The BaSSlines (was High Sensitivity Design)

[ttan98]

Audiomarketplace.com.au has them for $A260 + postage
PHL1120

However, I still think I'll buy some of the AE's to experiment with as I have a mate with the PHL and I'm very impressed with the other AE drivers I have.

By the time the product landed here it becomes very expensive, Dan is designing an open baffle he uses B&C 6MD38 6-1/2" Midrange costs $92.50, refer to this site:

http://www.parts-express.com/webpage.cfm?WebPage_ID=3&searchHeader=1&ObjectGroup_ID=841&so=1&manufacturer=327

Ask someone to buy on your behalf in the States and then send to you, this way you save heaps.

Dan is also making a comparison between AE 6.5" and 6MD38, hopefully he will report back with his findings.

[A9X]

By the time the product landed here it becomes very expensive, Dan is designing an open baffle he uses B&C 6MD38 6-1/2" Midrange costs $92.50, refer to this site:

http://www.parts-express.com/webpage.cfm?WebPage_ID=3&searchHeader=1&ObjectGroup_ID=841&so=1&manufacturer=327

Ask someone to buy on your behalf in the States and then send to you, this way you save heaps.

Dan is also making a comparison between AE 6.5" and 6MD38, hopefully he will report back with his findings.

I keep reading that Zalytron never have stock. US Speaker will ship USPS, but for me that is moot as I get trade prices with most of the pro distributors here anyway.

We have access to a couple of DEQX and measurement mikes, so swaps are quite easy to do.

[Mark Seaton]

I've been talking with John about the Lambda 6.5". I may end up with one for testing. Actually, Jeff Bagby is the one who is looking at the Lambda for Jim Salk.

Hi Dan,

I had to make a trip to AE Speakers last night to pick up some cabinets and drivers, and got to give a cursory look/listen to the new 6.5". What I heard mounted to a large test baffle was very promising. It has a very extended high frequency which was audibly quite consistent out to a useful angle (as is expected with any driver over 3" in diameter). Out further it was still very consistent without any audible gyrations well off axis. While I myself am less prone to use midrange drivers terribly high in frequency relative to their diameter, the added flexibility should be of interest to many. Of course that extension is also an indicator/symptom of the efforts in the motor design, and it's almost always preferred to have a driver with a well behaved raw response before executing a crossover.

PS - The machined AL phase plug looks pretty slick in person.

[dlneubec]

Thanks for the encouraging first hand report, Mark.

I'm anxious to get one in my hands!

[SamL]

Out further it was still very consistent without any audible gyrations well off axis.

PS - The machined AL phase plug looks pretty slick in person.

From photo, the phase plug do look a bit over size for 6.5". Wonder if a smaller phase plug will be equally good. Lighter driver will be cheaper to ship around the world.

[John_E_Janowitz]

From photo, the phase plug do look a bit over size for 6.5". Wonder if a smaller phase plug will be equally good. Lighter driver will be cheaper to ship around the world.

The trick with phase plugs is that the straight section before the curve needs to be long enough to keep the acoustic loading the same on the driver at all frequencies. That means that as the cone comes forward, the end of the coil former needs to still be adjacent to the flat section of the phase plug. Ideally you also want the phase plug to be long enough so the tip is at the same height as outer most point of the cone. Also, the larger the phase plug, the better it is at pulling heat from the coil. The more surface area it has, the better it is at dissipating heat to the outside world.

The phase plug weighs less than 100grams total. The whole driver is between 8-9lbs.

John

[JoshK]

FWIW, I think the phase plug looks quite cool. It looks like its own creation rather than a derivative of other off-the-shelf drivers.

[brucemck2]

John, a bit off topic, but would your new driver work well in a line array?

I'm trying to build an array that would be (a) 100db+ efficient, and (b) could be driven by 8w/ch SET amp.

Would cross to sealed subs +/- 100hz. Would cross to Raven or Fountek ribbons for high end. Use DEQX for crossover.

Back of the envelope suggests that 8 of your new drivers might do that?

