Know any great books on waveguides?

[GranteedEV]

I think I'm becoming obsessed with the idea of a waveguide based system, whatever that may be. Mark K's ER18DXT looked excellent, although I'd want to make an MTM tower at the very least... TM bookshelves are not my thing.

I need something clear and concise, not saturated with technical mumbo-jumbo that requires me to keep a "dictionary of what this guy's talking about".

What are the pros and pros and cons and pros of waveguides?

 

[Warpdrv]

Sorry I can't answer your question, but maybe post the question over at the AVS DIY area....

A quick search of waveguide in the titles yielded this for me.
http://www.avsforum.com/avs-vb/search.php?searchid=16346782

Lots of people more knowledgeable and messing with them there.

 

[TLS Guy]

Here is an article on waveguides, which are basically horns, by Robert C. White.

He is one of the most respected authorities on speaker design and problems. He has lot of useful references.

 

[GranteedEV]

That looks like exactly what I needed. I'll be sure to read it at work today

 

[jliedeka]

I'm also interested in wave guides. Zaph has a couple of articles pertaining to waveguides. One is actually a loudspeaker design that uses a waveguide. The other is the results of some experiments with waveguides.

The big win is that the right waveguide really increases the efficiency of a tweeter at certain frequencies. While that does mean you have to pad the tweeter down more, the upside is that less power is needed to drive the tweeter and therefore less harmonic distortion.

His article that summed up his experiments showed that the six inch horn seemed to be the sweet spot.

Here's the link to the design: Waveguide TMM

Here's the other link: Horn loading a standard dome tweeter

Jim

 

[jostenmeat]

jliedeka, the efficiency is improved you say, but is it mostly in terms of sensitivity, or really both? This is related to the Constant Directivity that is prevalent with the new hot commercial style HT speakers?

If I was to look towards new speakers for the HT, I'd want improved off-axis response as well as better midrange/midbass capability. So anyways, I guess once you are outside of the proper angle for CD, there is a substantial drop off, correct? I guess it's just a compromise for having such awesome sensitivity.

I don't think I need reference levels though, and would gladly trade some sensitivity for better offaxis response. Or can we have our cake and eat it too?

It could be a long time, or maybe even in fact never, before I build speakers, but I have become more interested in any case as of late. If anything, I will at least learn more about this hobby. Thanks.

 

[jliedeka]

Sensitivity is what I meant. By getting more SPL out of less power, you get lower distortion so you can use a cheaper tweeter. It also will allow a lower crossover point.

Off-axis is a little less important with a surround system because you aren't relying on side wall reflections to create a big soundstage. OTOH, you want the off axis response to be fairly well behaved out to 30 or maybe 45 degrees. Not everyone can sit in the sweet spot.

I want to learn more about waveguides at some point and get my brain around the article that TLS Guy linked to. That will have to wait until I get around to designing one or two speakers, at least. There is a lot that goes into driver selection and crossover design. I want to get a handle on that stuff first.

Jim

 

[TLS Guy]

Sensitivity is what I meant. By getting more SPL out of less power, you get lower distortion so you can use a cheaper tweeter. It also will allow a lower crossover point.

Off-axis is a little less important with a surround system because you aren't relying on side wall reflections to create a big soundstage. OTOH, you want the off axis response to be fairly well behaved out to 30 or maybe 45 degrees. Not everyone can sit in the sweet spot.

I want to learn more about waveguides at some point and get my brain around the article that TLS Guy linked to. That will have to wait until I get around to designing one or two speakers, at least. There is a lot that goes into driver selection and crossover design. I want to get a handle on that stuff first.

Jim

Actually Jim, it does increase efficiency and sensitivity. It is an acoustic transformer that increases the efficiency of the coupling of a diaphragm to the air.

However there is no free lunch. All horns suffer varying degrees of non linear distortion due to a non linear relationship between air pressure and air volume.

Methods for analyzing this and modeling it continue to improve.

The other issue is is a narrowing of dispersion with frequency.

 

[jliedeka]

There are a bunch of issues. Sound waves are more longitudinal at higher frequencies and omnidirectional at lower frequencies. In between you have baffle diffraction. That makes modeling complicated but early reflections can be treated as the same as the original signal as far as perception goes.

I'm not as worried about dispersion in a surround setup, especially with shallow conical waveguides as opposed to other types of horns.

There may also be advantages to horns that are horizontally wide but vertically narrow. They would eliminate ceiling reflections while giving what I hope would be good off axis response in the horizontal domain. The trick is finding the right horn that doesn't require a lot of extra parts in the crossover, especially with a passive crossover. A lot of extra peaks and valleys would be no fun to deal with.

Jim

 

[jostenmeat]

Jim, I'm going to ride your coattails just for a short bit here. Just how much does one, or you particularly, save on tweeter costs? Do they typically get that high in cost where it's truly worth dealing with a more (what I would guess to be) complex build, as well as dealing with the other compromises such as the narrowing of dispersion? Thanks. My uneducated guess is that I would splurge for the better tweeter than deal with more complexities. Well for that matter, I applaud you for making your own design, because I don't think I'd go that far, and would likely use "plans" created by someone. Cheers.

 

[jliedeka]

Currently I have some Jon Marsh designs in the works - Natalie Ps and Modula MTs. I hope to start working on them again but I got sidetracked by a home improvement project - replaced 5 windows.

After that will be a subwoofer for which I have the driver. That will sort of be my design but a lot of people have built subs with that driver and I don't plan on ignoring their experience.

Then I get to try something original. I'm considering a bipolar surround speaker for on-wall or possibly on-ceiling use. Will have to take boundary reinforcement into account but that probably means no BSC. The only criteria I have for it are that it isn't too expensive and that it can be crossed at 80Hz max, may try for 60Hz if I can find the right midwoofer.

Jim