MT102 Measurements & Results |
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DJ Nick
Registered User Joined: 24 June 2007 Location: Australia Status: Offline Points: 46 |
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Posted: 09 May 2008 at 4:20am |
Ok guys, i was asked let you kow how they sound so heres some data i collectd..
First the pics
The Mesurement setup...(they were too heavy to get any higher and use gating...so i used a 1/3 octave smoothing which gave an almost identicat result to the gated result but included floor bounce in the lower frequencies.. (those bumps at around 450 and dips at around 550) this bump and dip varied at the mic measurement distace varied.
a near field mesuremnet taken at the horn mouth i had prviously taken showed a flat response don to about 170hz with a slight bump at around 210hz.
the crossover
simle PTC plus resistor and bulb in parralel provide comp protection.. basic but effective for passive operation.. they are bi ampable as you will see from the power switch
the switch
the measurements
SPL response in/out of phse...this response was not gated
Measurements were taken at two meters 2v (4onhm) so at 1m 1w, sensitivity would have to be around 3db higher (or approxx between 105-108db) and include includes the floor bounce as a ground plane measurement was not taken at the time ... to combine the two...
phase matching took a while to get right.. (hours of simulations using varying slopes and crossover configurations) as you can see from the rev phase curve integration between the two drivers is very good and amongst these measurements, i took measurements at 4 meters and not much difference.
Crossover frequency was set at 1.2k which may be a tiny bit low, although i didnt think this would be a problem except when driving the cab at over 600w maybe (but i stand to be correctd on that one ) i drove it with 600 a side over my 186s and the sound was magic...
The roll off at over 12k was not noticable at all, it actually made for a very sweet and not a harsh sounding cabinet,, there is a sharp resonant peak in the beymas response at around 15k which probably makes up for this giving that tiny bit of air,, although this can not be seen on these graphs because of the octave smoothing.
High frequency boost is used in the passive crossover and was carefully adjusted to provide a natural and pleasant sound.
measured impedance between 3-4 ohms... a properly designed phase plug may have extended the rcfs upper roll of which may have in turn eliminated the need for the passive crossover to compensate at near the crossover freq. which in turn would have probably eliminated the slight dip at around 1.6k on the impedance graph although this is not really an issue for most amps...and in active mode a slight boost at these frequencies will easily fix that.
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this is the actual measured voltage curves
actual measured impedance
finnished babies:)
in active mode there is two 15u caps in parralell (30uf) to protect against any accidents) and the switch takes care of eliminating the passive from the connector +1-1 for rcfs and +2-2 for tweeter
having also taken an ETC cumulative spectral decay plot of the resonse,, there were surprisingly few resonances in the tweeter,,, just a bad one at 2.7k and another small one at 12k... the 2.7k was tamed using a RLC trap filter tuned to that frequency... this automatically made the sound more hifi and eliminated the "honk"..
beautiful sounding boxes thanks to rog..well worth the effort,
any comments or questions are welcome. thanks guys for having a read,
Edited by DJ Nick - 09 May 2008 at 4:39am |
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hifiger
Registered User Joined: 17 October 2006 Location: Canada Status: Offline Points: 82 |
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Wow, beautiful cabs, love the white/blue colour!
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odc04r
Old Croc Joined: 12 July 2006 Location: Sarfampton Status: Offline Points: 5483 |
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Cheers for the informative post Interesting way of analysising and nulling the horn output spike.
I would have not carpeted them and left them bluey/grey though! |
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Timebomb
Old Croc Joined: 11 October 2004 Location: Lancaster Status: Offline Points: 2716 |
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Nice one for taking the time to post this, what drivers did you use?
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James Secker facebook.com/soundgearuk
James@soundgear.co.uk www.soundgear.co.uk |
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DJ Nick
Registered User Joined: 24 June 2007 Location: Australia Status: Offline Points: 46 |
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Hi Timebomb,
The drivers used here were RCF L10P750YK Midbass (designed for horn loading), and a BEYMA CP800Ti Compression driver on a RCFh6040 horn.
Cheers,
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Mark James
Old Croc Joined: 15 January 2006 Location: rig side Status: Offline Points: 5309 |
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awesome some stuff mate, awesome stuff.
