I have a pair of Musical Fidelity MC4 loudspeakers which use TPX plastic bass/mid cones. The unit is a good performer, and is housed in a thick rigid MDF cabinet. The disadvantage with the thick cabinet is that the mid range suffers some congestion on loud choral passages. I have a pair of Spendor BC1s which use thin baltic ply bitumen paper loaded cabinets which do not suffer from the mid congestion. Transferrence of the MC4 units to a spare pair of BC1 cabinets confirmed the mid congestion caused by the high mass cabinet. As a long term BC1 user, I have little difficulty in hearing the effects of high mass, rigid cabinets.
Has anyone tried making a cabinet (2ft x 1ft x 1ft) using 2" polystyrene sheet?
Mass is very low, rigidity low, but could be braced with 1 x 1" batons internally. It would be interesting to know of any experiences in this area, before I go ahead with the experiment.
Yours sincerly, Peter Parsons.
Has anyone tried making a cabinet (2ft x 1ft x 1ft) using 2" polystyrene sheet?
Mass is very low, rigidity low, but could be braced with 1 x 1" batons internally. It would be interesting to know of any experiences in this area, before I go ahead with the experiment.
Yours sincerly, Peter Parsons.
Hello Peter!
High mass cabinet doesn't have a potential to cause a congestion in a strict sense, in that it restricts the frequencies coming out of the unit. Theoretically it is possible to hear the output of the walls resonating (very loud listening conditions) which might be interpreted as less clear sound. While transfering units, did you move the XO filter as well? There is an interesting article on thin cabinets construction here:
Factors in the design of loudspeaker cabinets - BBC R&D
How thick are the walls of MF? How does the baffle opening of the woofer unit look like?
High mass cabinet doesn't have a potential to cause a congestion in a strict sense, in that it restricts the frequencies coming out of the unit. Theoretically it is possible to hear the output of the walls resonating (very loud listening conditions) which might be interpreted as less clear sound. While transfering units, did you move the XO filter as well? There is an interesting article on thin cabinets construction here:
Factors in the design of loudspeaker cabinets - BBC R&D
How thick are the walls of MF? How does the baffle opening of the woofer unit look like?
Yes, it's been tried before; polystyrene is acoustically transparent unfortunately.....
This guy has tried: http://www.decdun.me.uk/loudspeakers2.html
there's a thread here about cabinets made from some sort of rubber matting, much more practical...
This guy has tried: http://www.decdun.me.uk/loudspeakers2.html
there's a thread here about cabinets made from some sort of rubber matting, much more practical...
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Thank you gentlemen.
The Musical Fidelity MC4 loudspeakers were designed by Martin Colloms in the eighties for Musical Fidelity, and did well in a Hi-Fi Choice blind listening test. They were later rated by Hi-Fi Choice in its reference section as Good++; the Quad ELS 63 was rated Good+ and the Spendor SP1 Good. The speakers use an advanced Audax bass/mid unit with a cone material named TPX (Polymethylpentene) a lighter, stiffer plastic than polypropelene, and, it seems, rather difficult to stick. The tweeter is the TDL 25mm metal dome, considered the best available at that time. The crossover/filter is second order for the bass/mid, third order for the tweeter, and uses poly caps. Oxygen free copper wire is used to connect the units. The cabinet, which is a little smaller than the BC1, is made from ¾" high density chipboard, with a "Wharfedale tray" inset back panel, and an internal shelf. The baffle is nearly two inches thick. Internal bracing and a tight filling of wadding completes the package. The performance is low distortion, low colouration, but features low level cabinet noise in the vital midrange. Interestingly, the cabinet noise is largely unnoticed by anyone who is not a long term BC1 listener. The thought occurred: How would the units sound in a thin wall mass loaded BC1 cabinet, a cabinet design known for its low midrange noise? A pair of spare BC1 cabinets was at hand. The experiment necessitated the fabrication of new baffles. The first trial was of the units without the MC4 stuffing, relying instead on the foam linings of the BC1 cabinets. The sound was marred by a constant echo; presumably internal cabinet sound exiting though the thin light cone. The BC1 uses a heavy coated cone and must therefore be more resistant to the transmission of internal cabinet sounds. The second trial was with the cabinets stuffed with wadding. Now the echo was no longer heard, the upper mid range splendidly clear and free of cabinet noise, but the upper bass and lower mid were plummy and unclear. The left hand of the piano and the lower reaches of the human voice lacked clarity. I encountered this to a lesser extent in the two pairs of SP1s I once owned but sold on for that very
reason. The thin wall, mass loaded cabinet apparently does not mate well
with 8" poly type cones. The return of the units and crossover/filter to
their own cabinets improved the clarity of the lower mid but restored the
mid range noises.
