Need help with project!!!

Hammerboy · « **on:** 25 Apr 2003, 01:02 am »

Hi everybody,
I attempted to build a 2 1/2 way floorstander using two 7" Vifa TC18SG49-08 Parts xpress #297-352 and a Bohlender Graebener NEO3PDRFP PLANAR TRANSDUCER Parts xpress #264-716. I built a 1.9 cu. ft. box tuned to 30 hz. I am using a first order x-over at 3500hz and 250hz. The problem is that there is no bass, none. I am wondering if these drivers aren't capable of bass reproduction or if my box volume is all wrong. Any help would be much appreciated.

JoshK · « **Reply #1 on:** 25 Apr 2003, 01:09 am »

Well I am no speaker builder *yet* but those dimensions sound quite a bit small for those speakers. Is this a ported or sealed design?

JoshK · « **Reply #2 on:** 25 Apr 2003, 01:12 am »

NM the ported/sealed question....what volume do those drivers call for? seems like they would want a lot more than 1.9 ft^3. what is the f3 for those drivers?

Hammerboy · « **Reply #3 on:** 25 Apr 2003, 01:21 am »

JoshK
It's a ported box, tuned to 30hz. The fs of the drivers is stated to be 37hz.

Tyson · « **Reply #4 on:** 25 Apr 2003, 02:52 am »

What's the Vas for the drivers? Remember, you have to double the Vas value when you add the 2nd woofer.

markC · « **Reply #5 on:** 25 Apr 2003, 03:58 am »

And by doubling the vas value, you double the box size.

Hammerboy · « **Reply #6 on:** 25 Apr 2003, 01:09 pm »

The VAS is 1.55cu.Ft. per driver. Is that the box volume I should be using for each one?

JoshK · « **Reply #7 on:** 25 Apr 2003, 02:38 pm »

Yep! 3.10cu.ft.

markC · « **Reply #8 on:** 25 Apr 2003, 09:26 pm »

Also port size, length especially, has a dramatic impact on bass response. If you like, I'll plug in the parameters for your drivers into my box program and let you know what it spits out. Another thought may be to raise the low pass cut off so that you can use a lower value coil to cut down on resistance to the bottom woof. The higher the value of the coil, the more resistance it offers, allowing less power to the driver.

Hammerboy · « **Reply #9 on:** 26 Apr 2003, 12:20 am »

Here are all the T-S Parameters:
* Le: .75 mH * Znom: 8 ohms * Re: 5.50 ohms * Frequency range: 40-4,000 Hz * Magnet weight: 8.5 oz. * Fs: 37 Hz * SPL: 86 dB 1W/1m * Vas: 1.55 cu. ft. * Qms: 2.62 * Qes .58 * Qts: .47 * Xmax: 4 mm
I'm using an Iron core inductor that has a pretty low DCR, but I will try a higher cutoff frequency and see if it helps too. I was also wondering if the VAS is the only way to calculate the proper box volume or is there some redily available software to use as well?

markC · « **Reply #10 on:** 26 Apr 2003, 05:52 am »

My boxmodel program shows an f3 of 45.2 and good transient response and driver excursion for your design. However, if you tune to 39.5 hz, the f3 goes to 41.64. This can be achieved with a 3" dia. vent 10.5" long. This however is for a single driver. When dealing with 2 you cut the vent length in half, so 5.25" should yield an f3 of 41.64. I would also cross the tweeter over as low as possible with a 2nd order filter because the woofer jumps up6db between 1khz and 4 khz. Also have you put an l-pad on the tweet to bring it down close to the sensitivety of the woof? I think that the top end of the upper woof may be over powering the bottom end of both. And if you don't have an l-pad on the tweet the problem is compounded.

Hammerboy · « **Reply #11 on:** 27 Apr 2003, 12:32 am »

Thanks for the info Mark. I have experimented with a couple of L-pads and I've found a 3db one to work well. I am going to start over next week and build a new box and see where it goes from there.