Raising the While Flag on 604 Project

[GM]

Any concensus which way to go?

By the way, how much of a difference does the port configuration make when it comes to bass response? Is diameter more important, or is length the key? Could a 6" port be too small for this cabinet?

Thanks!

You're welcome!

High SQ digital is the way to go in today's 'two bit' world and even if you want a passive XO/response shaping filter(s), finding its specs with digital really simplifies the process considerably.

Quite a bit. The diameter + length sets its efficiency and tuning frequency, i.e. whether or not it may 'wheeze'/'chuff' at high power. For some reason I thought you cloned Jay Fisher's MLTL, but the driver is in the wrong place, so to answer your Q I need to know the cab's net Vb and the port's length.

If it's around 10.3 ft^3 like JF's, then a 6" dia. port is plenty large enough to handle the Iconic 704's/GPA 604-8H II's 100 W rating.

GM

[Seadweller]

For some reason I thought you cloned Jay Fisher's MLTL, but the driver is in the wrong place, so to answer your Q I need to know the cab's net Vb and the port's length.

GM

Thanks GM. Indeed, I did clone Jay Fisher's MLTL. He was incredibly generous with his time and advice, and actually guided me through the construction details.

His instructions were explicit; to mount the driver so the center was exactly 19.625" from the inside top of the cabinet. The cabinet's internal height is 42.5" and my cabinet maker adhered strictly to these dimensions.

Best I can tell, if you take the insulation into account, the cabinets are around 9.9 cubic feet. They are around 10.4 cubic feet in raw dimension. Jay told me to keep the CSA at around 426. Currently the port is 6" in diameter, and 3/4" long (basically, the width of the bottom panel). I also have the 3 ohm resistor in place as instructed.

Jay's instructions were to have the port 6" round, and 2" in length, but I have not trimmed the 6" x 6" port tube inserts that I bought. I tried inserting them into the port hole, but they had no affect. I can't imagine trimming them down to 2" would matter, but again, I'm a complete novice with this stuff!

[GM]

You're welcome!

Going back to some docs and the MathCad sim I see you're right, we even had some correspondence about it, but I was comparing the pic he sent to yours which clearly shows it higher up, so for whatever reason he apparently didn't follow the plan: http://farm5.static.flickr.com/4014/...30408f64_b.jpg

Regardless, changing the vent from 0.75" to 2" long doesn't change the response a lot, so probably only noticeable when a 42 Hz tone of appreciable output is generated, but a 6" long vent drops Fb ~10 Hz, turning it into a near sealed alignment with F3 rising enough for a 3-4 dB loss at ~42 Hz which should be audible. Not night n' day, but a worthwhile difference if you've got some room 'boom' to deal with and the driver is less likely to audibly unload playing pipe organ symphonies.

If you're not hearing any change, then you've got one or more leaks that needs plugging.

WRT insulation, it not only doesn't decrease the acoustic volume, but up to a point actually increases what the driver 'feels': http://web.archive.org/web/200210070...ces/fiberfill/

GM

[RonSSS]

You're welcome!

Going back to some docs and the MathCad sim I see you're right, we even had some correspondence about it, but I was comparing the pic he sent to yours which clearly shows it higher up, so for whatever reason he apparently didn't follow the plan: http://farm5.static.flickr.com/4014/...30408f64_b.jpg

Regardless, changing the vent from 0.75" to 2" long doesn't change the response a lot, so probably only noticeable when a 42 Hz tone of appreciable output is generated, but a 6" long vent drops Fb ~10 Hz, turning it into a near sealed alignment with F3 rising enough for a 3-4 dB loss at ~42 Hz which should be audible. Not night n' day, but a worthwhile difference if you've got some room 'boom' to deal with and the driver is less likely to audibly unload playing pipe organ symphonies.

If you're not hearing any change, then you've got one or more leaks that needs plugging.

WRT insulation, it not only doesn't decrease the acoustic volume, but up to a point actually increases what the driver 'feels': http://web.archive.org/web/200210070...ces/fiberfill/

GM

I was going to mention that about the stuffing. One can change the amount to change the finger rap on the cone from a thump to more of a whack....you have to try it.

Also, a simple sine wave generator, a DVM, a power amp and a 100 ohm resistor can measure the box tuning.

