Open Baffle Project w/TB 1772 and AE OB15's

[bikinpunk]

I guess this is my first ‘official’ post here, so what better to start with than an open baffle project.

A brief preface:
The end goal is to have a true reference system (or as close as I can reasonably get). The setup will be in my upstairs room, which is roughly 17x22ft (recalling from memory). The motivation to do this actually came from my wife, who after listening to a pair of bookshelves I recently built, encouraged me to turn our upstairs space into a music room. Don’t have to ask me twice.
The room will be a dedicated ‘music room’ with my computer controlling source media.

The final setup will consist of the following gear:
Tang Band w8-1772 w/Adcom gfa-2535 @ 2x60w (only using 2 channels)
Acoustic Elegance OB15 (not yet ordered) w/Behringer 2500 @ 2x800w @ 4ohm

I have the miniDSP for a DSP purposes which has plenty of EQ and crossovers. Ultimately, I’d like to go completely passive, but the DSP will help me get close to the final design and then I’ll build what I need (having never built passives before).

I’ve been reading up on OB projects and works/literature by MJK, SL’s info on his Orion setup, and using programs such as Edge to generate baffle response curves, among reading many other posts/threads here. Here’s a few links I’ve gathered in case anyone is ever searching and comes across my thread:
OB Theory
ORION challenge to DIY
Single Driver Website
Home of the Edge
Open baffle study,


Right now, my main concern is in regards to the baffle shape itself. I’ve been reading up on h-frame and standard OB construction. H-frame actually is getting the nod due to it’s aesthetics combined with the boosted low end. However, since this room is upstairs and dedicated to my music, I can make the baffle as large as I like. I have a test sheet of ¾” MDF with dimensions of 5x4ft sitting in my garage right now. After modeling some simulations, I’m considering putting a hole in this for my sub and seeing what the response looks like. I’d like to make about 3-4 test baffles to see where the point of diminishing returns is, and I may wind up having to go this far.
In addition to the sub, I want the TB 8” to get to about 200-250hz and let it play the rest. As it stands, I have it crossed at 300hz 6dB/oct and it sounds pretty darn nice. I hate to put it in such a large baffle, so I may even go with an asymmetrical h-frame (a la the Orion setup). Needless to say, I have quite a bit of testing to do.

I’ve modeled the response for the low end with Edge and came up with the following options, which have been normalized, and also included the graph which corresponds with some of the models:





The 1600x1600mm results are a ‘best case’ scenario, which is a 63x63” baffle. Very large. Though, it helps me to know what I could achieve if I needed to, as I do have this kind of room in the listening room. It seems that 1200x1200mm (~48x48”) will lend good response allowing only a drop of 13dB from 200hz to 30hz, where a 1000x1000mm baffle (40x40”) gives a drop of 14.5dB from 200 to 30hz. 800x800mm (31x31”) is roughly 3dB down from the best case scenario at 30hz, with an overall drop of 15.4dB, compared to 12dB for the best case 1600mm^2 baffle. This might be a good ‘stopping point’ as the rule of double power for 3dB is starting to weigh in here which is telling me I could be running out of gas at this point.
With that said, I’ll likely build a 3ftx3ft baffle, place the driver in the center (as predicted for nominal output) and measure it as it is.
According to MJK’s quarter wavelength site, I can use a side piece of ~ 17 inches before I get to the quarter length of 200hz (some fudging here, but alas) and run into reflective issues with the sub. So, I could build a side panel and toy with that to see how the response changes.
*by the way, does anyone happen to know if there’s a way to model this up without sacrificing a lot of wood on the experiment?*

In the end, I'd like to go with a curved baffle just for the looks. I'll likely kerf the edges a bit to get a 3" radius (just a total guess right now). The baffle size is really going to determine this, as I may have one large rectangle or two rectangles: small for the TBs and large for the AE's.



The below are BY NO MEANS the final product. This was simply one portion of the build: experimentation and measurement. The baffles in the below pictures were pretty much built solely for the purpose of comparing to the Edge predicted baffle influence on FR. Again, this is NOT the final product… it is only a portion of testing. The pictures are to show some of the progress of testing. And, yes, the baffles I’ve used for the TBs are too small. This is not the final version. (did I mention this isn’t the final version?)









