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Preparing Speakers for Bi-amp'ing

Ledge

Standard Member
Hey guys
I have a pair of Mission 734's that I would like to bi-amp with my Rotel RC971/RB971 (one is the mark one, the other is the mark two) pre and power amps.

I have all the cables ready to go as well as an ART CX310 crossover.

My conundrum right now appeared when I opened the back of the speaker to remove the passive crossover.
I attached a pic of what I saw.

My question is, how would I prepare the wires for bi-amping? Would I simply connect the tweeter to the top terminal pegs and the bottom two speakers to the bottom terminal pegs?
I guess I was expecting to connect the tweeter and mid together and the sub on it's own. Now I'm not so sure.
I tried (and failed) to get a copy of a user manual for the speakers to find out the frequency of the existing passive crossovers to see if that would help answer my question...but alas, no luck.

Ok, another Google search revealed this:
I got in touch with Mission in the USA, but they have no documentation of my speakers.
I did find this online though:

Enclosure Type 3-Way Reflex
Freq. Response 70Hz-20KHz + / - 2 dB
-6 dB 38Hz
Nominal Impedance 8 Ohms
Recommended Amplifier 25-125 Watts / Ch.
Crossover Frequency 2.8KHz
Effective Volume 40 Liters
Drive Units LF: 2 x 170 mm Polypropylene
HF: 28 mm Composite Dome
Input Connectors 5-Way Post
Bi-Amp / Bi-Wire
Cabinet Dimensions (HxWxD) 840 x 204 x 335

It seems that the bottom two speakers are the same, but one is ported.
At the moment I am guessing I connect the top two to one power amp and the ported driver to the other power amp and set the crossover to 2.8khz.
Does this sound about right?

Thanks in advance for any help.
Lee.
 

Attachments

  • Wiring.jpg
    Wiring.jpg
    133.9 KB · Views: 2,103

Gixxerblade

Active Member
The crossover point of 2.8Khz will be from your mid to tweeter, if they are 3 way then they normally have 2 crossover points from the woofer to the mid and then from the mid to the tweeter. I would hold off doing anything until you have a diagram of the crossover design if you can get one.

Have a look here http://sound.westhost.com/bi-amp.htm for some tips and background. I usually leave a high value capacitor in for the tweeter to protect it and calculate the effect but you can leave the mid/tweeter passive crossover in place instead.

Have a good browse at the site I linked to as it is full of good stuff.
 

Ledge

Standard Member
Awesome info...thank you :smashin:

I'm checking out that link right after this post.
I guess my main confusion came from the mid and sub drivers being the same specs.
Keeping in the tweeter and mid passive crossovers seems totally logical.
Thanks again.
 

Ledge

Standard Member
YAY....I managed to get an info sheet on the crossovers for my 734's from Mission.
Can anyone help me with reading the diagram? I'm not sure what it's saying about the crossover points :confused:.

Thanks guys.
 

Attachments

  • 734 xover.PDF
    47.9 KB · Views: 356

Gixxerblade

Active Member
You may also find the cross over design cookbook pages useful, if you really want to get into the calculations for 1st and 2nd orders and even if you don't the information is well worth knowing. Some other good stuff on there too - highly recommended reading.
http://audio.calsci.com/X-Overs.html

In regards to your wiring, I normally solder direct to the drivers because I don't move my equipment around much but you can use the existing parts or tag strips.
 

Gixxerblade

Active Member
I've just had a quick look online into the Mission 734i specs. and they are a MTM driver design (mid, tweeter,mid). The 2 mids produce the low and mid range and the tweeter the high at a 3.2Khz crossover in a front ported enclosure (bass reflex). You quoted 2.8 so yours may be different but it is irrelevent for what you are doing.

You therefore need to remove the crossover completely or modify it and run the low/mid wires to the 2 mids and the high wires to the tweeter - start with 2.8 and adjust to taste. From the brief reading I've done the highs are criticised as harsh but I've never heard them, so you might want to stick different tweeters in sometime.

I would add tweeter protection myself though via a cap or the modified existing crossover, please don't do anything until you are confident you know the design and you actually want to go ahead. Read the cook book guide several times before doing anything would be my advice.

If you would like to see cross overs and speakers being built and how much work, time and money is involved see Troels site here:
http://www.troelsgravesen.dk/Diy_Loudspeaker_Projects.htm#SS-constructions

Have fun and if it smells of burning you have probably done something wrong :D
 

Ledge

Standard Member
LOL....thanks so much Gixxerblade.

