Help with a 2-way monitoring system in a concrete box

[Antares]

After a few months of reading and researching on speaker building I decided I want to build my own pair of active monitor speakers for my small 3m X 4m X 2.5m room in South America.

I understand that concrete would be a superb material for a sealed box due to the low coloration added to the sound as well as how inert it would make the box allowing for closer placement to the rear wall.
downside being it's weight mostly.

Due to the space available to me I plan on using a woofer size of 5-6 inches to control the bass response.

The drivers I selected for the system are:
-Fountek Neo X 1.0 Ribbon Tweeter Black - 20 watts RMS - 8 ohms - 92 dB 1W/1m4
-Dayton Audio DSA135-8 5" Designer Series Aluminum Cone Woofer - 50 Watts RMS - 8 ohms - 87 dB 2.83V/1m

The MiniDSP kit 2x4 for the active x-o system.

And I'm planning on using a separate mono amp board for each driver so I can place the system inside the boxes.

The TPA3116 D2 rated at 100w, which on a video review of this board was measured to actually output 51.8w @ 4 ohms with a 1Khz sine wave, and 28.1 @ 8 ohms, and a really low distortion

Link to the review of the amp board I watched: https://youtu.be/CULehzRVurc

other options would be the amp boards offered here but most would be overpowered for the tweeter

The questions I have are:

-Is a concrete cabinet a good idea at all.
-Is powering each driver with it's own amp a good idea.
-How would I supply the power for the whole system??, I've been told I would connect everything in parallel with a 24v psu though, and what about the amps needed???
-Would using 4 woofers instead of 2 be better?? so I can get the sensitivity better matched.

Sorry for the long post and would appreciate any help, if my building plans are fine I would be here posting my progress on the concrete speakers.

[Chris Roemer]

2 8ohm drivers (in parallel) will give the amp a (nominal) 4ohm load.
4 (in series-parallel) will result in an 8ohm load - with no gain in sensitivity (over a pair), but your amp will lose half its power.

Each pair of those woofers needs about 0.5cf for a vented box - but they'll only reach down to the mid 50s (personally, I'd want to use a sub with those).
If you go with a closed box, they only need half that volume - but then YOU'll need a sub, as they'll only reach 100Hz.

You can model boxes (low end response) yourself using WinISD from linearteam.org (it's free).

[donradick]

Antares - in general, concrete is a great material for speaker boxes.
What box size / bass extension / price are you thinking of?
That tweeter is really pretty great, I'd want to mate it up with a very good woofer like the ES140.
https://www.parts-express.com/dayton...8-ohm--295-396
or maybe the Tangband 1720 as used in the Speedsters.
https://www.parts-express.com/tang-b...river--264-872

[Kornbread]

Here we have some stuff commonly called backer board or cement board. It is as it sounds but IMO better for our purpose. It is concrete with tiny pellets of styrofoam embedded in it. It's lighter that straight concrete and can be cut with a knife. In the past I've lined the inside of wooden cabinets with 1/2" thick panels made from the stuff.

I'm thinking that's a really sweet tweeter and wouldn't be too worried about overpowering it. I'm using two 3 channel Acurus amps (arc welders) in an active setup with a couple mini2x4 driving an active 3 way where two 200+watt channels are dedicated to nothing but a tweeter.

How would that neo match with an rs or Rival?

Just an idea. You could also use one of the 4x100 watt amp boards per speaker. I think the Sure t-amps sound pretty darn good for the money. Could build another box for the minidsp and chip-amps and run 4 wire speaker wire to the speakers.

[donradick]

Kornbread - I am SO jealous of your setup. Maybe I can get some top amps like those Acurus some day.
Mating with a Neo X, you probably want to cross 2.5 - 3Khz, so you would want a midwoofer no larger than 5 inches.
Top PE choices would be the ES140 or Wavecor 120.
But we haven't heard back from the OP concerning size or budget.

[Kornbread]

Kornbread - I am SO jealous of your setup. Maybe I can get some top amps like those Acurus some day.

Straying from the OP's questions.

Guess I'm not quite sure how to take that. donradick The only way I can afford 'audiophile' gear is by shopping used on US Audio Mart and Audigon. There is some great gear at reasonable prices there.

Going against the grain of this forum, I'm one of those guys that does believe there are times when measurements don't tell the entire story. Most of the time, yes, but sometimes there are differences that just don't flesh out in measurements.

With that said and in my subjective opinion:

Regardless how the cheap t-amps measured, the bottom was tight and controlled, the midrange was surprisingly good with a bit of grain to it which really added life to vocals, but something seemed a little off in the top end.