Sub amp. Already has the fan mod for quieter fan and the guy sent me XLR/rca cables so I don't have to make my own now.



As a side note, it's crazy awkward to be behind speakers and still have an image in front of you.
These drivers need some break in time. The first listen was pretty rough and there was serious harshness. After about a day of music things are much better.

[Pano]

Nice looking project, thanks for posting.
There are so many ways to do open baffle, and so many more opinion about how to do it right!

Here's some stuff that I've worked with. Generally considered to be very nice sounding, good tonal balance, great bass extension, good imaging.
Big OB fun. Come hear!
and
Fast, fun, Inexpensive OB project

How are you liking the TB full range? It looks swell, but gets mixed reviews.
Anyhow, the TB with a 15" or 18" active helper woofer is the way to go. Not hard to do at all. The hardest part is going to be setting the crossover point.
Hint: Set the low pass on the woofer a least 1 octave below where you think it should be and adjust from there. Third order seems to blend well with the driver above.

Have fun! Keep us up to date.

[preiter]

Your selected drivers have a sensitivity mismatch that will make going completely passive difficult.

But there is nothing wrong with bi-amping. Between the boost you are getting from your woofer's high QTS and the ability to adjust the volume separately on the woofers you can get away with a much smaller baffle than you are considering. Plus since you are already using the mini-dsp you can use EQ to fine tune your response.

[bikinpunk]

Thanks for the feedback. This is definitely going to involve some trial and error. The link you provided to your friend’s setup looks nice. I noticed he used asymmetric H-frames, too, like Linkwitz did. I wonder if that was to help the low end response as well.




My take on the OB setup with these drivers so far is good. However, the baffle is too small to really give me anything below 500hz nominally, as this is where the OB steps in and starts the rolloff @ 6dB/octave. But, I tell you what… let me give you guys some background info which details what I heard when I heard these drivers ran OB compared to a local record producer’s various mark-daniels setups during the same weekend. Note, the setup I listened to used the 1808 version, whereas I’m using the 1772 version. Why? Because I got them for a good deal here. Also, the 1772 specs seem to be better: higher efficiency (2dB more) and higher fs. Although it has a lower qts and lower xmax, I’m using this with a sub so those two aren’t very important to me. Mainly, the higher sensitivity grabs me because I’m shooting for system dynamics and I’ve found more dynamic systems generally have more efficient drivers. This really shows in transients and dynamic recordings.

Bold notes the OB listening session:

Originally Posted by bikinpunk

had a great 'stereo' weekend...

Saturday I hung out with the recording engineer who lives about 5 minutes from me. He has so much gear it’s unreal. He has over 20k LPs/Cassettes/CDs throughout his house and set ups in 3 different rooms. I attached some pictures of the basement setup which had 2 Alesis mastering cd drives, and a couple other $3k CD players. There was a $3k tube amp which he said he preferred over his Mcintosh (which was why he sold the mc). He had a $15k amp and a couple other ‘cheaper’ ones (about $4k+ each).
He also had a lot of ‘budget’ gear, which contained $800 amps and cheaper CD players. Had a few tube pre-amps and a lot of misc gear laying around. I got to hear all sorts of setups and was blown away by the amount of detail. He let me bring my CDs in and compare all the setups, going from room to room listening to the same song and comparing. He asked my opinion and was helping me learn some things about setups in general. Cool thing was that he wasn’t a snake-oil salesman like I was afraid he may be. We talked about digital connections, variations in amps, amp sound, etc, etc. We discussed tuning and other things.
He let me hear some things he’s mastered and asked my feedback. It was cool because a lot of things I noticed, he said I wasn’t imagining. Really cool to sit down with THE ENGINEER and talk about his music. He even gave me a demo disk to take with me and gave me some notes he jotted down about what to listen for.

Dude was a total riot, too. We’d be listening to Korn and he was rocking out next to me, LOL. Found out he’s a huge RATM fan so we spun some RATM disks and rocked out. Spent about 4 hours over there. He listened to my car a bit and said it sounded really nice. Very well balanced and a very smooth feel to it. He had a couple pointers that I really appreciated. Cool part was he demo’d it using his own music.