[Dennis H]

Nice looking driver, John. I see you're planning an Alnico version as well. That would be nice for open baffles as the standard magnet is pretty big. Could you save any money by using Neo instead of Alnico?

[John_E_Janowitz]

John, a bit off topic, but would your new driver work well in a line array?

I'm trying to build an array that would be (a) 100db+ efficient, and (b) could be driven by 8w/ch SET amp.

Would cross to sealed subs +/- 100hz. Would cross to Raven or Fountek ribbons for high end. Use DEQX for crossover.

Back of the envelope suggests that 8 of your new drivers might do that?

I guess I hadn't considered using these in an array for the cost factor, but they could definitely work well. We are planning a version with different cone material and less Xmax for pro audio line array applications. You'd need a little EQ to bring up the bottom end if you do a sealed enclosure, but you have plenty of excursion there to do 100Hz. I'm looking at a vented MTM with a pair of them and a RAAL ribbon as well. That might be another ribbon you want to consider. From those I have talked to who have used them and the others, the RAAL are the best of all the options out there.

John

[John_E_Janowitz]

Nice looking driver, John. I see you're planning an Alnico version as well. That would be nice for open baffles as the standard magnet is pretty big. Could you save any money by using Neo instead of Alnico?

Neo isn't something we'll be looking at until we get much farther down the road. It's very difficult to assemble a motor properly with the neo charged. To charge it once assembled like the ceramic motors, we'd need to get a get a magntizer to charge neo which would be a $100k investment. Shipping assembled motors about 8 hours away and back to be magnetized also isn't practical.

The other reason for the Alnico is that it has this appeal that it sounds better. All the vintage alnico drivers are highly sought after. Alnico is less prone to flux modulation than ceramic magnets, which is good, and will lower distortion. The copper sleeve on the pole actually does as much or more to keep the flux fixed in the gap as the alnico magnet does. However, for the ultimate option we'll be doing the copper sleeve and the alnico.

John

[ttan98]

Dan,

If I am not mistaken you have so far made some measurements on the B&C 6MD38, the response looks good, but I don't think you wrote your listening impressions of this driver.

I find from experience that some mid range drivers can sound a little thin, some fuller. I prefer the latter. The sound of a driver I think is functions of many factors, incl the material in which it is made of, distortions, etc. Anyway can you tell us your impressions.

thanks.

[dlneubec]

ttan98,

Sorry, I missed your post. I find the B&C in my implementation in the BaSSlines to be full sounding, but I believe this may have more to do with crossover implementation, than the driver itself.

Here is an update to my progress. I now have a pair of prototypes with crossovers and I'm starting the "voicing" process on the design with the B&C mids. They are now in my living room to be used for both music and HT for tweaking purposes. This is the room they will eventually be in. I will still be looking at the Lambda mid as well.

Below are a few graphs illustrating where the design is at. It is using the 1/2" deep waveguide with a 1/2" roundover on the tweeter. The plot showing all three drivers is the on axis simulation in SoundEasy. SPL levels are not calibrated to real world levels. The single plot you see is the measured FR with a 5s gated window at about 8', so anything below 600hz or so is not accurate, in fact there is a bit of first relfection anamolies showing up in this plot. This is a plot at 15º off axis, which is the intended design axis, so they don't need to be toed in too much, if at all. Also included is a measured plot of the impedance/impedance phase.

[Undefinition]

I'm just going to chime in here. I heard these this afternoon at Lexington and I really enjoyed them. Maybe I'm biased towards dipoles, though.

Anyway, Dan, if I had one piece of advice to you at this point it would be to just listen to them at your normal listening volume (forget whatever 1 watt is... on those it's LOUD), and voice from there. Dipoles are finicky, and can change their perceived sound in a room depending on the volume you're listening. So I say, just go for the volume you enjoy.

...and enjoy! They're sounding great! :T

[ttan98]

I'm just going to chime in here. I heard these this afternoon at Lexington and I really enjoyed them. Maybe I'm biased towards dipoles, though.

:T

BTW what mid-range driver was Dan using, B&C or AE?

