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.
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.
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.
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 !
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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.
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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.
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.
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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.
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.
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.
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...
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...
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...
Neat stuff. I prefer European drivers because not only are they good, but they publish accurate specifications.
The driver you cited is 18", which is a little hard to shoehorn into a 15" hole. Still I could not find a driver lower than 30 something Hz for Fs.
I would consider another driver if someone has a recommendation and it doesn't cost too much for the crossover changes that it causes.
If the Q is just a little low you can raise QES and hence QTS by inserting a small amount of resistance in series with the woofer. You might however then have some issues with integration (levels) between the woofer/mids-tweeter. I'd try it and see.
The X-O design looks reasonable in that nothing "leaps"
out at me.. I don't have a sense from looking at this whether or not the designer assumed an amplifier behaving like a perfect voltage source or not.If the Q is just a little low you can raise QES and hence QTS by inserting a small amount of resistance in series with the woofer. You might however then have some issues with integration (levels) between the woofer/mids-tweeter. I'd try it and see.
The X-O design looks reasonable in that nothing "leaps"
The Solen inductor in series with that woofer might just give me a little resistance boost.
Solen 5.5 mH Perfect Lay Inductors 14 AWG from Madisound
Hi,
Here's how your response should look like with 25 resp 30Hz tuning in an 6 cu ft (170l) box, not bad at all.
Take one test with the mic inside cabinet (through one port) and post the response.
The result will tell a lot about your tuning.
Take care and do this with very low power as sound pressure is very high inside box.
I have used JBL 2235H and there should be no problem at all getting good bass out if it.
Here's how your response should look like with 25 resp 30Hz tuning in an 6 cu ft (170l) box, not bad at all.
Take one test with the mic inside cabinet (through one port) and post the response.
The result will tell a lot about your tuning.
Take care and do this with very low power as sound pressure is very high inside box.
I have used JBL 2235H and there should be no problem at all getting good bass out if it.
Attachments
I know that you need a 15" for your box, but you get so much better drivers in the 18" size - that's my experience anyway.
How many litres in the box?
Here is some inspiration: The history about the world's best loudspeaker...
A little bit provoking and irony that's the way we are here in Denmark
Holger4 has invited many people in to see and HEAR his LOUDspeakers - all have been quite surprised about the sound quality and SPL performance.
Unfortunately I haven't heard them, but I can imagine how they perform
How many litres in the box?
Here is some inspiration: The history about the world's best loudspeaker...
A little bit provoking and irony that's the way we are here in Denmark
Holger4 has invited many people in to see and HEAR his LOUDspeakers - all have been quite surprised about the sound quality and SPL performance.
Unfortunately I haven't heard them, but I can imagine how they perform
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...
They are really expensive here which is why so few hobbyists consider them, the 18LW1400 driver you're touting costs nearly $700 apiece here, and for that kind of money really should outperform almost anything. My 16" Iconics were just a little more than half as much each, which most of my hobbyist friends thought was obscenely expensive.
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I will run more comprehensive testing tonight and run a plot inside the vent as you suggest (with care).
I am also thinking I need to pull out a little stuffing inside as well.
Yes, it's fun to spend big bucks freely.
Our Commander in Chief does!I ordered som Transmission Line cabinet design software a few days back. I am interested in modeling a number of drivers with that software and see what happens.
I played around with the dcr of my inductors precisely for the same reason - I actually needed to decrease the resistance slightly in my case so I went to an inductor with a lower dcr. You would want to do the reverse of course, and I would recommend trying several of differing gauges, but see whether adding a small amount of resistance (<0.5 ohms) has a measurable or audible effect before spending the money.
Also note that if the speakers have not been fully broken in or have been sitting for a long time (many years) the spiders may have stiffened up and running them for a while might improve the situation. My Iconics took about 100hrs to settle in from new, and the low end response changed measurably during that time. (I should have broke them in on a test stand first.. lesson learned?)
There should be enough just lining the box walls with stuffing.
It's important that you place the mic well inside the box, away from ports, I was just suggesting the port for cable entrance.
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