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Multi-Way Conventional loudspeakers with crossovers

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Old 12th August 2007, 09:52 PM   #1
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Location: Wellington, New Zealand
Default Calling Johan - Seas L26 + L18/L15 + 27TBFCG

Hi Rojah / Johan,

Thought I'd start a new thread for similar projects we are working on rather than threadjack this one:
Need help selecting a driver for my 3 way

I too am looking at an all metal 3 way. Using Seas drivers, I chose the L26 and 27TBFCG. I intend to go passive and have also got an L15 for the upper bass / midrange.

I know you are planning a L26/L18/27TBFCG, basing the mid/tweet crossover on Zaph's successful L18/27TBFCG.

I'm not sure I've picked a good mid for a true 3 way. The L15 is a bass/mid and the tweeter crossover point is limited to about 2KHz (or 2.5KHz depending on who you read) due to breakup (at about 8KHz).

I'll post some baffle simulations here and crossover ideas. Would be good if you don't mind sharing your approach. We might even have a couple of metal 3 ways for people to choose at the end of it (which seems to be lacking in the DIY area - at least ones that use a 10" woofer).

Cheers,
DAvid.
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Old 4th September 2007, 09:29 AM   #2
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It's a slow moving project...

Here's a candidate crossover simulation and modeled on-axis (and reverse null) response.

Cavaets:
These are re-used driver measurements with simulated baffle diffraction added in
HBT generated phase using -1.018 and -7.677 inches for L15 and L26 offset respectively
SpeakerWorkshop used for crossover modeling

First the crossover:
Attached Images
File Type: jpg crossover.jpg (49.3 KB, 668 views)
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Old 4th September 2007, 09:34 AM   #3
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I've aimed for 4th order acoustic slopes. Reason being - kill the resonances of the metal cone drivers - 4KHz and approx 8Khz for the L26 and L15 (respectively). Crossover points are 240Hz and 2400Hz.

I'd like to cross the L15 lower to the tweeter (say 2KHz) and eliminate as much 2nd / 3rd order distortion as possible.
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Old 4th September 2007, 09:36 AM   #4
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Here is the modeled reverse null (L15 out reverse phase) - normally all 3 drivers are in phase (which seems odd to me).
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File Type: jpg reverse_null.jpg (90.7 KB, 611 views)
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Old 4th September 2007, 09:37 AM   #5
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Default 3 way - Seas L26 + L15 + 27TBFCG

And finally impedance. Minimums are around 3.1 ohms
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Old 4th September 2007, 11:23 AM   #6
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by Dave Bullet
- normally all 3 drivers are in phase (which seems odd to me).
Hi, perfectly normal, not odd, for 4th order acoustic slopes, /sreten.
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Old 4th September 2007, 11:15 PM   #7
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Thanks sreten. Good to know. I just haven't seen a 3-way where all 3 drivers are wired with the same polarity so assumed I must have done something wrong (well, I probably have somewhere!).

Although 14 components aren't bad for a passive 3 way crossover (esp. considering metal drivers are used and cone breakups must be dealt with), it will be expensive. I will try and rationalise it down. I'll also include a padding option of the upper mid / treble response for bright rooms.

baffle simulation to be posted...
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Old 5th September 2007, 04:55 AM   #8
simon5 is offline simon5  Canada
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Let say alot of cheap 3 ways are probably 2nd order acoustic slope... so that means 2nd driver out of phase. Also alot of exotic designs are built with as few crossover components as possible, because for that kind of designers, less is more.

2nd order = 180° out of phase, so reverse polarity on the center driver and it's back in phase.

4th order = 360° out of phase, but 360° = 0°, it's a full turn, so you're back in phase, all drivers need to have same polarity.
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Old 5th September 2007, 09:41 AM   #9
sreten is offline sreten  United Kingdom
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Hi,

I suppose that for most 3 ways 4th order acoustic bass to mid
is not an option as it uses too many parts, therefore bass/mid
are usually out of phase.
Tweeter may be in / out with the mid depending on c/o.

/sreten.
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Old 5th September 2007, 09:59 AM   #10
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Quote:
I suppose that for most 3 ways 4th order acoustic bass to mid
I really struggled with getting good phase tracking with 2nd order acoustic between woofer / mid (a bit beyond my design capabilities... ), so resorted to 4th order.

I will try again since I would like to minimise the parts count.

I wasn't happy with a 2.4KHz xo point with the L15. The breakup is 8KHz and I wanted to be 2 octaves clear of it.

I've modified the crossover and got a smoother response that has even better phase integration and brought the tweeter level down. However - I feel it might be a little too low now (1725Hz). Although 4th order acoustic has been maintained on the tweeter and it is only 5dB higher through the mid stopband than the previous version.

Thanks,
David.
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