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Super lightweight 12v 3way

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Dannyboy_086 View Drop Down
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    Posted: 02 June 2020 at 6:05pm
After over 10 years of geeking out on DIY speakers and a few half hearted failed attempts I've finally taken the plunge and bought my first DIY kit, Parts Express C-Notes and the build is progressing nicely.

As the weather here in the UK is rather blooming lovely at the moment and just because why not it's a nice lockdown project I'm looking towards another build, a compact mono 12v system but have a few things I'm not sure about, not been able to find the answers for online or just plain don't understand so please hit me with any tips/points/criticisms.  I hope that the tone of my post is okay and that some of the questions raised here will help others and may even lead to others building it if it turns out to be any good, any insights are very much appreciated!


The aim is for a very lightweight mid-top constructed using all neo drivers using 9 or 12mm ply to give a reasonably flat response 70hz-20khz -+3db @ over 90db @ 1w1m with little to no EQ that is compact <30L, as Hi-Fi as possible, cheap(ish) and easy (ish) to build.

I think I have some of the basics covered, and whilst I maybe just should build an established design like the halfinator or a PE boombox kit they look like they could end up being closer to 15kg and this seems like an interesting challenge/concept.

The other option is to try to build a Soundboks clone however the Soundboks is a heavier and larger design and this might be able to give decent sound quality at a much lower weight albeit with less efficiency and max SPL, but still be capable of over 105db when pushed hard.

 

I plan to buy a Mini DSP UMIK-1 measuring microphone and have plenty of outdoor space to measurements.

I already have a mini DSP 2x4 kit board so whilst I could use that and just get a cheaper 4ch amp I'll probably sell it to offset some of the costs and in the end it should simplify things and save some quiescent current using 1 board instead of 2.

 

Please excuse the brain dump and any stupid questions, , any and all suggestions/comments/links etc are welcome!


Big respect to this forum and all the knowledge that gets shared on it!

 

Here is the concept so far, UK approx. prices.

1x B&C 10CL51 10" 4 ohm 96dbspl 1.2kg Vas 36L £70 70-300hz

1x or 2x Faital Pro 3FE22 3" 4 ohm (paralleled to get 2 ohms) 91 dB SPL 250g each £15/30 300hz-3.5khz

1x P-Audio PHT 407-N 8-ohm 100db SPL 200g £25 3.5khz-20khz

1x Ultramaxx 12v 7ah Lifepo4 battery £70 includes charger

1x ZOUDIO AIO4CH (Lukteveld 4 channel amp with DSP, suitable for 8/4/2 ohms) £100

1x dc-dc 12-24v boost converter £10

 

£290/305 for parts

£75 + extra for fixings, wires and wood etc

Total = approx. £400

 

 

1.75-2kg for drivers

5kg approx. for 12mm Baltic birch ply or possibly 9mm?

1kg for battery

200g for amp

Total = <9kg

 

Internal dimensions

H 23"

W 11"

D 7"

= 29L tuned to 70-75hz.

 

Excluding the battery & electronics but minus the drivers that should give at least 25L which sims well in WinISD with the super lightweight B&C woofer.

 

 

Design concepts and challenges:

Use 3 of the amps channels to power the 3 drivers individually.

Selectable with SPDT switch 12-24v boost converter for the power hour.

The amp specs say the crossover slopes are 12db but with 3 drivers that shouldn't be a problem (I will ask the amp designer if I can stack filters in crossover blocks to achieve 24db per octave XOs.)

 


Enclosure

To keep weight down I plan to build this using 12mm Baltic birch ply, but given the relatively low levels of SPL what do you guys think to using 9mm ply but with more bracing?

Absolutely no idea about the best way to mount the battery and electronics though. It would be nice to make the battery removable/replaceable but snugly fit and possibly to leave enough space to add another one in to get to 24V or increase the runtime and have the whole thing be at least water(beer)-resistant as possible.

