First OB build, with 2x15" + FR.

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
 

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tinitus

diyAudio Moderator R.I.P.
2005-11-24 1:47 am
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
 
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!

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!

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!
 
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.
 
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.
 
Have anyone tried to use foam to separate the top from the H-frame? think a layer on top of the H-frame and place the FR-baffle-driver on top of the foam. That would prevent the vibrations to reach the FR. Maybe not the most effective way but one of the simpler :)

Will try to use wire to mount the FR-driver to the baffle but I doesn't have time to buy the equipment for some days. And I'll search for some wood sticks too...
 
1. I'll first try and stable the Frame with an mdf-board between the sides (and maybe top-bottom)
2. Then I'll probably going to place wool/foam inside the Frame and place triangle woods pieces in the corners.
3. There after I'll try to separate the FR from woofers.

does it sound like a great step-by-step plan?
 
You could place a tube under the H-frame as Stig Erick did, and "float" the fullranger on top of that with the same trick.

The wings of the H-frame will always "flap around" - make it stiffer as good as it gets - or swing the bass chassis inside the H-frame, if you feel for something crazy ...

http://www.diyaudio.com/forums/multi-way/159731-beautiful-swingin-speaker.html


Though those advice' may sound contradictory to you - it works...

Michael
 

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Thanks for the link, had missed it!

I'm not sure if I go for such solution this time, these speakers are for my little brother and he doesn't want it so "advanced" speaker. But I'll most likely gonna make myself a pair later on, than I probably use that mounting solution!

I've just figure put that the crossover point for Alphas are to high, I'm using 4.7mH now... which gives -3dB at ~250Hz. Thinking about ordering a pair of 8.2mH coiles instead... sound it reasonable?
 
Others my better reply to your passive XO questions, but anyway you will have to describe more detailed how your current network looks like.

A single coil / capacitor most certainly will not work very well - except in very rare cases where people *exactly* know why and how to use (for H-baffle a no-go IMO).

Michael
 
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jerome69

Member
2008-02-18 11:33 am
Lyon
....
I've just figure put that the crossover point for Alphas are to high, I'm using 4.7mH now... which gives -3dB at ~250Hz. Thinking about ordering a pair of 8.2mH coiles instead... sound it reasonable?

No because 250Hz -3dB is a good point of crossover, it is my opinion.
Unless you want to improve bass extension ?

Buy a tweeter instead ? :D
 
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I'm using 2nd order filter for both woofer and FR. Just took a relook at the measurement, the woofers starts to fall at 250 and have lost 3dB at 300Hz(?)

FR: 22uF / 3.9mH (+ L-pad circuit ~2.5dB)
Woofer: 4.7mH / 150uF

According to MJK the crossover for the woofers in an H-frame would have 125Hz crosspoint. which would mean that I must double up the coil size, right?

sorry for the bad measurement, done with my half broken iPhone 3G
 

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