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Multi-Way Conventional loudspeakers with crossovers

JBL LSR305 tweaking
JBL LSR305 tweaking
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Old 17th March 2018, 07:08 PM   #11
6L6 is offline 6L6  United States
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JBL LSR305 tweaking
Wow! Fantastic result!

Thank you for sharing!
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Old 17th March 2018, 07:30 PM   #12
tomtt is offline tomtt
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Juhazi,
Quote:
Wrap them in a towel around them and

ratchet strap a couple of bricks to the sides of them and

see what they sound like.
Was hoping, you would try this, as well ....
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Old 17th March 2018, 07:57 PM   #13
Rokytheman is offline Rokytheman  Denmark
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Thanks ! - Will try measuring Distortion myself. Is it possible to acutually damping distortion or resonances with DSP? I Think that Dynaudio in their XD series, claim to do that.
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Old 17th March 2018, 08:00 PM   #14
Rokytheman is offline Rokytheman  Denmark
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Can you elaborate a little bit how you do that in Audacity?
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Old 17th March 2018, 08:07 PM   #15
DPH is offline DPH  United States
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Originally Posted by Juhazi View Post
Legendary humour? But they really are extraordinary for the price!

An internal cross-brace made -25dB reduction in resonant sound, measured with backplate opened and knockin the side panel. Distortion peak measured at 60m (2') was reduced too. Me happy for solid 1 hour "work" on these. I hope that my daughter willl be happy too for her new desktop speakers!
Great work with the brace and love your workspace. And it's not like hot glue is even that intimate of a bond. (maybe playing a damping role?)

Anyone sealed the vent (aperiodic, aka, a sock or 3, or completely closed off) and then run them with a sub? 6L6 is that what you're doing? Seems like they'd do a whole load better.

Been thinking of getting a pair for my older brother as they've got nothing at home, but need to make sure I get something they can use a laptop/cell phone to drive as well.
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Old 17th March 2018, 08:51 PM   #16
Juhazi is offline Juhazi  Finland
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Daniel, they have adjustable gain, any cell phone can drive them. You just need to get adapters to XLR.

Roky, dsp can not do anything good for distortion. These obviously have so called baffle step compensation in dsp, which means that frequencies below 500Hz are boosted or higher frequencies attenuated. Either way distortion in bass is higher, with same spl at 1000Hz.

So these cheap boxes suffer from various rattles and resonances in the cabinet, plastic front plate, metallic back-plate and wires wibrating etc. The loudest noise came from the box panels ringing like a bell with signal of 240Hz and around. 2nd harmonic means buzzing at 480Hz, 3rd ringing at 960Hz etc.

Resonances from cabinet walls and other mechanical parts are usually easy to fix. But if I wanted to make these hi-fi, I would construct new heavy cabinets, fill the backside of plastic front plate with something heavy and puttery and place the amplifier board outside the cabinet or in an isolated chamber. I am sure that the wise engineers at JBL know this too, bet they had to fit a certain retail price and still make profit with manufacturing! Nothing wrong with that!

These same tricks can be used for any cheap loudspeaker. This was not first time for me either.
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Old 17th March 2018, 09:03 PM   #17
Juhazi is offline Juhazi  Finland
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So I used Audacity to analyze sound of knocking the cabinet. My calibrated UMIK-1 microphone was the source and recording was set to mono 16-bit. The opened cabinet was laying on the carpet, I held the mic's head on level with the open back and knocked the sidewall of cabinet with my midfinger knuckle several times.

Then I painted several knocks in the soundstream window and clicked "Analyze" and "Spectrum" to get spl/f graphics. You can adjust parameters of analyzer if you want, more samples means more low end and resolution.

The problem is that knocks aren't equal, but taking several knocks in analysis will make sort of averaging.

I have learned this myself and I use this or modified methods for several other purposes too. The challenge is to make it reliable/repeateble. Nice to check the sound of different guitars this way! Some luthiers use this kind of method too and there are several published articles.
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Old 18th March 2018, 08:15 AM   #18
Rokytheman is offline Rokytheman  Denmark
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Cool and thanks ! Will definitely experiment with that technique !
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Old 18th March 2018, 10:54 AM   #19
Dave Zan is offline Dave Zan  Australia
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Originally Posted by Juhazi View Post
...The problem is that knocks aren't equal...
Bruell and Kjaer actually make a mechanical knocker to standardize this sort of job.
It's mainly for structure-borne noise in architecture and drops half kilo masses about 40 mm.
Maybe you could just manually release a small hammer to fall from a measured distance?
Fairly repeatable and basically zero cost.

Nice result of your simple modification, well done.

Best wishes
David
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Old 18th March 2018, 07:35 PM   #20
Juhazi is offline Juhazi  Finland
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^Actually I have tried a pendulum system like that. However just knocking works. Knocking with a plastic hammer or other object would be better, but knuckles are always handy! Listening to knocks is in line with measurements!

My -25dB is "worst scenario", the cabinet's back wall was opened, cavity working as an amplifier in the measurement. But still, with music the fixed speaker sounds much better than original!
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