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Conversion of Monitor Audio Monitor 11 to Active Crossovers


bencat
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Yes - looks good Andrew. Have you found the setting that allows you to link pairs of channels so that changes to the settings on one are mirrored on the other? Makes life a lot simpler. especially when you get to tweaking the filters.

Edited by Tony_J
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Andrew - Something we didn't discuss while you were visiting....

You may find it useful when viewing measurements to change the 'smoothing' level which makes the frequency response graph easier to interpret, especially at higher frequencies.

To do this, go to the title bar at the very top of your screen and select 'graph', then choose something like 1/12 smoothing.

(I don't normally use REW because the Earthworks M23 mic, even with its calibration file doesn't produce data that I'm happy with compared to FuzzMeasure Pro or DEQX software. Having said that, your Umik mic measurements via REW were very close to M23/DEQX which is as it should be.... & reassuring!)

Tony J is clearly more familiar with REW & Minidsp so he will offer the best advice with those of course.

Good luck

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Thanks Andrew

Only put up one to save space but appreciate it will need to be duplicated for the other speaker. When I get round to doing this I can rename the outputs as Bass R and Treble R and Bass L and Treble L which will make it clear which way to plug things.

Doing it with the software only and no unit connected means I can check things and make sure I am doing things right before I connect everything up and give it a little trial . As you suggest will start off with very low volume and just raise it gradually to avoid any damage .

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1 hour ago, Tony_J said:

Yes - looks good Andrew. Have you found the setting that allows you to link pairs of channels so that changes to the settings on one are mirrored on the other? Makes life a lot simpler. especially when you get to tweaking the filters.

Hi Tony this is just a dry run with the software with lots of checking to make sure I do not make any obvious errors. It is my intention to set up a very flat option with no filters or other manipulation on Config 1 and retain this as a baseline . I intend to read through the manuals and the sample outlines that Minidsp have on their site before I do the real configuration on to the Minidsp unit .

Once this is done and I have tested it with music to see that everything is working as it should will then give it an extended listen and see both how it sounds and what I would like to get different .

Then I can create Config 2 to add filters , change crossover points , slopes etc and see what these do and if they produce more of what I want or make the sound worse . When I get to this stage will certainly be asking what I should tweak to achieve different results such as deeper bass , more air in the treble etc.

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  • 3 weeks later...

Okay due to a few things from the rest of life (i know hard to believe there is anyhting bu Music and Hif Fi but sadly there is) I have not been able to look at this project at all . I am now trying to review things again and I have two power amplifiers that I can use to at least get the MA units singing.

Problem now is the knwoledge gap so looking for a little guidance (I need this alought) . Not what I wanted to do as I wanted to keep things really simple I have two different power amplifers which I have no idea if they are matched for gain etc (probanbly not) . So using what I already have how do I find out the difference in gain for each unit and then change the settings in Minidsp to compenstate ?

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You could hook up & measure each amp in turn at something like 25% of its volume on the same channel (I would use the bass channel). This should enable you to view their relative outputs.

Once you have a general idea, then adjust the settings in MiniDSP & connect both amps/channels. If there is no easy way for you to measure again and view then you will need to adjust by ear.

As mentioned previously - I would expect Tony to have a more accurate & repeatable method.

Andrew

Edited by Drewan77
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On 03/09/2018 at 20:41, bencat said:

Okay due to a few things from the rest of life (i know hard to believe there is anyhting bu Music and Hif Fi but sadly there is) I have not been able to look at this project at all . I am now trying to review things again and I have two power amplifiers that I can use to at least get the MA units singing.

Problem now is the knwoledge gap so looking for a little guidance (I need this alought) . Not what I wanted to do as I wanted to keep things really simple I have two different power amplifers which I have no idea if they are matched for gain etc (probanbly not) . So using what I already have how do I find out the difference in gain for each unit and then change the settings in Minidsp to compenstate ?

Hi Andrew

Drewan 77's post has given me a timely reminder that I had forgotten that I needed to reply to this - as you say, day to day stuff intervenes.

There are two variables to deal with here when it comes to gain matching; the first is that the two amps you are using will have different gains, and the second is that there will be a difference in sensitivity between the tweeters and the (paired) woofers, and that will also be affected by how you choose to connect them - series or parallel. Typically, the tweeters will be more sensitive than the woofers, so typically, you would choose the higher power amp (if there is a difference) to drive the woofers. However, as you are using paired woofers, you also have to figure out whether to drive them series or parallel. If they are 8-Ohm units, then I would suggest parallel connection, which would mean that the amp sees a 4 Ohm load; if they are 4-Ohm units, then it is likely that you will need to connect them in series, so the amp sees an 8-Ohm load, unless you are sure that the amp doing LF service can handle a 2-Ohm load safely (some won't). The choice of series or parallel will also affect the sensitivity of the combination; you will get significantly more SPL when the drivers are parallel connected (by up to a factor of 4?), depending on how well the amp deals with different load impedances.

It isn't really the gain of the amps that is important; it is the SPL that the amp/driver combination generates for a given signal. When I was experimenting using a pair of integrated amps to drive my setup, for convenience I used the volume controls on the amps to get the level matching right between HF and LF, rather than using the gain settings in the MiniDSP, but you can use either to achieve the right result; obviously if you are using power amps rather than integrated amps then there is only the option of using the MinDSP settings to match the gain. I am assuming that there is no need to level match between the L and R channels of each amp - they should be well enough matched that it isn't worth the effort.

