Can't see it without talking off the dome.
Rob
Thanks for the picture and info
Loren, there's a lot of tech stuff, what is good in your case.
I imagine you measure your enclosure on the inside. I checked you mention to "calculate the true internal volume". If not discount ~3/4%, when measuring from the outside, to include only the wood on the outside of the cabinet.
I imagine you measure your enclosure on the inside. I checked you mention to "calculate the true internal volume". If not discount ~3/4%, when measuring from the outside, to include only the wood on the outside of the cabinet.
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Loren, there's a lot of tech stuff, what is good in your case.
I imagine you measure your enclosure on the inside. I checked you mention to "calculate the true internal volume". If not discount ~3/4%, when measuring from the outside, to include only the wood on the outside of the cabinet.
The process I use to calculate internal volume in CAD is to:
1. Build a complete 3-D model with every brace, port, and the 2235H driver installed.
2. Create a filled solid 3-D model of the overall shape of the cabinet.
3. Subtract each part, panel, driver, port, and brace from the solid 3-D model.
4. Let the software calculate the remaining 3-D shape volume.
Here is the inside volume of my cabinet:
An externally hosted image should be here but it was not working when we last tested it.
As long as I didn't forget any braces the calculated results should be very accurate. Even if I did forget a brace, the difference in volume is not going to be significant.
Loren, it should be perfect... but something is not, as you say.
Also, (late) congratulations because your speakers look very nice.
To see how a room may influence your audition look here
Loudspeakers Calculator - Room acoustics
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I don't know if this has been mentioned but a very simple way to try altering the tonal balance can be done with a computer.
Although not what one would consider true hi-fi, unless done right, something like Foobar's parametric EQ would give you a lot of options under the press of a button.
It would at least allow you to experiment around a bit and maybe you can find out what you're truly missing.
Although not what one would consider true hi-fi, unless done right, something like Foobar's parametric EQ would give you a lot of options under the press of a button.
It would at least allow you to experiment around a bit and maybe you can find out what you're truly missing.
I moved one of the speakers into our music room. I should say that the "music room" is actually a smaller formal living room, but we have a baby grand, three or four acoustic guitars, cello, and some other more exotic instruments populated around for our enjoyment. It is 15' by 14', but more importantly, it is carpeted. The cabinet is set up near the center of the room facing toward the corner with the mic 2 meters away.
As you can see in this plot (compared to earlier plots in this thread) that the bass profile is much different than the room we have the stereo set up in.
What is this speaker really doing? Hard to say when measuring in confined places, but the fact that it changed clearly states that the room is a major influence with the sound.
An externally hosted image should be here but it was not working when we last tested it.
Thank you!
If/when I get these speaker satisfactorily dialed in I have a large stack of Koa veneer sitting on an overhead shelf waiting to be applied to the cabinets.
They should look quite striking when they are done, but I want to make sure all the issues are ironed out first. Once I understand and fix anything major with the frequency response I need to work on any cabinet resonances. I would like to add a few more braces and then add some form of internal wall treatment similar to Damplifier Pro on the walls to cut down on resonances.
Ha! Just found a sort of local source for the JBL mass rings and dust caps cheap. Apparently, JBL still sells them, so I order 4 of each and should have them early next week.
Since the existing dust caps had been punched in at one time, it won't hurt to pull and replace them. If the mass ring is really missing on the voice coil, I'll just glue one of those in there, too.
Since the existing dust caps had been punched in at one time, it won't hurt to pull and replace them. If the mass ring is really missing on the voice coil, I'll just glue one of those in there, too.
Something is wrong, it's about 30% or 40% of the volume... please correct me, because I'm making this from my head. Editing: Ok, it can be ~20% considering 15mm wood (5/8") and area.
RE Enclosure Calculator
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I did a quick check of the total volume of the cabinet if you include the exterior and it came to 9 cubic feet (mid enclosure not included), so that is about 25% larger than the 6.7 cubic foot interior I calculated.
That is a nice cabinet and I'm not questioning your carpentry, but could there be a leak? I hope you didn't leave anything loose while working on it such as the input cup or something?
What does it do when you drive it hard at the tuning frequency? Is the port velocity high, cone motion low? You can check for leaks while doing this since the pressure is high at Fb.
Did you consider an active DSP XO like the Behringer? Then you'd have to triamp, or you could keep the mid to tweeter XO and bi-amp.
It would let you take out room peaks, and extend the bass with EQ but I agree that you should determine if something is wrong first.
What does it do when you drive it hard at the tuning frequency? Is the port velocity high, cone motion low? You can check for leaks while doing this since the pressure is high at Fb.
Did you consider an active DSP XO like the Behringer? Then you'd have to triamp, or you could keep the mid to tweeter XO and bi-amp.
It would let you take out room peaks, and extend the bass with EQ but I agree that you should determine if something is wrong first.
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I don't think there is a leak, but it is worth checking for.
I had an active system (tri-amped) with it awhile back, but when I finished building my tube amp I went back to a passive system and upgraded the midrange driver and some cabinet fixes. One tube amp is enough when it costs $1100 in parts.
