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Multi-Way Conventional loudspeakers with crossovers

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Old 18th September 2018, 09:11 PM   #1
mbrennwa is offline mbrennwa  Switzerland
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Default Open Source Monkey Box

Please see notes and updates at the end of this post!

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Following up on the earlier Open Source Speaker thread (part I and part II) I am starting a new thread to discuss the develpment of the "Open Source Monkey Coffin".

Here's an update of my earlier Monkey Coffin ideas. Sorry it's so long.

POINTS OF DEPARTURE (as I see them):
  • The first poll says it should be a three way, and it's okay to cost more than $500 per box.
  • The second poll says that the Monkey Box should be "amplifier friendly" (work well with ACAs or small tube amps, etc.), and it should not be too big (not more than 60-80 L).
  • The speaker should be straight forward to make for DIY novices (we don't want to scare them, we want them to run to the hardware shop and build stuff on their kitchen table). There is no point in designing for expert builders, because they will design their own speakers anyway.

MY IMPLEMENTATION IDEAS (I admit these are partially biased by my own preferences, because I need some motivation to actually put some work into this):
  • The box shoud be easy enough to make on a kitchen table. Dimensions roughly 30 x 65 x 30 cm or so (will depend on the requirements of the drivers and box tuning).
  • For "weak amp compatibility" I set the efficiency target to 92 dB/2.83V/1m, with bass extension to 45 Hz (-3 dB). Achieving this will not be very easy.
  • The impedance curve should be flatish and qualify as "8 Ohm". This means we can't "cheat" with the efficiency target by using low-impedance drivers.
  • Use high-quality drivers/parts with the right tech specs for the task. The look of the drivers has to be "right" for a HiFi system in a home environment, but is second priority after the tech specs (people may not want to build a speaker that does not look "right").
  • Woofer: The woofer will likely be the limiting factor that determines the size/bass-extension/efficiency compromise. I guess a 10" unit would be the right choice here. The earlier threads already mentioned a few units that might be interesting for this design (Fane Sovereign Pro 10-300SC, Ciare FXE 10-2.5, Volt BM251.3, some Beymas, etc.). We'll have to look at this some more.
  • Midrange: Needs to keep up with the SPL requirements, so many of the conventional "HiFi" midranges are out. I have some experience with the ATC SM75-150 dome, which is VERY good, expensive, and not available to DIYers anymore. When ATC stopped selling to the DIY market, Volt released the VM752 dome, which is a very good clone of the ATC driver. I really want to use the Volt VM752 dome. It can be used from its fs (400 Hz) up to about 3 kHz or so.
  • Tweeter: There are many good tweeters out there. I am a big fan of Be dome tweeters (ScanSpeak D3004/6640, SB Acoustics Satori TW29BN). I also read a bit about waveguides, which do good things. They help with matching the dispersion of the tweeter to the midrange, they reduce the effects of baffle diffraction, they increase the on-axis efficiency, and they reduce non-linear distortion of the tweeter (by reducing the drive voltage for a given SPL). At the moment I can't think of a reason why we should not use a waveguide.
  • Cross over filters: the x-over frequencies will depend quite a bit on the driver choices. However, if possible, I like to set the woofer/midrange x-over frequency such that it fits the baffle-step centre frequency. This makes it easier to compensate the baffle step by fiddling with the woofer SPL vs midrange SPL. If the drivers allow, I like using 6 dB/octave filters because it's easier to get the time-domain response of the loudspeaker right. In my experiments, my ears preferred 6 dB filters over 12 dB filters.
  • I will openly admit that costs are not my first priority. If the right parts cost a lot of money and there are no alternatives, so be it. The earlier threads indicated that it's ok if the parts cost is more than $500 per speaker. Some said $1000. My priority is to make this a very good speaker, and suitable parts may cost a bit of money. In the end, there will always be substantial flexibility with costs related to x-over parts and enclosure materials + finishing.

NEXT STEPS AND QUESTIONS (everyone has his/her own approach to loudspeaker design, but here's my suggestion):
  • In the first step we'll have to narrow down the driver choices. This will be a forward-and-backward process between driver suggestions and model runs using these drivers, always keeping the design targets in mind. I'd suggest choosing a woofer first, because that will define the box size, bass extension, and sensitivity. Let's say the midrange is set (yes, you are allowed to complain, but... ). The tweeter comes last.
    Question: What input data do we need for these model runs? Do we need actual measurements of the drivers in their baffle/box? I am not big with modelling tools, and I tend to replace detailed model runs by measurements from prototypes. Others might be more efficient than this by using their modelling tools.
  • The second step is to build an actual prototype. Now we need money to buy parts. If the design is still attractive to me (i.e., it's something that I'd like to build and use myself), I'd be willing to put in some money and go for it. I could also do measurements.
    Question: How will the funding work? Anyone experienced with raising and managing money for open source projects? Anyone willing to put some cash on the table? Who will manage the money, and how?
  • The third step is to tweak the prototype. Again, this will be another forward-and-backward process. And we may need more money.

