Vented Box Calculator questions?

[Cross Reference]

Good Evening,

I am trying out a speaker calculation program for vent boxes. I picked a driver and used it to see if it would match up with the speaker companys claims? Well it didn't match up? The test driver I used is the Fostex FE-126EN Drivers. They will work in a 10.5 liter box tuned at 61hz with a 2 inch round port and 4.5 inchs long. I understand that. So how come the other program is not matching with companys specs? . I tryed to post the program it but, it would not let me post the program on this web site. C.R.

[xrk971]

Be more specific when you say it didn't match up. I don't understand what the problem is? You put T/S parameters for FE126EN into a BR program (which one?) And the freq response output graph doesn't match the manufacturer's ?

[Bob Brines]

In general, your box program will not match the manufacture's plot because the manufacture doesn't measure his speakers in a standard QB3 box. Everything below 500Hz or so is highly dependent on the box. The problem is that you probably cannot know what kind of box/baffle the manufacturer uses. Most manufacturers do not specify this.

Bob

[Cross Reference]

Originally Posted by xrk971

Be more specific when you say it didn't match up. I don't understand what the problem is? You put T/S parameters for FE126EN into a BR program (which one?) And the freq response output graph doesn't match the manufacturer's ?

The program I am using is at MH-Audio-NL.com. The vented box program. Well to be more specific. This progeam didn't match up with the box size that fostex claims it will work or with the port at all. I was doing a test to see if this worked then I would go on to a woofer tester 2 and use a mic with it. Again maybe I am doing something wrong here? C.R.

[Cross Reference]

Originally Posted by Bob Brines

In general, your box program will not match the manufacture's plot because the manufacture doesn't measure his speakers in a standard QB3 box. Everything below 500Hz or so is highly dependent on the box. The problem is that you probably cannot know what kind of box/baffle the manufacturer uses. Most manufacturers do not specify this.

Bob

Hummm Bob I never would have though of that? Duhhh. Such a simple answer that is the right answer. Thanks Mr. Bob it clears things up. (Speaker Companys who can trust them?) C.R.

[Bob Brines]

Originally Posted by Cross Reference

(Speaker Companys who can trust them?) C.R.

Well, maybe. A driver manufacturer cannot know what YOU will put the thing in, so can't give you any guidance below ~500Hz. You know, baffle step, dipole hump, port output, etc,etc. Most manufactures will use an OB of some sort, usually the IEC standard baffle. Some will put the driver in a box behind the IEC baffle. Seas IIRC actually specifies the box they use, if you happen to want to use that box.

Manufactures get a bad rap for smoothing their FR plots. But the reality is that your ears are going to smooth anything you hear to ~ 1/6 octave, so what is the point of showing a raw 16k point FFT? If you want to hunt down potential problems, look at the impedance plot. If you see glitches in the IR plot, you need to look further.

Bob

[Cross Reference]

Originally Posted by Bob Brines

Well, maybe. A driver manufacturer cannot know what YOU will put the thing in, so can't give you any guidance below ~500Hz. You know, baffle step, dipole hump, port output, etc,etc. Most manufactures will use an OB of some sort, usually the IEC standard baffle. Some will put the driver in a box behind the IEC baffle. Seas IIRC actually specifies the box they use, if you happen to want to use that box.

Manufactures get a bad rap for smoothing their FR plots. But the reality is that your ears are going to smooth anything you hear to ~ 1/6 octave, so what is the point of showing a raw 16k point FFT? If you want to hunt down potential problems, look at the impedance plot. If you see glitches in the IR plot, you need to look further.

Bob

Hi Bob,

Thank you for your insightful point of view. I agree with what you have stated above. I guess I will have to rethink things out and do more research on the drivers I will be using? I am just glad again that I have some insightful help on all of the questions I have on speaker diying. Is there a good book I could buy that can help me out from the bottom and work my way up? Thanks C.R.

[Bob Brines]

Vance Dickason's "Loudspeaker Design Cookbook" might be a good start.

Bob