Started and finished another audio project yesterday afternoon in 5 hours flat!

[DrWho]

The longest dimension in your room is the distance from the bottom left

of the front corner to top right of the rear corner (the longest

diagnal in the room). I calculate that distance to be 23ft which

corresponds to 49Hz.

For the fp you can just slide the frequency up and down to get an idea

of what the possible room gain might look like. If you go to the

"Transfer Function Magnitude (EQ/Filter)" graph (bottom of the drop

down list) you can see how much gain the filter is presenting. I

generally try to slide the fp such that you see 10dB at 20Hz.

If you do an fp of 20Hz you will see ~13dB of gain

30Hz is ~8dB of gain

and 26Hz is ~10dB.

[efzauner]

I don't see anything wrong with using CD inputs and turning up the volume. The volume on most amps is just a potentiomenter between the preamp and poweramp.

As for phono stage input, sure you will get more gain, but you also have the RIAA equalization boost at low freqeuncies.

As for cancelling sound from the push pull. Of course the pushing of one will cancel the pulling of the other when the distance between them is half a wavelength. Using an infinite baffle is supposed to prevent that. Or better yet, I am thinking of building a box around the rear of the woofer to completely enclose it and prevent any cancellation from the rear radiation. I may call the new enclosure "Acoustic Suspension" . :-)

Are you mixing up push pull with Isobaric? In an isobaric the second woofer also has an enclosure around it. It does not produce any sound, but just helps the main woofer.

[chops]

Chops- kudos for speed and all, but are those really being held together with silicone caulk and drywall screws without any glue or screw blocks? Has your other cabinet of similar construction held up well? I can't help but think that this might self destruct when used in a subwoofer cabinet.

Or is that wood glue that I see in the photo?

M

I have never used wood glue, and have never had an enclosure fail on me yet. I have built some super high SPL enclosures over the years for car audio, and the vehicles and woofers start falling apart way before the enclosure even thinks about doing so. And the drywall screws I use are the 1-5/8 "grabber" kind with extra deep threads to get an extra bit on the wood.

[Guest " "]

Hey Chops...been trying to keep up....but your moving pretty quickly....you lost me when you said you were in the process of reversing one of the woofers...but later parts of the thread is focused on measurments....so can you summarize...what is current wiring or mounting config...what have you tried...which sounds better to you.

[chops]

Hey Chops...been trying to keep up....but your moving pretty quickly....you lost me when you said you were in the process of reversing one of the woofers...but later parts of the thread is focused on measurments....so can you summarize...what is current wiring or mounting config...what have you tried...which sounds better to you.

Well so far, I've inverted one driver and it's wiring. I think the sub sounds a little louder and tighter, maybe a hair deeper also. DrWho did some plots in WinISD that say the sub starts to roll off around 23Hz. I did the same thing and came up with just under 15Hz (w/ room gain), and someone else on another site PM'ed me thinking it might be around 18Hz.

Having 1 inverted driver seems to sound a little better. I feel that I'm getting considerable output well below 20Hz, and still getting very strong output below 16Hz.

I'm going to get out the ole' SPL meter (possibly tonight) and run some test tones through the system and see what I come up with.

Does anybody have a link to that corrections table for the Rat Shack SPL meters? []

[DrWho]

There really is no effective way to model room gain without taking

measurents of the actual room...at which point there is no longer a

need to model it [] (unless you want to anticipate room gain in the

future with other designs). The reason you've been getting different

results as to the new F3 is because everyone is making different

assumptions.

If you wanted to be hardcore you would measure the reflection

coefficients of all the walls in your room at various frequencies to

get an idea of how much sound is being trapped inside (which is

ultimately what causes the room gain). As you go down in frequency the

walls start to vibrate more (turning sound into heat) and more sound

starts to get through to the other side. Because your room isn't a

sealed box (open hallway) you are losing a lot of pressure buildup in

that direction.

