Narrow room - need narrow speakers for surround sound duties...

[Gary Lightfoot]

Hi.

My room is just 9 feet wide, and for Dolby Atmos to work well, there has to be a larger separation of side surrounds to ceiling speakers. This means having the side surrounds just above ear height when seated (40 to 50 ins from the floor)

I have two rows of seats that leave aisle space of 21 ins, so I don't want to encroach on the already narrow aisle space too much, and I can't sink speakers into the walls very much, as they're brick.

So, I thought about speakers that aren't very deep in cabinets that are around 3 inches deep but can be quite tall - maybe a 3 inch deep, 14 inch wide column that would give the necessary volume for whatever speakers I can fit in there - which brought me to this forum.

I have some 4" Wharfedale drives that are found in Modus Cubes I believe, so I was thinking of using those, though I don't mind buying something that is considered better from Visatron or TangBand etc.

I also don't mind doubling up to have two speakers in each column (or 4) if it will help - I did a quick WinISD with the drivers and 2 gives a few Db more than a single driver.

I have some T&S data for the Whrfedales:

Fs 89.98Hz

Qms 2.84

Qes 0.63

Qts 0.52

Db 88

I assume being full range, I won't need a crossover with these, but if I run two in series or parallel, that will need addressing.

Any pointers appreciated please.

PS. I'd like to try them vented for better bass so I can cross to my sub at 80hz.

Gary

 

[picowallspeaker]

PS. I'd like to try them vented for better bass so I can cross to my sub at 80hz.

You can do whatever you want, but I just wanted to say that usually a sealed box is considered 'cos it allows a Butterworth roll-off so that at crossover frequency (- 6 dB ) it merges with the subwoofer contribution thus creating a flat response - if the two emissions are in phase

 

[picowallspeaker]

I assume being full range, I won't need a crossover with these, but if I run two in series or parallel, that will need addressing.

Same thing for two coherent emissions: the distance between the two units determines the "interference pattern", so if you move around you'd find some "rise and fall" in freq. response. A "progressive crossover" may be implemented, being very easy but requires the two units to be connected in series, one bypassed by a capacitor, so only one emits the treble ( where trouble arise for the very little wave lenght )

 

[Gary Lightfoot]

I know I can do whatever I want, we all can, but that's not what I'm asking here is it

In a sealed box, these drivers will roll off long before 80hz - F3 is 122hz so a tad too high really.

Will I notice any issues at 80hz with an AV receivers sub output set to that value? I haven't in the past with my set ups (I'm no audiophile or golden-ear), so I guess I won't notice now, and I assumed the receiver did that.

Cheers

Gary

 

[Gary Lightfoot]

Same thing for two coherent emissions: the distance between the two units determines the "interference pattern", so if you move around you'd find some "rise and fall" in freq. response. A "progressive crossover" may be implemented, being very easy but requires the two units to be connected in series, one bypassed by a capacitor, so only one emits the treble ( where trouble arise for the very little wave lenght )

Thanks. That's helpful to know, and something I'll need to look into. As the speakers will be fixed, and the people in each row will not be moving much either, the problem probably won't be noticed, but I take it the two drivers will be acting as bass and treble rather than two full range with the capacitor in circuit to act as a crossover?

So other than that, what other problems would there be with a shallow box? I'll put something at the back behind the driver to reduce reflections back through the cone, and/or angle the box a little so they bounce more up than directly at the woofer.

Cheers

Gary

 

[Greg B]

So other than that, what other problems would there be with a shallow box? I'll put something at the back behind the driver to reduce reflections back through the cone, and/or angle the box a little so they bounce more up than directly at the woofer.

That's basically it. Put some carpet felt or whatever right behind the driver to help minimize reflections through the cone. If it was me I'd angle the baffle slightly side to side, mostly to reduce the standing wave between front and back.

It's not normally that important to have full bass extension in the surrounds. Sealed would be my inclination as well. You could vent them and plug the ports with a sock or whatever, to see which way sounds better.

 

[picowallspeaker]

You can leave the box open on the back: the area behind should be "acoustically treated" so that the back wave...
The same happens in a closed box: you eliminate the back wave but that produces a pressure on the cone, specially if the box is very shallow - think of a mirror and the cone is not transparent.
So you can start by simply build a frame with lateral "fins" and secure the two drivers on it. Then connect them in parallel ( not if they're 4 Ω ! ) and...hear. Then connect them in series and bypass only one with a 20-30 uF cap. The output SPL will be lower, though.

 

[Gary Lightfoot]

Thanks guys.

I was thinking about angling the baffle down at the top a little to reduce the standing wave and aim it at the persons head in the furthest seat so that would kill two birds...

Have you got a link to the fins idea? I'm not quite sure what you mean, sorry.

Also, if you guys were going to build a 3 inch deep box what drivers would you use, and if you wanted to keep the spl level up, how would you do it? Multiple drivers seems to be the answer if the drivers have a low db value but then the comb filtering issue rises (I assume that's what you were referring to?).

Would it work better if I used a tweeter instead of two full ranges? That would keep the spl up on the woofer and I'd have to add a crossover with padding resistor anyway.

Gary

 

[Greg B]

Angling the baffle down will be fine. That's what JBL does...

A point source is hard to beat for imaging, and that's part of the attraction of full range drivers. That said, multiple drivers aren't the end of the world either, especially since surrounds are basically for background noises. Note the popularity of line arrays, most of which have some unavoidable comb filtering.

My preference would be to go to a slightly larger full range driver, or a coaxial unit.

Another idea for a quasi point source would be to make a FAST 2 way. Perhaps choose something like the Fostex FF85WK and two 5" woofers. (Visaton W130S perhaps)

FWIW, various companies sporadically make 'reversed' low profile woofers with the magnet in the front. I don't know what is currently available.

