Lowther and 12” Woofer on Boston Acoustics A150 Cabinet

[hornwannabe]

Hi!

I’d like to ask some questions regarding a project I had in mind consisting of a Lowther dx55, a bass helper woofer (10 or 12”) inside a clone of a Boston Acoustics A150 Cabinet.

I’m moving to a small apartment and what attracted me to the BA 150 is the size it’s just 32” h x 16.5” w x 8” d. My target listening space is a measly 7 ft x 7 ft space so I’m going to be pushing these project speakers up the wall hence the need for a slim wide baffle.

Also intrigued by the design in which the drivers are on an “infinite baffle” that can aid in diffraction (Please correct me if I’m wrong as I’m a newbie). Also read up that having the woofer close to the floor can aid it in boundary reinforcement and efficiency (Again, do correct me if I’m wrong). It’s also a sealed design which is okay for me as I can be fairly happy if it plumbs down to 45hz.

Also I’m using a DIY SET amplifier with a 6c33c tube outputting 15 watts that’s why I’m using lowthers so I can have that efficient, point source midrange sound. I’ll be using a MINIDSP to mate it with a 10 or 12” woofer.

A local builder will be helping me with the cabinets but I’ll probably tune these using the minidsp.

Priority for me would be:

A.) Efficiency so I can use the SET Tube amp.
B.) Crossing the Lowthers at around 200 - 300hz or lower (so I can have a crossoverless midrange)
C.) Small (thin) Dimensions

Here’s a couple of build questions:

1.) Can’t seem to find data on what stuffing or what cabinet internals the A150 has. Can you guys refer me to a sealed build like this or data on how I should construct the insides? My local builder suggested using deflex or rock wool on the opposite baffle.

2.) Can I ask for help on the proper positioning of the drivers to maximize baffle advantages, like: should I place the Lowthers a bit off-center and the positioning of the woofer relative to the edges?

3.) Crossover values would be awesome so I can get a starting point. Or tips on how I can mate the woofers with the Lowthers seamlessly

4.) If the Boston Acoustics A150/A200 physics seem a bit wonky I’m open to suggestions just as long as I get away with a thin speaker with > 90++db sensitivity.

5.) Any cheap woofer that I can buy that’s up to the task?

6.) What’s the best way to mount the drivers on the cabs? Do I mount internally?

7.) Cheap SS amp or some Biamping insights.

Here’s a mockup I did in PS using pictures of a Boston Acoustic 150 with the drivers I mentiond.

Here’s an original Boston Acoustics A150

Thanks

 

[hornwannabe]

Here's a quick write up I found on the BA A150 and 200 / 400 series:

Andy Petite/Kostasos was the chief and founder of BA at the time of the "A" series. Andy had worked under the ingenious audio wizard Henry Kloss, of the legendary Advent loudspeaker company. Before that pairing, Henry Kloss also had a major role in starting up two other well-regarded and respected audio companies, AR (Acoustic Research) and KLH.

Boston Acoustics A150s and A200s were both offered in real wood veneer- oak and walnut. Later, vinyl was offered.

The A150 & A200 is a decent sized speaker- not huge, but wide at the shoulders, yet with a narrow depth of 8 inches and 6.5" inches, respectively. They are a 3-way design, with a 1" ferro-fluid cooled soft dome tweeter, usually a 4.5" ferro-fluid cooled midrange, and a 10" low mass, low-resonance, vaccume-formed cone long-throw woofer (midrange differences were possible within the model line-up).

The tweeter and midrange are positioned at ear level- a proper height to achieve realistic musical imaging, and are flush mounted on a wide smooth fascia to control early driver reflections for reduced driver refraction.

The 10" woofer is mounted lower to "couple" with the front baffle and floor, positioned to radiate at a proper distance height and angle with the floor for the best possible bass- in-phase with the woofer's direct output, preserving it's smooth response while raising it's efficiency.

all drivers are vertically aligned, so no worries about offset drivers mucking up the sound- by design, the A-series of speakers are always mirror-imaged.

A mark of detail and quality, the inner grill baffle is beveled to minimize early reflections that can blur the stereo image. The smooth fascia of the speaker along with the countersunk and flush drivers retained a crisp focused image- due to reduced infractions.

The wide-shouldered, narrow design was one of many possible design approaches to minimize diffraction of the drivers. By the speaker face acting as it's own "wall", and being unconventionally wide, there was a reduction of edge-diffraction, and side/rear wall reflection, or so the claims are made.