The Acurus feels a tad softer on the bottom (these things can pass some current but they're softer in the bottom than a tiny t-amp?) and smoother in the middle. The top end is now present but smoother? Weird. It's much easier to pick the music apart with these, but as bad as I hate to say it, I still like how the cheap t-amps sound in the middle.


YMMV

[Antares]

Thanks a lot for the support.

As this is my first time building speakers I want to make sure I'm on the correct path.

After looking all day for a better woofer to pair with the ribbon tweeter, I decided to go with

-Dayton Audio RS150-8 6" Reference Woofer - 8 ohms - 40 watts RMS - 88.7 dB 2.83V/1m

I understand that if I were to use 2 of these woofers per speaker I would need at least 80 watts to drive em' both in parallel @ 4 ohms right?

That would make them have a sensitivity of 94.7 dB / 1W right???

and using the Fountek Neo X 2.0 Ribbon Tweeter Instead of the X 1.0 would match the sensitivity perfectly would't they???

Since the Fountek Neo X 2.0 Ribbon Tweeter sesitivity is 94 dB 1W/1m.

as for the cabinet I forgot to mention I plan on building a sealed enclosure and add a subwoofer for the system later in the future.

I do have access to MDF and rented tools but I decided to go with concrete for it would be easier to seal the box and lower the sound escaping from behind the box wouldn't it???

as well for aesthetic and economics reasons.

Kornbread Using a multichannel amp would be a great idea, but wouldn't it be a problem to find something that won't blow the tweeter?? as it is rated for 25 watts RMS for the X2.0 and 20 Watts for the X1.0.

Please correct me if I'm wrong but, I understand that the amplifier should be rated for at least double the RMS of the speaker right??? How would I go about reducing and matching the wattage needed then???

Was looking at the boards offered here at parts express and the WONDOM AA-AB31184 100W Mono Amp Board would be a great option for driving the woofers in parallel right???

Sure Electronics AA-AB32971 2x100W Class D Audio Amplifier Board (T-Amp Technology) woud be perfect for the woofers as well and without any parallel connection needed right??

But I'm having trouble finding a good match here for the ribbon rated at 25 watts RMS and 43 Watts Max.

And for the power supply I was told I would be able to plug everything in parallel as well at 24VDC over 2 Amps per speaker is that right??

Planning on ordering before discounts are over and will post my progress as soon as parts arrive.

[Antares]

1. Would something like an attenuator work for lowering the power output given by an audio amp at 100W for example??
2. Would something like an in-line resistor lower the output of the amp as well??
3. Or I'm better off matching the amps for the drivers being:

• 2 Wondom mono 100w amps for the woofers in parallel so 4 ohms. and half the power for each driver.
• 2 TPA3116 measured at 28W over 8 Ohms with 24VDC for the tweeters

forgot to mention that the planned x-o point would be between 1.5kHz and 3kHz with the MiniDSP

---

The volumes given by WinISD for a 2 woofer box are

Sealed: 0.4 ft^3 with an F3 of around 100Hz

Ported QB3: 0.71 ft^3 with an F3 of around 60Hz

close to the suggested by Dayton:

• Sealed Volume 0.1 ft.³
• Sealed F3 116 Hz
• Vented Volume 0.26 ft.³
• Vented F3 68 Hz

I want a sealed enclosure as it would give a flatter response, but I can see that I can get a decent bass extension by designing a ported enclosure.

I want to add a subwoofer to the system but I don't see how could I integrate it via MiniDSP without upgrading to more outputs.

So I plan on buying locally the sub and getting another amp board for it with a low pass filter.

As for the cabinet material should I give a try to the concrete idea or ditch it??

I guess this post would go now to the Speaker Project Gallery section in a few weeks.

And sorry for the long post.

[donradick]

Kornbread - apologies, I certainly did not mean to express any disrespect.
I somehow thought that the Acurus was one of those pure Class A audiophile $$$$ amps.
Looks like they are solid Class AB amps at pretty reasonable prices.

That said, I'm currently "down" on Class D -- bought a couple of PE (Franklin) APA150 amps and really digging them.
And I totally agree with you - there are things that we clearly hear that somehow don't show in measurements.

[donradick]

Would something like an attenuator work for lowering the power output given by an audio amp at 100W for example?? If so I think the project's been solved...

or would something like an in-line resistor lower the output of the amp as well??

forgot to mention that the planned x-o point would be between 1.5kHz and 3kHz with the MiniDSP

Sorry for the thread pollution!
You are headed the right way, but have a few misconceptions.
Just because an amp is rated at 100W, does not mean that it will blow a 20W tweeter.
First of all, you are not going to run the system at 100% all the time, secondly, that 20W tweeter
rating is usually specified as something like 20W with a 2nd order crossover at 1800Hz.
So if you use a 3rd order crossover at 2500Hz, the tweeter can handle a lot more power -
but it won't have to, because it will produce 94dB at 1 watt, 97 at 2, 100dB at 4 watts, and you
really don't want to play at those levels.
I think you will be very happy with the RS150 woofers. Sounds like a very nice system.

