Cable Modems Review for Modems for Comcast, Time Warner & more!

Posted by Bryan Westover on 8th Aug 2016

Cable Modems Review

Why Buy a Cable Modem?

The top performers in our review are the Arris Motorola SB6141, the Gold Award winner; the Arris Motorola SB6121, the Silver Award winner; and the Netgear CM400, the Bronze Award winner. Here's more on choosing a cable modem to meet your needs, along with detail on how we arrived at our ranking of the top 10 products.

A cable modem is essential for connecting to a cable internet service, and most internet service providers (ISPs) rent a cable modem to you when you set up a plan. Usually, the modem isn't free – the cost for renting the modem is added to your monthly bill. That's an extra $5 to $10 every month that you could save by getting your own cable modem. Making an informed buying decision here will save you money in the long run. If your ISP provides DSL internet instead of cable internet, then you'll want to check out DSL modems.

Not only do you save money over time by buying your own modem, you're also likely to get a much better modem than what the cable company gives you. There's no guarantee what model you'll get from your ISP, and sometimes the modem isn't even capable of giving you the speeds you pay for. You can also take this modem with you when you move and don't have to deal with the hassle of returning a rented modem.

It's entirely possible that you'll see a boost in your internet speed when you buy a new cable modem. A good cable modem will never be a bottleneck and slow down your internet. For example, if you pay for 50 Mbps, but your modem can only handle up to 30 Mbps, then you're losing 20 Mbps of speed. Don't trust the cable company to get it right. We'll get into the specifics of what makes some modems capable of handling higher speeds than others later on in this article.

Cable Modems: What We Evaluated, What We Found

Speedy boot-up times are hard to find. Anyone who has had to call tech support in order to get their internet working again likely knows how frustrating it can be to reboot the cable modem. We found that some cable modems are faster than others at coming back online, though they're all somewhat slow.

Testing boot-up times is a relatively simple matter, but we made sure to subject every modem to the exact same environment. We also followed the same testing procedure for each modem, ensuring that our measurements were accurate and replicable.

We found that it took, on average, 34 seconds for a cable modem to boot up into full functionality. A couple of modems, the Arris Motorola SB6183 and the Zoom 5341J, beat the average by a fair amount with 29-second boot times. The Netgear CMD31T averaged a boot time of 47 seconds, which is significantly longer than most of the others.

While this may seem like a small thing to consider, the fact of the matter is that there are real differences in boot-up times. And in a world with instant-access smartphones, a 40-second boot-up time is quite frustrating. Still, there are many other things to look at in a cable modem.

Not all cable modems feature similar build quality. While build quality isn't the most important aspect of a device that sees little wear and tear, like a cable modem, it's still something to consider. A well-built cable modem is rigid and scratch-resistant. We prefer a matte finish, as it won't readily show fingerprints or other blemishes. As for ventilation, the best cable modems have large vents on most of their sides.

By and large, cable modems are made out of sturdy plastic. Most of the modems on our lineup are strong and rigid. However, a few – like the Zoom 5341J and the Netgear CM500 – feel a little bit flimsy. The Netgear CMD31T stands out a little bit, as it integrates some metal into its housing.

The Cisco DPC3008 and the D-Link DCM-301 are the best-ventilated modems we looked at. They both have large vents to eject hot air, and those vents are placed on four sides of the devices. Good ventilation gives these cable modems an advantage in handling heat dissipation.

Some cable modems generate and retain heat more than others. Heat is not good for electronics. You want your electronics and cable modem to run as cool as possible. Heat is an indication of inefficiency. What happens is the device draws more power than it needs and then has to radiate the extra power in the form of heat. That inefficiency can lead to a shortened lifespan for the device.

In order to measure the heat output for each modem, we plugged all of the modems in at the same time, in the same room. We measured the heat on each modem in three different places. Because the modems aren't all exactly the same shape, the locations varied somewhat between devices. To prevent any odd readings, we repeated the test three times.

