AV Rant #203: All About Projectors
Grammer Rob is back as co-host. Don’t worry those of you that have offered to be co-hosts. Tom has every intention of taking you up on it. He’s just been taking the easy road lately. As the name implies, Rob has a few things to say about projectors. If you are in to such technology, you might want to keep a pen and paper handy as he mentions quite a few model numbers. Netflix starts streaming in 5.1 – on the PS3 only. Tom has a few things to say to those that were complaining about having to use a disc for Netflix. Shifty get’s his day in court. A few thoughts on early announcements from Internet Direct companies. Jesse has a few insights into who is buying 3D displays. Buying Tom’s love. Thanks for listening and don’t forget to vote for us at Podcast Alley! To see our (mostly) complete collection of show videos, click here. To get our iPhone app, visit the iTunes store.
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Regarding subwoofer amps getting fried: Rob, you mentioned bypassing the subsonic filters on your subwoofer amp. Do you do that with some kind of defeat switch, or do you physically modify the sub’s input to bypass the internal filter?
I believe the subsonic filter is there to block signals that go below the sub’s tuned frequency. Once that happens, the woofer becomes “unloaded”. That is, it de-couples from the air and starts to operate without any air resistance. When this happens, it can go into over-excursion when being driven hard. Over-excursion can not only damage the driver but may also over-tax the amplifier, which isn’t designed to operate the driver under such extreme conditions.
The Axiom sub amps just have a high-pass filter on the bottom end so that you can “tune” the sub to either drop off like a brick wall below 20Hz or continue to produce sound below 20Hz. They call it a subsonic filter switch, but it isn’t really. It’s just a high-pass filter, but they didn’t want to confuse people since there is already a “high-pass” filter in either the receiver or the speakers :p
I don’t recall which Axiom sub you have – I think EP500? That sub produces no usable output below 18Hz.
http://axiomaudio.com/gallery_ep500_diagram.html
I think I would leave the 20Hz high pass engaged to protect the amp and driver. 20Hz is not really subsonic, but it is “subsonic” as far as the sub’s frequency response is concerned.
Yeah, I have the EP500. Its own, true, subsonic filter is the reason its frequency response plot pretty much has it dropping off like a cliff below 18Hz. The “subsonic filter” switch on the back of the amp is just the 20Hz high-pass filter that I talked about. That switch is really only there for analogue sources – something like a phono record player, in particular – where the analogue device itself might be producing subsonic distortion that was never meant to be reproduced. All of my sources are digital and don’t have this sort of potential problem. In the extremely rare cases where a digital recording has an 18Hz or 16Hz fundamental, I still want that signal to reach the subwoofer. The EP500 does reach down to 18Hz with useable output, so that is why I leave the “subsonic filter” switch on the back of the amp turned off 🙂 Due to the real, internal, subsonic filter that cannot be adjusted, the EP500 will likely never output those pipe organ 16Hz fundamentals :p But the switch on the back isn’t a safety issue. It’s just there in case you are a phono user with an unusually “rumble-y” turntable :p