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Multi-Way Conventional loudspeakers with crossovers

PMC OB1 clone
PMC OB1 clone
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Old 16th February 2007, 05:32 PM   #1
vincentrubble is offline vincentrubble  Canada
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Join Date: Sep 2004
Location: Prince George, BC
Default PMC OB1 clone

Does anyone know what 6.5"/170mm bass driver PMC uses in their OB1 speaker? It looks like it could be a Peerless 830946 or possibly a Morel HU631. PMC's web site says it is a doped 170mm driver with cast magnesium chassis. This would indicate to me that this is a paper coned woofer. Also, PMC seems to like using the Typhany Group's (Vifa, Peerless & Scan-Speak) drivers. Any suggestions? I have already selected the Scan-Speak R2904/7000 tweeter & ATC SM75-150S midrange and am now trying to pin down which woofer to use. Any ideas are more than welcome. I am using Martin King's transmission line tables to help out with the design. Has anyone used them before? They look like he really knows what he is doing.
Thanks to all,
John
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Old 16th February 2007, 11:21 PM   #2
Tenson is offline Tenson  United Kingdom
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Hi,

PMC do not use standard transmission line design ethos. So with a different midrange, tweeter and transmission line design it will likely sound nothing like the OB1 I'm afraid. Still probably sound very good though!
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Old 17th February 2007, 12:00 AM   #3
vincentrubble is offline vincentrubble  Canada
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Thanks for your reply.

I have emailed ATC and Solen (ATC's Canadian distributor) to see if there is any way to beg, borrow, or steal a pair of the 170mm drivers used in the ATC SCM40 speakers. I think that this might well do the trick. I need to keep the speakers as narrow as possible to improve the spousal factor or I would try to use an 8" or 9" bass driver.

Thanks again,
John
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Old 17th February 2007, 03:06 AM   #4
Tenson is offline Tenson  United Kingdom
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Take a serious look at the Hi-Vi D8.8+, it would do very nicely as a bass driver with an xover anywhere up to as high as 1.5KHz. Its a very, very good driver but with an affordable price tag

I also feel that both the tweeter and the midrange you mention are over-priced for the performance on offer. I would likely go for either the Vifa XT25 or more likely the recently announced Peerless 810921 which looks absolute irreproachable for the money, having performance on par with the best there is.

As for midrange I guess there is not a huge choice. The ATC is good, but is pricey. Volt do a midrange unit but its not on their site. PMC actaulyl use this with some slight mods in their big boys speakers Give Volt and email.
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Old 20th February 2007, 10:00 PM   #5
vincentrubble is offline vincentrubble  Canada
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ATC's 180mm bass driver is not for sale. They want to keep it for themselves. According to Solen, the Morel HU631 is not up to the quality of the SS R2904/7000 and ATC SM75-150S. Solen is recommending an Audio Technology custom built driver. This sounds like a pretty cool way for the hobbiests to pretend they are speaker manufacturers. You select your driver size, magnet size, voice coil diameter, coil height, gap height, desired fs, Qts, Vas & Qmin and 'voila!' they build you a driver. See http://www.audiotechnology.dk/iz.asp?id=4|a|119||| for more info. It turns out these guys started Scan-Speak & Vifa, among others. I am just starting out in the custom order process but I'm excited to see how it works. Solen has been very helpful with various questions I have had regarding desired parameters, etc. This is usually a process reserved for manufacturers.

Thanks,
John
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Old 28th October 2012, 08:12 PM   #6
Telstar is offline Telstar  Italy
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Did this project go anywhere?
__________________
"The response of the inner ear extends to at least 200khz" Dr W. Tempest
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Old 14th July 2018, 09:00 PM   #7
Ugg10 is offline Ugg10  United Kingdom
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Sorry for the thread resurrection but better to continue than start again and keep all info in one place.

Anyway, been looking into this one as there is quite a bit of info out there to make a clone of this fine speaker (cross sections that can be scales etc.).

