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Multi-Way Conventional loudspeakers with crossovers

Home audio loudspeaker - 8"/10"/15" Coaxials crossover at 1000Hz
Home audio loudspeaker - 8"/10"/15" Coaxials crossover at 1000Hz
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Old 6th September 2019, 11:55 AM   #11
krivium is online now krivium  France
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Hi,

" i want the CD to handle all the treble"

Well if you follow the recommended fc given by manufacturers in datasheet it should be all good. As already stated this will depend of the overall diameter of the driver choosen and don't worry, directivity of both the horn and direct radiator part will match.
In fact the frequency given by manufacturers are most of the time recommended for that purpose.
In some case it can be a little higher than what i told but in this case this is because the planned use is for P.A. where the compression driver have to handle much more power than in domestic use. In this case you could move x- over fc a little lower but nothing will guaranty you better outcome: the horn part may loose control if you go to low.
This is a balancing act and you'll have to experiment and pick what is convenient to you.

Beaming, well as already said it will probably happen in the ( very) high end... this will depend from the driver you'll choose in the end.

" i think that 15" coax... and tight bass"

Yes a 15" as a medium will be barely moving at this level and this is a good thing ( for direct radiators the more movement: the more distortion).
It is a good thing because if you use the direct radiator to reproduce bass signal the 15" will have to move much more ( and this can be a lot!) increasing 'natural' distortion but a second issue will arise: your membrane act as an horn for the CD so your high frequency signal will be modulated by your low frequency signal: intermodulation distortion will be high, and maybe probably higher than a typical horn+ direct radiator system.
If you filter low end around 250/300hz and make the woofer a mid, movement is kept minimal ( 'natural' distortion is lower) and intermodulation distortion will be low ( still there but much much less).

Obviously you can use a 15" or 12" coax as a 2 way and it will work ( Tannoy System 15 Dmt2 anyone? ), but you'll compromise on some area. Even Tannoy used their 15" coax in 3 way for the 'big' monitor systems ( Buckingham, Dreadnough) to have higher SPL output and cleaner sound.

The real cons i see about your project if going 2 way is you won't find a 15" coax which will accept to run closed box without serious limitations ( you can use a LT to run them closed but don't expect spl and low end extension...).

About bass reflex, closed box and modes you have misconception.
Like you i like closed box more than BR but this isn't related to one exiting mode more than the other: this is directly related to location of loudspeaker inside a room, whatever it is. Said differently it is an acoustical issue not related to the type of charge the driver see.
Where a closed box is 'better' to a bass reflex is about group delay. This is the technical term to define what audiophile call 'slow or fast' bass.

Bass reflex when not optimally implemented may exibit unlinear and/or excessive behavior about group delay. With closed box this rarely happen and you have the option to taylor the response to your room using a Linkwitz Transform which is not, or at least much less possible with a bass reflex.
And usually closed box transient response is easier to have right than with bass reflex ( without saying you can't have same thing with a bass reflex, it is possible but you need to know what to do and adjust the right thing in your room which isn't easy, at least for me).

"Since this driver are efficient..."

Well in my view high efficiency is a good thing. The 'shooty' sound you have concern with is related to the horn part or an issue with the driver frequency response but in no way is due to efficiency. Modern drivers are usually 'good' for the horn parts and if you run dsp you can eq the response.
That said yes with a plate amp you may run into trouble about plate amp and your overall system gainstructure.

But plate amp are not the only answer to run active dsp driven filters: software or dedicated harware solution exist and have the advantage to let you choose the amplifier you want to run ( even converters). But it'll be bulky compared to a plate amp.

What is your intended use ( music, HT,...) and the kind of music you listen to?
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Old 6th September 2019, 02:06 PM   #12
swara is offline swara  United States
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Thank you for a detailed response.
I will explore other DSP options.

I listen to a wide range of music such as classical, jazz, rock.
I once listened to Tannoy's and loved their sound. Hence I started thinking about this project.
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Old 6th September 2019, 02:45 PM   #13
gedlee is offline gedlee  United States
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As a test, I once built a coax based on a B&C 10", I believe. To KISS, I made it a dipole on an open baffle. I was amazed at how good this could get for a speaker system which cost almost nothing (no box to build, a somewhat complicated crossover, but all-in-all quite inexpensive.) Trouble was of course that it had no bass response at all. If one were to do this with multiple subs I bet that you could build a great system.

Coax can never be quite as god as a separate waveguide system, but the later are so much more difficult and expensive. For value, the coax wins out.

Generally speaking the narrower the directivity the less negative effects the room will have on their perception, but it depends on the room, of course. Directivity is irrelevant in an anechoic room, but all important in a reverberant one. Home listening rooms tend to be all over the map with European construction being clearly more reverberant than typical US construction. But high directivity is never really detrimental, it just gets a lot harder to achieve as one goes narrower and narrower.
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Old 7th September 2019, 12:09 PM   #14
krivium is online now krivium  France
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Hello Earl,
Yes i'm sure a multisub + coax will give great results. Even better if like you discribed in the '2 way high spl...' thread: as wideband as possible mains + mono multisub.

Swara,
Earl gave one important point in his answer: x over can be troublesome with coax.
That's why i didn't talk about passive but active dsp solution for your case. The electrical part of x over usually are asymetric for coax with something typically like 12db or 18db lp for woofer and 6db hp for CD.
Other options are possible but passive is usually like that. Sometimes you could find allpass cells used too.
This is related to the fact that emission points of both drivers are not always coincidents: direct radiator may be 'in advance' related to the CD ( iow the direct radiator is located 'in front' of CD emmission point). One other sneaky point is that emmission point 'move' with frequency, but with coax this is limited as directivity must match and 100hz difference shouldn't be dramatic difference.
This is not always true but it happend: my System 800 are the passive version and Tannoy didn't adress this issue with this one which is not the case with the active version.

