looking for an OB Fullrange driver (Alpha 15a)

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JeffB

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Re: looking for an OB Fullrange driver (Alpha 15a)
« Reply #20 on: 5 Jan 2018, 07:36 am »
I have an open baffle system I built.  It has been shelved for some time because I need to figure out how I'm going to deal with baffle step correction.
It consists of a 15" woofer on a 48" x 18" flat baffle.  The woofer is no longer made, but it was inexpensive with high Qts and high efficiency and I love it.
For the mid/high frequencies I can alternate between two drivers.  I have drilled holes for both of them, but run only one at a time.
One is the Visaton B200.
The other a 3" Tang Band w3-871, no longer available.

I am using  a JVC surround sound receiver to provide a cross-over to the woofer.
Without baffle step correction, the system sounds best crossed at the highest frequency allowed by the receiver 200Hz.
The woofer sounds excellent at this cross-over point, but it sounds even better crossed at 150Hz and better yet crossed at 120Hz.

The Visaton B200 has some great midrange magic.  However, without baffle step correction and its naturally rising response the top end is a little hard to take.
I suspect it can be tamed with the right network, but how that would effect the midrange magic I do not know.  The top end other than being bright though is not too bad.

The Tang Band w3-871 clearly has more accurate high frequencies than the Visaton B200.  As a whole I find the w3-871 more enjoyable than the B200.
Both drivers really need some baffle step correction to get flat to 200Hz.  Still the w3-871 seems flatter than the B200 across the listening band without any correction.
The setup with w3-871 almost works, and the system plays as loud as a care to listen, although it is not concert level loud by any means.
I suspect with a corrective filter though that I might run out of volume head room.  The bottom end of the w3-871 sounds great, but doesn't quite have the magic of the B200 in the lower mids.

Maybe someday I will run this setup as 3-way baffle step corrected.

I will also mention that I have experimented with wings and that creates resonances I don't like and it effects dipole dispersion.
I really think a flat baffle is the way to go.  It is also easier to move around.

I am really curious about the Tang Band 5" w5-2143.  I have never heard it.
The frequency response graph looks too good to be true.
The on-axis response graph is better than the 4" and 6".
I'm thinking that if I wanted to make a 2-way work this might fit the bill.

FullRangeMan

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Re: looking for an OB Fullrange driver (Alpha 15a)
« Reply #21 on: 5 Jan 2018, 05:58 pm »
Without baffle step correction, the system sounds best crossed at the highest frequency allowed by the receiver 200Hz.
The woofer sounds excellent at this cross-over point, but it sounds even better crossed at 150Hz and better yet crossed at 120Hz.

The Visaton B200 has some great midrange magic.  However, without baffle step correction and its naturally rising response the top end is a little hard to take.
Avoid active correction on the B200 use only 5 or 10mm felt over the baffle, active correction will blur the image and cut the sweet B200 harmonics.

MJK

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Re: looking for an OB Fullrange driver (Alpha 15a)
« Reply #22 on: 6 Jan 2018, 04:31 pm »
It has been shelved for some time because I need to figure out how I'm going to deal with baffle step correction.

There is no baffle step phenomenon in an OB speaker, this only occurs in boxed speakers where the rear wave from the driver radiates into the enclosure. Baffle step typically occurs in a boxed speaker in the several hundred Hz frequency range where the sound transitions from omni directional to forward directional based on the front baffle dimension.

In an OB speaker sound is radiated forward and backward so no baffle step will occur, low frequency cancellation will occur based on baffle size and woofer fs and Qts but this is a different design issue. Whatever problems you are hearing in your OB speaker is not baffle step, probably crossover design or a mismatch in driver output level between the woofer and the other driver(s).

JohnH12

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Re: looking for an OB Fullrange driver (Alpha 15a)
« Reply #23 on: 7 Jan 2018, 01:27 am »
As you are running a flat baffle you have the ability to run the 15 incher up to 500 to 1,000 then crossover to the 3 inch TB.  It's tough to design a OB without measuring but with an electronic 2-way crossover you would be able to tune your system more than what your surround receiver can do.

You can find some of the used Behringer, ART, or Dbx electronic x-os cheap or your could do the Rolls https://www.parts-express.com/rolls-sx21-tiny-two-way-crossover-w-level-controls--245-1182.

Then there's a mini dsp...

planet10

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Re: looking for an OB Fullrange driver (Alpha 15a)
« Reply #24 on: 7 Jan 2018, 01:42 am »
As you are running a flat baffle you have the ability to run the 15 incher up to 500 to 1,000 then crossover to the 3 inch TB.

MJK’s passive baffle article is the quintessential guide to using a 15” and a small FR in an open baffle. Well worth following even if you are going active. A 2nd order filter with offset turnovers to deal with baffle response. Few 15” will reach 1kHz, Martin XOs the 15 in the mid 200s and the small FR in the mid 400s IIRC. Martin used a Fostex FE103e but later user implemenrtaions (including ours) was that the less efficient FF85k 3” was a better fit.

http://www.quarter-wave.com/OBs/OB_Theory.html

dave

JeffB

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Re: looking for an OB Fullrange driver (Alpha 15a)
« Reply #25 on: 7 Jan 2018, 02:58 am »
Thanks for the comments.  I was really just trying to convey my impression of the B200 and w3-871.

I used the term "baffle step" perhaps too loosely.  I do understand that it is the back-wave canceling out the front-wave that needs to be accounted for.

I do have some fears moving forward though.
The first concerns how accurate a model I can get with a tool like Basta.
The second concerns how accurately I can measure the response.
I purchased a calibrated microphone a few years ago.  It has just sat in its box.  I don't know if it requires re-calibration or if usage will cause some break-in and then then need re-calibration.
I naively assumed the microphone itself was somehow tuned.  Instead I just have a sheet of paper with calibration numbers.  I don't really know what to do with these numbers.  I need some software that I can input them into and that will correct its display output accordingly.
I don't have a stock room full of inductors, capacitors, and resistors.  I don't look forward to having to tweak a circuit by experimenting with such parts.
So I lean towards something like mini-dsp.
Having to buy mini-dsp to further what was intended to be an inexpensive experiment is not too appealing.  If only I had money to burn.
I don't really have a great space for an 18" wide baffle.
If I ever get this right and want to live with it, I need a better looking baffle.
Unfortunately for me, I have heard the potential.  I'm sure someday I will get this working.

MJK

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Re: looking for an OB Fullrange driver (Alpha 15a)
« Reply #26 on: 7 Jan 2018, 12:40 pm »
The first concerns how accurate a model I can get with a tool like Basta.

Accurate enough to design an OB geometry and crossover that will work the first time, you will not need to have a whole box of parts to tweak the crossover after the fact. Assuming your drivers are good quality and well behaved, a simulation using measured T/S parameters (if possible measured impedance and SPL) in a program like BASTA should be sufficient to get you 95% of the way to your final system configuration. Building an OB speaker without some measurements and simulation is nothing more than guess work and wandering around in the dark as you try to optimize the results. Quickest way to an optimized result is to engineer the design using measurements and simulation.