Flint Acoustics: Rocketman Loudspeaker (one off build)

[Flint]

I am officially seeking a buyer for this new project. I posted an initial drawing of them in the Morel Tweeter thread, but here's an updated drawing reflecting some cosmetic and acoustic improvements:



They are a 3-Way speaker with an external crossover to allow for upgrades, customization, or even active crossover implementation (most ideal performance and my preference). I would prefer to tune the crossover to the buyer's tastes, so that will be the last thing I design, test, and build.

Preliminary specifications​

• Tweeter = 28 mm Hand coated Silk-Dome
• Midrange = 12 cm Polymer Composite Cone with oversized 54 mm voice coil
• Woofer = 28 cm High Power Sandwich W-Cone
• Impedance = 8 Ohms
• Power Handling = 300W RMS
• Sensitivity = 88dB SPL 1W/1M (anticipated)
• Frequency Response = 32 - 20,000Hz
• Bass Limit = 23Hz (-10dB)
• Finish = Red Stained Natural Oak with hand-rubbed Tung Oil (I can refinish to any desired color, but there will be an extra cost)
  
• Overall Dimensions = 40 x 16.5 x 19 inches (HxWxD)

The bass cabinets are large, so shipping will likely be costly and I don't have those contracts with the shippers yet to get killer rates.

They are designed to offer the best performance you can get in a tight, powerful 3-way with the crossover for the woofer to midrange designed to eliminate the floor bounce issue and the crossover between the midrange and the tweeter optimized to the effects of the baffle, ideal dispersion, and smoothest phase response possible. Since the placement of any speaker has a massive impact on the midrange and treble performance, I am also going to include a visual aid tool to aim and angle the upper enclosure to get the ideal performance at the listening position.

Please share with your audio nut friends and let me know if anyone is interested in these speakers.

 

[Flint]

Here are some photos of the work thus far:


Photo 1: Bass Enclosures when they were completed before installing the woofers


Photo 2: The 4 inch midrange driver - it has a HUGE voice coil for it's size


Photo 3: MDF portion of the upper baffle with cutouts for tweeters and midrange drivers.

 

[Flint]

Since the woofers and tweeters are older and have some years of use on them, I am not including them in my pricing model. The selling price of these speakers is based on performance quality, the work I am doing now, and the parts I am buying to complete them. I don't have any more audiophile grade woofers & cabinets laying around, so this is the last time I can make a speaker this large and powerful for the price I will be charging. I could make a few smaller speakers with the additional tweeters I have available, but that's a different story.

 

[Randy]

Flint, those are looking really good so far.

 

[Flint]

More progress over the past two days...



Photo 4 - Clamping one of the enclosures for the midrange driver



Photo 5 - Clamping the second enclosure for the midrange

The way I designed the midrange enclosures required that I clamp up all five sides on one process. This was tedious and difficult, but the result is more square, plumb, and aligned joinery which will look more attractive and finish more easily.

I chose to make the enclosures with a port (which will be plugged by default) to give options to the future owner to use these as small satellite speakers, if they so choose. The anticipated response for this enclosure with the port open will have a -3dB point of 73Hz, allowing for mating with a HT subwoofer crossed over at 80Hz. The power handling will suffer compared to the port being plugged, but it will create more options should they be appropriate. With the port plugged the bass is -3dB down at 123Hz. Based on experience, the baffle width, typical floor reflection nulls, etc., I am expecting to set the crossover between the midrange and the woofer to about 400Hz, or more than a full octave higher than the start of the roll-off in the midrange with the port plugged. This will provide the most linear phase and group delay response in the upper bass.

 

[Flint]

I also started gluing 1-1/2 inch blocks to the sides and top of the upper baffles:


Photo 6: Oak Edges being Glued onto the top baffles


Photo 7: Oak edges

This gets me to a near 16-1/2 inch wide baffle at the bottom, which aligns perfectly with the bass cabinets. It also creates an opportunity to get a furniture grade finish to match the oak veneer and solid oak edged on the bass cabinets. I am eager to see how this looks once stained.

My plan is to protect the wood with Tung Oil. as I did with the bass cabinets years ago. I am going to use alcohol to remove the protective wax finish on the bass cabinets and apply fresh coats of hand-rubbed Tung Oil on the visible surfaces to refresh their look.

I am going with a semi-gloss, or duller, finish to make the natural look of the wood center stage.

 

[Flint]

Among other tasks I completed on these speakers today is gluing the oak pieces to all four sides of the top baffles:

Here both baffles are still clamped up as the glue dries.

Photo 8: Gluing on top and bottom oak edges

The dark line along the edges is the moisture from using a sponge to wipe off the excess glue.

Once the glue dries I'll cut off the excess width and then sand everything flush.

 

[Dentman]

I am officially seeking a buyer for this new project. I posted an initial drawing of them in the Morel Tweeter thread, but here's an updated drawing reflecting some cosmetic and acoustic improvements:

View attachment 8567

They are a 3-Way speaker with an external crossover to allow for upgrades, customization, or even active crossover implementation (most ideal performance and my preference). I would prefer to tune the crossover to the buyer's tastes, so that will be the last thing I design, test, and build.