[dlneubec]

I'm just going to chime in here. I heard these this afternoon at Lexington and I really enjoyed them. Maybe I'm biased towards dipoles, though.

Anyway, Dan, if I had one piece of advice to you at this point it would be to just listen to them at your normal listening volume (forget whatever 1 watt is... on those it's LOUD), and voice from there. Dipoles are finicky, and can change their perceived sound in a room depending on the volume you're listening. So I say, just go for the volume you enjoy.

...and enjoy! They're sounding great! :T

Thanks for the advice, Paul. I will follow it with my voicing efforts.

The one thing I had been thinking about that I did not mention is to possibly slope the open baffle section back a bit, maybe just 4 degrees or so. Going on the Theil tour reminded me of that. I even have a revised plan drawn up for it already. That should let me rear mount the mid (behind the Lexan), with a 1/2" roundover. It would be a lot easier to do that in Lexan than the odd shaped cutout needed for a flush mount, will probably look better and will possibly improve phase alignment with the tweeter. That will probably require a little reworking of the crossover, but it shouldn't be too significant. Anyway, I'm at the prototype stage, so now is the time to consider any changes.



ttan98,

What I played in Lexington had the B&C 6md38 mid's in them.

[dlneubec]

It looks like a 4º slope on the BaSSlines open baffle section is working out about perfectly. It allows me to do an even better job of phase alignment in the crossover and to rear mount the midrange, which should be much easier than creating that odd shaped flange opening in the Lexan.

Also, I plan to do the waveguide tweeter mount 9/16” deep with a ½” roundover, for a pretty flat 15º off axis response. The Lexan is 7/16” thick (though spec’d at ½”), so I’m using 1/8” of wood between it and the tweeter body, giving me 9/16” total depth (see plan attached). That way you don’t see any of the tweeters except the dome and surround from the front. I also figured out that I could use the tweeter face plate as a template to drill holes from the front, through the baffle. This allows me to mount it with button head cap screws from the front side, directly to the tweeter body. That way I don’t have to press mount the tweeter from the back and the open baffle is better preserved. With this mount you do not have to be concerned about the tweeter position slipping, etc. I have a wood cap shown over the tweeter at the back, which I may or may not do, but it is only to improve aesthetics.

I will also be mounting the midrange the same way, 1/8” of wood sandwiched between the Lexan and the driver flange, which keeps the odd shaped flange hidden from the front. In side by side testing, the recessed mount measures virtually identically as the front mount, at least within the useable area of the driver's frequency response. The differences that do show up are well down in the passband.

[dlneubec]

Here are some photo's of implementing the rear mounted Peerless HDS in my ptototype mdf baffle, with the front screw mounts. I used the removed tweeter face plate to mark holes for the screws to go through the baffle and into the tweeter body. Here are a series of photo's:

Double sided tape on the tweeter face plate to hold it in place. Disregard the circles drawn in pencil on the mdf. That was the old tweeter position, which has been moved 1.5" closer to the mid to improve vertical lobing.



The for holes for the tweeter mount were drilled, then the center hole was located by connecting lines through the holes and a center hole drilled for using the Jasper guide.



Jasper circle guide used, to recess a hole for the tweeter at the back of the baffle at a 1/16" depth for an 11/16" deep waveguide. The center of the recess is left intact at this point for the 3/4" roundover bit that will be used in a later step. A simple 1/4" width slot is cut at the tweeter body dia. to form the outside of the eventual full recess.



1-5/16" dia. hole drilled through the mdf, using the center hole as a guide to form the sides of the waveguide, using a forstner bit.



This is shown for the midrange hole, but the same process is used for the tweeter waveguide. The depth of a 3/4" roundover bit is deeper than 3/4" to the bearing, so you have to have a equivalent size hole in a dummy piece of mdf, mounted behind the finished piece to act as a guide for the bearing of the roundover bit to run along. I again used double sided tape to stick the two pieces of mdf together and provide the guide for the bearing. The same process was used on the tweeter hole, but with a 1-5/16" hole.



