And you would achieve this with less than 500 lbs of sub, taking up merely a 4x4x4 cube with a piece of wood on top. It's brilliant. It's like playing with transformers but they're really fking loud

I wish I had the firsthand experience with the T48 that you have. However, I can agree with your comparisons on peak output based on the numbers alone. The numbers agree. I'll add that it's absolutely ridiculous how little power the T48's require compared to the reflex cabs to make the same noise. T48's have roughly the same peak outputs you mentioned... but they have way better sound quality, are way more cost effective, and do it on way less amplifier.

I don't know if you have any experience mixing live music and adjusting monitor levels for performers. Sometimes, a performer will ask for something specific in their monitor and while I'm rowing my way through the different screens on my control device to get to their screen they're saying "more, more, more, more, more..." and then "perfect!" before I have even made a single change or adjustment. Another similar situation is on me, where I was adjusting the reverb on a vocal track, little by little, until it was absolutely perfect... then realizing I wasn't even making the adjustments on the main mix and I heard a change that wasn't even possible to hear.

The reason I mention it is, it's highly likely that you heard what you wanted to hear with the PRV driver. I hope the measured results uphold and indicate the same trend the model indicates and also what you experienced. However, I wouldn't be shocked if the measured results aren't as impressive as we hope they will be. Still, my fingers are crossed.

[Rich4349]

Let's not forget, though, that there's no free lunch. The 15SW2000 DOES use / need 1,000 watts to get there. Ok, it might not need all of it, since we work in volts and will be voltage limited.

Seth... lol... what would the wattage max be at its voltage limit of 85v?

[Wylandright206]

While a thousand watts might seem like a lot, and it is, compared to a high end double 18 it's really not that much. And there's nothing stopping you from using a smaller amp. The prv has nearly 3mm additional xmax over the kappalite. This means you could limit at 60v just like the t48 but drop your crossover just a little bit lower. And its cheaper, that is the main point of all this. It's cheaper than any of the recommended high performance drivers. Just because it's rated at 1000w doesn't mean you have to give it such. It means you now have much more thermal and mechanical headroom than you did before. And the power would be there if you decided you wanted it. Testing will be the definitive answer about the frequency response of this driver in this specific box. Even if it tracks exactly the same as the kappalites, as I mentioned earlier the driver just has more VD and more power handling to take advantage of it. I call that a win. I'm a cheapo I want to get the most out of the cheapest drivers. That's a huge appeal of this group to me. Unfortunately the eminence components like the s2012 are no longer as good of a deal as they used to be, going from 104$ to 144$, but a lot of other manufacturers like SB audience, prv, and lavoce, are offering more competitive hardware at the moment. I know a lot of these high end speakers use cheap parts. My favorite bookshelf speakers use 15$ Dayton woofers. I have faith we can maintain high performance at a good price even if the ideal drivers are a little bit pricier now.

[Seth]

Let's not forget, though, that there's no free lunch. The 15SW2000-4 DOES use / need 1,000 watts to get there. Ok, it might not need all of it, since we work in volts and will be voltage limited.

Seth... lol... what would the wattage max be at its voltage limit of 85v?

I'm pretty sure we're talking about the 15SW2000 and not the 15SW2000-4, 4Ω variant. At least, I hope so. 85V at 8Ω is just over 900W. However, I think Wyland mentioned the PRV driver is actually modeling as displacement limited at 78V which equates to 760W nominal

The 36" 3015LF T48 "get's there" with 450/60V. At 40Hz, it will match an old school, but still a staple in the industry JBL SRX728 running on about 1800W. One for one. A single 15 on 450 vs dual 18's on 1800. Now, once we add a second T48 and are able to reap the benefits of a V-plate, the story changes dramatically. It would take 3 dual 18's on combined 4800 watts to match 2 V-plated single 15 loaded 36" T48's on a combined 900 watts. Six 18's on almost 5kW to match a measly two 15's on only 900W.