Preliminary specifications​

• Tweeter = 28 mm Hand coated Silk-Dome
• Midrange = 12 cm Polymer Composite Come with oversized 54 mm voice coil
• Woofer = 28 cm High Power Sandwich W-Cone
• Impedance = 8 Ohms
• Power Handling = 300W RMS
• Sensitivity = 88dB SPL 1W/1M (anticipated)
• Frequency Response = 32 - 20,000Hz
• Bass Limit = 23Hz (-10dB)
• Finish = Red Stained Natural Oak with hand-rubbed Tung Oil (I can refinish to any desired color, but there will be an extra cost)
  
• Overall Dimensions = 40 x 16.5 x 19 inches (HxWxD)

The bass cabinets are large, so shipping will likely be costly and I don't have those contracts with the shippers yet to get killer rates.

They are designed to offer the best performance you can get in a tight, powerful 3-way with the crossover for the woofer to midrange designed to eliminate the floor bounce issue and the crossover between the midrange and the tweeter optimized to the effects of the baffle, ideal dispersion, and smoothest phase response possible. Since the placement of any speaker has a massive impact on the midrange and treble performance, I am also going to include a visual aid tool to aim and angle the upper enclosure to get the ideal performance at the listening position.

Please share with your audio nut friends and let me know if anyone is interested in these speakers.

Is there anyway you could add the above post to the FB post you made? I think it would help emesely. Also, you are a member of some of the audio groups on FB correct?

 

[Flint]

FB sucks for long essay style posts like I can do here. I will post that photo to the Flint Acoustics FB photo album soon. I created a "Friebds of Flint Acoustic" FB group and added everyone from this forum who was a friend on Facebook. Anyone can join that group.

 

[Dentman]

FB sucks for long essay style posts like I can do here. I will post that photo to the Flint Acoustics FB photo album soon. I created a "Friebds of Flint Acoustic" FB group and added everyone from this forum who was a friend on Facebook. Anyone can join that group.

I'm a member a few audio groups that post gear for sale. I strongly recommend you look into it.

 

[Flint]

Thanks, I will.

 

[PaulyT]

So what's the reason for the oak outside pieces? Just aesthetics? Sorry, I don't quite understand from your comments in above posts...

 

[Flint]

So what's the reason for the oak outside pieces? Just aesthetics? Sorry, I don't quite understand from your comments in above posts...

The lower bass cabinets are covered with Oak plywood and have Oak edges. I am designing the upper cabinets to match.

 

[Flint]

Maybe this photo of the baffles shows what I am going for on these speakers.


Photo 9: Milled edges on top baffles with midrange cabinets in the background

After the glue dried on the edges I use a two different router round over bits to mill the edges. This could be a signature design feature of mine which greatly reduces edge diffraction resulting in vastly improved resolution of the midrange and treble versus have sharp corners on the edge of the baffle. Today many speaker designers addressing edge diffraction by modifying the edges go with a 45 degree chamfer which works to a decent degree. But a 45 degree chamfer is less ideal than a rounded edge.

This is also why I offset the drivers using a distance which is based on a prime number as the divisor to reduce any diffraction delays on the right and left from being the same frequency and angle.

 

[Flint]

I am going to use some very soft hemispherical feet under the top units with the midrange and tweeter in them. I got them today and they are exactly 3/4" in diameter. So, I used a 3/4 Forstner drill bit to make 1/16th in deep round pockets in the bottom corners of the baffles to hold and protect the feet. I then ensured the baffles were flat and level and put enough glue in those pockets and float a smooth flat surface. When it dries it will make a solid, hard, smooth surface on which the adhesive on the feet can grip securely. I am also considering making little metal protectors to put under the rubber hemispheres and make things seem more "audiophile" for the user to experience.


Photo 10: Glue being used as hard pad for adhering soft rubber feet to bottom

 

[Xgm3]

Maybe this photo of the baffles shows what I am going for on these speakers.

View attachment 8595

After the glue dried on the edges I use a two different router round over bits to mill the edges. This could be a signature design feature of mine which greatly reduces edge diffraction resulting in vastly improved resolution of the midrange and treble versus have sharp corners on the edge of the baffle. Today many speaker designers addressing edge diffraction by modifying the edges go with a 45 degree chamfer which works to a decent degree. But a 45 degree chamfer is less ideal than a rounded edge.

This is also why I offset the drivers using a distance which is based on a prime number as the divisor to reduce any diffraction delays on the right and left from being the same frequency and angle.

They look awesome!

 

[Flint]

Thank you, very much!

 

[TKoP]

How far back to the drivers go? With the recent build I did, the positive/negative tabs were fairly "short", so I had to notch out a portion of the circle. I'm assuming that isn't the case for these drivers, but with a double thick front baffle, i was wondering how much clearance you actually have.

 

[Flint]

How far back to the drivers go? With the recent build I did, the positive/negative tabs were fairly "short", so I had to notch out a portion of the circle. I'm assuming that isn't the case for these drivers, but with a double thick front baffle, i was wondering how much clearance you actually have.

The midrange driver has a rare earth magnet inside the voice coil instead of the traditional donut magnet which is larger and outside the voice coil:


Photo 11: Midrange driver side showing motor assembly

This makes the rear acoustic clearance just about as open as can be had.

In cases where there is a concern about airflow, I will round over or 45 degree angle the rear edge of the speaker hole.

 

[Flint]

Lots and lots and lots of sanding time later, I stained the baffles, and I really like the look - even the MDF (which I sanded almost half-way through the paper on the surface).


Photo 12: Freshly stained top baffles


Photo 13: different angle on freshly stained front baffles


Photo 14: Midrange Enclosures after first coat of gloss black enamel paint

So, these are coming along very nicely. They look good enough I may go with a high gloss urethane to bring out their beauty.