Ask any car audio product specialist or installer, and they will tell you that the most popular speaker size is 6.5 inches. Rockford Fosgate knows this well and offers 11 different speaker upgrade solutions in this format. You can choose from affordable options in the Prime Series, high-performance upgrades in the Punch Series or benchmark-level systems from the Power Series. In this Test Drive Review, we’ll look at the T1650-S set, the most affordable of the four component set options in the Power Series.
Rockford Fosgate T1650-S Features
The T1650-S is a component speaker set sized in what Rockford Fosgate calls a 6.5-inch Euro-Fit format. The kit includes a pair of woofers, a pair of 1-inch tweeters, passive crossover networks, grilles for the woofers and both surface- and flush-mount options for the tweeters.
The Euro-Fit sizing means the woofer has an overall diameter of 6.5 inches and a mounting hole requirement of 5.51 inches. The woofer needs 2.52 inches of depth beneath the mounting surface. The surround stands 0.51 inches tall from that same plane. However, with an Xmax specification of 0.2 inches in each direction, your installer will want to leave at least another 3/8 inch to ensure the cone doesn’t come into contact with the OE grille.
T1650-S Woofer Features
The woofers in the kit are based on Rockford Fosgate’s StampCast steel frame design. This unique stamped frame looks like a cast aluminum design. The deep draw of each of the eight spokes adds impressive rigidity. In short, you get most of the benefits of a cast basket without the significant price increase.
Four cooling vents are stamped into the basket under the spider mounting plateau. These vents allow heat to escape from the voice coil to improve power handling. Additionally, the vents prevent the air under the spider from compressing or rarefying as the cone moves rearward and forward. The result is improved linearity and less distortion at high excursion levels.
The woofer cone is made from injection-molded polypropylene mixed with carbon fiber strands to add rigidity, damping and thermal stability. In the center, there’s an inverted dust cap with the same gloss finish as the cone. A flat poly-cotton spider keeps the cone centered in the basket.
At the edge of the cone is a Santoprene rubber surround bonded to the basket with Rockford Fosgate’s famous Vertical Attach Surround Technique (VAST) design. VAST helps maximize the effective cone area by reducing space that would be wasted with a surround glued flat to the flange. In the case of the T1650-S set, the effective surface area of the woofer is about 147.4 square centimeters. Competing woofers are much smaller, typically around 120 to 130 square centimeters. The VAST feature effectively makes the woofer 20% larger than competing products, improving efficiency and bass output.
The woofer’s heart is a 1.2-inch-diameter high-temperature aluminum voice coil former and a winding with a nominal 4-ohm impedance. This large voice coil is key to the system’s 100-watt continuous power handling rating.
Attention to detail sets Rockford Fosgate apart. The woofer includes a foam mounting gasket already attached to the woofer’s mounting lip. Other companies might include a foam gasket, but your installer would have to install it separately, adding cost. Further, the basket has an impressive 16 mounting holes and slots. Rockford Fosgate calls this the FlexFit 2 basket. No matter what OE bolt pattern your stock speakers have, these provisions help ensure an efficient installation without the need to drill new holes in the vehicle.
T1650-S Tweeter Features
The tweeters in the T1650-S set feature a treated fabric dome design. The treatment improves damping and reduces unwanted resonance to keep the sound as clear and detailed as possible. A compact neodymium slug in the tweeter’s center ensures efficiency while acting as a heat sink. The black grille on the front of the tweeter is permanently bonded in place to provide proper protection.
Rockford Fosgate includes mounting hardware called the Discrete Dual Clamp (DDC) system for the T1T-S tweeters, allowing them to be flush- or surface-mounted. Angled surface-mounting brackets enable your installer to tilt the tweeters toward the listening position for improved high-frequency performance.
Passive Crossover Network Design
The passive crossovers are 1.38 inches thick and come in 4.57-inch square housings. They feature an 18 dB/octave low-pass network for the tweeter and a 12 dB/octave high-pass filter for the midrange. While mismatched crossover slopes don’t typically make sense, Rockford Fosgate has considered the natural attenuation of each driver in the system to ensure a smooth acoustic summing around the crossover point.
The filter networks have three adjustments:
- A bi-amp switch if you want to use separate amplifier channels for the woofers and tweeters. Your installer will leave the bi-amp option off when driving the crossovers from a single amplifier channel.
- An output level adjustment for the tweeter at -2, 0 or +2 dB. This helps tune the system based on the distance between the listening position and the tweeters and woofers.
- An on-axis or off-axis switch. If the tweeters are aimed directly at the listening position, the switch should be set to on-axis. The off-axis position is ideal if the tweeters are pointed across the vehicle.
Rockford Fosgate T1650-S Lab Measurements
The first step in characterizing the T1650-S is to take a set of Thiele-Small parameter measurements of the woofers. We used the delta-mass method with the Woofer Tester to generate an initial set of electromechanical parameters. Once that was done, we set the woofers up on the bench and fed them with a 30 Hz test tone at seven volts to break in the suspension for about eight hours. After the break-in, we let the drivers cool and repeated the measurements.