The furniture grade wood veneer is of high quality- some Tung oil or quality wood wax will bring out the full, beautiful lustre of these in all but the most abused models.

The A150 was an incredibly successful model, with many units sold. A decent price with exceptional all-around performance.

The A200 was the first no-holds-barred Boston Acoustics offered. The A100 was the first no-compromise speaker according to the company literature, the A150 the first no-compromise 3 way, but the A200 was the first all-out model.

Later, a dual woofer, extremely rare A400 was introduced. At 4 ohm loads, and a larger price tag, fewer were sold, as the A200 was so close in performance. and the A150 remained the hot seller, cheaper than the A200, and near it's performance level.

Frequency range for both is rated at 36-25,000 Hz =/- 3db from the factory, but I suspect the larger A200 goes lower. my guess? it' range is approx. 30-25,000 Hz =/- 3db.

Both are 8 ohms impedance, and decent efficiency at a sensitivity of 90 db at 1 meter.

The A150 is 32" tall by 8 deep by 16.5" wide, on a 1.5" black pedestal base.

The A200 is 41" tall by 6.5" deep by 21" wide, also on a 1.5" black pedestal base.

Both request a diet of 15wpc minimal, 75wpc recommended (150wpc peak).

 

[chrisb]

Many of us here are likely familiar with the original Boston A series- great kick-@ss systems for sure but I think the A150 - or even the A400 enclosures might be a bit too shallow to avoid reflections from back wall from causing serious perturbations of the Lowther’s FR. A small OB for the Lowther would likely give you much more transparent performance.

 

[hornwannabe]

Many of us here are likely familiar with the original Boston A series- great kick-@ss systems for sure but I think the A150 - or even the A400 enclosures might be a bit too shallow to avoid reflections from back wall from causing serious perturbations of the Lowther’s FR. A small OB for the Lowther would likely give you much more transparent performance.

My initial thoughts leaned towards an open bafffle design but I need the speakers close to the walls because of space constraints. As I understand putting OBs close to the wall can introduce other problems. But! If someone can enlighten me how to make an OB close to the wall work, I’d be happy to follow that route!

As for the lowthers back reflections, wouldnt putting an absorbent material like deflex inside the opposite wall of the speaker solve that problem?

 

[Retsel]

Lowthers in OB or cornu

You could try the Lowthers in OB and absorb the rear wave which might work well enough when the speakers are moved against the wall.

Another idea would be to mount the Lowthers on the wall in a Cornu backloaded horn.

Retsel

 

[chrisb]

Retsel -I’d srill be concerned about reflections through the lightweight Lowther cone with any shallow cabinet, but perhaps a member here can report succes with such a design?

 

[jrh0516]

So, the Mini DSP will be doing both the DX55 and the woofer?

The DX55 needs its own separate sealed enclosure. Anything from a .5 to 1 liter would be good. The woofer cabinets on my Boston’s were fully stuffed. Which should be the same for your woofer and mid, the enclosures should be fully stuffed.

You’ll need to calculate the internal volume for the woofer, but the Dayton SD270 and SD315 work well sealed. I’d target an F3 in the 50s sealed, plus with DSP you can boost if needed. The SD270 in 45 liters is F3 of 50. 30 watts gets close to the max of the Lowther + tube, so 60-90 watts per channel amp should work fine.

With no grills flush mounting the DX55 (if it has a square edge), flush mounting the woofer and using a large round over on the cabinet edge will create controllable diffraction.

 

[Retsel]

Retsel -I’d srill be concerned about reflections through the lightweight Lowther cone with any shallow cabinet, but perhaps a member here can report succes with such a design?

I agree, any backhorn has issues with sound reradiating back through the very light cones, such as that used for the Lowther drivers. Lining the backchamber with felt does help, but does not necessarily cure the problem.

I mentioned the Cornu because mounting the speakers on the wall might be a desirable solution given the small size of that room.

 

[phivates]

8" depth would allow for 3" of fiberglass or cotton or memory foam - and the width should help with the internal reflection issue. In other words, try it. I've always thought the side wall proximity as much of a problem as the back especially when the driver has a large magnet structure

 

[hornwannabe]

@jrh0516:

Thank you! Your replies are the direction and the information I was hoping for!

So, the Mini DSP will be doing both the DX55 and the woofer?

Yes! They'll be handling crossover and corrective eq functions. I plan to cross at around 200hz - 300hz for the Lowthers so I can get a single source for my midrange and so I won't tax the Lowthers too much. Any suggestions on curves?

