Best Choice Cab For GPA 604-8H-III

**Elitopus1** · June 21st, 2017, 02:19 PM

But speaker cabinets are not like musical instruments. Instruments like guitars or drum shells are made of thin wood so they vibrate and give the instrument tone.

Speaker cabs (at least good ones) are made of thick wood (like 3/4-1" plywood or MDF) so they are as dead as possible. The woofer cone and HF diaphragm should be the only parts vibrating.

You could build some speaker cabs out of 1/4" plywood and see how they sound

My Hillcraft made 620a cabs have a good amount of bracing from the factory. They sound good.

Also my 828 cabs tightened up when I added bracing.

If someone wanted to make their braces more aerodynamic or rounded, I don't see any problems with that.

**LowOhms** · June 21st, 2017, 02:34 PM

Originally Posted by Elitopus1

But speaker cabinets are not like musical instruments. Instruments like guitars or drum shells are made of thin wood so they vibrate and give the instrument tone.

I agree.

Speaker cabs (at least good ones) are made of thick wood (like 3/4-1" plywood or MDF) so they are as dead as possible. The woofer cone and HF diaphragm should be the only parts vibrating.

I suggest 1 inch Baltic Birch, or Europly, not 3/4s of an inch.

You could build some speaker cabs out of 1/4" plywood and see how they sound

Some people do !! Not me !!

My Hillcraft made 620a cabs have a good amount of bracing from the factory. They sound good.

No doubt E1, but what if they were made of 1 inch Baltic Birch and no braces were in there to disturb the flow ??? !!!

Also my 828 cabs tightened up when I added bracing.

No doubt, it took me 400+ pounds of added concrete mass per 825 enclosure , to stabilize and mass-load mine.

If someone wanted to make their braces more aerodynamic or rounded, I don't see any problems with that.

Oh yes, as GM suggests, dowels, and I think flat braces should have and all their in-cabinet edges rounded over.

Interior insulation should start with none, and added by ear, so that MINIMAL possible insulation is used. By EAR !!

I "think" Dennis' commercially available Serious Stereo 604 MLTL enclosures have NO braces internally, filleted corners where any panels meet, and is made entirely of ONE inch Europly.

- - - - - - - -

See my responses in BLUE. Generally concur with E1, but think NO braces, and a really good box, is best practice possible.

**Elitopus1** · June 21st, 2017, 03:03 PM

Jeff I pretty much agree with you. Dowels for cross braces would be great. And maybe half dowels for side braces.

I'd still be tempted add braces to 1" ply on big panels like the sides of the 828 cab. If you have enough pressure, anything will flex. Thats why the competition car stereo guys fill their car doors with concrete.

**Phil-G** · June 21st, 2017, 06:26 PM

Originally Posted by Elitopus1

Thats why the competition car stereo guys fill their car doors with concrete.

also handy for side impacts

**DaveCan** · June 21st, 2017, 11:37 PM

Originally Posted by oface1

Hello Dave,

Sorry I did not post the link, I usually do. I must've hit "reply" without proof reading!

Here ya go.... I found it to be a great thread!

Audio Asylum Thread Printer

Thank you very much! I tried some searches but didn't come across that thread. Cool!

Update: I believe he is going to go with the Bison cabs, and they seem like a good all round cab for him to have built with the plans he purchased. He was pressed for time as his cabinet builder is going on vacation in a few weeks, and he's eager to get some cabs built he mentioned. He also ordered his drivers from GPA today as well.

I'll make sure to update everyone here on his impressions. Wish I could hear them myself but I'm far away from his locale.

**valhallax** · June 21st, 2017, 11:49 PM

yeah..i thought the rear scoop horn was a little too jbl'ish

**mah** · June 24th, 2017, 02:08 AM

Dave, PM sent re contacting Billfort.

**DaveCan** · June 24th, 2017, 09:18 AM

Thanks mah! He's already given the Bison plans to his cabinet builder so those will be what he goes with. He was kind of impatient to get things going as his builder is going on vacation soon. I talked with the designer of the Bison cabs and they seem like a great all rounder cab, especially for someone who is not a diy type as he is not. They should have excellent SQ and get into the mid 20hz. They have the flexibility of rear ported, front ported, or bottom ported. He will be building them bottom ported as would be the choice of the designer, and offsetting the drivers for a mirror imaged set. Should be a really nice sounding cab in a modern design for these drivers. And they were designed specifically for the GPA 604-H-III drivers which is a big bonus and a good choice for someone who doesn't diy.

I'll post about his impressions when he has them up and running. I won't get to hear them myself or post about the build, so it's kind of left as is now until he messages about them.

If I could afford a pair of the 604's I think I'd go with super thick walls, like maybe 2" or more, and leave the bracing to just the back of the driver to take off some of the weight. Like the Gortnipper build. Maybe go up to 12 cubic feet and 28" - 30" front baffle.. Dunno, I'd need to hire someone like GM to help with the design, but I like an easy, rock solid, and a simple build.

A guy can dream

**Todd W. White** · June 25th, 2017, 10:49 PM

The enclosure that works best for the 604-8H-III's is the Stonehenge V-type enclosure. I have built many of them (well, had them built), and they work wonderfully and measure amazingly. It's about 9-cubic feet of internal volume, and you have to tune the port, depending on which LF cone is being used.

That being said, the internal bracing isn't a bad idea, but, in my experience and opinion, no bracing is a big mistake, just as big of a mistake as using too much (or too little) damping material on the inside walls of the enclosure. Too much, and it dampens the LF performance of the loudspeaker. Too little, and you end up with a speaker that sounds like it's mounted in a box.

The enclosure, unlike a musical instrument, isn't supposed to wiggle. In fact, in theory, it's not supposed to add or detract from the acoustical performance of the loudspeaker - it's supposed to enable the LF portion to perform at optimum efficiency and frequency response. Other than that, it should be acoustically neutral. Oh and rounding the corners of the box may look pretty, but I seriously doubt anyone's ability to hear the difference in an blind A-B listening test...

As with all things in life, there has to be a compromise - so, you do he best you can with what you've got, and learn to accept the differences between "optimal" and "practical", and overlook the rest (which isn't a bad idea when it comes to differing with the opinions of others, no matter how strongly we may disagree with them)....

**DaveCan** · June 26th, 2017, 09:51 AM

Thanks Todd for the response! Yes Bill at GPA recommended the Stonehenge V, but I wanted to suggest an MLTL cab design instead for something a bit newer and different.

I agree with the bracing, I guess what I meant was that I would go with thicker walls and minimal bracing rather than a whole labyrinth of bracing that you see in some designs. Just for an easier build etc. If I was ever able to build some 604 cabs, I'd probably go 2" thick for the cab and add some stiffening strips of either the same Baltic Birch or some spruce strips, and also support the weight off the back of the driver etc.

Anyhow the build is out of my hands and I'll never hear it unfortunately, but was great to have all the help here and elsewhere. Way cool!

Here's a different take on a 604 build. I wonder if the port is inside at the top of the rectangled see through cab section, and meant to release sound through that area for some benefit, or bottom ported?

Dave

Edit: Can't seem to add the YouTube link, sorry.