Raising the While Flag on 604 Project

[Seadweller]

Can you post the inside dimensions? There are a number of skilled box guys here, perhaps they can help. And the port size and length is important.

edit:
Hmmm.. looking again a doing a rough estimate, the boxes are not small. Maybe 42Hx24Wx21D.

The internal cabinet dimensions are 23.125"W x 18.4775"D x 42.5"H. The CSA is 426.3672. Internal volume is 10.486 cubic feet.

Port size is 6". The one thing I have not experimented with is port length. The port insert I have will allow a 3/4" to 6" port length (I'd have to trim it in increments).

The port fires downward, and is 10" from the floor.

edit: By the way, it's an MLTL design.

[Seadweller]

As for weak bass, these drivers either must have a huge cab tuned to blend as well as practical to the room and/or a very high output impedance source combined with good room boundary loading, so with such an acoustically small cab you apparently don't have the latter and I assume the Fs tuning required.

GM

Thanks GM...You've actually been very gracious with your time and input throughout this project, and I thank you for that. I actually moved to a tube amplifier to experiment with a high output impedance source to no avail. Funny thing is, I even thought my oldie but goodie Rotel CD player might be contributing to the excessive midrange and/or weak bass, but have yet to try another CD player to see if that might be the case.

The system is extremely shouty in the vocal range; so much so that listener fatigue is nearly immediate, making them unlistenable. I can only describe it as a "megaphone" effect in the frequency range where vocals appear. Any instrument in that frequency range is significantly "enhanced." It overwhelms the rest of the spectrum, and at times, is painful to listen to. It almost sounds like a giant clock radio, I'm sorry to say.

Other's that have listened to the system notice it immediately. It almost seems as if woofer beaming is the issue, and despite the inclusion of a notch filter in this range on my lastest round of XO's, the beaming persists.

Believe me, I hate to give up on this project, but I'm stuck, and my wife has been very nice about FedEx shipments, XO's lying on the floor, and a washer/dryer combination sitting in the living room! 8)

[Todd W. White]

From what I'm seeing, I agree with the others - the boxes are too small.

My guess is you've been treating the symptom and not the cause - the box isn't big enough for the LF part of the 604 to do "it's thing", so the LF suffers and the mid-band, which doesn't care about all that, is doing it's thing, and the lack of balance is what you're hearing.

I can tell you from personal experience that the 604's LF response is IMPRESSIVE in the right sized box when properly tuned - the 50" Bass Drum in the soundtrack from "Star Trek - The Motion Picture", for example, will almost knock you down with only about 15 watts of audio power needed. I've demonstrated this for people and they just can't believe how fantastic the low end from these sound.

But they were in 9-cubic foot boxes...

My advice is -

1. Take a nap.
2. Step away for a few days, but not too long.
3. Come back and revisit the project thusly:

A. Build one 9-cubic foot box (I suggest the Stonehenge V - I drew up plans for it several years ago, and they really work well and aren't so ugly, ie, bulky, as the Altec 620 box).

B. Install the 604 in it.

C. Use the GPA crossover.

D. Set all of your electronics to flat.

E. Play some LIVE recordings of music you are familiar with and see what you think. This way, you avoid mistakes in mixing that often occur on studio's, and the resultant problems that studio recordings often have due to crummy speakers they're usually mixing everything down on.

F. Let us know what happens.

If you're close enough to Oklahoma City, I could arrange to loan you a Stonehenge V enclosure to try...

[Seadweller]

From what I'm seeing, I agree with the others - the boxes are too small.

snip

But they were in 9-cubic foot boxes...

Thanks Todd. My boxes actually measure over 10-cubic feet. This is what perplexes me. If you deduct for the insulation, they're still over 9-cubic feet.

edit: By the way, while bringing up the bass response might provide a better balance accross the spectrum, the "beaming," megaphone effect of the frequencies in the vocal range still remains, abeit better masked by the greater bass output. Funny thing is, I don't believe it's the drivers. Many folks have used my identical cabinet with excellent results. You can see why I'm puzzled and somewhat disillusioned.

[Panomaniac]

9-10 feet is plenty. (good to know I was close on the dims). I'll try to run sims on the cabinet.

[Seadweller]

9-10 feet is plenty. (good to know I was close on the dims). I'll try to run sims on the cabinet.

Thanks Panomaniac! Actually, thanks to everyone!

I'd love to finish this project, but I'm out of airspeed and altitude with it. If there's a reasonably straightfoward fix, I'm all ears!!

[Panomaniac]

First we gotta figure out the problem, then we can fix it!

Below are sims of the box as a bass reflex. GM may be able to simulated it as a MLTL.
3 plots. One is for the GPA 604-8H-II published specs with your box and the port at 3/4"
Another for the 604-8H drivers I have here.
The green for your drivers but with a 3" port length.

The sims don't look that bad. Not enough to give you shouty sound. I suspect crossover issues, maybe even just the horn level.

[sba2]

The system is extremely shouty in the vocal range; so much so that listener fatigue is nearly immediate, making them unlistenable. I can only describe it as a "megaphone" effect in the frequency range where vocals appear. Any instrument in that frequency range is significantly "enhanced." It overwhelms the rest of the spectrum, and at times, is painful to listen to. It almost sounds like a giant clock radio, I'm sorry to say.

Other's that have listened to the system notice it immediately. It almost seems as if woofer beaming is the issue, and despite the inclusion of a notch filter in this range on my lastest round of XO's, the beaming persists.

The room appears to be overly "bright"...bare walls, no drapes, bare floor, etc. Have you tested them in any other rooms?

[Seadweller]

First we gotta figure out the problem, then we can fix it!

The sims don't look that bad. Not enough to give you shouty sound. I suspect crossover issues, maybe even just the horn level.

The midrange output was the most excessive with the stock GPA XO's. My latest set of XO's actually has a lift circuit for the bass, a notch filter around I believe the 1,500KHZ range, and L-Pads that allow for adjustment of the horn output. This is the third set of XO's in which we've tried to address the shoutiness.

Is it possible that the woofer could be beaming in this frequency range? Can that be addressed via the XO?

The driver was placed in a very specific location, evidently to ensure MLTL alignment. I also have a 3 ohm resistor in the woofer circuit as part of the alignment. The system has a tremendous amount of impact, but the bass is certainly lacking.

GM mentioned Fs tuning..How is this addressed? I'm still very wet behind the ears when it comes to this stuff.

Uh oh, looks like I'm starting over again!!

[Steve Schell]

Seadweller, I would also encourage you to continue your project until you are satisfied. After quickly reading the thread, two thoughts occur...

1) Judging from the pictures your room acoustics may be really awful. I looks like you may have a fairly small room with all hard, reflective surfaces. Boxing the enclosures in tightly between the wall and center cabinet strikes me as a bad idea as the closely timed reflections will smear imaging and exaggerate the upper mids. Try pulling your enclosures well out into the room and putting something soft against the side walls and floor to catch the bounce. Mattresses work well for quick experiments. Hard, reflective rooms can really exaggerate the upper mids in a most unpleasant way, and too much mids sounds like too little bass. Better yet, if you can, try moving your speakers outside and away from any reflective surfaces so you can hear what they really sound like, and prepare to be surprised.

2) Use a well recorded female vocal to set your high frequency driver level. Thick and chesty = too little, and thin and screechy = too much. With practice you can get it within a dB or so by ear. The top couple of octaves will also diminish as you turn the high frequency driver down, but these can be restored with work on the crossover, bypass caps etc. It is most important to get the vocals right, the rest can follow.