The DX55 needs its own separate sealed enclosure. Anything from a .5 to 1 liter would be good. The woofer cabinets on my Boston’s were fully stuffed. Which should be the same for your woofer and mid, the enclosures should be fully stuffed.

Noted on the stuffing. We’re they special stuffing? Or any generic material will do? Also were the Bostons chambered to seperate the drivers?

1 liter = 0.0353147 cuft right? Wow that’s small can it be larger? Or should I build a small cabinet for the Lowthers inside the cabinet? CABINET INCEPTION! Hehehehe!

You’ll need to calculate the internal volume for the woofer, but the Dayton SD270 and SD315 work well sealed. I’d target an F3 in the 50s sealed, plus with DSP you can boost if needed. The SD270 in 45 liters is F3 of 50. 30 watts gets close to the max of the Lowther + tube, so 60-90 watts per channel amp should work fine.

Thanks for the suggestions! If I enclose the lowther internally with an internal cabinet dimension of 16.5” x 8” x 10” I will be left with 22” x 8” x 16.5”. Is this enough to get your recommended specs? Or should I go with a smaller internal cabinet for the Lowther?

With no grills flush mounting the DX55 (if it has a square edge), flush mounting the woofer and using a large round over on the cabinet edge will create controllable diffraction.

Sorry, what do you mean by “large round over” ?



Again Many Thanks!!

 

[hornwannabe]

Also since I haven't closed in on the purchase of a DX55 any recommendations on the Lowther model that can work with this project?

 

[phivates]

The original midrange had a plastic pot isolating it from the otherwise undivided enclosure, and the tweeter was sealed off. Standard stuff for the time, except for the box proportions.
Which wide-range to pick? Oh boy. You might just stick with the Lowther to keep on track, but...there are alternatives. See the Full Range Forum for starters, or not. I have only heard a vintage PM6A powered by a SET and was impressed by that particular combination.

 

[hornwannabe]

The original midrange had a plastic pot isolating it from the otherwise undivided enclosure, and the tweeter was sealed off. Standard stuff for the time, except for the box proportions.
Which wide-range to pick? Oh boy. You might just stick with the Lowther to keep on track, but...there are alternatives. See the Full Range Forum for starters, or not. I have only heard a vintage PM6A powered by a SET and was impressed by that particular combination.

Thanks for the Info on the BA construction. It seems I will have to make a seperate chamber for the Lowthers if that’s the case.

Sticking within the Lowther brand models.

Hmmm... is this topic better off in the fullrange section?

 

[jrh0516]

With respect to curves I’d see how high up the woofer can play. With a sealed mid-tweeter enclosure and a protection filter the net will be something second order. LR2’s would be a good target up to about 500Hz.

The original Boston’s looked like poly. I like Roxul (rockwool) with a poly batting between the driver and the Roxul. The battling keeps the insulation fibers and dirt away from the driver.

You might want to check out some box modeling programs. I like Unibox but there are several others. Horn response can model the sealed box chamber resonances. For mids I shoot for a system qts of .65 to .70.

Your internal volume is a function of you wood dimensions. I’m not sure what you have there but it looks like over 10 liters. A large mid chamber is not great as you lose cone control due to less dampening.

A large round over in my book is ¾ inch radius router bit run along the front edge of the baffle. I’ve seen larger by people using CNC fabricated corners and carpet tubes.

 

[hornwannabe]

Thanks for the Info on the BA construction. It seems I will have to make a seperate chamber for the Lowthers if that’s the case.

Sticking within the Lowther brand models.

Hmmm... is this topic better off in the fullrange section?

Damn autocorrect:

*(he) will have to make a seperate chamber.....
*stick (within) the Lowther brand models

 

[hornwannabe]

Hmmm... is this topic better off in the fullrange section?

Well under the inpression that this falls under a 2 way system.

 

[chrisb]

Re the round-over; lots of controversy on just how large a radius would be required to be efficacious in mitigating edge reflections at the wavelengths likely to be a problem- if at all.

That said, 3/4” is not a particularly big radius, and to achieve anything larger with a router gets to be very expensive - for the bit itself, router capable of spinning it, and amount of material wasted.

A simpler method might be to offset the Lowther’s placement from centre of baffle - by a golden ratio dimension if you want to get geeky- and mirror image them. Oh, and from experience with only a single pair of Lowther’s, they are a royal pain to rebate for flush mounting - the “pincushion” style cast frames on the pair I was given weren’t symmetrical, or even exactly identical, so plan on chamfering the rear side of driver openings.