If the PRV in a 24" cab did in fact match the 36" 3015LF in sensitivity at 40Hz, it would also do all the above on 450W/60V per cab, not 1000. That said, I'm crossing my fingers, but not holding my breath about the PRV actually producing such dramatic results. If it shows to have a 2dB advantage at 40Hz over the 3015LF, a 24" T48 would take about 900W/85V (already beyond the displacement limit) to match the 3015LF 36" T48. If there's no low end sensitivity advantage over the 3015LF and no notable loss, then it is simply a good driver option at a good price.

[Wylandright206]

HornResp models aren't 100% accurate, as there are factors that it doesn't take into consideration. Predicted peaks and valleys are never as high or deep as the model predicts. Also, the modeled results shown here are off a bit. My model shows the PRV 2dB more sensitive at 38Hz, above that they're essentially the same.Below 38Hz it's 2dB lower in sensitivity. You won't get 36 inch wide results from a 24 inch wide box.

So actually, something I noticed with the hornresp sim is for some reason the program is forcing "lossy LE" on every time you import or input the prv driver. The lossy LE feature is supposed to roughly approximate the effect of high inductance OR a heavy moving mass on the response of the driver because some excessively heavy cones and or coils exhibit similar behavior despite having manageable inductance. Now the LE on the 8 ohm version of the driver that I've been simming is well within reasonable bounds for a driver with a DCR of 5.5ohms, and the moving mass is like 160grams. I have no idea why hornresp is forcing this setting by default but it is not accurate. If it was accurate this driver would perform almost exactly the same as the kappalite aside from around 38hz and below like bill said, so I see how it would be confusing. Seems like a bug worth reporting to mr Mcbean. I know for a fact that these two drivers don't sound the same I could hear it it was like night and day. I know I sound like a broken record but I spend way too much time with these subs and the new driver is different. Lossy LE does not apply here and for accurate simulations of the 8 ohm version of the 15sw2000 make sure to turn it off as it is forced by default. You can turn it off by double clicking on LE on the input menu or from the schematic menu in the loudspeaker wizard. I spent many nights confused about this and I've determined it is a very unhelpful bug. It also does the same thing to the SB audience rosso15sw800 and that driver sims much more similar to the prv with that setting off. These aren't car subs they're 15 inch pro audio woofers with light cones fiberglass coils and good inductance.

[Wylandright206]

I would also like to shine a light on this driver which is suffering from the same glitch as well. The SB audience rosso15sw800 has an MMS of 143.6 grams, an RE of 5.2 ohms and an LE of 1.18. It does not make sense to model these types of losses on a driver like this. The 800 watt Rosso driver without the glitch seems to perform pretty spot on to the prv if not even slightly better in the region of 42hz to 60hz, although costing 40$ more and being limited earlier by xmax. These two drivers look great and don't cost an arm and a leg. The prv is a better deal though which is why I decided to go that route. But I know the Rosso is also suited for horn loading because some popular bass horns are already loaded with the 18 inch version in the family. There is also a 500 watt version of the Rosso that is around the same price as the prv, which also suffers from the same glitch in hornresp that makes it sim pretty much spot on to the kappalite, but again without the glitch it sims pretty similarly to it's bigger brother and the prv.

[Wylandright206]

So I have returned after some repairs and some quick shop measurements. Bear in mind these were taken from 6 inches away from the mouth of the horn, groundplane, so they arent the most perfect measurements, but I laid tape on the ground, the mic was not moved, and all that was done is the cabinets were swapped. Same cable same amp same amplifier output voltage. These are far from any sort of spl calibrated so please ignore the spl here, it is merely for reference and scale. I have found that my simulations agree well with the measured results, even down to the cancellation caused by the offset of the driver in the throat. The benefit the kappalite had over the 15sw2000 at 60-70hz in simulations is much less pronounced in reality and the 15sw offers a smoother frequency response overall, down to around 33hz. -10 db from peak is around 55hz with the kappalite and below 35hz with the prv. This combined with higher xmax, and lower crossover points makes for more enjoyable listening with less cabinets and less eq. It may not be like a widebody t48, but it is in general louder than the 24" 3015lf t48 based on sensitivity alone from 33hz to 100hz. Once you factor in higher volume displacement and power handling, it has potential for a fair bit more energy at 35-45hz than the lightweight driver option. I have a suspicion that after applying filters the benefit below 33hz the kappalite has is diminished, but only tests would tell.