Next up is a shot of the front of the baffle after both the woofer hole and tweeter waveguide 3/4" roundovers were completed:



Here is a shot of the back of the bafle with the full recess removed for the mid and tweeter. The mid was roughly done here for the prototype. I would use a template in the finished version. Note the additional recesses drilled for the tweeter binding posts.



Drivers mounted:



Finished prototype baffle, tweeter moved 1-1/2" closer than previously, both drivers mounted from the rear at a depth of 11/16", with a 3/4" roundover. Counterbores were drilled for the screws to recess them below the baffle. In the finished version, this will allow for 7/16" of Lexan, backed by 1/4" of hardwood for an 11/16" depth on the drivers. That is the reason for the 11/16" deep mount in the mdf. The result will be that you will only see the driver opening from the baffle side and none of the tweeter or woofer flange will be visible through the Lexan. Also, as you can see, I'm thinking of doing a combination of 3/4" roundover and a chamfer at the baffle edge. I will also be testing a chamfer for the midrange hole, rather than the roundover.

[Paul Ebert]

Geez, Dan. Even your prototypes look better than anything I envision building any time soon

[dlneubec]

Well, after a gazillion crossover revisions, versions, etc. I think I finally have it where I want it. The woofer LP and mid HP are symmetrical and just slightly steeper than 2nd order acoustic. The midrange LP is 4th order acoustic and is asymmetrical with the tweeter HP which is 3rd order. The asymmetrical slopes yield a flat FR and and very good phase matching. There is a midrange attenuation that is greater than one would expect from a monopole design or that I found necessary in my omni designs.

I spent about an half-hour Saturday and then again yesterday listening to my test CD, which includes about 30 one minute cuts from various types of music. It is the first time, with any of my designs, that after a session like that (pretty high volume listening included as well) I was able to say to myself, there is nothing wrong that I can pick out. Of course, it pays to live with a design for awhile after you make changes to be sure you are still convinced after an extended period of time, so I will be doing that before finalizing it.

Next up is to start on the laminated hardwood and combined Lexan baffles and box veneer. I have to pick up the hardwood from Frank Miller Lumber Co. which is about a 3 hour driver. I hope to do that next Saturday and should be able to start on the construction soon after. I picked up some wood backed veneer that I will be choosing from. It includes dark red-brown figured veneer that I can't identify, some curly walnut and some Burl Maple. I will take samples of each to the hardwood lumber co and make a decision on the combination at that time. Below are some photos of these or images where they were used.

Dark Red-brown Veneer



Dark Red-brown Veneer with flash on finished Subwoofer



Curly Walnut



Burl Maple

[TacoD]

Wow, good work. How did you make the PHL woofer routing, you write you did not used a template. How do make the template?

Lexan baffle? How do you plan to mount this on the bas bin?

[dlneubec]

Wow, good work. How did you make the PHL woofer routing, you write you did not used a template. How do make the template?

Lexan baffle? How do you plan to mount this on the bas bin?

Well, I didn't know how to make the template, but I figured something out that worked. Its kind of hard to describe, however and thee me be a much easier way to do it. BTW, I'm using a B&C 6md38, not the PHL, but it has that same odd shape.

Here is what I did to make a template. First I mounted the driver to 1/4" hardboard (or plywood, Luan, etc.). Then I taped up the driver openings on the back so dust could not get into it. I mounted a flush trim bit in my router table and with the bearing riding on driver frame, I cut out a piece of the 1/4" hardboard that was the size of the driver. Then I used that cutout and attached it to a piece of 3/4" mdf. I then used the smalles bushing in my router buching kit with a 1/4" diameter bit and using the cutout as a guide, cut out a template that was approximately 1/2" larger in diameter than the driver size. This was tedious and I only cut the template out at about 3/16" depth at a time in order to make it possible to follow the cutout with the bushing and not wander away from it. Once that was complete I now had a template about 1/2" wider than the driver cutout. I then used the largest bushing in my kit, with the same 1/4" bit to run along the 3/4" template as a guide to cut out the driver hole. I hope you can follow that explanation! pictures would have make it much easier, but I didn't take any of the process.

