Fast, fun, Inexpensive OB project

[Bratislav]

Originally Posted by Pano

There is floor bounce that is avoided by the gap between baffle and floor.

Now, how is this possible ? The floor bounce is going to be there regardless of whether you have baffle under the bass driver or not. It may be at a different frequency, but it will still be there.
At several 100's of Hz (where it crosses over to Vifa, although it will go higher than that, there is huge overlap), wavelength is still in meters. Can it really be such a huge difference whether you have the baffle extending to the floor or not ?

BTW, another inspirational design, John.

[Rudolf]

EDGE floor bounce simulation for a listening distance of 3 m at 1 m height. This is simulating the woofer only:

One could do a more refined sim with the MJK worksheet, but in general the effect would be the same.

[heinz1964]

Would it help if you cut big holes (like 8 - 10") in the baffle starting under the height of the normal Manzanita?

I have some Tangband W4 1320. Can they be used instead of the Vifa? Or will there be major changes in the crossover.

[ra7]

Originally Posted by John Bsuch

ra 7

When you are working in the OB format, baffle dimensions become very important especially with a passive crossover set up. There is a direct relationship between the distance from the center of the driver to baffle edges relative to lower frequency response shape. If the distance increases, the driver net efficiency usually increases and will extend lower in frequency. The distance the Vifa is from any given baffle edge effects the roll off point and rate. Part of the bargain is that the crossover electrical function and the baffle induced mechanical roll off function combine to acheive a particular total roll off. All of the design elements come together to form a desired outcome and if you change baffle dimensions too much, the magic quickly goes away.

Thanks for the reply, John. I don't have EDGE in front of me right now, but I would imagine the response of the vifa driver would not be affected much by extending the baffle down below. The greatest change would probably occur in the bass response of the woofer.

As Rudolf has shown, the bass extends a little deeper, with slight gain in efficiency, which is what you would expect with a larger baffle. And I also understand that it will probably mess up the target response in combination with the crossover values and design.

But what I'm trying to understand is why you have designed it in this way. I have great faith in your design acumen and I'm sure there is a reason to go through the pains of making a separate stand instead of just extending the baffle. So, John, what is the effect or combination of effects that you have designed into the woofer position and baffle dimensions?

Pano, why would the floor bounce not be there?

[Pano]

I'll let John reply to that. It's his design and he's adamant about the stand mount. Says it just sounds better that way.

[FOXYE]

What C1 cap affects ? bigger value will give less/more treble?

[buzzforb]

Does anybody have some real world measurements of the FR Vifa driver listed?

[heinz1964]

Originally Posted by heinz1964

Would it help if you cut big holes (like 8 - 10") in the baffle starting under the height of the normal Manzanita?

I have some Tangband W4 1320. Can they be used instead of the Vifa? Or will there be major changes in the crossover.

What I meant was. What if you extend the baffle down to the floor. Then cut big holes in it from the bottom up to where the original Manzanitas start.

this way it might still aucustically work as the short Manzanita baffle but look like a full baffle down to the floor and you don't need a stand for them

[John Busch]

The interest in my baffle configuration decision(s) is a bit surprising to me. I made quite a few heavy cardboard prototype baffles. All sizes and shapes. Various wing depths, shapes. Various woofer and tweeter positions. A couple of things stood out during that process.

When the woofer was close to the floor it's response was quite uneven, both audibly and measured. And with larger width, taller baffles I noticed a large peak in the 52-56 Hz area. The greater the total baffle area, the greater the peak. Moving the woofer upward helped a bit. I also noticed that as the baffle narrowed and the woofer was placed 24-30 inches off the floor, the sense of stored energy was reduced by a great deal. It just sounded more natural and balanced and the sound stage also improved. By getting the woofer up off the floor was a kin to adding more distance from the rear wall in terms of sonic performance. I can measure and speculate until the cows come home as to why. But my intuition tells me that when the woofer is closer to acting like it is in free space, (as on a small baffle up off the floor) it is less influenced by reflections from near by surfaces such as the rear wall and the floor. You have to remember that the larger the baffle area is, the more the wall and floor bounce energy will be collected by it. Like it or not, the area behind the baffle forms a cavity at lower frequencies with the rear wall. The bigger the baffle, the bigger the cavity. Long wave lengths act that way in a residential sized room.

Anyway, I made the Manzi baffle large enough to provide some woofer loading, keep the woofer above the rear bass plate to minimize close reflections and still have enough real estate left to optimally load the Vifa in terms of target F = and F peak.

[ra7]

Very curious observations John. In the other thread, What is the ideal directivity pattern for stereo speakers?, it was determined that positioning the woofer next to the floor is one way to eliminate floor reflection. It is interesting that you prefer the woofer off the floor.

You mention that moving the woofer up off the floor is akin to more distance from the rear wall. This, to me, means that when the woofer is on the floor, the early reflection from the floor that is blended with the direct sound from the woofer is more audible (and annoying) than the deep notch produced by the woofer when it is off the floor.