I think Saturnas has designed the Boominator so that the recommended battery fits snugly into an existing space - this seems like a very neat and smart thing to do so I was thinking of doing something similar for this particular Lifepo4 battery, i.e. have an extended rear enclosure just big enough to fit one or possibly two of the batteries in it and then a door to cover it.

Or the simpler route might be to mount the battery and amp in an almost lid on top of the enclosure - struggling a bit with this, will check out more of the Boominator builds.



To mid-range or not mid-range

I like the idea of using a mid-range driver as AFAIK the 10" woofer will experience an off-axis drop of in frequency response due to beaming at higher frequencies and I'd be asking it to meet the PHT 407N at around 2khz without a mid. Now a 10" may only have say a 9" radiating diameter but won't it still start to beam at around 2khz. Although Saturnas recommends using the Eminence Basslite 2010 + PHT 407N in the signature version of the Boominator so perhaps I'm worrying about nothing?


 

Regarding baffle step losses.

Given that my baffle is going to be 12" or 30cm wide and at least that high then the calculation f3 = 115 / WB (Taken from Rod Elliot Sound products website and is the example he uses) gives  f3 = 115 / 0.3 = 383 Hz.

So does that mean that as long as I set the crossover to the mids at 383hz or a higher frequency I don't need to worry about correcting for baffle step losses?

And that therefore for the mid/s to match the woofers output I either need to

- Do nothing - due to baffle step losses of minus 3-6db the mids will have roughly the same output at the baffle step/crossover frequency as the woofer (90db @ 1w1m).

- Use 2x mids to gain +3db and match the woofers output.

- Use mid/s of a lower impedance so the amp supplies more power to them? E.g. an 8ohm woofer and a 4ohm mid.

- Or use 2x mids and wire them to present a 2ohm load to get +6db (+3db from a pair, +3db from twice the power).

 

 

The speaker is mainly going to be used outside and placed on the floor, so not sure if I need to account for this when trying to match the outputs of the mid and woofers? Or is that the case that because most manufacturers measure in half space, that as long as I match the output when taking into account power drawn by the drivers and the baffle step losses that I can try to just match 1w1m values.

 

 

Q and tuning frequency

Saturnas mentions in one of the Bomminator threads that he has tuned the Boominator to a specific Q and that is why it won't sound as good indoors. Is that something I can and should try to replicate as the main use of this speaker will be outdoors?

Is that why it is desirable perhaps to tune the enclosure & driver to have a peak in the response at or near to the tuning frequency either by tuning higher than Fs or by incorporating a peak in the response due to a too small enclosure size?

 

A neat feature of the amp is that you can wire up a switch that, I think, lets you to change between different pre-set EQ settings on the fly.

If so then perhaps it can have a setting for max SPL outdoors with no EQ and then at the press of a switch change the EQ to a more indoor friendly response especially if I can utilise a power outlet, then using power to EQ shouldn't be as much of an issue as the potential loss of playing time when EQing on battery.

 

 

Why is bass so expensive

I plan to use a HPF set to around 70hz for the mid-top but I've read it so many times on the 12v forum that bass absolutely saps battery power and that's why it's a waste to try to design subs and speakers that reach down low when they're going to be running of portable batteries, but I've never read anything that goes into the theory behind this, can anyone point me in the right direction?

 

Not for this design but possibly for a companion sub (utilising the remaining 4th ch) and given that I can set a HPF then is something like a F3 or 40, or 45hz just dumb to aim for if I care at all about battery life?

 

 

Crossover summing

As I understand it if you have 2 drivers and a given crossover frequency, depending on the type of crossover used this can result in either a peak, flat or dip in the response at the crossover frequency. And that different designs and designers are able to utilise this to smooth out and account for the differences in driver response at the XO frequency. If drivers are relatively flat and within 0.5 -+ dB of each other at the XO frequency then does the designer still need to take the summed response into account or can this be easily EQ'd away with a DSP?