The Lexan will be backed by 3/4" hardwood surrounds that the woofer and tweeter will be inset into from the back. The drivers will be mounted from the rear and the hardwood is sandwiched in between the drivers and the Lexan and bolted from the front, thought the Lexan and hardwood. There may end up being a couple other places where the Lexan is bolted to the hardwood backer. The hardwood backer will have legs attached to form the 86º inside angle (resulting in a 4º tilt to the baffle). The legs will be glued to the upright 3/4" wood section and may be augmented with a triangular wedge at the base of the baffle. You can kind of see this concept if you look at the latest color mockup I posted awhile back.

[BobEllis]

Sounds like you did what was described here (with pictures): http://www.exquisiteaudio.com/baffle.html

Works great

[dlneubec]

Well, that is close to what I did, but that method is probably a little easier. Thanks for the link. I will try it that way next time. :T

[TacoD]

Thanks for your explanation! It looks like it takes some fiddling .

[dlneubec]

After a 5-6 hour round trip to Shawn's neck of the woods, Union City Indiana, I now have the hardwood I will be using and the veneer.
I visted Frank Miller Lumber, which is a hardwood lumber company that has a great selection of hardwood and also hardwood plywood, all at very reasonable prices.

I took three samples of veneer with me to see what matched best, Burl Maple, Curly Walnut and and unknown darke red veneer that looks to be a Pomelle, all wood backed. After talking to the guys there and comparing the veneers to the hardwoods, we determined the dark red one to be Makore Pomelle. To match up with that veneer, which will be used on the boxes, I purchsed some Makore and Hickory. Below is a picture of the three together. These boards will be ripped and laminated on edge, so you won't see this side, but the egdes when the baffle is glued up. The bass bin baffles will be laminated to 1-1/2" thick and the hardwood portion of the open baffle 3/4" thick, making it about 1-1/4" when you include the Lexan on the front. I was warned to absolutely wear a respirator (not a dust mask) when working with the Makore (or just about any exotic). I got 10bf or Hickory and 12bf of Makore for about $100. Try getting something common like walnut, cherry or maple at Lowe's or Menards, etc. for that price!

So, Hope to start on the hardwood baffles for the bass bins and the hardwood/Lexan open baffles soon, perhaps next weekend.

[dlneubec]

I’ve been working on the laminated panels for the bass bins and MT section. I didn’t want to take the time and trouble to do a bazillion biscuit joints so I created a little base to allow me to do a simpler edge glue up, using a combination of bar clamps and c-clamps. The bass bins use a ¼” hdf backing and 1-1/4” ripped stock, edge glued and glued to the ¼” backer, for a total of 1.5” thick. The MT section is ¾” ripped stock, edge glued only. Here are a series of photos showing how I set it up and some of the bass bind baffles. I will follow this post with a step by step for the MT baffles.

Up first, I used a piece of ¾” mdf and clamped side pieces to use as stops to forming the laminated panels. Double sided tape was placed on the side boards so glue would not stick. The side pieces were ripped a little smaller than the laminate depths.



I started with the bass bin baffles. I decided to do them in 3 sections because I was concerned glue would start to set before I got all the pieces in place. Here is the first section glued and clamped. The jaws of the bar clamps are too deep, so spacers are used between the bottom of the bar clamps and the laminated pieces (w/double sided tape on the bottom of the spacers). The spacers allowed c-clamps to be used on each side of the bar clamp to press the laminated pieces flat and against the ¼” hdf backer.



Here is the first section dried, the clamps all removed and some of the excess glue removed.



I did not take photos of the other two sections being added, but the same procedure was used. Once they were glued up, I cut them to an oversized shape of the finished baffle and glued the two bottom pieces of the baffle on. You can see this in the final pic in the next post.

[dlneubec]

Here is a more step by step for the MT baffle. In this case, there is not backer piece, so they are only edge glued. I added a stop block inside the side pieces to allow me to correctly space the varied sized pieces of the baffle correctly in relation to each other.



