Shouldn't I Have More Bandwidth Leftover While Downloading?

Lenovo k450e
16 gb ram
i7-4790 cpu @ 3.6 ghz
Windows 8.1, 64-bit on solid state drive

I have questions about two Comcast modems/routers.
The first one is an 802.11 Wireless Gateway. Speedtest.net shows that I get about 30 mbps down.
I understand that my speeds can only be as fast as my connection to each specific web page, but why, while I'm downloading files at 3 mbps, does internet browsing slow down to dial-up speeds? Shouldn't there be plenty of bandwidth leftover to browse at better speeds?

The second Comcast modem/router is a dual-band 802.11ac Wireless Gateway. With this one, Speedtest.net shows I only get 15 mbps down. I also am not receiving any 5 GHz signals. Only 2.4 GHz shows in my list of available networks.. Browsing web pages is even slower than the other modem while I download.
What is causing this newer model to be slower than the other?

 

The first thing you need to do is look at your Comcast contract or service agreement and see what you are paying for. Then check with Speedtest.net via a direct Ethernet connection, not wireless. If your speeds are at least what you are paying for via Ethernet, then we can look at your wireless. If you are not getting what you are paying for via Ethernet, you need to contact Comcast.

 

Ethernet and wireless speeds are almost exactly the same for each respective modem.

 

That doesn't matter. You need to verify you are getting what you are paying for. Ethernet is consistent. Wireless can vary minute by minute because many factors can influence wifi performance.

So once again, you need to look at your service agreement and verify you are getting what you are paying for. Not doing that first is just wasting everyone's time.

 

My plan is called 'performance internet'. Comcast advertises 25 mbps.

 

It is not about advertising. It is about the specific terms stated in your contract. If it says "up to" 25Mbps, then you are hosed. If it says a "minimum" of 25Mbps and you are only getting 15Mbps via Ethernet, then you have ground to complain on. Until you determine that, you still wasting everyone's time - including yours.

 

UP TO 25 mbps, isn't that how it always is? I've never seen a speed guarantee ever for internet. Speedtest.net measurements are always right around 30 mbps and 15 mbps for each modem, however.. Very consistent speeds for both wireless and ethernet.
But if that's not enough for you to go on, maybe we can move on.. Whatever the contract terms are, it wouldn't explain why the dual-band modem/router is so much slower than the older one. I have both here and basically tested side by side.

 

It is not what I need. If you feel your provider is meeting their obligations, then that's fine by me.

As for the dual-band, unless it is a "simultaneous" dual band, it may slow down to the slowest. Are both DOCSIS 3.0 modems?

 

Both are DOCSIS 3 modems.. Only one line. I have two modems at the moment because wireless stopped working on the older model. Comcast concluded that the modem was defective but I eventually found a different cause.

I reinstalled the wifi driver for my computer and am now getting the same speed on the dual-band.

 

So it is working okay now?

Actually, your modem is serving as your "gateway" device.

Sadly, marketing weenies have interjected another misleading marketing term into the vernacular, and that is "gateway device". These are simply integrated devices where a router, modem, 4-port Ethernet switch, WAP (wireless access point) and sometimes VoIP are all integrated into one box. But technically they are totally separate, discrete network devices that just happen to share a case, circuit board, and power supply and may have a common menu.

I was wondering about this too when he said he had two modems. But now we know both are DOCSIS3.0 with only 1 line.

I was surprised how much better my service got when I replaced my DOCSIS2.0 with a new DOCSIS3.0. My download speeds jumped up 20Mbps to ~50Mbps. My contract says "up to" 50Mbps and 5Mbps down, so I cannot complain about this:

 

It's now working as well as the older modem, but there's still the issue of slow internet browsing at the same time I'm downloading (the question in the thread title).
Another issue is, it seems Windows 8.1 doesn't show 5GHz networks.

 

That's the same modem I had before I replaced it with a SB6141. And yes, those are both modem-only devices.

BTW, the USB connection was lousy. I know several folks who tried it and were disappointed. It was slow and lost connection often. Best to use with a router (even with only one computer) for better reliability and much better security.

 

Back in 2000, USB 2.0 was touted at up to 480Mb/s. Sounds like Comcast wasn't ready for that, either. Turned out 35Mb/s was the realistic figure for USB 2.0; ergo, use ethernet, about 100Mb/s.

Regardless of what a manufacturer might hype; e.g. USB 3.0, etc, just remember, "a chain is only as strong as its weakest link." Backward
compatible means connect if you can, but performance is is limited to that of the lowest level of the device, cable, plug/or jack, involved.