Hello Bjorno / All,
I am currently working with a friend to design a no compromise active 3 way monitor / speaker for him but to make the plans and drawings available to others in return for any design assistance from the DIY community. All design work is being done in Solid Works so can be sent direct for CNC routing etc - I currently own a pair of ATC SCM150ASL and PMC IB2 and we are using these as a guide and reference. The plan is to use the following drivers:
Volt RV3143
Volt VM752
Seas T25 CF001
The implementation of the mid and hf seems fairly straight forward - drivers to be offset on the front baffle and grouped as close as possible - the difficulty comes with he choice of loading for the LF driver; we would like to look at folded transmission line similar to the MB2 rather than another straight forward reflex enclosure. We are prepared to mock up the folded TL and test before finalising the design. I have Smaart Live and earthworks M30 mic / high quality mic pre for testing purposes.
Bjorno the TL design you posted in the previous pages looks like a good starting point for us, having never worked with a TL could you advise any common mistakes to avoid in trying to fold this up? I noted the advice to restrict 180 deg bend to 1 etc
Any input appreciated
I am currently working with a friend to design a no compromise active 3 way monitor / speaker for him but to make the plans and drawings available to others in return for any design assistance from the DIY community. All design work is being done in Solid Works so can be sent direct for CNC routing etc - I currently own a pair of ATC SCM150ASL and PMC IB2 and we are using these as a guide and reference. The plan is to use the following drivers:
Volt RV3143
Volt VM752
Seas T25 CF001
The implementation of the mid and hf seems fairly straight forward - drivers to be offset on the front baffle and grouped as close as possible - the difficulty comes with he choice of loading for the LF driver; we would like to look at folded transmission line similar to the MB2 rather than another straight forward reflex enclosure. We are prepared to mock up the folded TL and test before finalising the design. I have Smaart Live and earthworks M30 mic / high quality mic pre for testing purposes.
Bjorno the TL design you posted in the previous pages looks like a good starting point for us, having never worked with a TL could you advise any common mistakes to avoid in trying to fold this up? I noted the advice to restrict 180 deg bend to 1 etc
Any input appreciated
We are working on it, we didn't get any response on diy audio so we plan to build a TL for the Volt based on the suggested TL Bjorno posted earlier in this thread.
We haven't compensated for the effect of the midrange drivers protrusion into the first chamber of the TL as we are not sure how to tbh. Planning on building a prototype an testing with various amounts / densities of stuffing. The drivers have been bought and are sitting on the shelf so it will happen!
The box has been drawn up in Solidworks. Once we have the first one built I will post the measured response. I use Smaart v7 and and earthworks mic will measure outside.
They will be run 3 way active.
We haven't compensated for the effect of the midrange drivers protrusion into the first chamber of the TL as we are not sure how to tbh. Planning on building a prototype an testing with various amounts / densities of stuffing. The drivers have been bought and are sitting on the shelf so it will happen!
The box has been drawn up in Solidworks. Once we have the first one built I will post the measured response. I use Smaart v7 and and earthworks mic will measure outside.
They will be run 3 way active.
We have a pair of ATC MK2 3 way active amp packs we would like to re use; they have 24db crossovers at 380hz and 3.8khz. They have level and phase compensation trim pots per channel and PMC use these crossover points in the passive application of these drivers. The ATC SM75-150S is more sensitive by 3db but 16ohm vs the 91db and 8ohm for the VM752 so hoping there will be enough level trim available to make them work properly.
I intend to try other filters and points to make sure the above wont be compromising them in any way. Volt suggested we crossover to the mid higher and I plan on trying this using PC convolution based FIR filters generated from Acourate > Lynx AES16> 6 channels of Buffalo DAC out to MC2 amps.
