Help - Taming the HF on GPA's 604-III

[cradeldorf]

Got any pics of the backside? is there a shelf or anything? How did you know my name was Todd? lol

[atilsley]

Pics to follow.

No shelf as I used double walled ply throughout. Very heavy cabinets.

Todd = Tod White!!

Kind regards.

[atilsley]

Pic of back panel. approx 30 screws to secure. Inside back panel also lined with sound deadening. (1/2 inch rubber ribbed carpet underlay.)

[Todd W. White]

Hey there - sorry I haven't responded sooner. I was in a car wreck a couple of weeks ago and am trying to catch up.

The III is extremely well behaved, especially in that box. It's hard to tell from the picture, but you may not have enough bracing inside. My design calls for a front-to-back brace in the form of an "H" that is secured underneath the woofer hole and connects to the back of the cabinet. You may be spending a lot of LF energy wiggling the box.

What other items are in your system?

[atilsley]

Hi Todd

Sorry about the car wreck. At least you might get an upgrade?!

I'm reporting on this issue all second hand. The guy is comparing his Tannoy co-axes with the 604s...so I don't know what box he is comapring to...maybe a GRF horn. For amp, I think he was using a KT66 or 88's...not sure if SET or PP.

When I had the boxes before sending off, we had a good demo night with some qualified audio buddies. They loved the sound, as did I. In fact, given the US dollar value to AUD, I'd like to buy a pair for myself!

I note your comment on the brace. If the walls are double lined (38mm in total), wouldn't this negate the need for the brace?

You say, You may be spending a lot of LF energy wiggling the box.. What do you mean?

I had also asked about a simple attenuator switch for the HF. Is this do-able and would you recommend it? alternatively, would you recommend by-amping...using a bigger amp to drive the LF's?

Kind regards.

[GM]

Stiffness increases at the cube of thickness, so adding bracing with such a modest power handling driver isn't required, though such a heavy driver should be supported IME. I can't tell if the baffle is doubled up, but it and the top are the ones that need it most.

As a general rule, short of in-wall or corner loaded, speakers need some form of baffle step compensation (BSC) to balance out the mids, highs with the LF. Horn loading typically does it acoustically, the rest build it into the XO, so an adjustable XO is desirable at least for dialing it in to the room: General Speaker Related Articles

GM

[atilsley]

Thanks GM.

What's your view on adding a 'simple' attenuator switch just for the HF's...say -2, -4, -6 dB?

Andrew