10 minutes ago, davewantsmoore said:

What do you do about EQ needed for each driver, eg. the 6dB extra slope, or the 'dipole peak' EQ?

DSP is an essential part of my system, hence why I use the Dspeaker X4 as my DAC/DSP/Crossover. But what exactly do you mean by EQ needed? To tame peaks, boost troughs, or balance output or... something else? The sensitivies between them are balanced to the same 91dB, the peak from the bandpass crossover I mentioned needs one resistor on the midrange. The rest are balanced in an anechoic environment, but the DSP fixes it for a real world environment.

Edited June 24, 20187 yr by Ittaku

1 minute ago, Ittaku said:

DSP is an essential part of my system

Ah!

 

1 minute ago, Ittaku said:

But what exactly do you mean by EQ needed?

The response of a dipole has a peak in it.... and you would flatten the peak with EQ, if it wasn't substantially reduced in level by the crossover.

 

The peak frequency depends on the baffle width (wider baffle, lower frequency)

 

http://www.musicanddesign.com/Dipoles_and_open_baffles.html

1 minute ago, davewantsmoore said:

Ah!

 

The response of a dipole has a peak in it.... and you would flatten the peak with EQ, if it wasn't substantially reduced in level by the crossover.

 

The peak frequency depends on the baffle width (wider baffle, lower frequency)

 

http://www.musicanddesign.com/Dipoles_and_open_baffles.html

Sure, but I wasn't sure what particular part of EQ you were referring to. As you see the dspeaker DSP is essential - again part of why I hadn't tackled OB before because these problems had much more convoluted workarounds in the past. Fortunately the X4 sounds amazing as a DAC too, and does its DSP at much higher - native - sample rates than most setups so I don't need to rely on resampling and its attendant issues.

Oh, but that DSP, is stereo in/out (or did I read it wrong?) .... how do you get the filter slopes right for each driver?

 

9 minutes ago, davewantsmoore said:

Oh, but that DSP, is stereo in/out (or did I read it wrong?) .... how do you get the filter slopes right for each driver?

 

What? The crossover is passive. The DSP is for impulse and amplitude only.

Sorry I may have confused you by saying the dspeaker is a crossover as well - it's only a crossover to the subwoofer. I use 4 channels out from the dspeaker into a 4 channel preamp. The 2 main channels from the preamp go into the ARC amps which feed the main speakers while the 2 subwoofer channels from the preamp go straight into the subwoofer's own amplification.

What? The crossover is passive. The DSP is for impulse and amplitude only.

 

Then my original question remains. How do you account for the dipole peak for each driver?

Okay I spent a few hours playing with side walls for the woofer today. I went hunting for something suitable from Bunnings and it delivered in the form of some 16mm thick floating MDF shelves that were just about the right size. I did not try to secure them to the side of the speakers as such, just resting them at various angles upright along the side and performed a few measurements with them as parallel side walls, flared side walls, inside walls only, outside walls only. Simply placing them on both sides and having a quick listen revealed an immediate increase in low frequency amplitude and the measurements confirmed this.

 

Putting either inside or outside side walls on the speakers conferred a 2dB boost across the entire frequency spectrum that the woofers operate. Both changed the position and amplitude of various peaks and troughs in subtle ways, however adding just inner walls created an exaggerated trough at approximately the crossover frequency of 230Hz for reasons unknown - using just outside walls did not exhibit that. Putting both inside and outside side walls created a massive 5dB boost across all frequencies without any change to the overall shape of the frequency plot. This seemed to be quite a nice win in terms of how much DSP management would be required to balance outputs.