If your considering amps for your builds some of my personal findings: I highly recommend the class A/B MC2 pro amps; I have extensively compared a MC1250, T2000 MK2 and Bryston 4BSST level matched on pair of passive PMC IB2 over a period of time and the differences are surprisingly small!, slightly more detail in HF from the Bryston, MC1250 best bass. T2000 best value, Bryston winner all round but marginal and also due to lack of fans but £4k / 2ch. MC2 can be picked up cheap ish s/h but the fan noise needs consideration. Tried a pair of dual mono Hypex UCD400HG with HXR / SMPS but found them a bit fatiguing / hard in the upper mids over extended listening on the IB2 but very detailed. I'm sure they are great amps in some applications and maybe the NCore400 would be better. Will have to try at some stage.
I intend to try other filters and points to make sure the above wont be compromising them in any way. Volt suggested we crossover to the mid higher and I plan on trying this using PC convolution based FIR filters generated from Acourate > Lynx AES16> 6 channels of Buffalo DAC out to MC2 amps.
If your considering amps for your builds some of my personal findings: I highly recommend the class A/B MC2 pro amps; I have extensively compared a MC1250, T2000 MK2 and Bryston 4BSST level matched on pair of passive PMC IB2 over a period of time and the differences are surprisingly small!, slightly more detail in HF from the Bryston, MC1250 best bass. T2000 best value, Bryston winner all round but marginal and also due to lack of fans but £4k / 2ch. MC2 can be picked up cheap ish s/h but the fan noise needs consideration. Tried a pair of dual mono Hypex UCD400HG with HXR / SMPS but found them a bit fatiguing / hard in the upper mids over extended listening on the IB2 but very detailed. I'm sure they are great amps in some applications and maybe the NCore400 would be better. Will have to try at some stage.
The Volt specs seem to support a x-over frequency of 500Hz, their driver doesn't extend as low as the ATC it seems. Are you using Seas T25 CF001 because they are used in the PMC design? I agree about Bryston performance, and price! MC2 are good. I looked to see what studios and broadcasters used before Bryston and it turned out to be HH Electronics in a lot of cases in the UK. I have two of their VX900 amps bi-amping a pair of B&W M801 mk2 speakers and it sounds pretty good. I would be keen to hear what you find, and to be of any assistance (although I'm not sure exactly what at the moment!). What material do you intend using for the cabinets?
I agree re the Volt measurements but thought I would try at 380hz / 24db as this how PMC use them; I am told by a number of sources the PMC soft dome mid is the VM752 and was made for PMC when they stopped using the ATC SM75-150S. I am not sure if these crossover points were a carry over from the use of the ATC mid.. ATC use 380hz and 3.8khz.
The speakers we are working on are for a friend and he has the drivers waiting to go; at some stage I will measure one of the PMC mids in my IB2's and compare to the Volt VM752. They look physically identical. The aim wasn't to copy the PMC but its a very similar 3 way active using the same drivers and the PMC TL bass is very impressive so It made sense to look at them closely. Quested make similar 3 ways using almost the same drivers but reflex loaded.
We decided on the Seas Excel T25 CF001 as they are used in the current 3 way active ATC 150's and it sounds great for the money and works well with the mid. I am not sure what PMC use in their I series, Its probably very similar.
The HH amps looks like solid quality amps; they should go on forever!
We are using 25mm HDF and double thickness front baffle. As we haven't done anything with TL's before we will make a temporary cabinet to test the TL and then finish the drawings and get them CNC cut.
The speakers we are working on are for a friend and he has the drivers waiting to go; at some stage I will measure one of the PMC mids in my IB2's and compare to the Volt VM752. They look physically identical. The aim wasn't to copy the PMC but its a very similar 3 way active using the same drivers and the PMC TL bass is very impressive so It made sense to look at them closely. Quested make similar 3 ways using almost the same drivers but reflex loaded.
We decided on the Seas Excel T25 CF001 as they are used in the current 3 way active ATC 150's and it sounds great for the money and works well with the mid. I am not sure what PMC use in their I series, Its probably very similar.