We took away two key observations from the measurement process. First, the pair of drivers are impressively similar to each other—much more so than most speakers we see. The resonant frequency, suspension compliance and impedance are within a few percent of each other. We see variations of up to 10 percent in some products. This similarity speaks volumes about the attention to detail during the manufacturing process.
Second, we have the two sets of parameters themselves. The drivers showed a good amount of change during the break-in process. The resonant frequency (Fs) dropped from around 90 Hz to a little over 65 Hz. The suspension compliance increased from 10.6 to 13.9 liters. As such, you will notice that the T1650-S set sounds better after a few dozen hours of healthy playback.
Woofer Response Simulation
As has been typical of Rockford Fosgate products, the parameters are optimized for their typical application in a vehicle’s door. The Total Q (Qts) is 0.69 to give the woofers a warm, full sound. The resonant frequency is low enough (65.5 Hz) that the drivers will work sufficiently well in a vehicle without a subwoofer.
Taking the parameters and entering them into BassBox Pro, we can see the predicted change in response from before and after the break-in process. The trace in red shows the initial predicted response. The trace in yellow shows the extended bass response that comes with the softened suspension.
Of course, with any speaker, you sacrifice efficiency whenever you want more bass without increasing the cone area. The math says the driver dropped by about 1.4 dB.
Before you get upset about any changes in pre- and post break-in performance, know that these changes are not atypical for any moving coil speaker. The changes aren’t a lessening of performance, just a shift in characteristics. Aside from the increased low-frequency output, the reduction in total Q from 0.78 to 0.69 will make midbass frequencies tighter and more controlled. From those perspectives, this a worthwhile evolution.
Tweeter Measurements
The tweeter in the T1650-S set is called the T1T-S. If you need more sizzle in your car audio system, they are available separately with passive crossovers and the really cool DDC mounting hardware.
To characterize the tweeters, we measured their impedance and phase response to find their resonant frequency, which was measured at about 1.4 kHz. If you want to use these on a dedicated amplifier channel with the Rockford Fosgate DSR1 digital signal processor, a high-pass crossover point of 2.25 kHz with a fourth-order Linkwitz-Riley slope will work great. Of course, you’ll apply the same low-pass crossover point to the woofers and their amplifier channel.
Auditioning the Rockford Fosgate T1650-S Component Speaker Set
With all the poking, prodding and measurements complete, it was time to head into the listening room and set the speaker up in our reference enclosures. The enclosure mimics a floor-standing speaker with an internal volume of just under three cubic feet. This is large enough that the compliance of the air in the enclosure has no significant effect on the drivers’ performance. In short, these are large enough to simulate the effectively infinite-baffle installation that would characterize a car door mounting scenario.
We powered the speaker set with a 300-watt-per-channel high-bias Class-AB amp fed by a high-end stand-alone DAC and preamp. The DAC connects to a PC laptop using a USB cable and can decode any standard digital file format.
The first track we auditioned was Crazy by Seal. The midbass was impressive and clear. There was a slight emphasis when he sang the letter S, but not to the point of being sibilant or shrill. As we’ve found with other Rockford Fosgate speakers, the overall balance is slightly forward in the upper midrange. This helps make vocals clear and present. If you happen to have a subwoofer system, it makes it easy to hear the performer.
Next, we listened to Your Latest Trick by Dire Straits. The horn in the opening was very clear and detailed. The gentle cymbal work shared the same impressive detail. Knopfler’s vocals were rendered with good balance and weren’t as forward as Seal’s.
Last up was Darude’s Sandstorm. We cranked the volume on this one to give the speakers a workout. The elevated volume brought out the upper bass lines in the track. The T1650-S set did an admirable job staying composed at higher volume levels but didn’t have the dynamics of the woofers in the T2, T3 and T4 sets. If you want to play your music at concert volume levels, then invest in a subwoofer and apply a high-pass filter to these woofers. This will alleviate their need to reproduce low-frequency information that requires a lot of cone excursion. They’ll sound great and play a lot louder!
Conclusions on the T1650-S Component Speaker Set
As we mentioned at the start of the review, Rockford Fosgate offers many 6.5-inch speaker solutions. The T1650-S set borrows some technologies from the upper-end models in their crossovers and power-handling technologies. Will they get loud? If you use them with a subwoofer, we’d say the answer is an undeniable Yes! If you are playing them with a full-range signal where bass output is important, you might want to consider the T2652-S set. The T2652-S woofers have more than three times the woofer excursion capability, so they manage bass frequencies more effortlessly. That doesn’t mean the T1650-S set doesn’t perform well – you have to decide where your budget and performance goals intersect.
We have to applaud Rockford Fosgate again for their attention to detail. When shopping for speakers, features like the pre-installed foam gasket, flexible and highly adjustable passive crossovers and elaborate tweeter mounting hardware should not be overlooked. The large voice coil winding, vented basket design, and VAST surround design are noteworthy on the performance front. These items improve both installation and performance while adding value to the overall product.
If you are shopping for new speakers for your car, truck or SUV, drop by a local authorized Rockford Fosgate retailer and ask to check out the T1650-S Power Series components. You can find a retailer using the locator tool on the Rockford Fosgate website. Be sure to follow our friends from Tempe on Facebook, Instagram and YouTube to learn about the products they offer and the incredible events they attend.
