Raising the While Flag on 604 Project

GM · February 18th, 2010, 11:45 AM

Originally Posted by Seadweller

Anway, I've been fighting with extreme midrange energy and weak bass output through the entire project..........

Hmm, something doesn't 'ring true' as the 'spread' through the XO BW should solve the 'hot' mids, but for sure the larger HF horn that allows a nominally 1 kHz XO I'm a 'broken record' about will solve it. Ditto woofer diaphragm treatment, but this typically requires significant experimentation with the real possibility of ruining some before getting it right.

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

**Panomaniac** · February 18th, 2010, 11:58 AM

What I ended up with on the Mantaray orn 604s I have was nominally ~1600Hz, 3rd order crossover with a spread. I'll see if I can find my notes.

I found that the mantaray horn just would not play down lower and stay clean.

**Altec Best** · February 18th, 2010, 12:52 PM

This is one story I don't like to read.I guess it's the part where you may Give Up.You seem to be so close.The 604 should be in a box 9cu. ft/620a for best bass performance I have a pair of 612C's that are 6.8 cu. while the bass is good the extra 2.2 cu. ft will produce much better bass response.

If anything felt like a million bucks to me I would keep them !!! And I would be looking for a new Amp

I'll be building a set of 620/modds soon as soon as this 3 ft. of snow melts

I wish you the best and hope you can stick with it especially after putting 2 years into it.

**mah** · February 23rd, 2010, 10:57 PM

This GPA 604 project had to deal with 'shoutiness'. It might be helpful.

6moons audio reviews: Steph?n's Altec 604 Dream Speaker

Cheers, Marshall.

**Seadweller** · February 23rd, 2010, 11:46 PM

Originally Posted by mah

This GPA 604 project had to deal with 'shoutiness'. It might be helpful.

Thanks mah...I actually traded several e-mail's with Stephaen, and he was kind enough to give me some advice, and send me the schematic of the 4th order crossover he currently uses...I had it built and tried it, but the sound is very dark and subdued...In all fairness, he warned me this would be the case...

**Seadweller** · February 18th, 2010, 01:15 PM

Originally Posted by GM

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** · February 18th, 2010, 01:27 PM

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** · February 18th, 2010, 01:43 PM

Originally Posted by Todd W. White

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** · February 18th, 2010, 01:52 PM

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

**Seadweller** · February 18th, 2010, 02:06 PM

Originally Posted by Panomaniac

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!!