Anyway from a quick goggle it seems the drivers are -

Tweeter - PMC special version of Seas 27TFFC (stock version available)
Mid - 3" dome Scanspeak Discovery D7608/920010 (available)
Bass - 6.5" woofer Vifa M17WG-09-08 (unavailable).
Crossover : "380Hz and 3.8kHz, with a filter 24dB/oct; those are Linkwitz-Riley filters." from High Fidelity

A quick search for a similar spec driver trying to keep most of the Small Theil parameters the same came up with the Seas CA18RLY-08 H1217

The parameters seem to be pretty close (Vifa - Seas)
http://www.sea.vg/vifa/M17WG-09-08.pdf
http://www.seas.no/images/stories/pr..._Datasheet.pdf

Fs - 44hz - 42hz
Vas - 34l - 32l
Imp - 8/5.5 ohm - 8/5.8 ohm
Sd - 143cm2 - 136cm2
Qms - 2.77 - 2.92
Qes - 0.56 - 0.56
Qts - 0.46 - 0.47
MM - 11g - 10.6g
Sens - 89db - 90 db

The frequency plots also look similar except for the Seas hanging on a bit lower but they both have a rise at around 300hz.

So, potentially with the Seas bass river this could be a fairly economical way to come up with an OB1 clone - UK prices for driver seem to be about Tweeter 40, Mid 70, Bass 65 (inc vat).

If I get chance I will try and put this through Boxsim but this will only be for a BR set up not a TL but will give an idea if a fairy basic crossover may work.

Any comment on this alternative driver would be appreciated.
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Old 14th July 2018, 11:23 PM   #8
Dissi is offline Dissi  Switzerland
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The Vifa M17WG-09-08 certainly has been used in some PMC speaker models, but the woofer of the OB1 has a huge dust cap of 3.5". I rather would assume Dynaudio, Morel or a custom driver.

PMC OB1i or OB1 Signature Woofer Spare Photo #1503144 - Aussie Audio Mart
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Old 15th July 2018, 09:25 AM   #9
Ugg10 is offline Ugg10  United Kingdom
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Doh - School boy error - look at the pictures !!!

The link to pictures @Dissi posted are interesting as the speaker suspension only has 4 legs and the cross section (C or H) is very similar to the Vifa ones. A bit more digging shows the Vifa M17WG was used on the PMC FB1, (This site gives details of FB1 dimensions and crossover HIFIDIY??-??DIY?VIFA M17WG-09?? - Powered by Discuz!) , is it possible that they just changes the centre cap for the OB1 ?

The OB1 is stated as having a line length of 3.3m, so using the MH Audio transmission calculator with the M17WG parameters give:

mh-audio.nl - Home

A line length at Low frequency tuning (1/3 wave) of 227cm, port height of 11.9cm and a Fb of 30hz. This obviously does not match up with the PMC dimensions. (used 16cm internal width, 200mm as stated minus approx 20mm for cabinet walls)

So, I know the Scanspeak Discovery 18W/8542-00 is a bit of a favourite on here so I though I'd do come calcs. Using the Ml calculator you get:

A line length at Low frequency tuning (1/3 wave) of 302cm, port height of 15.6cm and a Fb of 23hz. This obviously is a closer match up with the PMC dimensions.

Now putting this through the DB Dynamix single folded front port calculators, you get:

Single Fold On-Axis Transmission Line Enclosure Calculator - DB DYNAMIX AUDIO

A recommended line volume of 1.6ft2 and a calculated volume of 1.56ft2 with a tuning frequency of 43hz. (5.5 in port height, which gives about the right speaker depth, all other dimensions as per PMC data).

This speaker looks like it would work nicely but with an increase in cost (18W is approx 140). So, is there any other TL style kits that use the 18W driver?
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Old 7th September 2018, 10:38 PM   #10
Ugg10 is offline Ugg10  United Kingdom
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Been playing around with Leonardo's TL calculator and a model of an OB1.


I have modelled a SB 23MFCL45-8 (8" mid range woofer/subwoofer) with the same geometry as the OB1 (as close as I could guess from various internet pictures) including the inclusion of a reduction due to the Mid driver enclosure. And the results look pretty good if you heavily (?) pack the TL out with stuffing at between 5 and 9 Kg/m^3 (0.3-0.56 lb/ft^3) to get rid of the higher frequency wrinkles (is this stuffing possible/appropriate?). I have added a 380hz 24db/octave low pass as per the OB1. This give a s nice f3 of 24hz and a f10 of 20hz.


Here is a screen shot of the TL calculator input/output and the SB data sheet. Can anyone verify that I have done this right - TL is 2.33m long and starts at 500cm^2 reduced to 150cm^2 at the mid driver (5" tube) and back up to 350cm^2 and finally down to 200 cm^2 at the exit. 22cm wide box give a volume of 73litres. I did re-organise this to be in the same orientation as the speaker but it made very little difference to the response.



Thinking of adding a W4-1337SD (the neo one with the small magnet) as the mid and then not sure on tweeter yet but the Satori TW29BN looks nice.


Comments/thoughts welcome.
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