Question about transfer function magnitude.

[massappeal129]

Hi,

I'm a novice speaker DIYer and want to build a sub-woofer cabinet for a Peavey Lowrider 18" PA sub-woofer. I've been playing around with plots on winisd pro and have a question.

Initially I thought to tune a vented box to produce as flat a transfer function magnitude plot as possible was desirable. At a certain point increasing the tuning frequency of any particular box volume I play with creates a hump or knee right before the lower end drop-off in transfer function magnitude.

Assuming a PA sub-woofer such as the Lowrider has a natural decrease in frequency response as it plays lower, would an intentional hump right before drop-off actually be beneficial in compensation to the drivers natural decrease in efficiency, and thus creating a true flat frequency response? I realize of course this would change the f3 point of the speaker, and I suppose an accurate measurement of the speakers free air frequency response would be necessary to actually determine at what rate its natural frequency response deteriorates.

Tell me what you think and thanks for the help.

[mashaffer]

I don't think so. The response plot is showing you the effect of the drivers parameters and the box design. The room you use it in will also often give a boost in the bass. if you intentionally put a mid bass bump in there you are likely to get a one note bass like the rappers in the Hondas with fart cans get.

I would rather have a slight bass shelf (google EBS subwoofer). With the 18" LR you are looking at almost 15 cubic feet and a couple of 4" diameter vents to do this and you still would start to roll off at about 30Hz.

Are you going to use this for sound reinforcement? If so a higher tuning is probably advisable since you won't have as much room gain and you are really just wanting good solid output down to about 40Hz. This would get your box down to about 10 cubic feet.

This driver might be a good candidate for a transmission line.

mike

[massappeal129]

Thanks for the help.

I will be using this for sound reinforcement and would really like it to play as low as it can. I intend to use a graphic equalizer for the whole system and therefore maybe none of my initial questions really matter, being that I can just attenuate the room gain and make other adjustments with that.

So you figure I should just shoot for a close to flat transfer function magnitude plot?

[massappeal129]

Never mind. It turns out I was modeling an EBS system all along. Unfortunately I can't go any larger than approx 9 cubic feet, which is around what you were recommending anyway for sound reinforcement. Anything larger than that would probably be too heavy or too large to fit in doorways. Thanks again.

[mashaffer]

No charge. Glad you got it figured out.

mike