Eminence Beta 15 ripole loaded

[ashok]

Hi Rudolf,
A few questions for you.
What are the dimensions of your 15" H frame . Looks like about
19"x19" by depth(19" ?).

Have you measured its response. Do you use any eq and any details on that ?
Thanks.

I have a Delta 15A ( couldn't get any other type) and so will have to build around it. I was also considering a Ypole . Y shaped rear !
I want to use only one driver per side with a 200 watt bass driver amp.

Cheers.
Ashok.

 

[bzfcocon]

I know you asked Rudolf, but I thought it might help: here are my Ypoles with Alpha15A and their response curve (equalized and unequalized, both with a notch filter in place against the TL peak). The bump at the lowest frequences is probably a measurement artefact (measurement has been taken at approx 1 m in the middle of my room, time window pretty long, 30 ms I think)

You can see that I have shorted them from the original length (to push the resonance higher out of the passband). Subjectively, I have preferred to cross them as low as possible (as permitted by the excursion of the midrange), currently 120Hz. Higher up would be theoretically better, but I get an unpleasant resonance.

I dunno what you would get out of the Deltas, which have significantlly lower Qts. Probably you will need more Eq.

 

[bzfcocon]

Response:

 

[Rudolf]

Is the driver baffle in your H-frame centered or offset? It looks centered, but I don't always trust my eyes.

It´s centered. I posted some more details over at audiocircle. Look at reply #3 for eq. I will post the component values for the PLLXO later. And please forget about my rant regarding that 800-900 Hz resonance. I still don´t know exactly what it is, but definitely NOT the H-frame.

Do you prefer the H-frame over your M-frame; and if so, why?

In this case I prefer the H-frame - simply because the driver can move more air.
Generally speaking I prefer M-frames because their dipole separation distance is like that of an U-frame of the same depth (double that of a H-frame).

If I wanted to build a H-frame with two drivers, would it be advantageous to put a separator between the two drivers, kind of like two single H-frames stacked?

Acoustically it will make ABSOLUTELY NO difference. Mechanically it is highly advisable to keep the front/back openings of the frame from resonating by some crossbar etc..

 

[ashok]

Thanks bzfcocon.

I was afraid of that much equalisation. The Delta 15A will need more than that. Possibly another 6dB more at 40Hz.

I have it mounted in a closed box ( about 120 liters) where it has a Qt of about 1.0and a Fc of 60Hz. Obviously doesn't go too deep but the bass is very 'tight'. Hope I'll get the same with the Ypole.
However before making the Ypole I think I will test it out on the open baffle which is ready. Let me see if I can take some meaningful measurements.

 

[Rudolf]

Hi Rudolf,
A few questions for you.
What are the dimensions of your 15" H frame . Looks like about
19"x19" by depth(19" ?).

Have you measured its response. Do you use any eq and any details on that ?

My PLL EQ for the H frame is a 1 kOhm resistor in line and a 6.8 µF cap parallel. In the diagram V1 is the preamp out (or whatever source you have) and 20k is the power amp input (assuming it is 20 kOhm).

 

[ashok]

Hi Rudolf,
That is a 6db/octave slope over the whole working range. Will not suit the Delta 15A . I checked the response curves on Basta!

I think I'll have to first measure the response before deciding what EQ to use.

 

[bigwill]

Can the U-Frame be used without EQ?

 

[Rudolf]

That is a 6db/octave slope over the whole working range. Will not suit the Delta 15A.

OK. I looked up the Delta. An additional 6 dB slope (resulting in a combined 12dB slope) looks more appropriate for that driver. If you see the need for some more EQ - that depends on your definition of working range.
Two things to consider: Don´t try to "lift" any additional roll-off below the Fs of the driver. It will rapidly lead to excess excursion.
Don´t try to use a dipole (excluding pure OB) above its dipole peak. My 6dB slope has to be combined with a steeper low pass filter at the upper end of its passband of course. I believe that goes without saying.

I think I'll have to first measure the response before deciding what EQ to use.

Thats always a good idea. Theory and sims only take you that far.

Can the U-Frame be used without EQ?

Regardless of dipole type you always need a way to compensate for the dipole roll off. At least you will need a driver with "built-in-EQ", meaning a Qts value near 2, if you don´t accept "external" EQ. I understand that some plate amps have a built-in bass lift that could work as EQ.

 

[john k...]

Generally speaking I prefer M-frames because their dipole separation distance is like that of an U-frame of the same depth (double that of a H-frame).

??? I'm not sure how you figure an M frame has greater effective depth than an H.

Acoustically it will make ABSOLUTELY NO difference. Mechanically it is highly advisable to keep the front/back openings of the frame from resonating by some crossbar etc..

There will be a difference. The resonance will be at a lower frequency when there is no divider.

Also see http://www.musicanddesign.com/Gradient_woofer_eq.html

for more extensive info on equalization. There are a lot more possibilities that shelving filters.

 

[Rudolf]

The original question was:
If I wanted to build a H-frame with two drivers, would it be advantageous to put a separator between the two drivers, kind of like two single H-frames stacked?

I answered that there would be NO difference

Originally posted by john k...
There will be a difference. The resonance will be at a lower frequency when there is no divider.

John,
when putting a diagonal separator across the H frame of a single driver, I got the following measurements:

An externally hosted image should be here but it was not working when we last tested it.

I can´t see any difference there. Regarding the proposed example I would - for symmetry reasons - see pressure (and pressure variations) on both sides of that dividing shelf exactly the same. So it should make no difference if the separator is there or not.

Of course you know much more about dipoles than I do, so I would be very interested to know where I am thinking wrong this time.

 

[Rudolf]

??? I'm not sure how you figure an M frame has greater effective depth than an H.

I was talking of frames of the same physical depth. That said I figure it the same way I figure a W-frame has greater effective depth than an H.
Uh, well.
May be I should not have called it separation distance. What I mean: My M-frames show their dipole peak at almost the same frequency as a U-frame of the same size.
If you could give me a bit more time: This weekend I have completed a selection of dipole test frames to compare: M-frame, U-frame, H-frame and Ripole (W-frame) - all of identical depth and front/back area. I will do measurements with the same driver to compare, what they do different. But this will probably take a month until finished.