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JBL LSR305 tweaking
JBL LSR305 tweaking
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Old 16th March 2018, 08:02 PM   #1
Juhazi is offline Juhazi  Finland
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Default JBL LSR305 tweaking

I have just purchased a pair of modern legendary active monitors JBL LSR305. They were on sale at thomann.de obviously because a MkII model has been released recently.

This little gem has been reviewed eg. here JBL LSR305 Studio Monitors

I ran some measurements and listened to a single speaker today. Measurements line up with noaudiophile well. Sound is very impressive but there is a strong coloration making them sound boxy, also knucle test result is poor. I put the mic almost in contact with panel and every measurement showed strong distortion around 240Hz. It is obviously a 1/1 wall resonance based on height of the cabinet. --> http://semimac.org/wp-content/upload...-Enclosure.pdf

Internal cross-bracing should kill that well, I'll try that during next days and report my findings!
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File Type: jpg LSR305 panel resonance disto.jpg (140.2 KB, 1355 views)
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Old 16th March 2018, 08:19 PM   #2
6L6 is online now 6L6  United States
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JBL LSR305 tweaking
Looking forward to seeing what you come up with! I have a pair of LSR305 with the subwoofer for my computer rig, I think very highly of them, but like anything built to a budget, there is room for improvement.
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Old 16th March 2018, 10:59 PM   #3
Rokytheman is offline Rokytheman  Denmark
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Interesting !
Which mic are you using- And how close to the cabinet?

Wondering if for instance MiniDSP umik1 can be used to test for distortion.
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Old 17th March 2018, 04:19 AM   #4
xrk971 is offline xrk971  United States
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JBL LSR305 tweaking
I got these a few years ago to try them out. The polar dispersion is very nice measurement - but the mid bass was very weak and distorted. Just lacked midrange power and presence. I had to return them because could not sound anywhere near as good as my FAST with 10F/RS225. But what bothered me was that despite being internally DSP’d - the response was not flat.

http://www.diyaudio.com/forums/full-...ml#post4347377

It’s the red curve:
lsr305-tg9fd-10f-fast-copare-4ms.png
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Last edited by xrk971; 17th March 2018 at 04:23 AM.
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Old 17th March 2018, 08:22 AM   #5
Juhazi is offline Juhazi  Finland
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Quote:
Originally Posted by Rokytheman View Post
Interesting !
Which mic are you using- And how close to the cabinet?

Wondering if for instance MiniDSP umik1 can be used to test for distortion.
I use UMIK-1 and REW. For this resonance test I held the mic's foam-covered head in contact with the panel. The metal body didn't touch panel. I played a normal sweep at same spl level as in other measurements (roughly 85-90dB/1m)

The amps are not terribly effective and like XRK said, bass gets stressed easily. Normal mesurements show remarkable distortion below 400Hz. Some of it may be resonance-based, but it is not as peaky as the panel measurement.

I have been thinking of cutting off the waveguide to be used in a semiactive 3-way that I am planning now. We will see... Other option is to make copy molds to clone the waveguide shape...
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Old 17th March 2018, 09:18 AM   #6
manninen is offline manninen  Finland
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Hi man, you´re going the wrong way! Those drivers are way too small for your Man cave

But amazed for the 105€/pc prize

Bitumihuopa 4 kpl - Aanenvaimennus Bitumihuopa - Biltema

I have some biltema bitum band-aid left if any help taking down those resonances
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Old 17th March 2018, 04:26 PM   #7
1audiohack is offline 1audiohack  United States
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Quote:
Originally Posted by Juhazi View Post
I have just purchased a pair of modern legendary active monitors JBL LSR305....
“Legendary”?!? That right there is hilarious to me.

They are a $90. internally amplified speaker and yes they perform pretty well for the price but c’mon, what did you really expect?

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.

The 708’s might acheive legendary status as the M2 is moving toward.

Barry.
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Old 17th March 2018, 04:48 PM   #8
Brinkman is online now Brinkman  United States
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JBL LSR305 tweaking
I have a pair of white LSR305s for my garage and a single LSR308 for my Etherwave theremin. Very interested in watching this thread.

I have considered removing the baffle and filling the backside with sikaflex sealant (self-leveling?) to deaden it a bit. An internal cross-brace is not a bad idea either.
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Old 17th March 2018, 06:52 PM   #9
Juhazi is offline Juhazi  Finland
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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!
Attached Images
File Type: jpg lsr305 center brace knock spectr.jpg (387.4 KB, 1220 views)
File Type: jpg lsr305 center brace inside.jpg (343.9 KB, 1202 views)
File Type: jpg mancave lab.jpg (276.7 KB, 1191 views)
File Type: jpg LSR305fix panel resonance disto.jpg (137.8 KB, 1079 views)
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Old 17th March 2018, 07:28 PM   #10
1audiohack is offline 1audiohack  United States
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Good work! That’s real improvement.

Barry.
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