Attached some pictures of his basement setup... cell phone pics so forgive me. He invited me back whenever so we are going to try to meet up in a couple weeks for some more listening sessions. Turns out his daughters went to school with my wife, so he actually knows my wife and her family, too. Crazy how things like that work out…




Then, yesterday I got to hear an open baffle setup building at a different person's house similar to what I’m going be building. Holy wow, that sounded amazing!
Long story short, I was talking to a mutual friend about my current OB build (all the gear is here… just waiting on the subs) and he told me about his boss’s setup that he built for him which is using the same full rangers I’m using. So, I made the drive up to my friend’s house and then we drove over to his boss’s house to listen..
Soooooo much detail! Stuff I literally have never heard before. I couldn't believe how good it sounded. A set of TB full rangers and a set of peerless xlss 12's (one driver per side) SHARING 25w. So, each driver getting 12.5w. The subs were in a sonotube enclosure as a temporary setup. Sounded exteremly nice. Whole cost for that setup was less than $500 for the drivers. The amp he was using was a Red Wine amp. He had a whole lot of other gear, too but we only listened to that one setup since it’s similar to what I’m building. When I say that setup sounded amazing, words don’t do it justice. I literally sat there wondering why I even bother doing it in a car (then I remembered that I do it because it’s fun and it’s a challenge… plus I love music). Easily the most detailed system I’ve ever heard. I would put it up against the engineer’s setups any day of the week. The only issue I had was some shoutiness at the higher volumes, but I’m talking about 115dB (measured with the rat shack meter c-weighted). He was WAILING on it to show me the limits and I was impressed, to say the least. Spent about 2 hours there and left knowing that I had made the right decision for my upstairs listening room.

So, my impressions of the OB setup I heard was fantabulous. I mean, unreal. So, that’s what I’m trying to achieve, albeit with OB subwoofers instead.


The more I model the setup, the more I lean towards a 3x4ft baffle, with the sub to the side of center and the TB just a smidge off center (in order to naturally boost the low end via Baffle step). This is all theory, of course. It may go out the window once I build it. But, hopefully tonight I’ll have this mocked up, cut out, and ready to measure. I’ve got a lot of MDF scraps to experiment with h-frame shapes.

The best part is that my wife is all for this project. In fact, she’s shopping for an entertainment center/shelf to put my gear on.

[bikinpunk]

Originally Posted by panomaniac

Hint: Set the low pass on the woofer a least 1 octave below where you think it should be and adjust from there. Third order seems to blend well with the driver above.

I borrowed my IB15’s from my car this weekend and took them upstairs. Having only spent about 15 minutes on the rudimentary setup, I wound up leaving the crossover on the subs at 140hz, 12dB and the TBs were 250hz, 6dB/oct. So, yep, likely going to wind up having a good gap between the two unless I go with steep slopes.

Originally Posted by preiter

Your selected drivers have a sensitivity mismatch that will make going completely passive difficult.

.

I’ve seen talk here that the subwoofer sensitivity should be a few dB higher than the full range driver used.
The AE OB15 is ~91dB @ 1w/1m, iirc. So, yes, there is a mismatch. But, as you said, I’m running the system actively essentially (bi-amping passively in the end).

Originally Posted by preiter

you can get away with a much smaller baffle than you are considering

I really hate messing with more EQ than I need, so I try to build the best I can before resorting to that (not saying there’s anything wrong with an EQ, just sayin’). But, in this case, I hope you’re right. That’s kind of why I’m going to start with the 3x4ft baffle first, to see what happens and just how much shelving is needed for the low end. Who knows, maybe I’ll get it right the first time. .. YEA, RIGHT! LOL.

Originally Posted by preiter

Plus since you are already using the mini-dsp you can use EQ to fine tune your response.

Yes. Definitely planned to implement a shelf EQ, either pulling the top end down or the bottom end up.

As noted, at some point I’ll build passives for the setup, after I nail down what I need. It’ll take some time to get there, though.


Thanks for the feedback, guys!


As a side note, I really am liking the veneer options I’m seeing out there. I’m thinking I may go that route for the final look.

[Pano]

Originally Posted by bikinpunk

I wound up leaving the crossover on the subs at 140hz, 12dB and the TBs were 250hz, 6dB/oct. So, yep, likely going to wind up having a good gap between the two unless I go with steep slopes.

