Bass boost for 2235

[scorpio]

I've recently changed my bass speakers to 2235H, they are in a ~5 cuft enclosure tuned to 33-34 Hz. I have a bi-amp system using an UREI 5235 crossover.

I've been using the bass boost function on the crossover to set a +6db at 30Hz, which does help extending the low end while keeping the slam alive. My question, is there any danger of doing this boost if it's below the tuning frequency of the cabinet? I seem to remember reading that it should not be done as it could lead to uncontrolled membrane excursion, but I can't find that thread back.

I have a fairly small room and am not much of a headbanger, but I still want to keep my speaker safe, and they are fed by a good 200W of Citation 22 power...

I've tried the +6db setting at 20Hz as well, but it does not seem to help so much, probably too low.

Thanks for any advice on this,

[spkrman57]

Then the EQ will respond better and the speakers will run safer.

Ron

[4313B]

Right, you pretty much want to keep the boost at the tuning frequency of the box. 30 Hz tuning frequency for 30 Hz boost, etc. I documented somewhere how to modify the 5234A/5235 for a 25 Hz boost to emulate the BX63/BX63A boost as used with the 2235H and 2245H in the B380 and B460. You can try 20 Hz boost at a 20 Hz tuning frequency as well but there will be a sag in power handling around 30 Hz.

[jbl]

Filter out the ferquencies below the box tuned frequency. That will protect the 2235H.

I'm running my 2235H in the 5ft3 4507. Tuned to 32 Hz. I'm not using a filter below the tuning frequency, though I should. My set-up is audio only, not HT or organ music.

I think I'll take my own advice and get a filter.:D

Ron

[JBL 4645]

2235H Low Frequency Loudspeaker: 380mm (15 in)

FEATURES:

300 W continuous program power capacity
100 mm (4 in}edgewound copper ribbon voice coil
20 Hz to 2 kHz response
93 dB sensitivity, 1 W@ 1 m
http://www.jblpro.com/images/components/2235h_sm.jpgThe JBL Model 2235H represents the latest developments in low frequency loudspeaker technology. It combines smooth response, extended low frequency bandwidth, and extremely low distortion, making it ideal for custom studio monitors and other critical applications requiring an optimum balance of efficiency and bass response.
The 2235H has a low-loss magnetic structure that weighs 8.5 kg (18 5/8 lb) and incorporates JBL's unique Symmetrical Field Geometry (SFG). This design, in combination with the aluminum Flux Stabilizing Ring around the pole piece, reduces second harmonic distortion to inconsequential levels. The 100 mm (4in) diameter voice coil benefits from new adhesive technology and optimized coil-former construction of aluminum, plastic and high temperature paper for increased power capacity. The 19 mm (3/4 in) length of the voice coil allows increased linear excursion capability and the extension of usable frequency response to 20 Hz in equalized alignments and subwoofer applications. Careful choice of suspension elements, taking into account their interaction with the voice coil motion, results in a driver with tight, controlled transient response and complete freedom from dynamic instabilities.
The heavy cast aluminum frame resists deformation and improves heat dissipation, and extremely tight manufacturing tolerances contribute to the high performance and linear frequency response.