 

Recalibrating the DSP room correction I had to create different profiles for the amplitudes to be similar to be able to conduct a meaningful listening comparison, otherwise tone balance would be different. Listening to the change, however, is where it got frustrating. My first impression was that it was boxy sounding suddenly when it hadn't been because I initially had the side walls parallel. Even though the woofer shouldn't be exciting frequencies that fit between those side walls, there is enough energy presumably from the radiated sound from the midranges to excite them. In essence I'd created half a box with now two parallel vertical walls and two parallel horizontal shelves. Then I moved them in a much more flared fashion as much as my space would allow and that seemed to improve that issue dramatically. Tonally there was no dramatic change though the extra bass headroom allowed me to set disco levels before excursion issues with the woofers. But it was not a universal win. In a nutshell, the more sidewalls I put on, the less air and openness I would experience from the sound. The inner walls' effect was relatively small but noticeable but the outer walls was much more dramatic, with the sound no longer "filling" space in the lateral directions. I tried them on and off numerous times with different sources of music and while it wasn't a blinded test, the difference was always there. I'm actually thinking the extra air I'm experiencing without the side walls is probably artificial and the out of phase dipole radiation is generating this extra ambience, and putting the side walls in place is partially neutralising that effect. Regardless, it unfortunately just didn't sound as good to me. It measured a lot better and required far less extreme DSP but just didn't sound as good.

 

A fun experiment indeed but alas not an approach I'd consider a way forward by itself. One thing that I have learnt, though, is that perhaps that horizontal shelf which is parallel to the base shelf is doing more harm than I'd imagined. I've certainly seen most OB designs have a large vertical shaft instead of a horizontal shelf for reinforcement and this would seem to be a better approach. No need to reinvent the wheel if someone's already done the work before!

29 minutes ago, davewantsmoore said:

The my original question remains. How do you account for the dipole peak?

We seem to be talking across each other. The DSP room correction applies to the entire frequency spectrum and nulls peaks and slightly boosts troughs. The nulling of peaks by the DSP room correction fixes the dipole peak.

I see.

 

(Sorry for any confusion....where I am coming from is)    I would want to EQ each driver individually, as the peak is different for each driver..... or perhaps not so much different seeing as they are on the same big rectangular baffle.

2 hours ago, Ittaku said:

No need to reinvent the wheel if someone's already done the work before!

 

The 'shelf' needs to be far enough away from the driver to no affect the radiation impedance too much  (you can see this reflected in the electrical impedance if this is an issue).

 

The shelf must not create any cavity resonances or reflections, this is related to wavelength size.    ie. close surfaces are OK at low frequencies, but become a problem at higher frequencies.

 

For mids operating up to ~4khz+ I'd want to have more clearance (and chamfer the back of those driver holes)....   but it's not 'binary world'.  Check the electrical impedance and acoustic measurements while moving the shelf around on a test mule is really the only way to see how big the effect is.

8 minutes ago, davewantsmoore said:

The 'shelf' needs to be far enough away from the driver to no affect the radiation impedance too much  (you can see this reflected in the electrical impedance if this is an issue).

 

The shelf must not create any cavity resonances or reflections, this is related to wavelength size.    ie. close surfaces are OK at low frequencies, but become a problem at higher frequencies.

 

For mids operating up to ~4khz+ I'd want to have more clearance (and chamfer the back of those driver holes)....   but it's not 'binary world'.  Check the electrical impedance and acoustic measurements while moving the shelf around on a test mule is really the only way to see how big the effect is.

Thanks. These mids cross over at 2500Hz.

4 hours ago, Ittaku said:

.... A fun experiment indeed but alas not an approach I'd consider a way forward ....

Thanks for doing the experiment and writing it up. Interesting findings in terms of the sound.

 

 

I wonder what happens if you stuff the U-baffles? You might still get the +5dB for free and lose the boxy sound?

 

If you are thinking you might need two x13" for the dipole bass I wonder if you might do better leaping up to a single 18" driver?

 

Or cross the subwoofer higher eg 60Hz?

 

Cheers.

1 minute ago, Nada said:

Thanks for doing the experiment and writing it up. Interesting findings in terms of the sound.