I wouldn't go beyond 3rd order on the woofer and 1st on the FR. Maybe nothing on the FR. You definitely need that gap, unless you do some serious EQ/DSP. But I have never found that to work well or sound good. Notch out some room peaks, yes. But "fix" the OB losses, no. Try rolling the woofer crossover point lower and bringing up the power. The lower crossover point will fight the natural rising response of the woofer on OB. But you lose SPL, so higher power is needed. You might loses as much as 10dB out of the woofer.

Where you end up will depend on the drivers and the baffle size, but don't be afraid to cross that woofer way low. Because of the open baffle bass losses, it will still have planty of mid-bass energy.

Looks like you are well on your way to a sweet system. Very nice that you have a room just for this! Most folks don't.

[bikinpunk]

Originally Posted by panomaniac

I wouldn't go beyond 3rd order on the woofer and 1st on the FR.

Just curious, any particular reason why? I know phase shifts are introduced here, but is there a reason why you suggest no higher than X order for X driver?
Home audio is pretty new to me, but I’ve been in car audio for many years now so I’m very familiar with most terms and especially in the realm of DSP. However, my hands on application of home audio isn’t that high. Most any issues I’ve had in the car have been resolved by extensive DSP. In this case, I’m hoping to build all passive components and not rely on DSP so I can free up the miniDSP for other projects. However, since this setup will be tied to my PC, I am capable of using the PC/software for permanent DSP work.

Ultimately, as you’ve stated, it’ll come down to the baffle. I’m going to try messing around with h-framing it and seeing what it does to the low end.

Originally Posted by panomaniac

The lower crossover point will fight the natural rising response of the woofer on OB. But you lose SPL, so higher power is needed. You might loses as much as 10dB out of the woofer.

I’m thinking I may be able to EQ in the bottom end losses via shelving filter… or cut the top end. Not sure of the implications of one over the other, other than power @ xHz.
Or, do as you've said and cross over very low, letting the crossover function get rid of the rising response.

Originally Posted by panomaniac

Looks like you are well on your way to a sweet system. Very nice that you have a room just for this! Most folks don't.

Thanks.

Not sure if you caught my question for you, but the link you provided for your friend’s setup… how did he arrive at the h-frame design he used? Was it an aesthetics thing or was it done to achieve x response?

[Pano]

Not sure which rig you mean. There shouldn't be any H baffles, but some asymmetrical U baffles. All that is done to give the bass driver more surface area and try to keep ripple to a minimum.

Why 3rd order? Short answer: Yes, phase is big part of it. It seems to be what blends best with a cone driver above it. Experience, not theory.

The hard thing about open baffle for me was understanding that I had to throw away most of what I knew about crossovers. This is not a box speaker and it can't use a box crossover. It just does not work. I've heard many that tried, mine and others, they did not sound right. It took me years to understand - even when I was told over and over. Doh!

The biggest issue you face with open baffle bass is the loss of low end. That can also be seen as "rising response" from the woofer. In theory, you should be able to use a shelf filter and correct it. Then do a normal crossover. Well, that theory never worked for me. I tried and tried every way I could, it just never sounded right. The simple trick of a very low crossover point on the woofer made all the difference.

That said - no need to take my word for it! Try the EQ and normal x-over points. I did, and wasted a lot of time on it but I learned a lot. The lesson will not be forgotten. Since you have the DSP, you should try different approaches. You'll learn a lot and it only costs you time. And who knows? You might be able to get it to work. As I said, there area a lot of approaches to OB. Just letting you know what worked for me. Part of the fun is exploring.

FYI, here is a set of OBees I built a few years back. Similar to your concept, but not with the fancy drivers. Shown here with Selenium 15" woofers and the Hemp Acoustics FR8. Later switched to some vintage Danish 8" full range(not shown).

[trusound]

No reason not to stick with an active dsp driven setup... it is the future for home and provides endless and easy ways to implement and tune..

[kevinkr]

Originally Posted by bikinpunk

<snip>
The best part is that my wife is all for this project. In fact, she’s shopping for an entertainment center/shelf to put my gear on.

WOW!

I am actually interested in the W8-1772 for a small back horn project a ways down the road.. So.. Keep the comments and subject impressions coming. I would have thought that all things being equal the 1808 would have been the better choice due to the higher qts, but if it works, it works..