[Kornbread]

You mentioned using a minidsp for active crossover duty; you do not have to worry about matching sensitivity of the drivers as that can be easily accomplished with the mini. IMO, it's a lot easier working with the mini than building a real crossover, but it still takes lots of time to get it right. The tinkering never stops.

Since you mentioned using a 'chip' amp in the original post.

Everybody has their own opinion as what is good, or not so good. Although they may not have the best specs, I have used a couple of these https://www.parts-express.com/wondom...2050)--320-335 and power supply https://www.parts-express.com/mean-w...upply--320-316 for a super cheap <$100 four channel amp that sounds much better than it should ... at least to my old ears. They are closer to 40+ real watts than 100 but they should get the job done. You could build an enclosure separate from the speakers as a sort of diy integrated amp that houses the small chip amp, smps, and minidsp. Connect that to the speakers with a double run of regular speaker wire.

As I alluded to earlier, don't be so fixated on power handling and watts.

donradick mentioned earlier the neox would probably want to cross around 2.5-3k. so finding a woofer that plays smoothly up to that point will make building the crossover easier. Having said that, the minidsp allows you to simulate steep crossovers and notch filters, with a keystroke. This might allow you to more easily (or is that less difficultly?) match that tweeter with a broader range of woofers.

You have not mentioned your listening habits or preferences.

And yes, we want to see step by step construction of your concrete enclosures.

[Chris Roemer]

If these will be on stands (a couple feet out into the room - highly recommended), then you're likely to "lose" about 6dB (4-6dB) for BSC (baffle-step correction).
That would put a (parallel) woofer pair more like 89dB or so. You basically can use any tweeter (then) that's rated at or above 89dB/2.83v. If it's got higher sensitivity, THAT would normally be compensated for in the (passive) crossover. In an active system, you'll just adjust the tweeter voltage down to match the woofer's output.

I would like to suggest that you do a LOT more reading before putting this project "in stone" (as it were). "SpeakerBuilding 201" by Ray Alden, is a good reference to have.

[Kornbread]

Kornbread - apologies, I certainly did not mean to express any disrespect.
I somehow thought that the Acurus was one of those pure Class A audiophile $$$$ amps.
Looks like they are solid Class AB amps at pretty reasonable prices.

Rows of those pretty glowing glass bottles do subdue me into a trance like state, but hey, I'm not that far out there! Considering they are the old Mondial units and ~20 years old, they were very reasonable. I'm sure many on here have spent more on a sweet pair of drivers.


OP: There is very little musical content that requires the tweeter to handle lots of power. Often heard at work, "Don't wury bout it" they will be fine.

Asking: Is it advisable, when using an active setup like the OP intends, to place some protection on the tweeter in case of stray current?

[Antares]

WOW thanks a lot for the feedback.

And thanks for clearing my misconceptions donradick , so using a 4x100w amp board for the whole system would likely be the best option for the project as Kornbread suggests right??

These would absolutely be on stands Chris Roemer and built in a concrete cabinet to reduce transmission to the stands and the rear wall.

I would go with sealed as they can be smaller and with a flatter response right??

I would use them for music production and listening to music, I love my ears so I try to listen at low dBs as low as the speakers go without losing too much dynamics and clarity.

I love listening to every kind of electronic music as well as live concerts in lossless formats if possible, from everything to reggae, to salsa, to jazz, to rock and, classic music.

---

Edit: I plan on using a cap in line with the tweeter just in case

and I want to be able to save during these discounts as every dollar counts as I'm located in South America but still want to get the most bang for the buck at least in audio quality.

Or should I as Chris Roemer suggests, research further before trying these parts and order "SpeakerBuilding 201" by Ray Alden instead?? and miss the discounts??

Wish I was born earlier so I could learn more and get something like those beautiful tubes...

Ohhh and the reason to better match the drivers was to leave more eq power for minimizing the acoustic issues of my room, even though I will have access to a somewhat acoustically sound mastering room in my local music academy to perform the calibration of the speakers for the first time.

Also plan on ordering a lb of Acousta-stuf polyfill for good measure

And I have no idea where I can find concrete panels for use instead of just concrete and molds.

[Antares]

A basic sketch of the design, keep in mind that the corners would ideally be rounded.

Measurment in inches and volume estimated around 0.3 - 0.4 cu.ft