The HH amps looks like solid quality amps; they should go on forever!
We are using 25mm HDF and double thickness front baffle. As we haven't done anything with TL's before we will make a temporary cabinet to test the TL and then finish the drawings and get them CNC cut.
It would be interesting to know why PMC put their x-overs at the ATC points, it could be that it made sense to continue with the previous x-overs. I have reason to think you are right about the Volt/PMC connection, the drivers I have in mind were from the original development of the PMC version and look exactly like the Volt version. In fact it makes me wonder if Volt made this driver specifically to fill a gap in the market when ATC stopped selling the driver (when it went to the SL version). I have a frequency response print out for the two individual drivers and would appreciate your opinion if you have the time?
Extended bass response is one of the reasons for my interest in this design. I was considering one of the Scan Speak Revelator tweeters - as used in Wilmslow Audio's Prestige series with various combinations of the Volt and ATC mids and bass drivers but the SEAS tweeter is an attractive option.
I am thinking of using an inexpensive active crossover initially but any recommendations would be appreciated. In fact I did wonder if a DSP might be could to tune the speakers to the room.
Yes, the HH amps are certainly solid (and VERY heavy) and have already been going on for a good part of forever! The only trouble is that the MOS-FETs they use are obsolete. Amazing 2nd hand value though and they made the amp packs for some of the active BBC speakers.
When are you thinking of making the temporary enclosures? Is it easy to find someone to do the CNC cutting?
Thanks for all your help/comments etc.
Extended bass response is one of the reasons for my interest in this design. I was considering one of the Scan Speak Revelator tweeters - as used in Wilmslow Audio's Prestige series with various combinations of the Volt and ATC mids and bass drivers but the SEAS tweeter is an attractive option.
I am thinking of using an inexpensive active crossover initially but any recommendations would be appreciated. In fact I did wonder if a DSP might be could to tune the speakers to the room.
Yes, the HH amps are certainly solid (and VERY heavy) and have already been going on for a good part of forever! The only trouble is that the MOS-FETs they use are obsolete. Amazing 2nd hand value though and they made the amp packs for some of the active BBC speakers.
When are you thinking of making the temporary enclosures? Is it easy to find someone to do the CNC cutting?
Thanks for all your help/comments etc.
certainly happy to try and help if I can; if you want to e-mail scan of the FR for your drivers or post them we can compare to the new VM752 and the parts fitted in my IB2's. Probably be a few weeks before I find the time to remove the driver from the IB2 and setup for test, most likely when we get the mock up TL built which I expect in the next 3 weeks. It's surprising how long these DIY projects take when trying to fit around work...
re the crossovers I have had some disappointing SQ trying lo cost commercial active x overs which wont do these drive units justice. I believe there are some diy projects available for discrete active crossovers which could be a good option price vs performance once points / slopes determined. also this could be an option: http://www.diyaudio.com/forums/digital-line-level/215379-dsp-xover-project-part-2-a.html
The Hypex DLCP also looks good but quite expensive. DSP has a lot of advantages if its a high enough quality implementation.
re the crossovers I have had some disappointing SQ trying lo cost commercial active x overs which wont do these drive units justice. I believe there are some diy projects available for discrete active crossovers which could be a good option price vs performance once points / slopes determined. also this could be an option: http://www.diyaudio.com/forums/digital-line-level/215379-dsp-xover-project-part-2-a.html
The Hypex DLCP also looks good but quite expensive. DSP has a lot of advantages if its a high enough quality implementation.
I have PMed you re email of FR graph. It shows about 93dB +/- 3dB from 500Hz to 4KHz although there are differences between the two drivers. I'm not sure how close drivers are usually matched. You're right about how long it all takes, I got the Volt bass drivers months ago! Someone else on this forum says they had surprisingly good results from a DCX2496. I know this brand is not highly thought of but it might be a good place to start. I will check the link, thanks.
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