Fi Q15 + AEspeakers 18" Passive Radiator / 3.3cf

[PaulNeves 0]

New Fi Q15 owner here. Fresh to these forums too. I just wanted to share about my project and also had a few questions and was hoping for some feedback/opinions.

Recently got my hands on BB6 pro and built a pretty bitchin' (and simple) PR setup for my buddy's Saturn ION that piqued my interest to try it again, but bigger and with more power. I used a Resonant Engineering SEx10 paired up with a TC sounds VMP12 (stock 390g mms) in a prefab 1.8cf sealed 15" box. Made a speaker ring adapter for the 12 in the 15" hole, and then cut a hole in the side of the box for the 10". We were very pleased with the amount of LF output this little bad boy has, and still being super clean all the while. He put down 136db peak at 47hz on 525w with one of the rear seats folded down, and 1 window down.

Before doing all this PR business, I had already placed an order with Fi Audio for a Q15 optimized for vented enclosures (dual 2, low QTS, cooling option, and spider pack) that I had planned to stick in my current 3cf slot ported (17x28x2.5" port) -- which I did. It sounds great in my 2000 Toyota Tacoma Ext cab which I calculate cabin gain starting at about 95hz. I hit 141.7db at 45hz with 1 door open. 1.7kw RMS was metered during the SPL burp. Amp is Rockford Fosgate T1500-1bdCP seeing about a 2.5-3ohm load.

I ran the same SPL test on the new PR setup just last night. Loudest I was able to get was about 137db at 45hz @ 1.7kw. The PR setup models 2-4db quieter through the entire musical bass range than the traditional vented enclosure, but this doesn't bother me much. All it did was get rid of the fat response peak that ended up getting rid of almost all the "boom" for a much more solid sounding bass. The best way I can describe it is a well engineered, flat response HT subwoofer. Low low bass, 20-35hz is where this setup really excels. Not so much in SPL, but instead just beautiful, full, even sounding bass that has remarkably *low* group delay at that frequency for how loud it gets. Effortless low low bass, low or high volume. The high bass also seems to have been enhanced a fair bit. It no longer sounds "hollow" and doesn't need a bunch of EQ on the top end. I'm crossed at 110hz with my midbass. All in all, I'm happy with the tradeoffs and think that I'll run this PR setup for a good while.

This brings me to my question though.... I bought a woofer that was designed/optimized for a vented box but i'd say my PR box is more akin to a sealed box than a vented one with respect to how the active driver behaves in the enclosure. I'm wondering what it is that Fi does exactly to their woofers to optimize (High QTS) it for a sealed enclosure. What I've noticed is that now in the PR enclosure, the active woofer MOVES a ton more than it ever did in my vented enclosure. It behaves almost identically to how it would in a sealed box, just goes louder and lower. With all this additional movement, and lack of atmosphere venting into the box to cool the coils, I noticed the dust cap getting pretty warm but not anything ridiculous. Never smelled coils... A disclaimer though, according to BB6, I shouldn't be able to overdrive (mechanically; xmax) either the passive or the active woofers with 1.7kw (can't make any more power) until I get down to 15hz. My subsonic can't go any lower than 20hz 6db/oct (JBL MS-8) which is what it is currently set at. At 15hz the box starts walking on me though

*If I would like to stay with this PR enclosure, do you think it would be worth my while to either A) sell this woofer and get a high QTS version, or B) send this one back to Fi and have them re-work it for the higher QTS. What should I expect to experience if I were to go to the high QTS woofer? Would it better cope with all the extra excursion i'm now seeing?

Below are some BB6 graph screencaps I took comparing my Q15 in a sealed box, my vented box, and my new PR box.

Acoustic Elegance PR18-1600

Green = Q15/PR18 Passive Radiator enclosure

Pink = Q15 vented enclosure

White = Q15 Sealed

Cone Displacement (xmax)

Group Delay

SPL

Edited June 22, 2011 by not1frak

[edouble101 314]

I like your thinking.

It doesnt appear that you have your pr tuned. Is it? You could be unloading the active driver above your ploted system f3.

