My Swansong speaker build

[Toppsy]

Phil, It's a lot of work to rebate these drivers and has to be done very precisely, no margin for error. The driver has to fit snug into the rebate. And if there is no sonic benefit to rebating them flush (hence the question to the more knowledgeable) then I'll likely not bother.

[IslandPink]

Given the dimensions of the step, it's unlikely to have much if any effect up to the limit of where those midranges are operating. I think Troelsgraven has a specific page on this subject, with measurements, for a tweeter, maybe I ( or someone ) can find this. I think from memory he showed some deviations from spec performance in the 10 or 12kHz area.

Sorry, edit, i see you have the midranges flush anyway. The bass will be fine sonically, I'm sure, just up to you how you want it to look.

[Daniel Quinn]

Once there veneered , personally rebating won’t make an aesethic difference .

I still worry about the integration of so many mid range drivers and subsequent crossover

[Toppsy]

Once there veneered , personally rebating won’t make an aesethic difference .

I still worry about the integration of so many mid range drivers and subsequent crossover

I'm leaning to agree with your after veneer comment.

However, personally I have no worries at all regards integration. The concept and application of polar and linear arrays is well established. You need to listen to more multiway speakers with properly designed and integrated crossovers that have been designed by people who know what they are doing. I don't necessarily include myself in that league of gentlemen.

[Ray P]

Clearly my little joke fell as flat as the pieces of chipboard the cabinets are made from...

[IslandPink]

D'Oh !
ps. you need to take the 'e' off breathe.

[Nick]

I still worry about the integration of so many mid range drivers and subsequent crossover

Just think of it as a three way, the multiple drivers will not have a crossover each they will be used as a distributed single driver. Well, I guess the upper and lower array may be slightly different but depends on what Scott finds with measurements.

[Toppsy]

Clearly my little joke fell as flat as the pieces of chipboard the cabinets are made from...

Sorry Ray. Get it now. Clearly a chipboard 'panel' cannot speak to give an opinion. Too clever for me at the time.

[Scottmoose]

Was over at Colin's yesterday, primarily for the purpose of measuring The Things (as I like to call them). I'm not posting detailed measurements of a work in progress yet, since although all drivers were mounted the tweeter, for example, is not currently recessed, meaning the acoustic centres are not currently in their final positions. That's still to be done. However, given that the circular midrange arrays are probably what gets the most interest, I've attached one of the frequency response measurements taken.

The speaker is in effect an MTMWW (top to bottom), where the midranges each comprise 7 individual drivers. The response here shows the response of the two midrange arrays, quasi-anechoic measured at 2m distance with calibrated microphone, on axis with the tweeter (which is the nominal listening axis). 3ms gate window, fairly minimal 1 /48octave smoothing applied. The levels were taken at a lower output than the usual 2.83v conditions to spare Colin & my ears, so ignore the absolute value.

The important thing here, given the use, is the approximate region 200Hz - 2KHz. The 200Hz - 400Hz region is corrupted by some room reflections as gating doesn't really work all that well < 500Hz or so in most situations (give or take). Overall, it's pretty linear, with a couple of minor exceptions remaining +/-2.5dB across that range (the nulls at ~1.25KHz & 2.4KHz are innate to the CHN-50). Higher up, you can see a gentle rolloff characteristic of arrays in this configuration & with drivers of this size -ditto the big null at 12.5KHz, both of which are fairly irrelevant as the drivers aren't being used in or anywhere remotely near this band; final crossover frequency to the tweeter is yet to be determined but likely in the 1.5KHz region as its rising LF distortion has not proven problematic in the Edingdale GT. However, given The Thing's higher outright output capability, a slightly higher filter frequency is preferable to avoid excess strain.

[Max N]

These are looking really good Colin & Scott. I’d love to hear how they turn out. I have a question - when I played with MTMs, I think I made the mistake of sometimes sitting too close to them while I was developing and auditioning cross-overs etc. When I finally started living with them, a lot of the concerns I had about the sound just disappeared. So is there a minimum distance you would recommend for these speakers? I guess I’m asking about the MM successfully merging into the same acoustic centre as the T.

[Max N]

BTW, I’m definitely not suggesting any concern about these speakers. In my case I was sitting closer than any realistic listening position. Just wandering if there is any theoretical minimum, and whether my explanation for what I experienced holds water.

[Toppsy]

These are looking really good Colin & Scott. I’d love to hear how they turn out. I have a question - when I played with MTMs, I think I made the mistake of sometimes sitting too close to them while I was developing and auditioning cross-overs etc. When I finally started living with them, a lot of the concerns I had about the sound just disappeared. So is there a minimum distance you would recommend for these speakers? I guess I’m asking about the MM successfully merging into the same acoustic centre as the T.

Hi Max,
One for Scott to probably answer but I would anticipate 2m distance as a minimum. They seemed to merge very well at the 2m distance we measured them at and had a fairly wide dispersion angle each side and with the tweeter to be recessed flush and a proper passive XO they should be much improved. My listening distance is 3m or 3.3m measured on the angle from seated position to each speaker.

[Max N]

I was definitely closer than that when I was having problems, so should be good Colin

[Toppsy]

Aye, speakers with a MTM, or D’Appolito, configuration are definitely not for near field listening. For listening to music (rather than films) a vertical configuration to my mind is better then the more usual horizontal format that is mainly used as a centre speaker in a surround sound system.

[Scottmoose]

For a speaker this size, 2m minimum, ideally the 2.5m - 4.5m range will be optimum, which is what we're designing to. In general, for a given crossover frequency and order, larger speakers with drivers that aren't physically coincident tend to require greater listening distances for proper integration due to the physical separation of the drivers on the baffle (the response measurement above is purely that of the midrange drivers by the way, no LF or HF units attached). In the case of MTMs this is componded by the narrowed vertical polars resulting from the configuration. Which can be a benefit in some cases, but not all. It's reduced with lower crossover frequencies; ideally you don't want to cross any higher than 1 wavelength apart between the centres of the midrange units to avoid excess lobing. The absolute ideal is within 1/4 - 1/3 wavelength, where the drivers will be acoustically coincident, but that's almost impossible with a regular dome tweeter.