Anyone in UK, Sussex area got measuring/modelling equipmernt? - diyAudio
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Old 31st January 2009, 04:23 PM   #1
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Default Anyone in UK, Sussex area got measuring/modelling equipmernt?

Hi all.

I have a modded pair of TDL RTL2's and would like to refine them with the help of an experienced speaker builder/modder.

The changes are:

Tweeter changed from Vifa D20TD-05-06 to Morel MDT 30S.

Crossover caps changed for equivelent value Janzen audio 'Crosscaps', tweeter cap changed from 1.5 to 1.8ohm.

Internal cable changed to QED silver anniversary. (I want to try a different cable as I didn't like this cable between my amp and SPKR's after modding my CDP. Its way too bright and muddled compared to my DIY multistrand copper cables.)

So far the improvements have been amazing and I really think these speakers sound competitive against much pricier models now. With a little more work to refine things I could realistically have myself a very, very good pair of speakers.

when fitting the Morels I had to open up the mounting hole on the front baffle and without the correct tools I made mess of it. I would like to make new front baffles from 1" Birch ply and have the midbass cut-out CNC milled to allow the awkward shaped driver to be flush mounted. I also would like to clad the rest of the enclosure in 1/4" or 1/8" Baltic Birch ply to improve the cabinet damping and aesthetics.

I'm basically looking for help/advice on 2 things:

1, Refining the crossover to exactly suit the new tweeter.

2, playing with the tweeter placement to see if off-centering it gives any improvement.

3, Enclosure modeling to see if increasing the volume slightly will have any adverse effect on the bass*.

*When fitting the new front baffle I have the idea of fitting it over the existing baffle. The original baffle will be cut out almost flush to the side top and bottom panels. This will increase the original volume of the cabinet slightly.

If anyone is fairly local to the Sussex area and can help with any of the above I am willing to provide ample Beer, Cake or Pizza!

Otherwise any help her on the forum would be greatly appreciated. For this I can provide Schematics of the Crossover and Cabinet dimensions/drawings.

Rgds,
Mike.
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Old 1st February 2009, 07:55 PM   #2
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Bump.

Anyone?
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Old 1st February 2009, 09:59 PM   #3
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Hi Mike,

I'm not in Sussex but am in Essex near Stansted airport. If you get stuck then you're welcome to come up one weekend and do some basic measurements. My garden is big enough to get decent results and I have the full version of trueRTA and ETF, with a measuring mic and preamp.

Hopefully you've only modded one so far so we could A/B them with the measurements. - maybe not....

Rob.
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Old 1st February 2009, 10:27 PM   #4
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Thanks Rob.

I have changed both and they do sound much better. I still have one of the original tweeters I think but the old lytic caps are long gone. If I don't find anyone more local I'll probably take you up on the offer please.

I basically changed like for like in terms of value on the tweeter cap (6uF). Someone on another forum suggested changing to 4.7uF was good due to the later roll off of the Morel over the Vifa. What do you reckon?

Can you measure the Fs of the midbass and model the cab? I want to find out if adding a little more volume to the enclosure will have any benefit. At some point not too far away I'll draw up a schematic of the crossover and plans of the cabinet and post them on this thread.

M.
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Old 1st February 2009, 10:49 PM   #5
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Mike,

I'm an active xo type so have very little to suggest about the subtleties of your xo. However the mic never lies as such... Basically you need to start by measuring each driver on it's own @ 0 / 30 /60 degrees and then start worrying about the xo...

tbh I'm kind of guessing your tweeter swap has given you some extra treble which you're hearing as 'detail'

Just looked up and found out your speakers are TL's - I really wouldn't be messing with the enclosure volume there.

I can help with the front baffle if you get stuck.

Rob.
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Old 2nd February 2009, 12:35 PM   #6
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My guess is that the midbass filter can be left alone and just the treble section needs tweaking to match the morel driver. However, moving the crossover point could bring results. This is why I want them measured so we can see whats really going on.

On the baffle I think as long as the internal dimensions remain the same the baffle can be a little thicker without causing any problems. Plan is to use either Baltic birch or MDF, about 1" thick. Back of midbass driver hole will be chamfered 45deg to ease airflow.

Are you able to model the crossover once the drivers are measured in the baffle? Then we can see what changes need to made to the pysical network. I dont want to change the FR too much, just make sure its nice and even. My hunch is that there is probably a hump in the upper midrange caused by the lower roll off of the Morel tweeter.
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Old 2nd February 2009, 03:39 PM   #7
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Try downloading speaker workshop and see if you can put your existing xo into it. That will be a start as you'll know where the xo points are and what order they are.

Then if you measure your midbass without xo and with xo you can see what it's doing. Same with old tweeter.

Then measure new tweeter and design the HP to mimic the old tweeters response. L-pad if you need to attenuate.

That should get you in the the ball park.

As I said above I'm not really into passive xo's so am not the best to answer your questions.

Also do a search on xo design software as there's loads of great info on this site.

Rob.
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Old 7th February 2009, 09:04 PM   #8
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Just a little bump in case anyone more local like in Sussex (Brighton?) might be able to help me?

Otherwise any suggestions on the crossover can be posted here too.

Thanks for reading,
Mike.
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Old 16th February 2009, 10:51 PM   #9
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One final Bump for any help here on the forum.

Also still hoping for someone local to offer their help with measurement please.

Come on guys, must be someone in Sussex, Kent or Surrey?
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