The BaSSlines (Lamda TD12H, B&C6md38, Peerless HDS)

I've not posted much here before, but I see great interest in higher sensitivity designs using Pro drivers, so I thought I would start a thread here. I heard this open baffle design by Jeff Bagby/Jim Salk at the inDIYana event in April. I thought they were perhaps the best speaker I've heard, stunningly clean, smooth, balanced and unrestrained with a great soundstage. They were very much live sounding. I was so impressed with them that I've been inspired to try and recreate my own version of it. I'm hoping for sensitivity in the 92-93db range. I believe Jeff said his design was about 93db.

Here is what Jeff is using in the Salk design, according to what he told us InDIYana:
12 Lambda TD12H ($259ea.), crossed at around 450hz.
6.5 PHL 6.5" mid (1120 is the available equivalent) midrange ($159ea.), crossed at 2.7khz
Morel MDT33 tweeter ($149ea.)
http://aespeakers.com/drivers.php?driver_id=6
http://estore.websitepros.com/1736754/Detail.bok?no=48
http://www.madisound.com/catalog/pro...roducts_id=570

For those who have not seen it, here is the Bagby/Salk design.


Goals:
My goal was to create a little smaller speaker (higher SAF, you know). My concept is about 16 wide at the base, tapering to 7 wide at the top and is about 42-43" tall. I'm thinking of doing the woofer bafflesout of laminated solid hardwood, 1.5" thick. The idea is to laminate them from 1"x2" hardwood stock laid flat and stacked vertically. I will mix a second hardwood as shown strictly for aesthetics. The open baffle section will be a mix of 1/2" Lexan with a contunaction of the same laminated hardwood as a bacer for mounting the drivers.

I'm also considering mounting the woofer, midrange and possibly the tweeter from the rear, leaving 1/2" wood between the driver and the baffle face. I would use a 1/2" round-over on the edge. The tweeter,in effect, would have a shallow, 1/2" deep waveguide. This serves to boost the low end output by about 3db over a broad range centered around about 3kHz. When equalized out in the crossover, it will allow the tweeter more headroom and lower distortion at the low end and also help in countering the rising response of the Peerless HDS at the upper end. Mounting the woofer from behind lessens the visual impact it has on the design. Of course, I will be doing some measurements to see just what effect this will have on the drivers natural frequency response before making a decision to use this kind of mount with any of the drivers. Below is a mock-up of what it is planned to look like.



Drivers:
The drivers of the Salk/Bagby design run in excess of $1100/pair. I would like to reduce that where possible, while losing little in either sensitivity or sound quality. Here are the drivers I've come up with to use, with an all passive crossovers at about 450 and 2500hz.

Woofer:
Lambda TD12H 12, 93db: $468/pair (link above)

Midrange:
B&C 6MD38, 96db: $92 ea.
http://www.partsexpress.com/pe/showd...number=294-651

Tweeter:
Peerless HDS 810921, 93db: $78
http://www.madisound.com/catalog/pro...oducts_id=1744
I pcked up two of these for $55 before the price went up.

The B&C 6MD38 seems to be well thought of, has very similar specs and published FR. Zaph has recently tested it and "it looks like a drop in replacement for the PHL" (Jeff's words, not Zaph's). The total driver cost will have been reduced to about $762/pair, and though still very expensive, is about a $340 savings.

The TD12H is in a 55L box. I'm using a slot port, exiting at the bottom rear of the box. Tuning will be such that the F3 will be about 35hz. It will put out over 110db at 100watts and not be even close to Xmax. I'm trying a new box deisgn that uses red oak ribs dadoed into the walls combined with simple cross braces for panel resonance control. According to my calculations, it will use about 17% less space than an equivalent window-brace type design.

I've done some diffraction modelling in BDS. Here are the results for the two drivers:


In addition, I've done some diffraction simulation and dipole simulations in John k.'s ABCDipole and in the Edge. Attached are the diffraction and then dipole simulations from ABCDipole:




Below is a graph from the Edge model showing dipole and diffraction results.


