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Conversion of Monitor Audio Monitor 11 to Active Crossovers


bencat
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Right this is the start of what might end up to be a very long thread . Apologies in advance to thise that will lose patience but due to my inexperience in trying anything like this there are many stupid questions I will need to ask .

Day One

Stripping of the Monitor Audio units down to component parts . I have taken the useful hot weather as an excuse to start getting these two units stripped out of the cabinets so that I can look and photograph everything . Sorry for the poor quality of the images these are all phone pictures . I may well get my camera out for later but at the moment my pc is locked in a disc copy so everything is slow .

So hopefully in sequence is a picture of the units complete . Then the bass and tweeter units . Then the crossover and then the empty cabinet . Both bass units were twinned to the earth connectors on the crossover then split to an Inductor and resistor each . Resistors were different in both cases with one a 10 Ohm the other a 3.3 Ohm . Think this means they were connected together and can be treated as a single unit but not certain . However as they are identical units I am going to treat them as one for this build.

 

 

 

 

Sorry ran out of space to post more pictures so will need to have a think about what I need to do to post the others .

 

https://bencat57.imgur.com/all/

Edited by bencat
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Use a Flickr account - upload to that, then post a link in here. The forum software will embed the pic in the thread. Flickr will give you more storage than you need. You have to make the image public on Flickr for this to work.

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Or imgur, which is definitely still free. Create a free account, upload your images by creating albums if you are neat and putting them in there, otherwise don't and just have images on your board on imgur. You get to choose whether to keep them private or shared with the imgur community, your choice.

Once images are uploaded, choose the image, there will be a drop down menu, choose copy link and copy the BB code for forums.

Paste on to your thread, easy peasy...

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Right I now have a plan of action . I am going to get the Speakers prepared and inside and out side finished before I try any attempts at the crossover. I have only been able to remove one of the passive crossovers and have used this to work on and give me directions of what to do with the other still in the speaker.

These have a hard wired crossover attached to a piece of MDF which covers the rear cut out . So will just snip all the components connected to the binding posts then direct wire from the posts to the drive units . Will keep to the normal of using the bottom set of left and right for the bass and the upper ones for the treble.

Have decided to just sand the outside cabinet as smooth as so I can then use Blackboard paint (two coats) and once fully dry then use Wax to protect and give a slight satin sheen .

Once the cabinets are done I will replace the foam back in to the units and then connect and attach the Drive units . I can then just load the Speakers in the boot and drive them to those kind people who have offered to help and I can see any procedures that need to be done performed on my speakers . Once I have gained a little bit of how to knowledge I can happily work away at home and fiddle hone the crossover to my tastes .

All of the above so far (apart from the issue with the crossover not coming out ) has been easy and has need no specialist tools or expert skills . Just be patient (not a skill I have but trying) and do things one speaker at a time. When you take drive units out have a piece of paper and a pen and note down what coloured wire went to which connection on each driver then put that somewhere safe it will be essential when you come back to reassemble the speakers.

How you deal with the passive crossover will depend on what you find . If it is a mounted circuit board inside the speakers then it is just a straight removal and wire direct to the binding posts. I on the other had it is a hard wired board that seals the unit like this one then would suggest leaving it just snip the connections for any of the components and rewire the cables directly from the drive units to the Binding posts.

Next couple of days are going to be sanding and painting leaving to dry and then waxing . Final finish is not going to be up with the high quality of most speakers but it will be enough for me . Will post a couple of pictures of the finished units later this week .

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     Glad to hear you've made a start, it'll be interesting (and not a little educational) to follow your progress over the build time. Good luck! :)

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Have you done the other one too? I'd be tempted to measure them acoustically first to see each driver behaviour. I reckon they are 2.5 way. This would help recreating crossover digitally.

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2 hours ago, insider9 said:

Have you done the other one too? I'd be tempted to measure them acoustically first to see each driver behaviour. I reckon they are 2.5 way. This would help recreating crossover digitally.

Sadly have done both speakers and have not tested either . I am going to contact a fellow wammer who has offered his help and seems to be very wel versed in this type of project so will take the completed units over and see what we can do .

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Right today with the kind help of Andrew who lives near Chester I have taken my now reconstructed speakers (with passive crossover no longer connected drivers directly sonnected to the Bi Wire Binding posts.) and completed a full set of measurements . Firstly with Andrews professional units which were able to give us the information to look at a starting crossover point (2000K) . We were also able to discover that the units are fully time aligned so nothing to look at there .