The problem with attempting to level match using measurements is to figure out what to measure. For example, if you choose to feed a sine wave at 400 Hz into the bass amp and measure the SPL it produces, then clearly you get a result, but then you have to figure out how useful it is. If 400 Hz happens to coincide with a dip or a peak in the driver's response curve, then that result may not be terribly useful, for example. So, you might instead choose to feed pink noise into the amp and see what SPL that generates; but then, what you are measuring is the average SPL that the driver produces across its frequency range, which again may not be ideal, although it may give you a better starting point. So rightly or wrongly, what I have chosen to do when balancing the amps in my system is to connect up the HF and LF drivers, with the MiniDSP crossover settings set appropriately, and then use the REW measurement sweep to see what the overall shape of the frequency response is for the speaker. My bass drivers go pretty low, so my standard sweep goes from 10 Hz to 20,000 Hz. You need to do this for only one (Left or Right) channel; if you drive both channels at the same time, interference effects between the two speakers will confuse the results. Apply smoothing to the response measurement in REW (I tend to use 1/12 octave smoothing) and it should be pretty apparent, knowing the crossover frequency, how well the HF and LF sections are balanced. You can then adjust the gain of the HF or LF accordingly, and repeat the sweep.

As you have seen from the testing you have done so far, the response curves are going to be far from flat at this stage, so getting the balance right will not be an exact science; bear in mind that later on you will be wanting to modify the FR of one or other (or both) drivers, so there may be some iteration involved before you're done with the level matching.

One thing that is worth setting up on the MiniDSP, if you haven't already done so, is to check the "link enabled" box in the input and output sections so that settings you apply to one channel get automagically copied across to the other channel. This makes one less area where you can cock things up - if you have different settings for L and R, you can waste lots of time trying to figure out why it sounds so crap...

Needless to say, until you have a good feel for how much noise the drivers will generate for a given input signal, it is best to start very low...the bass drivers are likely to be rather more tolerant of high levels than the tweeters.

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Tony apologies for how ignorant I am about these things but in elctrics I have alwasy struggled with the difference between in series and in a parallel . Easiest I think to easblish what I currently have is to tell you how the units are connected up and then you can tell me .

Currently I have the tweeters in each speaker wired directly to the top two binding posts . I then have both woofers directly wired to the bottom two binding posts. If you can tell what this connection is and then explain how it would differ for the oposite connection it may help me to get the difference in my head.

What this has made me realise is that at least for now things would be much easier if I had two identical amplifiers to work with .

I think if I decide (just because I am getting impatient to hear tthese units breathe and play) to use the two amps I currnelty have (Quad 405 / Trio Basic 1 M ) I will connect them up and look to use the Minidsp connected to my PC to adjust the gain by ear till it sounds right then leave it and just get on with a bit of familiarisation and listening . Once I have two matched amps (either by buying one of the other amps I already own or getting an AV Amp with at least Five channels ) I can then get in to using the other presests on the Minidsp to try changing Croos over filter types , cross over points etc and equalisation to see what I can achieve .

Thanks Tony and Andrew appreciate the advice and your patience .

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Hi Andrew

No problem - we all have to start from somewhere!. It sounds like you have the woofers wired in parallel. If you have access to a multimeter with a resistance setting, it would be worth connecting it across the woofer binding posts to see what the coil resistance is - this will give you an idea of what the speaker impedance is. If the woofers are nominally 8 Ohm impedance, then with 2 in parallel you would expect to see somewhere around 3 Ohms on the meter. 

Have a go with the amps you already have - the tweeters will have a different sensitivity from the woofers anyway, so it really isn't necessary to use two identical amps. As you say, getting them up and running will give you an opportunity to play with the settings and see what happens, which at this stage is more important.

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These might help you get your head around parallel & series wiring Andrew:

image.thumb.png.cb324206c2f708a4ac564289588248e3.png 

image.thumb.png.defe4bcd0c71eeba100b967d273cef1c.png 

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Andrew

Thanks for the diagrams but still not really clear as the diagram just really shows the path of the wiring  So just to see if I have got this correct if I wanted to wire my speakers in series then I would wire the Positive of that first Driver to the red Binding post . Then wire the negative of the first drive unit to the positive of the second drive unit and then wire the negative of the second unit direct to the  black binding post .

As Tony says I think at the moment I have them wired in parallel . Is there any advantages to either way ?

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Andrew

Yes, that would be correct for series connection.

As mentioned in my earlier post, if you have two 4 Ohm drivers, you would be better wiring them in series, because the amp may not like driving a 2 Ohm load, which is what it would see if you wired 2 4-Ohm drivers in parallel. 

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Do you know what impedance your bass drivers are?

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Hi Tony they are both marked as 8 ohm so this would give me a 4 Ohm load which should be fine for either power amplifier . As mentioned the treble units are fairly negligible in their demands and either amp would work well .

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1 minute ago, bencat said:

Hi Tony they are both marked as 8 ohm so this would give me a 4 Ohm load which should be fine for either power amplifier . As mentioned the treble units are fairly negligible in their demands and either amp would work well .

That's great Andrew - should be fine like that.

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