[kinku]

This is the SPL response of speakers at 1Meter.I have not included the port tuning plots.But I was not sure whether I am measuring ports accurately. I placed the mic at about 1 inch from port opening to measure the port tuning frequency.
I am using REW ,I am using calibration of mic response using an SPL meter during each measurement.So I guess, I am just monitoring the response.
I have not measured T/S parameters.Do not know how to .
These plots are 1/1 octave smoothed.

[MJK]

When I am looking to get just the driver or port response I place the mic 1/4" off the center of the driver or port. This should show the box tuning and any standing wave inside the box. Don't use any smoothing for these measurements. measuring the elenctrical impedance will also tell you the system tuning, it is between the twin impedance peaks.

I think the 1/1 octave smoothing you are applying to the 1 m on axis SPL plot is masking a lot of interesting details. My guess is that the bass goes lower then the plot would indicate but is being smoothed out by the lower frequency 24 dB/octave roll-off. Also, if your speaker is on a stand elevated above the ground you should see the floor bounce null between 100 and 200 Hz and the associated ripple at higher frequencies. If you don't use any smoothing the resposne will look very ragged. Try 1/24, 1/12, and 1/6 octave smoothing to see if any more detail can be seen. Getting good measuremernt results is tough, getting low frequency accuracy is even tougher. Make sure you are using a SS amp and not a tube amp.

[jparkhur]

I put these together today.  And the 125 driver tends to go to 70 very well but at high levels they do break up.  As the above mention, you may want to adjust the smoothing. My upper graph looks similar.

[kinku]

1/4 inch was never used ,it was always 1inch  . And I was using a tube amp for all these measurements  .Is there any write up/guide about how to measure impedence ?
I will get those plots and update soon.

[MJK]

The book "Testing Loudspeakers" by Joseph DAppolito is pretty good. You can get it at Parts Express or Amazon, probably many other places on the Internet too.

[kinku]

Here are the SPL from 1/4 inch and smoothed to 1/24 octave.
also see the port tuned plots attached.
For some reason right speaker does not show the dip between 110Hz-200hz.

[JohnR]

I wonder why the woofer doesn't come back up below the tuning frequency... Anyway, when you measure at say a meter your bass response now goes down to mid 60s?

Unibox:

[kinku]

I calculated the Fb 57Hz and F3 was 70 in my design.John  f3 of 173 is well above Fs of driver 67Hz. How did you get those numbers?Fb is the box resonance to which you tune using port to get the desired F3,which is -3dB roll of point in SPL,rt?
Jparkhur it does go to 70 but starts rolling of at about 109. Can you please post your plots? I do not know what I am trying to achieve here.

[JohnR]

John  f3 of 173 is well above Fs of driver 67Hz. How did you get those numbers?

From Unibox. I just entered the driver parameters, chose a 7L box, and set box tuning frequency to 70 Hz. The f3 of 179 is a red herring, it's because  of the shape of the curve, but it isn't the woofer rolloff. You can see from the curve that the bass rolls off (in theory) in the 60s.

Fb is the box resonance to which you tune using port to get the desired F3,which is -3dB roll of point in SPL,rt?

The port tuning interacts with the driver parameters to create a response curve. With standard bass reflex designs, you get a straightforward curve that rolloff with a clean -3 dB point. But it isn't always like that, as in this example

I do not know what I am trying to achieve here.

Well, you've retuned your port to 70 Hz and verified that with the nearfield measurements. So far so good Could you post the 1m measurement now? (That will include output from both the woofer and the port.) That may be as much bass as you can get from this driver, a BSC circuit will help to balance it out a bit more.

[kinku]

So the frequency from mouth of the port is Fb,which in turn is the tuning frequency of port and the resonance frequency of box, Fb?
Here are the SPL plots at 1M ,1/6 Octave smoothed.

[kinku]

Here is a comparison between plots with ports tuned to 55Hz,70Hz and 55Hz with 3dB BASS BOOST using tone control.Please let me know what yall think.
Yellow port tuned 70
Blue port tuned 55
Red with ports tuned to 55 and Bass boost of 3dB

[JohnR]

Here are the SPL plots at 1M ,1/6 Octave smoothed.

It's hard to tell but that does look a little better than the first plot, up more in the 60-70 Hz region. You'd have to do a direct comparison with same smoothing to see. Does it sound any better?

Perhaps try a BSC and see how that it looks/sounds then.

[kinku]

John please see the comparison of near field response from right speaker with two tuning frequency. I have a hard time figuring out both from graph and listening which is better.Hope someone can tell me the graph at least. It is still good with harshness gone with bass boost applied with tone control in my amp.

[JohnR]

John please see the comparison of near field response from right speaker with two tuning frequency.

It looks like your tuning frequencies are a bit lower than expected, at around 50 and 64 Hz. Bit hard to tell, probably better to have less smoothing for that plot.

It is still good with harshness gone with bass boost applied with tone control in my amp.

That suggests that the BSC would work well. However, it's still pretty shy down low, perhaps there is some room issue or perhaps that is all you can get from this driver.

[kinku]

Thanks John. I had a port with 2.25 inch length available to tune to around 68( 70). I can cut the port tube down to 2 inch and see how that look. But I am wondering if that will make a significant change in bass response from the trends of going up from 55 to 68. But may be there will be a sudden change when you tune to 72 Hz?

[JohnR]

According to Unibox that would lift it up a couple of dB in the 75-100 Hz range, and down a couple from 60 Hz down. Worth a try perhaps although it's not going to be a huge difference...

[kinku]

Fostex specs sheet says Fs for this driver is 67Hz. I am wondering how Martin and you picked Fs as 70?

[JohnR]

Hi, just use the box design program and try different values.

[MJK]

Fostex specs sheet says Fs for this driver is 67Hz. I am wondering how Martin and you picked Fs as 70?

I measured the T/S parameters for the pair I bought and found the average value of fs to be 73.1 Hz. This value might drop a little with more hours of use since they were still fairly new when I performed the measurements.

[kinku]

Thanks Martin and John.I tuned ports to 70 and the bass sounds more fuller.Not much change in plots. Thanks for helping me out. Any opinion about that peak in 7Hz.I do not know if it makes any difference.Heard in other forums using a glue to coat the rear surround to lower the peak.
Martin I saw your website and description of BSC with Zobel on lowther. I was surprised to see iron cored inductor. I was looking for aircored!
Do I need a Zobel with FF125WK?