I actually created an excel spreadsheet that lets you plug in the raw

SPL measurements, applies the compensation and creates a graph. I'll

see if I can't get it uploaded to the forum...

Just one comment...an SPL meter is going to measure only the sound

pressure level, which means it can't distinguish between the raw signal

and the harmonic distortion (which always exists at higher

frequencies). So a better tool for the job would be an RTA - but that's

a bit more expensive (it can be done for $100 with a computer). And

even better would be an ETF which would allow you to distinguish

between the original sound and the effects of the room.

Frequency Response.zip

[Guest " "]

very intresting...the sound of the one-inverted arrangement (can we call this push-pull, or is the jury still out on the correct term) being cleaner...distorion being cancelled out...with a possible db cost...is consistent with a projection earlier in the thread (good call).

now for the question I have been waiting to pop for two days....who will be the first to take a k-33, and after installing one of the lascala bass bin risers, setup a lascala in a push pull manner by mounting the k-33 in the dog house opening inside the elevated bass bin riser?

[DrWho]

I forgot to mention...by turning the driver "inside out" you are also changing the effective internal volume of the cabinet...probably a good 1/2 cubic foot?

[chops]

I forgot to mention...by turning the driver "inside out" you are also changing the effective internal volume of the cabinet...probably a good 1/2 cubic foot?

Yes, which might explain the slightly "deeper" sound to the sub. []

I do have the TrueRTA Level 4 software on my other computer. However, I sold the Behringer calibration mic I had. []

Thanks for that speadsheet. I'll check it out later tonight after work.

BTW, one of the CDs I played last night was Metallica's Load. It's the first time I have played that kind of music on my system since I have made all the mods to the CWs and built that sub. It sounded like a freakin' concert in here. LOL And my "other" brother at the other end of the house said he could feel the bass all the way in there, also through the floor (solid concrete slab)! Granted, it's not a huge house, but he was still about 100 feet away through 4 different rooms! []

[chops]

Well, thanks to DrWho on the spreadsheet, I finally got around to doing a little measuring today. I wish I still had that Behringer mic so I could use that TrueRTA software though, but for now, this spreadsheet should do the job.

Anyway, here it is. I did the test with 1 watt of input, the Cornwalls disconnected and the SPL meter on a Bogen 3001 tripod w/ 3265 "Pistol Grip" head at my listening seat set at "C" weighted and "Slow" response. Both bedroom doors and bathroom door in left rear corner were left open as well as the hallway opening which is always open.

Here's an older pic of the rear of the room as seen through a 10.5mm fisheye lens on a Nikon D50 digital SLR, just to give you an idea of the room layout. In fact, you can pretty much see the entire room in this picture. And go ahead and make fun of the chair on the left along with the two matching ottomans now and get it overwith! LOL []

[DrWho]

So to model your room gain I would use these settings on your linkwitz transform:

f0 = 49Hz

Q0 = .707

fp = 31Hz

Qp = .707

I know your ratshack meter is showing stronger output down lower, but

THD is going to be rather high at those frequencies which is going to

add additional output to the measurement...not to mention the 20dB of

compensation indicates that the meter isn't very reliable down that

low....every meter reads slightly different and I generated the

compensation for 10 and 12.5 Hz based on the quoted roll-off of the

mic. What do the measurements look like when you set the reference

volume at 50Hz to 90dB and 80dB? Nevertheless, it does appear that you

have some sort of resonance somwherew below 20Hz. What are the

dimensions of your hallway? Is it pretty much a "sealed tube"? It's

probably acting like a helholtz resonator.

And just curious...did you make your own bargraph? There should be

another "sheet" (a tab at the bottom) that automatically generates a

typical smoothed out frequency response. I was just curious if it

showed up as a bargraph on your screen or if you created that yourself.

Btw, one more comment...you'll notice that if you enter 1 watt into

winISD that it shows 94dB of output, but that's because winISD is

modelling the half-space situation. To get an idea of in-room

performance (effectively 1/8th space) you simply add 6dB to every

frequency.

