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Multi-Way Conventional loudspeakers with crossovers

New crossover for my current speakers
New crossover for my current speakers
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Old 25th November 2017, 11:50 PM   #21
EarlK is offline EarlK  Canada
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Quote:
Originally Posted by AllenB View Post
@EarlK, wouldn't an estimate be sufficient?
Allen, I am currently working with estimates ( for the offset ) using anywhere from 1.5" to 2.5" (with the woofers acoustic center set behind that of the tweeter ) .

A few of my mock-ups use 2" as the default offset ( which IME does seem like a lot for such tiny drivers > though the included closeup of the driver offers maybe a different perspective ).

Given Niklas's ( youngish ) age, I'm trying to keep the electrical crossover point right around the 2K mark ( so that he can contemplate having these components for a long long time ) .

New crossover for my current speakers-caw638a-jpg

I have already done some "curve-fitting" to roughly guesstimate an offset .

Here's an FR that belongs to Niklas ( taken from his blog ) that shows his twin subs added to the Morel MTMs .

New crossover for my current speakers-niklas_mtm_fr_m-tning-jpg

Specifically, I hope ( for my own edification ) to get to the bottom of some of the discrepancies seen in the following pic.

New crossover for my current speakers-niklas-curve-fitting-png

One can see there is good general agreement in the shape of the 2K to 4.5K notch ( but not so much, the notch depth ).

- The real problem here is, the displayed notch ( of my working files ) has something like a 4K bottom while in real life, the bottom of the notch ( from Niklas's actual measurements ) is @ 3500hz.
- If I add distance to the woofers offset to get my notch to move over to 3500 hz, then the general shape really goes to hell ( which then leads me to believe I have some errors baked into my files ) .

All my FR & ZMA files were created using tracing software ( of Morels own cut-sheets ).

The .Frd files were put through Blender ( to add 12db hipass & lowpass tails ) before Minimum Phase files were extracted ( for my use within XSim ).



PS; Here's a teaser for Niklas ( this is a few days old using a shallower offset > and is not a finished design )

New crossover for my current speakers-morel-mtm_parallel-xover_2-1k_b-png
Attached Images
File Type: jpg caw638a.jpg (38.0 KB, 228 views)
File Type: jpg Niklas_MTM_FR_mätning.jpg (156.2 KB, 137 views)
File Type: png Niklas Curve Fitting.png (42.9 KB, 128 views)
File Type: png Morel MTM_Parallel-Xover_2.1K_B.png (62.5 KB, 128 views)

Last edited by EarlK; 25th November 2017 at 11:53 PM.
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Old 25th November 2017, 11:56 PM   #22
EarlK is offline EarlK  Canada
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Quote:
Originally Posted by Rullknufs View Post
Thank you very much!

I'm up for it, I just don't know how to start. I'm away for work this weekend but I'm free the whole coming week so I'll have plenty of time for measurements.

Not to worry Niklas, when you're done with your shifts at the plant, I'll give you some guidance on making the measurements that I need .

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Old 26th November 2017, 02:32 AM   #23
system7 is offline system7  United Kingdom
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EarlK, I'm delighted you're having a serious go at "the speaker from hell", AKA the 6" bass. Especially since Lojzek has deserted us for his Peerless PPB 830874 project.

I do hate this one. I never get it sounding quite how I like, and it always seems to force me to a lower crossover than I really like.

I'd take a chance and go for 2" or 5cms acoustic offset here. I have seen some evidence that lively cone material brings the acoustic centre forward, but here we at the damped end with polycone Morel.

I took your idea and ran with it. 1.8mH and 6.8uF per driver is a regular sort of solution with a lot of 8 ohm drivers. I thought that rather than 0.9mH and 13uF, 1mH and 12uF is going to be very similar and easier to get hold of.

Click the image to open in full size.

My modelling is with different drivers, but gives a qualitative taste of what a 5kHz notch (if in doubt, notch higher and shallower...) might do to that troublesome 4.5kHz bump. You can do it two ways, can't you? Because it takes down the midrange a little, the tweeter might need taming a little too. Phase alignment improves for sure. Here's what I got for some second order solutions. But you crack on!

I think your modelling will be far better and more specific than mine.
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Last edited by system7; 26th November 2017 at 02:46 AM. Reason: Changed my mind about the offset from 1.5" ... LOL
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Old 26th November 2017, 09:41 PM   #24
EarlK is offline EarlK  Canada
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Thanks for the encouragement Steve ( and thanks for the link to the older backgrounding thread > I likely wouldn't have participated here if I hadn't read it ).

I'm hoping to learn a few things out of this exercise ( such as the pitfalls of creating and using Minimum Phase files from what are essentially 2D file sources ).

Early on I had tried a 4.5K notch ( though I only tried a series type across the driver with no impedance correction > anyways, it didn't work very well > actually, not at all ).

The parallel notch has worked much better & seems to be an option that Niklas might employ ( or not ) as his discretion .

- My added notch takes 4.5Khz down a good 10db, getting 4.5Khz close to 20db below the pass-band ( a figure that's somewhat an arbitrary & personal threshhold when looking to hide nastiness below the fundamental ).

