Transmission Line speakers

Speaker design is Paavo's special interest so post away.
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DuncJF
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Joined: Mon Oct 16, 2006 4:26 am

Transmission Line speakers

Post by DuncJF »

Hi Paavo,

I'm thinking of getting a Transmission Line speaker kit for my HiFi. Do you have any experience of this type of cabinet and if so, good or bad.
The company I have in mind are UK based (as am I) and seem to be pretty good at what they do. I was thinking of getting something in the New Year sometime, have a look, see what you think.

http://www.iplacoustics.co.uk/s3tlm%20Ribb%20Magnesium.htm

I'd be interested to know if you think I should be going the active route instead :?:


Cheers
HarBal
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Post by HarBal »

My advice is that if you can audition them before buying them then do so. I'm sure the bass response is pretty good and the layout of the drivers and the cambinet shape look very sensible.

The thing I would be concerned about though is how good the crossover behaviour is and how this translates into the speaker response (particularly polar response) at the crossover frequency. That, to my mind, makes the major difference between a good speaker system and an average one.

They've chosen a reasonably low crossover point of 2.8kHz though I'd be looking to design a system that crosses over at 2kHz (as mine does). The main reason for this is that the polar response of woofers quickly deteriorates above 1-2kHz so for 2 way systems you generally end up with a system that will sound mid-range shy between that 1-2kHz up to the crossover frequency where the tweeter takes over. The cost of having a lower crossover is the need for a more complex crossover (at least 3rd order with impedance equalisation on the tweeter).

On the crossover, it appears (from the picture) that it is a plain and simple 2nd order crossover without impedance Eq on the tweeter. For myself that suggests that the crossover design is probably less than optimal and you could probably do better in this department. One thing I take issue with for un-equalised 2nd order crossovers is that the speaker impedance gneerally goes very high at the crossover (say >50Ohm) compared with the nominal 4-8 Ohms elsewhere. That raises the possibility of strong colouration occuring through cabling and termination resistance. I'd personally have chosen a 3rd order crossover for this very reason as its impedance is essentially resistive and lacks this peaking at the crossover point. If you use a 2nd order you should really equalise this impedance peak out, which requires extra components but given the extra components required, why not put them into a 3rd order crossover instead and get the benefits of the improved cutoff slope.

The quality of the cambinet design and the drivers looks exemplary but I'd be a little concerned about the simplicity of the crossover. Fro that reason I'd recommend auditioning them before buying so you can hear for yourself how good the mid-range around the crossover frequency is. The crossover is essentially my only concern. If you like the rest I suppose you could always design a custom crossover for it!

Cheers,


Paavo.
DuncJF
Posts: 31
Joined: Mon Oct 16, 2006 4:26 am

Post by DuncJF »

Hmm. I did kinda wonder about the crossover point being that high myself. I think I'll email them to try and get more info regarding the crossover point.

I've also found one or two other companies that do similar kits, so I guess a bit more research is on the cards until I finally decide.

Thanks for the answer. :)
HarBal
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Post by HarBal »

I had another peak on that web site to see if I could find some more info on ther drivers. From what I found it looks as though the ribbon tweeter output is pretty low at the crossover point but in contrast the woofer output is quite high so it looks as though they are relying on that matching of responses to keep the output at the crossover up. On the face of it they may well perform well together though and the 2nd order crossover could be fine though I still think it should be impedance equalised. Like I said, if you can audition before buying then that is what I'd suggest as the proof is in the listening.

Cheers,


Paavo.
DuncJF
Posts: 31
Joined: Mon Oct 16, 2006 4:26 am

Post by DuncJF »

Yeah, I had a bit of a further look into it as well. Managed to track down the drivers on the manufacturers sites:

The Ribbon will only safely go down to 2500Hz and the Bass is actually classed as a Bass/Mid. The main reason for the higher crossover seems to be because of the Ribbon Tweeter and not having it just go phitt... :shock:
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