First OB build, with 2x15" + FR.

[oLjud]

Hi all,

I've just put together a 2-way OB speaker with 2xAlpha15a + Fostex FR166En per side with some help from this thread: What fullrange for OB?


I've done a measurement on the woofers, they play up to about 250Hz (12dB/oct filter), when I measured from 1m I got a 3dB resonance between ~200-250Hz. But since I only have iPhone to measure the speakers the response aren't to accurate.

I've tried to burn/play in the woofers with 20Hz sinus tones with the woofer out of phase and I already here some improvements. So now I only has to burn in the FR aswell...

The crossover for the speaker are:
Alpha 15a: 4.7mH and 150uF (12dB/oct)
Fostex: 68uF and 3.9mH with L-pad -2.5dB

Must say it sound awesome! Even thou I going to tweak the crossover, the cabinet and much it looks really promising! My main task now is to lower the frame-vibrations, the FR vibrates to much at the moment. When I placed a "hifi mouse" (to suck up all vibrations) the sound improved alot.

what do you fellas think of the build so far? Any suggestions how to eliminate the vibrations?

Best regards
Mikael Hörnqvist

[jerome69]

Hi

Originally Posted by oLjud

what do you fellas think of the build so far? Any suggestions how to eliminate the vibrations?

Nice work !

You can place between the woofers a plank ?

Regards.

[oLjud]

Hi!
Thanks for the reply! That's one thing I planing to do, have some MDF-board left. Most of the vibration problem lies on the top, but I'll guess if the "side" vibs gets reduced so will the top vibs be reduced aswell.

[tinitus]

Originally Posted by oLjud

what do you fellas think of the build so far? Any suggestions how to eliminate the vibrations?

Best regards
Mikael Hörnqvist

looks nice

"Free" edges always vibrate

regarding your FR baffle vibrations, you could try with one or two wooden sticks
connecting the free vibrating top to top of woofer frame

and I might try with foam inside the H-frame
and I might fill inside corners with wood
and ditto between woofers
wood would be triangles

[ra7]

Good work man.

Magnet mount the FR driver and keep that section independent of the woofers. The other way would be to just separate the baffle of the FR from the woofers. Keeping them independent of each other would rid you of the vibrations.

[skorpion]

Yes, you must separate bass- and fullrange baffles. That is mandatory to get the very best results. See my thread: The BlindStone OB . I would rather make a triangle of the upper baffle instead of circular because of response adversities. No doubt it sounds good already, but it will be bettered.

/Erling

[oLjud]

Originally Posted by tinitus

looks nice

"Free" edges always vibrate

regarding your FR baffle vibrations, you could try with one or two wooden sticks
connecting the free vibrating top to top of woofer frame

and I might try with foam inside the H-frame
and I might fill inside corners with wood
and ditto between woofers
wood would be triangles

I got some foam so I might try that, and i'll check if I got wood enough to place in the corners! thanks!

Originally Posted by ra7

Good work man.

Magnet mount the FR driver and keep that section independent of the woofers. The other way would be to just separate the baffle of the FR from the woofers. Keeping them independent of each other would rid you of the vibrations.

yeah, maybe it's best to separate the FR from the woofers as you says. thanks!

Originally Posted by skorpion

Yes, you must separate bass- and fullrange baffles. That is mandatory to get the very best results. See my thread: The BlindStone OB . I would rather make a triangle of the upper baffle instead of circular because of response adversities. No doubt it sounds good already, but it will be bettered.

/Erling

yeah I'd looked at it a few times, looks really effective! The circular shape was most only made because I have limited MDF board and had to use what I got. thanks!


I'll check out all this suggestions soon!

[chris661]

Fostex drivers seem to take a long time to break in.

I got some Fostex FE126eNs from Dave, and it took a really good thrashing (6mm p/p excursion for hours at a time) to get them sounding nice. Before that, there was too much sibilance. Put them face-to-face (out of phase) and play some bassy music on repeat, while covering the drivers with a blanket. The first time, watch through the track and listen for the drivers hitting the back plate. While it's difficult to get them to bottom out, it's not impossible. The voice coil will suffer damage if it's being smacked into the magnet on a regular basis. When you have the level adjusted, leave them to it for a couple of hours, then come back and have a listen. There will likely be a difference. It's recommended to be gentle at first, so I gave them a few weeks of moderate use, before going for it.

Chris

PS, I used YouTube - Radiohead - In Rainbows - 15 step as it has notes down to ~30Hz, giving plenty of excursion. All you need now is a repeat button for youTube.

[oLjud]

Originally Posted by chris661

Fostex drivers seem to take a long time to break in.

I got some Fostex FE126eNs from Dave, and it took a really good thrashing (6mm p/p excursion for hours at a time) to get them sounding nice. Before that, there was too much sibilance. Put them face-to-face (out of phase) and play some bassy music on repeat, while covering the drivers with a blanket. The first time, watch through the track and listen for the drivers hitting the back plate. While it's difficult to get them to bottom out, it's not impossible. The voice coil will suffer damage if it's being smacked into the magnet on a regular basis. When you have the level adjusted, leave them to it for a couple of hours, then come back and have a listen. There will likely be a difference. It's recommended to be gentle at first, so I gave them a few weeks of moderate use, before going for it.

Chris

PS, I used YouTube - Radiohead - In Rainbows - 15 step as it has notes down to ~30Hz, giving plenty of excursion. All you need now is a repeat button for youTube.

Thanks for the advice!
I'll break in the drivers tomorrow, the way you mentioned.

[jwmbro]

Originally Posted by chris661

All you need now is a repeat button for youTube.

www.youtubeloop.com