In other words are there any clever but simple to deploy methods I can use here to improve the response of these speakers?

I also haven't yet grasped the concept and impact of phase and impedance in crossover design, but again given that this will be an actively crossed over design is that something I need to worry about much?

 

 

 

Electronics:

Is it safe to power different impedance loads using the same amp, i.e. 1x ch each at @ 8,4,4 and 2ohms?

 

Is it okay to use a SPDT switch to select either standard 12v operation or route the circuit via the boost converter?

 

Would I wire it like this?

Battery + to switch input terminal

Switch A terminal to amp (for 12v)

Switch B terminal to boost converter to amp (for 24v)

Amp negative to battery negative

 

 

Is it possible to integrate a charger input in the same circuit so the speaker can;

A) Play whilst charging (not essential but nice to have)

B) Not have to disconnect the battery from the amp and connect to a separate charger to charge it - or does this depend on the amp being able to accept a charging circuit/connection?

 

 

 

Mono summing

Because this will be a mono speaker is there an off-the-shelf part that will sum stereo to mono or would I have to wire say a stereo 3.5mm female jack to a mono signal and then use that as an input on the amp? I might be able to just do this via Bluetooth but it would be good to have the option of using a cable and also to at a later stage add a second speaker to create a stereo setup but that is definitely a nice to have rather than essential - again the board mentions that you can setup wireless stereo using a second board.

 

 

 

Run time

Have read other posts that suggest with normal music you can expect 3-4x or more the runtime than the nominal specs might suggest.

E.g.

1 ch = 25w @ 24v  = 1.04 amp

1 ch = 50w @ 24v  = 2.08 amp

1 ch = 50w @ 24v  = 2.08 amp

 

Total consumption = 5.2 amps, minus 10-15% for boost converter losses = 5.72-5.98 amps per hour so the battery would run flat in just over an hour but is that likely to extend to 3-4x that in the real world, so at full tilt I'd expect about 5-6hrs - similar to what Soundboks speakers quote so I think this is realistic?

 

I'll leave this for another post but also considering building a light and compact sub to go with this and use the remaining channel so any suggestions welcome!

 

Well if you've got this far hope it hasn't bored the bits off you and hope some of my noob-y questions can help someone else someday.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote DJ-Dulux Quote  Post ReplyReply Direct Link To This Post Posted: 02 June 2020 at 6:31pm
This is my build log for my boominator, discusses weight etc. Maybe worth having look through...


Dupe...


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Post Options Post Options   Thanks (0) Thanks(0)   Quote fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 02 June 2020 at 6:41pm
Just a thought, have you considered using a fullrange driver such as the Fane 12-250TC, great sounding driver with a dsp to smooth it out, should do 70Hz in a 30L box and as it is a high QTS driver will have a 3dB + hump at around 100Hz, which makes it very efficient there. Only weighs 4.3Kg and is bloody loud on 30 Watts in. Would make for a much simpler build.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dannyboy_086 Quote  Post ReplyReply Direct Link To This Post Posted: 02 June 2020 at 7:16pm
Cheers guys

Dupe started reading the link to your post and thought it looked familiar! I stumbled into it over the previous few months and I think like you I was surprised about the difference in weight in the types of ply after reading your posts.

How did everything end up? Looks like a great build!

Is there anything you would have done differently or any tips you would give someone embarking on their first 12v build.



FatFreddiesCat: I have actually. It was a driver I came across sometime back but I have some reservations around the dispersion at higher frequencies, do you mean to use it in a 2way or run it full range? Also the weight is more than I'm looking at. If the numbers above are right then the 3 drivers should come in at less than 2kg in total. 

I would like this to be something that someone can lug around on their back for say an hour or so or walk to the park with without it destroying them. I actually started looking at 6.5" speakers but Neo ones with decent bass response are few and far between and that B&C driver at 1.2kg is incredibly light!