We found that the coolest cable modem is the Arris Motorola SB6141, followed closely by its little brother, the SB6121. They had average temperatures of 87.5 and 87.7 degrees Fahrenheit respectively. The hottest cable modems are the Arris Motorola SB6183 and the Zoom 5341J, with average temperatures of 102.4 and 97.9 degrees Fahrenheit respectively.

Please keep in mind that these are temperatures for the housing of the cable modems, not the internal electronics. The internal chips are likely hotter.

Some cable modems consume more power than others, which means a higher monthly cost. Most people leave their cable modems on for all hours of the day. Keeping a device powered 24/7 can have a measureable impact on your monthly electric bill. We calculated an estimated cost for constantly running each of the modems on our review lineup.

Most of the cable modems we reviewed pull in 1 amp at 12 volts. This translates into about 12 watts. With the cost of electricity across the United States being 12 to 13 cents per kilowatt-hour, it will cost you about $1.14 per month to keep these cable modems running 24/7. The yearly cost is $13.67. Some modems draw more power and could cost you upward of $20 per year to run.

The dollar amounts seem small at first. However, in a world with many electronic devices to charge and keep plugged in, it can have a significant impact on your electric bill to be aware of how much it costs to run every device in your home.

Top Ten Reviews seeks, whenever possible, to evaluate all products and services in a way that best serves the consumer. The manufacturers had no input or influence over our evaluation, nor was the evaluation method provided to any of them in more detail than is available through reading our reviews. Results of our evaluations were not provided to the companies in advance of publication.

What Else Is Important in Selecting a Cable Modem?

While we've covered some useful information so far, there is much more to consider before buying a cable modem. These devices are relatively simple, in that they either work and give you 100 percent performance according to their standards, or they don't work at all. However, a better understanding of those standards and what makes a cable modem work will help you make a better buying decision.

Cable Modems: Do All Cable Modems Work With All ISPs?
Unfortunately, not all ISPs support all of the modems on our lineup. We looked at the four largest cable internet providers in the United States to determine compatibility for each modem. Only the Arris Motorola SB6121, SB6141 and the Netgear CM400 are compatible with most of the ISPs we looked at. The major advantage of your cable modem being compatible with many ISPs is that you can use your modem when you move. A good cable modem should last for years without any issues.

The lack of compatibility is largely due to ISPs not wanting to maintain long lists of compatible products. While it would be nice if every cable modem would work with every cable provider, that isn't really possible. Check with your ISP if you're unsure about modem compatibility.

Cable Modems: What Is DOCSIS and Why Does it Matter?
The term DOCSIS is often plastered all over cable modem packaging and materials. DOCSIS stands for Data Over Cable Service Interface Specifications, which is a really long way of saying that this is how the modem talks to your ISP. You can think of it as a language. As long as your cable modem and ISP speak the same language, everything will be great.

The interesting thing about this DOCSIS language is that the latest versions allow your modem and ISP to say more things at one time. DOCSIS 3.0 is the current standard and generally what you want your modem to use. If your modem only uses DOCSIS 2.0, you may want to consider upgrading, as 2.0 isn't anywhere near as capable as 3.0.

Essentially, the version of DOCSIS your cable modem and ISP use determines the maximum theoretical speed of your internet. DOCSIS 2.0 only supports one channel with speeds up to 43 Mbps down and 30.7 Mbps up. DOCSIS 3.0 allows channel bonding, which means you can have multiple channels of up to 43 Mbps down and 30.7 Mbps up. There are modems and internet plans that can handle up to 24 channels down and eight channels up. That means over 1,000 Mbps download speeds and up to 246 Mbps upload speeds. Channel bonding is why DOCSIS 3.0 is a major improvement over DOCSIS 2.0.

What this all boils down to is that your maximum internet download and upload speeds are dictated by the DOCSIS standard your modem supports. DOCSIS 3.0 makes DOCSIS 2.0 obsolete. That's how big of a difference it can make. As long as your ISP and modem support the latest DOCSIS version, the limit on your internet speeds will be the plan you purchase from your ISP, not your hardware.