Yes, my plan is to get the speakers set up correctly first, then at some point we will rearrange the room and we can look into "room treatments" to tame issues with the room. After all that is done I can consider custom EQ to address remaining room and baffle step compensation.
I kind of like to keep things as simple as possible rather than add EQ as a bandaid, but I realize some amount of EQ will be required in the end.
You could try passive baffle step at line level just to make it easier, but I would agree with your suspicions that something is off given that the step is at such a low frequency. I wonder if you might have a strange cavity resonance going on there - have you measured the woofer near field just to see if there are any large deviations in the passband?
You may have multiple problems which is often the case with a new design, not enough baffle step,
a low bass issue, a few room effects, and perhaps a poorly chosen mid to tweeter crossover point.
Did you consider dropping this to 2 kHz?
You could use an inexpensive SS amp on the low end, refine the design with Digital EQ-XO,
which is very easy to tune, then move back to passive if you believe it is necessary. I'd like to
see 200W/ch on those woofers.
What are some of your test tracks if you don't mind my asking?
You may have multiple problems which is often the case with a new design, not enough baffle step,
a low bass issue, a few room effects, and perhaps a poorly chosen mid to tweeter crossover point.
Did you consider dropping this to 2 kHz?
You could use an inexpensive SS amp on the low end, refine the design with Digital EQ-XO,
which is very easy to tune, then move back to passive if you believe it is necessary. I'd like to
see 200W/ch on those woofers.
What are some of your test tracks if you don't mind my asking?
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Here is a composite of the port and the nearfield of the woofer very, very close to the dust cap:
An externally hosted image should be here but it was not working when we last tested it.
The two plots are not correctly scaled in SPL, but you get the idea...
It is a 3-way, so the lower cross point is 400 Hz and the upper is at 3K Hz.
I think I have a lot of room effects, too.
I don't know what is really a good sample to listen t, I use Shawn Colvin's Polaroids, but most of my work right now is with sine wave sweeps. My intent is to get the ugly peaks and valleys tamed, then work on timber and sound quality once everything is matched up level wise.
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OK, so the cone output looks reasonable no peaks in the response, notched at the
box resonance, but the port output must be attenuated since the summed output is shelved down.
Also, the peak frequency of the port is a bit high relative to
the notch in the driver output. Have you tried plugging one
port which will tune it much lower? Just to see what happens
to the total output? Might be high due to leakage from the woofer as you
stated earlier.
You might also try stuffing the upper chamber with damping material to reduce the cavity
resonances. There might be a top to bottom transmission line type resonance which will not
behave as a lumped box compliance as seen from the lower end of the box.
BTW - I really like this big beast of a speaker, nice work!
box resonance, but the port output must be attenuated since the summed output is shelved down.
Also, the peak frequency of the port is a bit high relative to
the notch in the driver output. Have you tried plugging one
port which will tune it much lower? Just to see what happens
to the total output? Might be high due to leakage from the woofer as you
stated earlier.
You might also try stuffing the upper chamber with damping material to reduce the cavity
resonances. There might be a top to bottom transmission line type resonance which will not
behave as a lumped box compliance as seen from the lower end of the box.
BTW - I really like this big beast of a speaker, nice work!
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"but the port output must be attenuated since the summed output is shelved down."
Well, that is the big question. How do I determine if this is true or false? The problem is idiopathic in that it is so hard to determine what is room artifact and what is deficiencies in the speaker system.
I can work the problem holistically, but it is better to know where the source of he problem lies, so I keep trying to unlock clues with the speaker first.
As for the possible cavity resonance, do you feel I should add additional layers of stuffing over the walls?
Thank you for your compliments. I like large speakers (as does my girlfriend) and the original design (shape) was one of my first speaker builds in high school when I did not have a clue as to what I was doing.
It still has the basic dimensions of the first build, but I sculpted the mid and tweeter section as you see it now.
This is a rendering of the first cabinet built many, many years ago. The woofer was a JBL D140 mated with some crapy tweeter made by AR.
An externally hosted image should be here but it was not working when we last tested it.
The port was a slot at the cabinet bass and the two 2X3s that acted as legs also worked as a ducted port. None of this was done very scientifically and I don't remember where the tuning was for the cabinet. T/S parameters were only just getting developed back then!
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Here is a link to Don Keele's original paper on the near field measurement method. Note that his measurement of a vented system shown in Figures 12 - 14 provides excellent agreement with theory. The system was similar to your situation in that the woofer was a 15" and the port was very close. The article also tells how to scale the port and cone output by area:
http://www.xlrtechs.com/dbkeele.com/PDF/Keele (1974-04 AES Published) - Nearfield Paper.pdf
You should be able to use nearfield measurements properly scaled, and outdoor ground plane measurements for a half space measurement.
You would normally bury it in the ground for a perfect half space measurement but sitting on the ground should be good enough below 100 Hz.
http://www.xlrtechs.com/dbkeele.com/PDF/Keele (1974-04 AES Published) - Nearfield Paper.pdf
You should be able to use nearfield measurements properly scaled, and outdoor ground plane measurements for a half space measurement.
You would normally bury it in the ground for a perfect half space measurement but sitting on the ground should be good enough below 100 Hz.
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