New DIY Mid High (90deg) - AKA PM90

Re: New DIY Mid High

Jack Arnott said:
On a related note, the link from Peter states an asymmetrical slope, 12 and 18 db/octave.
But I question this. There are three components, as seen in the pictures. Two caps, and one inductor.
It is my understanding that one cap would be 6 db/octave, and one cap one inductor would be 12 db/octave. Comments?
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The crossover is tricky in this case - I think (I may be wrong) from the quick look I had, its a series derived passive crossover and is connected as shown below.

If you ignore the low driver in the circuit the VHF has an 18dB crossover, and if you ignore the VHF the HF driver has a 12dB crossover.

Soooo I think it will not be a standard filter shape / slope and it will have an ultimate slope of 12 & 18 dB.
 

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Re: New DIY Mid High

Ossian Ott said:
Hi Jack, AFAIK BMS are produced in Europe, would it be possible to participate in the group buy and get the drivers shipped from BMS to avoid extra costs due to the roundtrip to US? (I live in Sweden)
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Hello Ossian, you are right, BMS is produced in Europe. But because my domain is North America, I can only ship here, or countries that do not have a distributor. So, sorry, to get in on the group buy you will need to buy from Jeff, and have them shipped back from here.

Edit, thanks for the clarification Peter.
 
Re: New DIY Mid High

Don J Davis said:
Sorry for the delayed response, been out of town doing a large Easter event.

Mark, ask away, I’m learning lots as we go too.

There is no need to have Part D if you don’t want it. Peter confirmed that before the drawings where released. I thought it might make the assembly easier and add a flat spot to mount the Speakon connectors in.

Yes, on the angles, you can use whatever you want, I just drew what the cad system suggested.

Yes, the ports need to be all the way to the edges per Peter. The adjacency to the horn wall adds length to the port depth. Also, Peter uses those as access to tighten some of the bolts on the 12s.

I plan to use blind inserts in that triangular piece of wood you spotted below the baffle. I didn’t detail it since I’m not sure how many people will build it that way. I do have an ulterior motive for the removable baffle too. I hope to be able to change out horns from the 90x50 to the 60x40 depending on the deployment. This would be done in conjunction with Peter’s design of the splayable version of the box. That way with a horn change the box can be used stand a lone or two aside. I haven’t gone much past the idea stage with this so far.

I haven’t chosen a gasket material yet. Something reusable and not to thick attached to bottom of the baffle. Some small pieces of wood will need to be installed like a ledge on the sides for it seal to as well. I’m a little concerned that the top edge of the HF950 may be very close to the front edge of the cabinet making it difficult to recess a grill if used. Per the plans there is 15mm offset but the HF950 flange is 13mm thick.
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Thanks Don,

Neat idea with the removable HF950 baffle.....and I thought you we're just doing it to make mounting the 12" drivers easier..... :o~:-o~:eek:
I guess cabinet depth might be the biggest issue with converting to a 60X40 later? And yeah, I saw the tight clearance for the speaker grill too.
Peter's done a heck of a job keeping it small, huh?!
 
Re: New DIY Mid High

Peter Morris said:
[SUB]This is what I used - http://www.plyco.com.au/index.php?main_page=product_info&cPath=48_49&products_id=142

It’s not good timber, but it was cheap, light and reasonably thick and I was building a prototype. To get this project to work you need to keep the weight down.

19mm would make it too heavy; I think you could get away with 15mm everywhere with some careful bracing. I would not use 12mm. Can you get 5/8 of an inch ply (16mm) ?

I used some pieces of pine 19mm x 40mm on edge to brace the sides.

What I do as a crude test is tap or knock on all parts of the box (like you knock on a door). It should make a dull thud; if you feel or hear some resonance then you need to add bracing.

The box volume is not particularly critical in terms of handles and bracing.

Just double check the compression driver will fit between the two 12" drivers before you glue it together -- its very close in there.

@ Don ... the HF950 is shown 50 x 90 ... not 90 x 50 - no need to change it ... the horn mouth is square :)~:-)~:smile:[/SUB]
Click to expand...

