Fr125S: wide or narrow baffle

[bro]

Hi gurus...

I've got CSS FR125S mounted in a pair of 2002 Mission 780 7 liter bookshelves. Although I like the timbre and resolution, the imaging in my small concrete-walled room of 9' x 11' x 9' (depth, width, height) seems less than desirable.

So I've been wondering if a project like Tom Zurowski's PAWO would give me the magic imaging. http://www.audio-resolution.com/zhorn/fr125s.html

I've read in many articles saying that narrow baffle would give pin-point imaging. But a wide baffle is easier to place since it is reported that these speakers don't mind being close to walls. Since I'm listen in a small room, I'd like to use them against the walls. Hence the Bipolar MLTL, with placement requirement to be well off the walls, would not be something I'd like to experiment with at the moment. So what would be my best option to obtain good soundstaging? Narrow or wide baffle?

Thanks in advance for any opinions!

Cheers!

[maxro]

If they're being placed right against a wall, I would go for wide and shallow. The wall will more smoothly blend in with and 'expand' the baffle that way.

max

[Geoff H]

Hi Bro,
Your room is similar to mine. I ended up with the front mains in the corners, at 45 deg. I biult triagular cabinets and they sit right in the corner. The center of the driver is about 1.4 metres from the floor.

This configuration gives a wide sweetspot, and the axis cross in front of the usual listening area. Imaging is good, with no need for centre fill.

If you use a subwoofer, place it in one of the front corners, not in the centre.

My baffles are 450mm wide. Is that wide or narrow? with a 10" driver, it's average in my book. Because it's in a corner, it doesn't matter.

Geoff.

[Scottmoose]

I'd go with wide. Imaging isn't quite as precise, but how many times do you get pin-point imaging at a live concert? IMO, wide baffles provide the more realistic sound, plus, if you design them right, you can push baffle-step down to the point where room-gain takes over, so if you design in a slightly more powerful bass than you'd normally have, you can compensate for it that way, no BSC circuits needed.

[lndm]

Originally posted by Geoff H
My baffles are 450mm wide. Is that wide or narrow? with a 10" driver, it's average in my book. Because it's in a corner, it doesn't matter.

Indeed. I'm curious, Geoff H, what steps if any did you take to address the "inverted" baffle step, and how do you find the bass?

[Geoff H]

There is no noticable baffle step. The sides are against the walls. The left cabinet is on the desk, the right is on a bookshelf. So the only physical place for a step to occour is from the driver to the top of the cabinet. 260 mm from the centre of the driver. Anything that spills over the top will reflect back into the listening area. Which would occur at about 230 Hz, and only 3db at the most. At that frequency there would be slight rise in radiation restistance of the cone (due to diameter/wavelength) before it falls away.

The bass is generated under the desk. It's fairly good, but struggles to keep up to the effiency of the Wharfedales. I have plans in that area, but I need to secure a panel in the back of the desk first - it rattles.
And then rejuvinate the big amp in the workshop.

In regard to imaging and baffle width, the driver plays an important role too. Deep apex and ribbed cones seem to give beter control than curvilinear cones. Less flex in the cone.

Cheers,
Geoff

[lndm]

Good to see you're having success. I also notice you're using a sub. That's interesting as it must give you a degree of control.

Originally posted by Scottmoose
if you design them right, you can push baffle-step down to the point where room-gain takes over, so if you design in a slightly more powerful bass than you'd normally have, you can compensate for it that way, no BSC circuits needed.

Have you noticed any concerns with the corner behaving as a waveguide at the lows? Apart from room mode issues, do you feel it is feasible to create a system that fits right into the corner and also extends right down to 20Hz?

[Scottmoose]

I never put my WB designs in a corner so I can't comment on that from personal experience I'm afraid.

From a general perspective, yes, of course it's possible to design for corner loading down to low frequencies. In fact, it's a positive benefit. There've been plenty of speaker designs for just this purpose, both DIY and commerical -think of all those huge Tannoy corner cabinets for example. For myself, I've built corner horns for a friend that were ~flat to 18Hz, and they work well to this day. These use the corners as a waveguide, and also to increase mouth are and acoustic impedence, while reducing pressure. Active Eq is a good idea as every room is different, but if you don't like this approach, you can go one of two ways. Engineer a smooth roll-off at a fairly high frequency into the design to allow room-gain to lift it ~flat. Or, design too much gain into it, and then damp it down. I always used to go with the former, but I generally now follow GM's advice to go with too much, as it;s always easier to damp down and over-eager bass than to boost something you don't have in the first place.

Regards
Scott

[lndm]

I've been contemplating an infinite baffle and these replies have been encouraging, thanks.

I feel as if using the corner as an extension to the baffle would give an effect similar to the common baffle step, only in reverse. If a common baffle step causes a loss of 6dB of SPL due to the transition from half-space to full-space radiation (before the room's boundaries come in at the low end), then, corner loading would be like going from half space (on the baffle) to quarter space with an increase of 6dB (before the ceiling and floor come in).

If I'm not mistaken, room gain is an independent phenomena. I figure that if I make the baffle large enough so that the step happens low, it may meet up with the room gain and produce an interesting inverse rolloff that could be matched. (I wish there was more info about on room gain. )

I've been contemplating a baffle of a few feet across, but haven't done the math yet. I have thought of hanging a transmission line behind it. From the work done in recent years on TLs, it would seem they can be quite happy set up for a lean response, even working far above the driver's f_s if desired.

I will do a search for GM's contribution to this, and look forward to reading it.

[Geoff H]

Corner cabinets have plenty of advantages. Rigidity being one. Everything is triagulated. The rear panels are at 45 deg to the baffle: min internal reflection. I haven't loaded any dampening material yet. Don't think I need to. And you are radiating into 90 degrees, not 180.

I had the bass in the centre of the wall, couldn't cancel the phase shift.
Standing waves usually occur in the corners of a room. Placing the bass in a corner reduces that also.

Wharfedale had a few models based on corner cabs. One was for the 12W and W3 combination, and one for the Super 10RSDD. A ducted port in the corner bled into the absolute corner of the room. The cabinets were on legs about 6 inches high. My old man had a recording of a pipe organ somewhere in the US, in a concert hall. The bass pedals rattled windows. And from a Pioneer amp with P-P 6BM8s providing 3 watts per channel. I still have those.

The pair I currently use are modified - shorter voice coils to improve efficiency and transient response further, and stiffer spiders, and a 3" dome radiator coupled to the voice coil. I used to x-over at 500 hz @6db/oct, with a 10dB attenuater paired to Altec Lansing 4118As. (93dB/w) They are quite happy at 180 Hz@12dB/oct.

Geoff