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Thread: Small but perfectly formed JBL home cinema

  1. #361
    JBL 4645
    Guest

    JBL centre HF sweep

    I raised the level by 4.7db on the graph just to get an idea of the frequency on the flat imaginary line.

    Level sent to HF was -16db fader AVR level set at -13db DynamicEQ was switched OFF

    I muted the LF and started the sweep on the HF tweeter from 900Hz to end at 16,000 KHz since 20 KHz is light-years out of my listening range now, no sense going there if the tone is hard to hear and rarely does it ever crop up in film today. Tones around 10KHz to 16KHz you might hear them on a few odd films a few.

    I knew the peak was there having done the sweep before and seeing it on the RTA with pink noise. I can hear tone just fine, I don’t want the tone in my face, I want to smoothness.

    I guess it wouldn’t be problem listening to the HF sounds on Alien3 (1992) or Whiteout (2009) where there’s a typing like computer sound effect typing out text on the screen, that’s in and around between 4KHz and 8KHz, DynamicEQ should make the softer sounds still audible, over the room, thou the sound effect on Whiteout is a bit fainter in the mix over Alien3 and The Hunt For Red October (1990) has similar effect, I wonder do computers really sound, like that when we type?

    Since the Marantz 1050 are powering the HF tweeters could be the amps adding in hump and slight roll-off still not bad amps for getting on 30 years plus

    Also the crossover on the HF tweeter is set at 2.03 KHz on the DCX2496 Link-Riley -24db
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  2. #362
    JBL 4645
    Guest
    Brought a set of x3 Piezo tweeter horns of fleabay for cool £1.99 each should get them around Monday-Tuesday for hook up.

    Power max. 150W
    Frequency response 1.8kHz - 30kHz
    SPL @ 1W/1m 96dB
    Dimensions 188 x 80 x 107mm

  3. #363
    JBL 4645
    Guest

    Jbl arachnophobia dolby stereo digital 4.1

    Done a little testing this evening with crossover DCX2496 on the lower end, rather than set at 50Hz or 80Hz I’ve experimented with setting at 168Hz Link-Riley -24db over the LCR LF while setting the crossover on the Eltax A-12R at 170Hz and balanced the level using the SPL db at within same level as the loud sound is on one of the LCR while then muting LCR and letting the sub bass extension play and setting for same level.

    So far it’s played without any snags. I’ve set the LFE.1 up by +2db higher over the LCR sub bass extension, the whole system plays fine.

    I’ve tested it out on an early 90’s bass sub bass heavy, that I saw at UCI High Wycombe in one the JBL/THX screens that sounded out of this world.
    Wow the SPL metre is picking up a high bright reverb. The rustling sound is, me setting the SPL db metre at high scale range to prevent the bass sub bass from overloading and distorting. I changed the SPL range from 80db to 90db as the low notes in Trevor Jones score are deep and high at times.

    I’m playing this back on the same JBL system and I’m a little disappointed of the rustling around, but the bass sub bass isn’t grossly overloading as it does on most of the videos that I’ve heard.

    I think I should solder up the lead for the SPL db metre, but hey its not booming with that farting like bass that you hear in those car Hi-Fi videos on youtube at silly 120/130db levels.
    The rest of the midrange to highs are at lower volume, if I wanted to capture that. I’d have to set the SPL db at lower scale range, and turn the sub bass extension down along with LFE.1 so they don’t overload the SPL db metre. So I can’t have it both ways.

    SPL at centre of room will be around 85db to 90dbc at present. So if you play this back on JBL thou the AVR it should sound near (not precisely, just near enough).

    Starting from 6:57 is where the lows get a bit deeper on the playback it seems a bit exaggerated, its more or less near to what I experienced at UCI High Wycombe WHOW! 7:44 starts to mildly distort as the Trevor Jones score is going down on few deep notes at high range.

    Maybe I should have set the SPL db metre at 100dbc. Not at one moment the sound was distorting in the room, it could have been the positioning of SPL db metre at my side a few inches away might have been in warm spot?



    Part2 0:17 was JBL nuts bass/sub bass at High Wycombe it was pressing on my body and pressuring my ears while at the same time, bass/mid and HF highs played loud and clearly, well at softer level as this was one of the quietist moments in the film.

    Also set the contrast range at lower level as it was set up a bit high for the last video I made later in week, the webcam is highly sensitive to bright contrast/brightness images, that tends to add an extra brightness on the image, lousy cheap webcam.

    3:45 I haven’t watched this film/DVD in while now, least of all, not on the LCD video projector and that spider did make me flinch and jump, I hate spiders!

    Most if not most of the low sub bass extension you hear in the videos is over LCR. The LFE.1 only comes on as and when need in the film/DVD.

  4. #364
    JBL 4645
    Guest
    I’ve ran a few frequency waterfalls graphs of the opening. I’ve used only the LCR combined though the audio mixer thou most of lows are covered by the centre channel with milder occasional lows over left/right.
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  5. #365
    JBL 4645
    Guest
    The lows seen here should reproduce in the exact same way in the room over seating area, unless there are dips where some of the lows will not show-off well. The same Spectrumlab can be used for in-room recoding to get a near enough or a precise mirrored matched frequency response.
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  6. #366
    JBL 4645
    Guest

    The Black Hole test

    While first placing the SPL db metre at several locations while analyzing the waterfall frequency response for hot colours and comparing them at seating location to see what frequencies have room gain and what frequencies have dips.

