Power/efficiency/enclosure - Quality and Detail at low volumes?

[JammyBStard]

I've just moved into a new house in a very quiet little village in North Yorkshire and immediatly set-about disturbing the peace with my whacking great floor standers.

They are a mongrell Hybrid of Heybrook HB1 drivers and X-Overs bolted into some massive 60's sealed enclosures; they look great and sound great but only once the volume knob is well past the neighbor disturbing mark. this wasn't really a problem at my last place but here I think they might save me a place in the wicker man if I put my bins out on the wrong day so I'd better play it safe.
But at lower volumes they sound muddy and a bit boomy.

I need to Modify/replace somthing in the set-up to improve low level performance.

The current rig:
NAD3130 (Continuous output power into 8 ohms: 30W, 15dBW)
Heybrook HB1 drivers (Sensitivity 90dBw) (oversised Cab)

I'm starting to get the idea about Amp-Power/speaker-efficiency but I'm still not sure about it; Is there any accepted way of designing a system for sound quality at lower volumes. i.e. High-Power low-efficiency or somthing like that?

[AllenB]

Muddy and boomy are words used to describe too much bass. If it sounds that way in a large enclosure at low volumes then I'd wonder whether the cabinet has some standing wave issues, and you have it placed properly in the room.

If it seems to lose some bass at higher levels, your woofer might be causing compression. Hard to say but it might improve with the smaller cabinet.

I think first though I'd stuff the top quarter of the existing cabinet to get some feedback on whether there is a standing wave issue, and move it around the room a bit.

[badman]

Start filling the bottom of the cabinet with bricks. They take up volume and can be stacked to break up top-bottom standing waves in the cab. Additionally, this will change the bass alignment to a higher Q one, which will increase midbass output and reduce deep bass output- which may be exactly what you need to help the low-level listening issue.

2 birds with one stack of bricks!

[JammyBStard]

the main driver has been mounted at the top and the tweeter about halfway down:

I thought what i might do is add a shelf just below the main driver to reduce the volume to the same as that of the original Heybrook HB1's (I assume Heybrook knew what they were doing) and damp and stuff the area behind the driver. the shelf would also brace the cab which isnt made of the thickest stuff.
I don't know if there would be any milage in modifying the area behind the tweeter too? do you think there would be any advantage in that?

[AllenB]

Your most effective braces would be ones stuck to the side walls and back running vertically, not necessarily tying the sides together.

The absence of any damping material means there's potential there. Try to keep clear of directly behind the woofer.

[JammyBStard]

the main driver has been mounted at the top and the tweeter about halfway down:

I thought what i might do is add a shelf just below the main driver to reduce the volume to the same as that of the original Heybrook HB1's (I assume Heybrook knew what they were doing) and damp and stuff the area behind the driver. the shelf would also brace the cab which isnt made of the thickest stuff.
I don't know if there would be any milage in modifying the area behind the tweeter too? do you think there would be any advantage in that?

[JammyBStard]

Report Back:

We added a shelf between the main driver and the tweeter and sealed all the edges, this reduced the space behind the driver to the same as the original donor HB1. I found a pic of the insides of the HB1 and did what I could to damp and stuff it in a similar way:









Also a decent quality re-wire and put it all back together for some listening.

I am usless at listening tests, but they are deffinatly much less boomy and muddy, altogether better defined bass at any volume; a bass guitar sounds like a bass guitar does live now. that sort of issue is much improved. they are possibly a bit tinny now though, like the highs and lows have become a bit too seperated. I'm wondering if the area behind the tweeters should have been modded too? would the size of the enclosure and the way it is damped/stuffed have any real effect on the tweeter?

[AllenB]

No, from this point in it's about the outside of the enclosure and also (mainly) about the crossover.