Next the baffle pieces are placed to allow me to determine the outline of the baffle and draw pencil lines around it.



The pencil lines were used as a guide to place double sided tape on the base so that the laminated pieces would not adhere to the mdf.



Here the laminated pieces have been edged glued.


Here the spacers were again added to allow the bar clamps to be clamped down on each end so the laminated pieces would glue up flat.



Here are the clamps all in place.



I decided to make it easy on myself and once everything was glued up and dried, I took them to a local hardwood mill and had them sand them down to smooth out any irregularities and remove any saw burn marks, etc. Here are the sanded results. The bass bin baffles were sanded on only one side, the MT baffles on both sides. I will mount the bass bin baffles to the box and probably trim them to size with a flush trim router bit.

[ThomasW]

Nice!......

[ttan98]

Dan,

I have been searching for a new high SPL mid-range drivers(use in an open baffle configuration), 4 potential brands are B&C(the one you are using now), the PHL 1120(J. Bagby was using),the Audax PR170M0(a new model, PR170N0 has been released) and the AE 6.5" Lambda. In terms of prices in ascending order are, Audax($89), B&C($92), PHL($120),AE($150). A real outsider is a hempcone 8" driver(about $85) from Tone Tubby, I heard good reports on this driver as well.

You have tested the B&C and so far have you tried and tested the AE 6.5" yet if so what are your impressions of both units. I have yet to read any feedback from anyone about their impressions on the AE 6.5" unit.

Comments from anyone in terms of their suitability are welcomed.

Cheers.

[dlneubec]

Dan,

I have been searching for a new high SPL mid-range drivers(use in an open baffle configuration), 4 potential brands are B&C(the one you are using now), the PHL 1120(J. Bagby was using),the Audax PR170M0(a new model, PR170N0 has been released) and the AE 6.5" Lambda. In terms of prices in ascending order are, Audax($89), B&C($92), PHL($120),AE($150). A real outsider is a hempcone 8" driver(about $85) from Tone Tubby, I heard good reports on this driver as well.

You have tested the B&C and so far have you tried and tested the AE 6.5" yet if so what are your impressions of both units. I have yet to read any feedback from anyone about their impressions on the AE 6.5" unit.

Comments from anyone in terms of their suitability are welcomed.

Cheers.

I also have tested and own the Audax PR170M0 as well. I have a used pair of them (if you want to get a pair to try yourself, let me know and I'll make you a great deal, say $70/pair +shipping).

After I had picked up my TD12H's and Peerless HDS's I had to wait a month or so for the B&C's to come in so I did a temporary crossover using the Audax. The Audax tested quite flat on my open baffle and sounded pretty good, as long as the volume was kept reasonable. I discussed it with Jeff and he indicatd he had considered the Audax as well, but determined that it just would not work for his open baffle crossed in the 450-500 hz range, due to limited Xmax. I figured this is what I was hearing that was bothering me about it when I crnked it up. The B&C and PHL have 2x the xmax and have no problem handling a 450hz crossover. Jeff has written some software to simulate a drivers performance in an open baffle in terms of xmax limitations, given the other TS parameters. He found the Audax too limited, but the B&C and PHL simulated fine.

I'm very happy with the B&C mid. Jeff has not heard it, but felt it would be a drop in replacement for the PHL he used in his original design for Salk, based on specs and measurments I sent him.

Salk is not going to be using the PHL. They have just had way too much trouble getting them, as I understand it. They are probably going to go with a version of the Lamba TD6.5, but that still seems to be up in the air a bit. I believe John is still working on a driver design for them. The Lambda TD6.5 version I tested for Jeff had a sizeable on axis dip at around 1500hz that the B&C does not have. I tested the Lambda and the B&C on my baffle and on a baffle that is shaped like Salks speaker and they were consistent. The Lambda had the on axis dip at about 1500 with both baffles. The B&C also has a dip, but it is up around 2500hz and not nearly as deep. I also tested off axis and it is important to note that the dip in the Lambda seems to flatten out off axis (as does the B&C). This may mean that it will be fine for dipole use since the extra energy off axis and to the rear on a dipole often fills in the midrange and can even make the midrange hot, if designed flat on axis. We have all exchanged a number of emails and the conclusion seems to be that the dip in the Lambda is open baffle/dipole related, perhaps the baffle shape and/or rear reflections off its larger motor. It apparently measures flat infinite baffle. One other point, the Lambda measured about 5 db or so less sensitive than the B&C, IIRC.