We were then able to play a little music with the single speaker out in the garden (open air testing) and I have to say they sounded very good indeed even at this stage. I was then able to switch over to using my PC and REW and my Umik Mic . Did a complete set of the same tests and sweeps and couple of images below of what they looked like. Sorry they may not be enough of the full test to see but they just agreed with what Andrews DSP units found any way .

Now have the DSPMini working with my PC (Netframes 3.5 issue needing me to download and install the full programme not just the update) so I can start to look at getting the crossover details loaded up and then synched to the DSPmini and then the next test will be paying some music and doind a few in room sweeps .

I will most likely set up for a full test again for both units in my garden more to give me another chance to go through the process and make sure I can do it again rather than doubting any of results I have already got .

Plan after this is to load the current crossover and use that as Configuration 1 in the DSPmini and as the base line for listening . I can then set up Config 2,3,4 with variations and changes to see what they do and then either delete or save them depending on how they sound .

All things considered (and only because of the support and brilliant help given by Keith and Andrew) this has been very easy . I know that there can be weeks (months ?) of tweaking I can do but as an easy step in to doing this I am really surprised at how simple the process is so long as you have someone with experience to bounce your ideas off and guide you . I had what was a very nice sounding speaker today playing music with an active digital crossover and I expect this to be fully running in about another two weeks or so.

If you ever wanted to try this I would asy just do it as the learning and additional things you gain are worth the work alone but the quality of the sound is very surprising .

Best tips - One if you are going to use an already made pair of speakers look for a Bi Wire pair it save time , woodwork and hassle .Two try the REW software out before you remove the crossover and test the passive units as these will give you hints for crossover points to start with. I lucked out in that Andrews DSP units are so advanced that they do not need anything to give you the information you need but these are rare and expensive so do the work before you disable to crossover.

Monitor Audio 11 graph.PNG

Monitor Audio 11 Impulse Graph.PNG

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Sounds like excellent progress Andrew!

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I'm the 'other' Andrew mentioned above!.....

Here are the outdoor measurements we took when using DEQX to set up the speakers via my own system so we could then move on to REW as in Andrews' posts above (only one speaker measured for this purpose):

1. Anechoic measurement from 1m showing only a slight mic reflection @10.2ms & then its decay refections 22ms, 33ms etc ('clean' data @10.2ms was therefore used for analysis)

ZwuQvLH.jpg

2. Raw measurement of woofers/tweeter (as this is outdoors & in 'free air' & because of the 10.2ms boundary, bass response below 200hz drops away in the plot even though the speakers actually produce bass well below this):

w3MITbP.jpg

3. Phase response of speakers - green = tweeter, blue = woofers.

WsdfGPP.jpg

4. Crossover applied at 2khz because above this, the woofers display a significant null & the tweeter is smoother. I 'guessed' that Mini DSP would only allow LR up to 8-way so I set at 48dB rather than the brick wall Xovers DEQX allows (up to 50-way 300dB) :

sE4gphZ.jpg

5. Just for fun - DEQX speaker correction applied within the blue box 'windowed' area (red line is the result - flat response for phase, time alignment & group delay)

NOTE: THIS WAS JUST TO ILLUSTRATE TO ANDREW WHAT FULL DEQX CORRECTION CAN ACHIEVE & WAS NOT USED FOR ANY OF THE SUBSEQUENT MEASUREMENTS TAKEN WITH REW - we played back some music outdoors using the uncorrected speaker & then using this correction filter with a razor flat speaker response 100hz - 22khz. The difference was significant, as I expected.

J43TX01.jpg

Andrew should have an opportunity to produce some pretty nice sounding music using these as 1st off active speakers & will learn a lot during the process.....

Edited by Drewan77
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Excellent! I look forward to hearing these at Kegworth.

Edited by Tony_J
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     I'm amazed at your rate of progress Andrew (Bencat), having an experienced hand must have been a great help. I can feel temptation creeping in but I'll try to resist!

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Wow Andrew, what amazing progress. You are going to love what these will be able to do. :^

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Right now the request for people ro check what I am doing before I connect anything to Minidsp . Please see the below settings based on the above readings for the crossover for the Bass and Treble. Does this look right

Minidsp Settings Bass.PNG

Minidsp Settings Treble.PNG

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Although I don't use Minidsp, that looks correct for one amp/speaker provided you connect CH1 to the woofers & CH2 the tweeter! (repeat with CH3 & 4 for the other amp/speaker)

Andrew

Edited by Drewan77
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