Thanks Peter,

All the 5/8 ply I can find is really 19/32, so it's only a fraction of a mm thicker than the 15mm baltic birch.
I think I'll use the 15mm BB and make sure to brace it really well, using your knock test. (I see JTR uses this wood, even on his Orbit Shifter sub.)

I'm also hoping to gain some 12" driver-to driver-clearance (8mm) by keeping the overall outside box dimensions, and the mid horn dimensions, both the same. I figure the 12" baffle boards (or part D) need to gain the difference in 4 thicknesses (eg top and part E).
8mm isn't much, but it sounds like the 12" cone-to-4594 clearance is super tight.
What clearance did you settle on as acceptable?
 
Re: New DIY Mid High

Mark Wilkinson said:
Thanks Peter,

All the 5/8 ply I can find is really 19/32, so it's only a fraction of a mm thicker than the 15mm baltic birch.
I think I'll use the 15mm BB and make sure to brace it really well, using your knock test. (I see JTR uses this wood, even on his Orbit Shifter sub.)

I'm also hoping to gain some 12" driver-to driver-clearance (8mm) by keeping the overall outside box dimensions, and the mid horn dimensions, both the same. I figure the 12" baffle boards (or part D) need to gain the difference in 4 thicknesses (eg top and part E).
8mm isn't much, but it sounds like the 12" cone-to-4594 clearance is super tight.
What clearance did you settle on as acceptable?
Click to expand...

Yes it is super tight - There is about 3mm clearance either side. The picture shows the gap (6mm) between 4594 and one 12". The 4594 is touching the opposite 12" driver.

I also added a picture of the back of the box. I cut a little bit out in the centre to make it a little lighter but mainly to make it look more interesting and less DIY.

What I need to do now is sand the box and give it a proper coat of duratex with the duratex roller.
 

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Re: New DIY Mid High

William Abel said:
Hope to build a pair of these.

Why isn't the BMS 4594HE listed on their website?
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I don’t know why BMS does not have it on their site. They don’t have the HE version of the 4599 on their site either. http://www.usspeaker.com/bms 4599ndhe-1.htm
The HE version of the 4594 is basically the same driver witha different phase plug and aluminium demodulating rings for reduced distortion and a slightly better frequency response.
 
Re: New DIY Mid High

If anybody is interested, here is the impedance plot of the two 12's and the Sim for comparison.
 

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Re: New DIY Mid High

Peter Morris said:
The FIR settings are quite complex.:?~:-?~:???: In comparison the IIR setting are relatively simple, however I want to do them again with the box flown before I post them.

These settings produce a flat amplitude response from about 80Hz to 20 KHz. The phase response flat from 300 Hz up.

In addition I have added a some group EQ -2 to -3 dB centred at 3.1 KHz and a very gentle shelving filter +3dB at 100Hz tapering off to zero at about 500 Hz. This is a personal "taste" EQ, so apply as you like.

Note: the Mid and Hi amp gains are 26 dB, the low gain was set to 35 dB. LM 26 FIR time 2.5ms
Click to expand...
Peter, by any chance, did you have the box "measured" with the original (bms) passive x-over on a lake?
TX again for all the efforts you put into this, as well the 60 degree version :thumbup:
 
Re: New DIY Mid High

Klaus Zimmermann said:
Peter, by any chance, did you have the box "measured" with the original (bms) passive x-over on a lake?
TX again for all the efforts you put into this, as well the 60 degree version :thumbup:
Click to expand...

No I have not measured the standard BMS with a passive crossover in this box. I do however use the that combination on the same horn in a double 10 and horn box. It sounds excellent, but not quite as perfect as the 4594HE all active ... but there is not much in it.
 
Re: New DIY Mid High

I have a question, would it be possible to use another CD driver(bigger?), which can go down to 600-700 hz but not as far up to 20k(say 10-15k) with the same SPL as the 4594HE, but not being Coax and considerably cheaper? Is this a bad approach or could it work without losing to much HF/air in the cab.
 
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