I’d still be concerned about reflections off the back wall of the A150 enclosures- the approx 8” of depth includes front and back panels, so net depth would be only 6.5”, or thereabouts. If you’re willing to seriously modify the enclosures, I’d consider opening up the top section of rear panel so that the Lowthers are running essentially open baffle. I think you’d get much more of the transparency for which the drivers are legend.
You could place some angled deflectors between the front and sides and line with felt . You’d likely still have enough volume in the lower section for a 10 - 12” woofer to provide the required support.

Check out Martin King’s site re OB
Quarter Wavelength Loudspeaker Design

 

[hornwannabe]

With respect to curves I’d see how high up the woofer can play. With a sealed mid-tweeter enclosure and a protection filter the net will be something second order. LR2’s would be a good target up to about 500Hz.

The original Boston’s looked like poly. I like Roxul (rockwool) with a poly batting between the driver and the Roxul. The battling keeps the insulation fibers and dirt away from the driver.

You might want to check out some box modeling programs. I like Unibox but there are several others. Horn response can model the sealed box chamber resonances. For mids I shoot for a system qts of .65 to .70.

Your internal volume is a function of you wood dimensions. I’m not sure what you have there but it looks like over 10 liters. A large mid chamber is not great as you lose cone control due to less dampening.

A large round over in my book is ¾ inch radius router bit run along the front edge of the baffle. I’ve seen larger by people using CNC fabricated corners and carpet tubes.

Thanks for the tips!

1.) Thanks for the crossover tips! Since I'm using a minidsp for the crossovers do I install the protection filter passively? Sorry, complete newb question but would the protection filter be standard for any build or more so on this? LR2 = Linwitz-Riley, right?

2.) Noted on the rockwool tip!

3.) Okay I'll try to find some modelling programs but I use a mac so I think it will be slim pickings

4.) Okay then, I'll follow your 1 liter tip from the previous post for the mid-tweet chamber

5.) Cool tip on the prefab corners!

Again, Many thanks!

 

[hornwannabe]

With no grills flush mounting the DX55 (if it has a square edge), flush mounting the woofer and using a large round over on the cabinet edge will create controllable diffraction.

Something like the Grimm LS1?

 

[hornwannabe]

Re the round-over; lots of controversy on just how large a radius would be required to be efficacious in mitigating edge reflections at the wavelengths likely to be a problem- if at all.

That said, 3/4” is not a particularly big radius, and to achieve anything larger with a router gets to be very expensive - for the bit itself, router capable of spinning it, and amount of material wasted.

A simpler method might be to offset the Lowther’s placement from centre of baffle - by a golden ratio dimension if you want to get geeky- and mirror image them. Oh, and from experience with only a single pair of Lowther’s, they are a royal pain to rebate for flush mounting - the “pincushion” style cast frames on the pair I was given weren’t symmetrical, or even exactly identical, so plan on chamfering the rear side of driver openings.

Would a combination of a large enough round edge (Like if I buy a premade corner like the suggestion above) and off-centering help mitigate edge reflections?

I’d still be concerned about reflections off the back wall of the A150 enclosures- the approx 8” of depth includes front and back panels, so net depth would be only 6.5”, or thereabouts.

Do you mean the internal backwall inside the speaker or the room’s rearwall? So stuffing it like a sealed box and adding deflex to the inside back of the speaker won’t mitigate it?

If you’re willing to seriously modify the enclosures, I’d consider opening up the top section of rear panel so that the Lowthers are running essentially open baffle. I think you’d get much more of the transparency for which the drivers are legend.
You could place some angled deflectors between the front and sides and line with felt . You’d likely still have enough volume in the lower section for a 10 - 12” woofer to provide the required support.

Thanks for this tip. Seriously considering this now and will read up on how to best approach an open baffle Lowther. Will horn loading it (even slightly) in an OB configuration (open back) lessen the effects of the edge and close to rear wall issues (again, a newbie question please bear with me).

When you say angle delfectors do you mean installing something like this in the back:

An externally hosted image should be here but it was not working when we last tested it.

Again my main problem with being unable to follow the open baffle format would be the close proximity this will have on my rearwall. I can afford maybe around a foot of distance from that wall. If the tweaks above solve that I may go the open baffle route. In my limited understanding, bass attenuation and freq nulls will occur if I place the OB near the rearwall. If the minidsp eq combined with your suggested tweaks ameliorate those concerns….. I think I’ll be persuaded enough to go OPEN BAFFLE and sealed woofer combo!

Check out Martin King’s site re OB
Quarter Wavelength Loudspeaker Design

Reading up!

Again Thank you!