Depending on the specs of your pr, your Fi Q maybe excedding the pr's mechanical xmas limits rendering it useless at higher power levels.

[95Honda 486]

In regards to the PR box, sweep it with test tones, try and go in 1Hz increments if you can, and see what frequency the passive moves the most and the woofer moves the least. Just make sure it is around 30Hz like you are predicting. If it is higher, you will need to add mass, if it is lower you will need to take away mass. You can do this in or out of the car, the cabin won't effect this.

If you are tuned lower than you think, you will loose output higher, where most music is. If you are tuned way to high, you are operating well below resonance, unloading and loosing all kind of output as mentioned above.

Here is the thing to think about in regards to overall Q of the driver. An easy way to explain it is the ability of the driver self-dampen. The lower the Q, the more the driver will dampen itself and the more you will require additional factors (Hemolitz resonation in the case of your vented and PR) to augment the output as you decrease frequency. The higher the Q, the less the driver self dampens and will have more output as you will decrease frequency without additional factors like a Hemolitz resonator.

In a nutshell, a driver with a higher Q that is put into an alignment with an additive effect of Hemolitz resonation will tend to exxagerate it's output as you decrease frequency. this can be a bad thing. You can have over excursion issues, increased ripple and group delay. Sometimes a driver will model super flat and super low in a decent sized vented box if it is a high Q driver, in practice the resluts may not be as favorable.

Save the high Q drivers for sealed boxes or IB, that is where they will perform optimally. The higher Q alows the driver to have decent output down low due to no over dampening the alignment.

If you PR sounds more like a sealed box, something may be wrong, or the ported box you were comparing it too was also way wrong...

Hope this helps...

[95Honda 486]

Also, look at the amount of ripple your 4th order vented box has, it should be much louder and more efficient over a majority of the audible band... That part isn't much of a mystery...

The box in my Avatar metered 142 db with 150 watts (total) on a Termlab at the headrest. How? I modeled for a nasty 11db hump of ripple just above the resonance point... It was much louder and efficent, but sounded like crap below 40Hz...

[Duran 387]

A high QTS Q motor is made by removing a bit of steel from the gap, thus less motor force.

[NDMstang65 403]

A PR acts just like a port, except you have a much better coupling of air.

You do not want a high qts woofer for that...unless you want a heck of a peak.

[PaulNeves 0]

I like your thinking.

It doesnt appear that you have your pr tuned. Is it? You could be unloading the active driver above your ploted system f3.

Depending on the specs of your pr, your Fi Q maybe excedding the pr's mechanical xmas limits rendering it useless at higher power levels.

It is tuned.. sorta-- more like carefully chosen. I modeled a TON of PRs, and this one was the best I liked due to the way it modeled in BB6 and its price. AEspeakers offers two 18" passive radiators. One being 1600g mms, the other, 2100g mms. The cones are a flat disc of MDF-- far from fancy, but seems to be effective for super low bass. Since this is MDF, I can totally add weight to it if I wanted. Would amount to using some wood screws and washers, perhaps some glue and a large nut, or a (ratchet) socket affixed in the center of the voice coil former where the dust cap would be -- Lots of possibilities here. I chose the lighter one because I figured it's going to be easier to add weight to this style PR than it would be to subtract it. I also went for this PR because of its price @ $100 USD. TC Sounds makes a nice line of PRs that are much lighter stock, but come with all the provisions to easily load it up with weight to adjust your Fb/tuning freq. They do come at a cost though...

http://www.parts-express.com/wizards/searchResults.cfm?FTR=tc+sounds+passive&search_type=main&WebPage_ID=3&searchFilter=tc+sounds+passive&x=0&y=0

I have some saved BB6 setups pairing the FiQ 15 with various weights added to both my AESpeakers PR18-1600, and the TC Sounds VMP18. I'll update this thread soon with those graphs to show you what I mean.

