Much of what LineSource posted is irrelevant to Colins intended build... but it does bring up a few more points.
Due to very large overlaps and drivers being in VERY close proximity, a 1st order XO is possible. A simple 2 component series XO worked really well in out example.
With XO so low baffle step can be dealt with by careful placement to coorespond with baffle width. ie sensitivity of woofers 2-6dB > JRX6's (specced at 85dB). This also allows the max possible efficiency. Active XO does allow more versatility.
With the proposed drivers baffles as narrow as 6 1/2" (700 nominal) are possible. 8" would be nominal 570 Hz.
dave
One advantage of posting to a USA forum is the replies appear in time for morning coffee in the UK.
Thanks for the many replies and links. To respond to some of the comments/queries:
- relative efficiency isn't an issue as I'll be using an active crossover and three Gainclone amps. Crossover will be 4th order.
- they will be sealed boxes. The 5" units are JX92s so overall enclosure volume will be around 15 to 18 litres.
- I'm using two 5" units to get headroom (and also moving the x/over point up a little from Jordan's usual recommendation of 500Hz)
- yes, I'll be using subs with these. It's my preferred method these days. So the MTM only needs to reach 90Hz or so.
The coincident drive approach from MTM was what attracted me plus the polar response, as indicated above. I currently use a pair of commercial active speakers on tall stands designed for studio use - so OH has got used to the idea of speakers placed high.
Dave - I like the look of your MTM. Why did you offset the tweeter - was that to reduce edge reflections or just to get the spacing as tight as possible?
Thanks for the many replies and links. To respond to some of the comments/queries:
- relative efficiency isn't an issue as I'll be using an active crossover and three Gainclone amps. Crossover will be 4th order.
- they will be sealed boxes. The 5" units are JX92s so overall enclosure volume will be around 15 to 18 litres.
- I'm using two 5" units to get headroom (and also moving the x/over point up a little from Jordan's usual recommendation of 500Hz)
- yes, I'll be using subs with these. It's my preferred method these days. So the MTM only needs to reach 90Hz or so.
The coincident drive approach from MTM was what attracted me plus the polar response, as indicated above. I currently use a pair of commercial active speakers on tall stands designed for studio use - so OH has got used to the idea of speakers placed high.
Dave - I like the look of your MTM. Why did you offset the tweeter - was that to reduce edge reflections or just to get the spacing as tight as possible?
Last edited:
Dave - I wondered about 1st order as a line level x/over (based on the calcs on your site). It would be a good starting point to test it.
The old JX125/JX53 system I had used 1st order and sounded fine to me (and even more wonderful on the system of the man I sold it to, dammit).
I'm not too concerned about baffle step as the location will be close to the rear wall - but I take your point about baffle width and crossover point. Another reason for choosing 700Hz rather than going any higher.
The old JX125/JX53 system I had used 1st order and sounded fine to me (and even more wonderful on the system of the man I sold it to, dammit).
I'm not too concerned about baffle step as the location will be close to the rear wall - but I take your point about baffle width and crossover point. Another reason for choosing 700Hz rather than going any higher.
Hoping I'm answering the right question here...the ideal 1st order (or third) filter will have 90 degrees of phase shift on axis with an off-axis lobe, and a null opposite it. This combined with the opposite from the other driver will produce a tall symmetrical lobe, as required.
Producing this phase shift can of course be done in many ways, and will not necessarily coincide with first order either passive, line level or otherwise.
Producing this phase shift can of course be done in many ways, and will not necessarily coincide with first order either passive, line level or otherwise.
Primary reason is to get them a bit closer together but i do like mirror imaged pairs with offset "tweeters"
dave
As far as I know, this was originally an Australian forum.
Owner from Melbourne, now in the Philipines. It did not take long for the forum to become international.
dave
At the same time as you are considering that, you need to bear in mind that the woofers will begin to take on a 'line array' effect at higher frequencies related to their spacing. In a manner of speaking I guess, for what it's worth, if you considered an equivalent larger woofer whose area encompassed the smaller woofers on their MTM baffle, you'd want to cross before it became directional.
Where the c/c spacing is a half wavelength, you'd need to be directly above the speaker to be in line with the cancellation. Which is great, but it does go sour quickly. At just 860Hz, the cancellation between the woofers happens at 60 degrees vertically off-axis and the response would be down a few dB there at only around 30 degrees.
However if you cross the tweeter there, and bearing in mind that the woofers and the tweeter will be equally 6dB down there, the cancellations will be limited to being holes of -6dB maximum, and partial cancellations (the -3dB points) will be reduced as well. As you go up in frequency, the cancellations will happen at more narrow angles, but their depth will be further reduced until it doesn't matter any more.
This could still be a more consistent result than a standard crossover considering the power response through the region, and assuming you sit somewhere around the 0 degree vertical axis.
However if you cross the tweeter there, and bearing in mind that the woofers and the tweeter will be equally 6dB down there, the cancellations will be limited to being holes of -6dB maximum, and partial cancellations (the -3dB points) will be reduced as well. As you go up in frequency, the cancellations will happen at more narrow angles, but their depth will be further reduced until it doesn't matter any more.
This could still be a more consistent result than a standard crossover considering the power response through the region, and assuming you sit somewhere around the 0 degree vertical axis.
You might want to pick up Dr. Joe's book on measurement and see what else he has to say. He does not talk about this specific, but does talk about measuring multi-driver systems.
Remember, all MTM is not built with his concepts in mind. Playing with my Paradigm center, MTM but unknown if it is a D'Appolito alignment, I do hear considerable differences in how it works with the room. I am not sure of my preference.
Remember, all MTM is not built with his concepts in mind. Playing with my Paradigm center, MTM but unknown if it is a D'Appolito alignment, I do hear considerable differences in how it works with the room. I am not sure of my preference.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.