What did you find was the ideal crosssover point? did the mids play okay up to say 1.5k??? very nice! |
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me so horny me love you long throw
horn loaded for her pleasure |
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DJ Nick
Registered User Joined: 24 June 2007 Location: Australia Status: Offline Points: 46 |
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Hi Markk,
I found that in passive mode, the raw response of the mids was about 10db down at 1.5k, which meant that after simulating many different combinations of slopes at various frequency points, the correct phase response as well as a smooth crossover was achieved at 1.2k (using assymetric slopes, as can be seen by the notch at the crossover frequency when the polarity of the tweeter is reversed).... which is not really a problem for the beyma CP800.
In active biamp mode though, where you have more flexability with the processor, a 1.5k crossover point could easily be acheived with minimal boost on the mids making for a pretty bullet proof design (provided limiters, gain structure etc are set correctly).
Heres a simulation i made using active filters.. in this simulation crossover was set at 4rth order LR 2k and a 6db boost with a Q of 2 at 1.4k was applied to the mids to provide correct phase and passband response.
For the tweeter a LR 4rth high pass was applied at 1.6k and also two parametric filters to notch out peaks at 1.7k, 3.7k and a 6db boost at 10k with a Q of 4 to smooth out the top end.
The overall response seems quite acceptable and obviously power handling of the comp would be increased at 1.5k. I have not tried these settings in my processor yet but will post a combined measured response with the MT102.s and the 186s as soon as i get a chance .
also here is a graph of the raw response...
hope this was helpfull, thanks for the nice feedback..
Cheers Nick A Edited by DJ Nick - 11 May 2008 at 12:43pm |
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darkmatter
Old Croc Joined: 26 February 2005 Location: LDN Status: Offline Points: 2425 |
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Beautiful cabs. Thanks for posting this up, it's really useful for me to see how someone goes about tweaking the x-over to match the speaker's response.
Sorry for the rather basic question but what are the two 15uf caps doing? Are they wired in parallel with the comp driver to avoid the risk of any huge spikes? Do they affect the sound at all? Just wondering whether I might need to think about doing something like this in my monitor cabs (they'll be run active only)...
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DJ Nick
Registered User Joined: 24 June 2007 Location: Australia Status: Offline Points: 46 |
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Thanks for the nice comments Darkmatter,
In regards to the 2 x 15uf caps,they provide a first order high pass filtering on the compression driver when in active mode, as they are wired after the +2 -2 pins of the neutrik NLP4 connector BEFORE the switch. The reason for this is to provide some sort of protection in case the compression driver is wired to the wrong amp on the other end, and accidentally recieving full range or sub range. It would also offer a mild sort of DC protection against turnon spike/thump... but is definately not a way of protecting your tweeters from being overdriven or a clipping amp.
It is something EV also used to do with thier MTH series of midtops. It does affect the sound slightly as it will provide a basic high pass filter, but this frequency will typically be lower than the frequency set on your processor if you choose to biamp the cabinet, so your settings will have to in some way complement 30uF high pass filter already in place.
An easy way to test would be to use an FFT analyser and pink noise generator when you are setting up your prossesor, so you can see how close your settings come to a target curve/freq.
Heres a schematic from the MTH cabinet..
Cheers Nick A
Edited by DJ Nick - 13 May 2008 at 10:07pm |
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darkmatter
Old Croc Joined: 26 February 2005 Location: LDN Status: Offline Points: 2425 |
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Cheers for explaining mate,makes a lot of sense especially if you're letting other people set your system up :)
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MarjanM
Old Croc Joined: 10 February 2005 Location: Macedonia Status: Offline Points: 7810 |
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Hmmm... i was expecting way more top end of that Beyma driver.
How much does it cost? I am sure BMS 4550 will do the job as good as that Beyma for a lot less money. |
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Marjan Milosevic
MM-Acoustics www.mm-acoustics.com https://www.facebook.com/pages/MM-Acoustics/608901282527713 |
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DJ Nick
Registered User Joined: 24 June 2007 Location: Australia Status: Offline Points: 46 |
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Hi Marjan,
The Beyma retails for around 700 aus dollars so your right.. not cheap, however the BMS 4550 can not do the job as well as the Beyma as it is only a 1 inch throat driver with a 1.75 inch diaphragm as opposed to a 2 inch driver with a 4 inch diaphragm. BIG DIFFERENCE..
The result is that the Beyma can be crossed over lower safely (1.2K) and will handle more power. so in my opinion it is not an equal candidate.
The Beyma is also capable of output out to 20k quite easily with a high shelving filter however i chose not to use this much boost at the top end simply because to me it sounded sweet.
Cheers Nick A
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