A port firing down into the floor, especially hardwod makes no sense to me.. In a box that large, firing forward makes more sense. Especially in a "hard" room like you have. The room is such a big part of the equation.

I built 8ft^3 boxes for my 411 subs. Also used a 6" round tube port. 8" long worked the best.......

I saw quite a diff from a 1" length to the 8" length. In fact, these are so cheap, you can cut them down and duct tape them together to make them longer.

3/4 of an inch is the thickness of the cab.

The TS parameters I measured for the reconed by GPA were no where near the stock specs, more like a 416, and the tuning worked well. I tuned them to 20hz.

I just don't get the downward firing port.

Ron

[Seadweller]

I just don't get the downward firing port.

Ron

Hi Ron,

Evidently, the downward firing port is intended to use the floor for boundary reinforcement in the low registers. I was experimenting with different cabinet designs, and was actually going to make a conventional tower cabinet with a false bottom (to maintain the 42.5" internal cabinet height), and a foward firing port.

In the end, because of the sheer size of the cabinets, I decided to go with my current design, both to take advantage of the boundary reinforcement, and also to give the cabinets a less "monolithic" look. I really didn't realize how big these were until I got them home. Even my wife was speechless!

[GM]

I was going to mention that about the stuffing. One can change the amount to change the finger rap on the cone from a thump to more of a whack....you have to try it.

A port firing down into the floor, especially hardwod makes no sense to me.. In a box that large, firing forward makes more sense.

Right, one way to ~critically damp the cab by ear.

Why? Acoustically there's no difference until the down firing port is close enough to the floor or other boundary to mass load it to a lower Fb except when there's padded carpet underneath, then it absorbs any out of BW noise that it may be pumping out.

GM

[Seadweller]

If you're not hearing any change, then you've got one or more leaks that needs plugging.

GM

Thanks GM. I guess it's possible that the changes could be too subtle for me to detect, or even more likely, that the excessive midrange energy is masking it.

Honestly, if worse comes to worse, I could add a subwoofer to the system to fill in that gap, but it's the midrange output that I've been unable to address.

I've had numerous folks tell me that I'm nuts, and that they've not experienced this effect with these drivers, but I'm telling you, there is a range of frequencies that when a voice or instrument fall in that range, the beaming is like the phaser on the Enterprise. It would cut through solid titanium.

Of course, my preference would be to get this system correct without the use of a subwoofer, as I like the minimalist style of the speakers, and I've really no room for a decent subwoofer.

Actually, for my own curiosity, would a passive radiator mounted in the bottom of the cabinet be an option? Or how about an active driver? Perhaps mount a 416 in place of the downward firing port? I'm not sure how it would interact with the other driver, but I'm just throwing spaghetti against the wall!

[LICORNE]

You're problem might not be your speakers but your amplifier. I remember in the 70's students testing all kinds of receivers they had purchased on A-7 and none sounded the same . The worse was Technics.

For low Price budget Harman Kardon Receiver 100 Watts per channel.
In the higher end Bryston and Mcintosh.


By the way Toyota run away car has to do with cheap electronics .

When buying an amp be careful where it is built.

[Seadweller]

You're problem might not be your speakers but your amplifier.

I began this process with a Parasound A-21, which was an incredible amplifier. An overwhelming majority felt that the low output impedance was impacting the bass, so reluctantly, I sold it, along with my pre-amp, and bought a Cary SLI-80 integrated, also a highly respected amplifier.

I can't say that the tube amp did much for the bass output, and I ran it in both ultralinear and triode mode. I think this time around I'm going to get a SS integrated, and steer away from separates.

[vuki]

When mentioned friend got drivers and enclosures he built jeff markwart's crossover and he was so confident in good result that he immediately bought expensive boutique parts. It was really unlistenable - just as you decribed - no bass with strong highly colored mids and dirty highs.
As I can see Jeff Markwart is a quite serious man, so I doubt that he made his crossover plans without listening and measureing. What I suspect is that he got some early version of GPA driver that was different from the current ones - that's the only logical explanation for such an awful sound.

Anyway - as Panomaniac said; buy the cheapest parts for my crossover (ferrite inductors, wirewound resistors and MKT caps or even bipolar elcos) and put it together "in the air" - you don't have to solder- use screw terminal strips if you like.