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-   -   Basic help with HiVi B3S design needed (http://www.diyaudio.com/forums/full-range/60325-basic-help-hivi-b3s-design-needed.html)

jimbo1968 6th July 2005 11:01 PM

Basic help with HiVi B3S design needed
 
2 Attachment(s)
I've got 20 HiVi B3S that I was about to sell-off in favour of the Tangband 871. Then I found this site http://www.zaphaudio.com/audio-speaker18.html which rates them above the tangband.

I was having trouble getting the tangband's to go low enough, but the HiVi's have no problem with 3mm xmax. I was worried by the HiVi freq response which falls off way below 20kHz, the in-box modelling shows it to be no worse than the Tangband though.

Anyway I plan to put 4 drivers each into 2 enclosures, and use my AVamp to crossover to 2 10" subs at 160Hz.

The enclosures will be tall and slim and wall mounted next to my TV like this:

jimbo1968 6th July 2005 11:04 PM

2 Attachment(s)
So my questions are:

1. How to space the 4 drivers on the baffle?

The design is not sensitive to the volume of the enclosure, anything from 4litre to 20 litre will do.

2. So what width/depth do you recommend. Or how should I choose these?

3. How should I position and shape the baffle next to the screen? eg here are some layouts:

jimbo1968 6th July 2005 11:09 PM

Oh yes, I practised mounting the HiVi to a baffle.

I put it behind the baffle with a 10mm roundover in front of it. (No picture for that I'm afraid)

It looks nice like that, but is that a bad design sonically?

Salas 7th July 2005 08:17 AM

You are going to experience comb filtering (i.e. successive additive and destructive interference ripples) with 4 in-line sources covering most of the spectrum. The solution is a tweeter in the middle of the four units and suitable crossover.

jimbo1968 7th July 2005 12:09 PM

hmmmm ... I was influenced by this design: http://www.seventh-veil.com/products_nonsuch4.htm

so is this idea fundamentally flawed then ?

jimbo1968 7th July 2005 02:21 PM

I don't think there is any problem with interference patterns at 3.2m and driver spacing 80mm (ie bunched as tight as possible).

Outer drivers are just 1mm further away than inners. Loss of amplitude is about 2% at 20kHz. (0.1dB ?)

GM 7th July 2005 05:16 PM

Greets!

Huh?! Effective CTC spacing is the primary issue in this case, not parallax error. I find the comb filtering unacceptable, but many don't, so if it works for ya'll, that's all that matters. Just looking at an FR plot though, a super tweeter seems the 'Hot Ticket', 'killing two birds with one stone'. A bit of fuzzy ambiance from comb filtering in music is one thing and quite another WRT TV/movie dialog intelligibility.

WRT positioning, you ideally want the focal point to be at 2/3 screen height and spaced apart/angled in at 60 deg included referenced to either the 'sweet spot' or the midpoint between rows, and until you in-wall mount them there's no such thing as too large a baffle IMO so I recommend spanning the gap between the speaker/TV with a baffle extension.

GM

jimbo1968 7th July 2005 06:21 PM

Quote:

Huh?! Effective CTC spacing is the primary issue in this case, not parallax error. I find the comb filtering unacceptable, but many don't, so if it works for ya'll, that's all that matters. Just looking at an FR plot though, a super tweeter seems the 'Hot Ticket', 'killing two birds with one stone'. A bit of fuzzy ambiance from comb filtering in music is one thing and quite another WRT TV/movie dialog intelligibility.

I didn't have much time, but a quick search pointed to comb filtering being about cancellation due to out of phase signals. The 2 sound waves will be out of phase by 1mm which is 1/17 wavelength at 20kHz, which results in 2% loss of amplitude. I don't think anyone claims that is perceivable (OK I'm sure someone will) but it's definitely not alarming.

If I've got the physics all wrong, could someone point me to the equations I need?

What was the size/spacing/distance away of the array you tried?

joensd 7th July 2005 07:08 PM

Jimbo, have you read Jim Griffin´s white paper?
http://www.audiodiycentral.com/awpapers.shtml
direct link to pdf : nflawp.pdf
looks like a good start

greets

jdybnis 7th July 2005 07:33 PM

You can solve the comb filtering problem by putting a 1st order lowpass on 3 out of the four drivers at say 1kHz. The 4th driver is the only one reproducing the high frequencies.

I'd also put a highpass on the 4th driver (the one acting as the "tweeter") at about 300Hz to relieve it of bass duty. The midrange clarity will improve and you'll actually increase the max spl that will sound good.

With the lowpass you have a lot of flexibility with driver placement. You can put them all in a straight line with the "tweeter" at the top, or second from the top, or you can cluster the other drivers around it.

If you have soundeasy, lspcad, or speaker workshop (free) try modeling a few different configurations and look at the polar response in the upper frequencies. You don't have to measure the drivers. Just input the correct diameter of the driver and model it as having a flat frequency response up to 20kHz.

P.S. Don't forget about baffle step correction if they aren't going to be flush against a wall.


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