LFE Wavelengths and audibility

[cwall99]

So, I was speaking with a sales guy about a sub-woofer the other day, and he said something that I'd never considered, and, not being an audio genius, I thought I'd turn to the forum for verification.

We were talking about subwoofers and getting down to 18 to 22 Hz, and his comment was that, unless your room was longer than 55 or 60 feet, you weren't going to hear those frequencies. Interesting notion, I thought, and so I went to http://www.mcsquared.com/wavelength.htm, where they have a wavelength calculator, and put in 20 Hz to see what the wavelength would be. Turns out it's 56.5 feet (assuming standard temp and air pressure).

Does this mean that if my room is shorter than 56.5 feet, that I won't hear these low-end frequencies?

If that's the case, I might as well not chase anything that runs lower than 45 Hz as its wavelength would be about the same length as my room (25 feet).

What's the group have to say about this?

Thanks.

 

[annunaki]

A room has boundaries and the wave is reflected. It is still quite audible down to 20hz (limits of human hearing) and tactile (meaning you can feel it) though the ear is less sensitive at those frequencies. They tend to be felt more than heard. In fact, many rooms will amplify extremely low frequencies. The sales guy needs to do more research.

 

[evilkat]

Yeah that doesn't seem to track right. It doens't seem to follow that you can't hear a wave just because a complete wave doesn't 'fit' in the room. I thought 'hearing' a sound has to do more with frequency (the limits at which u can detect the noise) and distance from the source (i.e. the wave has sufficient energy to reach you in order to be detected).

However, some room dimensions seem to promote reflectied waves that are exactly out of phase with the incident waves - perhaps leading to more nulls in the room than otherwise?

 

[TLS Guy]

So, I was speaking with a sales guy about a sub-woofer the other day, and he said something that I'd never considered, and, not being an audio genius, I thought I'd turn to the forum for verification.

We were talking about subwoofers and getting down to 18 to 22 Hz, and his comment was that, unless your room was longer than 55 or 60 feet, you weren't going to hear those frequencies. Interesting notion, I thought, and so I went to http://www.mcsquared.com/wavelength.htm, where they have a wavelength calculator, and put in 20 Hz to see what the wavelength would be. Turns out it's 56.5 feet (assuming standard temp and air pressure).

Does this mean that if my room is shorter than 56.5 feet, that I won't hear these low-end frequencies?

If that's the case, I might as well not chase anything that runs lower than 45 Hz as its wavelength would be about the same length as my room (25 feet).

What's the group have to say about this?

Thanks.

The salesman has spouted an error that was prevalent in the audio press, like Stereo Review etc. 20 years or more ago. It is nonsense because of the reflection of the wave. If anything domestic size sound rooms can cause amplification of those frequencies. In fact with most domestic sized speakers, it is usually difficult to work up a good bass in a large space. Tell the sales guy to update his information.

Before the sub craze few speakers had much output in the last octave. I have build speakers to reproduce into the last octave for around 35 years, so I always knew what the salesman told you was folklore.

 

[no. 5]

If what the sales guy said was true, you would hear very little bass in a car, and absolutely no bass or midrange when you listen to headphones.

 

[mike c]

last time a sales guy told me the same thing, i discovered all his subwoofers could not play anything below 30hz. always consider the source. sales guys cannot be trusted when talking about their product and their competitor's product

 

[mtrycrafts]

...
We were talking about subwoofers and getting down to 18 to 22 Hz, and his comment was that, unless your room was longer than 55 or 60 feet, you weren't going to hear those frequencies. Thanks.

I would go back to him and ask him where he got that notion from? And, ask about car subs if they have them there, or car sub woofer boxes and ask how low it goes in a car
Or, if you have a test disc with 20Hz on it, take it there and have that person use some headphones and see if it is audible
In reality he is/was out to lunch

 

[mtrycrafts]

by the way

We were talking about subwoofers and getting down to 18 to 22 Hz, and his comment was that, unless your room was longer than 55 or 60 feet, you weren't going to hear those frequencies. Thanks.

Tell him that you were thinking about this and was just wondering what the lowest frequency one might hear in a car, perhaps 90Hz? or higher?
Then ask why they are selling subs for cars, if they do that

 

[Adam]

I agree with everyone...the salesman is just plain wrong. I've measured SPLs down to 16Hz (the lowest tone on my test CD) in my room that is about 22 feet long, and I can hear 20Hz just fine.

 

[cwall99]

Thanks everyone

Thanks for all your replies everyone. Like I said, I'm not a audio expert, and, heck, I don't even play one on TV. The sales guy said something I'd never considered, and, without any context, it made sense, but, after reflecting on your posts, what he said seems considerably less valid.

BTW, he was demo'ing a Velodyne DLS3750-R for me. It sounded pretty good, and blended nicely with the DefTechs he had mounted on the wall.

I'm looking for a sub in the $500 to $700 range that will play nicely with my B&W 603 s3s. It's a good sized room (20 feet by 25 feet that's 60% family room/home theater - although with really bad lighting control - and 40% kitchen/dining area - a low wall / countertop splitting part of the two rooms).

I have a cheesy Harman Kardon sub that came with my first surround-sound speakers came with (those speakers and my original Onkyo receiver are now in the basement on my boys' XBox 360 - can anyone make a louder fan than the boys at Microsoft?), but the sub is still trying to fill out the bottom end of my primary home theater kit, and not doing a very good job of it.

Finances being what they are (hey! I live in Detroit where half the world is laid off), my wife is not keen on me spending a ton of cash on a sub. I've considered:

- The Velodyne mentioned above ($499)
- An Outlaw LFM Compact or LFM Plus
- B&W ASW 610 (just because my mains are B&W - I know, I know, I know)

But, frankly, I don't have any strong preferences in any direction. The only thing going against the Outlaws is that I'd rather listen before buying, and while Outlaw has a great return policy, I'm lazy and don't want to have to deal with all the hassle of returning something I don't want to keep.

However, I also know that any decent sub I get will greatly extend the bottom of my kit, and will probably sound pretty good - so long as it's not a one-note effect that sounds like hitting a couch with a salami.

Thanks again, everyone, for your quick responses. It's good to get educated.

 

[jcPanny]

Sub options

Also check out SVS, HSU, and the MFW-15 sub from av123.com in your price range.