Ultimate HT and music speakers

[paulspencer]

After reading Dr Earl's book Premium Home Theatre - design and construction I have concluded that the best approach to high fidelity reproduction of movies in a room includes:

1. a fairly live room to give a sense of spaciousness with diffusing treatment of walls and minimal absorptive treatment

2. speakers which can handle high output and that have constant directivity - as in comercial cinemas

I'd like to extend the use to music as well and I'm not totally satisfied that compression drivers can do this, so I'd like to hear views on the three candidates that stand out most:

1. high efficiency high output speakers designed for constant directivity - here's an example:



2. open baffle speakers - 3 way with multiple drivers to obtain high output - which are also constant directivity speakers as I understand (here I'm thinking Linkwitz Phoenix and here is an example:



3. line arrays - how do they compare?



What is your preference and why?

[johninCR]

I've found that the natural open sound of OB's is perfect for both HT and music. To really appreciate the difference you need to A/B OB with speakers in a box. Both dialogue and music are more natural. Going a step further and combining OB in a line array gives the same natural sound, but bigger. If your HT uses a projector and a big screen, then a line array works great. A big line array and a TV isn't going to work because the sound will dwarf the image. Also, a center channel may be problematic with an array unless you make it the width of your seating area because when you turn an array on its side the sound is seriously attentuated left or right of the last drive in the array.

Alot will depend on your budget. The right very cheap drivers can be amazing in an OB array. The right more expensive drivers can be amazing on OB in a single driver setup.

I started with Adire HE8.1 kits for my HT ($300/pr). Nice sounding, detailed and efficient bookshelf sized ported speakers. The bass rolls off at 80hz, but that's no problem with a sub. Then I started experimenting with OB line arrays and instantly I'm hooked on OB and that's with $1.50 drivers. Add a super tweeter since the cheapies roll off at 10500hz and I've got a great sounding speaker.

So I decided to try the HE8.1 drivers on OB and they sounded really thin because, due to their low Qts, they couldn't make bass on OB, at least without EQ. I didn't give up and found some 6" TV drivers for $3/ea that made bass on OB and tested them as bass support for the HE8.1 driver and that made all the difference. Now I'm in the process of building 5 dipoles using excotic hardwood available here in Costa Rica using the HE8.1 drivers with 4 of the cheap TV drivers in a W baffle in the bottom for a compact unit with great OB sound.

In A/B testing, the cheap array and the HE8.1 dipole prototype both blow the box sound away. The super cheap array struggles at very high volumes, but at moderately loud volumes the big tall soundstage is great. The dipole HE8.1 sounds much bigger, more natural and open than the boxed version and doesn't struggle at very high volumes, but otherwise the array beats it as far as "big" sound goes.

[Frode]

Thorsten Loesch recommends a fullranger in a fronthorn(Oris/Azura etc.) down to ~250Hz and dipole below. This might need help below 40Hz where you can use a monopole subwoofer.

Frode

[RobWells]

Hi Paul,

I haven't read the book, but always thought that for movies you'd need a 'deader' room than for music - reason being that they use the surrounds to give ambience, meaning no need for a 'live room'.

I *think* I read it in the master handbook of acoustics (F. Alton Everest)

JBL's speaks found in many theaters over here (UK) are twin ported 15's crossed at 500Hz to a horn for the mid/highs. (for the L/C/R), and twin 18's for subs.

Off to look at that link for the book you mentioned.

Cheers

Rob

[johninCR]

Paul,

Something to take into consideration is that you NEVER hear anyone say that any other type of speaker sounds more natural for dialogue and vocals than OB or other dipoles. That's because they all impart some type of "boxy" coloration to the sound and in a side by side comparison they sound like a box is making the sound. The difference is most apparent when listening to a single speaker and that's where most of your sound comes from in HT, your center channel.

While I know there are outstanding box speakers and horns, which are better than dipoles for certain applications and I'm sure many of them play great sounding musci. eg If you want razor sharp imaging that surpasses reality, there are box designs that are better than dipole, but that would only work perfectly for a one person HT audience and once you go to a 5.1 setup that imaging is likely to be lost. That's not to say the dipoles don't image well. They just put the singer up front where they belong and the other instruments in their proper soundstage locations.

A lot would depend on your tastes as well. If you want music to play at extreme levels with chest pounding dynamics that you can feel, then something like that 1st setup pictured or horns would be the way to go. For the HT effects you can always combine dipole subs to get the natural bass sound supported by a sealed monopole to cover the lowest frequencies.

