new idea? to eliminate need for BSC

[Fast1one]

Looks like our hunch was right then, now to figure out where to put the high pass filter Thank you once again for your findings, I got to go try this out for myself.

I do have an idea though, since you already have the set-up done and all

We have the magnet structure facing back for the front driver, why not invert the BSC driver (magnet side OUT) and simply reverse the polarity to remain in phase with the front speaker?

Originally posted by chris661
I know it's another post in quick succession, but I've been tinkering.

I decided I should try to get a LP filter in there somewhere. Then I noticed something handy. For my sub, I made an adjustable LP filter, ranging from 60Hz up to full range. So, using that (dunno what I set it to), I managed to re-enforce the lower midrange, and bass, without making too much higher mid (which doesn't need cancellation).

Sounds even better now. Even the most basic speakers can be made reasonable...

I'll find out what I set the filter to, (probably this evening, as I got school in 5 mins), and report back then.

Remembering that LP filter will definately push this project forwards. "To infinity, and beyond"



Chris

[chris661]

I wasn't aware of the need for a HP filter (perhaps you got mixed up with Low Pass...)

Anyways, I got some 4" with whizzers for free, so I'm playing with those atm.
8" Pioneer woofer for cancellation, sounds like overkill but does the job. And a big baffle (3'x2'), with the driver off-set on every dimension, so the wavelengths for cancelling are all different, so it would be an area of cancelling instead of the narrower band associated with square ones, with a central driver.

Big baffle is definately better, so I am looking for spreadsheets for calculating optimum baffles etc, when I get some of the 5s mentioned earlier (they were out of stock).

Chris

PS, your idea of reversing the cancelling speaker sounds like a good one. I'll let you know how it fares here.

[Fast1one]

Originally posted by chris661
I wasn't aware of the need for a HP filter (perhaps you got mixed up with Low Pass.. .)

Anyways, I got some 4" with whizzers for free, so I'm playing with those atm.
8" Pioneer woofer for cancellation, sounds like overkill but does the job. And a big baffle (3'x2'), with the driver off-set on every dimension, so the wavelengths for cancelling are all different, so it would be an area of cancelling instead of the narrower band associated with square ones, with a central driver.

Big baffle is definately better, so I am looking for spreadsheets for calculating optimum baffles etc, when I get some of the 5s mentioned earlier (they were out of stock).

Chris

PS, your idea of reversing the cancelling speaker sounds like a good one. I'll let you know how it fares here.

Yes that is exactly what happened, I meant lowpass, my apologies.

Offsetting the driver on the baffle is a very good idea. Looks like you are making good progress!

[chris661]

The big baffle, after a longer listen, resonates too much, so I'm experimenting with re-enforcing it... Nothing that will affect the sound, but hopefully stop it vibrating so much...

There's a definate need for higher-sensitivity drivers here, as even with 50W, it rarely extends above average listening levels, unless the music is highly compressed, which is when the baffle vibration comes in and adds wierd bass and lower mid...

I think I should go for a more medium-sized baffle, 2'x1', again with the driver offset, with some form of weighting (I've heard of OB speakers weighing over 43Kg - the weight of a 13 year old!)

I'll try weighting the 3'x2' baffle, but I'm not sure this will help as much as with the smaller ones...

At the end of yesterday, my favourite set-up was the 3" woofer for cancelling (in the previous picture) and the 4"+whizzer of OB. The difference between the 3" and the 4" is fairly minimal, except the 4" has higher sensitivity.

Thanks for all the encouragement

Chris

PS - any progress with the OB car project?

[Fast1one]

No progress yet. I just finished my third year in college and I am in the process of moving. It may take a couple weeks to actually start experimenting since I start my internship on Monday.

As far as the baffle goes, I found that you need to add some form of bracing to stop it from vibrating. But more importantly, using multiple layers is a good idea. I used two 3/4" (~19mm) sheets of Birch ply, cut the necessary holes, and glued them together. I have heard that using another material (say, vibration dampener) between the sheets is a good idea but couldn't find anything affordable at the time.

In addition to that, I am using a wooden brace perpendicular to the baffle, pushing the woofers against the OB. If that makes any sense...

[chris661]

Yes, that makes sense.

Something like might work - I have something similar under my speakers, to reduce the vibration going downstairs... Definately helps.

After messing around, a piece of 12mm MDF 20cm by 35cm, with a 4" hole drilled in one end is doing well, but those 4" drivers aren't that nice... but they were free so I can't complain.

I think this is the point where finance comes in, as a nice pair of full-rangers will cost a lot...

I may try the idea of 2 pieces stuck together, but the wood supply is short (using bits from the garage), so I might have to chop and change the bits of wood I have.

Which speakers are you using?

[Fast1one]

I am using the Fostex FF85KeN, the modified versions from Dave at Planet10. Baffle size is 42 x 20 inches IIRC with two Pyle Pro PPA15s per side (the ones with favourable OB specs). Here is the development and build thread: New project underway: Fostex and Pyle Pro

BTW, those pictures only show the temporary feet and no brace. I'll have to take updated pictures later.