 

 

I wonder what happens if you stuff the U-baffles? You might still get the +5dB for free and lose the boxy sound?

 

If you are thinking you might need two x13" for the dipole bass I wonder if you might do better leaping up to a single 18" driver?

 

Or cross the subwoofer higher eg 60Hz?

 

Cheers.

I've searched far and wide for drivers that I can use, those 13" are special drivers. 18" ones would sound terrible in this application without another driver between that and the midranges. Making 4 way passive crossovers is fraught with other problems. Stuffing the baffles will slowly start turning the speakers into boxes with acoustic suspension and lose the super critical damping the drivers currently have and introduce more group delay. I can cross the subwoofer higher, but why do that when I can add more drivers? The sound quality from the subwoofer is nowhere near that of the main drivers due to the quality of the driver and its amplification - I've tried all the way up to 80Hz and it just gets progressively worse sounding but more disco level sound pressure levels

2 hours ago, Ittaku said:

Thanks. These mids cross over at 2500Hz.

Yes, so we care about what is happening with them up to at least ~4khz

5 hours ago, Ittaku said:

A fun experiment indeed but alas not an approach I'd consider a way forward by itself.

The problem is that these types of changes affect the sound differently for different angles of radiation.... so the only sure fire way to visualise the 'peaks and dips' is with a more than a single axis response, which means outside or a huge room for low-mids and below.

 

Doing this also demonstrates that the dipole peak moves vs radiation angle ....which is why in very good speakers (eg. the LX521) the drivers are only used at frequencies below the dipole peak .... which is where the 'funny shaped' baffles come from (baffles which are 'acoustically small').

 

19 minutes ago, Ittaku said:

is fraught with other problems. Stuffing the baffles will slowly start turning the speakers into boxes with acoustic suspension and lose the super critical damping the drivers currently have and introduce more group delay.

Not sure I understand what causes the additional group delay?

 

Edited June 25, 20187 yr by davewantsmoore

14 hours ago, davewantsmoore said:

Not sure I understand what causes the additional group delay?

U baffles and padded U baffles both introduce group delay; the former in a more complicated way at and below the driver's resonant frequency, but the latter in a more controlled fashion. In reality the amounts of group delay will likely remain in the inaudible range of less than 10ms, but it's still there. It's hard to find good documentation on it and the maths is beyond me but this link discusses it briefly:

http://www.musicanddesign.com/u_frame.html

Here's the current frequency sweep in the listening position.

4 hours ago, Ittaku said:

U baffles and padded U baffles both introduce group delay; the former in a more complicated way at and below the driver's resonant frequency, but the latter in a more controlled fashion. In reality the amounts of group delay will likely remain in the inaudible range of less than 10ms, but it's still there. It's hard to find good documentation on it and the maths is beyond me but this link discusses it briefly:

http://www.musicanddesign.com/u_frame.html

Yessss.  Exactly....  This is all part of the "dipole peak" I was talking about.    The group delay exists because the driver response is not flat.... and you can see that where the dipole peak is larger (undamped case), that the peak in group delay is also larger.

 

I thought you might have been referring to something else.... which is why I said I was confused as to what it could be

 

You can see that the delay is constant below the dipole peak.... so is not an issue (just requires each source to be aligned in time.... which is one reason why you might want to use different DSP for each driver)

 

This is the problem using the driver above its dipole peak.... the frequency response (and subsequently the delay) is different for each position in space.... and so for the example drivers in that link, you would only want to use them below, say 150Hz to avoid the issue.

 

So I've gone and done an experiment that I've been running with for a few weeks. I've turned the preamp into purely a tube buffer. Since the DAC operates in 24 bit space, the volume control on it does not do any audible bit stripping to my ears. I opened up the preamp and bypassed the volume control and even the selector since everything runs through the DAC, thus taking a potentiometer and selector out of the signal path. This has cleaned up the sound even further and actually added quite a bit more gain than I expected - almost another 6dB. Even at the lowest setting the resistor in the volume pot was about 35 Ohms as far as I could measure - Mick uses ALPS pots.Tonally there was no obvious change, nor did there seem to be any changes to dynamics, just a sort of general loss of "grit" in the sound, especially at low volumes, and mostly in the top end, making it even more delicate.