I'm sorry if I come accross as preaching, but I only discovered dipoles very recently and the results I've gotten using super cheap drivers, which by the way did take alot of searching and listening, and components from a relatively cheap speaker kit all connected to mid-fi components, has simply astounded me.

[paulspencer]

Given that this discussion focuses on the "ultimate" I think a large screen would be in order! ... but this is a good point that John makes regarding using an array and a TV - it would be a mismatch.

I'm very interested in open baffle speakers. The aspect about them that interest me most in home theatre is this - constant directivity. Normallly this is achieved with horns. Which I think is fine for home theatre, but I'm suspicious of the coloration aspect. This is where dipoles seem to shine, however it seems expensive to be able to get high output.

Back to constant directivity - I think this is often overlooked. HT rooms are normally made to be dead because the off axis frequency response (or the power response) is not as well bahaved as the on axis response. This means that the reflected sound is coloured. Therefore with monopole speakers the room must be relatively dead, more so for home theatre. But with dipole and horns this is different:

1. their power response is such that the off axis sound is not as coloured
2. there is less off axis sound as they are more directional
3. dipoles - the reflected sound from the rear is delayed so that it is perceived as ambience rather than messing up the imaging

In the fidelity department, dipoles now start to look even better. It seems their main disadvantage is the cost and difficulty in design - to be able to get them high output compounds these difficulties and further adds to the cost.

[paulspencer]

I have actually experimented with dipoles a tad. I put my pair of AV12's in a H frame but found that they didn't quite fare like I would have hoped. I suspect they have some breakup that the 2nd order crossover wasn't enough to tame, that I might need a notch filter, and they seem to move so much air that even the fairly open cast basket makes air noise. It's extremely difficult to make a driver with 46mm pp xmax that won't make noise in open baffle.

I had also tried it with some car speakers. The cheap mylar tweeters messed things up a bit, but the did sound quite reasonable for what they were. I'd like to do a proper test of dipole though.

[Chris8sirhC]

i have a pair of OB line arrays using cheap 4'' drivers that can make you go deaf (16 drivers per side). With the right implementation, you can easily get very high SPL's with OB's.

[johninCR]

Paul,

I think you have some misconceptions about dipoles. First, they are more efficient than monopoles because the back wave from each driver is used. Yes, if you want dipole down into the LFE bass range it is more difficult to design (active EQ's etc.), but that can be covered by a sub in a box. For the higher frequencies it's easier than boxed speakers (no volumes to compute, no ports, etc.) , just a baffle width to consider for bass rolloff. Plus you can experiment using cardboard, so you can hear your designs before starting any construction. Cost wise it can be done very very cheap using arrays of cheap drivers with great results because each does only a little work. The only difficult part is that driver selection is more limited because you need higher Qts drivers.

[paulspencer]

Originally posted by johninCR
Paul, I think you have some misconceptions about dipoles.

Not at all.....

There are 2 approaches to dipoles:

1. conventional approach using high Qts drivers
2. Linkwitz approach

I favour the second approach.

The output of a dipole is much more limited by displacement. This is why Linkwitz Orion uses an 8" driver to get to 100 Hz with a 4th order rolloff. Yes, there is the rear wave reinforcement of the midrange but whether or not this translates into higher output in practical terms is another matter. For this to give higher output you would need something more like a 4 way speaker. If you look at the Linkwitz approach, it is really quite involved.

Here Linkwitz describes his approach

Linkwitz discussion of sensitivity for his Phoenix speaker is interesting:

Phoenix efficiency

2.83V sensitivity

tweeter: 90 db (SS D2904/9800)

midrange: 103 db above 250 Hz(2 x SS21W/8554 in parallel)
96 db @ 100 Hz

woofer: 97 db @ 120 Hz rolling off at 6db/octave (2 x Madisound 1252DVC)
91 db @ 60 Hz
85 db @ 30 Hz

It's interesting to note how the midrange efficiency is very high. If only the midrange was operated in dipole mode then it becomes easier to get high output. However, some may also argue that one of the strongest aspects of open baffle is the uncoloured boxless bass which doesn't excite as many room modes. However, for home theatre where a lot of the bass is noise, then perhaps monopole is the way to go, with the focus being on the uncoloured midrange of open baffle for voices.

Thanks, John, this has gotten me thinking a lot more .....