Here are some results on woofer/midrange floor bounce nulls.


Construction of a prototype is ongoing and I will post some photo's next.

Here are some construction photos:

Here are more photos. The slot port will be removable until a final version of the designis complete so adjustments can be made. Also, I will be able to pull it out and finish it separately, or possibly make it out of hardwood.

And three more.

Here are some more construction pics. FYI, the baffles are test baffles. The finished ones will be laminated hardwood and Lexan as planned. The box has been glued up (except the top). The woofer baffle will be removable. Here you can see the cross bracing implemented, including a "filler brace". This brace will be glued to front of the cross brace and have speaker gasket material on its face. It will physically connect to the back of the woofer. This will essentially connect the woofer to all four sides, to distribute vibrations and reduce motor movement. Nxt up are to add a small dowel, top to bottom, through the slot port (to control panel resonance in the top slot port wall), add front face cross braces that will be used for mounting threaded inserts for the baffle removal and pack the space between the ribs with insulation.

When the top and baffle are clamped on, the box does indeed sound quite dead, from a knuckle rap perspective. I have no other way to test it. Of course it will be even better when the top is glued on, the filler brace fully implemented and the final version of the port glued in.

You can see the woofer mounted from the back, 1/2" inset, with 1/2" roundover. I plan to cut a steeper chamfer on the top of the woofer baffle, probably 30º or less. That's all for now!

Thanks, Michael.

The rib placement is generally at golden mean distances on each panel, starting with one about centered where the most support is needed. The cross-braces are offset similarly, with the exception of having to work around the driver.

There are certainly benefits to the bass-bin shape, but ease of construction is not one of them.

I've got a prototype of my BaSSlines together, for testing purposes, though I don't yet have my midrange drivers yet, since they are on backorder until October 10th. Instead I popped in some used Audax Pro mids into the open baffle.

I started with Jeff's original crossover for his Salk speaker and just made some adjustments by ear and also knowing that the tweeter would have a boost at the low end due to the 1/2" deep waveguide mount. Based on my raw listening impressions, I'll say is I think these could be very, very good. The TD12H is one clean woofer. I think the Peerless HDS tweeter in the ½ waveguide is going to work out very well also, based on this test.

Here are a couple of photos of what I'm listening to as I build the second box and wait for the mids to get into stock. I should be starting on some measurements soon on the TD12H and the HDS. I have the Lexan for the open baffle section, but see no reason to mess with it until the design is nearly finalized.

Not really. I will do complete measurements for the final crossover design work. This was just to give me an idea of the potential and something to listen too while completing the other box.

While waiting for my B&C6md38 mids to arrive, (or the Lambda 6.5" ids to be ready) I thought I'd start on some measurements and xover design simulations. However, I will use the Audax Pro170 mid in the meantime.

I wanted to test the Peerless HDS tweeter in a 1/2" deep waveguide mount, a standard flush mount, and also wanted to see what would happen if I created a 3/4"+ waveguide by mounting the tweeter to the back of 3/4" stock, not removing the faceplate of the tweeter. The latter two I accomplished by making one baffle with a 4-1/4" through hole and a 1/2" rebate and several wood inserts that fit in that hole and rebate. I then installed the tweeter in those inserts. Sort of the same idea that Zaph uses for his infinite baffle testing. The 1/2" waveguide mount was already constructed on a separate test baffle.

I have completed some preliminary testing of the flush mount, 1/2" deep waveguide and 3/4" deep waveguide, both on and off axis. The 3/4" deep wavguide was done as follows, since I don't have a 3/4" roundover bit at the moment. First I rounded it over with a 1/2" bit. I actually tested it this way outside. Then I used a 1/2" chamfer bit to open up the hole a bit more. Then I sanded the sharper edges by hand to round them over. This is what I tested with indside. I'd still like to test that with the tweeter face plate removed, as it is in the 1/2" waveguide. I would guess having the faceplate on adds at least 1/8" to the depth of the 3/4" waveguide, making it closer to 7/8"-1" deep. The face plate itself is also recessed, which I filled by using speaker gasket tape.

