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Old 25th November 2002, 09:38 PM   #1
BAM is offline BAM
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Default taking advantage of bass boost

I'm probably getting a 250-watt PE sub amp for Christmas, and I am looking for some way to get good, solid, tight bass. I think a sealed box is the way to go, and if I get the 250w amp with the bass boost, I think I will be able to do it.

I know I've got an entire dance club designed right into my woofer, and I'm looking for ways to get it out. My woofer is one of the first-iteration Blueprint 1001 woofers, which has a double-stacked magnet structure, 12mm one-way Xmax (but I get more on bass hits), and 300w max power handling. My current enclosure is the port noise king, and whenever big bass tones are going, it's over there huffing and puffing. (I also know of a leak in the seal around the woofer, so that adds to the chuffing sound.) I like to listen to music mostly, and the subwoofer should be able to go nice and deep for me. My listening tastes are varied, with big-band jazz at one end of the spectrum and hardcore metal at the other end. As far as big-band jazz goes, I'm looking for nice tight, controlled bass. The hardcore metal, on the other hand, has lots of double-bass-drum that must be very tight so each kick is nice and distinct.

Now, here's my real question for you guys. How do I go about modeling a subwoofer to take into account a plate amp's bass boost? I want to use the bass boost of the plate amp to get good, deep ported-box lows. The current iteration of my enclosure design uses a 15" long port that is 12"x1" in the size of the opening. Its frequency response has a slight plateau from about 50 to 30 Hz, and an F3 of 25Hz. The woofer's resonance is 18 hz. It's a woof machine, but that's all it is. The amplifier has enough juice to cram the cone forward, but it runs out when it comes time to pull the cone back inward. That's why I'm upgrading to the 250w amp. I'm also getting the 250w amp because I want to be able to run this thing at such volumes that the suspension of the driver is near to bottoming if I decide that's what I am in the mood for. But I also want to take advantage of the sealed box's nice, tight transients. I'm looking for depth, but also a quick, more effortless characteristic to the attack. At high volumes and low frequencies it just looks like the cone is flopping around in the air. So apparently this present enclosure

So, I'm looking for your experienced opinions. Is this doable (sealed box with integrated bass boost)? If so, what do I have to take into consideration to integrate the amp's bass boost properly?

Also, I hear about air leaks with the PE amplifier (around the power switch). Can I patch these up with some good silicone-based sealer?

Thanks in advance, I know it's a lot of stuff to ask.
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Old 25th November 2002, 10:05 PM   #2
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I can't help you on the first part of your problem but the best way to overcome air leaks around the plate amp is to mount it in a seperate sealed section of the box, using a piece of MDF to create the partition. This will also increasing the box's strength by adding bracing. After all, there seems little point in making a super-strong box if there's a flimsy aluminium panel flexing all over the place...

Nice one,
David.
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Old 25th November 2002, 10:28 PM   #3
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Hi BAM,

I did something similar to what you're looking for with a pair of TAD 1601a's and a Nakamichi SF-100 Subsonic Filter/Bass Boost. I started by plotting the the boost of the Nak with frequency. Then determined the bass alignment necessary for flat response. I ended up using an overdamped ported alignment that was 6db down when the boost was 6db up. I have included a zipped spreadsheet that showns my initial guess at where I needed to align the bass speaker/box combination in relation to the Nak bass boost.

I'll include more info later as I am just leaving work.

Rodd Yamashita
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File Type: zip nak_sb100_boost.zip (23.8 KB, 33 views)
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Old 27th November 2002, 07:33 AM   #4
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BAM,

Excuse me if the Blueprint 1001 is not designed for a sealed enclosure.... but you could design a large enough enclosure (Qtc = 0.5 approx) and make it both sealed and ported.

In New Zealand - I can buy a screw on PVC cap for a standard 4" PVC pipe - in theory allowing me to "screw in" a sealed box in about 5 seconds for music, removing for the HT throbbing experience...

I agree with the separate sealed enclosure for a plate amp - even if they claim it is sealed - the thin aluminium on some (esp. if the box is small and the plate amp is a good chunk of the surface area on the panel) - will be flexing.

David.
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Old 27th November 2002, 07:48 PM   #5
palesha is offline palesha  India
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Dear Rodd Yamashita, Can u give circut details along with formula. I am interested in more information.
MP
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Old 27th November 2002, 08:56 PM   #6
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Quote:
Originally posted by palesha
Dear Rodd Yamashita, Can u give circut details along with formula. I am interested in more information.
MP
Hi Palesha,

The response curve of the Nakamichi SF-100 is from actual measurements. I don't have the schematics for this unit, but I believe it is just a Chebyshev hi-pass filter with a 24db/octave cutoff slope and a Q of about 1.4 (someone correct me if I'm wrong on the Q for 6db bump in the pass band).

I can provide the alignment information on the TD1601a woofer as I did that in Bass Box Pro. Are you interested?

Let me know and I'll dig it out when I get home this evening.

Rodd Yamashita
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