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In Reply to: Re: Another OB experiment posted by KCHANG on March 12, 2007 at 17:13:16:
"As to your OB system, I'd like to get a better understanding of your setup. Did you set the low-pass for the woofers at 50Hz? That seems too low, especially for a Lowther with a low Qts. I would not expect the Lowther on OB at a reasonable height to have any useful bass that low. Did you mean to say 150Hz? Also, I am confused by what you said: " but, the bass with my subs turned off is loud, tubby, and one note. TERRIBLE." I'd expect very little bass if your subs (did you mean the OB woofers or the transmission subs?) were turned off, for the reason above. "
Kurt,Yea, I definately meant that my Bash amps and 15 inch Emminece Beta 15" woofers are set to operate at the Bash's maximum 150 HZ and below.
I usually run a pair of corner loaded transmission line subwoofers with my Je Labs baffles minus added woofers (Just Lowthers). Those sub woofers are generally crossed via their own plate amps at around 85-100 HZ. Even though these subs remain in the corners six feet behind the JE Labs baffles they meshed quite naturally with the baffles. When I am using the new 30" x 48" OB's with the 15 inch woofers, then I had crossed the corner subs at around 45-50 HZ. The 15" OB woofers set to handle all below 150 HZ to their natural limit of around 45 HZ. This setup was waaaay bass heavy. So, my 1st assumption was that I did not need subwoofers at all for this setup and turned them off. But, still sloppy, tubby, one note bass using only the new 15" OB woofers to augment the Lowthers. Potentially some room mode problems hers? I just should NOT be overpowered by any kind of bass with one 15 per OB. I will move the baffles around a bit within my space limitations in my listening room to hear if things improve. Could be that my room benefits better from a less imposing (size) Open Baffle? So I will try and get to the bottom of this bass issue for a day or so and then move on to my second new pair of OB's Kurt. These are 21" wide instead of 30". All other dimmensions are the same. This started ot as a multi driver comparison to determine why in the hell my defunct (kind of) pair of Lowther PMMKII's just WIPE OUT all of my other full/wide range drivers in the JE LABS OB's. Now it has gotten complicated. I guess I deserve this for adding so many variables to the study. Three new different sized B's (Baltic Birch is expensive in West Central Florida) and my first attempt at OB woofers. I really really apreciate your advice from your own experiences. Thanks a bunch.
Lance
Follow Ups:
Your bass drivers may be shaking the baffles so much that they are making noises that is contaminating the bass. My suggestion is to play your bass drivers with your midrange drivers turned off to hear if there is some weird sounds coming from your baffles (or elsewhere in the room).You CANNOT run the Lowther drivers full range as the drivers CANNOT take the large excursions. This could be another reason for the noises you are hearing. You MUST high pass the lowther drivers no lower than 150 hz, but if you play at higher sound levels, then high pass them at 200 or 250 hz.
There is also a tonal balance to be respected.
I do not see how lowther in OB can sound ok.
They need to be loaded to boost the 200Hz the
1200Hz-5kHz.
I am playing AER without horns and use a DEQX
With +6db at 200Hz. (By the way use a better
digi source with DEQX and now sounds good)
You are right. I added a single air core inductor in series with the Lowther and a capacitor shunting the high frequencies around the driver. This is mostly consistent with the setup established by Dick Olsher in his Basszilla plans. Once the frequency response is made flat, the sound is spectacular.
Hi Lance,You are welcome.
You said the OB woofers sound bass heavy. Could you tell me how you matched the level of the woofers to that of the Lowthers?
Hopefully it is just a room mode issue, and response scans using test tones with different speaker locations should be able to reveal the nature of the problem.
Good luck with solving the bass issue.
Best,
FWIW, I use this 15" infinate baffle from Partsexpress: http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=295-455
I put it on an 18" wide baffle with 6" wings, same baffle my main speaker is mounted on (an EV SP-12B). The crossover is a line level set to 30hz, that goes into a seperate power amp. Given the response of the IB speaker, and the low crossover, it has no problem reaching up to the 150hz or so where the SP-12b falls off, and it give a pretty flat in room response to 30 or 34hz. Sounds great, integrates easily.
Hi Steve,I assume that the crossover at 30Hz is a first-order low-pass, and the idea is to use the 6db/oct slope to counteract the dipole roll-off to flatten the bass up to the onset of the dipole roll-off. Correct?
Best,
Works great.
'
See Kurt's note above - he's right on. 1st order low.
Kurt,
It do get triky, Don't it. Ya finds that purrrfect spot for the oft hard to please Lowthers. I mean a spot in the room on as simple an open baffle as one could imagine that seems to infuse every molecule of air in the room with life and light, then I gotta go and mess the whole thing up by changin things.Maybe I should have started out wth 8" woofers and titrated up to the right fit, minus obvious room mode excitement? I get a big kick out of your card board trial baffles (smart and cheap).
Try setting the plate amps at 80-100Hz, polarity at 180 degrees as Kurt sez and then dial in volume to taste.
"Try setting the plate amps at 80-100Hz, polarity at 180 degrees as Kurt sez and then dial in volume to taste. "Crossed at 80-100 HZ (as my subwoofers are set when running with my original JE Labs OB's) there appears to be a big hole and an obvious leanness that does not fill in until the crossover knob on the Bash amps are pegged at 150 HZ. This is definately going to require much more experimentation to get corrected.
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