I have to stress that I only did measurements of the Lambda and it was the first prototype model. I did not listen to it or do any listening comparison between it and the B&C. I did try and model a crossover for it using the measurements I took. I had trouble getting something that looked as good as what I had with the B&C. Given that I was thrilled with the sound of my speaker with the B&C and it was considerably cheaper, I decided to just stick with it rather than explore the Lambda further.

My understanding is that John may be working on a higher sensitivity model and doing some testing of his own on a Salk-like baffle to try and discover what the issue that showed up in my my testing with that dip. I believe he also has a higher xmax version in the works that he hopes to compete with the Scan Revelator line. I suspect he will work these issues out and Salk will be using a lambda TD6.5 version in his design.

[ttan98]

Dan,

Many thanks for a detailed response.

Have you considered using midrange as MTM configuration similar to Undefintion open baffle? I understand he used the mid in series, if I use them in parallel(4 ohms), then I can increase the the SPL by 6db, I plan to drive them separately so x-over to tweeter isn't a problem with 4 ohm.

[dlneubec]

I did not consider an MTM arrangement for this design, for lots of reasons, the first of which was that this design was inpsired by the Bagby Salk Sound design.

The MTM is certainly one valid solution to get higher sensitivity. However, any time you cover the same frequency with more than one driver, you potenially introduce other issues that could negatively effect imaging, time of flight, vertical polar response, etc. One of the benefits of using a high sensitivity pro mid is that you don't have to go MTM and deal with these potential drawbacks. I think most folks will agree that the MT arrangement offers improved imaging and polar response when compared to an MTM so the speaker sounds more the same whether seated or standing, etc. It certainly makes it much easier to attempt driver time alignment in a sloped baffle WMT than a WMTM or WMTMW.

I believe one uses two drivers in an MTM in an open baffle primarily because you has chosen to cross the mids lower, which requires either more excursion capability or more drivers to share the load. It also introduces the need for wings and/or a much wider baffle or active attenuation of the dipole rolloff to achieve the lower crossover point. This is not needed when crossing the B&C at 450hz like I am in this case. Excursion is not an issue at that crossover point and the baffle can be narrower, reducing the dipole peak and dip after the peak. Then there is the issue of effective piston area or Sd. The B&C has an Sd of about 133cm2, while the RS125, for example has an SD of around 50cm2, IIRC, so two of them in an MTM is still about 75% of the radiating area of one 6.5" mid. Same thing goes for two woofers. Two 8" RS225's for example, have a combined Sd of 412cm2, about 78% of a single TD12H, which has an SD of 530cm2. So, Sd is an important consideration in these decisions.

Also, in my case, the B&C is already a good 3-4db more sensitive than the TD12H and The Peerless HDS, so it is considerably attenuated in the crossover to match the mid and tweeter. That should give it even more headroom than it normally would have. If I had wanted an even higher sensitivity design, I might have had to consider multiple drivers. However I would probably have started with 2 woofers and a more sensitive tweeter as starting points, rather than more midrange drivers.

Finally, I wanted a narrower baffle for the tweeter to improve its imaging and a tapered side baffle allows for that, plus the tapered baffle offers the benefit of diffraction reduction. It's quite hard to narow the baffle in the tweeter area in an MTM configuration.

All that said, you can do a fine design with a WMTM or WMTMW or WMT arrangement, but each are done with a different set of constraints and assumptions from the start. In all cases, further design decisions are a reflection of that basic driver configuration decision. This one was destined to be a WMT from the start and all my design decision reflect that.

