new idea? to eliminate need for BSC

[pforeman]

Not sure if this is a good idea or not. Still in the planning stages for my open baffle speaker
Could it be done to add a small sealed box woofer in phase, but mounted on the back of the baffle firing backwards, therefore out of phase with the rear output, thus diminishing the cancellation of the front wave?
Probably best to add a series resistor to decrease its output, also this would make for an easier amp load
Paul

[ped]

I believe that's sorta the idea HERE...

[Rudolf]

Originally posted by pforeman

Could it be done to add a small sealed box woofer in phase, but mounted on the back of the baffle firing backwards, therefore out of phase with the rear output, thus diminishing the cancellation of the front wave?

What you are describing is known as a "Cardioid" loudspeaker. Google will show you lots of implementations - and it can be done even without a second driver.

[pforeman]

so thats what that back woofer is for on that speaker!
I was thinking of hot glue melting a box on the back, so it would be removable if not acceptable (for the trial phase).
The woofer would be pass band of around 150 Hz - 300 Hz with simple first order network
I wanted to use a full range on top with a H frame 2X 15 " eminence alpha on bottom, but instead of using BSC, using a rear firing woofer to eliminate the loss from the rear wave cancelling the rear output from the full range.
If the rear woofer was only going down to around 150 Hz, the box wouldn't need to be that big.

[jamikl]

Have I understood Ped's example correctly. I have two Eminence Beta 15 A for an open baffle, but as MJK rightly said they are a bit more difficult than the Alpha for this use. If I put one of them in a reflex box with the cone facing upwards behind the baffle and the port facing forwards through the baffle would the rear eminence, if run out of phase with the open baffle eminence, cancel out the rear radiation of the open baffle eminence. Would the port, being out of phase with that rear driver and facing forward then be in phase with the open baffle driver for its output range. The reflex box would be smaller than ideal and this would also give a lift in the response which may of may not do too much cancelling.

If this would indeed work it should give a lift to the front firing eminence in the open baffle just as it starts to run out of xmax. I don't know though if this would be better than the increase in efficiency of having the two eminence facing forward in parallel in the open baffle. I am very aware that there is no such thing as a free lunch as they say. Any ideas.
jamikl

[jamikl]

Does nobody have any idea whether the speaker by Tekton on Peds link will work or not as per my question which covers how I imagine it is supposed to work.

This is the trend I refer to in another post where all sorts of discussions take place over countless pages with none of the experts agreeing with each other on sometimes pretty esoteric topics but what seems on the surface to be a simple question seems to be ignored.

My thanks to anybody who can take time to offer an opinion, jamikl

[Pintu]

I think it is really good idea.

[pforeman]

That Tekton speaker is interesting.
My Idea was to build something like MJK's 2X alpha plus fostex open baffle speaker, but instead of using baffle step correction, use a smaller baffle for the FR, and use a second woofer (not a full range unit) mounted on the back with a passband of 200 Hz to 3 or 400 Hz to eliminate the back wave cancelling the front wave in this area.
Goal is to retain as high a sensitivity as possible.
Paul

[chris661]

Hi all

I've tried this method of rear-wave cancellation, and it definately works - more bass than the two speakers placed side by side, which is slightly confusing.......

I know it's a very late post, but that's because I had this idea buzzing around in my head (after reading several months back), so I got bored over a 3 day weekend, began cutting up wood etc, and tried it out, powered by a little 7W/channel stereo amp. So, using some cheap woofers from a broken 2.0 powered speaker set, I devised this: (see picture attached) and gave it a try. Now, I'm trying to figure out if the driver at the back should be in a huge box (same lack of damping as the OB speaker), or simply a larger driver, to compensate for the higher excursion of the smaller open-baffle driver. I suspect these measures wouldn't be needed if I used an open-baffle designed speaker, but these are rather
expensive. In contradiction to the above post, I ran both the drivers full-range.

The sound.
These drivers were originally used as woofers, so the very high frequencies aren't as nice as they could be, but this is a basic test.

The bass is pretty punchy, rather than deep and some of the notes in the song Do You Like The Way - Santana (has some deep bass), eluded the drivers used. The overall sheer volume of this set-up isn't up to much, mainly due to the drivers used, which aren't designed for an open-baffle speaker. So, reasonable listening levels only for now.

The plan.
I plan to get hold of some better suited drivers (have some Wharfedale modus speakers, just begging to be tested), and eventually make something with a single full-range driver, which might actually do the complete sound range which would be quite rare for an OB project.

Anyone else wanting to try something similar, perhaps with different drivers?

Chris.

[jamikl]

chris661, thanks for the photo. It made me realise the mistake I made above in that the port of course radiates with the cone, not 180 degrees out of phase therefore there would be no point in aiming the port to the front. Sometimes can't see the wood for the trees!
jamikl