Need advice on crossover design for Vifa XG18 + Seas 27TBFC/G (measurements included)

[owdi]

I'm building a two way sealed bookshelf with the Vifa XG18 and Seas 27TBFC/G, using a .5 cu ft. enclosure from Parts Express. My first two crossovers were 2nd order electrical at 2khz and 2.2khz, but neither turned out well. In both cases I end up with a 4db dip at 2500 - 3000hz.

This is a gated measurement of each driver, taken on tweeter axis at 1m. I suspect the 2.5khz dip in tweeter response is caused by baffle diffraction, and it's the reason why I'm having trouble with the crossover.



Given these measurements, could someone with a bit more experience suggest a different crossover frequency/slope? I've spent hours in Passive Crossover Designer without finding any satisfying results.

*NOTE: I have an active baffle step compensation filter, so don't need to included it in the woofer's passive lowpass filter.

Dan

[Keruskerfuerst]

1. Is it possible to give the measurements as a text based file?
2. Do you have a loudspeaker construction software like LinearX or Lspcad?

[Pjay]

I used that woofer and it did not look like that. I would look into the measurements first. There is a crossover for a two way, different box, on my site.

www.helarc.com

P

[owdi]

Originally posted by Keruskerfuerst
1. Is it possible to give the measurements as a text based file?
2. Do you have a loudspeaker construction software like LinearX or Lspcad?

ZMA and FRD files

The ZMA files are just an SPL trace of measurements found at zaphaudio.com. The FRD files were created using Arta. I used only FRD consortium's passive crossover designer, nothing like LinearX or Lspcad.

Originally posted by Pjay
I used that woofer and it did not look like that. I would look into the measurements first. There is a crossover for a two way, different box, on my site.

www.helarc.com

P

Measurements were taken using:

Behringer ECM8000 mic
Behrigner UB802 mixer
M-Audio Audiophile 2496 sound card, in 96khz/16 bit mode
The Arta software

The mic was not moved between taking measurements, and things were set up to avoid early reflections.

XG18 Impulse response and gate



Seas H1212 impulse response and gate




Dan

[Keruskerfuerst]

Datasheets for both drivers?

[owdi]

Originally posted by Keruskerfuerst
Datasheets for both drivers?

You can get the datasheets from madisound.

Vifa XG18
http://www.madisound.com/catalog/pro...d51dae79daef14

Seas 27TBFC/G
http://www.madisound.com/catalog/pro...roducts_id=795

Dan

[Dave Bullet]

Hi owdi,

You mentioned you are using the 0.5 cubic foot enclosure from parts express. Where is the tweeter positioned on the baffle?

Suggest you use a baffle diffraction sim. program to confirm your suspicions around the 2.5KHz dip.

Two excellent examples are Svante's Edge and FRD consortiums BDS spreadshset (don't have the links handy).

Also- Zaph uses the same enclosure with the 27TBFCG in his L18 design. Have you taken a close look at the in enclosure tweeter curve? Note his tweeter driver offset on the baffle to smooth out the diffraction ripple. His design would be a very good starting point to tune the 27TBFCG. There's no notch or other shaping circuitry in Zaph's L18 design for the tweeter part of the circuit, so presume the 27TBFCG can provide a nice flat response - esp. since you are crossing higher than Zaph in the L18 design.

DAvid.

[Keruskerfuerst]

Usually, you have to design the cabinet exactly for the drivers, the desired frequency response and Qt.

[owdi]

Originally posted by Dave Bullet
Hi owdi,

You mentioned you are using the 0.5 cubic foot enclosure from parts express. Where is the tweeter positioned on the baffle?

Suggest you use a baffle diffraction sim. program to confirm your suspicions around the 2.5KHz dip.

Two excellent examples are Svante's Edge and FRD consortiums BDS spreadshset (don't have the links handy).

Also- Zaph uses the same enclosure with the 27TBFCG in his L18 design. Have you taken a close look at the in enclosure tweeter curve? Note his tweeter driver offset on the baffle to smooth out the diffraction ripple. His design would be a very good starting point to tune the 27TBFCG. There's no notch or other shaping circuitry in Zaph's L18 design for the tweeter part of the circuit, so presume the 27TBFCG can provide a nice flat response - esp. since you are crossing higher than Zaph in the L18 design.

DAvid.

I looked very closely at the L18 project at zaphaudio.com... so closely that I started with a tweeter crossover using the same value cap and coil. I did perform a BDS simulation. I chose a slightly different configuration than John Kurtke because with my subwoofer stands, the front baffle will look more like a floorstander than bookshelf. Here's the sim:



I really don't know where my measured irregularity in the 2.5khz area of the tweeter's response comes from. Maybe it is my uncalibrated measurement setup, and I'm chasing a ghost.

Dan

[owdi]

Originally posted by Keruskerfuerst
Usually, you have to design the cabinet exactly for the drivers, the desired frequency response and Qt.

I agree. The modeled Qt of the Vifa XG18 in a .5 cu. ft. sealed cabinet is .74

Dan