Placing transmission line speakers

[bob91]

I am planning to build transmission line speakers (IPL kit). One doubt is this... My present speakers (sealed box) are placed near the corners of the room - about a foot (30 cm) from a wall at the back, and same distance from a wall at the side of each speaker.
What will be the effect of placing TL speakers in the same position. Would it be a good or bad idea?
Thanks,
Bob

[SimontY]

Hi Bob,

An old housemate of mine built some IPL kits, and had them close to a wall (small room). The bass was very boomy.

Transmission lines, such as his (the al. coned IPL ones), have a very strong bass output, that will likely crap all over your sealed boxes, making placement more critical

Good news is, despite the potential boominess, you get beautifully rich, 'smooth', and naturally deep bass. But you get no obvious punch, which is perhaps an artificial addition of normal ported speakers anyway. But as you currently use sealed boxes, you won't be missing anything in that department!

Hope that helps.

[SimontY]

Oh, one more thing, because I don't want to put you off what is probably a really great kit...

It would be useful to have some input from the TL experts, which there seem to be a few of round here, but I'd have thought you could weaken the bass by stuffing up the line-opening with foam/wadding/maybe wool. This might turn the loading into more of a closed box, but still have transmission-line qualities of more bass extension and cleaner midrange. Of course, if the bass was a disaster, sealing the line opening would be an effective short term measure for reducing the bass output. Then unseal it when space permits appropriate positioning. Adjusting the bass inductor windings has a subjective effect on bass, and using the suggested plinth is a must...

[Eelco]

Dear Bob,

I am afraid your question cannot be anwered in general terms. The room-woofer interface is a very complex issue, and having two sources (i.e. woofer and port), located some distance from
each other, makes things even more complicated. Without a proper simulation program (such as LSp CAD or Roy Allisons program) in which room dimensions and source(s) position(s) are fed, it -unfortunately- remains a matter of experimenting with uncertain outcome. Statements such as "my friend had loudspeaker X and its bass sounds like crap" usually say more about the sonic properties of the room/speaker interface than about the speaker itself.

Generally speaking, placing speakers that have reasonable output below 40 Hz in a room of less than 10 cubic meters will give you a fair chance of having problems in the low end.

Furthermore, one should be very critical about the alleged wonderbass of TLS. First of all, many behave actually like modified reflex closures, such as the IMF and TDL designs. ( the late John Wright will kill me, but I am afraid I am right on this one) Their impedance graph and cone excursion show typical reflex behaviour. A real TLS shows only a minor very smooth and wide bump in the impedance graph at system resonance.

To my best of knowledge, their is not one commercially available kit or ready made TLS that is a true TLS design. Having built half a dozen of TLS, their sound is not better than a properly designed closed box.


Good luck.

Eelco

[kneadle]

Originally posted by SimontY


It would be useful to have some input from the TL experts, which there seem to be a few of round here, but I'd have thought you could weaken the bass by stuffing up the line-opening with foam/wadding/maybe wool.

I'm no expert, but I think that's backwards. Visit www.t-linespeakers.org and http://www.quarter-wave.com/ for more info.

Dave

[Timn8ter]

I am afraid your question cannot be anwered in general terms.

Absolutely. Every room is different.
My experience with TLs, quarter-wave tubes and tapered quarter-wave pipes is that they sound better to me than ported enclosures, even overdamped ones, and you can get a surprising amount of extension from drivers without boominess (if it's done correctly). What I find many DIYers trying to do with TLs is get more bass out of them than is physically possible. This leads to some pretty ragged response. I say go for it! Here's a review from TNT in case you missed it.
IPL kit

[SimontY]

Originally posted by Eelco

one should be very critical about the alleged wonderbass of TLS. First of all, many behave actually like modified reflex closures

Sorry, but while you may be 'technically' correct, I've actually heard one of these kits, and you *do* get bass that would never in a million years come from a ported enclosure using a single 6.5" driver. And please don't reply saying, oh but its false, because I'm referring to its extended, smooth, natural quality, *not* the quantity.

[bob91]

Thanks everyone for the advice and suggestions.
Bob