Here are some measurements of the three. The flush mount and first 3/4" waveguide measurements were done outside, at 103" and only 0,22.5 and 45 degrees. The 1/2" waveguide and second 3/4" waveguide were done inside, at 1 meter and a 4ms window, with the tweeter up about 6' off the floor, at 0, 15, 30, and 45 degrees. The relative spl levels between inside and outside measurements are not comparable due to different levels when importing the impulse response.

The 1/2" waveguide provides a subtle boost that flattens out the rising response of the HDS tweeter from 4khz to 20khz on axis. For example, from 2khz to 17khz there is a 5db rise in the flush mount FR. With the 1/2" waveguide, that is reduced to about 1/2 of that.

The 3/4" waveguide provides a much larger boost, centered around 2.7khz. The modified 3/4" waveguide is not too much different, so opening it up with the 1/2" chamfer did not seem to have too much effect. I will probably test it with the tweeter face plate removed, but it looks like the 1/2" waveguide will solve the main issue, by boosting the low end FR just enough to flatten out the rising responce of the HDS tweeter at the top end.

Peerless HDS Tweeter tests:

Flush Mount: outside at 103", 0, 22.5 and 45 degrees horizontal off axis:


1/2" deep waveguide: inside at 103", 0, 15, 30 and 45 degrees horizontal off axis:


3/4" waveguide: outside at 103", 0, 22.5 and 45 degrees horizontal off axis:


Modified 3/4" waveguide: inside at 1m, 0, 15, 30 and 45 degrees horizontal off axis:

Here are some Lambda TD12H and Audax Pro170 mid measurements. The Audax is just temporarily being used while I'm waiting for the B&C 6md38's to come in. Both of these were tested on axis, mounted from the rear with a 1/2" roundover. The TD12H was measured outside and includes a far field and almost nearfield (about 10") merged.

Quite a response for a 12" woofer!

TD12H:


Audax mid:

Here is a preliminary passive xover simulation, currently using the temporary Audax mid, wth crossover points around 450hz and 2500hz.

Here is what I'm currently thinking on the finish. Padouk and Maple or Sycamore. This one is with maple.

Exo/Penn,

I wanted these to run full range and the slot ported TD12H's here have about an F3 of 35hz in this bass bin. Also, for reasons having to do with the open bafle dipole mid design, a crossover in the 400-500hz range is ideal. Since I wanted to use a dome tweeter, I didn't need the extra sensitivity of the other TD12 line. In addition, the Bagby/Salk speaker I heard back in April used the TD12H, though a different midrange and tweeter, and it was simply a fantastic speaker. The TD12H is probably the cleanest, most dynamic woofer I've heard. There is no question in my mind that I will be very happy with them.

I have two 12" subs that are sealed with Linkwitz transform circuits, flat to about 20hz, that pick up the very low end and these will cross to them, when used for HT, at 40hz. The subs are typically not used for music, though blend very well with my current mains which have an F3 of 29hz, for music or HT, when crossed at 40hz.

I mostly agree with you for music. My current mains have a 10" sub in each and they dig very deep in a tapered transmission line and I usually don't use the 12" subs.

That said, I have found that there is some music that has a more content below 30-40 hz than typical and using the subs with that music gives you something I don't think you can get with any woofer that has an F3 in the mid 30's. It is as much feel as sound in that range.

A9X,

Thanks. I've heard enough open baffle to know I really enjoy the soundstage and open, uncolored midrange it can present, when done right and the mid is not overdriven at the low end.

I guess one could do a design exactly like this one with a small section of 8" dia. sonotube behind the mid, providing a sealed chamber.

