John Sayers' Recording Studio Design Forum Archive

I've just completed a remodel of my studio, including the soffit mounting of my Dynaudio BM5As. I gave them a listen for the first time last night and felt that they sounded "off" in the bass response.

They have a rear bass port on the speaker, and they also have a switch on the back that allows for some filtering of the bass (three settings: +2 db, flat, and -2 db). I've tried all of them and I can tell that there is an audible difference between them, but the problem remains--not a really bad problem, but noticeable.

Here it is: There is a slight "boxiness", or "boomy" quality to the bass frequencies. I can hear it most with obvious things like bass and kick drums, but I can also hear it in any instrument that has a lower end (male vocal, some guitar, drums of all kinds). High frequency things like flutes, cymbals, etc. all sound great. This boxy/boomy sound makes it sound like someone has hidden a third speaker in a thin plywood box and put it behind the wall right between the monitors.

I'm attaching some pics and I'll try to be succinct and brief in my description of my space.

Two of the pics are schematics that I obtained on this forum, and they were my guides for building my soffits.

I'm working in a very small space: 7' x 11' before the room was reshaped. As a result, my soffits are quite narrow--about 15" across the face of them. Because space was tight, they share the same framing that holds up the slat resonators on either side (which you can probably see in the framing picture of the soffit).

The ceiling is 2x8 beams with exposed insulation between them covered with cloth. The ceiling slopes as well, and because of this my soffits and resonators are not actually attached to the ceiling (you can see the space above them).

However, both soffits have a “lid” on them that creates the chamber in which the speaker is mounted (within its tight fitting box, of course, as per the schematics).

The soffits were built pretty close to the plans below except that there are no “hangers” in the bottom chamber. By the time I had put it fiberglass insulation around the inner surfaces, there was no room to hang anything! Otherwise the design is the same. The framing is 2x2.

I’ve included pictures of the speakers in relation to the front of the room. With the exception of the soffit faces, the horizontal slats are all broad band resonators. The back wall of the room (not shown) is covered with 2” 705 sitting about 1 ½ “ off the wall (on the flat surfaces) and bridging the corners at 45 degrees (like a standard corner bass trap).

Speaker placement: The center of the big cone is 45” from the floor. The tweeters are 46” from one speaker to the next, and my listening position is 46” in front of them. The large cone is almost exactly half way between the floor and the ceiling (meaning the the ceiling that is above the cloth and insulation). The speakers are not perfectly flush mounted--the shape of the face makes it tricky, but if I add some trim on I can correct that.

I have not yet checked the tuning of the room. I got an SPL meter today and I’m getting the ETF software, but this seemed more like a speaker issue. When I listened to them on stands when the room was just a rectangular box with some 705 panels on the walls and corners, they sounded a bit more natural.

This is a long post, so thank you all for your patience. I would greatly appreciate any insights that can be offered. Did I blow it on the soffit design? Is it a mistake to have the soffits share the same frame that holds up the resonators? Are they not flush enough? Or (my worst fear) are they just not the right speaker for soffit mounting? I wrote to Dynaudio and this is what they said: “Well the problem is that the bass port is at the back. So you might have problems with the restitution of the low frequencies. Depending on the type of the structure where you soffit mount, you could loose bass response, or in the opposite, increase it. However we know that in some cases it is not possible to avoid it (OB vans.. ), and we know that they have been mounted this way in some setups. “

Last of all, is it perhaps just that I need to make one of those DIY filters that I’ve read about here?

Anyway…feeling pretty clueless and would welcome some experienced insights.

Many thanks,

Geoffrey

Here are the schematics I worked from.

besides the possible speaker-baffle compensation issue, you might have built a resonant chamber that is effectively amplifying some low-mid frequencies. also, with the speaker and listener at about the main room-height node, you might have some frequencies being attenuated also causing the imbalance. also you have a glass window on one side and wood on the other - right at your listening position - different properties as well.

can you take some measurements?

Your speakers are also protruding from the soffit a little, I'm sure it's unrelated to the issue at hand but it should be fixed anyway. Might help in some other areas, imaging, and who knows maybe even your boominess slightly.

Could also be from the speakers coupling with the entire structure. Can you get something under them like a chunk of foam even temporary to see if it helps?

Thanks for the replies guys--I had pretty much given up on this thread

All good advice, and I'll be looking into it. I've redone the front of the baffle, so now the speakers are truly flush mounted (picture included).

As to whether they are coupled...well, I don't know. I did the soffits as per the schematics above, taking great care to make sure that the front of the "speaker box" (meaning the box inside the soffit into which the speakers fit in such a snug fashion) is in no way touching the front of the soffit (there is a name for it that starts with a "b" that is slipping my mind).

Some measurements: The large cones (woofers) are exactly 45" from the floor. They are approx. 46" from the ceiling and they are 45" from one another (all measurements are from the center of the cones). There is a window on one side and a slat resonator on the other side.

There is a slat resonator between the soffits that is 33" across. The length of the room (from said resonator to the back wall bass traps) is 10'4". The widest part of the room is about 7'6".

I followed one of barefoots links to Marchand Electonics (a supplier of goodies for the DIYer) and he is making me a low frequency shelf filter as per barefoots instructions. Once I have that, I will try out the speakers. I have not heard them since I finished flush mounting them (I sent Phil one of my cables to make sure my speakers would hook into the unit correctly). I'll see how much of an improvement there is and then take the next step. If the problem is cured, that is great. If not, I'll start tackling some of the possible structural problems (if any).

I appreciate the input and welcome any further thoughts that occur based upon the measurements and the new pics. Many thanks!

Geoffrey

Well, an update is in order for those of you who have been following this thread, sitting on the edge of your seats and biting your nails...

The DIY low frequency shelf filter arrived! I didn't do it myself, obviously, but had it done for me--slightly modified. When I talked with Phil Marchand (after he had seen the schematic that barefoot posted) he suggested leaving out the op amps. Because my monitors are powered and the signal was coming from my RME Fireface, he didn't think the amps would be neccessary. As it turns out he was right and saved me some money!

I plugged the unit into the signal chain and lo! and behold! The boxiness is gone. In fact, I had to use the low frequency shelf control on the back of the speaker to boost it up by +2db to get it where it sounded right (it had been set at -2db).

The final judgement as to how accurate the speakers are will have to wait until I check the fine tuning of the room using the ETF software. In the short term, however, I have to say that they sound pretty friggin' tight and clear. I was worried that soffit mounting these speakers would be a total bust because of that rear bass port, but they seem just fine.

As a side note: John S., if you read this you will be happy to know that your room design (with the slat resonators and all) made a huge difference in the sound of my recordings. I had a chance to finally get my mic and preamp hooked up, and WOW! I can really hear a dramatic difference in the sound--I had no idea of what I was missing!

Cheers,

Geoffrey