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

[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

[GM]

Thanks GM.

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

Andrew

You're welcome!

Better than nothing to see if it gets the job done good enough, but lacking any hands on knowledge of this driver/cab combo, room conditions, etc. I have to assume that only a full BSC filter is required and in the case of switching between various output impedance amps that it be fully adjustable over two wide BW ranges like the M19's.

GM

[Todd W. White]

Hello again.

What I mean by wiggling the box is this:

If those large pieces, particularly the front baffle, aren't adequately braced, the LF energy coming off of the back of the cone will set them to vibrating. Damping the internal surfaces can get out of hand - you don't want to overdo or underdo it, but trying to stop the box from resonating by using damping material isn't going to help - it really needs that front-to-back brace for structural and acoustic reasons.

The client's ears are probably prejudiced against natural sound reproduction - he's SO used to hearing it the WRONG way that, when he hears it the way it REALLY sounds, he thinks there's something wrong with the 604. This is a common problem with people who've become acclimated to bad sound. Have him get a LIVE recording of something natural, like a symphony, a pipe organ, a choir, etc., turn ALL of his EQ's and tone controls to FLAT, and listen to it through the 604 - if the recording hasn't been processed and, therefore, is natural sounding, he'll be amazed at how real the 604's sound...especially if he then goes back and listens to the nasty Tannoy's...

[LICORNE]

Todd is 100% right. Last night on CBC TV live from Abbey Road. George Martin said that he made a recording to sound exactly the way he heard it on the 605 . The name of that Album is The Hollies greatest hits.

Enjoy