Edited July 11, 20187 yr by Ittaku

I'm wondering, did you ask Mick why/the cause of the interference to the preamp?

6 minutes ago, Lazz said:

I'm wondering, did you ask Mick why/the cause of the interference to the preamp?

Yes, he said the combination of the 2 stage high gain preamp (and a high gain power amp according to him) meant the preamp was picking up a lot of noise through capacitive induction. Personally I don't accept that the power amp had anything to do with it at all, and it was indicative of the very high gain preamp and not much in the way of shielding. If bringing a hand close to the side of a preamp makes it buzz, and touching a timber side wall makes it buzz madly, then... well anyway you get the picture. It was like going back to cheap 1970s hifi that I experienced when I was little and hum and buzz were routine... ugh. Position was critical, being next to other components was impossible, and even if I put it a long distance away it would buzz audibly in a way that could be heard from the listening position. The fact is his blog says this updated version he made for me is now his new design. If it had remained buzzing like that I would have gotten rid of it. Instead, I'm now enamoured with it.

Edited July 15, 20187 yr by Ittaku

Funny you mention about the 

24 minutes ago, Ittaku said:

bringing a hand close to the side of a preamp makes it buzz, and touching a timber side wall makes it buzz madly

I had the same issue with an Audio Space Reference pre that I had on loan. I thought it may have just been faulty { which it may have been, coz only one channel would work} but interference was ridiculous.

I couldn't really get much in the way of opinions from people about what changing the valves in the driver stage of the preamp would be like after putting in the globes into the output stage so I experimented myself with switching them from the output stage to the driver stage and using the NOS valves in the output stage. I lost that extra leading edge and added detail these valves provided in the output stage but it firmed up the presence of the instruments in the sound stage, solidifying them quite substantially and increasing their "presence" and body. So I caved in and bought another pair of these valves and put them into the driver stage.

 

 

Another quite obvious improvement now overall, with both qualities combined from the previous advantage of these valves now in both positions. Together they give instruments just that much more of that real world presence - if you're walking down the street and a busker is playing you know instantly if it's a real instrument or not. There are numerous times now that have the music on sort of in the background but I need to stare at the space between the speakers and appreciate that presence. The combined benefits also added another element when put together - drive, that inimitable quality that gives makes music just more impact and that snappy sense, emphasising the rhythm or beat somehow that makes you want to tap your feet... and I listen predominantly to classical music!

Edited August 3, 20187 yr by Ittaku

65dB.

Is there any kind of woman that does not put on real speakers and if you should have headphones in class with your "sound".
The so-called base you get is probably just limited and if the curve points to the right good, is it how many% distortion?
Nothing I believe the sound in the bass is the best with those speakers.
  Can I listen to music with 65dB for my cover, I have never tried.
  For the HE way of a couple hear and be surprised !!!

And so open baffell loudspeakers there is something sighing because the sound from the backside takes it out on the front.

Now, I do not want to recomend to throw out the lady but ..... it will be a headphone when you hear an unwanted bass. Deu can start with Bose.
  Has the dock ever heard of the Phon scale?

 

 

Now I have listened to max 65 dB and you do not listen to it as much as I'm sure.
Now it's time for real sound, start with Bose as a fresh fan because as it is now you can not continue. If you now have bullets for it.
(I'm upset!)

 

Now I saw the bass and I can suppose one sounds better than my gosses, I get into the stomach of all the noise it's priests.
  They are cute at the moment because they make speakers against all pricipers from before. What about standing sound waves is it no longer?
Anyone who knows?

Edited July 16, 20187 yr by 13000km