I know because some mix/works i've done with active sound 'weird' with my passive around 1,5k which you probably have guessed is around the xover point (1,6khz from Tannoy doc).

With a dsp solution i could probably fix that using a delay ( a allpass filter is a passive equivalent to a delay- up to a limit). Passive this is hopeless as i should have to rebuild xover from scratch and i don't find this either funny or easy ( i'm a lazy dsp guy ).

B&C drivers are GREAT drivers, their coax too i agree with Earl about that too.
Swara have you seen Seaton Sound offer?
The Catalyst is a great example of what could be done: 8" B&C coax + 2x12" sub in mtm dsp driven with classD amp.(edit: he added a new catalyst with 8" subs. Probably from Acoustic Elegance like most sub he use).
The latest TAD effort are worth a look at too: 6,5" ( or 8" idon't remember) coax + 2x 8" (or 10") in a TMM form factor ( making it a 3,5 way).
(edit: just checked: 6,5" and 2x 10". This seems to be approximately the same balance of cone area as seaton's sound between coax and sub drivers. This could be a 6,5" and a 15" too and i bet it could sound even better this way than with 2x10").

Both are great source for inspiration imho.

Swara two other questions: what is your ceiling height? And what are your main source?
The height is to determine overall volume of your room ( and thus have an idea of the membrane area you'll need for sub) , the source is to give you hint about what could work for dsp filter solution.

One last thing: you should go to Earl's site and read the whitepapers! Lot of knowledge and practical answer to reallife issue to be gained.

Last edited by krivium; 7th September 2019 at 12:31 PM.
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Old 7th September 2019, 01:49 PM   #15
Pano is offline Pano  United States
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Home audio loudspeaker - 8"/10"/15" Coaxials crossover at 1000Hz
Quote:
Originally Posted by gedlee View Post
Coax can never be quite as god as a separate waveguide system, but the later are so much more difficult and expensive. For value, the coax wins out.
Agree. Tho I do ultimately love a separate horn system, the coax has a lot of good qualities and great value. I've used and heard everything for 8" to 18" coaxes and enjoyed them all. Getting the crossover right is all important, of course. Generally you don't need an active crossover.
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Old 7th September 2019, 02:11 PM   #16
Zvu is offline Zvu  Serbia
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Think of the Kef coax Uni-Q scaled up and working 100Hz and up. Or 300Hz and up for that matter.

Kef UniQ measures and sounds better than any other waveguide loaded two way i have ever heard - regardless of being coax or classic arrangement of drivers.
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Last edited by Zvu; 7th September 2019 at 02:24 PM.
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Old 7th September 2019, 02:23 PM   #17
Zvu is offline Zvu  Serbia
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Here are measurements of Kef LS50 with my (revised) crossover 0-90 degrees horizontal in 10 degree increments. Gated, 1m distance, using HolmImpulse, m-audio USB with phantom and calibrated Behringer ECM8000. Bare in mind that this is 1dB grid resolution.

0, 10 and 20 degrees
0.10.20 степени.png

30, 40 and 50 degrees
30.40.50 степени.png

60, 70 and 80 degrees
60.70.80 степени.png

Here i had to make the grid 2dB to be able to see the level of 90 degree against 0 degrees

So 0, 80 and 90 degrees
0.80.90 степени.png
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Last edited by Zvu; 7th September 2019 at 02:25 PM.
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Old 7th September 2019, 03:33 PM   #18
krivium is online now krivium  France
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Hi Zvu,
Yes kef uniq are very good too but... if Swara liked Tannoy he heard it may be due -in part- to use of CD for high end.
In fact for me this the main point choosing Tannoy ( and the point source behavior of course) as i'm bored of dome tweeters.

In the same vein PHL have some good coax with dome tweet too, maybe not as good as Kef's but it must be said.
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Old 7th September 2019, 04:51 PM   #19
mayhem13 is offline mayhem13  United States
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I agree with Earl......for sheer value vs performance, a Coax can be a great option......BUT

.....my method has always been 3 way and NOT have the cone move at all to keep the intended waveguide properties as stable as possible, and that's using an 8" coax crossed in the 250hz range steep filter. For AMAZING midrange, run the coax open baffle as Earl did. Bottom the system with a big closed box 15" woofer with a Linkwitz transform function filter and batten down the hatches!

.....cross that Eminence Coax to the CD at 1.8khz or so.....a good directivity match. There's a small speaker company making high end pro audio monitors ( i forget the name) that's rear mounting the coax to a mild horn loaded baffle of 15" or so that extends the directivity of the woofer lower. He does it with 2" thick foam insulation and fiberglass with epoxy resin......that foam can be shaped by hand with sandpaper beautifully.
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Old 7th September 2019, 04:58 PM   #20
Zvu is offline Zvu  Serbia
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Quote:
Originally Posted by krivium View Post
Hi Zvu,
Yes kef uniq are very good too but... if Swara liked Tannoy he heard it may be due -in part- to use of CD for high end.
In fact for me this the main point choosing Tannoy ( and the point source behavior of course) as i'm bored of dome tweeters.

In the same vein PHL have some good coax with dome tweet too, maybe not as good as Kef's but it must be said.
There is a bit of compression effect because of surface that tangerine phase plug covers. Jack Oclee-Brown explains it in an interview with John Atkinson talking about Reference 5 model. Kef UniQ tweeter is probably one of the best tweeters i have heard regardless of price - i too do not like most dome tweeters. I listened and worked with DE250, DE500. Soon the Tymphany compression drivers are coming to me. With all that rave and good measurements through the internet i just had to try them
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Last edited by Zvu; 7th September 2019 at 05:25 PM.
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