The benefit of the 1/2" waveguide mount may have nobeen too clear from the graphs posted above, because they were taken under different conditoins. The graph for the flush was taken outside at 103inches and the 1/2" I showed was taken inside at 39.375". I did take one, however, for the 1/2" outside. Here is the on axis fo the two overlayed when taken under the same conditions, spl levels, etc., outside at 103". Sorry for the confusion. This shows a little more difference bewtween the two than what is apparent in the graphs above. At any rate, it made dealing with the rising top end of the HDS a moot point and what it shown is a simple 3 part xover in the simuation above.

Thanks, Shin, I value your opinion highly.

For those interested, here are some new and more accurate and comparable measurements of the Peerless HDS tweeter in a 1/2" waveguide mount (1/2" deep. 1/2" roundover) and a 3/4" waveguide (3/4" deep, 3/4" roundover) both show spl measurements on axis, 15, 30, and 45 degrees off axis (horizontally). These were taken at 1m, with a 5ms gated window, tweeter at about 80" above the floor (vaulted ceilings).

First 1/2" deep waveguide:


Next 3/4" deep waveguide:

Hi All,

I have been doing some testing with shallow waveguides for my BaSSlines project that I thought you all might be interested in. These are more thorough results than I have posted before. I created an insert into the baffle that would allow me to make multiple WG's and insert them into the same baffle, with same tweeter, same mic setup, position, etc. The tweeter is the Peerless HDS with the face plate removed. The tweeter is mounted by pressing it to the back of he WG cutout, held by a woof fixture. The measurements were all taken at 1 meter, with the mic 80" high, in the center of a room with vaulted ceilings probably 15' high at that point and with a 4ms gated window.

All the WG's were created from mdf by boring a hole with a forstner bit, then rounding over the appropraite amount and then routing from the back for the palnned depth of either 1/2" deep or 3/4" deep in these cases. These are something just about any DIYer can build petty easily, which was the idea. There are a few tricks to doing this, most notably, when using a 3/4" rounvoer bit, you have to have a backer piece to you mdf baffle that you also bore a hole through. This backer piece is needed for the bearing of the deeper 3/4" roundover bit to ride on. All the bore through holes on these were adjusted so the final throat sizes are about 1-1/4" +- 1/32" at the final size.

Most of the plots show the waveguide perfomance at 0-15-30-45 and 60º of axis horizontally, so you can see the effect on axis and the directivity off axis. The first plot is the HDS with a standard flush mount. My goal with the waveguide is to get some boost at the low end so that when qualized out in the crossover you get the possible benefits of lowered distortion, slighly higher sensitivity, better off axis directivity and a counter to the typical rising responce of the HDS tweeter on axis, which might be fatiguing to some over time. Also included are some comparisons of the favorite WG results on axis with each other.

HDS mounted Flush: 0-15-30-45-60º


1/2" deep WG, 1/2" roundover: 0-15-30-45-60º


1/2" deep WG, 3/4" roundover: 0-15-30-45-60º


3/4" deep WG, 3/4" roundover: 0-15-30-45-60º


3/4" deep WG, 3/4" roundover, with 1/2" deep 45º chamfer after, sharp edges sanded round by hand: 0-15-30-45-60º


3/4" deep WG, 3/4" deep 45º chamfer, sharp edges sanded round by hand: 0-15-30-45-60º


Here are the flush mount (red), 1/2" deep/1/2" roundover(pink), 1/2" deep/3/4" roundover (blue) and 3/4" deep/3/4" roundover (black), all on axis.


My conclusion is: it depends on what you are looking for. The deeper wavegides have more boost, but all peak at about 4kHz on axis. The 1/2" deep waveguide, with 1/2" roundover has the flattest FR on axis from 4kHz and up on axis. The 1/2" deep/3/4" roundover WG and the 3/4" deep/3/4" roundover WG have the best off axis responce when you get out to 30º and beyond and the most directivity. I'm now leaning toward either the 1/2" deep/3/4" roundover of the 1/2" deep/1/2" roundover WG's from a raw response point of view. I will see how they look in the crossover design.

I hope these results will encoorage some of you to experiment with this concept. I think it has a lot of merit and is not at all hard to do with just a router and standard bits. It helps if you have a drill press and a router table as well.