My first OB loudspeaker, seeking advice.

[Kim Schultz]

I have decided to make an OB loudspeaker after having listened to this experimental setup.


This is inspired by Simon's OB with Eminence and Skytronic drivers.

My project will use an Eminence PSD2002 driver with a 90 degrees OS waveguide as tweeter. I had the driver already, and it was easy to remove the backchamber to make it dipole.

The mid will be an Eminence Beta 8a and the woofer a Fostex FW405.

The Beta 8a will cover as much as possible and hopefully run wide open without any crossover.

The tweeter will use a single cap and a lpad to bring the level down, to match the mid.

The Fostex will be in a H-baffle with a separate woofer amp and electronic crossover.

I have played around today and can see I need to have the front of the Beta 8a, about 7cm back compared to the mouth of the waveguide. This is need to time align the drivers.



I can do this by mounting the horn flush with the baffle, and then mount the mid on an extra spacer behind the baffle, with a 90 degrees flare out to minimise reflections.

After reading some info about OB's I don't know how wide I should make the baffle.

The H-baffle will be about 45cm wide, and I thought about a 40cm wide baffle for the mid to help it go down lower, but I don't know if it is to wide.

I've also considered to make the baffle ready for a second mid like the Bastanis loudspeaker.

This would mean the tweeter will be lower than the mid, is this ok?

Should the drivers be offset on the baffle, or placed in line ?

Thx in advance, all help appreciated.

[tinitus]

Originally Posted by Kim Schultz

and the woofer a Fostex FW405.

thats a very expencive woofer

any special reason to use Eminence PSD2002 driver ?

[Kim Schultz]

I have it from an old 3way studio type loudspeaker, and the previous owner had it refoamed with a smaller roll surround.
This has caused the fs and qts to go up a bit and actually making it better for OB, it sounds quite good in the simple baffle.

If the mid and tweeter section turns out good, I might get a more suitable woofer later.

Only reason for using PSD 2002 is that I had it already and it was easy to remove the backchamber.

[tinitus]

Originally Posted by Kim Schultz

I need to have the front of the Beta 8a, about 7cm back compared to the mouth of the waveguide. This is need to time align the drivers.

why ?

btw, Im still waiting for someone to try diaphragm coating on Beta-8

[Kim Schultz]

I needed to move the the tweeter forward to have the impulse measurement align.

Simon did ENabl his Beta8 and some coating too I think.

[tinitus]

Originally Posted by Kim Schultz

I needed to move the the tweeter forward to have the impulse measurement align.

caused by crossover ?

[tinitus]

Originally Posted by Kim Schultz

I've also considered to make the baffle ready for a second mid like the Bastanis loudspeaker.

This would mean the tweeter will be lower than the mid, is this ok?

Should the drivers be offset on the baffle, or placed in line ?

with double Beta-8 I would suggest to use them as 2.5way (MMT)
and upper 8" would be your listening height

With a compression driver especially Im not sure its wise with just a small series cap
and you may best try to match its rolloff with that of the midrange
not too difficult, but still a bit more tricky than just a small series cap

btw, your impulse measurement will change with a crossover

[Kim Schultz]

I'll experiment with a test baffle and some different crossovers tomorrow, to see how it affects time alignment.

[Godzilla]

Good luck with your project. I see you have some neat waveguides turned over there. I am curious how the Beta 8 sounds to you without a circuit and on open baffle.

Zilla

[Kim Schultz]

I had a board 38cm x 68cm already cut that fit nearly perfect, so I used it to make a test baffle.

The mid driver is mounted behind the baffle with the edge rounded over, the waveguide is mounted flush and offset to the left, in case I want to use another mid below the other.

The measurements are taken 1m out and 30cm to the right.

The mid is run wide open and the tweeter with a 1uF series cap.

I think it looks very promising.

Sorry for the crap photos, they were taken in poor light with my phone.