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Multi-Way Conventional loudspeakers with crossovers

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Old 2nd February 2010, 07:09 AM   #11
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Have you checked polarity?/
if one is out of phase then cancellation occurs.
I've made this mistake and now it is one of my double checks ( read ID10t check )
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Old 2nd February 2010, 08:58 AM   #12
godfrey is offline godfrey  South Africa
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Too much stuffing/damping in the box?
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Old 2nd February 2010, 10:16 AM   #13
Borat is offline Borat  United States
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First check the polarity as Cal Weldon suggested.

But then frankly there is nothing wrong with the graph you posted. That's what those JBL speakers more or less should look like. And you should NOT expect to hear any bass out of them.

Modern hi-fi systems come with built in house curve:

DIY-AV &bull; View topic - House Curve ( Part 1 of 2 )

take a look at the measurement of Sennheiser IE-8 headphone which gets rave reviews:

Click the image to open in full size.

when your system measures like that - then you will have the bass you want !

in fact that's what my system more or less looks like except the bass doesn't stop rising at 100 hz. in fact it is rising the fastest at around 30 hz.

you have a GOOD SYSTEM man. just throw an equalizer and a pair of 1,000W subwoofers (50hz crossover) in the mix and you're good.

Last edited by Borat; 2nd February 2010 at 10:25 AM.
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Old 2nd February 2010, 10:41 AM   #14
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Quote:
That's what those JBL speakers more or less should look like. And you should NOT expect to hear any bass out of them.
LOL! Have you ever actually used a pair of the woofers he's using??

Rob
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Old 2nd February 2010, 11:05 AM   #15
Borat is offline Borat  United States
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Originally Posted by Robh3606 View Post
LOL! Have you ever actually used a pair of the woofers he's using??

Rob
no but i have 15" JBL DJ speakers and they have no bass.
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Old 2nd February 2010, 11:13 AM   #16
terry j is offline terry j  Australia
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It would not surprise me in the slightest that borat could well be correct.

I have not done any sims on those drivers.

however, I run PHL 18's. Pro drivers (and I assume the JBLs have the same heritage??).

they do not go below seventy hz naturally.

I eq the hell out of them (and the lowest I can get them even then is thirty) but I have the most visceral, impressive bass you could want for. (after eq I mean)

does that follow in this case? dunno.

but I can well imagine it.

eq them, throw power at them and you will be in heaven.

50 w will not cut the mustard for that amount of eq.
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Old 2nd February 2010, 11:16 AM   #17
godfrey is offline godfrey  South Africa
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Hmm ... I checked the vent calculation and did a quick sim.
Looks like you got the math right - it should go much lower.

Some ideas:
1) Is the box properly sealed - no gaps/cracks/leaks?
2) What about the microphone you measured with?
(Maybe the mic has a lousy response)
3) New drivers will still be stiff and need breaking in.

Here's something I never heard of before:
Lansing Heritage Forums - Le15A...how low does yours go?
Suspension of old JBL drivers stiffen with age and need to be treated with brake fluid!?
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Old 2nd February 2010, 11:35 AM   #18
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Lack of bass could be caused by room cancellations. Do a near-field measurement as close to the cabinet as possible, and halfway between the woofer and the port. That should tell you if the speaker itself outputs any low bass. This kind of measurement isolates the room pretty well. You could also measure impedance to check if the bass port tuning frequency is wrong.
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Old 2nd February 2010, 12:02 PM   #19
Loren42 is offline Loren42  United States
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Well, many different questions by everyone and thank you so much for your responses.

I can take some far-field measurements, but my understanding was that a 1-meter distance, on-axis plot is pretty standard in the industry. Going far field would add more room acoustics to the mix, I presume.

I coud drag one outside and run a sweep, but these are not easy to tote around. I need a dolly to move these and the step from inside to outside is a bitch, too.

I could also actually listen to one speaker, but it doesn't seem to make sense to me as I know the bass is lacking and I can measure what I subjectively hear with a sweep.

As far as the amp goes, it is one I built. It is just a power amp, so no tone controls are in the circuit. I already measured the amps frequency and distortion characteristics and it is flat down to about 10 Hz. I don't know what the damping factor is.

Kevin, this is the LEAP designed crossover file:

http://www.mdbq.net/pyramid/leap.pdf


Let me know what you think. All components are good quality components.

Johan, the drivers are older, but have new surrounds. The cones got beat up during shipment some time ago. Actually, it was the domes. I pulled them back into shape with tape, did a impedance measurement sweep, and put them into service.

Today I will do an impedance sweep of the cabinet and I will also do a near-field sweep with the mic located between one port (there are two ports, one on each side of the woofer) and the woofer.

Here is a little picture of the cabinet:

Click the image to open in full size.
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Old 2nd February 2010, 12:08 PM   #20
Loren42 is offline Loren42  United States
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Quote:
Originally Posted by godfrey View Post
Too much stuffing/damping in the box?
Hi! 1" of poly fill stapled to about 80% - 90% of all walls. There is one additional sheet that is suspended a few inches behind the woofer on some cross braces.

Ports are clear, even though it looks like they are not in the picture.
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