[Hdale85]

Those baffles look freaking awesome :B

[---k---]

Dan,
those are really starting to take shape. :T
And, that was a lot of good insight. thanks.

[dlneubec]

I completed one woofer baffle today (except final sanding and finishing) and got a start on the open baffle hardwood/lexan combo. I should have one of the open baffle sections complete tomorrow, hopefully. I'll take some photo's if I do.

I may finish one speaker completely, including veneer, hardwood slot port, etc. (but not finish) before I start work on the second one. So far I couldn't be more pleased with how they are looking and I'm very anxious to see one completed speaker. This also allows me to troubleshoot my process on the first speaker and avoid repeating any mistakes on the second, though overall, it will probably take longer that way.

[dian1511]

Looking forward to the pics and continued process description.

You are truly amazing! You have an amazing amount of energy and determination. And you do marvelously detailed work, both in the design and implementation process.

Is there a special pill for productivity and energy? If so, please order me lots of it!

Darren

[dlneubec]

We have a speaker (almost)

Here are some updates photos. It's starting to come together nicely.

[Jed]

Words can not describe the beauty of that one Dan... keep the pics coming.

[dlneubec]

Thanks, Jed.

One question I'm still considering is whether to leave the cut and/or routered edges and roundovers on the Lexan rough or try and smooth them out. Right now they are unsanded. I'm sure they could be smoothed out if sanded and perhaps there is a way to polish the edges.

I've experimented with heating some scrap edges with a propane torch and it essentially melts it slightly and makes it smooth and clear, but it is very easy to overheat and make it bubble.

[John_E_Janowitz]

there are lots of compounds for buffing out acrylic or lexan. one of the keys is to use a large buffing wheel on fairly slow speed to prevent any burning.

John

[matt12v]

WOW, was staring at the pics for like 10 minutes.... Totally Unique and some serious speaker porn too! I bet it sounds just as good as it looks. Looking forward to seeing more pics. Keep it up Dan!

[dian1511]

Just Wow! Simply beautiful and elegant. Thanks for sharing the journey.

I checked out Lexan at the local hardware store and they only had thin stuff and it was expensive for the thin stuff. I'm curious how much the thick piece cost you? Supplier?

Also, is there an issue with wood movement regarding the hardwood laminated bass bin baffle onto hdf? I had laminated a circular piece of edge glued oak strips, the kind you find at the hardware store, onto mdf. I noticed the edge glued pieces started to come apart after about 6 months. Perhpas it was a poor edge glue job. I used it as the top for a sonotube sub.

Darren

[dlneubec]

Just Wow! Simply beautiful and elegant. Thanks for sharing the journey.

I checked out Lexan at the local hardware store and they only had thin stuff and it was expensive for the thin stuff. I'm curious how much the thick piece cost you? Supplier?

Also, is there an issue with wood movement regarding the hardwood laminated bass bin baffle onto hdf? I had laminated a circular piece of edge glued oak strips, the kind you find at the hardware store, onto mdf. I noticed the edge glued pieces started to come apart after about 6 months. Perhpas it was a poor edge glue job. I used it as the top for a sonotube sub.

Darren

Thanks Darren. When I do the other speaker I will documnet the process, since there are steps that have to be taken in a certain order or you can make it very hard on yourself. I found a few of those steps the hard way this weekend. :E

The Lexan I got was a 24"x24" piece, nominally 1/2" thick, though actually closer to 7/16" deep. I just checked and the price has dropped to $66 for a 24"x24"x1/2" sheet or for a 12"x48"x1/2" sheet. Here is where I got mine:
Polycarbonate sheet

I don't there there will be a wood movement problem. The Lexan and the wood are sandwiched together between the drivers, not glued. I made enlarged bolt holes in the hardwood and the driver openings are also slightly larger which allows for some movement. Of course, the hardwood will be sealed all around. The way I built it, it all comes apart, so if there is a problem, I can always take it apart and repair or rebuild with some other material.

[EdL]

http://www.novuspolish.com/

I found the above in my search for a solution for my scratched turntable cover