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Old 26th November 2017, 11:19 PM   #25
Dissi is offline Dissi  Switzerland
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Quote:
Originally Posted by EarlK View Post
which then leads me to believe I have some errors baked into my files
Impedance and electrical response of your teaser crossover are different from what I get. Is there possibly no valid phase data in your zma files?
Attached Files
File Type: zip MorelZmaFiles.zip (8.8 KB, 6 views)
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Old 27th November 2017, 03:52 AM   #26
EarlK is offline EarlK  Canada
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Thanks Dissi

You were right on when your assessment.

I just opened my ZMA files and I found the phase is all a bunch of zeros.

Thanks for spotting that ( as well as posting the correct ZMA files ).

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Old 27th November 2017, 12:47 PM   #27
Rullknufs is offline Rullknufs  Sweden
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New crossover for my current speakers
Now I'm finally back from a weekend at work. So, how do I perform the measurements?
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Old 27th November 2017, 01:37 PM   #28
EarlK is offline EarlK  Canada
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Hi Niklas,

I'll put together a small guide for you and then post it by end of today, ( today = my day, on this side of the atlantic ).
- Then you can start making some measurements.

Also, do you own any other large ( non-polarized caps ) 20uF, or larger ?
- ( it'll be useful as a dc blocking cap when doing the offset tests > though it's use isn't critical > it's more for safety purposes )

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Old 27th November 2017, 03:20 PM   #29
Rullknufs is offline Rullknufs  Sweden
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New crossover for my current speakers
Quote:
Originally Posted by EarlK View Post
Hi Niklas,

I'll put together a small guide for you and then post it by end of today, ( today = my day, on this side of the atlantic ).
- Then you can start making some measurements.

Also, do you own any other large ( non-polarized caps ) 20uF, or larger ?
- ( it'll be useful as a dc blocking cap when doing the offset tests > though it's use isn't critical > it's more for safety purposes )

Excellent, thank you!
No, have no other filter components, only a MiniDSP if it is of any help.
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Old 28th November 2017, 12:25 AM   #30
EarlK is offline EarlK  Canada
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Hi Niklas,

So, moving forward.

Here's an older pic of your setup;

Click the image to open in full size.

SPEAKER Preparations :

(1) Remove both crossovers from the speakers ( we need all 4 capacitors to obtain a largish value, and we certainly don't want those inductors involved here ).
(2) Make sure the woofer wires are paralleled together ( and are marked as such ) and hanging out the bottom port ( extend if necessary with some 2-conductor wire ). Clearly mark on the wires which wire is connected to the positive terminal of the woofers .
(3) Do exactly the same for the tweeter
(4) Wire together ( Parallel ) all 4 of your existing caps and attach one end to the wire that's connected to the positive terminal of the tweeter.

The following diagram shows the wiring configuration ( that we'll be using ) for the 3 drivers being measured. ( Forget about R1, for our purpose here, it doesn't exist ).

Wire your 2 sets of speaker leads together ( woofers & tweeter in parallel ) taking care that the woofer signal is derived from before the 4 inline capacitors ) .

New crossover for my current speakers-curve-fitting-acoustic-offset-calcs-png

MEASUREMENT Location & Orientation ( within your room )

(1)If you still have that nice ( cube like ) white cardboard box ( to the left of the left-most speaker ) , place it within corner of that green carpet ( assuming the box will hold the weight of 1 speaker, if not, use a stool ) .
(2) Place the speaker ( previously ) prepared for testing on top of the box facing at the camera ( that took this pic ) .
(3) Shuffle about both pieces ( speaker & box-plinth ) a bit so that they are a good meter away from any hard objects ( to their immediate left or right ) .
(4) Point your test mic on-axis ( not 90deg pointed upwards ), centered on the tweeter, from 1 meter away.
- Distance from center of each woofer's dustcap, to the tip of the test mic should be the same distance.
- FWIW, make sure you load the 0deg calibration file into REW.
- Make sure that there's a good meter to meter & 1/2 of space behind the mic ( to minimize reflections )
(5) Connect a test amp to the speaker, then connect your computer ( that runs REW ) to the amp ( either directly or through a pre-amp of sorts ).
(6) Open up REW and power up the amp and run some REW pink noise into the system. See if you can with-stand a 90db level ( it's pretty loud, so 80db is also acceptable ).

MEASUREMENTS Needed :

****NOTE**** Don't move the mic ( or speaker ) in between measurements.

(1) Tweeter and woofer together ( as per the wiring diagram above )
(2) Tweeter only ( with the 4 capacitors still inline )
(3) Woofers only ( but still paralleled together as a working pair )

MEASUREMENTS Delivery :

Zip the .mdat file and upload it here within a post.
- If you can't do that, let me know & I'll PM you my email address.

Attached Images
File Type: png DSC_0114_01_hme_setup_sml.png (752.3 KB, 114 views)
File Type: png Curve-Fitting for Acoustic OffSet calcs. B.png (61.1 KB, 102 views)

Last edited by EarlK; 28th November 2017 at 12:46 AM.
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