I guess I didn't realize what I was getting myself into :blush:.

I do plan on replacing my speakers at some point if I can see an improvement from this Bi-Amping effort. You could say I am a born again Audiophile, but I am certainly enjoying this experience :smashin:

Ok, so to clarify, rather than sending power amp one to the sub (mid #2) with no passive crossovers in place and power amp two to both the tweeter and mid (mid #1) with the passive crossovers left in place, I should send power amp one to both the mids (connected together) and the tweeters to amp two (with the existing tweeter crossover in place for protection)?
I ask as it looks like both the mids are being sent different frequencies from the existing passive crossover...or does that become irrelevant with bi-amp'ing?

One last question (although I cannot confirm or deny that this will actually be my last question...lol), will I benefit from running my system in your second suggested config? Only a small amount of power goes to the tweeter right?

Thanks again :thumbsup:
 

Gixxerblade

Active Member
I'm not sure why you are calling it a sub!
Currently you are sending a full range signal to the 2 mids and the tweeter which your crossover filters and sends the lows (below 2.8) to the 2 mids and the highs (above 2.8) to the tweeter. This is called a parallel passive crossover and there are different orders such as 1st, 2nd etc. and remember they are not "brick wall filters" the cook book will explain what I mean far better than me.

If you connect 1 of your amps to the mid and tweeter you will blow your tweeter if it is the amp sending the below 2.8 frequency, if it is the amp sending above 2.8 then your mid will not be working properly.

Please read the cook book link I sent because trying to explain in a few sentences is virtually impossible (for me).

I'm probably confusing things rather than helping so I'll just say read the cook book and see a couple of Troels' designs.
 

Ledge

Standard Member
I was saying sub but was referring to the second mid...my bad.
Looking at the passive crossover, I was under the impression that each mid was being sent a slightly different frequency. Thanks for clearing that up.

Ok, off to read the cookbook again.

I'll keep you posted as to my progress, or lack there of :smashin:.

Thanks again.
 

Gixxerblade

Active Member
This design from Troels' site is a good starting point and relates to your speakers well - once you have mastered cross overs :eek:
http://www.troelsgravesen.dk/CA18RNX.htm

The ART crossover you have bought uses Linkwitz-Riley 4th order 24dB/octave filters so you might want to research what that means as well - I'll see you in 6 months!
 
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BlueWizard

Distinguished Member
Let's take a step back here.

First and foremost, have you purchased ACTIVE CROSSOVERS, because, given what you have said, you are going to need them -

http://www.google.co.uk/search?q=Active+Crossovers&hl=en&tbm=shop&aq=f&oq=&aq=f

Running from a little over £100 to nearly £500 each, and likely you are going to need TWO. Or in your case, it these really are full standard 3-way speakers, you will then need THREE active crossover for EACH speaker. That is about £300 to £600 in additional cost.

Then you are going to need to know where to crossover, and you are going to need to know the slopes of the crossovers, and you are going to need to know which Active Crossover will allow you to set those parameters.

Given that these are 3-way, and best guess from the photo of the crossover, I'm guessing -6db slope for the bass and mids, and -12db slope for the Tweeters, thought to be honest, there seems to be one capacitor missing. The Midrange needs two components, one to filter out the high frequencies and another to filter out low frequencies leaving a band in the middle.

So, if you don't have ACTIVE CROSSOVERS, then you SHOULD NOT be removing the internal passive crossovers.

The ART CX310 crossovers you mentioned are two channel (stereo) but only 2-way crossover, and with no control of the slope. They are fixed at a slope of -24db/octave.

Next the Mission 734 is an MMT design (Midbass, Midbass, Tweeter) given that some components are missing from the passive crossover, I would venture a guess that the are not 3-way, but instead 2.5 way. In this configuration -

0.5-way = one coil for a -6db/oct very low crossover, in the 300hz range.

1.0-way = one coil for a -6db/oct crossover between the bass and the tweeter at 2.8khz.

1.0-way = one coil and one capacitor for a -12db/oct crossover for the Tweeter at 2.8khz.

Until you know these details, you can't duplicate the existing crossover.

Now, you could change the speaker from a 2.5-way, if that is indeed what it is, to a more standard 2-way by running the bass drivers in parallel, and crossing at 2.8khz.

The only other alternative to accurately use an active crossover, is to determine the exact crossover frequencies of the various drivers, and of course, buy a second set of Active Crossovers.