    I first tested the centre channel (with other channels muted) at various crossover settings on the low end from 168Hz to 100Hz and 50Hz while testing sub bass extension at the same range distance. Crossover I tried 170Hz and 40Hz. I had to trim the level for centre low output so that it looked normal, but showed the high tympani beat in the bottom part of the spectrum.

    I trimmed some of the other peaks like, 37.2Hz / 74.3Hz / 107Hz / 155Hz while actually playing the filmDVD in “real time.” This is not usual how to test the, performance I’d sooner look for new approach rather than running a series of frequency sweeps.

    Usual it’s the loudness of the LCRS that I think, makes us turn up the sub bass because are ears are less sensitive to low notes, just like we’re less sensitive to tone over 10KHz.
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  7. #367
    JBL 4645
    Guest
    Tested the Eltax A-12R near to the sub while making an output level adjustment, some portions show where instruments like tympani is beating down on the lower end between 30Hz and 40Hz. The red outline is showing only noise maybe air blowing on the SPL db metre nothing to worrying to about.
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  8. #368
    JBL 4645
    Guest
    Centre channel tested with 100Hz same location near to the centre channel.
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  9. #369
    JBL 4645
    Guest
    Centre channel tested with 100Hz while expanding the spectrum response up to 1KHz
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  10. #370
    JBL 4645
    Guest
    Now tested at Rocker seat location with (centre sub bass extension) no that means centre is muted only the, lows from centre output is being sent to the sub. With PEQ already applied earlier the room gains a bit towards the back.
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  11. #371
    JBL 4645
    Guest
    Same location again, with a bit extra PEQ trimming the warmer peaks down for a calmer level.
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  12. #372
    JBL 4645
    Guest
    Well my package up and after unpacking I switched ON the sound system for testing.

    Well my first test was to set the SPL db metre up at the front centre and test the JBL tweeter (set to a calm level 60db).

    Next was unattached the wires and connect up (I noticed the tone was different and these would have to be EQ).
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  13. #373
    JBL 4645
    Guest
    I noticed screws holding the backs together and undid the backs for inspection. I noticed the paper cone was properly aligned inside the housing and one of the pizeo was slightly pulled to one side due to wire pulling out of the centre of throat.

    I then attached them all back together and tested with pink noise. The SPL came within tiny variables 0.1db of each other. Hey I wasn’t expecting a lot for £1.99.

    I have my eye on some compression HF horns (nope not JBL, why is JBL so expressive?) They have range from 400Hz to 20KHz and cheap rate cost so that might be on the list after I’ve finished building the floor and getting all the Rocker seats set up.

    Anyway back to the piezo horn tweeters. After playing a few sine wave tones to see how they performed as I was bit sceptical and since I have no test RTA equipment that goes monitors above 20KHz I mean 30 KHz really like I’m going to hear that easily.

    I managed to get the pink noise frequency response flatted out up to 16 KHz. It was bit of pig ears, foundling around with PEQ on the DCX2496 and few bands on the other EQ to flatten the peaks out.

    I’ll get a few more for the other two, JBL control 5 later in the week.

    How do they sound with The Black Hole that is presently playing! A bit “horny” LOL what I mean is I can hear a hollow like sound when muting the LF while the piezo horn tweeter plays. I curious as to what they’re technical tolerances are?

    What SPL db peak can they reach within they’re operating range at @1meter.
    What is the real maximum wattage/voltage before the piezo fails?
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  14. #374
    JBL 4645
    Guest
    Measured the piezo horn tweeter @16” from the outside, inside about @19” to the SPL db meter. Not sure if this is accurate but I could test it on Sooty as he has the top end hearing range.

    I started the sweep from 800Hz not that it will respond down that low and I have the DCX2496 crossover set at 1KHz -24db Linkwitz-Riley with audio limiter set to ON for extra protection.

    Frequency sweep won’t go any higher above 23KHz it’s a bit bumpy at the top end and this, with the EQ that I applied earlier on with just adding a few PEQ filters with the (pink noise on the RTA mode).

    I ran two sweeps one at 800Hz to 16KHz and the other at 800Hz to 23KHz

    I’ll have a few more tweaks with this, later on.
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  15. #375
    JBL 4645
    Guest

    ALIEN3 pizeo horn tweeter test



    Here is a recoding of how the pizeo horn tweeters sound at present after another adjustment I made late afternoon, as I was just a bit unsatisfied with the PEQ. I only have few PEQ bands to play with (three) for the HF end as the rest of the 9 PEQ are all used up on the LF range.

    One thing I’ve sussed out is the paper cone inside the horn tweeter needs to be properly aligned, I have slight issue with another piezo horn tweeter that need adjustment. I really need some soft tacky like clue to hold each of them in place.

    Well this is how it sounds for now with ALIEN3 which has good use of dialogue panning.

    Some portions of the peaks are around the 85db range @8 feet.

    Made some changes to the LF crossover to trick or give the illusion while monitoring the RTA of each LF / HF with pink noise. Alesis RA300 now set at full for each LF. Marantz 1050 set half way for each for each HF.

    I placed captions on the video to show which side the dialogue panning and centre channel is sounding from. I only placed a few captions in as there is lots of subtle voices panned left and right on the opening scene.

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