What are you using for the front speakers?

 

[Gary Lightfoot]

Hi Greg,

I'm using waveguide speakers for the fronts (econowave style) because they will be behind an AT screen, and I'll probably go for coaxials in the ceiling. I wanted coaxials for the sides and rear too, but they're too deep to fit on the walls in the aisles, so that's what made me start to look into small speakers that I could fit in a very shallow enclosure and full range seemed an option. The MK150 on walls are only 4.5ins deep but I wanted something much cheaper and a little shallower.

A single 4" might do the job, but if its a rear surround too, it might run out of puff trying to get to the front row. So now I'm wondering if a tweeter with a waveguide will be better than two full range drivers back there, which means too many different types of speaker arrangements unless I goo woofer/tweeter for all surrounds, but again, they'll need to be able to fit into a shallow box.

If I could double or quadruple the full range drivers, that would give me the extra spl I'd need from the back wall and the voicing/timber would be much better.

How does the fast two way work? It sounds like an option. I have some Wharfedale 5" drivers too, but I'll have to see if they'll fit in a 3" deep enclosure. I may even be able to fit a waveguide on the tweeter for the rear speakers so more energy is going forward than to the walls and ceiling.

I've enough 5" drivers and tweeters to make a few M&K 150 look-alike clones, but the crossover would be a lot of work and I'm very much a newb. I also won't be able to get the time to do any real testing for a while yet to be able to measure and see what the results are like.

Gary

 

[Greg B]

FAST is more or less using a small full range as a tweeter, and crossing over much lower in frequency. The idea is that you get the point source of a full range with the bass extension of a 2-way. It's nothing new really, except the name.

 

[Gary Lightfoot]

Gotcha, so that's like what picowallspeaker suggested by using a capacitor across one of the drivers?

Another thought - I've seen some speakers that have the woofer on top of the tweeter which is different to the usual method of tweeter above. If I was to use a 5" and a dome tweeter so that I could get the backwave into the larger part of the enclosure, what problems would that give?

Thanks again

Gary.

 

[picowallspeaker]

Gotcha, so that's like what picowallspeaker suggested by using a capacitor across one of the drivers?

No, the idea is to have two fullrange connected in series and to make a very simple series crossover with the cap bypassing one driver, in order to have both emitting at low frequencies and only one the treble freq's. It works best with little units. Though I don't like multiple drivers...
The Fast idea is to relieve the duty of reproducing (deep) bass ( Fullrange And -or Aided- Subwoofer Technique ) from a fullrange so letting it do mid-tw duty; the crossover might be simple 1st order depending on driver's characteristics ( natural roll-off )

 

[Gary Lightfoot]

Well so far I have a lot of options which is good, plus a lot of learning to do. I think the most important part is that you don't seem to think a shallow box is going to be a major problem provided I angle the baffle and add something behind to help dissipate the back wave.

I can experiment with what I have and then get better drivers if I think the set up needs it.

I can search for the stuff you've mentioned so far but is there anything else, suggestions or even some shallow builds that you could link me to?

Thanks again.

Gary

 

[picowallspeaker]

Hmm...3" is very little space behind the driver, it means that the acoustic absorber, be it polyfill or natural wool/felt, is very close if not to touch the cone.
I suggest to leave the back open; the laterals ( the " fins") could be made angled, from 30° to 45°, with the purpose of adding more surface in order to prevent acoustic short circuit. Indeed, the most fatiguing thing is the in-ambient placement

 

[Gary Lightfoot]

Hi,

You mentioned leaving the back open and the fins before, but I'm still not sure what you mean. Can you link me to a picture or something please? Then I'll know what I should be looking at doing.

Also, what do you mean by in-ambient placement?

Gary

 

[picowallspeaker]

Here
Consider that the acoustic absorber is always present.
When you leave the back open, you don't need to make a floorstander, as you don't have to maximize any footprint/volume.
The in-ambient placement means the room and how do you locate the speakers. if you place them against a wall, or far from it. THE LATTER IS BETTER as the first reflections come delayed and attenuated...
FOR CLOSED BACK: it doesn't matter, just changes the radiation in space - hemispherical when placed very close to the wall - I guess

 

[Brisso57]

Have you thought about this FR design?
92TLMDFK - MDF Transmission line enclosure kit (pair) - Decibel Hi Fi

Cheers

Doug

 

[Gary Lightfoot]

Well they need to be fixed to the wall and be as shallow as possible, I'm hoping because they'll be so close they won't need any BSC and will gain a little low end db from the wall.

When you say leave the back open, you mean like an open baffle?

The TL looks promising because it's only 4ins deep and not far from what I'd like to achieve size wise.

Cheers

Gary.

 

[Greg B]

Gotcha, so that's like what picowallspeaker suggested by using a capacitor across one of the drivers?

Another thought - I've seen some speakers that have the woofer on top of the tweeter which is different to the usual method of tweeter above. If I was to use a 5" and a dome tweeter so that I could get the backwave into the larger part of the enclosure, what problems would that give?

A capacitor across a driver shunts the highs to ground. In effect it is a low pass filter. Anyhow, this isn't really a crossover. It makes one of the drivers carry the bass only. (commonly called a 1.5 way)

Crossover design is difficult and involved. I would suggest a full range driver unless you have a desire to spend many hours learning how to make a crossover that sounds good. That Jordan TL is a good one. I'd go with that or something like it.

IME a shallow depth cabinet is not a big deal in practice. I've made shallow TL's less deep than the Jordan TL with no issues. Spheres OTOH - now there's a problem...