Also looked at other 8/10/12" drivers but a lot of the PA 8" drivers have lower sensitivity or their bass response drops off significantly when the enclosure is tuned to Fs of the driver. 
Other 10's and 12's are, apart from the Eminence Basslite 2010 a fair bit more expensive, not available in 4phms, a lot heavier or have much less sensitivity so I think I'm kind of stick with this or the eminence and this is £20 cheaper. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 04 June 2020 at 4:14pm
Originally posted by Dannyboy_086 Dannyboy_086 wrote:



To mid-range or not mid-range

I like the idea of using a mid-range driver as AFAIK the 10" woofer will experience an off-axis drop of in frequency response due to beaming at higher frequencies and I'd be asking it to meet the PHT 407N at around 2khz without a mid. Now a 10" may only have say a 9" radiating diameter but won't it still start to beam at around 2khz. Although Saturnas recommends using the Eminence Basslite 2010 + PHT 407N in the signature version of the Boominator so perhaps I'm worrying about nothing?


I think a midrange would be an over-complication for your first build. Perfectly smooth off-axis response is nice, but not really necessary in order to achieve a good sound for the majority of listeners.

Originally posted by Dannyboy_086 Dannyboy_086 wrote:

Why is bass so expensive

I plan to use a HPF set to around 70hz for the mid-top but I've read it so many times on the 12v forum that bass absolutely saps battery power and that's why it's a waste to try to design subs and speakers that reach down low when they're going to be running of portable batteries, but I've never read anything that goes into the theory behind this, can anyone point me in the right direction?

 

Not for this design but possibly for a companion sub (utilising the remaining 4th ch) and given that I can set a HPF then is something like a F3 or 40, or 45hz just dumb to aim for if I care at all about battery life?

Put simply, reproducing low frequencies at a given SPL with any given loudspeaker requires much, MUCH more electrical energy than reproducing higher frequencies at the same SPL. This is simply because the driver has to move much further per cycle, is therefore pushing a much greater mass of air and will absorb more power to do so. 

Have a look at this graph: https://www.researchgate.net/figure/Power-spectral-density-of-a-typical-Pop-music_fig2_256067532

This shows how the power requirement to reproduce music increases steeply with decreasing frequency. So the bottom end of the frequency scale is not very clear, but you can see that if you set some "pop" music playing at a volume such that the frequencies around 30-50Hz take one watt to play, then the frequencies around 5kHz will be taking 30dB LESS to play - that's 1000 times less, or 0.001 watts. Or from the other perspective, the hi-mids of your music require 1000x less electrical energy to play than the deep bass content.

So, you can see that setting a highpass filter as high as you can possibly get away with, saves a lot of battery power. Not everyone does it, but it really can make a big difference in battery life. Moving it up half an octave (eg from 30 to 60Hz) might mean that the bass content of your music takes 10x less power to play. 

Originally posted by Dannyboy_086 Dannyboy_086 wrote:


Crossover summing

As I understand it if you have 2 drivers and a given crossover frequency, depending on the type of crossover used this can result in either a peak, flat or dip in the response at the crossover frequency. And that different designs and designers are able to utilise this to smooth out and account for the differences in driver response at the XO frequency. If drivers are relatively flat and within 0.5 -+ dB of each other at the XO frequency then does the designer still need to take the summed response into account or can this be easily EQ'd away with a DSP?

In other words are there any clever but simple to deploy methods I can use here to improve the response of these speakers?

I also haven't yet grasped the concept and impact of phase and impedance in crossover design, but again given that this will be an actively crossed over design is that something I need to worry about much?


Basically, it depends on your crossover slope. You're using 12dB/oct slopes - these introduce 180 degrees of phase shift at the crossover frequency. This is inherent to the 12dB design. A 6dB filter has 90 degree shift, an 18dB filter has 270 degrees, a 24dB filter has 360 degrees.

