40hz ratings/speaker response

Speakers of various designs and tuning will respond differently when fed a signal below their natural resonance ( point of max output ). Well designed acoustic suspension ( sealed box ), infinite baffle ( designs that make use of huge volumes of air and a baffle to isolate the rear wave from the front wave ) and TL ( transmission line ) designs will respond relatively linearly but at reduced output.

Vented designs, such as ports, passive radiators, slot loaded, etc... will produce much lower output below that point with greater potential for distortion and even driver damage.

If you doubt this, try playing a highy warped record with a large speaker that is vented at high volume. The woofer will want to pop out of its' basket. This is one of the reasons why the "high pass filter" or "rumble filter" was invented.

While you would have similar results with a sealed box, the driver would not be nearly as "out of control". This is due to the damping that the "air spring" in the box supplies. Vented designs are "unloaded" or have no "damping" below the point of box tuning. The driver is therefore subject to greater excursion, which could result in damage. This damage could be immediate or accumulative over time.

With that in mind, most people with educated ears are able to discern the differences between vented and sealed designs simply by listening. One obviously sounds more natural and linear than the other. Sean
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Thanks for the info folks. You have to be careful about jumping to conclusions based on that spec.

I would much rather have a speaker rated 40hz or so that handled that really well than most speakers sold today rated below that number. Northcreek is a good example.

Cheers,

Sean, I believe I understand you correctly when I assume you favor non-vented designs. I am not clear on some of the basic design concepts of transmission line and infinite baffle (are these vented or sealed box types) while I believe the acoustic suspension aspect of the sealed cabinet seems relatively straight forward. Forgive me, but could you elaborate?

Also, Clueless, do you mean that the NorthCreek ratings are conservative, and that their designs subjectively go lower than their rated output?

Thanks for the information gentlemen.
Mike

As Scott Campbell (and others) said in the first post your number was the frequency where your sound is down three decibals(-3db). This does not say much about the quality of any speaker despite the fact that it is used that way sometime. Lots of speakers with really low specs sound horrible. One the other hand, you look at a North Creek, I think their Rhythm has a rolloff/F3/-3db point (what ever you want to call it) that is not that deep by today's standards. Maybe 44hz. And it has a tuning frequency (Fb) of 39hz or so. Sean pointed out that vented designs progressively lose damping below that point.

However, the design of the speaker does a great job reproducing sound in the high 30hz and they sound very musical. The www.northcreekmusic.com site is worth a look. You can listen to this speaker in the right room without feeling you have lost the last octave of music. At least I can.

I remain,

Well, looks like I'm back in business. I had my electronics tested. The tech said there were no spikes, square waves etc. In fact, he said it had one of the "flatest" frequency response deviations he'd ever seen. so I can trust my Classe gear. BW has sent me a brand new replacement speaker so I'm back to music nirvana.
Thanks to those of you who shared your knowledge.
joeb