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Old 2nd February 2010, 12:13 PM   #21
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Yes, please do the measurements I suggested.

Far-field in-room measurements are useless if you want to see what the speaker actually does. Such measurements below 200 Hz will show you what your room is like in the current mic position and speaker position, and almost nothing else.

That being said - those measurements are good if you want to find the speaker placements and listening position with the smoothest bass response.
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Old 2nd February 2010, 02:10 PM   #22
Loren42 is offline Loren42  United States
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A quick and dirty try to determine tuned frequency of the cabinet yields 25 Hz.

All I have is a PC to act as a signal generator and a voltmeter. So, the box does seem to be tuned a little too low, but I would like to confirm that.

I did a number of near-field and far-field tests on both speakers at various places in the room. I moved the speakers and pointed them in various directions and the plots came up pretty consistent.

I seem to loose bass at almost 15+ dB / Octave after about 45 Hz.
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Old 2nd February 2010, 02:15 PM   #23
Borat is offline Borat  United States
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Quote:
Originally Posted by Loren42 View Post
A quick and dirty try to determine tuned frequency of the cabinet yields 25 Hz.

All I have is a PC to act as a signal generator and a voltmeter. So, the box does seem to be tuned a little too low, but I would like to confirm that.

I did a number of near-field and far-field tests on both speakers at various places in the room. I moved the speakers and pointed them in various directions and the plots came up pretty consistent.

I seem to loose bass at almost 15+ dB / Octave after about 45 Hz.
using PC as signal generator the tuning frequency is the frequency at which the driver doesn't move yet below and above which it moves.

also if the tuning is indeed at 25 hz i would leave it where it is. i once had a box tuned to 26 hz and it pounded like there is no tomorrow.

only difference is my box was 88db and powered at 1000W class D.

the problem is the driver has a Q that is too low. this will require either an amp capable of large voltage swing combined with a powerful EQ.

or a subwoofer.

i would do both !

Last edited by Borat; 2nd February 2010 at 02:25 PM.
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Old 2nd February 2010, 02:28 PM   #24
Loren42 is offline Loren42  United States
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Originally Posted by Borat View Post
using PC as signal generator the tuning frequency is the frequency at which the driver doesn't move yet below and above which it moves.
I think that a Voltmeter set to AC Volts RMS should have a magnitude reading with a double hump. The center valley between the two humps is the resonance, or port tuning, point for the cabinet, if I understand it correctly.

That point appears to be 25 Hz. I might have calculated my internal volume of the cabinet wrong, but I know the two ports' dimensions are 3.95" internal diameter and 6" total length from the end of the flare to the end of the tube.

Only one end of the port is flared.

One of my primary goals was a system with a high SPL. The amp in the picture is what I built and only delivers between 50 to 60 Watts per channel. That should be plenty of power to drive a speaker with a 93 dB/Watt/Meter rating, but I really thought I would have deeper bass with the 2235H.

Last edited by Loren42; 2nd February 2010 at 02:32 PM.
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Old 2nd February 2010, 02:32 PM   #25
Borat is offline Borat  United States
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i don't know what you can possibly measure with a voltmeter but hey if it works for you.

are you sure you don't want to be measuring amperes instead ?

the point between the humps should correspond to lowest cone velocity, lowest impedance and highest current.

voltage is unaffected.

Last edited by Borat; 2nd February 2010 at 02:36 PM.
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Old 2nd February 2010, 03:04 PM   #26
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A port tuning of 25Hz is supported by the graph you showed on page 1.

Out of curiosity, try blocking one of the ports, see what happens.
I'd say 25 Hz is far too low for said speakers, especially when you said the tuning frequency was meant to be 50Hz...
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Old 2nd February 2010, 03:23 PM   #27
Loren42 is offline Loren42  United States
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Quote:
Originally Posted by chris661 View Post
A port tuning of 25Hz is supported by the graph you showed on page 1.

Out of curiosity, try blocking one of the ports, see what happens.
I'd say 25 Hz is far too low for said speakers, especially when you said the tuning frequency was meant to be 50Hz...
Cabinet tuning frequency was actually targeted for 30 - 32 Hz. So, I am about 5 to 7 Hz too low if my measurement was correct.
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Old 2nd February 2010, 03:38 PM   #28
cbdb is offline cbdb  Canada
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I see its a tube amp. Did you measure the f response of the amp with the speakers attached?
If your measureing the AC voltage at the speaker it should be constant. (set it to 1 Volt and see if it stays 1 volt for all freq.) If the voltage drops, your SPL will drop the same amount at that freq.
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Old 2nd February 2010, 03:42 PM   #29
Loren42 is offline Loren42  United States
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Originally Posted by cbdb View Post
I see its a tube amp. Did you measure the f response of the amp with the speakers attached?
If your measureing the AC voltage at the speaker it should be constant. (set it to 1 Volt and see if it stays 1 volt for all freq.) If the voltage drops, your SPL will drop the same amount at that freq.
I put an 829 Ohm resistor in series with the amp so that the voltage could vary at the speaker terminal.

I also repeated the same experiment driving the speaker with my PC's sound board and got the same result. I only wish I had an old HP or other type of simple function generator. They work very well for this application without an amp.
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Old 2nd February 2010, 03:53 PM   #30
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I'm not surpriced - it's JBL....

I know you are American, but for once could you please try out something like Eighteensound?
I know for a fact that their 18LW1400 driver outperforms all JBL drivers I have been in contact with...
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