Do with this information as you please but we are very happy with ours and plan to load all future BB cabinets with them. The weight isnt really that bad, the additional horsepower it offers is well worth it in my eyes. If you wanted to use a more compact rig for dnb you could comfortably transport a pair of prv loaded titans with a vplate, and 2-4kw of amp in a pickup, and still achieve the meat and potatoes you want, at the volume you want it, albeit at the cost of power and increased throat distortion, which was not particularly noticible to us even while we blew the driver up with sine waves in the horn from 3 feet away, but that wasn't really a definitive test. That just told us that we could literally deep fry the voice coil and the suspension would be fine with a single cabinet crossed at 36hz.

And again, my measurement technique isn't perfect here, my shop is crowded, we've got 10 full range horns and 11 subs and 11 raw drivers as well as all sorts of power tools and tables sharing the space. This is why I applied a frequency dependant window and placed the mic in such close proximity.

I hope that if someone like me is reading this and wants to save a couple bucks on drivers but also doesn't want to skimp on low end, this gives them the info they need to try this driver, or even try experimenting with their own. Seems like every week manufacturers are dropping new high performance drivers. And class d is getting denser and denser.... All this Chinese gan-fet stuff coming out lately is pretty wild and AFFORDABLE. And their customer service actually responds to your messages (cough cough peavey)

[Seth]

I'm definitely liking what I see there
If I were building T48's, I'm thinking I would more than likely go the PRV route.

[Wylandright206]

So I have taken these exact same measurements, and applied a 40hz 24db BW HPF to the kappalite, and a 36hz 24db BW HPF to the PRV, as well as an 80hz 30db LPF to both. The low frequency delta between these two drivers in this enclosure is actually pretty staggering. No wonder I could hear such a massive difference XD much less eq required. Even just a single peak filter would have this sounding close to its best outside.

[Wylandright206]

here are all 4 plots on the same graph

[Wylandright206]

if you changed all those filters to 48db the gap widens dramatically

[Bill Fitzmaurice]

If you want to have insight into what's going on do some simulations making changes to the rear chamber volume. With the 3015LF making it smaller will give a curve closer to the PRV. With the PRV making it larger will give a curve closer to the 3015LF. Tweaks to the rear chamber size may be done with any driver to get a desired result. Smaller for higher sensitivity at the low end of the pass band, at the cost of extension. Larger for lower extension, at the cost of sensitivity. There are changes in excursion as well. The larger the chamber the longer the excursion, which means the lower the voltage limit. There's no such thing as a free lunch.

[Wylandright206]

I'll have to mess around with the chamber size. I figured it had to do with the qts of the prv being higher and the VAS being lower than the 3015lf. I was skeptical as a qts of 0.55 is a bit out of recommended spec but I was pleasantly surprised. Despite being aimed at the car audio market these are surprisingly stout. I was reading somewhere that PRV was founded by JBL Selenium alumni, so maybe they were off to a good start.

I've noticed that the 3015lf has a very fragile surround and that seems to be the thing I'm not infrequently popping holes in with the music we play (I accept responsibility for that I am very hard on my horns) . Granted it needs to be lightweight, it's definitely a fragile part. The stout soft parts of the prv and the extra xmax basically eliminated popping holes in the surround the way we use them. They're just totally different tools for different jobs. The kappalites are the lightest woofer of its kind I'm aware of so if your goal is one man team maybe radiata pine and 3015lf is the target. We have 8 boxes configured like this and they are comically lightweight. If you don't mind weight and want something stout for an install, dubstep, bass music, whatever have you, Baltic birch with the PRV will eat whatever you throw at it. And if you want high performance at the lowest price possible, radiata pine with PRV makes sense. Although the prv needs mounting blocks, with the pine maybe it might be a good idea to use some sort of hardwood for the mounting blocks? We have trouble with T-nuts slipping with our pine enclosures.

[Bill Fitzmaurice]

I stopped using T-nuts many years ago. Screws don't back out, or strip.

[Wylandright206]

Do you have screws in particular that stand out to you for mounting heavy subwoofers? We mounted the new lavoce drivers in our otops like that and its sturdy. But that's a 12lbs woofer.