So, because of the 180deg shift, you will want to wire your tweeters out of phase with respect to the woofers. This is done simply by reversing the connections at the tweeter (red to black and black to red). This should, all things being equal, put your drivers in phase with each other and there should be no dip at the crossover point. Whether or not there is a peak there, depends on the flavour of 12dB filter you use. Linkwitz-Riley filters will not make a peak, Bessel and Butterworth filters will make a small peak. You can pull the crossover frequencies apart a little bit to get rid of a peak, or overlap them slightly to correct a small dip. This more efficient use of DSP than adding a PEQ to correct.

 

Originally posted by Dannyboy_086 Dannyboy_086 wrote:

 

Electronics:

Is it safe to power different impedance loads using the same amp, i.e. 1x ch each at @ 8,4,4 and 2ohms?

 

Is it okay to use a SPDT switch to select either standard 12v operation or route the circuit via the boost converter?

 

Would I wire it like this?

Battery + to switch input terminal

Switch A terminal to amp (for 12v)

Switch B terminal to boost converter to amp (for 24v)

Amp negative to battery negative

 

 

Is it possible to integrate a charger input in the same circuit so the speaker can;

A) Play whilst charging (not essential but nice to have)

B) Not have to disconnect the battery from the amp and connect to a separate charger to charge it - or does this depend on the amp being able to accept a charging circuit/connection?

Perfectly safe to run the amp like that, as long as it is happy with 2r loads (is it?)

I wouldn't wire up the switch that way - you'll be shorting out/ feeding 12v back into the output of the boost converter which may result in sparks. Plus, I don't think you need to run the amp at 12v; it will be louder at 24v! You shouldn't have a problem with battery life if you get some good cells - I would consider lithium, especially for backpack use.

There are many battery management boards available that will integrate charging control and overdischarge/ overcurrent protection. It's a very good idea to include one.

Originally posted by Dannyboy_086 Dannyboy_086 wrote:

 

Mono summing

Because this will be a mono speaker is there an off-the-shelf part that will sum stereo to mono or would I have to wire say a stereo 3.5mm female jack to a mono signal and then use that as an input on the amp? I might be able to just do this via Bluetooth but it would be good to have the option of using a cable and also to at a later stage add a second speaker to create a stereo setup but that is definitely a nice to have rather than essential - again the board mentions that you can setup wireless stereo using a second board.


You can make a mono sum adapter using a 3.5mm jack plug, socket and short length of wire, plus three resistors. See here for details: https://www.ranecommercial.com/kb_article.php?article=2106

 

Originally posted by Dannyboy_086 Dannyboy_086 wrote:

 

 

Run time

Have read other posts that suggest with normal music you can expect 3-4x or more the runtime than the nominal specs might suggest.

E.g.

1 ch = 25w @ 24v  = 1.04 amp

1 ch = 50w @ 24v  = 2.08 amp

1 ch = 50w @ 24v  = 2.08 amp

 

Total consumption = 5.2 amps, minus 10-15% for boost converter losses = 5.72-5.98 amps per hour so the battery would run flat in just over an hour but is that likely to extend to 3-4x that in the real world, so at full tilt I'd expect about 5-6hrs - similar to what Soundboks speakers quote so I think this is realistic?

 

I'll leave this for another post but also considering building a light and compact sub to go with this and use the remaining channel so any suggestions welcome!

 

Well if you've got this far hope it hasn't bored the bits off you and hope some of my noob-y questions can help someone else someday.



For pop music, the rule of thumb is 1/8th power as your equivalent constant figure. So if your amp is doing peaks of 100 watts, the long term average draw will be equivalent to 12.5 watts. This is assuming a reasonably balanced system without a ridiculous number of subwoofers in it, and "average" music ie not crazily bass-heavy like some dubstep and modern digital dubs.
Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dannyboy_086 Quote  Post ReplyReply Direct Link To This Post Posted: 04 June 2020 at 4:33pm
Nice one

I was totting up the numbers and it was looking a bit worrying so thats great to know. 


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