Soffit mount transmission line speakers (PMC)

What a great forum You have here! I´ve read the threads regarding soffit mounting of speakers with growing interest. A year ago I changed my nearfields to PMC (tb2+) and the sound of these transmission line speakers still blow me (and my clients) right off the chair. The particular difference with these is that they seem to "even out" room response in a very pleasant way and sounds very natural even in average rooms. (even my friend´s untreated concrete "boom box" living room. Is it overkill to soffit mount these kind of speakers? I¨m hesitating since i think they have special designed internal filter equal to PMC:s $alot-series. Does anyone have experience of soffit mount transmission line monitors or PMC in particular? Looking forward to hear Your opinons on this issue. Regards AnaMix

Anyone with expeience with transmission line speakers? Anyone else care to comment? Regards AnaMix

No experience with them, although they sound like they'd be really good; I checked out a few reviews and their home page, and without having tried it I would think they'd work as well as other rear-ported speakers when soffited - but before you go to all the work of building soffits, I'd recommend a heart-to-heart talk with their design people - I guess it's possible that forcing them into 2 pi space might negatively affect their low end, but I wouldn't expect that. Still, asking questions is almost always a good idea before committing... Steve

Got your message Anamix. The LB-1's that I have are front ported as are most of their larger cabinets. With the rear porting TB-2's, it could be an issue. Call their offices. They are very helpful for this sort of information. What amps are you using? I have a pair of TB-2's with the Flying mole amps and enjoy them but don't think they have the low end depth of the Bryston I use on the LB-1's. -ashley

Great advice guys, I´ll give PMC a call. bassman: Yes, I´ve got the moles as they were recommended by PMC. Perhaps I change to Bryston 4B but the performance/price/heat dissipation on these monoamps are just great. best regards AnaMix

Hi guys Im now awaiting the swedish representative as he forward the questions to PMC. Actually he (the swede) wasn´t to excited to soffit mounting mostly due to problems with transmission line port at the rear. He also pointed out the need to modify the internal filters. What do you think, is he right? Bassman: I read Your earlier post on pretty much the same issue, did you completed the soffit mounting of the LB-1? -AnaMix

Hi Guys Now I got answer from PMC, qoting "Biggest issue with Sofit mount is 3 db lift at base frequencies. There is a larger problem with TB2 and DB1 in Sofit as the vent is at the rear. If the vent is restricted then the units will distort. You would need to ensure full clearance BEHIND the units for them to work . They would not be good mounted in a hole in the wall" Comments? Best Regards ANAMIX

I'd still try it' the wide baffle smooths out room modes and reduces unwanted reflections. If you use John's basic plan of a vented soffit, I doubt it would cause any distortion from the rear port comment... Steve

Hi there, Johns soffit mounts for speakers looks like a great design, however, there are no dimensions in terms of the depth from the front of the speaker to the rear of the cavity? Can anybody please clarify the measurements from the rear of the speaker to the wall of the cavity ect ?

Allow me to wake this thread up... I have PMC TB2+S and I too was wondering about this soffit thing... I know that they are nearfield but pack such a punch that I could use them as big boys too, and am wondering if I should put them in soffit or not. I understand how to to build 'vented holes in the wall' but I am no techie or sound engineer though so what about this '3 db lift at base frequencies'? Is it something that can be sorted... or am I better off leaving those PMC's outside? Thanks!

Saying nothing about it being possible or not, but I think PMC designed their smaller speakers to be free standing nearfields. I would be cautious about moving them too far away.

Maybe it would be a good idea to contact the manufacturer, and ask them about soffit mounting their speakers? Is it advisable? Do they sell a kit for doing it? How do they suggest you roll of the bass? Etc. - Stuart -

In the deep dark alleys which are my memory I seem to recall a thread specifically about flush mounting PMC TB2s. I think the manufacturer was contacted aswell. Like Stuart said, they could potentially be a very big help. EDIT: http://www.johnlsayers.com/phpBB2/viewtopic.php?f=12&t=6456&hilit=PMC

Cheers guys - Sigert I'm sure you didn't realise it but you actually linked... to this very thread I woke up with my post! I guess they were not designed for soffit so they shouldn't - I'll contact PMC anyway to ask them their thoughts about it. Thanks again!

fail :D

I too have been looking into this for TB2's. The australian sales rep informed me that soffit mounting was unadvisable as the speakers will overheat. There needs to be adequate ventilation behind them. that being said i am using the passives... so i think I will go with in wall mounting, but with plenty of ventilation, mainly for the reflection advantages of in wall mounting.

The australian sales rep informed me that soffit mounting was unadvisable as the speakers will overheat. There needs to be adequate ventilation behind them.

If overheating is the only issue then there is no problem! A correctly designed soffit for active speakers (such as the designs on this forum) always includes ventilation. Surprising that the rep didn't know that. - Stuart -

even without an active monitor you want venting because the speakers in use will generate heat...

got this from the UK rep "HI Evan, I would not recommend soffit mounting the TB2 speakers. This is mainly due to the fact that the TB2 has a rear vent.   Soffitt mounting is a tricky one with any speaker, if not carefully designed can cause more problems than benefits Avoid in wall mounting like the plague! Unless you get an acoustician involved."

Just spoke to him on the phone (ill find out what the international call costs in a few weeks) he stressed that it was ok to soffit mount the TB2's, just his issue was that he has seen it done incorrectly many times. which really just leaves me with the problem of the bass boost. the TB2's are already fairly bassy, so it may become too much. when talking with him about eqing or filters, he said the active model have a roll off which could be used, but i have the passives which have none. He was saying that adding eq will add phasing and other issues, so it seems to me it is just a trade off of issues? benefits of soffit mounting versus problems of the bass boost? wish i had the actives... :cry:

you´re not alone :) i got the same problem with my IB1s :horse:

maybe you want to have a look on my thread here how i managed to soffit mount my passive IB1 viewtopic.php?f=1&t=16399 but without ventilation... just have a look... maybe you find something useful cheers Andi

gullfo wrote:

even without an active monitor you want venting because the speakers in use will generate heat...

Even if the monitor in question is a closed box, or front ported? I've never noticed my bass speaker cab get warm on the outside (and its absorbing 500+ watts) Cheers,

Even if the monitor in question is a closed box, or front ported? I've never noticed my bass speaker cab get warm on the outside (and its absorbing 500+ watts)

Right, but is it mounted in a very small sealed soffit, with huge amounts of thermal insulation all around? :) Right now, your speaker is likely sitting out in the open, exposed to air on all sides (or most sides) so it can easily dissipate those 500 watts into the air. But enclosing it inside a box that isn't much bigger than it is, then surrounding it with many inches of insulation, is a different story. Try tucking a couple of really thick blankets around it, really tight and really thick, run it for a while at high levels, then put your hand inside the blankets to feel how warm the speaker cabinet itself got. Don't forget that speakers are very, very inefficient at converting electrical power into sound power: Somewhere around 1% efficient, for a very efficient speaker. So if you are pumping 500 watts of electrical power into that box, likely only about 1 watt of actual sound power is coming out of it, best case, and probably much less than that. The other 499 watts are wasted in many ways, and most of that ends up as heat. - Stuart -

You make a good point. I have a multimeter with a thermocouple. I'll put the thermocouple on the back of the magnet, stick a 1khz sine wave into the speaker and watch the temperature with the speaker naked, in its usual cab and in a cab buried in blankets. Watch this space... :-)