First time OB builder

[Silent Screamer]

Yes that was my observation too. The Raal / 12MUs lost their beautiful natural sound and become quite tinny sounding on the wide baffle. I dropped the xover back from 4000 to 2500 and it helped a lot.

This is only a test baffle but if I was staying with these drivers I would narrow the baffle around the tweeter and mids.

I was hoping the new Raal 140-15D AM dipoles would have turned up yesterday but they got posted too late. I'm leaving the baffle as is for now so I can try the dipoles in the same arrangement, then I will start on a new baffle with H box on the bottom.

Not sure what I will replace the 10" Vifas with yet but will look at that after the H box is done to see if they are still required.

Extremely happy with the sound so far.

[jerome69]

Originally Posted by Silent Screamer

Not sure what I will replace the 10" Vifas with yet but will look at that after the H box is done to see if they are still required.

Sure they will be more required. A H frame cannot be use after 100Hz.
Perhaps you will have to cut below 100Hz.

[Silent Screamer]

Thanks Jerome my original plans were to cut over lower, but the 12MUs just won't go low enough. Just out of curiosity why a 100Hz cut off? Does the H frame dictate this?

[studiotech]

Originally Posted by Silent Screamer

Thanks Jerome my original plans were to cut over lower, but the 12MUs just won't go low enough. Just out of curiosity why a 100Hz cut off? Does the H frame dictate this?

100hz is not a hard and fast number. It depends in the dimensions(depth) of your H. See here for 1/4 wavelength calculations to determine it's resonant frequency:

http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf

[Silent Screamer]

Thanks Greg I went to download it and found I already downloaded 4 days ago, but I haven't read it yet. That looks exactly like what I need to work out cabinet dimensions.

[jerome69]

Originally Posted by Silent Screamer

Thanks Jerome my original plans were to cut over lower, but the 12MUs just won't go low enough. Just out of curiosity why a 100Hz cut off? Does the H frame dictate this?

No you can't go lower than 800Hz with one 4", there is a relation (known by experiment) with the surface and the point of crossover (to minimize distortion), in an OB you move air and you need surface. Perhaps you can go near 400Hz with 2x12MU ?

Yes 100Hz is an experimental approximative number when you use 2x10" in the H Frame It is just a point of reference for discussion.
Imagine a 18", bigger the point will be lower.

[StigErik]

I run my dual 21" H-frames up to 200 Hz.... works like a charm.

The point is that you should not go above the dipole peak, which in my case is around 200 Hz.

[Silent Screamer]

I asked Tc Sounds for a frequency response but to date they haven't responded to my request. What does the dipole peak look like?

[StigErik]

Dipole peak described in details. In this example at 680 Hz.

Electro-acoustic models

[jerome69]

Originally Posted by StigErik

I run my dual 21" H-frames up to 200 Hz.... works like a charm.

The point is that you should not go above the dipole peak, which in my case is around 200 Hz.

I am not very agree with that, I think an octave below the dipole peak
But if you ears support this that is OK. Mine not.