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Old 5th April 2014, 04:37 PM   #1
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Default HSU MBM else build myself for more midbass

So my BP7000SC Definitive Technology have great lower bass, but the mid bass is a bit of a black hole between 70Hz and 150Hz.

I was thinking about getting a HSU MBM but also interested in maybe trying to build something myself. The HSU MBM I would run sealed, but it's down firing, so I'm not sure if that would be good or bad since I need to fill in between 60HZ and 150HZ.

I also don't want any additional to be too large in size, but understand that they need to be big enough to keep up with the BP7000SC towers.

Thoughts? Should I go with a HSU MBM? Build myself? If so what driver, enclosure type, and amp? I do have a Minidsp I'm not currently using and my preamp is a Denon 2808 with Audyssey XT
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Old 5th April 2014, 05:33 PM   #2
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A "black hole between 70Hz and 150Hz" sounds more like a room mode problem than a speaker problem, adding more power in to a room mode "black hole" won't solve it.

Have you experimented with different speaker positions or listened in various locations to determine the response hole is universal?
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Old 5th April 2014, 05:48 PM   #3
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I guess it's possible to be a room mode, however, I tried measureing the speakers several times. Actually measured just the mids and woofers separately. The mids crossover at 150hz and the subs appear to kick in around 80hz. These subs in the towers are dsp controller too.
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Old 6th April 2014, 06:35 AM   #4
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http://www.definitivetech.com/downlo...12109_read.pdf
Are they new speakers, that could have some influence in the quality.
Looking at the summation at crossover range from the woofer and mids and after you check for the best position, maybe there's an issue with the sub crossover.

Others like this type of Bash 500 Plate Amps have EQ settings at crossover from 50-150Hz to the woofer/sub and some have also by-pass switch. A wrong setting at 40-50Hz could be a problem.
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Old 6th April 2014, 06:49 AM   #5
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Or just PHASE also.
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Old 7th April 2014, 10:03 PM   #6
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I uploaded a frequency response. Red is just the mids and highs. Purple is with the bass drivers turned up 1/4 of the way.
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Old 7th April 2014, 10:59 PM   #7
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Quote:
Originally Posted by Truwarrior22 View Post
I uploaded a frequency response. Red is just the mids and highs. Purple is with the bass drivers turned up 1/4 of the way.
Assuming room modes (or lack of phase alignment) are not responsible for the response dip, it appears the system was designed for a low frequency "haystack" response, the lack of response at the acoustic crossover would fill in when the LF is brought up, but result in a huge bass hump.

Humped up LF response is popular with many people, kind of a built in "loudness contour". Room response and placement can also increase LF response greatly, requiring quite a bit of EQ to make for flat response if one can't move the cabinets to compensate.

If the low pass filter of the LF drivers was raised to match the acoustical roll off of the mid drivers, response could be smoothed out without resulting in the bass hump.

Last edited by weltersys; 7th April 2014 at 11:03 PM.
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Old 8th April 2014, 03:27 AM   #8
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I was thinking about this speaker after I posted and maybe if you placed the speakers straight (like the bass pointing at you/sweet spot) this is, place them in the usual space on the sides but facing the room straight, not toe in, in a manner that the bass/sub will be in view of the sofa so to speak. This would make you get more of the upper LF in your spot. Another would be to try to have more reflection from the side walls. That is a difficult set-up or there is something wrong with those speakers. If they are new, you can ask someone to have them checked for the right (DSP) equalization or at least if that's the set-up with all the speakers/model, maybe everybody else is having the same problem.

note: if you describe your speakers would be better, do they have one sub/woofer on each side totaling 4 drivers or just 1 per speaker.
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Old 8th April 2014, 04:17 AM   #9
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Quote:
Originally Posted by weltersys View Post
Assuming room modes (or lack of phase alignment) are not responsible for the response dip, it appears the system was designed for a low frequency "haystack" response, the lack of response at the acoustic crossover would fill in when the LF is brought up, but result in a huge bass hump.

Humped up LF response is popular with many people, kind of a built in "loudness contour". Room response and placement can also increase LF response greatly, requiring quite a bit of EQ to make for flat response if one can't move the cabinets to compensate.

If the low pass filter of the LF drivers was raised to match the acoustical roll off of the mid drivers, response could be smoothed out without resulting in the bass hump.
I think the biggest hump is caused my the bass radiators. I think they are tuned very low. Appears to be a very high quality radiators though. I really don't have any way to control the slope of the woofer roll off (seems very steep!). It's all DSP controlled.
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Old 8th April 2014, 04:27 AM   #10
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Quote:
Originally Posted by Inductor View Post
I was thinking about this speaker after I posted and maybe if you placed the speakers straight (like the bass pointing at you/sweet spot) this is, place them in the usual space on the sides but facing the room straight, not toe in, in a manner that the bass/sub will be in view of the sofa so to speak. This would make you get more of the upper LF in your spot. Another would be to try to have more reflection from the side walls. That is a difficult set-up or there is something wrong with those speakers. If they are new, you can ask someone to have them checked for the right (DSP) equalization or at least if that's the set-up with all the speakers/model, maybe everybody else is having the same problem.

note: if you describe your speakers would be better, do they have one sub/woofer on each side totaling 4 drivers or just 1 per speaker.
These are bipolar speakers.

Two mids in the back and a tweeter. I think I was told the mids are crossover higher then the fronts (around 250hz).

Two mids and a tweeter in the front. I was told the front are crossover at 80Hz, but I don't believe it.

One side has a active DSP controlled woofer and a radiator. The other side has a radiator. I have the active woofers facing in on both sides. With the woofer facing the wall, it doesn't sound as tight.

Measurement were taken with only one speaker connected, so the response is from just a single tower in it's typical position. I've measured these several times in different positions, and the response seems very consistent. Audyssey helps bring a little more lower mids, but also tends to have some issues with the woofers.
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