Cable Modems: Why Is Channel Bonding Important?
On the technical specifications for DOCSIS 3.0 cable modems, you'll often see a section for channel bonding. It usually looks something like this: 4 x 4 or 8 x 4. Those numbers indicate the number of channels in the upstream and downstream to and from your cable modem to your ISP. Downstream is the first number and upstream is the second number.

Generally, the more channels you have for both upstream and downstream, the better. Even on low-speed internet plans, more channels can help you achieve your plan's full speed. Essentially, a larger number of channels helps you avoid network congestion in your geographic area.

Cable Modems: Not All Cable Modems Are Alike
There are a few important things to consider when looking at cable modems. First you need to determine what kind of performance you want for your home network. If you want the highest speeds possible, then make sure your cable modem and router have a gigabit Ethernet port. This ensures that your hardware won't be the limitation in speed.

It seems odd, but only the Zoom 5341J and the D-Link DM-301 modems have a button to toggle them on and off. While this button may seem like a frivolous feature, it can save you money on your electric bill. It can also prevent damage to the modem during a thunderstorm if you switch the modem off. Of course, you can achieve the same effects by simply unplugging a modem that doesn't have an off button.

Some cable modems have a reset button that makes the modem run through its power cycle. Like the off button, the reset button isn't essential, as you can achieve the same effect by unplugging the modem and then plugging it back in. The difference here is a matter of convenience. It's easier to hit the reset button.

Should I Get a Cable Modem and Wireless Router Combination?
In the case of your home network, it is almost always better to have the cable modem and the router be two separate devices. A modem and router combo puts all of your eggs in one basket. If the device breaks, not only do you need to replace your entire home network setup, you don't have any access to the internet because the cable modem is down.

When you connect your modem to the ISP, the modem becomes subject to the terms of service for your internet plan. More often than not, those terms of service give the ISP administration authority over your cable modem. This allows the ISP to download any firmware and configuration files it needs to for the modem. It often results in locking you out of the modem's configuration settings. With a combo device, this also prevents you from installing custom firmware on your router.

Modem and router combos generally don't perform as well as their stand-alone counterparts. Commonly, the router side of the combo just doesn't have the signal strength or feature set to compete with a stand-alone router. Essentially, it's trying to jam too much stuff into one box.

There are some advantages to a modem and router combo. You don't have to worry about as many cords. You only need one plug for power instead of two. The combo units also tend to be around the same price as a modem and router, if not cheaper. If looks or space is a primary concern for you, then a combo device may be exactly what you need. However, make sure that you understand what the device is capable of and the compromises it makes.

What's the Difference Between a Cable Modem and a DSL Modem?
Cable modems and DSL modems are similar in function. They both serve to connect your home network with your ISP's network. The major difference between the two is how they do it and the infrastructure they use. Most ISPs provide strictly cable internet or DSL internet, and your ISP will let you know which kind of modem you need.

Cable modems and internet use the same infrastructure that transmits data for cable television. This is why you often see cable TV providers that also offer internet service. An ISP that provides DSL internet uses the same infrastructure as landline phones. The copper wire that's in place for telephone services is plentiful and allows the ISP to provide internet access anywhere you can get a landline phone. Because of the two different kinds of infrastructure, you need two kinds of cable modems to interpret the data – one for cable and one DSL.

To make things more confusing, there is a third infrastructure that still isn't widely available. Known as fiber, this infrastructure has a much higher bandwidth than either DSL or cable options. However, because it's relatively new and new lines need to be laid, it's somewhat expensive – if you even have access to it.

Cable Modems: CableLabs and UL Certifications
CableLabs and UL are independent third-party organizations that ensure the safety and interoperability of consumer products. In this case, we looked at the certifications both entities provided for the cable modems on our lineup. While certifications like these aren't sole indicators of a device's quality or capability, they are a standard that you can rely on.

Nearly all of the cable modems we reviewed are certified by CableLabs, which ensures that they meet the communication standards necessary to work with most other networking equipment. This means that, in most cases, you shouldn't have any trouble with your cable modem talking to your wireless router – just connect them and you're good to go.

Most of the modems we looked at were also certified by UL. What this tells you is that the modems are completely safe for consumer use. UL ensures that products adhere to industry standards for safety and design.