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Multi-Way Conventional loudspeakers with crossovers

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Old 3rd February 2009, 04:00 PM   #51
jm_kzo is offline jm_kzo  France
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Hi all, I had not updated this thread for a while, and I apologize for this.

I have been quite busy with finishing my HT room and focused on it instead of this project...
Devils is in the details as you say, and it is what suck time!

Anyway this came to a (first) conclusion around Christmas time.
It is still missingg decoration and furniture, but is it now useable.

The front looks like this:
Click the image to open in full size.


And the back look like that:
Click the image to open in full size.

So, when this cleared from my mind, I could focus again on my speaker project...

You might remember that the drivers I choose where the B&C DE250 compression driver for the high, loaded by a H100 horn and a Beyma 10G40 for the mid.

My target is to cover 20K to 80Hz with those and add a sub (flavour to be decided, but "financially efficient ).

So I had the driver and built a test box for them in order to start measurement (using a home made "Wallin 2" mic pream, a WM61A Pana mic, SpeakerWorkshop and associated "jig").

The box look like this :
Click the image to open in full size.

It is 17 x 36 x 50 (centimeters internal), so the "raw" volume is 30l (minus drivers and events). This is probabaly too much as I am targeting 23l tuned at 60Hz (F3=59Hz).

I did not work on the box or alignment a lot yet... I decided to first focus on the filter...

And it is where my woes started....
[tbc]
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Old 23rd February 2009, 11:58 AM   #52
jm_kzo is offline jm_kzo  France
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[continued]
The filter design has been long and painful... I have abeen a bit on and off on this project, it it was long and hard work nonetheless.

I was really starting from ground 0 and it took me quite some time to understand the basic concepts, but as well to get a measurement-simulation combo that worked which really was necessary to me .

I made a few false start and explored a few dead ends, came back on my steps, started again...

Though there is quite some information available on the web on XO design and speaker measurement, I found it often difficult to understand waht in the mass of information ammplies to your set up and how it applies.

Anyway, I finally got in a position where I can model a XO with Speaker Workshop, measure it and check they are quite close one from each other (1dB to 1.5dB max).

Regarding the filter itself, I tried to follow the "Le Cléach" concepts, exactly a variation of these concepts proposed by Francis Brooke, another French well known DIYer (I think Jean-Michel Le Cléach is well known here as well).

After much iterations, I have currently narrowed down my options to 2 filters.

The first one I called "v6.1" looks like this.
Click the image to open in full size.

Key:
Measure
Simulation
10G40 target, simulation and measure (dotted line)
DE250 target, simulation and measure (dotted line)
Reverse null measure


The second one, that I call "v6.3" looks like this (same key).

Click the image to open in full size.

I have not "voiced" any option yet and I must say that I only hear little differences between 2 versions (but as I have to mount/dismount) filters between 2 tests I cannot really do a quick A/B comparison.

Version 6.1 seems to have a cleaner/more punchy/sharper low medium (might even be "un natural"), but high/high mids tend to be "tiring" and can sound a bit like "disorganised" (hard to translate this).

I would like to work on the enclosure now has I do not get the bass output promised by WinISD or UniBox and it is impacting listening tests.

Currently, bass starts to roll off above 300Hz and there there is hardly "anything" below 200Hz. Simulation says that F3 should be around 60Hz... Not sure where the missing bass has gone.
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Old 23rd February 2009, 11:59 AM   #53
jm_kzo is offline jm_kzo  France
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Reader, if you have any comment/advice on the filters, feel free to fire, you are welcome!
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Old 24th February 2009, 06:48 PM   #54
sek is offline sek  Germany
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Hello Jean-Michel,


Quote:
Originally posted by jm_kzo
I have been quite busy with finishing my HT room and focused on it instead of this project...
Well, first off I'd like to say that I like how the room came out. I would have done differently with the wood tiling and floor, but I really like the colours and build.

I also like the test box and your measurement arrangement, both very simple and clever, straight forward approaches.


Quote:
I did not work on the box or alignment a lot yet... I decided to first focus on the filter...
This is where I'd like to ask some questions before dealing with the filter details.

Are all measurements on axis? If so, the filters seem to significantly shift the main lobe upwards, v6.1 more so than v6.3. This usually indicates either too large mounting distance and/or too strong acoustic phase shift (uncompensated diaphragm offset).

You can see it in the upper range of the 10G40 just below the crossover frequency: the bump around 1.3kHz seems to shift like 100Hz upwards. This also shows through in the reverse polarity plot, again more so in the plot of v6.1 than v6.3.

This phenomenon significantly influences the mid fequency coverage throughout the listening room, as the acoustical crossover point audibly shifts when moving left or right throug the room. This should also be measurable with the microphone off center (i.e. subsequently moving the microphone a couple of cm to either side and taking subsequent measurements).


Quote:
The filter design has been long and painful... I have abeen a bit on and off on this project, it it was long and hard work nonetheless.

I made a few false start and explored a few dead ends, came back on my steps, started again...
Did you consider a digital crossover as a design aid (for prototyping purposes)? Can even be had in software while using Speaker Workshop.


Quote:
I have not "voiced" any option yet and I must say that I only hear little differences between 2 versions (but as I have to mount/dismount) filters between 2 tests I cannot really do a quick A/B comparison.
I like v6.3 as the starting point for v6.4: compensating for the horn length (delay) while also measuring phase response (on axis) and polar response (off axis) as described above.

The delay can only be accomplished reasonably in the digital domain, because otherwise you would end up requiring a huge amount of passive components in order to go through iteration steps.


Quote:
Version 6.1 seems to have a cleaner/more punchy/sharper low medium (might even be "un natural"), but high/high mids tend to be "tiring" and can sound a bit like "disorganised" (hard to translate this).
You are essentially describing tweeter distortion through mechanical modulation (too large diaphragm excursion, too low acoustical crossover point).

But v6.3 looks way better in that regard. It should sound a lot cleaner in the upper end while having a more laid back mid range.

The H100 can't load the DE250 down to it's lowest possible corner frequency. But the 10G40 is forgiving enough to be used that far up (in a high efficiency HT application).


Quote:
Currently, bass starts to roll off above 300Hz and there there is hardly "anything" below 200Hz. Simulation says that F3 should be around 60Hz... Not sure where the missing bass has gone.
This steep rollof is clearly caused by some kind of (electrical or acoustical) filtering action.

As you describe that you can't hear any low frequency output, I recommend an electrical measurement after the amplifier output (both before and after the crossover circuit) using an attenuator before the soundcard input. I suspect a configuration error...

You also mentioned that you didn't look too much into box alignment as of yet. Please post your reflex port dimensions and your T/S parameters (in case they deviate from the datasheet).

As for alignment steps, simply use sand filled up in 1l plastic bags or 1l wood/plastic/styrofoam blocks for playing with the internal volume.

Cheers,
Sebastian.
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Old 22nd April 2009, 07:54 PM   #55
jukkie is offline jukkie  Australia
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Sorry about being really late to the party.

The dudes at the loudspeakerkit have several kits that would suit your purposes:

This one is below your budget:

http://www.theloudspeakerkit.com/sho...&ProcessType=1

But sounds like it would pretty much suit your purposes

And this one is just over your budget, and probably comes with bigger bragging rights:
http://www.theloudspeakerkit.com/sho...&ProcessType=1
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