SPECIFICATIONS
Nominal Diameter:380 mm ( 15 in)Rated Impedance:8 ohmsPower Capacity:300 W continuous program Continuous program power is defined as 3 dB greater than continuous sine wave power and is a conservative expression of the transducer's ability to handle typical speech and music program materialSensitivity: (The sensitivity rating of JBL low frequency loudspeakers is based on a signal Swept from 100Hz to 500 Hz, rather than the conventional 1 kHz single frequency test signal since these drivers are usually used below 800 Hz Therefore, usable sensitivity of the 2202H may be substantially greater than that of loudspeakers with higher published ratings The half-space reference efficiency percentages will give a consistent method for comparison of E series, Professional Series, and competitive loudspeakers in low-frequency applications.)93 dB SPL, 1 W. 1 mFrequency Range: 20 Hz to 2 kHzHighest Recommended Crossover Frequency:1000 HzRecommended Enclosure Volume:85-285 L (3-10 ft3)Effective Piston Diameter:337 mm ( 13 1/4 in)Maximum Excursion Before Damage:22 mm (7/8 in peak to peak)Minimum Impedance:7.0 ohms ± 10% @ 25°CVoice Coil Diameter:100 mm (4 in)Voice Coil Material:Edgewound copper ribbonVoice Coil Winding Depth:191 mm (3/4 in)Magnetic Gap Depth:7.1 mm (0.28 in)Magnetic Assembly Weight:8.5kgFlux Density:1.2 T ( 12,000 gauss)Bl Factor: 20.5 N/AEffective Moving Mass:0.155 kg Positive voltage on black terminal gives forward diaphragm motion.THIELE - SMALL PARAMETERS:fs:20 HzRe: 6.0 ohmsQts:0.25Qms: 2.5Qes:0.28Vas:460 L ( 16.2 ft3)Sd:0.089 m2 ( 138 in2)Xmax:8.5 mm (0.33 in)Vd:757 cm3 (46 in3)Le:1.2 mHno (Half space)2:1.3%Pe (Max):150 W Continuous sine waveMOUNTING INFORMATION:Overall Diameter:388 mm (15 17/64 in)Bolt Circle Diameter: 370 mm ( 14 9/16 in)BAFFLE CUTOUT DIAMETER:Front Mount:355 mm (13 31/32 in)Rear Mount:343 mm ( 13 1/2 in)Volume Displaced by Driver When Mounted in Enclosure:6 L (0.2 ft3)Depth:137 mm (5 1/2 in)Net Weight:10.1 kg (22 1/4 lb)Shipping Weight:11.2 kg (24 3/4 lb)



http://www.jblpro.com/pages/components/2235h.htm

http://www.lansingheritage.org/images/jbl/specs/pro-comp/2235/page1.jpg

[JBL 4645]

I’ve managed to get the JBL 2240 to respond below 20Hz on some program material with a little help from spectrumlab and Behringer BFQ2496 parametric EQ.

I took a different approach angle last Saturday while monitoring the input of the signal on several films LFE.1 content only and only the LFE.1 track.

(The Goonies 1985) chapter 15, at 44 minutes 18 seconds Jake Fratelli (Robert Davi) bumping his head on the low ceiling in the basement that peaked at high level for bump! I monitored the level directly patched into spectrumlab and so an alarming level that I knew would curse issues if not addressed in some way.

So I applied a few filters and took some guesses to the type of Q size I want to use uniformly over the various different LFE.1 effects and while also monitoring the barograph level on the Alesis RA300 and the placement of the sub as well, which may not be the best placement in the world as different position location or space in the room, might just well add an extra enhancement boost, resulting in less power to drive sub.

I managed to reduce the frequency level while turning it up a few db and the level was less on theRA300 even thou its in bridge mode 8ohms 300watts which is not really enough as I worry about one day possibly clipping the amp for short term.

I’m just worrying that you might so close to the max at certain frequencies that need smoothing out due to the room’ or ironing the frequency for more flatter level. Then you’ll need a few more of the same to make up for some loss, that’s just the way it is sometimes.

Filters applied
30.2Hz -13db Q 0.10
32.8Hz -6.0db Q 0.10
35.9Hz -6.0db Q0.10
45.2Hz -5.0db Q 0.10
48.5Hz -3.0db Q 0.10
55.0Hz -3.5db Q0.10
62.5Hz -3.0db Q0.10
67.7Hz -3.0db Q0.10
70.1Hz -5.0db Q0.10
72.6Hz -3.0db Q0.10

-It could’ve been a tremor, Ma.
-I’ll show you a tremor [smack around the face]


http://i282.photobucket.com/albums/kk279/SpectrumsubbassLFE13417/TheGoonieschapter15Jakeandhisbrothe.jpg

http://i282.photobucket.com/albums/kk279/SpectrumsubbassLFE13417/TheGoonieschapter15Jakeandhisbro-1.jpg

[Russellc]

Filter out the ferquencies below the box tuned frequency. That will protect the 2235H.

I'm running my 2235H in the 5ft3 4507. Tuned to 32 Hz. I'm not using a filter below the tuning frequency, though I should. My set-up is audio only, not HT or organ music.

I think I'll take my own advice and get a filter.:D

Ron
4507 @ 32, is that 2 ports closed?

Russellc

[jbl]

4507 @ 32, is that 2 ports closed?

Russellc
Yes, 2 ports closed.
3 ports closed is for 28 Hz tuning. Sub woofer use. 28 Hz tuning yeilds a sharp cutoff. Down a few db at 40 Hz.