This being a 2.5-way speaker is the only thing that make sense given the crossover components I see in the photo you supplied.

The crossover diagram (PDF) supplied by Ledge somewhat confirms this, though between the photo and the diagram, one capacitor seems to be missing.

The alternative would be to use the passive components that couple the two bass drivers together and treat that combination as a single unit.

To use Active Crossovers, you really need to know the details of your speakers inside and out.

In your case, using a single Active Crossover, you have no choice but to retain the L3 (7.5mH) and the C1 (100µF) components on the second bass driver. Then run the bass drivers together as a single unit driven by the Active Crossover which will be set to 2.8khz.

To the best that I am able to determine, that is my assessment.

Steve/bluewizard
 

Gixxerblade

Active Member
The pdf states mk2 on it and shows 4 coils 2 caps and a resistor. It is clearly not the same as the photograph Ledge has posted so maybe they are mk1 or i or something else :D.

He also states he has bought active ART stereo crossovers which have a LR4 cross over.

The brief look I had online showed a sticker on the speaker of a 734i describing them a 3 way bass reflex but with only 1 crossover point at 3.2Khz.

I would run 1 amp to both mids and 1 amp to the tweeter and remove the passive cross over but would place a large value cap 22uF - cheap and cheerful variety, in line with the tweeter which would give a 3dB high pass at 900Hz and protect the tweeter.

It might be worth contacting Mission with the serial number to see what they say as regards to what exact model they are and whether a schematic is available.
 
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BlueWizard

Distinguished Member
I'm thinking the large capacitor might be hiding the smaller capacitor. I think the largest is a 100µF and the cap in the tweeter is a 4.7µF.

Also, if you look at the diagram (PDF) the mid is clearly not a mid. I need double the crossover components because it is both a high pass and a low pass to create the mid-band. Based on the Diagram, it seems almost certain that this is a 2.5-way with low-bass and mid-bass, rather than the bass and Midrange you would find on a true 3-way.

If the diagram is right, then we appear to have a -12db/oct of the low bass, -6db/oct on the midbass, and -12db/oct of the tweeter, and given that the midrange is NOT configure as a midrange should be, we most likely have low-bass, mid-bass in a 2.5-way system.

I still say, keep the passive components on the low-bass driver, treat the two bass drives as a single unit, and drive the combined bass speaker with the amp being fed by one section of the Active Crossover.

The alternative is to buy a second Active Crossover.

Though, simply pairing the two bass drivers together in parallel, and coverting the system to a standard twin bass 2-way is also an option.

Given the components in the photograph, this can't be a true 3-way system unless there are component located at other locations that we can't see.

Steve/bluewizard
 

Gixxerblade

Active Member
Steve
I found another picture of a crossover for sale online which looked identical to the one he has posted. It is probably a good idea for him to contact Mission.
 

Ledge

Standard Member
Thanks so much for your help guys.

When I spoke to Mission, this was the only document they had with regards to the Mission 734's. Granted, the .pdf may very well be from the 734i (MkII) speakers. Basically, I have attained all the info I can from Mission.

So moving forward, I think I may go ahead and give both suggestions a try and if for some reason things are just not working out, I am very tempted to keep the cabinets and replace the drivers so I know exactly what I have and the best way to set them up with my current system.
Do you think that sounds like a feasible plan?
 

BlueWizard

Distinguished Member
Did you find out from Mission if these are really 2.5-way speakers, and if so, what the low-bass to mid-bass crossover is?

We have a general idea of what the Mid-bass to tweeter is, though we've had two different number, they are both around 3khz.

So, you really have three choices -

1.) Get a second Active Crossover unit, and three amps. One crossover to the low-bass in the form of a low pass at about 200hz. The second Active Crossover would be 2.8khz between the low/mid-bass and the tweeter.

Below the 200hz crossover, both bass drivers are running in parallel, about that the low-bass fades out and the mid-bass continues on up to 2.8khz. The Low-Bass is considered a 'half'-way because it share a frequency range with the mid-bass driver, since it doesn't have a isolated frequency band all its own, it is not consider a 'full'-way.

2.) Continue to use the passive crossover between the Low-Bass and Mid-Bass driver. Then treat that combination as a single unit and cross it with the Active Crossover at 2.8khz. So, the 'half'-way aspect is still controlled by the passive components, and the full way, between the bass and tweeter are controlled by the Active Crossover. The advantage is, this only take two amps, where are number 1 above, takes three amps.