I'm pretty darn sure that there is NO way I can (realistically) overextend the Fi Q with 1.7kw in this alignment. According to the BB6 graph (which supports what I see and hear in person quite accurately) My active woofer will start "unloading" below 18hz at 1.7kw. According to BB6, 1600g mms on that PR was enough to push the typical PR "notch" where it unloads, well into the subsonic frequencies, below my subsonic filter in fact where I should rarely if ever touch that freq. Just as BB6 modeled, when I play a 18hz sine wave, the active woofer is hardly moving at all, but that passive radiator is going absolutely apeshit... somehow? -- which is fine. The passive radiator has 3.5" peak-to-peak xmax mechanical limits, and I do believe if I put 1.7kw at 18hz into that sub, my PR would eject up the passengers ass! When the PR blows up (and depressurizes the enclosure) because of some crazy bass like what I just described, then yeah, woofer might unload too and go boom This will never happen though. I am not the bass head I once was. I like my hearing

My intent here was to find a happy (and unique) medium between a ported enclosures low-extension and SPL, but with the musical fidelity and accuracy a sealed enclosure offers; especially in the higher bass range (60-110hz). I do believe that is exactly what I got. To be clear, I am not at all unhappy with how it sounds, or the fact that it is quieter. I probably should have put less emphasis on my SPL measurements. I want like 80-90% SQ and 10-20% occasional boom. Which I still do get if I just roll a window down.

[PaulNeves 0]

Also, look at the amount of ripple your 4th order vented box has, it should be much louder and more efficient over a majority of the audible band... That part isn't much of a mystery...

The box in my Avatar metered 142 db with 150 watts (total) on a Termlab at the headrest. How? I modeled for a nasty 11db hump of ripple just above the resonance point... It was much louder and efficent, but sounded like crap below 40Hz...

Niice man. Yeah, I have designed some SPL boxes like that in the past, though much simpler and usually with slot-vents with single or dual woofers. It's cool and all, but with this sub I specifically engineered out that "ripple" you speak of. I wanted flat, low and accurate response. Granted... I am running a JBL MS-8 and do have much EQ-ability to compensate in other areas outside of port and cabin gain, and while I was running that ported box, it sounded great because of this! Even still with all the EQ I did, it was not enjoyable to listen to the stereo loud with the window down; I'd have to attenuate the bass every time. Also it got more "sloppy" if that makes any sense. Sounded great with the windows up and cabin sealed. Also, with this box being extra "efficient" (which I perceive as boominess) because of the port gain, I would find that certain tracks irritated me to listen to. I would have to again turn the bass down. This is no longer a thought with the PR setup. It all just sounds so damn even. Like a well balanced and very loud HT.

When I got the MS-8, and finally a center channel so that I could run L7, my truck went from sounding like a standard "car stereo" to sounding like a home theater. Now with the addition of this PR/enclosure, it sounds dead-on like HT bass. Just much much louder The bass just sounds "airy" and "dry" completely devoid of that resonating "boomy" bass I'm so accustomed to. I do feel that I lost some of the "crispiness" in the higher bass, but the higher bass now sounds *considerably* warmer and more musical/detailed. It's kinda hard to explain. I hope you guys kinda see what I'm talking about. It just sounds sealed, but louder and way, waay lower; lower than the ported box hit by quite a bit all in a relatively small box for this woofer. Just a little less efficient.

I'll reply to your other post when I have more time to read and absorb the info, and I have my other screen caps ready to post.

Edit: The Fi Q15 has a FS if 25hz and 28mm of xmax (each way presumably). At max power that I can produce (1.7kw) excursion peaks at 21.4mm @ 32hz. It then drops as we head down to the assumed box tuning frequency of 18hz, where at 1.7kw the active woofer is moving its least at a whopping 2mm?!?! While the passive is @ 28.7mm xmax! -- Continuing down, the active woofer will hit its 28mm xmax at 15hz-- where I'll never take it anyway. On the other side of things, at 50hz the PR box models the same exact cone excursion as in the ported box all the way up but the vented enclosure is 4db more efficient than the PR alignement with the gap gradually decreasing until they are equally as efficient at around 100hz. So yeah, I traded off efficiency and boom in the musical range for a flatter/tighter/accurate response and considerably more LF extension.

Thanks for the input guys! Keep it coming

Edited June 24, 2011 by not1frak