---------------------------------------------

Notes and updates:

Important note 31 Oct. 2019: DIYers may profit from this open-source project for their own private purposes, for example by building and enjoying a copy of the Open Source Monkey Coffin speaker. Please do not use the information developed in this open source project on a larger scale (for example by selling speakers based on the Open Source Monkey Coffin design or substantial parts of it) without written permission.

Note 4 Oct. 2018: This project has received financial support from LORDSANSUI, Paul Vancluysen, George Wright, KaffiMann, Charles Bueche, zimmer64 and others (anonymous) here. Thank you!

Note 4 Oct. 2018: post 162 with summary of woofer selection
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Last edited by mbrennwa; 1st November 2018 at 09:54 PM.
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Old 18th September 2018, 10:07 PM   #2
Aatto is offline Aatto  United States
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Old 18th September 2018, 10:59 PM   #3
KaffiMann is offline KaffiMann  Norway
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I've started checking out some drivers, there is a slight chance we can get away with a really nice 12".
Will look into it tomorrow.
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Old 19th September 2018, 12:03 AM   #4
Brett is offline Brett
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If the group buy includes the VM752, I'm in for a pair.
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Old 19th September 2018, 01:53 AM   #5
Aatto is offline Aatto  United States
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Quote:
Originally Posted by KaffiMann View Post
I've started checking out some drivers, there is a slight chance we can get away with a really nice 12".
Will look into it tomorrow.
yes, someone mentioned Fane SOVEREIGN series woofer, looks good if I remember correctly, I would really like to see a very good low crossed mid range/mid woofer, like maybe Acoustic Elegance TD6M (high end, reasonably priced and high sensitivity) ? I personally prefer a good mid woofer to carry the sound (maybe over 200Hz) I don't like my woofer to have anything to do with my busy bottom heavy music and vice versa, to my ears it makes it a little boomy.
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Last edited by Aatto; 19th September 2018 at 02:02 AM.
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Old 19th September 2018, 05:36 AM   #6
mordikai is offline mordikai  United States
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I think a mid like the Volt or TD6M deserve a better woofer than the Fane Sovereign series.
I'm all for the Volt, sounds cool!
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Old 19th September 2018, 07:26 AM   #7
mbrennwa is offline mbrennwa  Switzerland
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Well, Fane may not sound like one of the great names. I am not particularly biased towards the Fane, but the TSP of the Sovereign 10-300SC do look like a good match for what we're after. What is it you don't like about the Fane?
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Old 19th September 2018, 07:51 AM   #8
KaffiMann is offline KaffiMann  Norway
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What I think Mordikai is saying:
The Sovereign series lack some fancy bits like cast frame and shorting rings etc. The brand or manufacturer does not matter so much, it's more the build quality.
(I like Fane, it's good stuff, and value for money!)

I am still checking around, nothing nailed about the driver, design or anything, but I got the compact volume part at least...
It may be hard making a 30 x 65 x 30 box, mbrennwa.

... xo at 300hz?
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File Type: jpg Faital Pro 12FH530_preliminary.jpg (376.2 KB, 1057 views)
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Old 19th September 2018, 08:07 AM   #9
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by KaffiMann View Post
What I think Mordikai is saying:
The Sovereign series lack some fancy bits like cast frame and shorting rings etc. The brand or manufacturer does not matter so much, it's more the build quality.
(I like Fane, it's good stuff, and value for money!)
Ok, I see. Is there a way to tell if a driver has copper rings etc? Some data sheets are not very specific about this? Is slow impedance rise at frequencies above the responance peak a reliable indicator?

Quote:
Originally Posted by KaffiMann View Post
I am still checking around, nothing nailed about the driver, design or anything, but I got the compact volume part at least...
I tried to reproduce your result for the Faital 12FH530 in a bass reflex box. I could not reproduce your result using AJ Horn. No matter what I tried, a 59 L box would give a nasty response peak at the low end. I can get it flat with a volume of 30 L or so, with a -3dB frequency of about 52 Hz. Quite a difference to your result. Hmm.

What about the Beyma SM-110/N or SM-112/N? I get decent results with AJ Horn from these.

Quote:
Originally Posted by KaffiMann View Post
It may be hard making a 30 x 65 x 30 box, mbrennwa.
Sure. I am flexible with this.

Quote:
Originally Posted by KaffiMann View Post
... xo at 300hz?
Not with the Volt dome midrange. Need to go up to about 400 Hz I guess.
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Old 19th September 2018, 08:21 AM   #10
KaffiMann is offline KaffiMann  Norway
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It is not so easy to use bass reflex as "Type of design", I am not familiar with AJ horn, but hornresp and MJK's excel sheets are good, use horn simulation software, do not use bass reflex software. It is a slot port design.
If you want I can try and get an Akabak simulation going to verify, but I got so consistent results from hornresp that I stopped verifying, it may take some time to do this, have not used it for some years.

And I like to have the combined phase from port and driver together, it is hard to get good (PROPER!) results with bass reflex software.

Edit:
Do you mind posting the data you entered into AJ horn? Maybe the dimensions are different?
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Last edited by KaffiMann; 19th September 2018 at 08:25 AM.
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