[DrWho]

Here's what the graph looks like:

[DrWho]

And here's what winISD says it should look like:

[DrWho]

And for what it's worth, here is the compensation for the ratshack meter:

[chops]

So to model your room gain I would use these settings on your linkwitz transform:

f0 = 49Hz

Q0 = .707

fp = 31Hz

Qp = .707

I know your ratshack meter is showing stronger output down lower, but

THD is going to be rather high at those frequencies which is going to

add additional output to the measurement...not to mention the 20dB of

compensation indicates that the meter isn't very reliable down that

low....every meter reads slightly different and I generated the

compensation for 10 and 12.5 Hz based on the quoted roll-off of the

mic. What do the measurements look like when you set the reference

volume at 50Hz to 90dB and 80dB? Nevertheless, it does appear that you

have some sort of resonance somwherew below 20Hz. What are the

dimensions of your hallway? Is it pretty much a "sealed tube"? It's

probably acting like a helholtz resonator.

And just curious...did you make your own bargraph? There should be

another "sheet" (a tab at the bottom) that automatically generates a

typical smoothed out frequency response. I was just curious if it

showed up as a bargraph on your screen or if you created that yourself.

Btw, one more comment...you'll notice that if you enter 1 watt into

winISD that it shows 94dB of output, but that's because winISD is

modelling the half-space situation. To get an idea of in-room

performance (effectively 1/8th space) you simply add 6dB to every

frequency.

Before I forget, the hallway is 3' 5" x 23' 6" x 8'. You can see in that picture above that the kitchen door is about 5' 3" down on the left, and all the way down the hallway is the foyer that leads into the living room.

Yes, I did make my own bargraph, but it was taken directly from the spreadsheet. Since I only went to 50Hz, I never scrolled down to the bottom of the page.

I'll do some more testing at 90 & 80dB at 50Hz like you asked. I'm not too sure about THD between 10-20Hz, since there was very little cone movement at those frequencies and levels. But, you never know...

So what do you think so far? Does this sub seem rather promising?

[DrWho]

Well it definetly doesn't suck []

And you would have to move to a bigger cabinet if you wanted to increase performance (regardless of driver being used).

How much have you spent so far on this project?

[chops]

Well it definetly doesn't suck []

And you would have to move to a bigger cabinet if you wanted to increase performance (regardless of driver being used).

How much have you spent so far on this project?

LOL! I was cracking up when I read that! [8-|]

If I move to a larger cabinet, then I'm affraid I'd start losing some of that "crispness" and attack that the sub has right now. Besides, wouldn't that only improve the performance below like 15Hz or something? I'm already getting a crap load of output.

How much have I spent? Considering I already had the drivers, the amp and all the screws and silicone... $10.70 and 5 hours of my spare time. []

I still haven't had the time to do the rest of the testing yet, but will get to it sometime today.

[chops]

Okay, Doc...

Here's the charts you were asking for.

The first two charts are 80dB Ref @ 50Hz...

The two last charts are 90dB Ref @ 50Hz...

Sorry, but I couldn't help putting my own charts up there as well. []

[DrWho]

Btw, you can move the reference lines up and down...just click on one

of the lines and then hold shift and it'll keep it all aligned. If they

don't all move together (I'm not sure which revision I posted) then

you'll need to hold shift as you select all of the lines - right mouse

click - and click on group items together.

Do you have a

parametric EQ available? One thing you could totally do is notch out

that ~40Hz peak and then crank the overall gain on the sub...this would

greatly improve the apparent low frequency extension. Something like

-6dB at 40Hz with a Q of 2.

Another thing you might mess around with is taking measurements from

different locations in the room. It'll give you a better idea of what

is the driver and what is the room.

[DrWho]

Another option would be to set a seperate low pass filter on the

subwoofer at around 35Hz such that when you boost the overall gain on

the sub you return to the 50Hz crossover point from the highpass on

your mains.