3.) Run both bass drives in parallel with no 'half'-way components. In essence you are converting the speaker to a true 2-way. Both bass drivers running all the time between 0hz and 2.8khz. This save you the need for a third amp.

It is a little more complex than that, but in essence, those are the realistic options for making this work.

Steve/bluewizard
 

Ledge

Standard Member
I had a little help from a friend figuring out what the crossover is between the low-bass and mid-bass. It's between 100 and 150hz.
As far as if it's a 2.5way speaker, Mission could tell me no more than that .pdf they sent me :confused:.

Thanks so much for your input. Before considering a third amp and active crossover, I think I will try option 3 first and then option 2 and see how things sound.

I'll report back. Thanks again :thumbsup:
 

instigator

Active Member
Quick question, you are converting speakers that aren't bi-ampable ( 1 set of +\- posts) to a bi-amp-able speaker with 2 sets of +\- posts?


Reason I ask is I just bought Wharfedale Diamond 9.1 speakers that have 2 sets of +\- posts on each speaker and my Cambridge Audio A5 amp says its bi something or other and has extra sets of +\- posts on back with instructions to the effect of "if not bi amping use lower posts"

Does this mean it has an extra set of amps for feeding the 2nd set of +\- posts?

On the back it also says 400 watts but I thought it was a 100 watt amp... I'm confused, I just take the gold bridging bar off the speakers posts and then run 2 sets of cables from the corresponding posts from amp?

Either the speaker or the amp must have its own crossover? I'm guessing the speaker has the crossover?
 

BlueWizard

Distinguished Member
You haven't told us what the specific amp is, but no, if it is a stereo amp, it has two and only two internal amps.

The extra speaker terminals on the amps are usually designated Speaker-A and Speaker-B, and internally they are both connected to the same amps. Which is why the combined load on one amp channel should never drop below 4 ohms.

As has been explained, if you Bi-Wire you simple add a second set of wires. If you do basic Bi-Amping, you use a second amp, and you continue to use the existing internal passive crossovers inside the speakers. If you do Bi-Amping with Active Crossovers, then you need a stereo pre-amp, two stereo power amps, and a two channel Active Crossover. The Active Crossover goes between the Pre-amp and the Stereo power amps, and the internal passive crossovers are removed from the speakers.

I don't recommend Active Crossovers for anyone but the most knowledgeable, or the most daring. If you don't know what you are doing, there is a high likelihood you will damage something, either the speakers, the amp, or both.

'I just take the gold bridging bar off the speakers posts and then run 2 sets of cables from the corresponding posts from amp?'

That would be common Bi-Wiring, and while some people say it works, most assume it make no difference, but you are free to try.

Steve/bluewizard
 

Gixxerblade

Active Member
Steve, Instigator has listed the amp as a Cambridge A5.

Instigator the answer to your questions can be found in the various links I have posted for Ledge the original poster.

Ledge how many components does your cross over have - was there a cap and a resistor we can't see in the photo i.e. does it match the pdf?
 

instigator

Active Member
ok, i downloaded the usermanual for my Cambridge A5... this is how i have it hooked up now:
biwire1.preview.PNG


so it doesn't have more amps, it's just giving me two paths to go directly to the tweeter and the mid/bass speaker? I guess the benefit is the speaker's built in crossover doesn't need to do as much work? and it could somehow enhance or clear up separation between drivers?

I'm slightly dissappointed that it isn't actually another seperate amp feeding the low and high drivers...

i guess this option is more ideal?
biwire%202.preview.PNG


i would just need to buy another amp?

hmm... is first way of doing it simply called bi-wiring as there isn't a second amp? so i've just bi-wired?

are there skeptics on the benefit of bi-wiring?
 

Gixxerblade

Active Member
Yes you have bi-wired. I've always found it a waste of time and money.

Bi-amping with a passive crossover in the speakers I found to be a subtle improvement but not worth the money for the 2nd power amp but some do find big improvements and consider it worthwhile.

Bi-amping actively where the crossover is removed or modified from the speaker is what this thread is about.
 

Ledge

Standard Member
Ledge how many components does your cross over have - was there a cap and a resistor we can't see in the photo i.e. does it match the pdf?


Good point. I went back and checked. It seems that my cross over is missing a 7w Resistor that the Mk2 has (as per the .pdf).
Interesting.
 

Ledge

Standard Member
The only thing I see different is the capacitor. My crossovers have four components in total and the Mk2 has 5...
Do you see more?
 

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