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What should the bass be like on HDTs? (Read 1304 times)
Steve Harman
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What should the bass be like on HDTs?
08/27/18 at 08:46:50
 
Hi,

I'm helping a family member who has just completed building a pair of HDTs.  He's using the  modified Decware Fostex drivers and passive radiators and has followed the DIY plans to the mm!

Now they're finished and we're testing them out, it's fair to say the midrange and treble are incredibly impressive with great precision and excellent staging.

However if i'm honest I'm a little surprised with low frequencies / bass - I'd say things sound very light, not much punch or low-down weight to the bass - which if Wikipedia is to be believed sn't characteristic of transmission line designs?  

In fact referring to the Decware manual for the factory produced HDTs it notes that in smaller rooms there might be too much bass and suggests some steps to limit this, involving blocking the back port and wall positioning.   This is the opposite of our situation - too little bass.

We're new to HDTs and TL speakers so don't have others to compare against - my "lack of bass" comparison is against my own Decware Radial ERRs which deliver a great deal of energy at the low frequencies.

Back to the family-built HDTs - there seems to be plenty of activity and sound from the passive radiators but, again something we noted that's different to the manual for the factory built units - there doesn't seem to be much audio in the rear transmission chamber when we lift the "lids" off of the HDTs - in fact hardly anything. I believe the manual states that there will be "a lot" !

We're a bit stuck as to what to investigate - can any seasoned HDT owners comment please?

Thanks in advance.

Steve
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Steve Harman
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Re: What should the bass be like on HDTs?
Reply #1 - 08/27/18 at 12:47:01
 
Forgive the poor etiquette replying to my own post, but I have an idea.

The attached photo of someone else's build shows the bottom chamber where the internal ports send sound through to the rear transmission line chamber.

We have lined the BOTTOM of this chamber - the panel closest to the floor which isn't shown in the photo - with egg foam - so the internal pipes transfer sound straight down into foam.  Is this correct?  

It feels counter intuitive that the ports should send sound down into foam, but instead the sound should hit naked wood so it can "bounce around" into the transmission line space?

Thanks again.

Steve

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Steve Deckert
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Re: What should the bass be like on HDTs?
Reply #2 - 01/04/19 at 03:37:11
 

Hi Steve,

Boy do I feel bad, not seeing this post until now!!!  

The egg crate foam in the base is typically 1 inch thick and there to attenuate some of the high frequencies that accidentally make it through the port tubes.  Of course this foam is optional, and easy to install and remove through the rectangle rear port opening so you can experiment.

You know, the HDT was really the first speaker offered and over the years we have added several more speakers to the line up.  The reason for this is that speakers are like clothes...  everyone can't wear the same shirt despite how perfect it might be.  

The HDT compared to our entire line up of speakers that we have expanded to today, can and would be considered by many to still be the best sounding/performing speaker we have.  It has a live sound with great presence and the bass can be outstanding with the right placement, amps and room.  I've heard the speaker get into the high to mid 20's in one of our rooms...

Regardless of where the cut-off ends up being in a given room, the bass is tight and textured.  

Anyway, now that I've seen this I would be more than happy to help you solve your bass issue.  I would need to see a picture of the speakers in the room before I can start giving ideas.

One thing I would point out is that one way to increase bass is to turn the bass up, another way to increase the bass is turn the highs down.  Both methods are exactly the same - relative.  The HDT has a lot of midrange and treble presence making it touchy in untreated rooms.  The ERRx is on the opposite end of that spectrum with a very laid back almost recessed by comparison, midrange.  Side by side the ERRx will either sound right or the HDT will sound right depending on room acoustics so no doubt this is somewhat at play with regards to what you are experiencing.

-Steve


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