brixvold... theoretically, the dual woofers in parallel will yield a sensitivity around 93 db around 150 Hz on most OB baffles. Due to parasitic loses you don't quite get there. That is close to the true sensitivity of the Seas 8" full range below around 3K.
However, if you cross over above 250-350 Hz, (assuming a 17"-24" baffle width) the Seas rear radiation adds, give or take 4-6 db more output. The variance is due to reflection and other parasitic loses. And the Seas forward radiation is constantly rising with frequency above around 3K or so if I recall. This is were crossover design is so important. Getting the levels correct AND ending up with a more or less flat frequency response at the listening position. Hope this all makes sense.
J
However, if you cross over above 250-350 Hz, (assuming a 17"-24" baffle width) the Seas rear radiation adds, give or take 4-6 db more output. The variance is due to reflection and other parasitic loses. And the Seas forward radiation is constantly rising with frequency above around 3K or so if I recall. This is were crossover design is so important. Getting the levels correct AND ending up with a more or less flat frequency response at the listening position. Hope this all makes sense.
J
Just to add a note on the Seas.
Some years back a friend of mine had the Seas on open baffle. Can't remember if he measured it or I did for him, but on OB it was remarkably flat at the listening position. It did not show the rise seen in the factory specs. I had to scratch my head about that one for awhile.
IIRC, the conclusion was that on an open baffle the rear radiation of the Seas was helping to fill in the bottom end. Not enough high end was getting past the magnet in the rear and then bouncing off the wall to matter. The low end did come on around, filling in just perfectly. At least it did in that room.
Some years back a friend of mine had the Seas on open baffle. Can't remember if he measured it or I did for him, but on OB it was remarkably flat at the listening position. It did not show the rise seen in the factory specs. I had to scratch my head about that one for awhile.
IIRC, the conclusion was that on an open baffle the rear radiation of the Seas was helping to fill in the bottom end. Not enough high end was getting past the magnet in the rear and then bouncing off the wall to matter. The low end did come on around, filling in just perfectly. At least it did in that room.
The Ultra Plus (two 15" woofers and the SEAS driver) were clean and dynamic sounding. There were only a couple of other speakers at The Lone Star Fest that could touch them that year and most of them were really expensive.
OK, back to the topic at hand. Ultras.
Moved them from the living room to the dining room a while back and it's been hard getting them to sound right in the smaller room. Kept them 2 feet from the side walls and played with moving them between 3 and 5 feet from the front wall. Yet they remained boomy no matter where they were.
Finally moved them so they were 3 feet from the side walls. It wasn't done earlier because in this position they are only about 2 feet from each other. But 3 feet from the side walls made the sound snap into place. Just beautiful - their rhythm and drive is back. No idea if it fixed a room mode or that open baffle speakers just like more space from the side wall but it really worked well.
Given they are in a less than ideal room (and the total cost of the system is really cheap and cheerful) they shine. As John said, they clearly reflect the electronics that feed them. Even replacing a cheap power strip with another strip with good outlets, cord and plug was clearly heard. More than I'd expected, actually.
The Ultras also seem to come alive with a bit of juice, too. Goose 'em a bit.
OK, back to the topic at hand. Ultras.
Moved them from the living room to the dining room a while back and it's been hard getting them to sound right in the smaller room. Kept them 2 feet from the side walls and played with moving them between 3 and 5 feet from the front wall. Yet they remained boomy no matter where they were.
Finally moved them so they were 3 feet from the side walls. It wasn't done earlier because in this position they are only about 2 feet from each other. But 3 feet from the side walls made the sound snap into place. Just beautiful - their rhythm and drive is back. No idea if it fixed a room mode or that open baffle speakers just like more space from the side wall but it really worked well.
Given they are in a less than ideal room (and the total cost of the system is really cheap and cheerful) they shine. As John said, they clearly reflect the electronics that feed them. Even replacing a cheap power strip with another strip with good outlets, cord and plug was clearly heard. More than I'd expected, actually.
The Ultras also seem to come alive with a bit of juice, too. Goose 'em a bit.
Ok guys, I need help understanding OB design and issues. I'm throwing together a pair of OBs for a shootout in a couple week. When I started messing around with the Edge program it shows a very complicated network just to tame the woofers, 2 per baffle, which I never thought of. I just assumed that I'd put two woofers on a baffle and call it good.
What am I missing?
What am I missing?
Up and running
Well i have them up and running. Except that the tonal balance sounds very promising i can not yet coment on the sound quality. Considering the huge coils i presume that it will take more than 100 hours of playtime until they settle in.
But here are some photos
Well i have them up and running. Except that the tonal balance sounds very promising i can not yet coment on the sound quality. Considering the huge coils i presume that it will take more than 100 hours of playtime until they settle in.
But here are some photos
Attachments
Give them a few days then start experimenting with placement. It can make a big difference.
How do you mean, the coils will effect how long it takes for the drivers to break in?
A couple Manzi thoughts
Boufos: Thanks for sharing info and pictures! Needless to say, the drivers will change and improve with time. How long can vary quite a bit. Sometimes just a few hours, sometimes several weeks. Does not seem to mater how they measure when new.
You may have a problem with the little Vifa rear reflections with it sitting down in the rear baffle well. This can lead to a peaky response in the lower treble. If you can, you may want to round the rear of the baffle cut out. If you do not have a router, you can use a wood file. A pain to do that way, but it can really yield improvements. Best J
Boufos: Thanks for sharing info and pictures! Needless to say, the drivers will change and improve with time. How long can vary quite a bit. Sometimes just a few hours, sometimes several weeks. Does not seem to mater how they measure when new.
You may have a problem with the little Vifa rear reflections with it sitting down in the rear baffle well. This can lead to a peaky response in the lower treble. If you can, you may want to round the rear of the baffle cut out. If you do not have a router, you can use a wood file. A pain to do that way, but it can really yield improvements. Best J
I have made the baffle out if 15mm baltic birch plywood sandwiched with 6mm HPL (High pressured laminate). At work we have a lot of scrap from these materials so i used some of it. To be honest when i glued them together I haven't noticed the part with the explanation about the backside of the mid-tweeter cutout being routed. But I did noticed it in later stage and that gave me some headache becouse the HPL plate is glued on the backside, maby it adds waight and stability at the baffle but it is a totaly not handy material to work it with handtools. Luckily at home i have a set of rotary grinder tools. I took a bowl shaped one and placed it on a electrical drill. It was a pain in the ... to do it, the result wasn't the most beautiful one but i did routed it . It's bowl shaped form and the angle of which i took the photo probably doesn't show it. Here will be a bit more visible i hope
. It's bowl shaped form and the angle of which i took the photo probably doesn't show it. Here will be a bit more visible i hope Attachments
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Thanks Pano. I'll be using 2 of these per side and the big a$$ Heil on top. How close together should I put the woofers?
6-1/2" Poly Cone Midbass Woofer 4 Ohm
I plan on using the MiniDSP.
The lower you cross the woofers, the farther apart they can be. Do some moving around in Edge to see where the peaks and nulls are as you separate the woofers. Closer than a 1/4 wavelength is said to be optimal, but you can fudge that some.
FYI, you won't get much bass from 6.5" woofers on OB unless you use a lot of them.
FYI, you won't get much bass from 6.5" woofers on OB unless you use a lot of them.