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Bass Reflex Enclosure Tuning Using Impedance Plot

Pete B said:
The box tuning has little to do with the driver specs.
Would you post a picture or provide dimensions of the box with woofer and port placement?
The basic model assumes a lumped model where the box is a simple compliance
and the port is a mass. A long enclosure will behave more like an MLTL with the tuning
being off.
There is an end correction when calculating a port tube so be sure to use a "good"
calculator.
You could block the port and then with a piece of wood block off the waveguide opening
until you get the desired tuning, then use that cross sectional area for the final
cut out. You could use a slot without a duct, shape shouldn't matter much.

Which port tube calculator did you use and what were your input values?

A low tuning should sound good actually, have you tried listening to it?
Click to expand...
That's what I thought, the box tuning should basically be box volume and port volume. The enclosure is indeed fairly long with the woofer up high to get it as close as possible to the horn and the ports are low for aesthetic reasons. I built these about a year and a half ago and have been using them occasionally since then. They do sound pretty good, but I felt like the bass was weak and the highs had some harshness. I decided to get a measurement mic and determine how they actually performed. I was using a rather generic crossover obtained from the Zilch's Econowave thread. These started life as Norman Labs Model 10's. I did not care for those at all and decided to give the Econowave mod a shot. Initially, they sounded much better than the stock Model 10's, but as I have spent more time with them I started to notice the harshness. My goal is to develop a better crossover, but the first thing I noticed from the impedance plot was the box tuning at 41Hz when I was aiming for 57. I have been stuck trying to get the box tuned where I think it should be ever since.

I use this calculator with an end correction factor of .732 - http://www.mh-audio.nl/Calculators/WVC.html

The box inner dimensions are 10" deep, 13.5" wide, and 35" tall. I'm using a box volume of 2.7 cu.ft., but realize it might be less with the driver and horn displacement. I am using two ports that I had my son 3D print for me. They are 3" ID and 3.5" long so they can be shortened as necessary. I originally cut two holes the correct diameter calculated for the front baffle thickness of 1.25", but when the tuning was measured to be so far off, I kept enlarging them and never could achieve the tuning I wanted. I have since switched to the printed tubes.

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Oh, that looks very cool. Which horn driver are you using on the waveguide?
I'm doing something similar to Rect III boxes, but do not plan to use a sub:
https://audiokarma.org/forums/index...a-rectilinear-econowave.812079/#post-13609023

I'm planning to start with the Econowave SR design, and adjust as needed:
http://techtalk.parts-express.com/forum/tech-talk-forum/34467-flex-your-pcd-mettle/page33#post507940

I'd just shorten the ports until you get the target tuning.

If you have a means to EQ the system I'd try more baffle step to help with the
harshness and a peaked high pass to provide more bass extension. If you leave
it tuned to the low or mid 40s try 3 to 6 dB of a peaking high pass with the peak
at 42 (low E on a bass guitar).
 
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Pete B said:
Oh, that looks very cool. Which horn driver are you using on the waveguide?
I'm doing something similar to Rect III boxes, but do not plan to use a sub:
https://audiokarma.org/forums/index...a-rectilinear-econowave.812079/#post-13609023

I'm planning to start with the Econowave SR design, and adjust as needed:
http://techtalk.parts-express.com/forum/tech-talk-forum/34467-flex-your-pcd-mettle/page33#post507940

I'd just shorten the ports until you get the target tuning.

If you have a means to EQ the system I'd try more baffle step to help with the
harshness and a peaked high pass to provide more bass extension. If you leave
it tuned to the low or mid 40s try 3 to 6 dB of a peaking high pass with the peak
at 42 (low E on a bass guitar).
Click to expand...

