View Full Version : 604-8G in 620 cabinet - Bass responce

09-22-2005, 07:43 AM
Good day @ all

I have built a pair of 620 cabinets for my 604-8Gs but the bass is less than satisfying. Especially the mid bass is nowhere leaving the mid band hanging with no authority. Some very low bass <60 is there but that is all.

Calculating using TS parameters of the speaker, the cabinet suited is about 100liters!!! less than the 620. The result calculates at about 150liters and not 250 of the 620.

Where is the mistake?

Thanks in advance

Earl K
09-22-2005, 09:11 AM
Here is Bills' work at BillForts' Strange Audio Obsession (http://www.wardsweb.org/Billfort/)

- As his testamonial articulates, he has none of the complaints that you've just voiced.

- I do consider your observations as 100% valid, but you need to explore why some people are able to coax wonderful music out of these legacy systems .

- Dealing with these guys is becoming a lost art .

- Here are a few hints to consider ;

(a) These drivers were designed in the day when tube amps ruled. ( ie extremely low damping factors vs todays solid state stuff ) .

(b) These drivers have extremely low Qtc figures / meaning , as long as you are not going to abuse them with too much power you can put them in a reflex box that is way , way , too big for an "optimal: computer generated tuning .

(c) Tied to the above point ; these drivers "predate" computers and more importantly TS parameters . They won't do well ( on screen ) when the tyrannical logic of a TS voicing is applied .

Where is the mistake?

- Most likely, you are just thinking like someone from the 21st century would / rather than someone from the 1950s' .

- Again, ask Bill how he does it . ( He mostly posts over at the Altec Forum (http://www.hostboard.com/cgi-bin/ultimatebb.cgi?ubb=forum&f=3729) ) .

- Here's another thread on the 620 (http://audioheritage.org/vbulletin/showthread.php?t=5707&highlight=billfort) , with comments from Bill in the last post


09-22-2005, 08:02 PM

Perhaps your problem is related to amplifier output impedance. The vintage Altec designs were suited to vintage amplifiers which in general had output impedance of some ohms (not zero). You could rerun your simulation with non zero source impedance which will increase Qes. If you need the equation it is available in Small's AES paper or I can look it up for you.

If you prefer to experiment you can put 4 or 8 ohms in series with your speaker and listen for any changes. The resistor will dissipate some watts so be sure to use a resistor with enough dissipation.


09-23-2005, 01:53 AM
Thanks for the replies.

First of all the amp used is a SET with DF 2.45 which doesn't put much control on the drivers. I have tried also solid state with high DF and I do agree that these fantastic drivers don't like to be controlled by the amp.

As for the mind setting I'm way back in the 50s on my amps. As for the speakers the last 5 years I have traveled thru modern single driver in back loaded horn, Tannoy MG in back loaded horn to land finally on the Altec universe.

Last night was time for tweaking again. My findings were quiet surprising. I managed to improve the bass playing with the stuffing.

But let me layout the steps followed from the beginning. I don't use fiberglass or rock wool because of the kids in the house and the health issues related with these materials. So I use foamed wool. The first try was to cover sides, back, top and bottom. This way killed all the dynamics. It was removed leaving only the top, bottom but dynamics suffered still. Removed the bottom and dynamics were restored but the bass was gone.

Last night I reinstalled the stuffing on the back and the bass improved a little. The big change was when I placed two bags of sand on the bottom of the cabinet about 10Kgs each.

I would appreciate any information regarding the stuffing even thou I understand that using wool is completely different than the usual fiber glass.

09-23-2005, 10:15 AM
Although the cabinets I was using were undersized and therefore not ideal, based on my experience I agree with what's been said about the interaction between the 604-8G and various types of amp outputs. The best bass I got with mine came from using Harman Kardan Citation II's (early sixties 60 wpc tube amp), and second-generation McIntosh solid state with output transformers (MC2200, 200 wpc). Both of these amps have moderate damping factors.

I've noticed a similar effect with my 4333A's. At my usual listening levels, the Audio Research Vt60 gives a fuller, well-defined bass, whereas the UREI 6260 bass with that speaker is quite dry and reticent. When driven hard the tube amp runs out of gas, but most of my listening is at quite moderate levels, and in that range the tube amp is best, and of course the mid-range and treble are very fine. At high levels the solid state amps work better because they have more power and the amount of control they can exert over the woofer becomes an important factor. The MC2200 and UREI 6260 both work well on bass, the 6260 a little tighter, but I prefer the midrange and treble of the McIntosh. These speakers don't have much in the way of slam (if I understand that term correctly) with any amp I've tried.


10-03-2005, 02:15 AM
Downsizing the port from 177cm2 to 120cm2 impoved the low bass a lot. Still missing the upper bass.