The combination of the heavily doped thick and stiff rubberised polystyrene
cone and the thin wall mass loaded cabinet evidently is a part of that mid
range magic of the BC1. I have in recent years regularly attended the
Bristol Hi-Fi Show, and have each time, as a long term BC1 user, come away
all too aware of the mid range cabinet noises of the box speakers on demo.
Polystyrene is too soft and fragile for commercial loudspeaker cabinets, but could prove interesting in the protected domestic setting. Thus my enquiry to see if anyone has experience with polypropelene cabinets. No point making them if polypropelene is most unsuitable. Peter Parsons, Cornwall, UK.
The Musical Fidelity MC4 loudspeakers were designed by Martin Colloms in the eighties for Musical Fidelity, and did well in a Hi-Fi Choice blind listening test. They were later rated by Hi-Fi Choice in its reference section as Good++; the Quad ELS 63 was rated Good+ and the Spendor SP1 Good. The speakers use an advanced Audax bass/mid unit with a cone material named TPX (Polymethylpentene) a lighter, stiffer plastic than polypropelene, and, it seems, rather difficult to stick. The tweeter is the TDL 25mm metal dome, considered the best available at that time. The crossover/filter is second order for the bass/mid, third order for the tweeter, and uses poly caps. Oxygen free copper wire is used to connect the units. The cabinet, which is a little smaller than the BC1, is made from ¾" high density chipboard, with a "Wharfedale tray" inset back panel, and an internal shelf. The baffle is nearly two inches thick. Internal bracing and a tight filling of wadding completes the package. The performance is low distortion, low colouration, but features low level cabinet noise in the vital midrange. Interestingly, the cabinet noise is largely unnoticed by anyone who is not a long term BC1 listener. The thought occurred: How would the units sound in a thin wall mass loaded BC1 cabinet, a cabinet design known for its low midrange noise? A pair of spare BC1 cabinets was at hand. The experiment necessitated the fabrication of new baffles. The first trial was of the units without the MC4 stuffing, relying instead on the foam linings of the BC1 cabinets. The sound was marred by a constant echo; presumably internal cabinet sound exiting though the thin light cone. The BC1 uses a heavy coated cone and must therefore be more resistant to the transmission of internal cabinet sounds. The second trial was with the cabinets stuffed with wadding. Now the echo was no longer heard, the upper mid range splendidly clear and free of cabinet noise, but the upper bass and lower mid were plummy and unclear. The left hand of the piano and the lower reaches of the human voice lacked clarity. I encountered this to a lesser extent in the two pairs of SP1s I once owned but sold on for that very
reason. The thin wall, mass loaded cabinet apparently does not mate well
with 8" poly type cones. The return of the units and crossover/filter to
their own cabinets improved the clarity of the lower mid but restored the
mid range noises.
The combination of the heavily doped thick and stiff rubberised polystyrene
cone and the thin wall mass loaded cabinet evidently is a part of that mid
range magic of the BC1. I have in recent years regularly attended the
Bristol Hi-Fi Show, and have each time, as a long term BC1 user, come away
all too aware of the mid range cabinet noises of the box speakers on demo.
Polystyrene is too soft and fragile for commercial loudspeaker cabinets, but could prove interesting in the protected domestic setting. Thus my enquiry to see if anyone has experience with polypropelene cabinets. No point making them if polypropelene is most unsuitable. Peter Parsons, Cornwall, UK.
I think you have focused on the cabinets difference as the source of the issue and then stopped "thinking" and started "believing." "Congestion" is not a word that diagnoses anything.
Before going to the trouble of making new cabinets you would do yourself a favor to do a little more investigating around the difference between the two speakers. Use science, not audiophoolery.
If you want to make cabinets out of styrofoam, try a sandwich with masonite or the like on each side. The joints will be challenging 😉
I was going to say the same thing. You have two very different speakers, different drivers, different xovers and different cabinets so stating that some performance defect is the result of one without testing is jumping to a huge conclusion.
I build all of my speakers with 3/4 MDF or ply using matrix bracing and there is no mid congestion because of the construction. I'd also be wary of following design articles from 40 years ago as construction, measurement and design techniques have come a long way since.
I put as much trust in the opinions of subjective reviews and reviewers as I do with the likelihood of still having money in my bank account after giving my PIN to a thief.
I did some large sub towers out of industrial styro and laminex many years ago. It was a mongrel of a job, and I doubt I'd ever do it again.
Doesn't matter if the bbc article is 40 years young or not, the principle works and the reason why they did it was to make the cabinets as light as possible without compromising the performance. That it's not important to a modern DIYer who is obviously in no need of moving a piece of a loudspeaker on an everyday basis, that's obvious. In those times the designers were less corrupt thinking more straight without worrying what will happen to company income in the next 3 decades. Now we have programmed electronics with timers built in, set to disable itself out of function so the people don't forget to get a new one. 😀
Yes it does, as the knowledge base has moved on. For a DIYer, who cares re the mass of the cabinet as you're not loading it in/out every evening.
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