Pete, he mentioned something odd, that with even the ports removed, leaving just the 3/4" thickness of the front baffle, that the tuning is still far too low. Any idea?
 
kevintomb said:
Pete, he mentioned something odd, that with even the ports removed, leaving just the 3/4" thickness of the front baffle, that the tuning is still far too low. Any idea?
Click to expand...
Yes, exactly. The front baffle is actually 1.25" because I laminated 1/2" MDF over the existing 3/4" plywood, but even with two 3.5" ports that are 1.25" long (minus the radius), the tuning is still only about 49Hz. Pete mentioned this behaving more like a MLTL - do you still think it would?
 
If you follow the links about ports most people find tuning significantly lower
than predicted when using the port calculators.
I'd either go to a larger diameter which I view as difficult, or remove some
material from the back of the baffle to make them shorter.
Or just live with the 49 Hz tuning.

A vented box has a 4th order rolloff, what is your plan for the crossover to a sub?
 
Pete B said:
Oh, that looks very cool. Which horn driver are you using on the waveguide?
I'm doing something similar to Rect III boxes, but do not plan to use a sub:
https://audiokarma.org/forums/index...a-rectilinear-econowave.812079/#post-13609023

I'm planning to start with the Econowave SR design, and adjust as needed:
http://techtalk.parts-express.com/forum/tech-talk-forum/34467-flex-your-pcd-mettle/page33#post507940

I'd just shorten the ports until you get the target tuning.

If you have a means to EQ the system I'd try more baffle step to help with the
harshness and a peaked high pass to provide more bass extension. If you leave
it tuned to the low or mid 40s try 3 to 6 dB of a peaking high pass with the peak
at 42 (low E on a bass guitar).
Click to expand...
I chose the high efficiency pro driver so I can use these with tube equipment. I do not have anything more than basic analog EQ in the preamp, so setting up what you are suggesting would be difficult.

The compression driver is the JBL Selenium D220Ti with the JBL waveguide #338800-001 from the JRX series speakers. It seems there are other combinations of drivers and guides that perform better at this point, but that's what was suggested when I found the thread.
 
Pete B said:
If you follow the links about ports most people find tuning significantly lower
than predicted when using the port calculators.
I'd either go to a larger diameter which I view as difficult, or remove some
material from the back of the baffle to make them shorter.
Or just live with the 49 Hz tuning.

A vented box has a 4th order rolloff, what is your plan for the crossover to a sub?
Click to expand...
I will give it a listen. It is definitely much better than the 41Hz it started at. By 4th order rolloff, I assume you mean it will roll off sharply at 24dB/octave. I'm not sure how to do it yet. I have been looking at the miniDSP units for my HT and maybe if I like it I could use something like that. The cost seems high to me is what's holding me back.

Honestly, I'm regretting not searching a little harder for a driver that would go a lot deeper and still have reasonably good efficiency. There's no reason that a good 12" driver in a box that big shouldn't go plenty low.
 
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Actually, to hit really low 28 to low 30s with high efficiency I'd guess we'd
need something like 6 to 8 cuft. I'm hoping to get to the mid to high 30s ( -3dB)
with the PA310 but more likely it will be mid 40s - I have to check it out in
the simulator. I don't know PA drivers that well but most that I've looked at
will not do 30s in 2-3 cu ft - if you find one please let me know.

Most high efficiency drivers have a Qts that is too low and you end up with
what's called an extended bass shelf (EBS) as a result. You can use a high
DCR air core woofer inductor to add some resistance and raise the effective
Qts when you need to nudge it up a bit - but then you throw away some
efficiency due to the resistance.

The PSB Stratus Gold is a medium efficiency speaker that's 3 cu ft tuned to
28 Hz that sounds amazing and clearly digs very deep. Well, I thought it was
medium efficiency, they measure 84 dB/2.83V into a 4 ohm speaker:
https://www.stereophile.com/content/psb-stratus-gold-loudspeaker-1997-measurements

Yes, a 4th order vented alignment rolls off at 24 dB/oct and if you add a
high pass you'll end up with 6th order. It can be made to work just keep it
in mind. You might want to plug the ports when you integrate with the sub
so that the woofer then has a 2nd order roll-off and 4th when you add the
2nd order high pass filter.
 
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